impact of processing on potato phytochemicals

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Impact of Processing on Potato PhytochemicalsAmber Nicole FurrerPurdue University

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Graduate School Form 30Updated 1/15/2015

PURDUE UNIVERSITYGRADUATE SCHOOL

Thesis/Dissertation Acceptance

This is to certify that the thesis/dissertation prepared

By

Entitled

For the degree of

Is approved by the final examining committee:

To the best of my knowledge and as understood by the student in the Thesis/Dissertation Agreement, Publication Delay, and Certification Disclaimer (Graduate School Form 32), this thesis/dissertation adheres to the provisions of Purdue University’s “Policy of Integrity in Research” and the use of copyright material.

Approved by Major Professor(s):

Approved by: Head of the Departmental Graduate Program Date

Amber N. Furrer

Impact of Processing on Potato Phytochemicals

Master of Science

Mario FerruzziChair

Bill Aimutis

Fernanda San Martin-Gonzalez

Mario Ferruzzi

Mario Ferruzzi 7/28/2015

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IMPACT OF PROCESSING ON POTATO PHYTOCHEMICALS

A Thesis

Submitted to the Faculty

of

Purdue University

by

Amber N Furrer

In Partial Fulfillment of the

Requirements for the Degree

of

Master of Science

August 2015

Purdue University

West Lafayette, Indiana

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For Ana Steen, my partner in crime and friend through all the ups and downs.

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ACKNOWLEDGEMENTS

This thesis and the work therein was directly supported and influenced by my advisor,

Mario Ferruzzi, Anne Kurilich of McCain Foods, and my committee members Bill Aimutis

and Fernanda San Martin-Gonzalez. Thank you for all of your guidance and advice. This

thesis and the work therein was indirectly supported by the grace of God, my family, friends

and fellow grad students, and many cups of coffee, which I only started drinking in graduate

school. I would like to specifically thank my lab mates Tristan, Sydney, Ben, Dennis, Darwin,

and Ingrid for all of their help when I needed it. It was a pleasure working with all of you,

and I couldn’t have asked for a better lab group. To the lunch table- thanks for brightening

my days. To all of my friends in grad school, thank you for sharing these past two years

with me and putting up with all of my shenanigans. I will miss each and every one of you.

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TABLE OF CONTENTS

Page

LIST OF TABLES ..................................................................................................................................................... vii

LIST OF FIGURES .................................................................................................................................................. viii

LIST OF ABBREVIATIONS ................................................................................................................................... ix

ABSTRACT ................................................................................................................................................................... x

CHAPTER 1. LITERATURE REVIEW ......................................................................................................... 1

1.1 Introduction ............................................................................................................................................ 1

1.2 Potato Varieties, Cultivation, and Forms in the Diet .............................................................. 3

1.2.1 Potato Variety and Selection .................................................................................................. 4

1.2.2 Cultivation, Harvest, and Storage ......................................................................................... 7

1.2.3 Value-Added Commercial Processing of Potatoes ........................................................ 8

1.3 In-Home Processing .......................................................................................................................... 10

1.4 Nutritive Value and Perception of Potatoes & Potato Products ...................................... 12

1.4.2 Protein ........................................................................................................................................... 17

1.4.3 Lipid ................................................................................................................................................ 19

1.4.4 Vitamins ........................................................................................................................................ 20

1.4.5 Minerals ........................................................................................................................................ 21

1.5 Potato Bioactive Phytochemicals Content and Bioavailability ........................................ 23

1.5.1 Phenolic Acids and Flavonoids ............................................................................................ 23

1.5.2 Carotenoids and Tocochromanols ..................................................................................... 28

1.5.3 Glycoalkaloids ............................................................................................................................ 30

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1.5.4 Factors Impacting Phytochemical Content in Potatoes and Potato Products . 31

1.5.5 Bioavailability of Phytochemicals in Potatoes .............................................................. 38

1.6 Health Benefits of Potatoes and Potato Products ................................................................. 42

1.6.1 Contribution to Dietary Nutrients of Concern and Bioactive Compounds ....... 42

1.6.2 Potatoes and Risk of Chronic Diseases ............................................................................ 44

1.6.3 Potatoes and Modulation of Oxidative Stress ............................................................... 46

1.6.4 Potatoes and Modulation of Inflammatory Stress ....................................................... 47

1.6.5 Glycemic Effect of Potatoes ................................................................................................... 48

1.6.6 Potato Influences on the Microbiota ................................................................................. 51

1.7 Opportunities to Improve Nutritional Value of Processed Potato Products ............. 51

1.7.1 Lipid Reduction ......................................................................................................................... 52

1.7.2 Resistant Starch Formation .................................................................................................. 53

1.7.3 Management of Acrylamide Formation ........................................................................... 55

1.8 Research Needs and Future Directions ..................................................................................... 55

CHAPTER 2. RESEARCH RATIONALE AND OBJECTIVES ............................................................... 58

CHAPTER 3. PHYTOCHEMICAL CONTENT IN COMMERCIALLY RELEVANT POTATO

VARIETIES AND PROCESS STABILITY IN COMMERCIAL AND FRESH POTATO PRODUCTS. 60

3.1 Abstract .................................................................................................................................................. 60

3.2 Introduction .......................................................................................................................................... 61

3.3 Materials and Methods ..................................................................................................................... 64

3.3.1 Chemicals and Standards ....................................................................................................... 64

3.4 Sampling and Processing Procedures ........................................................................................ 64

3.4.1 Experiment 1: Preparation of Fresh Potatoes for Determination of

Phytochemical Content .............................................................................................................................. 64

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3.4.2 Experiment 2: Sampling of Commercially Processed Samples for

Determination of Phytochemical Content .......................................................................................... 65

3.4.3 Experiment 3: Sampling and Reconstitution of Commercially Processed

Frozen Products for Comparison of Phytochemical Content. .................................................... 65

3.4.4 Experiment 3: Preparation of Freshly Prepared Products for Comparison of

Phytochemical Content. ............................................................................................................................. 66

3.4.5 Phenolic Acid and Anthocyanin Extraction and Analysis......................................... 68

3.4.6 Carotenoid Extraction and Analysis .................................................................................. 69

3.4.7 Statistical Analysis .................................................................................................................... 70

3.5 Results and Discussion ..................................................................................................................... 71

3.5.1 Experiment 1: Phytochemical Content in Fresh Commercial Varieties ............. 71

3.5.2 Experiment 2: Chlorogenic acid and Anthocyanin Content Through

Commercial Processing.............................................................................................................................. 78

3.5.3 Experiment 3: Comparison of Chlorogenic Acids and Beta-Carotene in Fresh

and Commercially Produced Potato Products. ................................................................................ 85

3.6 Conclusions ........................................................................................................................................... 90

CHAPTER 4. GENERAL FINDINGS AND FUTURE DIRECTIONS .................................................. 91

LIST OF REFERENCES .......................................................................................................................................... 94

APPENDICES

Appendix A. Other phytochemicals detected but not quantified in potatoes……………….115

Appendix B. Chlorogenic acid content in raw Covington potatoes destined for sweet

potato fries and wedges……………………………………………………………………………………………....116

Appendix C. Nutritional data and % moisture for raw potato varieties……………………...117

Appendix D. Nutritional data for commercial and fresh processed potato products…...118

Appendix E. PDCAAS data for raw varieties……………………………………………………………..119

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LIST OF TABLES

Table Page

Table 1. Common US fresh market potato varieties and uses ............................................................. 5

Table 2. Common Commercial Potato Products Grouped By Processing Type ......................... 11

Table 3. Proximate composition and nutritive value of potatoes, potato products, and

comparable carbohydrate sources per 100 g of product ...................................................................... 14

Table 4. Potato phytochemicals: Range of content of main phytochemicals in key

commercial and select specialty varieties, grouped by phytochemical and potato flesh color

....................................................................................................................................................................................... 25

Table 5. Effects of several processing methods on potato phytochemical content, grouped

by processing type and author. ........................................................................................................................ 35

Table 6. Percent of dietary nutrient provided by potato for US adults (1994-96) and rank

among 112 food/food groups ........................................................................................................................... 43

Table 7. CQA and caffeic acid in whole potatoes and potato flesh of nine commercial potato

varieties and one commercial sweet potato variety. .............................................................................. 73

Table 8. Anthocyanin content of three pigmented potato varieties, expressed by class of

anthocyanidin. ......................................................................................................................................................... 76

Table 9. CQAs in four varieties of potatoes through various levels of commercial

processing. ................................................................................................................................................................ 82

Table 10. Anthocyanins in three pigmented varieties of potato through various levels of

commercial processing, expressed by class................................................................................................ 84

Table 11. Chlorogenic acids in freshly prepared and commercially processed products. ... 87

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LIST OF FIGURES

Figure Page

Figure 1. Structures of primary phytochemicals found in Solanum tuberosum varieties. ... 27

Figure 2. Overview of the digestion and intestinal absorption of phytochemical from

potatoes. .................................................................................................................................................................... 39

Figure 3. Schematic of commercially processed potato samples obtained from McCain

foods for phenolic and anthocyanin analysis.. ........................................................................................... 65

Figure 4. Preparation of samples for Experiment 3- comparison of CQAs and beta-carotene

in commercially processed and freshly prepared products.. .............................................................. 67

Figure 5. Average total CQA’s in flesh and whole of nine commercial Solanum tuberosum

varieties.. ................................................................................................................................................................... 74

Figure 6. Example anthocyanin chromatograms for three varieties of pigmented potato: (1)

ADR, (2) ADB, (3) AR2009-10 .......................................................................................................................... 77

Figure 7. Example chromatogram of the Norland variety, whole. m/z 353- CQA; m/z 179-

caffeic acid.. .............................................................................................................................................................. 80

Figure 8. Total CQAs (sum of averages of 3-,4-, and 5-O-CQAs) quantified in four varieties

of commercially processed potatoes ............................................................................................................. 81

Figure 9. Total anthocyanins (sum of averages of individual anthocyanidins) quantified in

three varieties of commercially processed potato. .................................................................................. 85

Figure 10. Total CQA’s (sum of averages of 3-,4-, and 5-O-CQA) compared in commercial

and fresh products.. .............................................................................................................................................. 88

Figure 11. Total CQAs (sum of averages of 3-,4-, and 5-O-CQA) compared in commercial

and fresh products…………………………………………………………………………………………………………88

Figure 12. Beta-carotene content in fresh and commercial products. .......................................... 89

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LIST OF ABBREVIATIONS

CQA Caffeoylquinic acid (Chlorogenic acid)

FWS Flesh with skin (whole)

FNS Flesh

BF Blanched, frozen

BFM Blanched, frozen, microwaved

BFF Blanched, fried, frozen

BFFF Blanched, fried, frozen, fried

BFFO Blanched, fried, frozen, fried

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ABSTRACT

Furrer, Amber, N. M.S. Purdue University. August 2015. Impact of Processing on Potato Phytochemicals. Major Professor: Mario G. Ferruzzi.

Potatoes (Solanum tuberosum) are an important staple crop in both developed and

developing countries around the world. These tubers offer an important source of

nutrients, micronutrients, and health-promoting phytochemicals to the diet. However,

reported content and process stability of phytochemicals in commercial potatoes and

potato products is inconsistent. The objectives of this research were to compare

phytochemical content in white/yellow and pigmented commercially relevant varieties,

determine changes in phytochemical content of select potato varieties through commercial

processing, and assess differences in phytochemical content between freshly “home”

prepared and reconstituted, commercially processed white and sweet potato products. To

carry out the first objective, phenolic acids, anthocyanins, and carotenoids were analyzed in

whole and flesh of nine commercial potato varieties. Total chlorogenic acids (CQAs), the

primary phenolic acid in potatoes, ranged from 43-953 mg/100 g dw and were found in

greater concentrations in the whole of all varieties compared to flesh, suggesting

concentration in the peel. Higher levels of CQAs were also observed in in pigmented

potatoes compared to white/yellow-fleshed potatoes (318-953 and 43-88 mg/100 g dried

whole potato, respectively). 5-O-Caffeoylquinic acid (5-CQA) was the primary chlorogenic

acid isomer detected in all varieties of potato, followed by 4-O- and 3-O-caffeoylquinic acid

(4-CQA and 3-CQA). Acylated anthocyanins in red potatoes were primarily cyanidin and

pelargonidin derivatives, while those in purple varieties were primarily derivatives of

petunidin with smaller amounts malvidin and delphinidin.

For the second objective, four varieties (2 purple, 1 red, 1 white) of processed, dried,

and ground commercial products were obtained from McCain foods, including raw flesh

without skin (FNS), blanched+frozen (BF), +microwaved (BFM), and blanched+par-

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fried+frozen (BFF), +baked (BFFO) or +fried (BFFF). Retention of phenolics ranged from

49-85% for pigmented varieties and 32-55% for white. For purple and red varieties, CQA

levels were significantly lower (p<0.05) in BFF, BFFO, and BFFF compared to FNS, BF, or

BFM products. For white, CQA levels were lower (P<0.05) in all processed products

compared to FNS, but no differences were observed between processing levels. Retention

of anthocyanins through all forms of processing was found to be high (69-129%).

For the last objective, CQA and beta-carotene were compared in freshly prepared

versus commercially produced and reconstituted classic fries, fresh-style fries, hash

browns, sweet potato fries, and sweet potato wedges. Levels of CQA did not differ for

classic fries, fresh-style fries, or sweet potato fries, but were significantly (p<0.05) lower in

industrial baked and fried sweet potato wedges and baked and pan-fried hash browns.

Sweet potato -carotene was higher in commercial baked wedges (30 mg/100g dw)

compared to fresh prepared (26 mg/100g) (p<0.05), but no other differences between fresh

and commercial products were found. These results suggest that commercial blanching,

freezing, and microwaving have an overall mild impact on phytochemical levels in raw

potatoes compared to par-frying and subsequent baking or frying. Additionally, industrial

products compare favorably to freshly prepared products in recovery of phytochemicals

suggesting that both commercially prepared and freshly prepared products would provide

similar delivery of health promoting phytochemicals.

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CHAPTER 1. LITERATURE REVIEW

Introduction

The potato (Solanum tuberosum) is currently the fourth most important agricultural

crop, after rice, wheat, and corn, grown for human consumption (USDA Economic Research

Service, 2014). Potatoes are known to have high agricultural yields and significant nutritive

value as a source of macronutrients (carbohydrate and protein), micronutrients (vitamin C,

potassium, magnesium) and potentially healthful phytochemicals (Camire et al., 2009).

This, combined with the ability of potato varieties to be grown, processed and transformed

in many temperate as well as tropical/subtropical regions of the world (Govindakrishnan

and Haverkort, 2006), gives this tuber the potential to impact several dimensions of health

and nutrition ranging from under-nutrition and basic food security to products associated

with over-nutrition.

Since initial domestication by natives of the Central Andes in South America almost

8000 years ago (Food and Agriculture Organization of the United Nations, 2008a) the

potato has been consistently bred and improved resulting in tremendous diversity over

4500 cultivated varieties (“New World Catalogue of Potato Varieties,” 2009). Two main

subspecies exist, S. tuberosum: andigena, known as Andean; and S. tuberosum, or Chilean

(Zaheer & Akhtar, 2014). S. tuberosum varieties remain the most commonly grown and

consumed representing ~10% of cultivated species and over 200 wild species (Global Crop

Diversity Trust and FAO Plant Production and Protection Division, 2008). Tremendous

variation in physical (size, shape and color), organoleptic, and nutritional quality exists in

commonly consumed potatoes, providing an opportunity to meet an array of food

requirements around the world. In the developing world, the need exists to diversify the

diet with nutritious and high yielding crops that can endure less-than-ideal conditions

(Bradshaw, 2007). The potato is a critically important “food security” crop for many

developing nations, as it is not traded as a commodity and thus is less vulnerable to world

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food price increases. Many countries have begun to use potatoes to reduce their

dependence on commodity crops, and in 2005, for the first time, the share of potatoes

produced by developing nations surpassed that of developed nations (FAO Trade and

Markets Division, 2008). In the developed world, there is need for varieties which are high-

yielding, pest-resistant, and sustainably-produced to meet the growing convenience,

specific health, and quality demands of consumers (Bradshaw, 2007).

While global consumption of potatoes is increasing, in developed markets such as the

US, consumption of fresh potatoes is actually decreasing relative to consumption of

commercially processed potatoes (frozen, fried, chips and snacks) which is increasing

(USDA Economic Research Service, 2014). This increase in prevalence and preference of

processed products is often met with criticism due to the perception that processed potato

products do not deliver the same nutritional value as freshly prepared products. In fact,

while potatoes in their raw state are an excellent source of key nutrients and

phytochemicals, both traditional (in home) and commercial processing and preparation

methods can result in loss of micronutrients and other perceived negative nutritional

changes including addition of fat and salt as well as conversion of natural resistant starch to

highly digestible starch (Ek et al., 2012). Considering the diversity of potato varieties and

processing technologies, opportunities exist to leverage basic principles of food science and

technology to improve the nutritional profile of potatoes in all forms from basic in-home

products to processed products including meal components and snacks.

The purpose of this review is to summarize key information on potatoes and potato

products commonly consumed as key source of nutrients and biologically active

phytochemicals and describe the state of the science relative to the impact of processing (in

home and commercial) on nutritional quality and health impacts of potato products. As

several reviews already exist on potato genetics and agronomic characteristics

(Arvanitoyannis et al., 2008; Mori et al., 2015; Watanabe, 2015), the nutritional quality and

impact of potato (Brown, 2005; Camire et al., 2009; Ezekiel et al., 2013; King and Slavin,

2013; McGill et al., 2013), and overall contribution of potato products to the human diet

(Keijbets, 2008; Zaheer and Akhtar, 2014), this literature review strives to build on these

previous efforts and includes discussion of research gaps, novel technologies, and potential

targets that can be leveraged to enhance the value of this critically important food product

in all forms in the human diet.

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Potato Varieties, Cultivation, and Forms in the Diet

As of 2014, China ranked first in global potato production, followed by Russia, India,

and the United States (USDA Economic Research Service, 2014). However, the United

States, the Netherlands, Germany, and Canada lead the world in production of processed

potato products (Keijbets, 2008). As of 2008, world per capita consumption of potatoes

(average 31 kg) was led by Europe (88 kg), followed by North America (60 kg), then Asia

(24 kg), Latin America (21 kg), and Africa (14 kg). However, when total consumption was

considered, Asia/Oceania was the global leader with 94 million tonnes, followed by Europe

at nearly 65 million tonnes (Food and Agriculture Organization of the United Nations,

2008b). In the United States consumption of fresh potatoes has decreased from 81

lbs/capita/year in 1960 to 42 lbs/capita/year in the 2000’s. This drop in fresh potato

consumption was marked by an increase in processed potato consumption to 55, 17, and 14

lbs/capita/year of frozen potato products (mostly French fries), potato chips, and

dehydrated potato products (including flakes and potato flour), respectively (USDA

Economic Research Service, 2014). Changes in consumption patterns have implications for

the nature and quality requirements of potatoes from cultivation through harvest and

processing. The following sections will briefly review common potato varieties and the

selection of varieties for fresh market and commercial production of potato products,

potato cultivation, post-harvest handling, and processing. For more in depth information

see additional references: (Pieterse and Hils, 2009), (Jai Gopal and S. M. Paul Khurana,

2006), (Hawkes, 1990), (Vreugdenhil et al., 2011).

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1.2.1 Potato Variety and Selection

Potato varieties can vary significantly in physical and chemical characteristics,

nutrients, micronutrients, and phytochemicals. The genetic diversity of potatoes has made

it possible to breed for specific functional and nutritional qualities critical to producers and

consumers alike. Potato varieties have been broadly characterized by many features of

both the plant and tuber. Some characteristics relating to the tuber include orientation

relative to the stolon (stem connected to root), shape, number of buds, or ‘eyes’, skin

texture, skin and/or flesh color and distribution of pigmentation, maturity type, and disease

resistance (Burton, 1989).

Potatoes are also categorized based composition, cooking quality characteristics,

and use. In 1926, Salaman described four categories: floury (often burst spontaneously,

crumble easily), close (do not burst, readily break, don’t crumble), waxy (firm flesh, only

breaks down by kneading), and soapy (same as waxy, but also watery and translucent).

These differences in texture correspond to differences in starch type and content. Floury

potatoes contain more starch than other varieties (20-22%) with a high proportion of

amylose, giving them a drier, mealier texture. Waxy potatoes contain lower amounts of

starch (16-18%) with a high proportion of amylopectin. Starch type and content contribute

to performance differences in certain dishes (see discussion below). The British Potato

Council provides a categorization of popular fresh market varieties as “fluffy” (13 varieties),

“salad” (18 varieties), and “smooth” (20 varieties) (Agriculture and Horticulture

Development Board: Potato Council, 2012). Relative to industrial processing, the US Potato

Board summarizes 15 major varieties used for chip stock in the United States: Alturas,

Andover, Atlantic, Chipeta, Dakota Pearl, Ivory Crisp, Kennebec, LaChipper, Marcy,

Megachip, NorValley, Norwis, Pike, Reba, and Snowden (United States Potato Board, 2007a).

Other varieties, like Russet Burbank and Shepody, are more suitable for French fry

production (Keijbets, 2008). Cultivar use for processed potato production varies by country

(Keijbets, 2008).

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Table 1. Common US fresh market potato varieties and uses (United States Potato Board, 2007b).

Type Description/Notes Common Varieties

Russet

Most common variety High in starch, floury

All purpose, good for baking, frying, roasting and mashing

Burbank, Norkotah, Ranger, Shepody

Round White

Medium starch Thin skin

Creamy texture All purpose, good for salads, scalloped

dishes, steaming, frying, roasting

Atlantic, Katahdin, Norwis, Reba, Superior

Long White

Medium starch Firm, creamy texture

All purpose, good for boiling, microwaving, and pan frying

Kennebec, White Rose, Cal-White

Red

Firm, smooth, waxy texture Often found as "new potatoes"

Good for salads, roasting, boiling, and steaming

Chieftain, Dakota Rose, La Rouge,

Norland, Red La Soda

Yellow

Dense, creamy texture Mild buttery flavor

Good for mashing, roasting, baking, boiling, and steaming

Yukon Gold, German Butterball, Sierra Gold

Blue and Purple

Mainly available in fall Subtle nutty flavor

Good for microwaving, salads, steaming, grilling, and baking

Purple Peruvian, All Blue, Congo, Lion's

Paw, Vitillete, Purple Viking, Purple Majesty

Fingerlings

Restaurant trend Firm, waxy texture

Good for steaming, boiling, baking, and salads

Russian Blue, Red Thumb, French Russian

Banana

Petite, or New Potatoes

More concentrated flavor Always starchier than their mature

counterparts Good for salads, roasting, frying

C-size and smaller of any potato variety

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Breeding and selection of varieties is dependent on several factors that can be

broadly separated on the intended use of the potato, specifically fresh market or for further

processing. However, several of these factors clearly overlap. For fresh market potatoes,

critical characteristics include shape and overall appearance (free from blemishes and

defects). Consumers have rated appearance of the skin and location of growth (interest in

“locally grown”) as important factors in potato purchasing (Jemison et al., 2008). Cooking

quality is important as it relates to color, texture, and flavor of the final dish. For example,

selection is often based on stability to preparation and absence of cooking defects such as

enzymatic browning- resulting from oxidation of tyrosine through reactions catalyzed by

polyphenoloxidase- and stem-end blackening- resulting from a reaction between iron and

chlorogenic acid (Burton, 1989, chap. 11; Storey, 2007). Starch type and content greatly

affects performance in different dishes. For example, high starch and high amylose potatoes

are most appropriate for baking, mashing, and frying due to their more crumbly texture and

because amylose molecules separate easily when cooked in water (Hassanpana et al., 2011).

In contrast, high amylopectin varieties hold together better upon boiling (Dresser, 2007).

The common uses of several types of fresh market varieties are found in Table 1.

Selection of commercial varieties can be more complicated considering both the commercial

process and in some cases the in home final preparation (for products such as frozen

potatoes). All of the “fresh market” characteristics are also important for potatoes used in

commercial processing, with the addition of more specific factors. In general, potatoes

should be uniform and not disfigured, without sprouts or blemishes, and within an

appropriate size range depending on the application. A short, oval shape with a transverse

axis ratio less than 1.33:1 is desired for chip manufacturing. In French fry manufacturing,

long varieties are desirable (transverse axis greater than 50 mm). Dry matter concentration

is also important; dry matter less than 19.5% and 20% for French fry and chip

manufacturing, respectively, is considered unacceptable (Kirkman, 2007).

Final color (control of excessive browning) is a critical component of quality in fried

potato products, which is a result of reactions occurring during heating between both

reducing sugars and sucrose (especially at higher temperatures) and amino acids

(Shallenberger et al., 1959). The amino acid glutamine has been highly associated with dark

fry color in crisps, as well as arginine, asparagine, and others, depending on concentration

of reducing sugar (Khanbari and Thompson, 1993). Thus, lowering sucrose and reducing

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sugar content in addition to certain amino acids in commercial varieties is desired to limit

darkening. This is also a critical factor in controlling acrylamide formation. A byproduct of

the Maillard reaction, acrylamide is considered a potential carcinogen (Tareke et al., 2000)

produced from the reaction of reducing sugars and the amino acid asparagine, which is

abundant in potatoes, during high heat (>1200C) processing including baking, frying and

roasting. Reducing sugar concentration is the limiting portion of the reaction, and therefore

steps taken to lower reducing sugars in potatoes are a key strategy to control acrylamide

formation in final processed products (Kirkman, 2007). Several factors impact sugar

concentration, including genetic characteristics, weather patterns and agronomic practices

during growth, maturity at harvest, and temperature and air composition during storage

(Kirkman, 2007). Concentration of free amino acids, citrate, phosphate, and vitamin C may

also have an effect on browning reactions (Burton, 1989, chap. 11).

Additional important functional and nutritional factors in variety selection for

commercial processing include type of starch, high yields, improved micronutrient and

antioxidant content, reduction in anti-nutritional components such as glycoalkaloids and

acrylamide precursors, and resistance to various environmental stresses, pests, and

diseases (Bradshaw and Bonierbale, 2010; Jansky, 2009).

1.2.2 Cultivation, Harvest, and Storage

Potatoes are grown from “seed potatoes”, which can comprise 5-15% of a year’s

crop. They can be grown in a variety of climates, but cannot flourish at temperatures less

than 10°C (50°F) or more than 30°C (86°F) (Food and Agriculture Organization of the

United Nations, 2008a). High temperatures during growth and storage advance potato

physiological aging- a combination of chronological age and environmental conditions

which affects composition and sensory qualities (Wszelaki et al., 2005). Potatoes which age

faster and reach the incubation (sprouting) phase of growth earlier will have a higher sugar

content and lose significantly more water. The speed at which a potato advances into the

incubation phase is determined by variety, maturity at harvest, weather and soil conditions

during growth, and irrigation. Cool, wet weather is considered ideal for growth

(Govindakrishnan and Haverkort, 2006). While potatoes are quite adaptable to different

soil and growing conditions, the best soils are rich in organic matter and loose and loamy to

allow for appropriate aeration and drainage (Thornton and Sieczka, 1980).

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Typical yields (tonnes/hectare) for potatoes are reported to be highest in North

America (41), followed by Europe (17), Latin America (16), Asia (15), and Africa (10) (Food

and Agriculture Organization of the United Nations, 2008b). The size of the potato harvest

in the United States continues to expand, due to both increases in land area and average

yields. In 2013, US farmers harvested 467 million hundredweight (cwt) of potato tubers

(Wells et al., 2013). Potato tubers are harvested when at maturity, usually determined by a

sucrose rating test (levels should be less than 1 mg/g fw). 90% of potato harvest occurs in

the fall, but many varieties are suited for long-term storage in climate controlled conditions.

This allows them to be sold throughout the year to both the fresh and processing markets.

Fresh market potatoes are sold on the open market upon harvest, while potatoes intended

for commercial processing are usually contracted before spring planting (USDA Economic

Research Service, 2014). Potatoes that are meant to be stored can be left in the soil to allow

skins to thicken, which helps to prevent moisture loss (Food and Agriculture Organization

of the United Nations, 2008a). Stored potatoes should not be washed first to minimize

spread of disease and limit moisture. However, potatoes intended for processing should be

stored in a dark area at high relative humidity, and between 6-8°C to prevent greening or

loss in quality (Bradshaw and Ramsay, 2009; Food and Agriculture Organization of the

United Nations, 2008a). Colder temperatures during storage lead to accumulation of

reducing sugars, which increase sweetness, promote excessive darkening during frying, and

as described previously, can contribute to acrylamide formation (Amrein et al., 2003). For

additional information on storage, as well as sprouting inhibition, see Gopal and Khurana

(2006).

1.2.3 Value-Added Commercial Processing of Potatoes

Early processing of potatoes had the goal, similar to that for most perishable foods,

of minimizing spoilage and extending shelf-life. In this regard, dehydration was uniquely

suitable for potatoes. Early examples of processed potatoes can be traced to the Incan

Empire (~1400 A.D.), which created a dehydrated product known as chuño, made through a

natural freeze drying process leveraging the conditions of the Andean region (Bradshaw

and Ramsay, 2009). This product is still made today in some South American communities

(Kirkman, 2007). The first reference to more modern processed potato products appeared

in France around 1780 describing dehydrated potato biscuits (Burton, 1989, chap. 9). In

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1845, Charles Edwards filed a US patent for the first dehydrated potato process, in which

potatoes were pressed and dried on tubes heated with steam (Edwards, 1845). In general,

dehydrated products were the most common potato product until the second half of the

20th century, at which point more diverse forms of processed potato products became

increasingly popular (Bradshaw and Ramsay, 2009).

Currently, around 50-60% of fresh potatoes undergo commercial processing in

some form. This includes transformation into chips, frozen potato products (mostly French

fries), dehydrated potato products (including flakes, granules, flour, meal, and dried

potatoes), chilled-peeled potatoes (mostly in Europe), canned potatoes, and other potato

products (Bradshaw and Ramsay, 2009; USDA Economic Research Service, 2014). Potato

products with significant market presence driven by consumer and restaurant demand are

summarized in Table 2. Frozen French fries are the United States’ top potato export

product (valued at $635 million), followed by potato chips ($178 million), and dehydrated

potato products ($82 million) (USDA Economic Research Service, 2014). Beyond typical

application in potato based food products, potatoes are also processed into potato starch,

and also fermented into alcoholic beverages or as feedstock for pharmaceutical, textile,

paper, and other industries. Examples of these products include biodegradable plastic

substitutes, fuel-grade ethanol, and farm animal feed (Food and Agriculture Organization of

the United Nations, 2008a). These kinds of products are important to consider as potential

avenues for waste stream disposal. Many other applications exist for use of potato

processing waste. Potato juice secondary stream obtained from potato starch processing

can be used as a high quality protein source for further applications (Kärenlampi and White,

2009). Potato peelings contribute certain superior functional and nutritional properties

and have been successfully used to replace wheat bran as a fiber source in bread (Toma et

al., 1979). Potato peel waste is also rich source of polyphenols (Mattila and Hellström,

2007) and minerals, especially iron (Tarazona-Díaz and Aguayo, 2013). According to

Maeder, et al. (2009), waste mash from dried potato flake processing contained similar

amounts of glycoalkaloids and phenolic compounds as the final commercial product,

making it a suitable byproduct to consider for animal feed. Data from Rodriguez de Sotillo

et al. (1994) suggests that antioxidant activity of freeze-dried potato peel extract compared

to that of BHA (butylated hydroxyanisole). Use at 200 ppm in foods kept concentrations of

glycoalkaloids below toxicity thresholds (discussed in Section 4.3). The ability to leverage

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these secondary product streams and capture beneficial compounds from potato waste

streams may prove useful for future applications and aid in enhancing sustainability of

potatoes in all forms. This would require consideration of safety and quality of waste

streams (including pesticide residue and glycoalkoloid content) but also investment into

processing lines suitable for transforming these products into usable materials or

intermediates.

In-Home Processing

While processed potato products remain the primary end use, a significant portion

(40~50%) of potatoes are distributed and sold on the fresh market to be used in homes and

for food service applications. Fresh potatoes that are home-grown or purchased in the fresh

market are processed/prepared, in order of popularity, via boiling/steaming,

baking/roasting, frying, microwaving, and other methods (Vreugdenhil et al., 2011).

Variations within each of these methods can produce hundreds of recipes, including soups,

salads, mashed potatoes, baked potato dishes, dumplings, pancakes, French fries, and on.

Other than differences in scale and intensity, approaches in home are similar to those

employed in commercial operations relying on similar unit operations such as peeling, size

reduction (slicing, cubing, etc.), thermal treatment, roasting, baking, boiling and frying. One

exception may be commercial French fry processing. Industrially, French fries often

undergo par frying and frying before consumption, which means there are two

opportunities for heat and mass (water for oil) transfer at the surface of the potato.

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Table 2. Common Commercial Potato Products Grouped By Processing Type (Bradshaw and Ramsay, 2009; Kirkman, 2007).

Product Category Common Products Sold in USA

Snacks Potato chips Sheeted or extruded products

Frozen Products Baked, frozen whole potatoes and half shells Blanched, IQF slices or cubes

Dehydro-frozen dices Hash Browns, patties, tots

French fries, crinkle cut, waffles, wedges, curly Various child products

Dehydrated Potato Products

Standard flakes Standard flakes, ground

Low peel flakes Flour

Granules Slices, dices, and shreds

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Nutritive Value and Perception of Potatoes & Potato Products

The nutritional value of potatoes and their derived products have long been

misunderstood by many consumers, based in part on the manner in which potatoes are

processed and prepared as well as the assumption that all potatoes result in high glycemic

response. In 1973, a survey of British women showed that 65% considered potatoes to be

fattening, 13% thought they provided a good source of energy, and only 2% thought that

they had any nutritional value (Burton, 1989, chap. 10). A study by Monteleone, et al.

(1997) revealed that in general, participants viewed potatoes in general as “filling”, and

boiled and baked potatoes were seen as “healthy”. However, these preparations were also

seen as bland and boring. Chipped and roast potatoes were viewed as more flavorful, but

they were also rated as highly fatty and fattening. Fearne (1992) also observed positive

attitudes in a population of British consumers. In regards to starch content, a study of UK

consumers revealed that participants thought starch-rich foods like potatoes were high in

energy and wouldn’t help them control weight (Stubenitsky and Mela, 2000). Results of a

study on “good foods gone bad” by Oakes (2004) showed that if a food contained added fat

and sugar (e.g. baked potato with sour cream), it was considered by respondents to be

lower in vitamins and minerals than the corresponding primary food alone (baked potato,

skin on). Participants viewed French fries as “very, very fatty” and “just carbs and fat”, and

stated that “fatty foods have no vitamins”. Spinach and potatoes (baked/skin on) contained

the highest overall levels of vitamins and minerals per serving out of 17 primary foods

tested including apples, strawberries, raisins, peanuts, carrots, mushrooms, milk, and corn.

However, respondents considered spinach, carrots, and apples highest in vitamins and

minerals (both carrots and apples would actually be close to the bottom of the list). Overall,

the study conveys that perception of the nutritional value of potatoes is strongly influenced

by factors (possibly historical, social, and cultural) other than their nutrient and

micronutrient content. In addition, this perception is strongly influenced by presence of

added fat.

In reality, potatoes are an inexpensive staple source of energy, contain relatively high

amounts of high-quality protein compared to other vegetables and starchy foods, and are an

important source of vitamin C, potassium, and other key micronutrients. However, as

stated previously, potatoes are often prepared and served with ingredients such as salt and

fat to increase their palatability, and fully gelatinized potato starch in these products

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contributes to a high glycemic index. Considering the complexity and variation in

preparation, it is more difficult to determine the nutritional benefits of potato products with

increased sodium and fat content of finished products (Table 3). This is further complicated

if the context of the full finished product or meal is not considered. Furthermore, potato

preparation practices are known to influence micronutrient and phytochemical profiles

through thermal degradation and leaching (reviewed in Decker and Ferruzzi, 2013).

In that context, the nutritional perception of processed potatoes should include their

carbohydrate content, in the form of starch, protein content/quality, fiber and presence of

key micronutrients including potassium, magnesium and vitamin C (Table 3). When

compared to other common sources of starch in the diet- cooked pasta or brown rice- a

serving of potatoes (with skins) contains less energy and carbohydrates and contains more

fiber, iron, Vitamin C, folate, and Vitamin B6 (US Department of Agriculture Agricultural

Research Service, 2014). While promising, these data do not take into account the

considerable diversity that exists in raw potato nutritional quality (Augustin, 1975), which

represents an opportunity to leverage breeding/selection and agronomic practices to

maximize the nutritional value of potato products. Combined with post-harvest and

processing strategies (discussed later) significant opportunities exist to better position

potato nutritional perception and value for consumers.

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Table 3. Proximate composition and nutritive value of potatoes, potato products, and comparable carbohydrate sources per 100 g of product (US Department of Agriculture Agricultural Research Service, 2014).

Component Unit Potato w/ Skin, Raw1

Sweet Potato Raw2

Potato, Flesh, Boiled

w/ Salt3

Potato, w/ Skin, Baked

w/ Salt4

Macaroni, Unenriched,

Cooked5

Brown Rice, Long grain,

Cooked6

Potato Chips, Plain, Salted7

French Fries Frozen, Baked,

w/ Salt8

DRV/ RDI

Moisture g 79 77 77 75 62 73 1.9 64 Energy kcal 77 86 86 93 158 111 532 158 2000 Protein g 2.0 1.6 1.7 2.5 5.8 2.6 6.4 2.8 50 Fat g 0.09 0.05 0.1 0.13 0.9 0.90 34 5.5 300 Carbohydrate g 17 20 20 21 31 23 54 26 300 Total Sugars g 0.78 4.2 0.85 1.1 0.56 0.35 0.33 0.37 Fiber g 2.2 3.0 2.0 2.2 1.8 1.8 3.1 2.0 25 Potassium mg 421 337 328 535 44 43 1196 478 4700 Phosphorus mg 57 47 40 70 58 83 153 87 1000 Magnesium mg 23 25 20 28 18 43 63 24 400 Calcium mg 12 30 8 15 7 10 21 12 1000 Sodium mg 6 55 241 10 1 5 527 324 2300 Iron mg 0.78 0.61 0.31 1.1 0.50 0.42 1.3 0.57 18 Zinc mg 0.29 0.30 0.27 0.36 0.51 0.63 1.1 0.35 15 Thiamin mg 0.08 0.08 0.10 0.06 0.02 0.10 0.21 0.13 1.5 Niacin mg 1.1 0.56 1.3 1.4 0.40 1.5 4.8 2.1 20 Riboflavin mg 0.03 0.06 0.02 0.05 0.02 0.03 0.09 0.03 1.7 Vitamin B6 mg 0.30 0.21 0.27 0.31 0.05 0.15 0.53 0.26 2 Folate ug 16 11 9 28 7 4 29 23 400 Vitamin B12 ug 0 0 0 0 0 0 0 0 6 Vitamin C mg 20 2.4 7.4 9.6 0 0 22 8.6 60 Vitamin A IU 0 14187 0 10 0 0 0 5 900 Vitamin E mg 0.01 0.26 0.01 0.04 0.06 0.17 10.5 0.39 30

1Report #11352. One medium potato (2.25-3.25”) is about 213 g. One cup is about 150 g. 2Report #11507. One 5” sweet potato is about 130 g. One cup is about 133 g. 3Report #11833. Flesh boiled without skin. One medium potato of 2.25” is about 167 g. One cup is about 156 g. 4Report #11828. One medium potato (2.25-3.25”) is about 173 g. One cup is about 122 g. 5Report #20400. One cup elbow macaroni is about 140 g. 6Report #20037. One cup of long-grain brown rice is about 195 g. 7Report #19411. Serving size is 28 g (1 oz). Values given equal about 3 servings. 8Report #11403. All types. 10 French fries weigh about 76 g.

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1.4.1.1 Starch and Resistant Starch

1.4.1.2 Content and Digestibility

Potatoes typically contain between 16-20% starch (Food and Agriculture

Organization of the United Nations, 2008a) in the form of extensively branched amylopectin

(70-80% of total starch), and more linear amylose (~20-30% of total starch) (Hoover,

2001). Potato starch is unique in the significant amounts of mono-phosphate esters

covalently bound primarily to amylopectin (Hoover, 2001) resulting in a very high swelling

power by provide repulsive forces within amylopectin chains, which allows water to more

easily penetrate the structure (Ek et al., 2012). Additionally, a small percentage of potato

starch is complexed with protein.

Potato starch can provide unique functionality in food applications due to its high

content of smooth medium (11-25 𝜇m) and large (>25 𝜇m) granules, high content of

covalently linked phosphate, long amylopectin chains, and high-molecular-weight amylose

(Bertoft and Blennow, 2009). It is commonly used as a thickener, stabilizer, gelling agent,

bulking agent, or water-holding agent. Limitations include low shear and thermal

resistance and high tendency to retrograde, however, starch modification can improve

these properties (Singh et al., 2009).

Native potato starch is classified as resistant starch, or starch that is undigested

within 120 minutes of consumption but rather passes on to be fermented in the large

intestine. Resistant starch can be classified as a type of dietary fiber and has demonstrated

benefits for colonic health (Nugent, 2005). In 1992, Englyst and others classified resistant

starch into three groups: RS1- physically entrapped starch; RS2- un-gelatinzed starch

granules that are resistant to digestive action of amylases; and RS3- retrograded starch

resulting from cooling after gelatinization. Now, another classification, RS4, exists to

describe starches that have been chemically modified in a way that reduces digestibility

(Sajilata et al., 2006). Native potato starch is characterized as RS2. It is crystalline in nature

(B-type) and highly compact, which protects it from action by amylases and digestive

enzymes. Extent of resistance is dependent on several factors including size, shape and

porosity of the potato starch granule, extent of molecular association, amylose:amylopectin

ratio, amylose chain length, and presence of amylose-lipid complexes (Ek et al., 2012;

Hoover, 2001). Starches with B-type crystallinity have been found to be more resistant to

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digestion than those with A-type crystallinity because enzymatic damage is confined to the

surface of granules (Sajilata et al., 2006). Native potato starch has been found to be less

digestible than other starches, such as maize, likely due to its high phosphorous and

amylose content as well as the large size of the starch granules (Noda et al., 2008).

1.4.1.3 Effect of Processing

Upon cooking, starch in potatoes is gelatinized and converted to rapidly digestible

starch (RDS), which means that it can be digested to glucose in 20 minutes or less (Englyst

et al., 1992). The amount of RDS present in cooked potato products will largely determine

glycemic response (Raigond et al., 2014). However gelatinized RDS present in cooked

potatoes (especially amylose) has a tendency to retrograde upon cooling and become slowly

digestible starch (SDS) or resistant to digestive enzymes (RS3 type) (Englyst and

Cummings, 1987). While dietary fiber content is relatively low in potatoes, generation of

resistant starch type RS3 through processing has been demonstrated to enhance dietary

fiber content (Sajilata et al., 2006; Thed and Phillips, 1995). Therefore, method of

preparation and consumption can have significant impacts on fiber content and glycemic

response of potatoes (Slavin, 2013). Strategies to increase dietary fiber content and

modulate glycemic response of potato products has been the subject of several

investigations which will be discussed further in Sections 5.5 and 6.2.

1.4.1.4 Fiber

Recommendations of daily fiber intake are 25 and 38 g of fiber per day for women

and men, respectively (Institute of Medicine, 2005). Potatoes contain approximately 1-2%

dietary fiber by weight, which is concentrated in the peels. While potato cannot be

considered a good source of fiber, a medium potato with skins can provide 3 g. At the level

that potatoes are consumed in many diets, potato may provide a significant portion of

dietary fiber (Kolasa, 1993). As stated in the previous section, processing can be used to

enhance the dietary fiber content of potato products.

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1.4.1.5 Sugars

In addition to starch, simple sugars are an important carbohydrate component of

potatoes. Wilson, et al (1981) found that glucose is the sugar at greatest concentration in

three varieties of potatoes, followed by fructose and sucrose, measured at both 3.3 and

7.2°C. However, Zhu, et al. (2010) reported that fructose had highest mean content in 16

varieties from Hong Kong, followed by sucrose, then glucose. Total sugar content can vary

significantly between and within varieties, and even within a tuber (Watada and Kunkel,

1955). Amrein, et al. (2003) reported free sugar content of 17 varieties to range from 30-

1537 mg/kg and 97-2550 for glucose. Values for sugar content reported in these studies

and throughout the literature range from <100 to >2000 mg/kg.

Overall, concentration of sugars are highest in immature tubers and decrease over tuber

development as starch synthesis is increased (Navarre et al., 2013; Payyavula et al., 2013).

However, the starch to sugar ratio can be impacted by storage conditions (See sections 2.1

and 2.2). For example, cold induced sweetening of potatoes is a significant problem where

potatoes stored at refrigerated temperatures undergo a biochemical conversion for starch

to reducing sugars (Watada and Kunkel, 1955). This process has detrimental impact on

finished processed products by promoting excessive brown color (Shallenberger et al.,

1959) and acrylamide formation (Zhu et al., 2010). Currently strategies including biotech

approaches are being leveraged to limit cold sweetening and enable refrigerated storage of

potatoes for fresh market and processing (Sowokinos, 2001).

1.4.2 Protein

Potatoes contain between 2-2.5% protein, making them one of the richest protein

source of any root or tuber crop (Food and Agriculture Organization of the United Nations,

2008a). In addition, because of its amino acid composition, potato protein is considered to

be a very high quality plant protein source (Desborough et al., 1981; Kärenlampi and White,

2009). However, it is important to recognize that many other plant and animal foods

contribute more protein to the diet than potatoes (Cotton et al., 2004). Potato proteins have

been classified as patatins, protease inhibitors, and other proteins (Kärenlampi and White,

2009). Protein content, like other nutritional components in potatoes, decreases with

maturity and is dependent on the cultivar/variety (Payyavula et al., 2013).

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In general, potatoes are high in amino acids asparagine, glutamic acid, and aspartic

acid, and low in methionine, cysteine, and histidine. Differences exist in amino acid content

between varieties (Brierley et al., 1996; Zhu et al., 2010). However, the amino acid

asparagine is most abundant in potatoes and has been positively correlated to acrylamide

formation during potato frying (Zhu et al., 2010). Therefore, as with reducing sugars,

interest in factors influencing free asparagine content have received significant attention.

Amrein, et al. (2003) reported asparagine content from 17 potato cultivars grown in

Switzerland ranged between 2010 and 4250 mg/kg FW. Interestingly, while varietal

differences existed, there appeared to be little influence of farming system or extent of

fertilization in this study (organic compared to conventional and integrated). Processing

approaches to reduction of asparagine content include addition of asparaginase to convert

asparagine to aspartic acid, yeast fermentation, lowering pH to protonate and/or partially

hydrolyze asparagine, blanching, addition of glycine or lysine to compete with asparagine

for binding, and addition of metal ions, among others (Friedman and Levin, 2008; Pedreschi

et al., 2014). Agronomic approaches include limiting excess nitrogen during fertilization

(asparagine is a nitrogen reservoir), choosing appropriate climate conditions, and of course

breeding for selection of low asparagine content (Morales et al., 2008). More recently,

transgenic approaches have been applied to the development not only of low reducing

sugar tubers (Rommens et al., 2008) but reduction in free asparagine up to 95% (Rommens

et al., 2006). In March of 2015 the FDA issued an evaluation of J.R. Simplot’s submission of

potatoes genetically engineered to reduce levels of asparagine and reducing sugars. It was

concluded that these genetically engineered potatoes are as safe for human consumption or

feed as parent varieties (U.S. Food and Drug Administration, 2015)

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1.4.3 Lipid

1.4.3.1 Natural Content

Potatoes have very little natural lipid, which comprises about 0.1% of fresh weight.

The large majority (90%) of fatty acids in potato are palmitic, linoleic, and linolinic acids.

Combined, polyunsaturated lipids make up approximately 70-76% of potato lipids. These

lipids are mostly associated with lipoprotein membrane structures (Galliard, 1973). In

contrast to other nutrients, lipid content in potato varieties does not widely vary. However,

potato products often consumed have large amounts of added lipid, usually mono- and poly-

unsaturated oils, through frying or panfrying.

1.4.3.2 Lipid Addition through Processing

Processing potatoes by frying or roasting involves the addition of fat, which

contributes additional energy and has potentially undesirable health effects. For example,

relative to the low lipid levels in raw potatoes, commercial frozen French fries typically

have about 15% lipid after final frying (Aguilera and Gloria-Hernandez, 2000). The French

fry and chips industries have developed ways of reducing fat content, and uptake and

retention of fat is often greater in home prepared, fried products compared to commercial

fried products (Bradshaw and Ramsay, 2009). For example, home-fried chips had

considerably more fat than commercial fried chips (40-45% compared to about 36%)

(Burton, 1989, chap. 9). Studies suggest that oil absorption during frying is mainly a surface

phenomenon and that most absorption occurs after the product is removed from the oil

(Aguilera and Gloria-Hernandez, 2000; Bouchon et al., 2003). Between structural,

penetrated surface, and surface fractions of oil, penetrated surface oil contributes the most

to total oil content (Pedreschi et al., 2008). Strategies to reduce lipid content of potato

products are discussed further in Section 6.1.

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1.4.4 Vitamins

1.4.4.1 Content

Potatoes are a naturally good source of many vitamins, and high consumption rates

make them a significant source of these vitamins in the US diet. Based on USDA nutrient

data, a serving of whole, baked potato provides an excellent source (>20% of DV) of vitamin

C and vitamin B6 and a good source (10-19% of DV) of niacin and folate (US Department of

Agriculture Agricultural Research Service, 2014). A serving of potato equates to 1 cup of

mashed/diced potato, or about one medium (2.5-3” diam.) boiled or baked potato (United

States Department of Agriculture, 2015). However, content of vitamin C and other vitamins

and nutrients have been shown to vary widely depending on potato variety, growing year or

environment, and storage length (Augustin, 1975; Love et al., 2004; Singh et al., 2009).

Folate analyzed in >70 potato cultivars varied between ~0.5 and 1.4 ug/100 g dw (Navarre

et al., 2009). In general, vitamin C is lost over storage of potatoes, but reported levels vary.

Dale et al. (2003) reported a two-fold difference in the average vit C. content between the

highest and lowest vitamin C-containing varieties analyzed (n=33) and significant losses in

content (35-55%) through storage for 4 months at 4°C. Mazza (1983) observed similar

losses in Kennebec, Norchip, and Russet Burbank varieties over several months of storage.

Linneman and others (1985) found that L-ascorbic acid (vit. C) content only decreased from

8.2 to 7.8 mg/100 g fresh weight in Bintje potatoes during 12 weeks of storage at 7°C

(1985). Interestingly, they also discovered a slight increase in ascorbic acid content over

11 weeks of storage at 16°C. Tudela et al. (2002) reported a small increase in vit. C content

in some varieties (Agria, Cara, Liseta, Monalisa) of potato strips stored in open air at 4°C for

6 days after cutting from long term-stored potatoes. However, vit. C in potatoes stored

under frozen and modified atmosphere conditions decreased over the storage period. Lee

and Kader (2000) discuss several pre-harvest, harvest, and post-harvest factors which

affect vitamin C content in potatoes and other vegetables.


Studies have shown relatively high retention of vitamins in heat-processed potatoes.

Augustin et al. (1978) measured retention of vitamin C, thiamin, riboflavin, niacin, folic

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acid, and vitamin B6 in whole boiled, baked, and microwaved potatoes (R. Burbank,

Katahdin, Norchip, and Pontiac). Discounting boiled peeled potatoes, retention (dry weight

basis) of vitamin C ranged from 73-80%, thiamin 86-95%, riboflavin 77-87%, niacin 93-

103%, folic acid 71-88%, and vitamin B6 91-100%. Navarre et al. (2010) also reported 120-

140%, 116-122%, and 118-155% retention of vitamin C in Bintje, Piccolo, and Purple

Majesty varieties, respectively, after microwaving, steaming, boiling, or baking. In a study

by Golaszewska and Zalewski (2001), cooking methods without water resulted in 73-92%

retention of vit. C. However, in other studies retention of vit. C and other vitamins through

processing is low and/or varies depending on processing method (Keller et al., 1990). Han

and others (2004) reported retention as low as 12-23% in boiled potatoes and as high as

67-79% in microwaved potatoes (ranges for Sumi, Chaju, and Dejima varieties). Lachman et

al. (2013) measured retention of vit. C in Agria (yellow-fleshed), HB Red, Rote Emma (red-

fleshed), Blaue St. Galler, Valfi, and Violette (purple-fleshed) potatoes. On average, boiled

peeled potatoes retained 70% compared to fresh peeled, and microwaved and baked whole

potatoes retained 66% and 38%, respectively, compared to whole fresh potatoes. In this

study, peeling did not significantly affect vit. C content. In general, it appears that potatoes

best retain vitamins after microwaving compared to other cooking methods. Vitamin C

from processed potatoes has demonstrated similar bioavailability to that of water (Kondo et

al., 2012).

1.4.5 Minerals

1.4.5.1 Content

Potatoes are an important source of many minerals, including (in order of percent

contribution to DRI), copper (Cu), iodine (I), potassium (K), iron (Fe), phosphorous (P),

manganese (Mn), magnesium (Mg), zinc (Zn), and calcium, (Ca) (Kärenlampi and White,

2009). When ordered by concentration, potatoes contain significant amounts of K, P, Mg,

Ca, Fe, Zn, Mn, Zn (US Department of Agriculture Agricultural Research Service, 2014).

Depending on soil and growing conditions, potatoes can also be a source of trace elements

such as Se. Many minerals, such as Ca, K, Mg, Fe, and Mn are far more concentrated in the

skin than the flesh, so peeling before processing reduces levels in finished products

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(Wszelaki et al., 2005). Mineral content can vary widely among cultivars, depending on

genetics and the environment in which the potato was grown (Ereifej et al., 1998; Rusinovci

et al., 2012; True et al., 1979; White et al., 2009). In addition, complex mineral interactions

within the soil and plant can impact mineral levels observed in different cultivars (White et

al., 2009). Andre, et al. found the iron concentrations varied from 30-155 ug/g dw, calcium

from 272-1093 ug/g dw, and zinc from 12.6-28.8 ug/g dw in 74 potato cultivars (2007a).

Concentrations of minerals inside the potato seem to especially depend on the availability of

minerals in the soil. Thus, the local soil composition as well as agronomic practices will

affect mineral composition in potatoes. As overall productivity and yield increases, there is

some concern that mineral content of commercial potatoes is decreasing as a results of

dilution or depletion, however, this relationship has not been firmly established

(Kärenlampi and White, 2009). Applying mineral fertilizers can increase mineral content,

accelerate plant growth, and increase yield (White et al., 2009). Variation among cultivars

also implies the potential for selective breeding to enhance mineral content of potatoes to

address micronutrient deficiencies in the developed and developing world.


True et al. (1979) conducted a study in which three varieties of white potatoes were

processed by four preparations: boiling with skin, without skin, oven baking, and

microwaving. Few significant mineral losses were found in any mineral through any

method of cooking in two of the three varieties. However, retention of minerals fell as low

as 42% in the Norchip variety. In a variety of Irish Potatoes, boiling did not affect calcium

levels, decreased magnesium levels, and actually increased iron levels compared to the raw

form (Dilworth et al., 2007). Overall, processing does not seem to greatly effect mineral

content, except by leaching and perhaps more so in some varieties than others.

1.4.5.3 Bioavailability

Human studies on the bioavailability of minerals from potatoes are limited.

Information on the bioavailability of key shortfall nutrients including potassium,

magnesium, calcium and iron has also been primarily limited to in vitro assays. Iron in vitro

bioaccessibility was found to be generally lower than calcium and magnesium (Dilworth et

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al., 2007). Using in vitro assays, Gahlalwal and Segal (1998) demonstrated that roasting or

baking could enhance the availability of potatoes’ minerals. It is of interest to note that

potatoes are high in compounds that improve absorption of minerals (such as Vitamin C),

and low in phytate and oxalate, which limit absorption of minerals (Brown et al., 2005;

Frossard et al., 2000). Phenolic compounds have also been shown to limit absorption of

minerals, which should be taken into account when considering breeding high-phenolic

varieties because this may reduce mineral bioavailability (Frossard et al., 2000). However,

further human studies are needed to better understand the true contribution of potatoes to

micronutrient status. This is particularly important for shortfall nutrients such as

potassium, calcium and iron.

Potato Bioactive Phytochemicals Content and Bioavailability

In addition to their macro- and micronutrient content, potatoes are well known to be

a source of several classes of dietary bioactive compounds, including phenolics,

polyphenolics, polyamines, tocochromanols, carotenoids and glycoalkaloids (Table 4). The

phytochemical content of potatoes has been the subject of several studies and also

summarized in previous reviews (Brown, 2005; Camire et al., 2009; Ezekiel et al., 2013).

Potatoes contribute significantly to dietary intake of phytochemicals, which are associated

with several health benefits (Section 6).

1.5.1 Phenolic Acids and Flavonoids

Phenolics belong to a broad class of plant compounds structurally defined as

containing one or more phenolic functional groups (Manach et al., 2004; Crozier et al.,

2009). While thousands of individual phenolic species exist in nature, several broad classes

have been defined based on specific structural conformations, oxidation states and/or

substitution patterns including: simple phenolic acids, and complex polyphenols including

stilbenoids, tannins and ellagitannins, lignans and flavonoids. Typically, flowers of the

potato plant have much greater levels of phenolic acids than any other part, followed by

leaves, stems, and then the tubers (Im et al., 2008). It is well-established that tuber skins

consistently have greater concentrations of phenolics than the flesh. The most abundant

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class of phenolic compounds in potato tubers are caffeoylquinic acids commonly known as

chlorogenic acids (CGAs) which may account for up to 90% of the total amount of phenolic

compounds in tubers (Payyavula et al., 2014). CGAs are synthesized in the potato through

esterification of trans-cinnamic acids, primarily caffeic acid, with quinic acid (Stöckigt and

Zenk, 1974). The most abundant CGAs in potato are 5-O-caffeoylquinic (5-CQA, chlorogenic

acid) and its isomers 3- and 4-CQA known as, neochlorogenic and cryptochlorogenic acid,

respectively (Andre et al., 2007b; del Mar Verde Méndez et al., 2004; Deusser et al., 2012; Im

et al., 2008; Manach et al., 2004; Zhu et al., 2010). Free caffeic acid has been reported at

significant levels in potatoes (<1-50 mg/100 g dw), however, the reported levels may

depend on experiment methodology, as chlorogenic acid can be hydrolyzed to caffeic and

quinic acid by acidic or alkaline conditions (Antolovich et al., 2000).

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Table 4. Potato phytochemicals: Range of content of main phytochemicals in key commercial and select specialty varieties, grouped by phytochemical and potato flesh color.

Name Range1 Mean1 Potato Part

Potato Flesh (Skin) Color3

Number of Varieties

Source

Chlorogenic Acid 2.6 23 7.2 Flesh2 W,Y (Y,R) 16 Deusser (2012)

(5-Caffeoylquinic acid) 24 170 68 Whole W, Y 21 Navarre (2011)

mw 354 39 85 11 Whole W (Bl,R,B) 4 Mendez (2004)

17 146 31 Whole W,Y (W,Y,P,R) 18 Andre (2007)

3.3 203 54 Whole W,Y (Y,B,R) 24 Im (2008)

42 318 138 Whole W,Y (Y,B,R) 8 Xu (2009)

42 219 89 Whole unk. 16 Zhu (2010)

22 231 74 Whole unk. 19 Navarre (2011)

44 1275 404 Whole R, P 5 Andre (2007)

383 383 Whole P 1 Deusser (2012)

80 330 230 Whole R, P 9 Navarre (2011)

Cryptochlorogenic Acid 2.8 124 15 Whole W, Y 21 Navarre (2011)

(4-Caffeoylquinic acid) 0.2 12 3.2 Flesh2 W,Y (Y,R) 16 Deusser (2012)

mw 354 1.4 46 9.8 Whole W,Y (W,Y,P,R) 18 Andre (2007)


9.1 77 32 Whole R, P 5 Andre (2007)

13 64 39 Whole R, P 9 Navarre (2011)


Neochlorogenic Acid 0.7 20 3.6 Whole W, Y 21 Navarre (2011)

(3-Caffeoylquinic acid) 0.3 12 2.5 Flesh2 W,Y (Y,R) 16 Deusser (2012)

mw 354 0.6 9.6 3.4 Whole W,Y (W,Y,P,R) 18 Andre (2007)

16 83 29 Whole unk. 16 Zhu (2010)

0.1 19 4.0 Whole unk. 19 Navarre (2011)


3.1 20 9.2 Whole R, P 5 Andre (2007)

2.9 44 24 Whole R, P 9 Navarre (2011)

Caffeic Acid 0.02 0.07 0.04 Flesh2 W,Y (Y,R) 16 Deusser (2012)

mw 179 0.5 14 6 Whole W, Y 21 Navarre (2011)

3.5 5.5 4.5 Whole W (Bl,R,B) 4 Mendez (2004)

0.5 15 6.7 Whole W,Y (Y,B,R) 24 Im (2008)

0.9 3.1 1.6 Whole unk. 16 Zhu (2010)


0.9 6.2 2.8 Whole W,Y (W,Y,P,R) 18 Andre (2007)

2.4 2.4 Whole P 1 Deusser (2012)

1.3 14 7.2 Whole R, P 5 Andre (2007)

5.2 15 10 Whole R, P 9 Navarre (2011)

Ferulic Acid 0.02 0.06 0.03 Flesh2 W,Y (Y,R) 16 Deusser (2012)

mw 194 0.5 4 2 Whole W (Bl,R,B) 4 Mendez (2004)


p-Coumaric Acid n.d. n.d. n.d. Flesh2 W,Y (Y,R) 16 Deusser (2012)

mw 164 n.d. 0.6 0.4 Whole W (Bl,R,B) 4 Mendez (2004)

n.d. n.d. Whole P 1 Deusser (2012)

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Name Range1 Mean1 Potato Part

Potato Flesh (Skin) Color3

Number of Varieties

Source

Rutin n.d. 14 3.6 Whole W, Y 21 Navarre (2011)

(Quercetin-3-rutinoside) n.d. 1.6 0.36 Flesh2 W,Y (Y,R) 16 Deusser (2012)

mw 610 n.d. 19.1 4.6 Whole V 18 Andre (2007)

n.d. 1.7 0.8 Whole unk. 19 Navarre (2011)


n.d. 16.6 4.9 Whole R, P 5 Andre (2007)

0.5 3.5 1.4 Whole R, P 9 Navarre (2011)

Kaempferol-3-rutinoside n.d. 4.5 0.9 Whole W, Y 21 Navarre (2011)

mw 594 n.d. 0.3 0.03 Flesh2 W,Y (Y,R) 16 Deusser (2012)

n.d. 22.4 2.8 Whole W,Y (W,Y,P,R) 18 Andre (2007)

n.d. 2.5 0.9 Whole unk. 19 Navarre (2011)


n.d. 22.7 6.1 Whole R, P 5 Andre (2007)

n.d. 10.6 3.5 Whole R, P 9 Navarre (2011)

Catechin n.d. 0.07 0.007 Flesh W,Y (Y,R) 16 Deusser (2012)

mw 290 48.5 66 57 Whole W (Bl,R,B) 4 Mendez (2004)


Total Anthocyanins n.d. 54 33 Flesh W (P) 9 Lewis (1998)

1.4 5.2 3.8 Whole W,Y (W,Y,P,R) 5 Andre (2007)

2 46 18 Whole W,Y (P,R) 13 Jansen (2006)

15 1160 640 Flesh R, P 4 Lewis (1998)

n.d. 1633 468.8 Whole R, P 5 Andre (2007)

42 785 238 Whole R, P 17 Jansen (2006)

1All units given in mg/100 g dw. If originally on ww basis, converted to dw using 80% moisture. 2Values for inner flesh and outer flesh were averaged 3W= White, Y= Yellow, R= Red, P=Purple, B=Brown/Tan, Bl= Black

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Figure 1. Structures of primary phytochemicals found in Solanum tuberosum varieties. Top six structures illustrate anthocyanidin aglycones which are found as acylated glucosides in potatoes. Common epimers of chlorogenic acid (bottom) include 3-O-caffeoylquinic and 4-O-caffeoylquinic acids where caffeic acid is at the 3 or 4 position, respectively.

Chlorogenic Acid

Cyanidin Peonidin

Malvidin Delphinidin Pelargonidin

Petunidin

5-O-caffeoylquinic acid (5-CQA) (chlorogenic acid)

quinic acid caffeic acid

28

Flavonoids are a diverse subgroup of polyphenols characterized structurally by a 15

carbon (C6-C3-C6) flavan skeleton (Bravo, 1998; Beecher, 2003; Pietta, 2000). Flavonoids

are subdivided into six major groups including anthocyanins, flavonols, flavan-3-ols

(flavanols), flavanones, flavones and isoflavones (Beecher, 2003; Manach et al., 2004). In

general, levels of flavonoids are lower in potatoes than those for phenolic acids and

chlorogenic acids. However, appreciable levels (~0.6-21 mg total/100 g dw ) of flavonols,

including quercetin-3-rutinoside (rutin), quercetin, myricetin, and kaempferol-3-rutinoside

(Blessington et al., 2010; Lewis et al., 1998; Navarre et al., 2011; Payyavula et al., 2013)

have been reported in certain potato varieties. Mendez, et al. (2004) quantified levels of the

flavan-3-ol catechin in four varieties of potatoes from the Canary Islands. For these

varieties, catechin levels (~48-66 mg/100g dw) were comparable to those of chlorogenic

acid. Brown et al. (2005) and Reddivari et al. (2007) have also reported similar catechin

levels in select potato varieties. However, generally, flavan-3-ols have not been routinely

reported, or if reported, only at low levels in select varieties (Deusser et al., 2012; Navarre

et al., 2011).

In pigmented red and purple potatoes, anthocyanins are the primary flavonoid

present. These flavonoid pigments provide red, purple to blue colors common to many

flowering plants, vegetables and berries (Veitch and Grayer, 2008). In plants, anthocyanins

exist almost exclusively as glycosides of anthocyanidins (defined as the aglycones) in

acylated and non-acylated forms (Eichhorn and Winterhalter, 2005). Six main

anthocyanindin forms in potatoes include: cyanidin, malvidin, delphinidin, peonidin,

petunidin and pelargonidin (Del Rio et al., 2010, Brown, 2005). In purple varieties

petunidin, malvidin, and peonidin derivatives are most common, while cyanidin and

pelargonidin derivatives dominate in red-fleshed varieties (Brown et al., 2003; Eichhorn

and Winterhalter, 2005; Payyavula et al., 2013). Anthocyanin content has been report up to

1600 mg/100 g dw in whole pigmented potatoes, but values range widely between varieties

(Andre et al., 2007b; Jansen and Flamme, 2006; Lewis et al., 1998).

1.5.2 Carotenoids and Tocochromanols

Carotenoids are a class of lipid-soluble plant pigments that impart the bright yellow,

orange, and red colors commonly seen in fruits and vegetables. While greater than 700

carotenoid species have been identified in nature, only six are commonly found in the

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human diet and have been associated with health outcomes in humans (Maiani et al., 2009).

These include lutein, zeaxanthin, - cryptoxanthin, -carotene, -carotene, and lycopene.

Bright orange, red and yellow fruits and vegetables are often associated with having high

carotenoid content. Orange-fleshed sweet potatoes have been reported to have a diverse

range but generally high levels of carotenoids, mostly in the form of provitamin A -

carotene. In a review by Bovell-Benjamin (2007) levels of -carotene were found to range

between 4.5 mg/100g FW to upwards of 16,000 mg/100g FW. Biofortified orange sweet

potatoes varieties have been reported to have levels reaching 79.1-128.5 mg/100 g DW

(Donado-Pestana et al., 2012) . With such high levels of provitamin A carotenoids present

in these tuber, it is not surprising that orange-fleshed sweet potatoes have become

increasingly important in food security and nutritional intervention strategies for at risk

populations in developing countries (Bovell-Benjamin, 2007).

In contrast to orange-fleshed sweet potatoes, white- and yellow-fleshed and other

colored (purple, red) Solanum tuberosum varieties do not typically accumulate high levels of

carotenoids. In potatoes, non-provitamin xanthophyll carotenoids (lutein and zeaxanthin)

predominate (Breithaupt and Bamedi, 2002; Payyavula et al., 2013). An analysis of 23

native Andean potato varieties of all colors, lutein, zeaxanthin, neoxanthin, violaxanthin,

and antheraxanthin were the most common carotenoids, followed by beta-cryptoxanthin

and beta-carotene at minor levels of <1 mg/100 g dw (Andre et al., 2007b).

Tocochromanols are a class of eight related compounds that collectively contribute to

Vitamin E content in foods. These include four tocopherols (, and ) and four

tocotrienols (, and ), which differ structurally by the position and number of methyl

groups on the chromanol ring (Dörmann, 2007). Potatoes are not considered to be a rich

source of tocochromanols (Chun et al., 2006). In studying oxidative damage to potatoes

through low temperature storage, Spychalla and Desbourogh (1990) reported a-tocopherol

contents ranging between 13 and 29 ug/100g FW. Similarly, Andre et al (2007) reported

that typical potato varieties contain about 0.7-4.5 ug/g fresh weight of alpha-tocopherol,

although some wild Andean varieties contain up to 21 ug/g dry weight. Only alpha-

tocopherol, not beta- or gamma-tocopherol, was identified in these varieties (Andre et al.,

2007b).

While the potato itself is not considered a good source of vitamin E, potato products

often have higher levels of tocochromanols by virtue of the oils in which they are prepared.

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Vegetable oils are a rich source of tocochromanols (Falk and Munné-Bosch, 2010). During

frying, potatoes can absorb significant amounts of oils and by extension the tocochromanols

that these oils possess (Fillion and Henry, 1998). Tocopherols can deteriorate through

frying operations, leading to changes in both tocopherol and lipid profiles (Gordon and

Kourkimskå, 1995; Rossi et al., 2007). Andrikopoulos et al. (2002) reported significant

retention of these compounds has been reported through up to eight frying uses, typical of

household preparation. However, while susceptible to oxidation during frying, tocopherols

from vegetable oils can provide some measure of oxidative stability to finished products

(Ruiz et al., 1999).

1.5.3 Glycoalkaloids

As with other members of the nightshade family, potatoes produce glycoalkaloids that

function as phytoalexins protecting tubers from infections but also possess potentially toxic

effects in humans. In potatoes two main a-solanine and a-chaconine predominate with

minor forms including leptine, demissine and leptinine also found in potatoes tubers

primarily accumulating the peels of potatoes (Friedman, 2006).

Historically viewed as potentially toxic compounds, potato glycoalkaloids, when consumed

at high levels (>3-10 mg) have been documented to produce neurotoxic effects through

inhibition of cholinesterase activity (Bushway et al., 1987) and proinflammatory effects in

the GI and other tissues through disruption of cell membrane integrity, specifically

cholesterol containing cell membranes (Keukens et al., 1992). However, at lower levels

these compounds have also demonstrated the potential to promote anti-inflammatory

responses (Kenny et al., 2013) and anti-cancer effects primarily through disruption of

cellular membranes of cancer cells (Lee et al., 2004).

The extent to which adverse health effects could be attributed to glycoalkaloid

intake as part of a normal diet containing potatoes is not clear. Regardless, significant

efforts have been made to mitigate levels of these potentially toxic compounds in potatoes.

New commercial potato cultivars should have glycoalkaloid levels below 20mg/100g fw

(~1 mg/g dw) to meet recommended safety guidelines (Friedman et al., 1997). Most

commercial varieties evaluated have levels below this mark, but some primitive germplasm

and wild-species have much higher levels. Glykoalkaloids other than solanine and

chaconine contribute to these high levels (Navarre et al., 2011). Glycoalkaloids also appear

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to decrease in concentration over tuber maturation (Papathanasiou et al., 1998; Payyavula

et al., 2013). The higher glycoalkaloid content of younger potatoes could be a potential

limiting factor in the commercial use of immature potatoes. Peeling significantly reduces

glycoalkaloid content (by ~75%) (Mäder et al., 2009), and blanching also significantly

reduces glycoalkaloid content via leaching. Glycoalkaloids are reported to be relatively

stable to heating, so further heat processing appears to have little effect on glycoalkaloid

concentration (Mäder et al., 2009).

1.5.4 Factors Impacting Phytochemical Content in Potatoes and Potato Products

1.5.4.1 Natural Variation

As with diversity in other fruits and vegetables, phytochemical content can differ

widely among potatoes varieties. Blessington et al. (2010) found that genotype influenced

levels of 80% and 50% of phenolic acids and flavonoids, respectively. Overall, purple and

pink-fleshed potatoes have higher concentrations of phenolics than yellow and white-

fleshed varieties, and these differences are often dramatic (Payyavula et al., 2013). Navarre,

et al. (2011) conducted a study on 50 varieties of potatoes, including colored-, yellow-, and

white-fleshed potatoes, and found a 6-fold difference in content of total phenolics between

the lowest (~170 mg/100g R. Burbank) and highest (~950 mg/100g Magic Molly)

varieties. As previously stated, similar diversity can be observed with carotenoid content in

both orange and other colored potatoes varieties (Bovell-Benjamin, 2007). Much of this

diversity is a result of centuries of breeding for traits such as color, texture and flavor. More

recent efforts to increase the content of select nutritive phytochemcials including

carotenoids (Ducreux et al., 2005) and tocopherols (Crowell et al., 2007) continue to add to

this available variety.

1.5.4.2 Effect of Environment/Storage

Location of growth may impact phytochemical content. Researchers found that

Colorado tubers had higher levels of anthocyanins when compared to the same tubers

grown in Texas, while the tubers grown in Texas grew slightly larger than those grown in

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Colorado. These differences could be explained by cooler temperatures, yet longer days

(more solar radiation) in Colorado. Phenolic acid content did not significantly differ

between locations (Reyes et al., 2004).

Research also indicates that wounding treatment, light, and temperature can affect levels of

polyphenols in potatoes during storage, though content and effects can vary widely among

cultivars. Petersson, et al.(2013) show that wounding and light treatment both increased

glycoalkaloid content in 21 tuber varieties, but heat treatment did not. Tudela et al.(2002),

demonstrated significant flavonol and caffeic acid derivative accumulation in fresh cut

potatoes after 6 days of storage. Accumulation was greater in the light than in the dark.

Some research indicates that long-term stored fresh potatoes have greater amounts of

phenolic compounds than short-term stored or non-stored fresh potatoes, though effects

vary depending on compounds analyzed and type of storage treatment (Blessington et al.,

2010; Juan A. Tudela et al., 2002).

1.5.4.3 Effect of Maturity and Plant Part

Immature potatoes, or “new potatoes” are often reported to have greater amounts

phytochemicals and vitamins, and in general concentration of these compounds per unit

weight decreases as the tubers mature. The percent decrease at final maturity varies widely

and seems to be influenced by variety type and growing conditions (Navarre et al., 2011;

Payyavula et al., 2013; Reyes et al., 2004). Reyes, et al. (2004) discovered that for three

varieties of purple-fleshed potatoes grown in both Texas and Colorado, the decrease in

anthocyanins through maturation (ranged from 19-57%) was greater than the decrease in

phenolic acids through maturation (ranged from 1-29%). However, total yield of phenolics

and anthocyanins in this study was greater at later maturity stages because the size of each

tuber was greater.


In recent decades, several authors have demonstrated decreases in phytochemicals

and antioxidants through processing, though degree of degradation varied widely (See

Table 5). For example, Im, et al. (2008) investigated the effect of several types of processing

on phenolics in the Superior potato variety. Potatoes were boiled with 1% salt, boiled with

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3% salt, oven heated, steam heated, microwaved, sautéed, and fried. Results indicate that

chlorogenic acid was best retained via oven heating, and that most all the processing

methods had between ~60-80% retention of chlorogenic acid. Maeder et al. (2009) suggest

that decreases in chlorogenic acid during processing could occur through isomerization to

neochlorogenic acid. Though they found that cryptochlorogenic acid levels remained

relatively stable during processing, this may actually be a result of simultaneous

degradation and formation from isomerization, rather than truly static levels.

However, more recently, evidence has emerged suggesting that polyphenols do not always

decrease during processing, and may actually increase. Deusser and others (2012)

demonstrated that boiling did not significantly affect chlorogenic and ferulic acid or rutin

levels, but the levels of neochlorogenic and cryptochlorogenic acids, vanillin, and catechin

were increased. Navarre et al. (2010) also noticed marked increases in content of

chlorogenic acids as well as flavonols and Vitamin C after boiling, microwaving, steaming, or

baking, which they do not attribute to enhanced extractability of these compounds post-

processing. It is notable that these authors endeavored to apply the gentlest process

possible while still fully cooking the potato, which may partially explain the greater levels of

phytochemicals post-processing compared to those found by most other authors. In

addition, the authors suggest that inactivation of degradative enzymes through heating

could improve polyphenol content. It appears that processing may affect phenolic

compounds differently. Blessington et al. (2010) found that average levels of phenolic acids,

including 5-O-CQA and caffeic, vanillic, and p-coumaric acids, and epicatechin actually

increased, while levels of quercetin dehydrate decreased. Total carotenoids in this study

did not change through processing, except a slight decrease after boiling. Jaarsveld et al.

(2006) also observed high retention (70-90%) of beta-carotene in sweet potatoes through

boiling.

Some research has been conducted on the process stability of anthocyanins in

various foods (Patras et al., 2010), though studies specific to potato appear to remain

limited to storage, rather than processing, conditions. In regards to other vegetables,

Volden et al. (2008) observed that blanching, boiling, and steaming reduced total

monomeric anthocyanins in purple cabbage by 59, 41, and 29% respectively. Kirca et al.

(2007) found that black carrot anthocyanins (45 Brix, pH 4.3) had a half-life of 14.8, 6.9, and

3.2 hours when held at 70, 80, and 90°C, respectively. These authors postulate that the

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relatively high stability of carrot anthocyanins during heating could be due to their acylated

form (Giusti and Wrolstad, 1996). Because pigmented potatoes also contain primarily

acylated anthocyanins (Giusti and Wrolstad, 2003; Rodriguez-Saona et al., 1998), their

anthocyanins, like those of black carrot, may also be relatively stable.

Some research does point to the potential for an increase in antioxidant capacity

with certain types of cooking (Pellegrini et al., 2009). In a study conducted by Navarre et al.

(2010), Trolox equivalent antioxidant capacity increased or stayed the same in two

varieties of potatoes after microwaving, steaming, boiling, and baking. Retention ranged

from 101-174% in whole processed potatoes compared to raw whole potatoes. However,

Xu et al. (2009) found that boiling, baking, and microwaving decreased ORAC values in 8

varieties of potatoes, with retention ranging from 68-97% depending on variety and

cooking method. Here, the differences in measurement must also be considered.

While various forms of phytochemicals have traditionally been viewed as highly susceptible

to degradation through heating, some results suggest that when the process is minimized,

levels of phytochemicals and antioxidants may be unaffected, or may be altered physically

or chemically in a manner that facilitates their ability to act as an antioxidant. However, it

seems that the observed effect of processing on phytochemicals may vary more based on

research method than on the processing method or type of potato. More research is needed

which controls for the high natural variation in potatoes as well as potential changes in

extractability with processing to understand these disparate results.

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Table 5. Effects of several processing methods on potato phytochemical content, grouped by processing type and author.

Processing Type

Processing Methods Potato Part Varieties Polyphenol(s)/Nutrients Effect of

Processing1 Approx.

Retention2 Source

Peeling Whole potato steam peeled 9 sec @220°C

Flesh Karlena Sum of phenolics by HPLC

55% from raw whole

Maeder (2009)

Boiling Whole potato boiled 18

min Whole

(New Potato) Purple Majesty, Piccolo, Bintje

Total phenolics, CGA, NCGA, CCGA, Rutin, Kaempferol, Vit C.

100-300% from raw whole

Navarre (2010)

Whole potato boiled, then flesh and peel

separated Flesh Bintje

CGA, ferulic acid, rutin 100-110% from

raw flesh Deusser (2012)

caffeic acid, NCGA, CCGA, catechin,

vanillin

600-900% from raw flesh

Flesh boiled 15 min Flesh HB Red, Rote Emma, Blaue St.

Galler, Valfi, Violette, Agria chlorogenic acid


Lachman (2013)

Potato dices (with peel)

boiled 25 min Whole

Atlantic, ATX85404-8W, Innovator, Krantz, NDTX4930-W, R. Burbank,

Santana, Shepody

CGA, caffeic acid, vanillic acid, p-coumaric acid, epicatechin

106-300% from raw whole Blessington

(2010) quercetin dihydrate

40% from raw whole

Slices blanched 20 min @

70°C Flesh Karlena Sum of phenolics by HPLC

90% from raw flesh

Maeder (2009)

Strips boiled for 1.5 min

in pressure cooker Flesh Monalisa

Quercetin derivatives, caffeic acid derivatives


Tudela (2002)

Whole potato boiled 30

min Whole NDA 1725 CGA

40% from raw whole

Dao (1992)

Whole potato boiled 15

min Whole

Dakota Pearl, Goldrosh, Nordonna, Norkotah, Red Norland, Sangre,

Viking, Dark Red Norland

Total phenolics (Folin)


Xu (2009) CGA, CCGA, NCGA


Plugs boiled 10 min Whole Superior CGA, CGA isomer (unidentified)


Im (2008)

Whole potatoes boiled 18

min Peel Van Gogh, Rosamund, Nicola

caffeic, ferulic, sinapic, vanillic, p-coumaric, syringic

90-140% from raw peel

Mattila (2007)

Steam Cooking Whole potato steamed

15 min Whole




Navarre (2010)

Slices steam cooked 30

min @ 100°C Flesh Karlena Sum of phenolics by HPLC

80% from raw flesh

Maeder (2009)

Strips steamed 2 min in

pressure cooker Flesh Monalisa


55% from raw flesh

Tudela (2002)

Plugs cooked 10 min in

steam cooker Whole Superior CGA, CGA isomer (unidentified)


Im (2008)

Microwaving Whole potato

microwaved 2.5 min Whole




Navarre (2010)

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Whole potato cubes microwaved 10 min

Whole HB Red, Rote Emma, Blaue St.

Galler, Valfi, Violette, Agria chlorogenic acid


Lachman (2013)

Potato dices (with peel)

microwaved 2.5 min Whole


Santana, Shepody




30% from raw whole

Plugs cooked for 1 min on

high heat Whole Superior CGA, CGA isomer (unidentified)


Im (2008)

Whole microwaved 30

min @ 218°C Whole NDA 1725 CGA

54% from raw whole

Dao (1992)

Strips microwavved 4 min Flesh Monalisa Quercetin derivatives, caffeic acid

derivatives


Tudela (2002)

Whole potato

microwaved 5 min Whole





Xu (2009) CGA, CCGA, NCGA


Baking Whole potato baked 30

min @ 350°C Whole




Navarre (2010)

Baked, hot air oven, 45

min @ °C Flesh

HB Red, Rote Emma, Blaue St. Galler, Valfi, Violette, Agria

chlorogenic acid


Lachman (2013)

Potato dices (with peel) microwaved 15 min @

204°C Whole


Santana, Shepody




40% from raw whole

Whole baked 45 min @

212°C Whole NDA 1725 CGA

0% from raw whole

Dao (1992)

Plugs baked in foil 10 min

@ 200°C Whole Superior CGA, CGA isomer (unidentified)


Im (2008)

Whole tubers baked 40

min @ 178°C Whole





Xu (2009)

CGA, CCGA, NCGA


Frying Potato dices (with peel) fried in tea balls 1 min @

191°C Whole


Santana, Shepody




20% from raw whole

Plugs boiled for 7 min, fried 30 sec twice @

170°C Whole Superior CGA, CGA isomer (unidentified)


Im (2008)

Frozen French fries Flesh Unk. CGA

0 mg/100 g dw Dao (1992)

Strips fried 4 min @

190°C Flesh Monalisa



Tudela (2002)

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Panfrying/ Sautéeing

Pieces sautéed in pan 3 min

Whole Superior CGA, CGA isomer (unidentified)


Im (2008)

Drying Mashed slices drum dried

@ 160°C Flesh Karlena Sum of phenolics by HPLC

80% from raw flesh

Maeder (2009)

1Shapes represent general increase, decrease, or no change in potato phytochemical based on retention from flesh 2Retention reported or calculated by [amount remaining in processed sample/original amount in raw flesh or whole]

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1.5.5 Bioavailability of Phytochemicals in Potatoes

In addition to providing nutrients, potatoes may serve as a unique matrix to delivery

bioactive phytochemicals. While the bioavailability of carotenoids and phenolics from

plant foods has been the subject of intense investigation (reviewed by Crozier et al., 2009;

Del Rio et al., 2010; Ferruzzi, 2010; Manach et al., 2005b, 2004; McGhie and Walton, 2007;

Neilson and Ferruzzi, 2011) much less is known regarding availability of potato derived

phytochemicals. The process of phytochemical absorption is complex and involves both pre-

absorptive and absorptive events that ultimately determine the site and extent of

absorption as well as circulating forms and tissue profiles. Interactions in the gut with

macronutrients and micronutrients and the availability of these phytochemicals for

absorption and reaction is a critical component to the health benefits potentially derived

from potatoes. Focusing on food matrix and gut specific pathways, the overall absorptive

process can be compartmentalized to include (1) release and solubilization of the

phytochemical in the gut during digestion followed by (2) intestinal absorption/metabolism

and (3) entrance into circulation and further tissue distribution prior to (4) final

elimination (Neilson and Ferruzzi, 2011). Differences exist depending on the nature of the

phytochemical (lipid versus water soluble) as well as affinity for transporters (active versus

passive transport). This is summarized in Figure 2 and described in more detail for potato

phenolics and carotenoids.

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Figure 2. Overview of the digestion and intestinal absorption of phytochemical from potatoes. Both lipid soluble and water soluble phytochemicals require initial release from the food matrix by digestion and solubilization either in bulk oil or aqueous continuous phase of chime in the gut. This digestive release is dependent on specific association in the food matrix between phytochemcials and macronutrients (starch, protein and lipid). Lipid soluble carotenoids and tocopherols released from potato matrix associate initially in bulk oil during initial oral and gastric processing. Subsequent digestion of the oil in the small intestine facilitates partitioning of carotenoids and tocopherols to bile salt lipid micelles. Similarly, phenolics associated with starch and protein in the potato matrix must be released by digestion in the stomach and small intestine. Intestinal absorption of can then be mediated by both passive diffusion and active/facilitated processes involving transporters such as SCRB1 (carotenoids) and MCT and GLUT2 (phenolics). Active/facilitate transport may be modulated by presence of macronutrients released during digestion (fatty acids and glucose). Once internalized in the enterocyte, phytochemicals can be metabolized prior to their transport/secretion into circulation and further metabolism (hepatic) or tissue distribution and excretion. Unabsorbed phytochemicals would be made available for metabolism by gut microbiota. (Adapted from mechanism described by Neilson and Ferruzzi, 2011).

PotatoPhytochemicals

FatsolubleCarotenoids(CRT)Tocopherols(TOC)

WatersolublePhenolicacids(PA)

ChlorogenicAcid(CGA)Flavonoids(FLA)

Smallintes ne

Stomach

ColonMicrobiota

CGAPAFLA

FLA

CGAPAFLA

Ac veTransport

Ac ve

Metabolism

PP-M

CGAPAFLA

PP-M

CGAPAFLA

FLA

PP-M

MicrobialMetabolism

Feces

PAPP-CMPP-CM

Lipid(TAG)

Ini alReleaseFromfoodmatrix

CRTTOC

Solubilizedinbulkoil

LipidDiges on

CRTTOC

TransfertoBilesaltlipid

micelles

CRTTOC

CRTTOC

CRTTOC

CRTTOC

CRTTOC

Enterocyte Hepa c/portalcircula on

EnterocyteLympha cCircula on

BloodCircula on

ChylomicronSynthesis

Packaging

FFAMAG

ChylomicronSecre on

CRTTOC

Passivetransport

StarchDiges on

a-amylase

Furtherreleasebydiges on

CGA,PAFLA

Glu Glu

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1.5.5.1 Bioavailability of Potato Polyphenols

The bioavailability of chlorogenic acid and anthocyanins from foods can be

categorized as modest to very poor, respectively. While approximately one third of ingested

chlorogenic acid has been reported to be absorbed in the small intestine following a

supplemental dose (Olthof et al., 2001), anthocyanin bioavailability is substantially lower-

typically ranging below 2% in many animal and human studies (Faria et al., 2013). In

addition, bioavailability of acylated anthocyanins, the primary forms found in pigmented

potatoes, is thought to be lower than that of non-acylated anthocyanins (Kurilich et al.,

2005). For chlorogenic acid, significant bioavailability research has been reported for other

matrices such as coffee. Between 10-30% absorption has been observed when including

both free and metabolized chlorogenic acid in circulation (Erk et al., 2012; Farah et al.,

2008; Stalmach et al., 2014). While in vivo studies are limited with potatoes, evidence of

phenolic absorption from sweet potato tubers (Ipomoea batatas) confirms absorption of

both phenolics in animals and humans (Harada et al., 2004; Oki et al., 2006; Suda et al.,

2002). Generally absorption of anthocyanins was observed to be rapid with Tmax values of

30min or less and modest Cmax values only in the nM range. These results are consistent

with those reported for other phenolics from other plant food matrices.

Similar findings were observed using an in vitro model to assess the bioaccessibility

of phenolics from various potato varieties. Miranda, et al. (2013) observed that polyphenols

in potatoes and sweet potatoes are released during the gastric and small intestinal digestion

phase, but only modestly absorbed (0.1-0.9%) by Caco-2 human intestinal cells. These

results suggest that release from the food matrix may not be a limiting factor for potato

phenolics, but consistent with other food matrices, intestinal transport and metabolism

likely remain the rate limiting step (Neilson and Ferruzzi, 2011).

One factor to consider regarding potato phenolics is the potential for direct and

indirect interactions between potato starch and endogenous phenolics. The presence of

carbohydrate in a food matrix either as simple sugars or digestible starch have

demonstrated the ability to enhance flavonoid absorption in both humans (Cohen et al.,

2011; Schramm et al., 2003) and animal models (Neilson et al., 2010; Peters et al., 2010).

This impact is believed to be due both to pre-absorptive increases in flavonoid solubility

and to interaction with specific absorptive mechanisms at the intestinal level likely

including competitive interactions with glucose transporters, notably SGLT1 and GLUT 2

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(Farrell et al., 2013). The extent to which potato starch may serve to enhance

bioavailability of chlorogenic acid, anthocyanins or other phenolics remains to be

investigated in detail.

1.5.5.2 Bioavailability of Potato Carotenoids

As with phenolics, absorption of lipid soluble carotenoids is a complex, multistep

process that is dependent on including: 1) Digestion and release from the food matrix, 2)

Solubilization in the gut lumen by transfer into bile-salt lipid micelles, 3) Transport into

intestinal epithelial cells, and 4) Incorporation into chylomicrons and secretion into the

lymphatic system (Goltz and Ferruzzi, 2013). This process is highly aligned with and

dependent on consumption of lipid in the form of triacylglycerides to potentiate carotenoid

and tocopherol micellarization (Reboul et al., 2006) and intestinal secretion with

chylomicron (Goltz and Ferruzzi, 2013). Considering the low natural level of lipid in

potatoes, it becomes critical to consider final product form and formulations including

inclusion of fat as a cooking medium (frying), in the product formulation, or in the context

of the full meal.

Similar to the body of evidence available for potato phenolics, very little work has

been done on absorption of carotenoids and tocopherol from potatoes (S. tuberosum ) but

significantly more has been done with sweet potato (Ipomoea batatas). Therefore both will

be discussed in the context of this review.

In one of the few reports on carotenoid bioaccessibility, Burgos et al. (2013) reported in

vitro digestive recovery (70-95%) and relative bioaccessibility (33-71%) of lutein and

zeanxanthin from yellow fleshed potatoes. These values are similar to those reported for

typical salad vegetables (Failla et al., 2014; Huo et al., 2007) and select thermally processed

foods (Garrett et al., 2000; Kean et al., 2008; Reboul et al., 2006). While modest compared

to dark green vegetables (Vinha et al., 2015) this level of bioaccessibility can provide up to

600 ug/100g serving of boiled potatoes (Burgos et al., 2013).

Significantly more is known regarding orange flesh sweet potato as a food vehicle for

vitamin A (through provitamin A carotenoids) (Berni et al., 2015; Failla et al., 2009; Mills et

al., 2009). Bioaccessibility of b-carotene from orange fleshed sweet potato was reported to

be low (0.6-3.0%) (Failla et al., 2009). This low level is in fact consistent with low

bioaccessibility for carotenes relative to xanthophylls (Huo et al., 2007). Leveraging lipid in

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product formulation is known to enhance carotenoid bioaccessibility and absorption in vivo

(Mills et al., 2009). Bengtsson et al. (2009) further reported that heat processing and lipid

addition (2.5%) could enhance b-carotene in vitro bioaccessibility up to 22% from orange

fleshed sweet potatoes In humans, deep frying sweet potato was reported to provided a

higher relative serum response of b-carotene compared to green leafy vegetables but

significantly lower than supplemental doses (Huang et al., 2000). Considering the

similarities between potato tubers and sweet potatoes, it is logical to assume similar effects

from processing of sweet potatoes would be applicable to carotenoids from yellow and

orange fleshed potatoes. However, these effects must be assessed directly.

Health Benefits of Potatoes and Potato Products

Potatoes hold a confusing and often controversial role in human health and nutrition.

While potatoes play a critical role in food security, they are simultaneously associated with

the shortcomings of the Western diet by being associated with high fat, salt and glycemic

index. Interestingly, studies suggest both positive and negative effects on energy balance

and chronic disease risk are associated with potato consumption. These effects are clearly

associated with the nature of the potato processing and in home preparation, which can

greatly impact final nutritional quality, and to a larger extent, the nature of the foods

potatoes are often consumed with. Reviews by Camire (2009) and King and Slavin (2013)

have previously discussed potatoes and human health with a focus on the potatoes overall,

and, to a more limited extent, commonly consumed products. The following sections

address primarily the potential positive nutritional impacts of potatoes and the potential for

potato products to leverage this value.

1.6.1 Contribution to Dietary Nutrients of Concern and Bioactive Compounds

As previously described, potatoes of all forms and colors remain an important

source of nutrients and bioactive phytochemicals in the diet. Table 5 highlights that for US

adults, white potato ranks in the top 15 contributors among 112 foods/food groups for 15

key nutrients (out of 30 total). This includes key shortfall nutrients including potassium

and fiber (2015 Dietary Guidelines Advisory Committee, 2015). By more recent NHANES

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(National Health and Nutrition Examination Survey) data (2009-10), potatoes provided

12.9-24.9% of daily potassium intake and 14.4-26.2% of daily fiber intake for US men and

women. Overall, this is a result of both the nutrient content and the relatively high

consumption of potato products by the population. NHANES data reveals that average

intake of white potatoes from 24-hour recall varied between age groups (highest for 19-30

year old women and 51-70 year old men), but was between 37.9-54.6 g/day for men and

30.0-40.8 g/day for women. French-fried potato products provided additional potato

intake of 3.5-16.0 g/day for men and 1.4-18.5 g/day for women. When compared to other

vegetables, potatoes and French-fried potatoes together comprised about 30% of total

vegetable intake for men and 27% for women (Storey and Anderson, 2013).

Table 6. Percent of dietary nutrient provided by potato for US adults (1994-96) and rank among 112 food/food groups (Cotton et al., 2004).

White Potato2 Potato chips/corn chips/popcorn2

Sweet Potato2

Nutrient1 % Rank % Rank % Rank

Energy 2.8 10 2.5 15 -- -- Carbohydrate 5.3 5 2.3 14 -- -- Protein 1 15 -- -- -- -- Total Fat -- -- 3.9 10 -- -- Fiber 7.5 3 3.6 7 -- -- Vitamin C 5.8 5 -- -- -- -- Vitamin E -- -- 3.4 9 -- -- Vitamin A (IU) -- -- -- -- 4.6 5 Folate 2.9 7 1 <20 -- -- Thiamin 3.8 9 -- -- -- -- Riboflavin -- -- 1 <20 -- -- Niacin 3.9 5 1 <20 -- -- Vitamin B6 8.5 4 2.1 11 -- -- Phosphorus 2.8 8 1 16 -- -- Sodium -- -- 1 14 -- -- Potassium 8.9 2 2.3 11 -- -- Iron 2.6 9 1 19 -- -- Zinc 1 13 1 19 -- -- Magnesium 4.7 5 11 2.8 -- -- Copper 8.5 1 1 <20 -- --

130 nutrients were assessed. Nutrients that no potato product significantly contributes to (at least 1%)

were not included. These are cholesterol, vitamin B12, calcium, and selenium. 2Blank spaces indicate that the potato provided <1% of the nutrient to the diet and had low ranking.

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In line with the previous discussion of potato phytochemicals, potato products are

often overlooked as significant dietary sources of bioactives. White potatoes, while

relatively low in polyphenols compared to fruit and green vegetables (Brat et al., 2006),

contribute significantly to overall dietary polyphenols due to overall consumption. In

France, potato polyphenols account for about 45% of total polyphenol intake- more than

any other vegetable (Brat et al., 2006). In the United States, potatoes follow only oranges

and apples in contribution to phenolic intake among commonly consumed fruits and

vegetables (Chun et al., 2005). More recent estimates suggest that potatoes may account for

~25% of the phenolics in the American diet highlighting just how overlooked these

products may be in terms of contribution of dietary bioactive components (Liu, 2013).

While typical white- and yellow-fleshed potatoes are most commonly consumed, colored-

flesh varieties are potentially impactful as a significant source of phytochemicals, relative to

all vegetables consumed (Navarre et al., 2011). Shifts in consumption towards more

phytochemical-rich varieties could have significant impact in the overall nutrient density of

these foods. There is an opportunity for potato to serve as carriers for phytochemicals that

have been associated with prevention of several chronic and degenerative diseases.

Furthermore, evidence has accumulated that phytochemicals, such as phenolics and

polyphenols, may alter nutritional functionality of foods by virtue of interactions with

macronutrients (reviewed by Bordenave et al. 2015) suggesting that these non-nutritive

components may play a significant role in the nutritional quality of potato products and

merit further discussion and investigation.

1.6.2 Potatoes and Risk of Chronic Diseases

Potato consumption has often been associated with elevated risk of certain chronic

diseases, most notably, type 2 diabetes (Halton et al., 2006; Khosravi-Boroujeni et al., 2012)

and colon cancer (Miller et al., 2010). For diabetes, the association is often attributed to the

high starch content of potatoes and high glycemic response induced by many forms of

cooked potatoes. Further, addition of ingredients such as fat and sodium (in fried products)

that have been associated with negative health outcomes (Shikany and White Jr., 2000) or

consumption with red meats and other “high risk foods” has made for a complex mixed

message on the nutritional value of potato products. Several potential health benefits of

potato consumption have been previously reviewed. This includes prevention of cancer,

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cardiovascular disease, and obesity (Camire et al., 2009; McGill et al., 2013). Generally,

while associations have been made, both positive and negative, much remains to be studied,

as consistency in reporting of potato forms and other potential confounding factors,

including context of potato consumption in the overall diet, remains limited.

Still, many of the potential benefits are believed to be due to the combination of macro and

micronutrients as well actions promoted by potatoes bioactives including phenolic and

carotenoids (Liu, 2013). As a key dietary source of potassium, vitamin C and dietary fiber

potatoes contribute significantly to nutrients with defined roles in cardiovascular health

(McGill et al., 2013). Reported health benefits derived phytochemical rich foods with

similar phenolic profiles to those found in potatoes (anthocyanins and chlorogenic acids)

include reduction of cardiovascular diseases, cancer and amelioration of diabetes (Akash et

al., 2014; Ghosh and Konishi, 2007; He and Giusti, 2010; Manach et al., 2005a; Van Dam and

Hu, 2005; Zafra-Stone et al., 2007). While the mechanism behind these effects and the

extent to which these effects can be extended to potato products remain unclear, these

observations combined with the contribution of potatoes to phenolic intake in the diet

highlight the potential potato products may play in modifying risk factors. In these efforts it

is important to consider the form of potato consumed as well as the potential for

improvements in processed potato products in which the nutritional value of the potato can

be leveraged.

More recent research also supports the potential of potato products to contribute to

weight management through promotion of satiety, despite the relatively high glycemic

index of many potato forms (consumed alone) (Ek et al., 2012). Subjects in a study by

Erdmann et al. (2007) consumed less energy when consuming potatoes compared to rice or

pasta. Holt, et al. (1995) found that satiety ratings for potato were higher than other 37

foods measured, including fruits, bakery products, snack foods, carb-rich foods, protein-rich

foods, and breakfast cereals. In general, higher protein, fiber, and water content in foods

correlated with greater satiety ratings, whereas higher fat content correlates with lower

satiety ratings (Holt et al., 1995). Diets that are high in satiating power and low in energy

density may have positive implications for weight management (Drewnowski, 1998).

However, while research suggests that low glycemic index foods can promote satiety in the

short term, there is not strong enough evidence to conclude that consuming low glycemic

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foods can regulate satiety and body weight in the long term (Bornet et al., 2007; Niwano et

al., 2009; Raben, 2002).

1.6.3 Potatoes and Modulation of Oxidative Stress

Oxidative stress is defined as an imbalance in the organism’s production of reactive

oxygen species (ROS) and the action of dietary or endogenous antioxidant systems

(Betteridge, 2000). While antioxidant micronutrients (vitamin C), minerals (selenium) and

bioactive (phenolics, tocopherols and carotenoids) present in potato are commonly

considered to contribute to overall antioxidant activity of potatoes (Brown (2005) Lachman

& Hamouz (2005), it is the phenolic fraction that has been found to be directly proportional

to in vitro antioxidant activity (Leo et al., 2008). As with other fruit and vegetable extracts,

higher phenolic and flavonoid content of colored-flesh potatoes has been correlated to a

higher antioxidant activity. Specifically, colored-fleshed potatoes have been found to have

250-300% higher ORAC values than white potatoes (Brown et al., 2003; Navarre et al.,

2011). Reddivari, et al. (2007) found that magnitude of antioxidant capacity (trolox eq.) of

25 specialty potato varieties grouped by skin/flesh color followed the order of

Purple/Purple, Red/Red, Red Yellow/Yellow, Purple/Yellow, and Yellow/Yellow.

While many in vitro antioxidant assays may not directly represent in vivo

modulation of oxidative stress (Amorati and Valgimigli, 2015), these measures are still

commonly used to assess the potential of potatoes to provide protection in vivo (Andre et

al., 2009, 2007a; del Mar Verde Méndez et al., 2004). Ultimately, modulation of in vivo

markers remains the most critical evidence to consider. Consumption of potatoes both with

and without skins was found to positively influence lipid metabolism and antioxidant status

in rats (Robert et al., 2008, 2006). Kaspar et al. (2011) demonstrated that consumption of

colored potatoes reduced multiple markers of inflammation and oxidative stress in humans.

However, in commonly consumed products from typical white potato varieties, such as

baked and fried chips and fries, ascorbic acid may still remain a critical contributor to the

ability of potato products to modulate markers of oxidative stress in vivo. Using a

SMP30/GNL KO mice Kondo, et al. (2014) demonstrated that feeding fried potato chips

elevated ascorbic acid levels and in turn lowered levels of reactive oxygen species (ROS) in

tissues compared with AA-depleted mice. While promising, more evidence is needed to

understand the specific role of potatoes and/or potato bioactive in modulation of oxidative

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stress. To date, evidence on availability of potato phenolic antioxidants and carotenoids

remains limited. Without more detailed pharmacokinetic assessments of potatoes

bioactives in conjunction with long term trials conducted in relevant animal models and

humans it will be difficult to leverage on preliminary findings and in vitro assessments of

antioxidant content and activity for selection and application of strategic potatoes cultivars

or for connection to specific health benefits including cardiovascular and GI health.

1.6.4 Potatoes and Modulation of Inflammatory Stress

Inflammation is a complex physiological response to an adverse stimuli presented

by cellular/tissue damage or infection (Ryan and Majno, 1977). Oxidative stress is one

mechanism that can trigger an inflammatory response, thereby linking the two underlying

mechanism in disease pathologies (Federico et al., 2007). Most often studies investigating

the impact of food on inflammatory stress assess specific molecular markers typical of the

pathways for acute and chronic inflammation. This includes many (1) platelet activating

factor (PAF) and derivatives of arachidonic acid, (2) inflammatory regulating cytokines and

nitric oxide (Feghali and Wright, 1997).

Data on the anti-inflammatory activity of potatoes has generally been limited to in

vitro and animal studies and a focus on GI inflammation in particular. A chloroform extract

of the peel from a colored-flesh potato (Jayoung) demonstrated the ability to attenuate

oxidative and inflammatory processes both in LPS stimulated RAW 264.7 macrophages and

in a dextran sulfate sodium mouse model of colitis (Lee et al., 2014). Kaspar et al. (2011)

found anti-inflammatory effects in healthy men consuming white and pigmented potatoes

with greater effects from pigmented potatoes. As described previously, potato peels are a

rich source of both phenolics and glycoalkaloids. While phenolic from potatoes and other

foods have demonstrated similar anti-inflammatory effects (Bogani et al., 2007; Vitaglione

et al., 2015) potato glycoalkaloids have also shown evidence of both pro- (Iablokov et al.,

2010) and anti-inflammatory activities (Kenny et al., 2013) dependent on application of

sub-cytotoxic dose paradigms in rodent and cell models respectivly.

While interesting, few studies have focused on the impact of potato products as part

of an overall meal/diet. Further, the contribution of resistant starch or fiber from select

potato products may have direct impact on inflammatory stress in the GI. Indigestible

carbohydrates including resistant starch and fiber have demonstrated the ability to

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modulate inflammatory markers in both animal models (Bassaganya-Riera et al., 2011; Fan

et al., 2012; Vaziri et al., 2014) and human clinical trials (Jiao et al., 2015). Sweet potato

resistant starch was also shown to ameliorate pro-inflammatory status in insulin resistant

rats (Chen et al., 2013). Additionally, the potential for synergistic interactions between

phenolics and prebiotic/anti-inflammatory effects of fiber resistant starch from potatoes

exist and remains to be investigated. Therefore, in a manner similar to evaluation of impact

to oxidative stress, experimental evidence in humans and relevant animal models is still

lacking. Furthermore, mechanistic studies investigating synergistic effects of potato micro,

macro and phyto-nutrients are clearly required to better understand the extent to which the

potato as a food contributes to positive modulation of inflammatory stress and related

disorders.

1.6.5 Glycemic Effect of Potatoes

An area that is perhaps more directly associated to nutrition and health outcomes is

that of starch digestion and glycemic response. Considering the carbohydrate density of

potatoes it is not surprising that glycemic response and effect of potato consumption

remains central to many of the nutritional concerns and benefits related to products. The

glycemic effect of potatoes has been the subject of numerous investigations and more

recently reviewed in detail by Ek et al. (2012). Potato-based food products are generally

classified as medium to high glycemic foods (Ek et al., 2012) by virtue of the starch content

and general association of the highly digestible nature of potato starch. The term “glycemic

index” (GI) was first introduced to classify carbohydrate-containing foods by their ability to

raise blood glucose (Jenkins et al., 1981). High GI foods have values of 70 or above, medium

GI have values between 56 and 69, and low GI foods have values lower than 55 (Bornet et

al., 2007). High GI foods are generally regarded to be absorbed quickly and result in higher

postprandial blood glucose spikes, which over time may increase risk of diet-related chronic

diseases such as obesity, type-2 diabetes, cardiovascular disease , and some cancers (Liu

and Willett, 2002; Ludwig DS, 2002).

As a starch food, potatoes are often perceived as having a high GI and by extension

potentially negative long-term health effects. However, the glycemic index of potato

products can vary widely depending on the potato variety, maturity, and level of

processing/preparation, including addition of other ingredients that modify glycemic

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response. Using glucose as a reference food, values range from 41 (white, cooked) to 95

(instant), however, most fall between 50 and 90 (Atkinson et al., 2008). Glycemic load is

another value developed to describe the carbohydrate digestibility of a food in the context

of the amount typically consumed. The GL is the GI of a food normalized by the

carbohydrate content of a typical serving size, allowing for comparison between foods. GL

of potato products often falls between 11 and 25, which is lower than values typical for

starchy foods including pasta (~15-40) and white rice (~15-35), but higher than wheat

breads and several kinds of fruits, vegetables, and legumes (Foster-Powell et al., 2002).

Potato variety and maturity can significantly impact glycemic response. In a study

by Fernandes et al. (2005), baked Russet Burbank had a higher glycemic index than baked

Prince Edward Island (PEI) or roasted California white potato. Henry et al. (2005)

measured glycemic index of eight British potato varieties classifying four varieties (Estima,

Charlotte, Marfona, Nicola) as “medium” glycemic response foods, while the other four

(Maris Peer, Maris Piper, Desiree, and King Edward) were classified as “high” glycemic

response foods. Generally, potatoes with more floury texture (low moisture and sugar, high

starch) had higher GI than those with waxy texture (high moisture, low starch). Soh and

Brand-Miller (1999) also found that the Desiree variety had higher glycemic index than

Pontiac and Sebago varieties (peeled and boiled). In regards to maturity, these authors

found that “new” (or young, immature) potatoes had lower glycemic index compared to

mature Desiree, which is attributed to lower starch digestibility in new potatoes.

Glycemic response to potatoes is also affected by preparation method, including

extent of processing and ingredient addition. It has been shown that the formation of

resistant starch in cooked and refrigerated potato products attenuates blood glucose

response (Kanan et al., 1998). In data from Fernandes et al. (2005) with glucose as a

reference food, cold boiled red potatoes had the lowest GI (56.2), and hot boiled red

potatoes had the highest (89.4), which illustrates the significant impact of retrograded

starch. From highest to lowest, values for instant mashed, baked Russet, baked PEI, roasted

California white, and French fried potatoes fell between those two. The large reduction in

GI between the hot and cold boiled red potatoes was greater than what could be explained

by reduction in amount of starch digested alone, thus the authors pose that the majority of

the reduction in GI was likely also due to a reduction in rate of starch absorption. In a study

by Brand et al. (1985) in vitro digestibility of potato products was greatest for potato chips,

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followed by instant potatoes and boiled potatoes. However, the GI of potato crisps was

found to be the same as boiled potato and both were found to be significantly lower than

instant potato. This may be due, in part, to the contribution of fat in the chips, which can

serve to slow gastric emptying and thus starch release in the small intestine (Gentilcore et

al., 2006). However, potato chips in this study exhibited lower glycemic index compared to

corn chips and rice puffs, which could indicate some contribution from other nutrients

specific to potato. While the data on glycemic effect of potatoes is varied, it is also

important to note that in general, the glycemic effects of potato products have not been

considered in the context of the diet. That is, as potatoes are generally consumed as a side

dish, and thus the response of potatoes alone may have less relevance that the response

within the context of a more complex meal. Other meal components, such as fat, protein,

and acetic acid have been shown to modulate glycemic response (Collier and O’Dea, 1983;

Gulliford et al., 1989; Liljeberg and Bjorck, 1998).

Along with formulation factors and meal complexity, potato phytochemical

composition may directly play a role in modulation of potato glycemic response. In

addition to antioxidant and anti-inflammatory activities of phenolic compounds, more

recent evidence points to the abilities of these dietary polyphenols to influence

carbohydrate digestion, absorption and metabolism. Interestingly, Thompson et al. (1984)

reported that phenolic content of foods including potatoes was inversely proportional to

glycemic index. This observation was initially attributed to potential for interaction

between complex phenolics and starch making starch less digestible (Barros et al., 2012;

Deshpande and Salunkhe, 1982). However, more recently smaller molecular weight

phenolics from multiple dietary sources including tea, cocoa, fruits and cereals have

demonstrated the ability to modulate carbohydrate digestion, intestinal glucose transport

and metabolism leading to reduced glycemic response (Hanhineva et al., 2010).

A recent report from Ramdath et al. (2014) found a similar inverse correlation

between polyphenol content of potatoes and glycemic index (GI) with colored anthocyanin

and phenolic-rich potatoes having a more pronounced decrease in GI. While promising,

these studies are preliminary and, to date, rely on differences between potato varieties that

are not as commonly leveraged in fresh market or commercial products. Further, it remains

unclear if the observed effects are related to alteration of starch structure (to form more

resistant starch), starch digestion rate (through inhibition of digestive enzymes) or through

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modulation of glucose transport. Further efforts to characterize impacts of processing and

formulation on interactions between phenolics and potato starch are needed to better

understand the potential of leveraging the native phenolics present in potatoes.

1.6.6 Potato Influences on the Microbiota

The recognition on the role of intestinal microbiota in general health and

modulation of obesity and chronic disease has grown in recent years (DuPont and DuPont,

2011; Greiner and Bäckhed, 2011; Kootte et al., 2012). It is logical to consider potatoes, as a

key source of starch, fiber and phenolics, as a potential modulator of gut microbiota

communities and by extension selected benefits. Surprisingly, little is known regarding the

impact of potato products on gut microbial diversity or metabolic activity. Raw potato

starch has been shown to alter both purine base secretion and short chain fatty acid

production in a growing pig model (Martinez-Puig et al., 2003). Raw potato starch fed at

9% of the diet was also shown to increase lactic acid bacteria in the caecum and proximal

colon of rodents (Le Blay et al., 2003). While interesting these results have little practical

application to processed and cooked potato products. Further, they do not consider the role

of potato phenolics, such as chlorogenic acid, which have demonstrated the ability to alter

bacterial communities in vitro and in vivo (Gonthier et al., 2006; Jaquet et al., 2009; Mills et

al., 2015). Considering the potential for interactions between starch and phenolics and the

ability to alter starch substrate utilization by bacteria (Wang et al., 2013), more research is

needed to clarify the impact of potatoes on gut microbial communities.

Opportunities to Improve Nutritional Value of Processed Potato Products

Processing and preparation can both positively and negatively impact potato

nutritional quality. Previous sections of this review have discussed opportunities to

improve the nutritional quality of processed potato products, including variety and process

selection to improve phytochemical and micronutrient content and retention. Additionally,

emerging insights into the potential for interactions between potato macronutrients and

phytochemicals in relation to bioavailability and glycemic response may impact overall

nutritional quality. This section will give more depth on other processing strategies that

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have the capacity to improve the nutritional profile of processed potato products. These

have been the subject of several reviews (Burton, 1989; Decker and Ferruzzi, 2013; Foot et

al., 2007; Keijbets, 2008; Nayak et al., 2014) with the focus primarily on salt reduction,

improved lipid profiles, acrylamide reduction in fried products, and improvement of slowly

digestible and resistant starch content.

1.7.1 Lipid Reduction

There are several factors that influence the absorption of fat into potato products

which are discussed in depth by Burton (1989, chap. 11). Briefly, fat absorption is

increased by larger surface area/volume ratio, lower frying temperature for chips, potato

immaturity, and low dry matter (high moisture) content. Potato variety may also impact fat

uptake (O’Connor et al., 2001). Prefrying treatments can be applied to potato products to

limit lipid absorption. Pedreschi et al. (2008) found that potato chips which were pre-

blanched absorbed more oil than control chips. However, others suggest that blanching

gelatinizes starch on the surface of French fries and creates a moisture barrier (Miranda

and Aguilera, 2006). Surface drying or pardrying (e.g. microwave, hot air) is currently used

in the French fry industry to reduce oil absorption. Other treatments which have been

shown to reduce oil absorption in fried products include cryogenic freezing, soaking in a

sodium chloride solution, blanching with infrared radiation, and coating with film forming

materials or hydrocolloid solutions (Mehta and Swinburn, 2001; Miranda and Aguilera,

2006).

Lipid content and fatty acid profile of potato products will depend greatly on the

fat/oil used in the processing or final preparation of the product. Therefore strategies to

improve lipid profiles of fried potatoes have focused on (1) improvement of fat and oil

nutritional quality and (2) minimization of fat absorption during the frying process

(Bouchon, 2009; Fillion and Henry, 1998; Matthäus, 2006; Ziaiifar et al., 2008). As such,

significant attention has been placed in improving the nutrition quality of frying oils by

eliminating trans fat content (Berger and Idris, 2005; Daniel et al., 2005; Katan, 2006) and

minimize saturated fat content to be more in line with recommendations of the 2010

Dietary Guidelines for Americans (Dietary Guidelines Advisory Committe, 2010).

Technically this has been achieved through application of high mono-unsaturated fatty acid

rich oils and blending technologies that have generated products of higher nutritional

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quality with minimal impact to sensory properties of the final fried potato (taste, aroma and

texture) (Farhoosh et al., 2008; Man et al., 1999; Matthäus, 2006).

A second approach to improve the nutritional profiles of fried potatoes has been to

leverage coatings technology and novel frying methods to minimize the absorption of fat

into the final fried product. Considering that in a traditionally immersion fried product fat

absorption occurs both following the loss of moisture from the potato during frying and

continues after cooking (Bouchon et al., 2003), technologies that can minimize water loss

and minimize fat absorption have been the focus for product improvements. Hydrocolloid

based coating systems composed of gums, cellulose and proteins applied to raw potato

surface have been shown to minimize fat uptake during frying by forming a protective

barrier that minimizes both water loss and fat absorption during cooking (Garcıa et al.,

2002; reviewed by Mellema, 2003). Technologies that can improve on traditional

immersion frying include vacuum frying and centrifugal frying which reduce frying

temperatures and drain more oil after cooking respectively. While these technologies have

been shown to decrease fat content of fried potatoes up to 75%, capital investment and

suitability for all product types has limited their broad application. Similarly, new frying

technologies such controlled dynamic radiant frying (CDRF) have demonstrated significant

promise as an alternative to immersion frying reducing oil content by up to 50% in potato

products (Lloyd, 2004). This technology relies on infrared radiation to simulate the heat

transfer of the frying process and requires minimal oil to replicate the color, texture and

flavor of typical fried products (Lloyd et al., 2004). While promising, the adoption of such

technologies is often limited by the nature of the application. The potential of these

technologies if leveraged across broad product types remains to be realized.

1.7.2 Resistant Starch Formation

As described previously, potato starch is a natural resistant starch in the RS2 form.

When heated in water, hydrogen bonds within and between amylose and amylopectin

molecules are broken, allowing the starch granule to swell, lose crystallinity, structural

organization and gelatinize forming rapidly digestible starch (RDS). Upon cooling, starch

molecules from the disrupted granules form a gel, and eventually retrograde into a semi-

crystalline form producing both slowly digestible starch (SDS) and resistant starch type

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RS3, which is resistant to digestive enzymes and may therefore slow glycemic response and

contribute to dietary fiber (Raigond et al., 2014).

Considering that retrogradation of gelatinized potato starch after cooking results in

formation of SDS and RS (type 3) it is not surprising that interest in strategies to control

starch digestion through formation of either slowly digestible (SDS) and resistant starch

(RS) has grown. Implications for control of glucose release/response from potato products

through functionalization of starch may serve to counteract the moderate to high glycemic

characteristic of potatoes or alter substrate availability for microbial populations

throughout the gut.

The extent of formation of SDS and RS3 in potato products is dependent on the type

and extent of processing (Brand et al., 1985; Thed and Phillips, 1995) as well as the manner

in which they are consumed (Englyst and Cummings, 1987). Specifically, the extent of

initial gelatinization through thermal processing or cooking is a critical first step as raw

potato starch is as rich source of RS (type 2). Strategies to preserve a portion of the starch

granule and RS2 structure could increase the relative levels of RS in finished potatoes.

Some research suggests that cooking methods which provide sufficient water and heat for

complete starch gelatinization may increase digestibility compared to dry heating methods,

such as baking and frying (García-Alonso and Goñi, 2000; Lunetta et al., 1995). Others have

found no effect of cooking method on glycemic index (Soh and Brand-Miller, 1999).

Following gelatinization through boiling, baking frying or other heating mechanism; cooling

of potatoes has been demonstrated to generate appreciable levels of SDS and RS3 and

decrease glycemic index in vivo (Fernandes et al., 2005; Monro et al., 2009). Decrease in

glycemic index is still observed upon reheating compared to products consumed

immediately after processing (Tahvonen et al., 2006). Resistant starch content has been

increased by temperature cycling, or more than one heating and cooling sessions (Englyst

and Cummings, 1987; Leeman et al., 2005). Freeze drying chips before frying has also

increased resistant starch to 32% compared to 1% in non-freeze dried chips (Goñi et al.,

1997). These authors also observed formation of 7% resistant starch in whole French fries.

This has applications for select product categories including prepared dishes or snacks

where such approaches can be integrated into the processing unit operations resulting in

novel products with improved glycemic response and by extension nutritional profile.

Insoluble amylose-lipid complexes have been observed when amylose was heated with fatty

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acids (Mercier et al., 2013). More research is needed on the effect of these complexes on

glycemic index in fried potato products. Additionally, the extent to which these structures

may impact microbial communities through the extent of the gastrointestinal tract needs to

be better elucidated.

1.7.3 Management of Acrylamide Formation

Acrylamide, a byproduct of the Maillard reaction, occurs in a range of baked, fried,

and roasted foods. It is produced from the reaction of reducing sugars and the amino acid

asparagine, which is abundant in potatoes. Agronomic, genetic, and processing approaches

to mitigation of acrylamide in processed potato products has been the subject of several

reviews (Amrein et al., 2003; De Wilde et al., 2005; Foot et al., 2007; Muttucumaru et al.,

2008; Zhang and Zhang, 2007). Briefly, methods to reduce acrylamide include reduction in

reducing sugars and asparagine, reducing cooking time and/or temperature or exposure to

high heat, addition of antioxidants, lowering pH, blanching or soaking to remove surface

acrylamide precursors, and cutting with larger surface area to volume ratio. Additionally,

Zhu, et al. (2010) found a fairly strong negative correlation (r=-.6918) between phenolic

acid content of potato varieties and acrylamide formation during processing, suggesting

that selection of high phenolic varieties may mitigate acrylamide formation.

Research Needs and Future Directions

Potatoes products remain an important dietary source of macronutrients,

micronutrients and biologically active phytochemicals that have associated nutritional and

health implications. While potato consumption has been both positively and negatively

associated with select health endpoints, inconsistencies in definitions of potato products,

their role in a broader diet pattern and differences in study designs, have made

interpretation of these associations difficult. However, these outcomes have resulted in

increased interest in nutritional value of potatoes and potato products. Mostly recognized

as a starch rich vegetable, potatoes are less recognized for their contribution to overall

dietary fiber or micronutrients including Ca, K, Mg, Fe, and Mn as well as vitamin C. In

regards to bioactive phytochemicals, potatoes remain a significant contributor to overall

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intake of phenolics, predominantly in the form of phenolic acids and specifically chlorogenic

acids for white potatoes. While nutritional profiles of potato products have been

characterized, information on the bioavailability of potato nutrients and phytochemical

remains limited mainly to preclinical models and select clinical studies. In addition, many of

the positive nutritional characteristics of potatoes are lost in consumer perception due, in

part, to the suggestion that nutritional profile of potatoes can be altered by preparation and

processing method which introduce limiters such as fat and sodium. Significant work has

been done to capture the impact of in home preparation on potato nutritional profiles,

suggesting that finished products do in fact carry substantial amounts of nutrients and

phytochemicals. However, much less is known regarding the impact of commercial

processing on these endpoints including bioavailability. This information remains critical to

establish considering the increased prevalence and interest in processed products by

consumers and the potential for these products to be optimized.

As a starch rich food, the nutritional perception of potatoes still remains highly

associated with the glycemic response from commonly consumed prepared or processed

products. This has been the subject of intensive investigation yielding the general

consensus that potato glycemic response will vary widely from low to high based on variety,

starch structure, preparation and processing as it relates to generation of slowly digestible

or resistant starch. However, more recently, phenolic profile of potatoes has shown promise

as a modifier of starch digestion, intestinal glucose transport and ultimately may play a role

in modifying glycemic response. While promising, insights into the response from

commonly consumed potato forms, application of novel phenolic rich potato varieties (such

as colored potatoes), and impact in the context of broader diet pattern are needed to

determine the potential benefits provided by unique nutrient and phytochemical profiles on

their own or in synergy. This includes a need to better understand how these interactions

may impact functionality both in products and in the gut with specific consideration of the

potential for impact to microbial communities and activities in the gut as these relate to

specific underlying factors that modulate disease risk (gut function, substrate utilization,

oxidative and inflammatory stress).

Despite these gaps in knowledge, clear opportunities exist to capitalize on the known

nutritional profile of potatoes. Considering the prevalence of processed potato products,

leveraging new varieties or processing technologies to limit perceived negative nutritional

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attributes (fat and sodium) while optimizing positive attributes (phytochemical content,

micronutrient retention, resistant starch) holds promise for building better potato

products. Additionally, the development of new strategies for leveraging nutrient dense

waste streams, including peel waste, may offer novel approaches for enhancing nutrient

density of commercial products. Finally, as our understanding of the nutritional attributes

and quality of potato products grows, it is important to recognize that processing will be a

key player in translation of nutrition enhancements to consumers.

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CHAPTER 2. RESEARCH RATIONALE AND OBJECTIVES

As highlighted in the previous chapter, nutrient and micronutrient content of

potatoes and potato products (including both potatoes and sweet potatoes) in addition to

their wide consumption give them an important role in human nutrition. In addition,

potatoes contribute significantly to the overall dietary intake of health-promoting

phytochemicals (Chun et al., 2005; Liu, 2013), providing another dimension to their

potential relationship to human health. While promising, the shift in consumer preference

for more convenient “processed” products compared to freshly prepared has coincided with

the negative nutritional association of potato products and health. However, limited

information is actually available on the extent to which commercial processing of potatoes

impacts nutritional quality. In the case of our research, it is unclear the extent to which the

type and amount of processing may affect the phytochemical content of commonly

consumed products.

While the phytochemical content of select pigmented and commercial non-

pigmented potatoes has been well-researched, very few investigations have directly

compared phytochemical profiles between commercially relevant pigmented and non-

pigmented varieties. In addition, existing research on process stability of potato

phytochemicals has yielded disparate results due to a number of factors that may or may

not be controlled. Existing research on process stability of potato phytochemicals also

usually includes laboratory- or kitchen-scale cooking or preparation methods, rather than

commercial processing methods (which are more relevant to the American diet). Finally,

there is a lack of comparison of the effects of commercial and fresh preparation methods on

phytochemical content and composition.

Based on these gaps, the overall objective of this research was to investigate

phytochemical content in commercially relevant cultivars and determine the effects of

commercial and fresh processing on phytochemical content. To achieve this objective, three

experiments with separate aims were conducted.

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Experiment (Aim) 1: Determine phytochemical content in fresh commercially

relevant potato varieties.

Nine commercial varieties (6 yellow/white, 2 purple, 1 red, 1 sweet potato) were obtained

from McCain foods and analyzed for phenolic acids, anthocyanins, and carotenoids. It was

hypothesized that potato varieties would differ significantly in levels of chlorogenic acids

and anthocyanin derivatives with pigmented varieties having higher overall phenolics.

Also, sweet potato varieties would contain high levels of carotenoids.

Experiment (Aim) 2: Determine the extent to which key phenolics including

chlorogenic acid and anthocyanins are recovered through commercial processing.

Four varieties of commercially processed, dried, and ground potato samples (1 white, 2

purple, 1 red) were obtained from McCain foods. Whole potatoes and potato flesh were

compared through five processing treatments (blanched and frozen; blanched, fried, and

frozen; blanched, fried, frozen, and fried; blanched, fried, frozen, and baked) for each

variety. It was hypothesized that peeling and progressive processing would reduce

chlorogenic acid and anthocyanin content in each variety, though effects of treatments

would vary in impact based on phenolic species (anthocyanins would be more stable than

CGA).

Experiment (Aim) 3: Compare the impact of fresh preparation to commercial

processing on chlorogenic acid and beta-carotene recovery.

Five frozen and reconstituted commercial samples (Classic Fries, Fresh-Style Fries, Hash

Browns, Sweet Potato Fries, and Sweet Potato Wedges) were compared to similarly-

produced fresh products. It was hypothesized that phytochemical content in freshly

prepared products would be greater than that of commercially produced and reconstituted

products.

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CHAPTER 3. PHYTOCHEMICAL CONTENT IN COMMERCIALLY RELEVANT POTATO

VARIETIES AND PROCESS STABILITY IN COMMERCIAL AND FRESH POTATO

PRODUCTS

Abstract

Potatoes (Solanum tuberosum) are a significant source of health promoting

phytochemicals. However, reported content and process stability of phytochemicals in

potato products is inconsistent. The objectives of this study were to compare

phytochemical content in white/yellow and pigmented commercially relevant varieties,

determine changes in phytochemical content of select potato varieties through commercial

processing, and assess differences in phytochemical content between freshly “home”

prepared and reconstituted, commercially processed white and sweet potato products.

Total chlorogenic acids (CQAs) ranged from 43-953 mg/100 g dw and were found in greater

concentrations in the whole of all varieties compared to flesh, as well as in pigmented

potatoes compared to white/yellow-fleshed potatoes. 5-0-CQA was the primary

chlorogenic acid isomer detected in all varieties of potato, followed by 4-0- and 3-0-CQA.

Acylated anthocyanins in red potatoes were primarily cyanidin pelargonidin derivatives,

while those in purple varieties were primarily petunidin with smaller amounts malvidin

and delphinidin derivatives. Commercial products included raw flesh without skin (FNS),

blanched+frozen (BF), +microwaved (BFM), and blanched+par-fried+frozen (BFF), +baked

(BFFO) or +fried (BFFF). Retention ranged from 49-85% for pigmented varieties and 32-

55% for white. For purple and red varieties, CQA levels were significantly lower (p<0.05) in

BFF, BFFO, and BFFF compared to FNS, BF, or BFM products. For white, CQA levels were

lower (P<0.05) in all processed products compared to FNS, but no differences were

observed between processing levels. Comparing fresh to commercial products, levels of CQA

did not differ for classic fries, fresh-style fries, or sweet potato fries, but were significantly

(p<0.05) lower in industrial baked and fried sweet potato wedges and baked and pan-fried

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hash browns. Retention of anthocyanins through all forms of processing was high (69-

129%). Sweet potato -carotene was higher in commercial baked wedges (30 mg/100g

dw) compared to fresh prepared (26 mg/100g) (p<0.05), but no other differences between

fresh and commercial products were found. These results suggest that commercial

blanching, freezing, and microwaving have mild impact on phytochemical levels in raw

potatoes compared to par-frying and subsequent baking or frying. Additionally, industrial

products compare favorably to freshly prepared products in recovery of phytochemicals.

Introduction

Potatoes, encompassing both common tubers (Solanum tuberosum) and sweet

potatoes (Ipomoea batatas), are important staple food in both the developing and developed

world. High yields, agronomic versatility, resilience in world markets, and nutritive value

give potatoes high potential to be an excellent “food security” crop (Camire et al., 2009;

Food and Agriculture Organization of the United Nations, 2008a; Govindakrishnan and

Haverkort, 2006). Potato tubers are the most widely consumed vegetable in the American

diet, comprising about 30% of total vegetable consumption for men and women (Storey and

Anderson, 2013). Potatoes are an important staple source energy as well as several

vitamins and minerals, including vitamin C, vitamin B6, niacin, folate, potassium, iron, and

magnesium (Cotton et al., 2004; Kärenlampi and White, 2009; US Department of Agriculture

Agricultural Research Service, 2014). While botanically distinct from S. tuberosum tubers,

sweet potatoes (I. batatas), a root member of the Convolvulaceae family, also have several

vitamins and minerals, most notably high levels of vitamin A and carotenoids (in orange-

fleshed varieties) (Bovell-Benjamin, 2007).

While the combination of high consumption and nutritional quality make both forms

of potatoes a key nutritional contributor to overall diet nutrition, it is important to note that

potatoes also contribute a significant amount of health promoting phytochemicals to the

American diet (Chun et al., 2005; Liu, 2013). Diets high in phytochemicals, including

phenolics and carotenoids, have been associated with a reduce risk of chronic and

degenerative diseases including cardiovascular disease and some cancers (Crozier et al.,

2009; Manach et al., 2005a; McGill et al., 2013). While not contributing to traditional

nutritional value, these phytochemicals are believed to modulate disease risk through

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several mechanisms including combinations of antioxidant and anti-inflammatory activities

(Kaspar et al., 2011; Liu, 2013; Robert et al., 2006). Some studies suggest that these

phenolic compounds are also able to modulate glycemic index of potatoes (Ramdath et al.,

2014; Thompson et al., 1984). Potatoes are broadly considered to be rich sources of

phenolic acids and flavonoids. Chlorogenic acids (3-,4-, and 5-O-caffeoylquinic acids) are

reported to be the most common phenolic derivative in potatoes with levels ranging from

30 to 1360 mg/100 g dw. Caffeic acid has also been commonly reported in various potato

cultivars at lower levels (0.5-14 mg/100 g dw) (Andre et al., 2007b; Navarre et al., 2011;

Zhu et al., 2010). Other phenolic acids such as ferulic and p-coumaric acids are reported

inconsistently at low levels (del Mar Verde Méndez et al., 2004; Deusser et al., 2012).

Flavonoids in potatoes may include quercetin, kaempferol, rutin, and catechin, with the

addition of anthocyanins in colored (red and purple) varieties (Andre et al., 2007b; Deusser

et al., 2012; Jansen and Flamme, 2006). In general, purple-fleshed varieties are rich in

petunidin, malvidin, and peonidin glycosides and derivatives, while red-fleshed varieties are

rich in cyanidin and pelargonidin glycosides and derivatives (Brown, 2005; Eichhorn and

Winterhalter, 2005). Sweet potatoes, like potatoes, contain phenolic acids and flavonoids,

especially in purple- or red-fleshed varieties (Oki et al., 2002; Teow et al., 2007). However,

orange fleshed sweet potatoes, common in the American diet, are rich sources of

carotenoids including beta-carotene (Huang et al., 1999; Takahata et al., 1993).

Potatoes are unique compared to other vegetables and fruits in that they are

exclusively consumed in processed forms, whether industrially processed or prepared in a

restaurant or home. Approximately 60% of the fresh potato crop is typically used for

industrial processing into products such as French fries and chips, whereas the remaining

~40% is sold on the fresh market for home and fresh food service applications (Bradshaw

and Ramsay, 2009; USDA Economic Research Service, 2014). Considering the diversity of

types and extent of processing that potatoes are subjected to, it is important to understand

the potential impact on potato nutritional quality including the recovery of potato

phytochemicals through the process. This is particular critical considering the growing

consumer distrust for “commercially processed foods”, including potato products, has risen,

due in part to the notion that processing leads to significant reductions in nutritional and

functional qualities compared to freshly prepared products.

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Existing reports suggest both high and low stability of phytochemicals to typical

processes. Navarre and others (2010) reported increases in various phenolics and

flavonoids through boiling, steaming, microwaving, and baking. Other groups have

reported similar increases, especially for phenolic acids (Blessington et al., 2010; Deusser et

al., 2012; Mattila and Hellström, 2007). However, several studies suggest poor retention, as

low as 0% and commonly around 60%, for several varieties and preparation methods (Dao

and Friedman, 1992; Im et al., 2008; Lachman et al., 2013; Juan A. Tudela et al., 2002; Xu et

al., 2009). While insightful, these reports are highlighted by the high level of variability that

can be attributed to many factors including compound analyzed and analytical recovery,

variety type, growing location, food matrix, and processing conditions. Processing

conditions are perhaps most critical considering that most studies have relied on in home or

fresh processing (Blessington et al., 2010; Im et al., 2008; Navarre et al., 2010; Xu et al.,

2009) to investigate recovery of phytochemicals rather than commercial scale processing

used to make typical consumer products. Insight into the impact of commercial processing

on potato phytochemicals is needed in order to define optimal conditions to deliver high

quality and health promoting commercial products. The overall goal of this research was

therefore to understand the effects of various forms of processing on potato phytochemicals

and the influence of potato variety and extent of processing on recovery of bioactive

phytochemicals. Additionally, phytochemical recovery was compared between

commercially processed and freshly prepared products, in order to determine the extent of

difference between commercially processed and in home preparations.

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Materials and Methods

3.3.1 Chemicals and Standards

Citric acid, chlorogenic acid (5-O-caffeoylquinic, 4-O-caffeoylquinic), ethyl gallate,

and cyanidin-3-glucoside standards were purchased from Sigma-Aldrich (St. Louis, MO).

Beta-carotene and lutein standards were purchased from Sigma Aldrich, Fluka (St. Louis,

MO). Formic acid, LC and MS grade water, LC methanol, and acetonitrile were obtained

from Avantor, J.T. Baker (Center Valley, PA). Fresh and processed potato samples were

donated by McCain Foods USA, Inc. (Lisle, IL).

Sampling and Processing Procedures

3.4.1 Experiment 1: Preparation of Fresh Potatoes for Determination of Phytochemical

Content

Ten varieties of fresh 2013 field samples were obtained from McCain Foods. These

included nine Solanum tuberosum varieties (Innovator (yellow), Bintje (yellow), Challenger

(yellow), Yukon (yellow), AR2009-10 (AR2; purple), Adirondack Blue (ADB; purple),

Adirondack Red (ADR; red), Russet Burbank (white), Norland (white flesh, red skin)) and

one Ipomoea batatas variety (Covington; orange-fleshed). Fresh samples were held in

storage at 10°C until sampling for analysis. Potatoes of varying sizes were randomly

selected, three for peeling and three for whole. Potatoes were rinsed in cool water, peeled

or left whole, sliced to 1/8 in., dipped in 0.5% citric acid solution, frozen at -80°C overnight,

and lyophilized (SP Scientific, VirTis; Warminster, PA) over 51 hours. Dried potato slices

were pooled, transferred to zip-lock bags, double bagged, and stored at -20°C until grinding

using a KitchenAid coffee grinder (Benton Harbor, MI) and analysis.

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3.4.2 Experiment 2: Sampling of Commercially Processed Samples for Determination of

Phytochemical Content

Four varieties of processed, lyophilized, and ground samples (AR2, ADR, ADB, R.

Burbank) were received from McCain Foods and stored at -20°C. Samples included

potatoes collected and processed to freeze dried powder from each step in the commercial

processing to French fries (Figure 1). This included fresh flesh with skin (FWS); fresh flesh

without skin (FNS); flesh blanched and frozen (BF); flesh blanched, frozen, and microwaved

(BFM); flesh blanched, fried, and frozen (BFF); flesh blanched, fried, frozen, and fried

(BFFF); and flesh blanched, fried, frozen, and baked (BFFO).

Figure 3. Schematic of commercially processed potato samples obtained from McCain foods for phenolic and anthocyanin analysis. All treatments were conducted on four varieties of potatoes with different flesh colors: AR2 (purple), ADB (purple), ADR (red), R. Burbank (white).

3.4.3 Experiment 3: Sampling and Reconstitution of Commercially Processed Frozen

Products for Comparison of Phytochemical Content.

Five types of commercial frozen prepared products were obtained from McCain

Foods: classic cut fries (MCF), fresh-style fries (includes peel) (MFF), hash browns (MHB),

sweet potato fries (MSF), and sweet potato wedges (MSW). MCF, MFF, and MHB were

produced from R. Burbank potatoes, while MSF and MSW were from the Covington variety.

Three bags of each product were sampled and equivalent portions of each bag were pooled

to make one sample. All pooled samples were reconstituted by baking or frying according

to the instructions provided on the package.

Frying. (MCFF, MFFF, MSFF, and MSWF) Frozen potato slices or wedges were fried

in an electric fryer (Keating of Chicago, Inc., McCook, IL) for 4 min. in oil (Clear Liquid

Canola Frying Oil, Bunge Oils, St. Louis, MO) at 176°C.

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Panfrying. (MHBP) Frozen hash browns were pan-fried in canola oil for 12 min. at

176°C.

Baking. (MCFB) Frozen product was baked in a convection oven (Vulcan (ITW Food

Equipment Group, LLC.), Baltimore, MD) for 15 min. at 230°C, stirring once. (MSFB, MSWB)

Frozen products were baked for 10 min. at about 218°C. (MHBB) Frozen product was

tossed in canola oil until coated and baked for 8 min. at 218°C.

3.4.4 Experiment 3: Preparation of Freshly Prepared Products for Comparison of

Phytochemical Content.

Fresh versions of the above commercial products were prepared using fresh raw

potatoes provided by McCain foods from the same lot used to make the commercial frozen

products. These included fried and baked classic fries (PCF), sweet potato fries (PSF), sweet

potato wedges (PSW), and hash browns (PHB) and fried fresh-style fries (PFF). At least 6

raw potatoes of various sizes were sampled and pooled for preparation of each product.

PCF, PHB, and PFF products were prepared from R. Burbank potatoes, and PSF and PSW

were prepared from Covington. Cooking procedures followed typical recipes for homemade

potato products.

Classic Fries (PCF). Potatoes were lightly washed, peeled, and sliced to 3/8”

thickness. Slices were rinsed in cold water, soaked for 45 min. at 4°C, drained, patted dry,

and either fried or baked. Fried. (PCFF) Slices were par-fried in canola oil for 5 min. at

150°C. After resting for 30 min., slices were fried again at 176°C for 3 min. Baked. (PCFB)

Slices were tossed in canola oil to coat and baked at 230°C for 15 min., stirring once.

Fresh-Style Fries (PFF). Potatoes were lightly washed and sliced (unpeeled) to 3/8”

thickness. Slices were rinsed in cold water, soaked for 45 min. at 4°C, drained, patted dry,

and par-fried (PFFF) in canola oil at 5 min. at 150°C. After resting for 30 min., slices were

fried again at 176°C for 3 min..

Hash Browns (PHB). Whole potatoes were scored with a knife, boiled for 8 min.,

transferred to ice water, then the peel was removed. Peeled potatoes were grated in a food

processor then squeezed dry and pan-fried or baked. Pan-fried. (PHBP) Grated potato was

panfried in canola oil at 176°C for 6 min., flipping once. Baked. (PHBB) Grated potato was

tossed in canola oil and baked at 218°C for 8 min.

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Sweet Potato Fries (PSF). Sweet potatoes were lightly washed, peeled, and sliced to

3/8” thickness. Slices were rinsed in cold water and drained to remove excess water,

shaken with corn starch in a zip-lock bag, then either fried or baked. Fried. (PSFF) Slices

were fried in canola oil at 176°C until golden brown, or about 7 min. Baked. (PSFB) Slices

were coated in canola oil and baked for 15 min. at 218°C, stirring once.

Sweet Potato Wedges (PSW). Sweet potatoes were lightly washed, peeled, and cut

to ~1 in. wedges. Wedges were boiled for 5 min., cooled and patted dry, then either fried or

baked. Fried. (PSWF) Wedges were par-fried in canola oil at 150°C until just browning, or

about 3 min. After resting for 30 min., wedges were fried at 176°C until puffed, or about 5

min. Baked. (PSWB) Wedges were coated in canola oil and baked for 15 min. at 218°C,

stirring once.

After processing by baking or frying, all commercial and fresh products were cooled

to room temperature, transferred to zip-lock bags, double bagged, and frozen at -80°C.

Frozen products were subsequently broken into pieces then lyophilized over 51 hours.

Dried samples were stored at -20°C. Samples were ground before analysis using a coffee

grinder and a mortar and pestle for high fat samples.

Figure 4. Preparation of samples for Experiment 3- comparison of CQAs and beta-carotene in commercially processed and freshly prepared products. Codes beginning with “M” correspond to commercial version and codes beginning with “P” correspond to the fresh version for each of the products (Classic Fry, Fresh Style Fry, Hash Browns, Sweet Potato Fry, Sweet Potato Wedge). Products on the left were prepared from R. Burbank potatoes; products on the right from Covington sweet potatoes.

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3.4.5 Phenolic Acid and Anthocyanin Extraction and Analysis

Extractions were conducted using ~0.4 g of lyophilized materials. Sample were first

extracted twice with 5 mL of hexane to remove lipids, then dried under a stream of nitrogen

at 37°C to remove residual solvent. After re-weighing the powders, 5 mL of extraction

solution (80% methanol, 20% water, 2% formic acid) was added to each sample tube.

Tubes were shaken for 15 min., sonicated for 45 min., and shaken for another 5 min., then

centrifuged and supernatant was collected and dried under nitrogen. The remaining pellet

underwent a second heated extraction to facilitate release of remaining polyphenols. 1 mL

of 2% formic acid in water was added to each tube, then the sample was heated for 15 min.

in a water bath at 60°C. 5 mL of the extraction solution was added, and after vortexing the

tubes were sonicated for 15 min. at 45°C. The samples were centrifuged and the combined

supernatants were dried under nitrogen. Dried samples were reconstituted with 5 mL of

2% formic acid in water prior to analysis. Overall extraction recovery, determined using

spikes of 1000 M ethyl gallate as an internal standard added to potato poweder prior to

extraction, ranged between 80-115%.

For phenolic analysis, 2 mL of sample was filtered through a 0.45 𝜇m PTFE filter and

10 uL were injected into a Waters 2695 HPLC (Milford, MA) with a Waters X-Bridge Shield

RP18 column (2.5 µm, 2.1x100 mm) heated to 40°C. HPLC and mass spectrometer

conditions were adapted from Song et al. (2013) Anthocyanins and phenolic acids were

analyzed in two separate methods but both using gradients of 2% formic acid in MS grade

water (mobile phase A) and 0.1% formic acid in acetonitrile (mobile phase B) at a flow rate

of 0.25 mL/min. For anthocyanin separation, solvent composition was 95, 65, 30, and 95%

mobile phase A at 0, 15, 18, and 19 min., respectively. For phenolic acid separation, solvent

composition was 95:5 (A:B) followed by a linear gradient to 65:35 (A:B) over 15 min and to

50:50 (A:B) at 17 min followed by a reset to initial conditions at 18 min. Column effluent

was split (50:50) to a Waters 2996 photodiode array detector and a Waters Micromass ZQ

mass spectrometer. Positive mode electrospray ionization (ESI) was used to detect

anthocyanins. Conditions included: source temperature set to 150°C ; desolvation

temperature set to 250°C.; nitrogen flow rates for desolvation and cone gas were 250 and

25 L/hr respectively. Capillary, cone, and extractor voltages were set to 2500, 50, and 3 V

respectively. Anthocyanins were detected by single ion responses set to m/z 272, 287, 301,

303, 317, and 331 for pelargonidin, cyanidin, peonidin, delphinidin, petunidin, and malvidin

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aglycone fragments respectively. All anthocyanins were quantified using cyanidin-3-

glucoside standard. Peaks for each respective anthocyanidin SIR were quantified and added

together to obtain a total anthocyanin content. Phenolic acids were detected in negative

mode ESI. Conditions included: source temperature set to 150°C and desolvation

temperature set to 250°C; nitrogen flow rats for desolvation and cone gas were 400 and 60

L/hr respectively. Capillary, cone, and extractor voltages were set to 3000, 40, and 5 V

respectively. Single ion responses (SIRs) were set to m/z 353 and 179 for chlorogenic and

caffeic acids. Identification of chlorogenic acids were made using standards 5-O-

caffeoylquinic (5-CQA) and 4-O-caffeoylquinic (4-CQA) acids and comparison with previous

literature. 5-CQA standard was used for quantification of all chlorogenic isomers. Limits of

detection and quantification for chlorogenic acids were 5 and 17 ug/g dw, respectively.

Cyanidin-3-glucoside standard was used for quantification of all anthocyanidin peaks.

Anthocyanin limits of detection and quantification were .06 and 0.2 ug/g, respectively.

3.4.6 Carotenoid Extraction and Analysis

For extraction and analysis of fat soluble carotenoid pigments, ~0.3 g of lyophilized

potato powder was vortexed with 2 mL of deionized water for 10 s, then left on ice for 10

min. 5 mL of chilled acetone was added and the mixture shaken for 5 min. and cooled with

ice for 5 min. After centrifugation, the supernatant was collected and set aside. Extraction

was repeated and the combined supernatants were dried under nitrogen until acetone had

evaporated. The remaining potato solids were then extracted with 3 mL of methyl-tert-

butyl ether (MTBE) containing 0.1% butylated hydroxytolulene (BHT) following the same

procedures as the acetone extraction. Supernatant from the MTBE extraction was added to

the dried supernatant from the acetone extraction. The mixture was vortexed and

centrifuged and the organic layer transferred to a new test tube. The MTBE extraction was

repeated on the potato solids and the organic layer combined in the same test tube. Each

sample was dried under nitrogen and then resolubilized in 200 uL of ethyl acetate with

0.1% BHT, filtered through a 0.45 𝜇m PTFE filter, allowed to rest for 10 min. before analysis.

10 uL of each sample was injected onto a Waters Acquity H-class UPLC equipped with

a Waters Acquity UPLC BEH C18 column (1.7 𝜇m, 2.1x100 mm) heated to 40°C. A gradient

of 93:5:2 water:acetonitrile:2M ammonium acetate (mobile phase A) and acetonitrile

(mobile phase B) at a flow rate of 0.8 mL/min was used. For carotenoid separation, solvent

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composition was 23, 20, 5, 0, and 23% mobile phase A at 0, 3, 4, 10, and 11 min.,

respectively. Compounds were detected using a Waters Acquity UPLC PDA detector with a

QDa detector monitoring from 250-550 nm and peaks were integrated at 450 nm. Pure

beta-carotene and lutein standards were used for quantification. Percent recovery (average

78%) was determined by spiking samples with internal standard before extraction and

comparing the resulting value to pure internal standard. Limits of detection and

quantification for beta-carotene were 0.03 and 1.0 ug/g dw, respectively, and 1.3 and 4.5

ug/g for lutein.

3.4.7 Statistical Analysis

Commercial samples from Experiment 1 included three true replicates (each

replicate consisting of a pooled sample from several potatoes) for each treatment. Each of

these replicates was extracted and analyzed once. Samples for Experiment 2 and 3 were

pooled samples containing at least 3 individual potatoes and were analyzed in triplicate.

Statistical analysis for significance on data from Experiments 1 and 2 was conducted using

2-way ANOVA with Tukey-Kramer for pairwise comparison (significance level p ≤ .05) with

JMP version 11 (SAS Institute, Inc., Cary, NC). Statistical analysis for significance on data

from Experiment 3 was conducted using least squares comparison of means and a

Bonferroni correction with SAS version 9.4.

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Results and Discussion

3.5.1 Experiment 1: Phytochemical Content in Fresh Commercial Varieties

3.5.1.1 Phenolics

Chlorogenic acid derivatives (CQAs) were the most abundant phenolic species found

in all varieties of potatoes analyzed. This is consistent with previous reports on potato

phenolic profiles (Brown, 2005; Ezekiel et al., 2013). Also in agreement with previous

reports, 5-O-caffeoylquinic acid (chlorogenic acid; 5-CQA) was the primary chlorogenic acid

form (p<.05) in all varieties, followed by 4-O-caffeoylquinic (crytochlorogenic acid; 4-CQA)

and 3-O-caffeoylquinic acid (neochlorogenic acid; 3-CQA) (Navarre et al., 2011; Zhu et al.,

2010). While all varieties contained significantly different amounts of 5-CQA in the flesh,

many varieties contained similar amounts of 3 and 4-CQA, indicating that 5-CQA is the main

contributor to differences in total CQAs. All varieties contained significantly (p<.05) greater

amounts of 4-CQA than 3-CQA except for Yukon and Challenger. Order of varieties in terms

of total CQA levels in flesh was ADR > AR2009-10 > ADB > Innovator, R. Burbank, Norland,

Yukon, Bintje, Challenger. When looking at whole varieties, Norland would move higher up

in the list (after ADB) because its phenolics are more concentrated in its red peel. Overall

levels of CQAs in pigmented varieties are similar to levels (~375 mg/100 g dw) found in

brewed Robusta coffee (Rothwell et al., 2013).

3-CQA and 4-CQA were not detected in whole or flesh of the Covington sweet potato.

However, these acids are present in processed forms of this variety (Table 11). Dawidowicz

and Typek (2014) demonstrated increases in 3-CQA, 4-CQA, and other 5-CQA degradation

products in blueberries, though the time and temperatures were higher than those used in

this study. Takenaka (2006) also reports the increase in 3-CQA and 4-CQA in sweet

potatoes upon processing by heating suggesting the increase is generated through

enzymatic action. The extent to which this may have occurred was not investigated in this

study.

Overall, colored-fleshed (red and purple) varieties contained much higher levels of

total CQAs (358-953 mg/100 g dw in whole) than white or yellow-fleshed varieties (43-88

mg/100 g dw in whole) (Figure 3). In general, as previously reported, whole potato

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contained greater concentrations of CQAs than the flesh alone suggesting a higher

distribution of these phenolic into the skin (Deusser et al., 2012; Lewis et al., 1998).

However, the peel to flesh ratio varied between cultivars. For example, in purple-fleshed

ADB and AR2009-10, CQAs in flesh and whole were relatively equal, while whole R.

Burbank contained 75% more than R. Burbank flesh. This suggests that especially for

pigmented potatoes, products which contain only the flesh and no peel still offer significant

levels of CQAs originating from flesh.

Free caffeic acids were found are relatively low levels (3.7-23 mg/100 g dw) in the

peel of all varieties except R. Burbank and Covington sweet potatoes and in the flesh of only

the ADR variety (Table 7). Other hydroxycinammic and hydroxybenzoic acids (ferulic, p-

coumaric, vanillic, and gallic acids) and non-anthocyanin flavonoids (rutin, kaempferol,

kaempferol-3-rutinoside) were detected in several varieties but not quantified due to low

and inconsistent levels (Appendix A). Other studies have quantified these phenolics in

several varieties (Deusser et al., 2012; Navarre et al., 2011). Though some have detected

significant levels of catechin in other varieties (del Mar Verde Méndez et al., 2004; Mäder et

al., 2009), this study did not detect catechins in any varieties.

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Table 7. CQA and caffeic acid in whole potatoes and potato flesh of nine commercial potato varieties and one commercial sweet potato variety.

Each value represents the average of three analytical replicates with standard deviation. Lowercase letters represent significance (p<.05) within variety and potato part (across a row). Number represents significance (p<.05) between potato parts. Uppercase letters represent significance (p<.05) between varieties and potato parts (down a column; flesh used for comparison). Total CQAs are the sum of the three CQA after quantification. W= whole; F= flesh. Innovator= cream flesh, tan peel; Bintje= light yellow flesh, tan peel; Challenger= light yellow flesh, tan peel; Yukon= yellow flesh, tan peel; R. Burbank= white flesh, brown peel; AR2009-10 and ADB= purple flesh, purple peel; ADR= red flesh, red peel; Norland= white flesh, red peel; Covington= orange flesh, brown peel.

mg polyphenol/100 g dw

Variety Neochlorogenic

(3-CQA) Cryptochlorogenic

(4-CQA) Chlorogenic

(5-CQA) Total CQAs Free Caffeic Acid

Innovator W 12.8 ± 0.2a1 14.5 ± 0.2b 47.1 ± 2.5c1 74.4 ± 3.61 11.9 ± 0.5

F 10.3 ± 0.0a2,D 11.4 ± 0.0b,E 58.7 ± 2.1c2,E 80.3 ± 5.41,DE n.d.

Bintje W 10.4 ± 0.1a 10.9 ± 0.2a 22.6 ± 1.2b1 43.8 ± 2.71 9.62 ± 1.3

F 10.2 ± 0.2a,D 10.1 ± 0.2a,G 14.1 ± 0.9b2,H 34.4 ± 1.32,F n.d.

Challenger W 10.8 ± 0.1a 11.4 ± 0.3a 21.1 ± 2.4b1 43.3 ± 9.91 21.7 ± 0.9

F 9.91 ± 0.2a,D 10.0 ± 0.2a,G 15.0 ± 0.5b2,H 35.0 ± 1.92,F n.d.

Yukon W 10.7 ± 0.2a 11.6 ± 0.2a 38.5 ± 0.2b1 60.8 ± 2.61 6.34 ± 1.2

F 10.1 ± 0.1a,D 10.5 ± 0.1a,FG 17.5 ± 0.4b2,G 38.1 ± 1.61,EF n.d.

R. Burbank W 11.3 ± 0.1a 13.3 ± 0.1b 62.2 ± 1.0c1 86.7 ± 3.61 n.d.

F 9.86 ± 0.1a,D 10.8 ± 0.6b,EF 40.5 ± 5.9c2,F 61.1 ± 7.91,DE n.d.

AR2009-10 W 14.5 ± 0.2a 48.2 ± 2.8b 553 ± 8.9c1 616 ± 121 15.7 ± 3.4

F 12.7 ± 0.5a,C 43.1 ± 1.1b,B 566 ± 22c1,A 622 ± 331,B n.d.

ADR W 24.9 ± 1.6a 89.5 ± 1.2b 839 ± 5.7c1 953 ± 4.61 23.4 ± 2.5

F 18.5 ± 0.4a,B 64.9 ± 1.5b,A 731 ± 18c1,A 814 ± 252,A 14.6 ± 1.5

ADB W 16.9 ± 0.4a 27.2 ± 3.8b 314 ± 45c1 358 ± 8.01 3.69 ± 2.3

F 12.1 ± 0.1a,C 25.8 ± 0.3b,D 291 ± 2.0c1,B 329 ± 6.11,C n.d.

Norland W 17.5 ± 0.4a 22.4 ± 0.8b 48.4 ± 1.8c1 88.3 ± 9.21 8.46 ± 1.7

F 10.5 ± 0.3a,A 11.8 ± 0.2b,C 17.8 ± 0.9c2,D 39.4 ± 1.32,EF n.d.

Covington W n.d. n.d. 149 ± 77 149 ± 77 n.d.

F n.d. n.d. 100 ± 36 100 ± 36 n.d.

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Figure 5. Average total CQA’s in flesh and whole of nine commercial Solanum tuberosum varieties. Error bars represent standard deviation.

3.5.1.2 Anthocyanins

The LC-MS method utilized in this study was adapted from that reported by Song et

al. (2013). This method uses higher cone voltages to fragment native anthocyanins to their

corresponding anthocyanidin backbone and thus facilitate quantification by corresponding

response of aglycone. As such results are expressed as total anthocyanin content by class of

anthocyanidin.

Three colored raw varieties were analyzed- AR2009-10 (purple), ADB (purple), and

ADR (red). Petunidin derivatives were the primary anthocyanin forms in AR2009-10 with

smaller amounts of delphinidin, malvidin, and peonidin, while cyanidin and pelargonidin

derivatives dominated the red-fleshed ADR (Table 8). ADB contained all anthocyanidin

derivatives, though petunidin again dominated in this purple-fleshed variety. This

illustrates that even varieties of very similar color can vary in anthocyanin profile. Flesh

and whole of purple varieties contained similar levels of total anthocyanins, while red ADR

had significantly more anthocyanins in whole than flesh.

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While individual glycosides and other anthocyanin derivatives were specifically

identified, tentative identification of simple anthocyanidin-glucosides – arabinosides and

galactosides were identified by comparison to previous separations in our group (Song et al

2012; 2013) and corresponding elution order compared to cyanidin-3-glucoside standard.

Further, it has been established that colored-fleshed potatoes and sweet potatoes contain a

variety of acylated anthocyanins, and lower levels of simple glycosides (Mulinacci et al.,

2008; Song et al., 2013). The predominance of acylated anthocyanins in the pigmented

potatoes analyzed in this study was also confirmed by the later retention time (Figure 4),

again consistent with previous separations by our group (Song et al). Andersen et al.

(1991) identified the major anthocyanin in purple-fleshed potatoes as petanin (petunidin-3-

p-coumaroylrutinoside-5-glucoside). Petunidin derivatives were high in both purple

varieties, indicating the possible presence of petanin. Lewis et al. (1998) and Eichhorn and

Winterhalter (2005) report the presence of petanin in three varieties of purple-fleshed

potatoes, and additional anthocyanins of the same structure as petanin with peonidin and

malvidin aglycones. Eichhorn and Winterhalter (2005) also identified peonidin- and

malvidin-3-rutinoside-5-glucosides in purple varieties, and Fossen and Andersen (2000)

describe petunidin- and malvidin-3-rut-3,5-diglucosides acylated with ferulic acid. The red-

fleshed variety in their study contained primarily pelargonidin-3-p-coumaroylrutinoside-5-

glucoside (pelanin) and pelargonidin-3-rutinoside-5-glucoside (pg-3-rut-5-glu). Rogriguez-

Saona et al. (1998) identified the same pelargonidin derivatives, with the addition of ferulic

acid acylation on pg-3-rut-5-glu and pg-3-rut. This literature, along with elution time of

major peaks (Figure 4), that the purple-fleshed potatoes in this study likely contain

primarily petunidin and malvidin-3-rut or petunidin and malvidin-3-rut-5-glucosides

acylated with p-coumaric and ferulic acids. Red-fleshed varieties likely contain the same,

with pelargonidin and cyanidin derivatives rather than petunidin and malvidin.

3.5.1.3 Carotenoids

Lutein was detected in all varieties, with values ranging from 0.07 to 0.25 mg/100 g dw.

Beta-carotene was not quantifiable in any variety except Covington sweet potato, at 40.3

and 46.4 mg/g in flesh alone and whole potato, respectively.

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Table 8. Anthocyanin content of three pigmented potato varieties, expressed by class of anthocyanidin. mg anthocyanidin/100 g dw

Cyanidins Peonidins Delphinidins Petunidins Malvidins Pelargonidins

Total Anthocyanidins

AR2009-10

F n.d. 0.72 ± 0.1 7.44 ± 0.8 49.8 ± 4.8 2.24 ± 0.3 n.d. 60.2 ± 1.0

W n.d. 0.78 ± 0.1 9.56 ± 0.6 56.0 ± 1.1 2.36 ± 0.1 n.d. 68.7 ± 0.3

ADR F 7.86 ± 0.1 n.d. n.d. n.d. n.d. 25.5 ± 0.91 33.4 ± 0.9

W 15.7 ± 1.6 n.d. n.d. n.d. n.d. 36.7 ± 1.78 52.4 ± 3.1

ADB

F 8.39 ± 0.4 14.5 ± 0.8 3.67 ± 0.2 29.9 ± 2.5 1.06 ± 0.1 15.9 ± 1.66 73.4 ± 0.3

W 7.47 ± 0.5 13.5 ± 0.8 3.56 ± 0.3 33.0 ± 2.7 1.25 ± 0.0 15.9 ± 0.33 74.7 ± 1.7

All anthocyanins quantified using cyanidin-3-glucoside equivalents. Each value represents the average of three analytical replicates with standard deviation. “n.d.” used to indicate values too low for quantification. Total anthocyaninss are the sum of each anthocyanidin SIR after quantification. W= whole; F= flesh. ADR= red flesh, red peel; ADB and AR2009-10= purple flesh, purple peel.

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Figure 6. Example anthocyanin chromatograms for three varieties of pigmented potato: (1) ADR, (2) ADB, (3) AR2009-10. Examples represent whole, raw samples. Each SIR is one class of anthocyanidn. m/z 287- cyanidin; 301- peonidin; 303- delphinidin; 317- petunidin; 331- malvidin; 271- pelargonidin. Note that SIRs are not to the same scale. The boxes surround acylated anthocyanins (peaks with retention time of ~11 min. or later) which are likely anthocyanidin-3-rutinosides or anthocyanidin-3-rutinoside-5-glucosides acylated with ferulic or p-coumaric acids.

1

2

3

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3.5.2 Experiment 2: Chlorogenic acid and Anthocyanin Content through Commercial

Processing.

Commercially processed potato products are the primary form of potatoes

consumed in the United States. Thus, insight into effects of processing on content and

profile of phytochemicals in commercially relevant cultivars will enhance our

understanding of the role and potential of processed potato products to contribute to the

nutritional quality of the American diet. Existing literature on process stability of main

Solanum tuberosum phytochemicals (including phenolic acids and flavonoids) is

inconsistent, and the majority of studies conducted use only small-scale lab procedures for

processing. As the most abundant phenolic compounds in potatoes, CQAs were the main

focus for understanding the effects of commercial processing, and anthocyanins were an

additional focus for colored-fleshed varieties. A simple summary of the processed samples

used in this study can be found in the methods section (Figure 1).

3.5.2.1 Chlorogenic Acids

In general, total CGAs were lower in peeled and whole potatoes (FNS and FWS)

compared to the same raw varieties assayed in Experiment 1 (Tables 7 and 9). This

variation is not uncommon and may be due, in part, to harvest year differences, variability

in sampling of individual potatoes as well as storage stability in frozen samples. It is

important to point out that materials for Experiment 2 were collected from the 2012

harvest and subsequent commercially processed products. By comparison potato samples

for Experiment 1 were from 2013.

Retention of total CGA through processing from fresh whole potato (FWS) to final

products (BF, BFM, BFF, BFFO, BFFF) was moderate to high, ranging from a low of 32% (R.

Burbank BFFF) to a high of 85% recovery (ADR BF). Retention was overall lowest for the R.

Burbank cultivar (ranging from 32-55%), whereas the colored varieties displayed greater

retention through the various forms of processing (ADB 49-72%; ADR 64-85%; AR2 52-

76%). Significant differences in retention were not determined, but this suggests that not

only do pigmented varieties have greater concentrations of phenolic acids in raw flesh, but

these phenolics may be more stable to processing. This could indicate protective effects of

other components present in these varieties, or simply that higher phenolic content is

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protective. Some studies which have measured vitamin C, antioxidant activity, and phenolic

content through processing do not indicate that a higher ascorbic acid or antioxident

content is protective (Navarre et al., 2010; Xu et al., 2009). However, Narita and Inouye

(2013) found that stability of 5-CQA was improved with addition of EGCG (epticallocatechin

gallate) and ascorbic acid. Nardini et al. (2002) also found that ascorbic acid and EDTA

could prevent degradation of phenolic acids during alkaline hydrolysis.

In the white R. Burbank variety, total CGAs were significantly lower (p<.05) in all

processed products when compared to raw whole, but no significant differences were

observed between flesh and processing levels or within processing levels. In all colored-

fleshed varieties, BF and BFM treatments did not significantly affect total CQA levels

compared to raw flesh (FNS). BFF, BFFO, and BFFF treatments were also all significantly

(p<.05) lower in CQAs than FWS or FNS (except ADB BFFO compared to FNS) and in general

were lower than BF and BFM treatments, though significance varied. For the ADB variety,

BFFF products was significantly (p<.05) lower in CQAs than BF and BFM, but not

significantly different from BFF or BFFO. BFF, BFFO, and BFFF products also did not

significantly differ from each other for ADB and AR2 varieties. Overall, these results

support the notion that thermal treatment by blanching and microwaving may have a

modest effect on potato phenolics compared to harsher treatments such as frying and

baking. Mäder et al. (2009), whose study also used commercial processing methods, found

high retention of phytochemicals throughout blanching, cooking, mashing, and drying.

Some processed products (Table 9, Table 10, and additional unpublished data)

displayed a slight, but insignificant increase in chlorogenic acids and anthocyanins

compared to flesh or other processed methods. While not commonly reported in the

literature this has been previously observed (Blessington et al., 2010; Navarre et al., 2010)

for microwaving and other forms of processing. These groups attribute these effects to an

increase in extractability upon heating, which theoretically could also lead to an increase in

digestibility upon consumption. The extraction methods for our study did use an added

heating step to enhance the extraction of phenolics from both native and retrograded starch

of cooked products, which should have also generally corrected for the effects of heating on

extractability.

Within the different isoforms of CQAs, it appears that processing most affected

levels of 5-CQA. The greater reduction in 5-CQA relative to other isoforms lead to an

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increase in the relative proportion of 3-CQA and 4-CQA, which was also observed by Mäder,

Rawel, and Kroh (2009).

Figure 7. Example chromatogram of the Norland variety, whole. m/z 353- CQA; m/z 179- caffeic acid. Note that SIRs are not to the same scale.

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Figure 8. Total CQAs (sum of averages of 3-,4-, and 5-O-CQAs) quantified in four varieties of commercially processed potatoes. Significant differences determined within each variety (p ≤ .05).

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Table 9. CQAs in four varieties of potatoes through various levels of commercial processing.

Each value represents the average of three analytical replicates with standard deviation. Lowercase letters represent significance (p<.05) within a treatment (across a row). Uppercase letter represents significance (p<.05) between treatments (within a variety; down a column). Total CQAs are the sum of the three CQA after quantification. FWS= Flesh with skin; FNS= Flesh without skin; BF= Blanched, frozen; BFM= Blanched, frozen, microwaved; BFF= Blanched, frozen, fried; BFFO= Blanched, fried, frozen, baked; BFFF= Blanched, fried, frozen, fried

mg polyphenol/100 g dw

Sample 3-CQA 4-CQA 5-CQA Total CQA % Ret. From FNS

R. Burbank

FWS 4.40 ± 0.4a 11.0 ± 1.8b 65.0 ± 7.3c 80.4 ± 9.0A 276%

FNS 2.24 ± 0.1a 2.90 ± 0.2a 24.4 ± 4.3b 29.6 ± 4.5AB 100%

BF 1.96 ± 0.0a 2.14 ± 0.2a 11.8 ± 4.5b 15.9 ± 4.6B 55%

BFM 4.40 ± 0.1a 2.22 ± 0.2a 8.51 ± 4.4b 15.1 ± 4.7B 43%

BFF 1.37 ± 1.2a 2.11 ± 0.1a 5.84 ± 0.9b 9.32 ± 0.2B 32%

BFFO 2.18 ± 0.0a 2.24 ± 0.1a 6.12 ± 2.0b 10.5 ± 2.2B 36%

BFFF n.d. 2.28 ± 0.0a 6.33 ± 1.6b 8.61 ± 5.6B 38%

ADR

FWS 29.5 ± 2.5a 41.9 ± 2.1b 255 ± 4.8c 327 ± 8.7A 112%

FNS 26.0 ± 3.3a 36.8 ± 1.8b 229 ± 3.1c 292 ± 6.5AB 100%

BF 24.3 ± 1.2a 33.7 ± 3.3b 189 ± 12c 247 ± 14B 85%

BFM 29.5 ± 1.7a 37.6 ± 5.2b 175 ± 30c 242 ± 36B 83%

BFF 16.8 ± 0.3a 22.4 ± 1.0a 149 ± 8.9b 188 ± 8.1C 64%

BFFO 21.8 ± 1.4a 28.2 ± 1.6a 137 ± 16b 187 ± 16C 64%

BFFF 20.2 ± 0.9a 26.6 ± 1.3a 157 ± 14b 204 ± 14BC 70%

ADB

FWS 21.3 ± 8.6a 36.9 ± 21a 195 ± 49b 253 ± 78AB 119%

FNS 17.8 ± 2.6a 29.8 ± 5.7a 165 ± 3.5b 212 ± 12A 100%

BF 12.7 ± 1.9a 15.9 ± 5.3b 100 ± 25c 128 ± 32BC 60%

BFM 21.3 ± 5.9a 24.2 ± 12a 108 ± 26b 153 ± 44C 72%

BFF 9.80 ± 0.9a 12.1 ± 1.6a 81.9 ± 9.0b 104 ± 9.5CD 49%

BFFO 12.3 ± 1.4a 16.6 ± 3.5a 83.6 ± 3.3b 112 ± 8.2CD 53%

BFFF 12.0 ± 3.4a 15.8 ± 8.1a 91.3 ± 30b 119 ± 42D 56%

AR2009-10

FWS 7.81 ± 2.6a 28.2 ± 4.9b 312 ± 20c 348 ± 17A 139%

FNS 4.14 ± 0.5a 14.6 ± 6.8b 232 ± 38c 251 ± 44B 100%

BF 4.49 ± 1.0a 12.5 ± 4.0b 174 ± 12c 191 ± 16C 76%

BFM 7.81 ± 2.5a 17.8 ± 3.3b 154 ± 11c 180 ± 15CD 72%

BFF 3.19 ± 0.3a 6.13 ± 1.5a 123 ± 5.2b 133 ± 4.0CD 53%

BFFO 6.97 ± 2.3a 12.4 ± 3.5b 119 ± 8.2c 139 ± 13CD 55%

BFFF 3.85 ± 0.3a 7.57 ± 0.6b 118 ± 16c 130 ± 16D 52%

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3.5.2.2 Anthocyanins

No significant difference was observed in total anthocyanin content within the three

varieties (ADR, ADB, and AR2009-10) for commercial processing method. Retention

through processing for all varieties ranged from 79% (ADB BFFF) to 129% (ADR BF).

While anthocyanins in some foods are highly susceptible to heat, acylated anthocyanins

such as those that predominate in colored potatoes, purple carrots, and black currant, for

example, have been reported to have greater stability to heating (Brouillard, 1981;

Brownmiller et al., 2008; Malien-Aubert et al., 2001; Patras et al., 2010; Sadilova et al., 2006;

Song et al., 2013). Other studies have also demonstrated an increase in phytochemicals

after processing (see above discussion in section 4.2.1).

Overall, anthocyanin content in FWS samples did not differ significantly from FNS

for any variety, confirming that anthocyanins are well distributed throughout the flesh

rather than being concentrated extensively in the peel. Anthocyanin profile for these

varieties differs slightly from that of the same varieties in Experiment 1, which could be due

to differences in crop year.

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Table 10. Anthocyanins in three pigmented varieties of potato through various levels of commercial processing, expressed by class.

All anthocyanins quantified using cyanidin-3-glucoside equivalents. Each value represents the average of three analytical replicates with standard deviation. “n.d.” used to indicate values too low for quantification. Effect of treatment was not significant for any variety, but effect of variety was significant (p<.05). Total anthocyanins are the sum of each anthocyanidin SIR after quantification. FWS= Flesh with skin; FNS= Flesh without skin; BF= Blanched, frozen; BFM= Blanched, frozen, microwaved; BFF= Blanched, frozen, fried; BFFO= Blanched, fried, frozen, baked; BFFF= Blanched, fried, frozen, fried.

mg anthocyanidin/100 g dw

Cyanidins Peonidins Delphinidins Petunidins Malvidins Pelargonidins

Total Anthocyanins

% Ret from FNS

ADR

FWS 2.81 ± 0.36 0.67 ± 0.11 n.d. n.d. n.d. 19.4 ± 2.27 22.9 ± 2.66 107%

FNS 2.39 ± 0.48 0.22 ± 0.07 n.d. n.d. n.d. 18.7 ± 1.45 21.3 ± 1.98 100%

BF 2.73 ± 0.12 0.24 ± 0.02 n.d. n.d. n.d. 24.6 ± 2.79 27.5 ± 2.92 129%

BFM 2.34 ± 0.22 0.28 ± 0.03 n.d. n.d. n.d. 23.8 ± 3.51 26.4 ± 3.71 124%

BFF 1.76 ± 0.20 0.18 ± 0.01 n.d. n.d. n.d. 20.4 ± 3.53 22.4 ± 3.54 105%

BFFO 1.87 ± 0.11 0.23 ± 0.02 n.d. n.d. n.d. 20.2 ± 3.22 22.3 ± 3.33 104%

BFFF 1.95 ± 0.13 0.21 ± 0.05 n.d. n.d. n.d. 20.2 ± 3.65 22.3 ± 3.74 105%

AR2009-10

FWS n.d. n.d. 0.63 ± 0.23 20.1 ± 4.24 2.76 ± 0.49 n.d. 23.4 ± 4.96 109%

FNS n.d. n.d. 0.66 ± 0.16 18.8 ± 3.96 2.08 ± 0.54 n.d. 21.5 ± 4.65 100%

BF n.d. n.d. 0.72 ± 0.28 18.4 ± 4.82 1.84 ± 0.57 n.d. 20.9 ± 5.67 97%

BFM n.d. n.d. 0.62 ± 0.28 17.1 ± 4.30 1.58 ± 0.38 n.d. 19.3 ± 4.95 89%

BFF n.d. n.d. 0.53 ± 0.10 15.6 ± 1.36 1.50 ± 0.13 n.d. 17.6 ± 1.58 82%

BFFO n.d. n.d. 0.56 ± 0.23 15.7 ± 2.71 1.34 ± 0.18 n.d. 17.6 ± 3.11 82%

BFFF n.d. n.d. 0.49 ± 0.09 15.7 ± 1.97 2.00 ± 0.84 n.d. 18.2 ± 1.24 85%

ADB

FWS 0.64 ± 0.09 5.56 ± 0.18 n.d. 9.40 ± 0.86 n.d. 2.97 ± 0.33 18.6 ± 0.99 100%

FNS 0.78 ± 0.19 6.11 ± 0.56 n.d. 9.80 ± 0.52 n.d. 1.94 ± 0.97 18.6 ± 2.05 100%

BF 0.71 ± 0.26 5.29 ± 1.59 n.d. 8.71 ± 2.21 n.d. 1.86 ± 0.67 16.6 ± 4.58 89%

BFM 0.73 ± 0.22 5.45 ± 1.03 n.d. 8.57 ± 1.60 n.d. 2.28 ± 1.13 17.0 ± 3.67 91%

BFF 0.71 ± 0.18 4.98 ± 0.71 n.d. 8.39 ± 1.23 n.d. 2.18 ± 0.74 16.3 ± 2.31 87%

BFFO 0.67 ± 0.12 4.79 ± 0.68 n.d. 7.94 ± 1.24 n.d. 1.96 ± 0.53 15.4 ± 2.24 82%

BFFF 0.64 ± 0.24 4.55 ± 1.51 n.d. 7.28 ± 2.24 n.d. 2.30 ± 1.09 14.8 ± 4.92 79%

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Figure 9. Total anthocyanins (sum of averages of individual anthocyanidins) quantified in three varieties of commercially processed potato. Effect of treatment was not significant for any variety, but effect of variety was significant (p<.05).

3.5.3 Experiment 3: Comparison of Chlorogenic Acids and Beta-Carotene in Fresh and

Commercially Produced Potato Products.

Current consumers often regard commercially processed foods as more unhealthy

than freshly prepared versions, even when methods and ingredients of preparation are very

similar. While the “healthiness” of a food is a multifaceted concept, this portion of the study

specifically investigated differences in CQA and carotenoid content between commercially

processed and reconstituted and freshly prepared versions of the same products. Beta-

carotene, as the primary carotenoid in orange-fleshed sweet potatoes, was chosen for study.

In this experiment, five fresh products were prepared by baking and frying/panfrying

(except for fresh-style fries, which were only fried) to match five reconstituted commercial

products (classic French fries, fresh-style French fries, hash browns, sweet potato fries, and

sweet potato wedges). The former three products were all prepared from R. Burbank

potatoes, while the latter two were prepared from Covington sweet potatoes.

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3.5.3.1 Chlorogenic Acids

Total CQA were significantly greater (p<.05) in freshly prepared fried classic fries

and baked or pan-fried hash browns than commercially processed fries and baked or pan-

fried hash browns. It is possible that because hash browns have a large surface area to

volume ratio, the multiple heating steps sustained from processing to reconstitution have a

greater effect on phytochemical retention. Baked classic fries and fresh style fries did not

significantly differ between fresh and commercial versions. Fresh and commercially

processed fried sweet potato fries and wedges also did not significantly differ in total CQA

content. Total CQAs were significantly greater (p<.05) in fresh baked potato wedges (95.4

mg/100 g dw) than in the commercial product (77 mg). However, total CQAs were

significantly great (p<.05) in commercially processed baked sweet potato fries compared to

the freshly prepared version. Overall, these results suggest that while select differences can

be observed, generally, there is not a large difference in phenolic content between freshly

prepared and commercial French fries made from the same lot of potatoes. Differences,

whether significant or not, were sometimes in favor of commercial processing, and

sometimes in favor of fresh preparation. For products like hash browns, it is possible that

fresh preparation may better retain phytochemicals as the cycle of heat treatments is

reduced for this high surface area product. Because CQA were generally greater in fresh

versions of products made from Russet Burbank potatoes, it could be that fresh and

commercial processing differentially affect this variety. When interpreting the data, one

should keep in mind that potatoes are a highly variable vegetable, and further studies would

be needed to conclusively answer the “fresh vs. commercial” question.

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Table 11. Chlorogenic acids in freshly prepared and commercially processed products.

Each value represents the average of three analytical replicates with standard deviation. Total CQAs are the sum of the three CQAs after quantification. M= commercial sample; P= fresh sample. B= baked; F= Fried.

mg chlorogenic acid/100 g dw

Sample Neochlorogenic

(3-CQA) Cryptochlorogenic

(4-CQA) Chlorogenic

(5-CQA) Total Chlorogenic

Acids

Classic Fry

Commercial B 2.56 ± 0.1 2.54 ± 0.1 7.37 ± 1.0 12.5 ± 1.2

F 2.50 ± 0.0 2.68 ± 0.0 9.72 ± 0.9 14.9 ± 0.9

Fresh

B 3.27 ± 0.5 3.09 ± 0.4 10.2 ± 2.5 16.5 ± 3.4

F 3.97 ± 0.2 4.18 ± 0.3 16.7 ± 1.5 24.8 ± 2.0

Fresh-Style Fry

Commercial B 2.85 ± 0.4 3.18 ± 0.4 30.5 ± 7.0 38.1 ± 10

Fresh F 2.03 ± 0.1 3.19 ± 0.3 42.6 ± 6.9 36.9 ± 5.4

Sweet Potato Fry

Commercial B 2.62 ± 0.1 3.42 ± 0.2 39.4 ± 3.0 45.4 ± 3.4

F 2.48 ± 0.02 2.86 ± 0.1 31.8 ± 3.6 37.2 ± 3.6

Fresh B 2.88 ± 0.03 3.18 ± 0.2 21.6 ± 2.6 27.7 ± 2.7

F 2.06 ± 0.1 2.54 ± 0.1 27.3 ± 3.3 31.9 ± 3.3

Sweet Potato Wedge

Commercial B 4.12 ± 0.2 6.04 ± 0.3 67.0 ± 2.2 77.2 ± 2.4

F 3.86 ± 0.5 5.13 ± 0.2 71.6 ± 4.5 80.6 ± 5.2

Fresh B 6.09 ± 0.6 11.0 ± 0.3 118 ± 3.3 135 ± 3.6

F 3.43 ± 0.1 4.47 ± 0.2 83.7 ± 9.3 91.6 ± 10

Hash Browns

Commercial B 2.60 ± 0.1 2.86 ± 0.1 3.08 ± 0.2 8.54 ± 0.4

F 2.64 ± 0.03 2.67 ± 0.1 3.62 ± 0.2 8.93 ± 0.3

Fresh B 3.53 ± 0.02 3.58 ± 0.1 7.00 ± 0.2 14.1 ± 0.3

F 3.74 ± 0.04 3.91 ± 0.1 7.68 ± 0.3 15.3 ± 0.2

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Figure 10. Total CQAs (sum of averages of 3-,4-, and 5-O-CQA) compared in commercial and fresh products from Russet Burbank potatoes. Significant differences determined between commercially and freshly prepared products are designated by different letter within bar (p ≤ .05).

Figure 11. Total CQAs (sum of averages of 3-,4-, and 5-O-CQA) compared in commercial and fresh products from Covington sweet potatoes. Significant differences determined between commercially and freshly prepared products are designated by a different letter within bar (p ≤ .05).

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3.5.3.2 Beta-carotene

Beta-carotene content did not significantly differ between any fresh and commercial

sweet potato product except for baked sweet potato wedges, where the commercial product

had significantly greater levels of beta-carotene (30 mg/100 g dw and 25 mg/100 g dw,

respectively). As previously mentioned, this single difference likely represents an anomaly,

not a rule, and overall it appears that beta-carotene content does not significantly differ

between fresh and commercial products. Raw Covington sweet potato contained 40.3 ± 2.4

and 46.5 ± 5.7 mg beta-carotene/100 g dw in flesh and whole, respectively. This indicates

retention ranging from 59-74% throughout commercial and fresh products. Previous

studies have shown similar moderate retention of carotenoids in processed sweet potato

products (Berni et al., 2015; Donado-Pestana et al., 2012; van Jaarsveld et al., 2006), though

literature directly comparing fresh and commercial products could not be found.

Figure 12. Beta-carotene content in fresh and commercial products. Significant differences determined between commercially and freshly prepared products are designated by a different letter within bar (p ≤ .05).

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Conclusions

This study demonstrates that nine commercial Solanum tuberosum cultivars contain

high levels of CQAs (3-,4-, and 5- CQA), with 5-CQA comprising the majority of total

chlorogenic isomers. Pigmented varieties ADR, ADB, and AR2009-10 contained greater

levels of chlorogenic acids than white/yellow-fleshed varieties, in addition to acylated

anthocyanins. Retention of CQAs through commercial processing appeared to be greater for

pigmented varieties than white R. Burbank, and retention of anthocyanins was high. While

white/yellow-fleshed varieties contribute phytochemicals to the diet, this study highlights

the potential for pigmented potatoes to contribute greater levels, especially if retention

after commercial processing is better. Use of whole, rather than peeled, potato in fresh or

commercial applications will also contribute greater levels of phytochemicals to the diet. In

general, commercial microwaving and blanching resulted in better retention of chlorogenic

acids than frying and subsequent baking or frying, though the latter processes still resulted

in moderate retention in pigmented varieties. In general, freshly prepared and

commercially processed products were comparable in chlorogenic acid or beta-carotene

content with some exceptions, suggesting that fresh and commercial products can provide

similar levels of phytochemicals to the diet.

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CHAPTER 4. GENERAL FINDINGS AND FUTURE DIRECTIONS

The overall objective of this research was to investigate phytochemical content in

commercially relevant cultivars and determine the effects of commercial and fresh

processing on phytochemical content. To achieve this objective, three experiments with

separate aims were conducted. Experiment (Aim) 1 was used to determine phytochemical

content in fresh commercially relevant potato varieties. In experiment (Aim) 2 we

determined the extent to which key phenolics including chlorogenic acid and anthocyanins

are recovered through commercial processing. In experiment (Aim) 3 we compared the

impact of fresh preparation to commercial processing on chlorogenic acid and beta-

carotene recovery.

In regards to experiment 1, the nine potato cultivars and one sweet potato cultivar

used in this study all contained levels of phytochemicals comparable or greater than other

common fruits and vegetables, such as apples, peaches, and carrots. Pigmented varieties

contain chlorogenic acids (318-953 mg/100 g dw) similar to that of Robusta coffee (~375

mg/100 g dw) and highbush blueberries (~655 mg/100 g dw), both high-phenolic foods

(Rothwell et al., 2013). For all potato cultivars, chlorogenic acids (3-, 4-, and 5-CQA acids)

were the primary phytochemicals analyzed. As expected, 5-CQA was the primary CQA in

both whole and flesh of these cultivars. Whole potatoes generally contained significantly

greater levels of CQAs than flesh (though the ratio varied) and anthocyanins did not follow

the same pattern. Pigmented potatoes contained greater (p<0.05) levels of CQAs than

white/yellow potatoes. In addition, the non-significant differences between CQAs in whole

and flesh of pigmented varieties indicate that peeling pigmented varieties can still result in

high-phenolic products, while less likely for white/yellow varieties assessed in this study.

All of these findings are consistent with previous research (Summarized in Section 1.5).

Though there are many existing studies on the phytochemicals in potatoes, generally the

small number of varieties included within one study often makes comparison difficult due

to differences in research methodology.

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Experiment 2 revealed low to moderate process stability of chlorogenic acids in

processed potato products, which is consistent with some existing literature and

contrasting to others who have demonstrated either very poor (as low as 0%) or very high

retention (>500%) upon heat treatment (Blessington et al., 2010; Dao and Friedman, 1992;

Deusser et al., 2012; Navarre et al., 2010). Some methods of processing (microwaving and

blanching) appear to be gentler on phytochemicals present in these varieties as compared

to par-frying, frying, and baking. The effects of processing varied by cultivar. Not only did

white-fleshed R. Burbank contain lower levels of CQAs in its raw state, it retained fewer

CQAs through processing than its pigmented counterparts. This research suggests that

whole pigmented commercially relevant varieties offer more phytochemical potential in the

raw state and also may be more stable to degradation through processing than traditional

commercial varieties such as R. Burbank and Bintje. Potato anthocyanins displayed high

stability to heat processing in all forms, which is likely due to their acylated nature.

In experiment 3, some fresh products (pan-fried and baked hash browns, fried classic

fries, and baked sweet potato wedges) were significantly higher in CQAs (p<.05) than the

commercial versions. However, commercial baked wedges were higher in beta-carotene

than fresh baked wedges and commercial fries were higher in CQAs. In general commercial

products compared favorably to fresh products in chlorogenic acid and beta-carotene

content.

Overall, this study found wide variety in phytochemical content of commercially

relevant cultivars. Certain popular cultivars used in the processing industry, such as R.

Burbank and Innovator, while having beneficial functional characteristics, do not deliver as

high a level of phytochemicals as may be desired. Varieties higher in phytochemicals

(especially pigmented varieties) may better maximize the health potential of potato

products. It is encouraging that pigmented varieties displayed moderate retention of

phytochemicals through processing, however, these results do not necessarily extend to

other varieties (especially white and yellow-fleshed). Additional studies on phytochemical

content and process stability in commercially relevant high-phenolic varieties can guide

industry and fresh markets on variety usage.

This research has not addressed micronutrients in these commercial varieties, and

it obviously did not evaluate consumer acceptance of pigmented potato products. While

this study focused on phytochemicals, additional studies on micronutrient content and

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stability through processing (and their interactions with phytochemicals) would provide

valuable data. Potatoes are naturally highly variable in micronutrient and phytochemical

content (Section 1.5.4), which can be affected by many factors from growth to harvest,

storage, and processing. Additional studies are needed which control all of these variables

from farm to manufacturing facility and beyond into the research laboratory, and these

studies should incorporate commercial processing to better relate to the American diet.

Further understanding of the types and conditions of processing that better retain potato

phytochemicals and the mechanisms by which they do so can also be used to enhance the

quality of commercially processed (and fresh) products. This is the first known study

directly comparing phytochemical content in multiple fresh and commercial products.

While this data suggest that fresh and commercial products are likely comparable in

retention of phytochemicals and thus may provide similar dietary levels of these health

promoting compounds, additional highly controlled studies including more varieties can

improve understanding on the “fresh vs. commercial” question. In addition, the extent to

which bioavailability of phytochemicals may be modified by extensive commercial

processing relative to fresh preparation is unknown.

The results of this study are important for understanding effects of processing on

commercial cultivars as well as the differences between those cultivars, but additional

research is needed to elucidate reasons that literature on processing and polyphenols yields

such vastly different results (even when the same varieties are used). In addition, while

understanding phytochemical retention in processed potato products is important,

bioavailability is another key element to understanding the overall impact of these

compounds on health. In vitro and in vivo research should assess changes in polyphenol

bioavailability that occur with processing, including a comparison of different types of

processing. Some research has demonstrated an effect of polyphenols on starch

bioavailability (Section 1.6.5), and the reverse could also be true. In regards to

anthocyanins, existing literature focuses largely on the process stability of acylated

anthocyanins in purple-fleshed sweet potato and other root vegetables, and more research

also is needed on polyphenol composition through processing in pigmented Solanum

tuberosum varieties. Research is additionally lacking regarding potato anthocyanin

bioavailability.

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APPENDICES

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Appendix A: Other phytochemicals detected but not quantified in potatoes

m/z Compound Associated Varieties Detected In

137 Salicylic acid -

153 Protocatechuic acid -

163 p-Coumaric acid Bintje, ADB, AR2009-10

167 Vanillic acid Innovator

169 Gallic acid ADB, AR2009-10, Bintje, Innvoator, Norland, Yukon

193 Ferulic acid ADB, ADR, Bintje, Innovator, Norland, Yukon

197 Syringic acid -

223 Synapic acid ADR, Norland

285 Kaempferol ADB, ADR

289 Catechin -

301 Quercetin -

593 Kaempferol-3-rutinoside ADB, ADR, AR2009-10

609 Rutin (quercetin-3-O-rutinoside) AR2009-10, ADR, Bintje, Yukon

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Appendix B: Chlorogenic acid content in raw Covington potatoes destined for sweet potato

fries and wedges

mg 5-CQA/100 g dw

Covington for Fry F 68.1 ± 1.5

W 75.1 ± 25

Covington for Wedge F 132.9 ± 8.7

W 222.8 ± 26

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Appendix C: Nutritional data and % moisture for raw potato varieties1

Variety Part Calories Total Carb.

(g) Fiber

(g) Sugars

(g) Protein

(g) Vitamin A (IU)

Vitamin C (mg)

Iron (mg)

Calcium (mg)

Magnesium (mg)

Potassium (mg)

Zinc (mg)

% Moisture

R. Burbank Peel 86.0 19.0 3.93 0.36 2.50 <5 8.74 33.2 20.1 31.9 437 0.48 76.7

ADB Peel 72.7 16.0 3.33 0.72 2.18 14 15.3 25.0 13.8 27.9 372 0.35 80.3

ADR Peel 65.4 14.0 4.28 0.71 2.34 <5 6.75 23.4 18.5 27.9 315 0.37 82.4

AR2009-10 Peel 68.8 14.9 3.54 0.33 2.30 <5 8.55 23.8 16.4 35.1 418 0.41 81.2

Bintje Peel 75.4 17.0 2.90 0.58 1.84 <5 8.19 18.9 23.0 28.0 395 0.38 79.8

Yukon Peel 71.5 15.4 3.10 <0.25 2.24 <5 10.0 18.8 16.4 32.8 486 0.28 80.7

Challenger Peel 70.9 15.8 5.52 <0.25 1.93 <5 12.8 18.0 14.2 29.7 408 0.34 80.9

Innovator Peel 76.6 16.8 5.71 <0.25 2.36 <5 15.0 32.5 21.8 32.7 260 0.39 79.3

Norland Peel 59.1 12.1 3.10 1.31 2.68 24 2.23 58.4 13.8 47.4 466 0.58 82.4

R. Burbank Flesh 90.6 20.9 1.13 1.03 1.74 <5 11.1 1.0 6.5 22.7 252 0.28 76.6

ADB Flesh 64.4 14.3 1.28 0.89 1.79 <5 16.4 1.2 3.2 21.4 175 0.30 83.3

ADR Flesh 76.2 17.4 1.59 0.66 1.64 <5 8.71 0.9 5.2 21.9 254 0.26 80.4

AR2009-10 Flesh 77.4 17.3 1.55 0.40 2.05 <5 10.5 1.2 4.6 28.2 310 0.33 79.8

Bintje Flesh 85.5 19.7 1.18 0.40 1.67 <5 13.6 1.3 25.0 23.4 299 0.35 77.9

Yukon Flesh 91.7 20.8 1.74 0.59 2.12 <5 14.4 1.2 4.4 25.6 308 0.24 76.4

Challenger Flesh 83.2 19.2 1.53 <0.25 1.61 <5 15.6 1.1 5.3 23.8 297 0.27 78.3

Innovator Flesh 95.1 21.8 2.52 0.28 1.97 <5 13.5 1.5 7.0 25.1 234 0.35 75.5

Norland Flesh 82.0 15.2 1.14 2.38 2.12 <5 5.75 2.2 2.2 22.0 265 0.30 82.0

1All data per 100 g of raw flesh or peel

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Appendix D: Nutritional data for commercial and fresh processed potato products1

Sample Code

Description Fiber

(g)

Total Fat (g)

Sat. Fat (g)

Poly & Mono

Unsat Fat (g)

Trans Fat (g)

Vit B6 (mg)

Vit C (mg)

Iron (mg)

Sodium (mg)

Magnesium (mg)

Potassium (mg)

Zinc (mg)

MCFBK McCain, Classic Fry, Baked 5.1 10.2 1.5 8.2 0.08 0.56 10.8 1.7 969 54.7 878 0.91

MCFFD McCain, Classic Fry, Fried 4.7 19.1 1.9 16.4 0.05 0.54 10.4 1.5 922 54.2 771 0.84

PCFBK Purdue, Classic Fry, Baked 5.9 7.1 0.6 6.2 0.02 0.92 19.2 1.6 351 64.9 1250 1.5

PCFFD Purdue, Classic Fry, Fried 5.3 16.1 1.5 13.9 0.04 0.78 11.2 1.7 254 63.7 934 1.3

MHBBK McCain, Hash Browns, Baked 5.7 22.0 1.6 19.4 0.03 0.55 12.3 1.6 66.0 69.9 1130 1.2

MHBPF McCain, Hash Browns, PanFried 6.1 17.7 1.4 15.5 0.03 0.65 9.4 3.2 71.2 68.1 1130 1.2

PHBBK Purdue, Hash Browns, Baked 4.9 13.5 1.0 11.8 0.02 0.66 11.5 1.5 357 75.4 1530 1.3

PHBPF Purdue, Hash Browns, Panfried 4.7 20.6 1.5 18.2 0.03 0.66 11.6 1.5 149 41.3 505 1.2

MSFBK McCain, Sweet Pot. Fry, Baked 7.0 14.0 2.2 11.1 0.07 0.33 15.1 2.2 805 54.4 656 0.76

MSFFD McCain, Sweet Pot. Fry, Fried 9.1 22.0 2.3 18.7 0.06 0.30 11.5 2.1 622 55.1 644 0.72

PSFBK Purdue, Sweet Pot. Fry, Baked 8.4 11.3 1.0 9.8 0.02 0.43 31.7 2.8 338 56.4 973 0.82

PSFFD Purdue, Sweet Pot. Fry, Fried 7.5 16.0 1.6 13.7 0.03 0.34 31.7 2.1 228 52.9 1080 0.80

MSWBK McCain, Swt Pot. Wedge, Baked 13.5 17.9 2.8 14.2 0.08 0.42 23.2 3.5 206 78.2 918 1.1

MSWFD McCain, Swt Pot. Wedge, Fried 7.4 26.4 2.9 22.3 0.07 0.40 23.1 2.4 210 77.6 843 1.0

PSWBK Purdue, Swt Pot. Wedge, Baked 13.4 7.3 0.8 6.2 0.01 0.65 32.0 2.5 334 98.9 1630 0.85

PSWFD Purdue, Swt Pot. Wedge, Fried 10.9 15.7 1.6 13.4 0.04 0.74 23.6 1.5 165 82.9 1390 0.92

MFFFD McCain, Fresh Style Fry, Fried 2.7 25.3 2.3 21.8 0.05 0.35 4.5 0.88 287 30.2 464 0.42

PFFFD Purdue, Fresh Style Fry, Fried 2.8 9.3 0.88 7.98 0.03 0.45 2.7 1.3 196 46.2 804 0.72

1All data per 100 g potato product

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Appendix E: PDCAAS data for raw varieties

Potato Variety (Flesh, without skin)

PDCAAS

Russet Burbank 51%

Innovator 67%

Bintje 53%

Challenger 71%

Yukon Gold 60%

Norland Red 60%

AR2009-10 43%

Adirondack Blue 50%

Adirondack Red 39%

impact of processing on potato phytochemicals

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