impact of processing on potato phytochemicals
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Purdue UniversityPurdue e-Pubs
Open Access Theses Theses and Dissertations
January 2015
Impact of Processing on Potato PhytochemicalsAmber Nicole FurrerPurdue University
Follow this and additional works at: https://docs.lib.purdue.edu/open_access_theses
This document has been made available through Purdue e-Pubs, a service of the Purdue University Libraries. Please contact epubs@purdue.edu foradditional information.
Recommended CitationFurrer, Amber Nicole, "Impact of Processing on Potato Phytochemicals" (2015). Open Access Theses. 1108.https://docs.lib.purdue.edu/open_access_theses/1108
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
1
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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Page
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.
1.4.4.2 Effect of Processing
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.
1.4.5.2 Effect of Processing
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).
25
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)
1 145 17 Whole unk. 19 Navarre (2011)
9.1 77 32 Whole R, P 5 Andre (2007)
13 64 39 Whole R, P 9 Navarre (2011)
428 428 Whole P 1 Deusser (2012)
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)
94 94 Whole P 1 Deusser (2012)
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)
2 48 20 Whole unk. 19 Navarre (2011)
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)
1 1 Whole P 1 Deusser (2012)
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. n.d. Whole P 1 Deusser (2012)
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. n.d. Whole P 1 Deusser (2012)
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)
n.d. n.d. Whole P 1 Deusser (2012)
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.
1.5.4.4 Effect of Processing
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
60-120% from raw flesh
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
33-50% from raw flesh
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)
58-95% from raw whole
Xu (2009) CGA, CCGA, NCGA
30-360% from raw whole
Plugs boiled 10 min Whole Superior CGA, CGA isomer (unidentified)
60-70% from raw whole
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
(New Potato) Purple Majesty, Piccolo, Bintje
Total phenolics, CGA, NCGA, CCGA, Rutin, Kaempferol, Vit C.
90-300% from raw 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
Quercetin derivatives, caffeic acid derivatives
55% from raw flesh
Tudela (2002)
Plugs cooked 10 min in
steam cooker Whole Superior CGA, CGA isomer (unidentified)
50-60% from raw whole
Im (2008)
Microwaving Whole potato
microwaved 2.5 min Whole
(New Potato) Purple Majesty, Piccolo, Bintje
Total phenolics, CGA, NCGA, CCGA, Rutin, Kaempferol, Vit C.
90-130% from raw whole
Navarre (2010)
36
Whole potato cubes microwaved 10 min
Whole HB Red, Rote Emma, Blaue St.
Galler, Valfi, Violette, Agria chlorogenic acid
15-50% from raw whole
Lachman (2013)
Potato dices (with peel)
microwaved 2.5 min Whole
Atlantic, ATX85404-8W, Innovator, Krantz, NDTX4930-W, R. Burbank,
Santana, Shepody
CGA, caffeic acid, vanillic acid, p-coumaric acid, epicatechin
116-675% from raw whole Blessington
(2010) quercetin dihydrate
30% from raw whole
Plugs cooked for 1 min on
high heat Whole Superior CGA, CGA isomer (unidentified)
65-80% from raw whole
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
28-42% from raw flesh
Tudela (2002)
Whole potato
microwaved 5 min Whole
Dakota Pearl, Goldrosh, Nordonna, Norkotah, Red Norland, Sangre,
Viking, Dark Red Norland
Total phenolics (Folin)
61-95% from raw whole
Xu (2009) CGA, CCGA, NCGA
5-147% from raw whole
Baking Whole potato baked 30
min @ 350°C Whole
(New Potato) Purple Majesty, Piccolo, Bintje
Total phenolics, CGA, NCGA, CCGA, Rutin, Kaempferol, Vit C.
92-250% from raw whole
Navarre (2010)
Baked, hot air oven, 45
min @ °C Flesh
HB Red, Rote Emma, Blaue St. Galler, Valfi, Violette, Agria
chlorogenic acid
20-80% from raw whole
Lachman (2013)
Potato dices (with peel) microwaved 15 min @
204°C Whole
Atlantic, ATX85404-8W, Innovator, Krantz, NDTX4930-W, R. Burbank,
Santana, Shepody
CGA, caffeic acid, vanillic acid, p-coumaric acid, epicatechin
110-440% from raw whole Blessington
(2010) quercetin dihydrate
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)
80-95% from raw whole
Im (2008)
Whole tubers baked 40
min @ 178°C Whole
Dakota Pearl, Goldrosh, Nordonna, Norkotah, Red Norland, Sangre,
Viking, Dark Red Norland
Total phenolics (Folin)
70-99% from raw whole
Xu (2009)
CGA, CCGA, NCGA
4-465% from raw whole
Frying Potato dices (with peel) fried in tea balls 1 min @
191°C Whole
Atlantic, ATX85404-8W, Innovator, Krantz, NDTX4930-W, R. Burbank,
Santana, Shepody
CGA, caffeic acid, vanillic acid, p-coumaric acid, epicatechin
100-575% from raw whole Blessington
(2010) quercetin dihydrate
20% from raw whole
Plugs boiled for 7 min, fried 30 sec twice @
170°C Whole Superior CGA, CGA isomer (unidentified)
75-85% from raw whole
Im (2008)
Frozen French fries Flesh Unk. CGA
0 mg/100 g dw Dao (1992)
Strips fried 4 min @
190°C Flesh Monalisa
Quercetin derivatives, caffeic acid derivatives
28-45% from raw flesh
Tudela (2002)
37
Panfrying/ Sautéeing
Pieces sautéed in pan 3 min
Whole Superior CGA, CGA isomer (unidentified)
65-80% from raw whole
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]
38
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.
39
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
40
40
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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42
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%
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