Effect of drying Condition on the physicochemical properties of oil

extracted from two varieties of tiger nuts from Northern Nigeria.

ABSTRACT

Two varieties of tiger nuts grown in Northern Nigerian were studied to

determine the effect of drying temperatures on the physicochemical

properties of oil extracted from the nuts; to compare the parameters and

evaluate the qualities and quantities of the oil at the drying conditions and

also determine varietals and geographical impacts on those parameters. The

drying protocol used were sun drying, and oven drying at 600C, 1200C, and

1800C. The following physicochemical parameters were evaluated: Free fatty

acid, peroxide value, Iodine value, percentage oil yield, specific gravity and

smoke point. Results from this study revealed that the free fatty acid,

peroxide value, Iodine value, percentage oil yield, specific gravity and smoke

point of oil from the two varieties ranged from (0.01-0.03%) as oleic, (0.63-

2.83) meq/kg, (124-131) wijs, (8.20-12.77%), (240-263oC) respectively.

However, there was general decrease in the free fatty acid, peroxide value,

Iodine value and smoke point of oil from the two varieties tiger nut tuber

after exposure to different temperature conditions which indicates an increase

in the quality of the oil. There was also a significant difference in the

physicochemical properties of the oil from the two varieties of tiger nut tuber

which shows that varietal differences and difference in geographical location

had a significant effects on the oil. The values from the free fatty acid and

peroxide values of the oil from both varieties confirm that the oil is edible

and can be consumed directly without further processing. There is also

possibility of using the oil from both varieties for deep frying and other

industrial applications without further processing of the oil. There were

significant difference at (P<0.05) of the percentage oil yield of oil from the

two varieties of tiger nut tubers.

CHAPTER ONE

INTRODUCTION

The demand for vegetable oils has ever been widening in Nigeria as

industrialists rely mostly on the popular vegetable oils like palm kernel oil,

groundnut oil and soybean oil for the preparation of various products

(Akintayo, 2004).

The study of the physicochemical properties of food (oil) is fundamental in

the analysis and design of the unit operations involved in the food industry

and also in determining the suitability of the final product for human

consumption and other subsidiary uses (Arubi, 2009). These properties

influence the handling and treatment received during processing and they

allow for a better control of both product and processing (Ramos and Ibarz,

1998). Operations such as heating, transportation, packaging, extraction and

milling can be applied with ease in food system if the data on

physicochemical properties such as specific gravity, % oil yield, smoke point,

iodine value, free fatty acid and peroxide value are available.

Seed oil are known to deteriorate when processed inadequately with the

principal decomposition reaction being oxidation. Oxidation of seed oil

occurs through a free radical mechanism, initially characterized by the

emergence of unpleasant odour and flavour which becomes progressively

worse until it attains a characteristic smell of rancid fat (Gouveia et al; 2004).

Heating is one of most commonly used methods of food preparation in the

home and industries and prolong use of oil for this purpose causes change in

its physicochemical properties ( Morette and Fett, 1998).

Under the influence of temperature, fats and oils are susceptible to oxidation

primarily leading to formation of hydroperoxides. Due to their high

reactivity, these hydroperoixde especially at high temperatures rapidly react

with secondary oxidative products e.g aldehydes, ketones, peroxides,

hydrocarbons as well as cyclic compounds that exhibit very different possible

toxic or carcinogenic properties (Kowalki, 1995).

Tiger nut (Cyperus esculentus) a grass like plant of the family cyperaceae

(sedge family), order cyperales or Graminates (Takhatajah, 1992) and genus

Carex (Swiff 1989) is widely distributed in many parts of northern

temperature locations (Anon, 1992) within South Europe as its probable

origin (Childers, 1992). Like other sedges the plant is most frequently found

in wet marshes and edges of streams and pounds where it grows in coarse

tufts (Swiff, 1989). In most countries, the plant is grown as a weed of

cultivation to serve as sand or soil binder.

Tiger nut produces rhizomes from the base with somewhat spherical tubers.

In Egypt, it is used as a source of food, medicine and perfumes (Devries and

Feuke, 1999). Tiger nut is commonly known as earth almond, chufa, yellow

nut sedge and zulu nuts. In Nigeria where three varieties (black, brown and

yellow) are cultivated, it is known as “Ayaya” in Hausa, “Ofio” in Yoruba

and “Akiausa” in Igbo (Umerie et al., 1997). Among these three varieties,

only two (yellow and brown) are readily available in the market. Tiger nut

can be eaten raw, roasted, dried, baked or made into a refreshing beverage

called “Hochata De Chufa” or tiger nut milk (Oladele and Aina, 2007). Also,

it can be used as a flavouring agent for ice cream and Biscuit (Cantetejo,

1997).

Tiger nut oil can be used naturally with salads or for deep frying. Tiger nut

oil can be used in preparation of therapy for some cardiac and intestinal

pathologies, because of its high content of monounsaturated fatty acids (Oleic

acid) and vitamin E (natural antioxidant) ( Adejuyitan et al; 2009). It has also

been reported that the tubers contain about 25% oil, 50% digestible

carbohydrate, 4% protein and 9% crude fibre (Shilenkoo et al; 1979,

Emmanuel and Edward 1984).

Tiger nut tuber can be processed for solvent extraction in different ways such

as sun drying, oven drying and other drying techniques (such as vacuum

drying, solar drying, and continuous or batch atmospheric drying ). It is

expected that these drying techniques influences the physicochemical

properties which eventually affects the quality of the oil. Several works have

been carried out on tiger nut oil but no attempt was made to study the effect

of drying conditions on the physicochemical properties of oil from tiger nut

tuber.

OBJECTIVE

The objectives of this work therefore are:

i. To determine the effect of drying temperatures on the

physicochemical properties of oil extracted from two different

varieties of tiger nuts,

ii. To compare free fatty acid, peroxide value, iodine value, specific

gravity, percentage oil yield and smoke point of the oil from the two

varieties tiger nut tubers and evaluate their qualities and quantities at

different temperature conditions.

iii. To study drying temperatures of nuts in relation to varietals

differences and geographical location.

CHATER TWO

LITERATURE REVIEW

2.0 TIGERNUT (ORIGIN AND DISTRIBUTION)

Tiger nut, also called nut sedge (Cyperus esculentus ) is a perennial

grass-like tropical plant that has a rhizomious growth habit. It produces nuts,

which are attached to its fibrous root endings under the ground. About 90

general of the family cyperaceae are known. Two varieties of tiger nuts are

available in Nigeria and they either grow wild or are domesticated. (Arubi,

2009).

wikipedia (2000), reported that this tuber ranks among the oldest

cultivated plants in Ancient Egypt although nothing that “Chufa” was no

doubt an important food element in ancient Egypt during dynastic times, its

cultivation in ancient times, seems to have remained (totally or almost

totally) an Egyptian specialty. They were used to make cakes in ancient

Egypt.

Presently, they are cultivated mainly, at least for extended and common

commercial purposes, in Spain, where they were introduced by Arabs, almost

exclusively in the Valencia region. They are found extensively in California

and were grown by the paiute in Owens valley. ( wikipedia, 2000).

Egypt through North Africa, before reaching the Iberian peninsula and

sicily with the influx of Islamic culture during the middle Ages (13th century).

Islamic culture was also responsible for the expansion of the cultivation of

tiger nut in the Mediterranean areas of the Valencia region, as well as the

introduction of revolutionary techniques that were, at the time far ahead of

those employed in the agricultural sector. Thus its growth in most savannah

region of Africa like Ghana, Burkina Faso and Mali. No wonder why its

growth in Nigeria mostly concentrated in the middle belt and Northern parts

which have the highest percentage of Islamic believers.

2.0.1 SCIENTIFIC CLASSIFICATION OF TIGERNUT

kingdom: Planatae

(Unranked): Angiosperms

(Unranked): Monocots

(Unranked): Commelinids

Oder: Poales

Family: Cyperaceae

Genus: Cyperus

Species: Esculentus

Binomial name: Cyperus Esculentus

Also, in Nigeria tiger nut nut has a specific name given to it by a

particular tribe as shown below:

Housa: Ayaya

Yoruba: Ofio

Igbo: Akiausa

2.0.2 TIGERNUT

Tiger nut (Cyperus esculenturs) unlike a great variety of nuts, which

are fruits or seeds that have a hard and dry shell, which encloses a kernel

(Mac Daniels, 1987), the nuts of Cyperus esculentus are rhizomes, which are

enlarged storage organs at the fibrous root endings of the plant. The tubers

are edible, with a slightly sweet, nutty flavour, compared to the more bitter

tasting tuber of the related cyperus rotundus (purple Nutsedge). They are

quite hard and are generally soaked in water before they can be eaten, thus

making them softer and giving them a better texture. (http://online.

Wsj.com/article/sb1250180464983695.html).

The kinds of oil produced by plants are non-volatile oils and the

essential volatile oil. The first kinds of oils are food reserve and are by far the

most important in commerce. The second kinds of oils are aromatic and are

commercially important in scents and perfumes. Millions of tones of non-

volatile vegetable oils are consumed as food or used in industry each year.

They are used either as fluid or converted into edible fats source as

margarine. (Onwueme and Sinha, 1991). Edible oils are converted into fats

by a process of catalyzed hydrogenation in which relatively unsaturated oils

become saturated by combining them with hydrogen. Large quantities of

vegetable oils are used to make soap and detergent. Vegetable oils are also

used as lubricants and the least saturated of them are used in paints and

varnishes and to make linoleum. Currently, a lot of efforts have been made on

the production of biodiesels from vegetable oils. Tiger nut oils also contain

minerals, the composition of which are shown below.

Table 2.1: MINERAL CONSTITUENTS/COMPOSITION OF TIGERNUT FLOUR (MG/100G FLOUR).

MINERAL ELEMENT YELLOW VARIETY BROWN

VARIETY

Calcium 155 140

Sodium 245 235

Potassium 216 255

Magnesium 51.2 56.3

Manganese 33.2 38.41

Phosphorus 121 121

Iron 0.65 0.80

Zinc 0.01 0.01

Copper 0.02 0.01

Source: Oladele and Anina (2007)

2.1 IMPORTANCE OF TIGERNUTS

2.1.1 AGRICULTURAL IMPORTANCE

Tiger nut as a grass-like plant serves as a good forages for support of

livestock pastures and range grazing lands and also for hay and silage crops.

(Robert, 2001). Oladele and co-workers, (2009) reported that raw tigernut

contains 4.27% crude protein, 13.5% crude fibre, 2.32% ash and 47.9%

carbohydrate, thus making the tiger nut cake an excellent source of basal

feeds for livestock specifically monogastric animals. Tiger nut is equally used

as a fishing bait. For instance, the boiled nuts are used in Uk as a bait for carp

and have high reputation for success. It has also been reported by Bamgbose

(2003) that tiger nut meal (TaN) could serve as a replacement for maize in

the diets of cockerel starters especially at 33.33% level.

2.1.2 SUBSIDIARY USES TIGERNUT

Apart from the used of tiger nut meal in animal feed as pig feed in parts

of the Southern USA, it has other application or uses in industries. Tiger nut

is used in the following ways:

i. As a confectionary: tiger nuts are sometimes used in certain types of

confectionary, often as a substitute for almonds.

ii. As a coffee and cocoa adulterant: the ground tubers are sometimes

used as a substitute or adulterant of coffee and cocoa.

iii. As a source starch: tiger nut tubers are potentially a rich source of

starch which may be extracted after the oil has been removed from

the tubers. This serves as a major raw material for textile industries.

iv. Flour: the tubers can be ground to produce nutritious flour, which

can be mixed with wheat flour in baking. It has the following

composition: protein 3.4%, fat 27%, starch 38%, ash 2.4 (Bailey,

2006).

v. Alcohol: tiger nut tuber can be used for the production of alcohol by

fermentation in silily, a cultivars with a very high sucrose content is

grown and used commercially for this purpose.

vi. Leaves: it has been suggested that the leaves of the tiger nut could

be utilized for paper making, simple digestion with soda Lye will

give a yield of 35-40% of a deep-yellow coloured pulp.

2.1.3 MEDICINAL VALUE AND HEALTH BENEFITS OF TIGER

NUT

Tiger nuts have long been recognized for their health benefits as they

are high in fibre, proteins and natural sugars. They have a high content of

soluble glucose and oleic acid. Along with a high energy content (starch, fat,

sugar and proteins), they are rich in minerals such as phosphorus and

potassium and in vitamins E and C.

It is believed that they help to prevent heart attacks, thrombosis and

caners especially of the colon. They are thought to be beneficial to diabetics

and those seeking to reduce cholesterol or lose weight. The high fibre content

combined with a delicious taste, make them ideal for healthy eating. Tiger

nut milk can be used in conjunction with other foods, to fight cardiovascular

diseases (Djomdi and Ndjouenken, 2006). The tiger nut has 20-30% oil

which helps in the nourishment of the epidermis, nullifies hard-knots in the

stomach and acts as a coolant to hot flushes associated with premature

menopause. The high fibre content of the tiger nut also makes it a wonderful

colon evacuator and cleanser. Other medicinal benefits of the tiger nuts are:

1. It prevent constipation

2. It contains necessary essential minerals; calcium, magnesium and

iron necessary for bones, tissues repairs, muscles and the blood

stream.

3. It contains enough protein and carbohydrate

4. Tiger nut contains a good quality of vitamin B, which assists in

balancing the central nervous system and helps to encourage the

body to adapt to stress.

5. It supplies the body with enough quantity of vitamin E, very

essential for fertility in both men and women.

6. It is excellent for colitis and assists proper digestion in China, tiger

nut juice is used as a liver tonic heart stimulant, drank to heal

serious stomach pain, to promote normal menstruation, to heal

mouth and gum ulcers, use in Ayurvedic medicines, and is a

powerful aphrodistiac (sexual stimulant).

7. The black specie of the tiger nut is an excellent medicine for breast

lumps and cancer (any type of internal concretion and

inflammations). It can be used as eye compress and to bandage

wounds.

8. Tiger nuts give a heating and drying action to the digestive system

in general and this gives it the potency to alleviate flatulence.

9. Tiger nut promotes the production of urine, this is why it is a

preventive measure for cyst, prostrate hernia, rectum deformation

and prolapsed (anal feature-small painful flesh and the tip of the

anus) and to prevent endometriosis of fibrosis as well as blockage of

the tip of the fallopian tube.

Martinez, (2003) reported that tiger nut have high content of oleic with

positive effect on cholesterol level due to the high content of vitamin E. thus,

the nut was found to be ideal for children, older persons and sportsmen.

2.1.4 NUTRITIVE VALUE OF TIGERNUT

Tiger nut is one of the nutritionally underutilized tubers especially here

in Nigeria. Since such factors like non-availability of nutritional information

and presence of antinutritional factors in the nut, its use in food formulating

is yet to gain popularity (Oladele et al, 2009).

However, it has been reported that processing techniques such as

soaking, roasting and germination improve the nutritional value and reduces

the antinational factors in the nut (Oladele and co-workers, 2009).

The federal institute of Research Oshodi has reported their success in

the development of a technology for the production of ice cream from tiger

nut milk. According to the consejo regulator de Chufa Valencia (Regulating

council for Valencia’s Tiger nut), the nutritional composition/100ml of a

classical horchata de Chufas, or orxata de xufes in Valencia language,

contains energy content around 66kcal, proteins around 0.5g, carbohydrates

over 10g with starch at least 1.9g, fat at least 2g. Even though too low in

proteins and in fats and tool high in carbohydrate, to be considered equal to

milk, Horchata de Chufa (Tiger nut milk) can be useful in replacing milk in

the diet of people intolerant to lactose to a certain extent.

Tiger nuts have excellent nutritional qualities. Arubi, (2009) reported

that the nut has a percentage fat of 19.6%, thus a good source of energy. It

has also been reported that tiger nut has fat composition similar to olives. The

oil of the tuber was found to contain 18% saturated (palmitic acid and stearic

acid) and 82% unsaturated (Oleic acid and linoleic acid) fatty acids.

(http://online.wsj.com/article/sb125051804649836445.html). Oladele and

Aina (2007) also reported that tiger nut is very rich in minerals especially

sodium and potassium. These minerals (sodium and potassium) play vital

roles in normal cell function including neurotransmission, muscle contraction

and maintenance of acid – based balance of the body (Okaka, 2005).

Table 2.2 shows the nutritive values of two different varieties of tigernut.

Nutrient Variety of tiger nut

Creamy yellow Dark brown

Crude protein (%) 2.62 + 0.13 2.54 + 0.08

Fat (%) 19:71+ 0.08 19.5 + 0.06

Moisture (%) 23.26 + 0.04 23.46 + 0.02

Fibre (%) 15.46 + 0.17 17.63 + 0.05

Ash (%) 2.80 + 0.14 3.82 + 0.15

Carbohydrate (%) 36.15 + 0.06 33.05 + 0.07

Reducing sugars (mg/100g) 25.00 + 0.25 18.63 + 0.34

Sucrose (mg/100g) 21.18 + 0.16 16.22 + 0.09

Energy value (Kcal/100g) 332.47 + 47 0.13 317.86 + 0.05

Ascorbic acid (mg/100g) 1.60 + 0.12 1.54 + 0.06

Source Arubi (2009)

Footnote values are means + SD. Standard Deviation.

2.1.5 VEGETABLE OILS

Oil is classified as lipid. Lipids are hertogeneous collection of

biochemical substances which are soluble in organic polar solvent such as

ethanol, hexane and diethyl ether. Chemically, oils are mixtures of fatty acid

esters of the trihydroxy alcohol, glycerol (Morris, 1999). The fatty acid

composition of common vegetable oils and their physicochemical

characteristics are given in table 2.3 and 2.4 respectively. Oil is very

important in our daily life activities. It is used as raw material for the

manufacture of margarine, mayonnaise shortening and cosmetics. One

important role of oil in our diet is their supply of essential fatty acids and they

are good sources of energy. Examples of the essential fatty acids are linoleic,

linolenic and arachidonic. These fatty acids play key roles in the maintenance

of tissue integrity and in spermatogenesis. (Okaka et al, 2006).

Vegetable oils are derived from the seeds, and fruits of plants, which

growths in many different parts of the world. Several hundred varieties of

plants are known to have oil bearing seeds but in fact only about a dozen are

significant commercially (Table 2.3) are soybeans, palm kernel, cottonseeds,

groundnut, sunflower, coconut, linseeds, olive, sesame, rapeseed, fung and

castor. (Elaine and Moore, 1973).

2.1.6 IMPORTANCE OF VEGETABLE OILS

The chief importance of vegetable oil lies in their food value. Oil and

fat are recognized as essential nutrients in both human and animal diets.

Nutritionally, they are good sources of energy (9cal/gram), they provide

essential fatty acids which are the building blocks for the hormones needed to

regulate bodily systems, and they are carries for fat soluble vitamins A, D, E

and K. They enhance the foods we eat by providing texture and mouth feel,

imparting flavour, and contributing to the feeling of satiety after eating.

(Okogeri, 2009). In resent years, vegetable sources of oil and fat have

accounted for about three-fifths of the world’s consumption; the rest comes

from animal and marine oil.

These edible oils, are the mixed triglycerides of fatty acids, so treated

as to be wholesome foods (Morris, 1999), are consumed in various ways in

their natural liquid state, they are used in warmer climates for cooking. In the

West world they are eaten chiefly in spread able form, and the main demand

for them comes from margarine industry. Other food industries, which need

vegetable oils, use it in the manufacture of cooking fats and oils, salad

dressings and ice-cream. In addition, oils are equally important functionally

in the preparation of many food products such as bread, cakes, biscuits where

they acts as tenderizing agents and shortener, facilitating aeration, carry

flavours and colours, and provide a heating media for food preparations.

In addition to their value as a source of oil, the seeds of several of these

plants as well as their nuts have a huge protein content, in particular

groundnut and soybean. For this reason, the residue after the oil has been

extracted in many cases serve as animal feed. Outside the realm of food

manufacture, vegetable oils feature in a wide variety of industries, ranging

from soap manufacture, (by far the most important) to the production of

paints, varnishes, lubricants and plastics (Elaine and Moore, 1973).

All oils used in industry must be refined, and the degree of refining

depends on the intended use of the oil. No vegetable oil is equally suitable for

all purposes, since each oil has unique characteristics. Nevertheless, it is

possible to divide them into tree broad groups, firstly, those which are used

mainly for edible purposes examples include soybeans, groundnut, cotton

seeds, sunflowers, rapeseed, sesame and olive. Secondly, those suitable for

both edible and other industrial purposes, examples palm kernel oil, palm oil,

tiger nut and coconut oils. Thirdly, those suitable only for other industrials

purposes, examples linseed, fung and castor seed oils.

Vegetable oils can be obtained commercially from oil seeds by one of

the three basic methods, which can be modified or combined to suite specific

conditions. These are batch hydraulic pressing, expelling method and solvent

extraction (Wesis, 1983).

2.1.7 METHOD OF OIL EXTRACTION FROM TIGERNUT

Solvent extraction in the oil seed processing plant is principally the

same as extraction processes used in the chemistry laboratory. A material to

be extracted is placed into a container with solvent, agitated for a time, and

then the solvent with dissolved oil is removed by filtration or centrifugation.

The residue may be repeatedly extracted with fresh solvent to increase the

yield.

Alternatively, the material may be placed in a percolating column and

solvent poured in through it. This method results in more complete removal

of oil with a lower usage of solvent and is the basis for most commercial

solvent extraction plant today. This method has been described by Thieme

(1968) as the most efficient method of oil extraction. This is because while

mechanical pressed oil cakes still contains about 4-5% of oil, the solvent

method has about 1% or as low as 0.5% in the residue.

The theory of solid-liquid extraction involves the removal of a desired

component (the solute) from a food using a liquid (i.e suitable solvent like

Hexane, ethanol, petroleum ether, methanol etc), which is able to dissolve the

solute. This involves mixing the food (i.e after drying, crushing and flaking

of the raw material) and solvent together, either in a single stage or in

multiple stages, holding for a pre-determined time and then separating the

solvent. During the holding period there is mass transfer of solutes from the

food material to the solvent, which occurs in three stages:

1. The solute dissolves in the solvent.

2. The solution moves through the particle of food to its surface.

The solution becomes dispersed in the bulk of the solvent. During

extraction, the holding time should therefore be sufficient for the solvent to

dissolve sufficient solute and for the changes in composition to approach

equilibrium. The time require depends on the solubility of a given solute in

the solvent selected and also on the following factor such as temperature of

extraction, the surface area of solid exposed to the solvent, the viscosity of

the solvent and finally the flow rate of the solvent. (Fellows, 2009). Oil

produced by this method is of high quality because very little treatment is

required. (Thieme, 1968).

Table 2.3 Typical percentage composition of fatty acid of vegetable fats

and oils

Fatty acid Carbon Cocoa Coconut Corn Cotton Olive Palm Palm

Peanut Rapeseed Saf- Secame Soy Sun

Atoms butter seed kernel

flower bean flower

Cprylic 8 - 6 - - - - 3 -

- - - - -

Capric 10 - 6 - - - - 4 -

- - - - -

Lauric 12 - 44 - - - - 51 -

- - - - -

Mytistic 14 - 18 - - - 1 17 - -

- - - -

Palmitic 16 24 11 13 24 13 48 8 6 4

8 10 12 8

Palmitolic 16 - - - 1 1 - - - -

- - - -

Stearic 18 35 6 4 3 2 4 2 5

2 3 5 2 5

Oleic 18 39 7 29 18 75 38 13 61 19

13 40 24 21

Linoleic 18 2 2 54 53 9 9 2 22 14

75 43 54 66

Linolenic 18 - - - - - - - - 8

1 2 8 -

Arachidonic 20 - - - - - - - 2 -

- - - -

Gadoleic 20 - - - - - - - - 13

- - - -

Behenic 22 - - - - - - - 3 -

- - - -

Frulic 22 - - - - - - - - 40

- - - -

Lignoleric 24 - - - - - - - 1 -

- - - -

Iodine value - 37 9 127 109 84 51 16 101

104 146 114 134 134

Source: Norman and Hotchkiss (2007).

TABLE 2.4: CHEMICAL AND PHYSICAL CONTESTANTS OF

VEGETABLE OILS AND FAT

Oil Specific 130C Specification Iodine Acid value

Refractive Unsaponitiable Reichert Hehner

Gravity 150C value value 250C index

at matter mess value value

Almond 0.914-0.921 183-207 183-207 93-103

1.4593-1.4646a 0.75 0.5 96.0

Coconut 0.926 253-262 6-10 2.5-10 1.4477-

1.4495a 0.2 6.6-8.4 82.3-905

Cocoa butter 0.950-0.974 192-202 33-42 1.1-1.9

1.4537-1.4580a - 0.3-1 94-95

Corn 0.921-0.928 187-193 111-128 1.4-2.0

1.4733-1:477 1.5-2.8 4.3 93-95

Cotton seed0.918-0.923 194-195 89-103 - -

- - 96

Olive 0.915-0.920 185-196 79-90 0.3-1.0

1.4657-1.4667 0.4-10 0.6-15 95

Palm 0.923-0.924 196-204 49-59 10 1.4603-

1.4639a - 0.9-1.9 94-97

Peanut 0.917-0.926 186-194 85-100 0.8

1.4620-1.4653a 0.5-0.9 0.5 95-96

Poppy seed 0.924-0.926 190-195 128-141 2.5 1.4739-

1.4743 0.4 0.6 95-96

Rape 0.913-0.917 168-179 94-105 0.4-1.0

1.4649-11.4659a 1.5 1.1 95

Sesame 0.921-0.925 188-193 103-117 9.8

1.4723-1.4756 1.3-1.5 0.5-28 93-95

Soya 0.924-0.927 189-194 122-134 0.3-1.8

1.4723-1.4756 1.3-1.5 0.5-28 93-95

Sun flower 0.924-0.926 188-194 120-136 11.2 1.4659-

1.4721a 0.3 0.5 95

Tea seed 0.911-0.927 188-196 88-90 - 1.4707

- - -

White mustard 0.912-0.916 171-174 94-98 5.4

1.4649 - - 96-97

Morris (1999). At 400C

2.1.8 COMPONENTS OF CRUDE OILS

According to Thieme (1968) crude oil produced by rendering

expression or solvent extraction contains reliable amount of non-glyceride

components which add up to 5%, and include:

1. Free fatty acids resulting from partial hydrolysis of oil

2. Sterols

3. Carotenoid pigments

4. Phosphatides

5. Carbohydrate and its derivatives

6. Tocopherols

7. Protein fragment and

8. Various resinous and mucilaginous materials some of these

compound are desirable while others are undesirable and are

removed during various stages of processing.

i. Sterol-colourless, heat stable and for all practical purposes

inert. They are not noticed except when they are present in

large amount.

ii. Tocopherols-protects the oil from oxidation by stabilizing

hydroperoxy and other tree radical whose presence in oil gives

it off-flavour. (i.e Tocols acts as a natural antioxidant).

All other non-triglyceride components undesirable since they cause some

changes in the oil, which includes:-

a. Acceleration of deteriorative process (rancidity)

b. Promotion of undesirable colour of the oil (i.g dark coloured)

c. Promotion of foaming or smoking of the oil

d. Promotion of precipitation in the course of processing especially when

the oil is heated.

2.1.9 OIL REFINING

The aim of refining oil is to remove all unwanted substances that may

have harmful effects on the consumers and to improve oil quality (Ojeh,

1981). The crude fats and oils obtained from oilseeds and animal tissues can

vary from pleasant-smelling to quite offensive-smelling, only a few of the

crude fats and oils are suitable for edible purposes without undergoing

processing in some manner. Processing techniques allow us to refine fat and

oils, make them melt more slowly or rapidly, change their crystal habit,

rearrange their molecular structure, and literally take them apart and put them

back together again to suit our requirement of the moment. (Okogeri, 2009).

The process of refining is done by four major processes which include

degumming, Alkali Refining, leaching and deodorization (Ojeh, 1981).

2.1.10 PHYSICAL AND CHEMICAL PROPERTIES

A number of physical and chemical “constant” have been established

for the purposes of assessing quality and purity as well as for identification of

fats and oils. Although many of them are empirical, others are quite specific

in measurements of the fats (see table 2.4).

The most commonly used to establish identities are:

Saponification value, iodine value, refractive index and reichert-polensk-

kissecher values. Other data are determined on the oil and fat in order to

assess quality. They include free fatty acid, peroxide value and

unsaponitiable residue.

2.7.1 SPECIFIC GRAVITY

This is the ratio of the density of a substance to the density of a

reference substance. For solids and liquids, specific gravity is numerically

equal to its density since the reference substance for solids and liquid is

usually 1g/cm3, it can be used to exclude certain compounds from the list of

possibilities. It varies with the composition as well as the structure of the

compound positioning of the double bond nearer the middle of the molecules

and also presence of functional groups cause an increase in the specific

gravity. Generally, compounds containing several functional groups

especially those groups that promote association have a specific gravity more

than 1.0 (Hawley, 1981). If a compound contains no halogen and has a

specific gravity less than 1.0 it probably does not contain more than a single

functional group in addition to the hydrocarbon or other portions. And if

heavier than water, it is probably polyfunctional.

2.1.12 SMOKE POINT

When oils are heated to increasingly high temperature, they reach a

point at which they begin to smoke. This is a factor in choosing oils for deep-

frying application. Thus, oil smoke as a result of the decomposition of

volatile compounds from the oil followed by the production of a blue haze or

smoke and a characteristic burnt odour usually at a temperature above 2000C.

In general, vegetable oils have a higher smoke point than animal fats (Gaman

and Sherrington, 1977). Decomposition of the triglyceride produces small

quantities of glycerol and fatty acids. The glycerol decomposes further

producing a compound called acrolein. This decomposition is irreversible and

when using a fat or oil for deep frying, the frying temperature should be kept

below the smoke-point. Repeated heating will also produce oxidative and

hydrolytic changes in the fat and result in the accumulation of substance

giving undesirable flavours to the food fried in the fat.

In the analytical test the sample is heated while being held in a

chamber. A strong beam of light is shined horizontally above the surface of

the sample, and the analyst looks through this beam at a white background.

Detection of the first wisps of smoke is the end point and depends on the

visual acuity and experience of the person running the test. Nevertheless, it is

a useful characterizing test.

2.1.13 IODINE VALUE

Is a measure of the properties of unsaturated acid present. The degree

of unsaturation of the fatty acids in a fat or oil can be qualitatively expressed

by the iodine value (Norman and Hotchikiss, 2007). The unsaturated

glycerides of an oil or fat have the ability to absorb a definite amount of

iodine especially when aided by a carrier such as iodine chloride or iodine

bromide, and thus form saturated compounds. The quantity of iodine

absorbed is a measure of the unsturation of an oil or fat. The iodine value is

generally expressed as the number of grams of iodine absorbed by 100g of

the oil, (Morris, 1999). Since the iodine reacts at the sites of unsturation,

much as would hydrogen in hydrogenation, the higher the iodine value the

greater the degree of unsaturation in the fat (Norman and Hotchikiss, 2007).

The two methods usually employed for the estimation of the iodine

value are the Hanus method using iodine bromide as the carrier and the Wijs

method using chloride as the carrier. The preparation of iodine bromide

solution is easier than the Wijs reagent, thus Hanus method is often used.

However, there is some difference in the iodine values obtained by these two

methods, but the difference is not greater than the variation in the iodine

values of the oil or fat themselves.

2.1.14 ACID VALUE OR FREE FATTY ACIDS

This is the measure of the amount of free fatty acid present in a fat. Oil

and fats contain more fatty acids according to the conditions of manufacture,

age and storage. The glycerides are hydrolyzed to a small degree by enzymes,

air, and possibly bacteria. The increase in free fatty acids is generally

accompanied by a rancid odour, although the odour itself is not due to the

rancidy. The acid value is the number of milligram of potassium hydroxide

required to neutralize the fatty acids in 1g of the oil or fat (Morris, 1999).

According to Norman and Hotchikiss, (2007), fats also are degraded by

the process of hydrolysis, which in the presence of moisture splits

triglycerides into their basic components of glycerol and free fatty acids. The

free fatty acids, especially if they are of short-chain length, cause off odour

and rancid flavour in fat and oils. This type of deterioration, referred to as

hydrolytic rancidity does not require oxygen to occur but is favoured by the

presence of moisture, high temperatures and natural lipolytic enzymes. The

term acid value refers to a measure of free fatty acids present in a fat.

2.1.15 PEROXID VALUE

This measure is usually used as an indicator of deterioration of fats and

oils. According to Norman and Hotchikiss (2007), the degree of oxidation

that has taken place in a fat or oil can be expressed in terms of peroxide

value. When the double bonds of unsaturated fats become oxidized peroxides

are among the oxidation products formed. Under standard conditions. These

peroxide can liberate iodine from potassium iodine added to the system. The

amount of iodine liberated is then a measure of peroxide content, which

correlates with the degree of oxidation already experienced by the fat and

probable tendency of the fat to subsequent oxidative rancidity. Oxidative

rancidity results from the liberation of odourous products during breakdown

of unsaturated fatty acids. These commonly include such compounds as

aldehydes, ketones and shorter-chain fatty acids. This is the type of fat

deterioration that can often be prevented or minimized by the addition of

chemical antioxidants such as butylated hydroxyanisole (BHA) and butylated

hydroxytoluene (BHA). This peroxide value can be used therefore to estimate

oxidation levels (De Bussy, 1975, ihekoronye and Ngoddy, 1985). Hence,

peroxide value is an index of quality and stability of an oil.

2.1.16 DETERIORATION OF FATS AND OILS

Deterioration of fats and oils is produced by the auto-oxidation of the

unsaturated components. The reaction proceeds with the addition of

molecular oxygen to the double bonds of the unsaturated acids with the

production of labile peroxides which then further isomerize or decompose

spontaneously into, series of products including aldehydes, ketones, and acids

of lower molecular weight (Morris, 1999).

After processing, oxidation is the main problem affecting fats and oils,

leading to formation of peroxides which in turn decomposes to products

(aldhydes, ketones alcohols and others) which impart objectionable flavours

and odoures. Generally, the rate of oxidation depends on the degree of

unsaturation of the oil, its temperature and the presence of antioxidants.

Oxidation occurs at varying rates throughout the life of the oil: during storage

and distribution of the oil, and during food preparation and storage of the

final food product, (Okogeri, 2009).

2.1.17 AUTOXIDATION

Autoxidation is the direct reaction of atmospheric oxygen with the

unsaturated fatty acids attached to triglyerides, under mild conditions.

(Okogeri, 2009). Fats and oils absorb oxygen at a very slow rate, but

depending on atmospheric condition (temperature, humidity, light), presence

or absence of an antioxidant, and degree of unsaturation, the rate of oxygen

absorption can increase significantly, leading to rapid formation and

decomposition of hydroperoxides. Autoxidation reaction proceeds by a free

radical chain mechanism, which can be described in terms of initiation,

propagation and termination stages.

Initiation

RH R. + H.

Propagation

R. + 02 ROO .

ROO. + R1H ROOH+R1

Termination

ROO. R1OO. ROOR1 + O2

RO. + R11. ROR11

2.1.18 PHOTOXIDATION

The oxidation of unsaturated fats is accelerated by exposure to light.

Direct photoxidation is due to free radical produced by ultraviolet light

irradiation, which catalyses the decomposition of hydroperoxide (ROOH) and

other compound such as peroxides (RCOR), or other oxygen complexes of

unsaturated lipids. This type of oxidation proceeds by normal free radical

chain reactions and can be inhibited by chain-breaking antioxidants, or by

ultraviolet deactivators (e.g o-hydroxybenzophenone) that absorb irradiation

without formation of free radicals.

2.1.19 PHOTOSENSITIZED OXIDATION

Photoxidation provide an important way to produce hydroperoxides from

unsatureated fatty acids in the presence of oxygen, light energy and a

photosensitizer. Pigments in foods (e.g. chlorophyll) can serve as a

photosensitizer by absorbing visible or near-UV light to become

electronically excited. Sensitizers have two excited states: by absorption of

light, the singlet (1sens) is converted to the triplet state (3sens), which has a

longer life-time and initiates photosensitized oxidation. Pigments initiating

photosensitized oxidation in foods include chlorophyll, heme protein and

riboflavin (Okogeri, 2009).

CHAPTER THREE

MATERIALS AND METHOD

3.0 SOURCE OF RAW MATERIALS

The two varieties of tiger nut tuber (Cyperus esculentus) yellow and

Brown varieties used for this work were purchased from Mafara market

and Wuruko market in Gusou Zafara state and Markudi Benue state

respectively.

3.1 PREPARATION OF SAMPLES

Fresh yellow and brown varieties of tiger nut tuber were used. The two

varieties were pre-processed by sorting and washing, after which each

variety was divided into four samples of the same quantity, making a total

of eight samples for the two varieties (four from each variety). The samples

from the yellow variety were coded YDS, YD60, YD120, YD180, while samples

from the Brown variety were coded BDs and BD60, BD120, and BD180.

Samples YDs and BDs were sun dried; samples YD60 and BD60 were oven

dried at 600C; samples YD120 and BD120 were oven dried at 1200C; and

samples YD180 and BD180 were oven dried at 1800C which took 1month,

12hrs, 6hrs ,4hrs respectively to dry to a constant weights, after which the

samples were milled into flour using harmer mill.

Extraction of oil from nuts was carried out according to AOAC method

(1980). Precisely, 100g of milled sample was weighed into a labeled separate

plastic containers with lid. The sample was mixed with 400ml of n-hexane

and then covered and sealed with a masking tape. The mixture was allowed

to stand under environmental conditions for 48 hours with periodic shaking;

then filtered through a sieve cloth and further through a 12.5mm filter paper

to remove the fine particles from the solvent mixture. The filtrates subjected

to distillation to recover the solvent (n-hexane) . The oil obtained was

heated in a water bath set at 70oC to remove residual hexane. The

percentage oil content was calculated using the formular :

% oil content = B-A x 100 Oil Content (%) =

W 1

Where A = weight of container in grams

B = weight of container and extracted oil samples in grams

W = weight of samples in grams

3.2 ANALYSIS OF THE SAMPLES

The oil samples extracted from each variety of tiger nut tuber were

evaluated for : Free fatty acid (FFA), Peroxide value, Iodine value, specific

gravity and smoke point.

3.2.1 DETERMINATION OF FREE FATTY ACID (FFA)

The method described by Onwuka (2005) was used for the

determination. precisely 25ml of diethyl ether, 25ml of alcohol, and 1ml of

phenolphthalein solution (1%) were mixed together and carefully neutralized

with 0.1M NaOH by titration. .Precisely 1g of oil from each sample was

weighed in a conical flask and the neutralized solvent was added to the

sample and then titrated with aqueous 0.1M NaOH shaking constantly until a

pink colour which persisted for 15 second was obtained. This was repeated

for the rest of the samples and % FFA, expressed as oleic acid was

calculated as follows:

FFA (as % Oleic acid) = Titration (ml) X 0.0282

Weight of sample used

FFA (%) =

Where:

V = volume of NaOH used during titration (ml)

W = weight of sample (g)

3.2.2 DETERMINATION OF PEROXIDE VALUE

The method described by Onwuka (2005) was adopted for the

determination.Precisely 1g of oil was weighed into a dry conical flask and 1g

of powdered potassium iodide and 20ml of solvent mixture ( acetic

acid/chloroform, 2:1 (v/v)) were added to the sample). the flask was placed

in a water bath set at 100oC for 30 minutes. In continuation, the contents

mixture was transferred to a titrating flask containing 20ml of potassium

iodide solution (5%) and the flask was washed twice with 25ml water and

added into the titrating flask. The mixture was then titrated with 0.002M

Sodium thiosulphate solution using starch as indicator. The blank was also

performed at the same time.

Calculation:

Peroxide value = 2 V Meg/kg

Where V = volume of Na2S2O3 used during titration (ml)

3.2.3 DETERMINATION OF IODINE VALUE

The method described by Morris (1999) was used for the

determination.Precisely 0.5g of the oil sample was weighed into a glass

stopper bottle of about 250ml and 15ml of chloroform was added to it and

then 25ml of Wij’s iodine solution, with the aid of a safety pipette, which was

allowed to drain for a definite time. The stopper bottle was placed in a dark

place and was allowed to stand for 30 minutes. At the end of the period, 20ml

of 15 percent potassium iodide solution was stopped and shaked thoroughly.

The sides of the bottle and the stopper was washed down with 100ml of

distilled water. The mixture was titrated with standard 0.1 N sodium

thiosulphate solution of which the reagent was added with constant shaking

until the yellow colour of the iodine almost disappeared. About 2ml of 1

percent starch solution was added and the titration was continued until the

blue black coloration disappeared. Blank determination on an equal portion

of the wijs reagent was also carried out of which the pipette was also allowed

to drain for the same length of time.

Calculation:

Iodine value = (b-a) x 1.269 Iodine Value =

Weight of sample in grams

Where a = volume of the standard sodium thiosulphate used for the

sample (ml).

b = volume of the standard sodium thiosulphate used for the

blank (ml).

W= weight of sample (g).

3.2.4 DETERMINATION OF SPECIFIC GRAVITY

The specific gravities of the oil samples were determined using the

method described by Onwuka (2005). A 50ml pyconometer bottle was

thoroughly washed with detergent and water and then dried and weighed. The

bottle was filled with water and weighed after which the bottle was dried and

filled again with oil sample and then weighed again. This was repeated for

the rest of the oil samples.

Calculation:

Specific gravity = weight of Xml of oil

Weight of Xml of water

3.2.5 DETERMINATION OF SMOKE POINT

The method described by Onwuka (2005) was adopted. About 20g of

the oil was poured inside an evaporating dish with a thermometer suspended

at the centre of the dish ensuring that the bulb just dipped inside the oil

without touching the bottom of the dish. The dish was placed on a stove and

gradually, the temperature of the oil was raised. The temperature at which the

oil samples gave off a thin bluish smoke continuously was noted as the

smoke point in 0C.

CHAPTER FOUR

4.0 RESULT AND DISCUSSION

The effect of drying temperatures conditions on the physicochemical

properties of oil extracted from yellow and brown varieties of tiger nut tuber

obtained from Zafara and Benue state were studied; as well as the

relationship between drying conditions and varietal difference of these tiger

nuts.

Table1: Effect of drying on physicochemical parameters.

Sample FFA

(%)

PV

(Meq/kg)

IV

(Wijs)

oil

yield

(%)

Specific

gravity at

300c

Smoke

point

(oC)

Yds 0.034a 2.833 a 129.861 b 10.900 b 0.863 c 263.000 a

YD60 0.019 b 2.267 b 129.523 cd

9.267 e 0.857 cd 247.333 c

YD120 0.015 c 1.867 c 128.930 de

10.767 c 0.853 df 241.667 ef

YD180 0.012 c 1.807 cd 124.024 h 9.433 d 0.863 c 240.000 fg

BDs 0.013d 1.873 c 131.299 a 14.767a 0.860 cd 252.667 b

BD60 0.0010 1.473e 129.607 8.200 h 0.877 ab 244.000

d bc d

BD120 0.009e 0.793f 128.846 ef 8.833f 0.883 a 241.333 ef

BD180 0.007 e 0.633 g 125.716 g 8.333 g 0.877 ab 240.333 fg

The values are means of triplicate determinations. Means in the same

column with different superscripts are significantly different at (P<0.05).

Where : YDs = Yellow variety tiger nut tuber sun dried

YD60 = yellow variety tiger nut tuber oven dried at 600C

YD120 = yellow variety tiger nut tuber oven dried at 1200C

YD180 = yellow variety tiger nut tuber oven dried at 1800C

BDs = Brown variety tiger nut tuber sun dried

BD60 = Brown variety tiger nut tuber oven dried at 600c

BD120 = Brown variety tiger nut tuber oven dried at 1200c

BD180 = Brown variety tiger nut tuber oven dried at 1800c

4.1.1 FREE FATTY ACID

Free fatty acid is one of the products of odour and rancid flavour in fat

and oil especially when they are more of short-chain length ( Norman and

Hotchkiss, 2007 , Ogundele et al; 2006). Thus, it is a measure of hydrolytic

rancidity of an oil (Arawande, 2008, Ihekoronye & Ngoddy, 1985 ). The free

fatty acid of oil extracted from the yellow and brown variety of tiger nut

tuber subjected to sun drying and oven drying at 60, 120, and 180

respectively are shown in table 1 above. Results from this table reveal that

the free fatty acid values were in the range of 0.70 – 3.4 % with oil from the

sun dried yellow variety tiger nut tuber having the highest FFA value among

all the samples. However the FFA values decreased when the tubers from

both variety were dried at 60. and maintained a liner trend of decrease in the

FFA of the oil extracted from the two variety as the drying temperatures was

increased. The stability could be attributed to the high content of

4.1.2 PEROXIDE VALUE

According to Norman and Hotchikiss (2007) the degree of oxidation

that has taken place in a fat or oil can be expressed in terms of peroxide

value. The results in table 1 show that the peroxide values of the oil samples

ranged between 1.807 – 2.833 Meq/kg of oil. The peroxide values of all four

samples decreased with increase in drying temperature however, the oil

extracted from sun dried tiger nut tuber recorded the highest value. This can

be probably attributed to prolonged sun drying of the tiger nut tuber which

may have promoted enzymatic hydrolysis, and therefore increase in FFA .

The peroxide value of 10 meq/kg of oil has been recommended by SON

(2000), as standard for fresh vegetable oil . All the oil samples conformed to

this standard. This shows that all the oil samples would have stable shelf life

as rancid taste often begins to be noticeable when peroxide value is between

20 and 40 meq/kg (Pearson, 1976, Oderinde and Ajayi 1998). . Under the

influence of temperature, fat and oils are susceptible to oxidation primarily

leading to the formation of hydroperoxides. Due to their high reactivity, these

hydroperoxides especially at high temperature rapidly react with secondary

oxidative products e.g. aldehydes, ketones, peroxides, hydrocarbons as well

as cyclic compounds that may exhibit possible toxic or carcinogenic

properties (Kowalki, 1995). The values were equally lower than codex

standard values of (10Meq/kg and 20Meq/kg) allowed for refined and

unrefined olive oil respectively (FAO/WHO, 1993). However, the recorded

PV values are higher than the value of 0.3 meq/kg reported by Shaker and

coworkers (2009) for tiger nut oil.The different could be do the fact that PV

values of oils depends on a number of factors such as the state of

oxidation( quantity of oxygen consume), the method of oil extraction used

and the type of fatty acid present in the oil (Oluba and co-worker, 2008).

Statistically, the peroxide value of sample YDs and YD60 differed

significantly at (P<0.05) however, there was no significant difference

between sample YD120 and YD180 at (P>0.05). Also from table 1, the peroxide

value of the oil samples from brown variety tiger nut tuber ranges from 0.633

– 1.873 meq/kg of oil. The results reveal that the peroxide values of all the

samples decreased as the temperature was increased however, sample YDs

recorded the highest value which suggest hydrolytic deterioration which must

have probably taken place during the long period of sun drying of the tiger

nut tuber. According to Kowalki (1995), fat and oils under the influence of

temperature are susceptible to oxidation primarily leading to the formation of

hydroperoxide which further reacts with secondary oxidative products like

Ketones, aldehydes etc that is responsible for rancid and off flavour found in

a rancid oil. However, the result in table 1 did not agree with this report and

is probably attributed to the high content of monounsaturated fatty acid

(Oleic acid) and tocopherol (gamma tocopherol) present in tiger nut oil (Tiger

nut Traders, 2008). Reported from Tiger nut Traders (2008) equally shows

that tiger nut oil does not show any important change in its structure when

subjected to high temperature which could also be the reason why the

peroxide value decreased as the oven temperature was increased. Thus, tiger

nut oil can be used in prevention and therapy of some cardiac and intestinal

pathologies (www.tigernut.com). Statistically, all the oil samples differed

significantly at (P<0.05) at the end of the drying process.

4.1.3 IODINE VALUE

The degree of unsaturation of fatty acids in a fat or oil can be

quantitatively expressed by the iodine value (Norman and Hotchikiss, 2007).

From table 1, it shows that the iodine value of the oil samples extracted from

tiger nut tuber subjected to different temperatures ranges from 124.024 –

129.861 wijs. It was discovered from the results that the iodine values of all

the samples decreased with an increase in temperature.

The decrease in iodine values of the oil samples as the temperature was increased suggest the

loss of unsaturation in the fatty acids of the triacylglycerols (Nzikou et al; 2010). The quantity of

iodine absorbed is a measure of the degree of unsaturation of an oil or fat. Hence, the iodine

value is generally expressed as the number of grams of iodine absorbed by 100g of the oil

(Morris, 1999). Since the iodine reacts at the sites of unsaturation, much as would hydrogen in

hydrogenation, the higher the iodine value the greater the degree of unsaturation in the fat and oil

(Norman and Hotchikiss 2007). The iodine values of all the oil samples were very close to the

value (131 wijs) reported by Alasela (2006). However, the values were higher than values

reported by Shaker et al; (2009) and Ezebor et al; (2005). The high values obtained suggest the

presence of unsaturated fatty acid and this places the oil in the drying groups (Nzikou et al;

2010). Also, the values were above the range of codex standard values (80 – 106 Wijs) for

groundnut oil however, the values were within the codex standard

values (124 – 139 wijs) for crude soybean oil (FAO\WHO, 1993). Statistically, all the samples

were significantly different at (P<0.05) at the end of the drying. Table 1 also reveal that t

he iodine values of oil samples from brown variety tiger nut tuber varied from 125.716 – 131.299

wijs. The result shows that the iodine value decreased as the temperature was increased,

however, sample BDs had the highest iodine value of 131.299 wijs. This suggest that

temperature of the sun has little if any effect at all on the iodine value of Brown variety tiger nut

oil. Also, sample oven dried at 600c,1200c, and 1800c had the same trend of decrease in iodine

value as the temperature was increased which was in agreement with the report from Nzikou and

co-worker; (2010) which suggest loss of unsaturation in the fatty acids of the triacylglycerols.

However, the values were higher than the value (104.2 wijs) reported by Ezebor et al; (2005) but

were in agreement with the value (131 wijs) reported by Alasela (2006). The values equally

conformed to the codex standard value (124- 139 wijs) for crude soybean oil (FAO/WHO, 1993).

The high iodine values obtained in the oil samples suggest the presence of unsaturated fatty acid

and this places the oil in the drying groups (Nzikou et al; 2010). Statistically, all the oil samples

from the brown variety tiger nut tuber differed significantly at (P<0.05) at the end of the drying.

4.1.4 PERCENTAGE OIL YIELD

This can be seen as the quantity of extractable oil present in a given

quantity of an oil seed expressed in percentage. From table 1, the percentage

oil yield ranges from 9.267 – 10.900%. The values did not follow a particular

linear trend which could be traced to method of oil extraction (cold

extraction method) adopted. According to fellows (2009), solid-liquid

extraction involves the removal of a desired component (the solute)from a

food sample (oil seed) using a liquid (i.e. suitable solvent like Hexane,

ethanol, petroleum ether, methanol etc.) which is able to dissolve the solute.

Further studies by fellow (2009) indicates that extraction rate (% oil yield) is

dependent on the temperature of extraction, the surface area of solid exposed

to the solvent, the viscosity of the solvent and finally the flow rate of the

solvent. Report by Ezebor et al; (2005) shows that yellow variety tiger nut

tuber had a percentage oil yield of 22.3% after the solvent extraction. Which

was higher than the values in table 1. This suggests that soxhlet extraction

method is more efficient than cold extraction method since there were a

significant difference between the percentage oil yields from both methods.

Also, the values were not in agreement with the specification of codex

Alimentarius commission of 20% oil content for edible oil (Pearson 1976).

Since the percentage oil yield from the cold extraction method is low, it may

limit the utilization of the method in vegetable oil industries. Statistically, all

the samples were significantly different at (P<0.05) at the end of drying.

Table 1 also reveal that the percentage oil yield from the brown variety tiger

nut tuber ranges form 8.333-14. 767%. The decrease in percentage oil yield

from the tiger nut tuber did not follow a particular linear trend also which

could be attributed to the inefficiency of the cold extraction method adopted.

However, sample BDs recorded the highest percentage oil yield of 14.767%.

This suggests that sun drying increases the percentage oil yield than over

drying in the brown variety tiger nut tuber. The percentage oil yield from the

entire sample fell below the codex alimentarius commission specification of

20% oil content for edible vegetable oil (Pearson, 1976). The yields were also

below the value (20.4%0 reported for brown variety tiger nut tuber by Arubi

(2009). This implies that cold extraction method is not a reliable means of oil

extraction to be adopted by commercial oil processors. Fellow (2009)

reported that percentage oil yield depends on the temperature of extraction,

the surface area of the solid exposed to the solvent, the viscosity of the

solvent as well as the flow rate of the solvent statistically, the result obtained

from the percentage oil yield of the brown variety tiger nut tuber shows that

all the samples differed significantly at (P < 0.05) at the end of the drying

process.

4.1.5 SPECIFIC GRAVITY

This is the ratio of the density of a substance to the density of a

reference substance otherwise know as relative density. Table 1 shows that

the relative density of the oil samples varied from 0.863 – 0.853. The values

decreased as the temperature of the oven was increased however, when the

tuber was subjected to a temperature of 1800c, there was an increase in the

specific gravity of the oil. This suggests that there was no direct relationship

between the temperature and specific gravity of oil extracted from yellow

variety of tiger nut tuber. The values also suggests that the oil is less dense

than water. According to Codex Alimentarius Commission, specific gravity

of 0.919 – 0.925 at 200c have been recommended for soybean oil

(FAO/WHO, 1993). However, the values were lower than the above

specification but is within the range 0.86g/ml reported for water melon seed

oil by Taiwo and co-workers(2008). This shows that the oil contains lower

molecular weight of fatty acid (Mowla et al; 1990, Ching Kilang cho 2000).

According to Hawley (1981), compounds containing several functional

groups especially those groups that promote association have a specific

gravity more than 1.0. Since all the oil samples had specific gravity less than

1.0 it implies that the samples were made up of fewer functional groups

within the triglyceride structures. Statistically, there was no significant

difference at (P>0.05) among the samples at the end of drying. Table 1

equally shows that the relative density of the oil samples from the brown

variety tiger nut tuber varies from 0.860- 0.883. The result revealed that there

was no particular pattern or trend followed by the oil sample as the

temperature was increased. This suggest that temperature has little or no

direct relationship with the specific gravity of oil samples extracted from

brown variety of tiger nut tuber. However, there was an increase in specific

gravity as the temperature was increase to 600C, 1200C but later deceased

when the tiger nut tuber was dried at 1800C. t The results from table 1 were

equally below the codex alimentarius commission specification (0.919-0.925

at 200C) for soybean oil (FAO/WHO, 1993). This suggest that the brown

variety tiger nut oil contains low molecular weight of fatty acids (Mowla et

al; 1990, ching Kuang Cho 2000). This also indicates the possible use of the

oil in soap manufacture (Arubi 2009). Statistically, sample BDs and BD60

differed significantly at (P < 0.05) while sample BD120 and BD180 did not

differ significantly at (P > 0.05) at the end drying processes.

4.1.6 SMOKE POINT

When a fat or oil is heated to a certain temperature, it starts to

decompose producing a blue haze or smoke and a characteristics acrid smell.

The temperature at which this occurs is known as smoke point (Gaman &

Sherrington, 2001). The smoke points of different oil samples in table 1

ranges from 240.000 – 263.0000c. The smoke point of all the samples

decreases with increase in the oven temperature. According to Onwuka

(2005), the smoke point is used in determining the thermal stability of the oil.

A good quality palm oil will have a smoke point at least 215 – 3330c when

fresh but this can be lowered by the free fatty acid present. The values of the

smoke points of the oil samples were in agreement with this report.

Studies from Ezigbo (2009), indicates that smoke point vary with the chain

length of free fatty acid. Hence sample YDs and YD60 with smoke points

(263.0000c and 247.0000c) respectively had higher free fatty acid values

which is in agreement with the report. However, the degree of unsaturation of

oil has little, if any effect on its smoke point (Hui, 1996). Sample YDs and

YD60 were significantly different at (P<0.05) while there was no significant

difference at (P>0.05) between sample YD120 and YD180. Table 1 also shows

that the smoke point of oil of oil

Samples extracted from brown variety tiger nut tuber ranges form 240.333-

252.6670C. The result also reveal that the smoke points of the oil samples

Decreased as the temperature was increased. However, sample BDs had the

highest smoke point of 252.6670C. According to report from Ezigbo (2009),

smoke point vary with the chain length of the free fatty acid which was in

agreement with the result in table 1. The values were equally within the range

(215-3330C) reported by Onwuka (2005) for a good quality palm oil.

Statistically, sample BDs and BD60 differed significantly at (P <0.05) while

there was not significant difference between sample BD120 and BD180 at (P>

0.05).

FFA as %

oleic

PV meq/g IV Wijs’ % oil yield Specific

gravity

Smoke point

Y B Y B Y B Y B Y B Y

0.034a

0.019b

0.015c

0.012c

0.013d

0.0010

d

0.009e

0.007e

2.833a

2.267b

1.867c

1.807cd

1.873c

1.473e

0.793f

0.633g

129.861

b

129.523

cd

128.930

de

124.024

h

131.299

a

129.607

bc

128.846

ef

125.716

g

10.900

b

9.267e

10.767

c

9.433d

14.767

a

8.200h

8.833f

8.333g

0.863c

0.857cd

0.853df

0.863c

0.860cd

0.877ab

0.883a

0.877ab

263.000

a

247.333

c

241.667

ef

240.000f

g

Table 2. Relationship between drying condition and variety

The values are mean of triplicate determination. Means in the same column

with different superscript are significant difference at (P < 0.05)

Where y = yellow variety tiger nut tuber

B = Brown variety tiger nut tuber

Ds = Sun dried

D60 = Oven dried at 600C

D120 = Oven dried at 1200C

D180 = Oven dried at 1800C

4.3.1 FREE Fatty Acid

Free fatty acid is one of the products of odour and rancid flavour in fat

and oils especially when they are more of short-chain length

(Norman and Hatchikiss, 2007, Ogundele et al; 2006). Thus, it is a measure

of hydrolytic randicty of an oil (Arawande 2008, Ihekoronye & Ngoddy

1985).

Table 2 shows the relationship between drying conditions and variety on the

physicochemical properties of tiger nut oil from two varieties of tiger nut

tuber. The data obtained for free fatty acid of the two varieties indicate that

the free fatty acid varies form 0.007-0.034%. The results indicate that oil

from sun dried tiger nut tuber had highest free fatty acid content among the

samples but the FFA of the oil from sun dried yellow variety tuber (0.034%

oleic) was higher than the oil form sun dried brown variety tuber (0.013%

oleic). Generally, the rest of other oil samples maintained a linear trend of

decrease as the temperature was increased. This suggest that oils form brown

variety tiger nut tuber are more hydrolytically stable than the yellow variety

and thus will have a higher shelf life (Oyedeji et al; 2006). The difference in

the results between the oil from the two varieties could be probably traced

from the difference in their fatty acid composition, tocopherol content, soil

type as well as agronomic practices. The data obtained were below the values

(0.3 and 0.4% oleic) reported by Arubi (2009) for oil from yellow and brown

variety tiger nut tuber respectively. This is probably attributed to difference

in conditions of manufacture, age and storage (Morris 1999). Statistically, oil

samples YDs and YD60 differed significantly at (P < 0.05) while oil samples

(YD120 and YD180, BDs and BD60, BD120 and BD180) did not differ significantly

at (P > 0.05) respectively.

4.3.2 PEROXIDE VALUE

Is the measure of primary product of lipid oxidation (oxidative

rancidity) (Rossel, 1994). Seed oil or nuts are known to deteriorate when

processed inadequately with the principal decomposition reaction being

oxidation which occur by free radical mechanism, initially characterized by

the emergence of a sweetish and unpleasant odour which becomes

progressively worse until it attains a characteristic smell of rancid fat

(Grouveia et al; 2004). Data obtained in table 2 reveal that peroxide value of

oil form the yellow and brown variety tiger nut tuber varied from 0.63-2.83

meg/kg. The result also indicates that the oil from the yellow variety tiger nut

tuber had higher peroxide values (1.81-2.83 meq/kg) than the oil from brown

variety tiger nut tuber which had peroxide values (0.63-1.87Meq/kg).

Generally, all the oil samples from the two varieties recorded a linear trend of

decrease in peroxide value as the temperature was increased but was more

pronounced in the oil from sun dried tubers which had peroxide values (2.833

and1.873meq/g) respectively. This suggest that tiger nut oil is more prone to

hydrolytic rancidity than oxidative rancidity since there was a decrease in the

peroxide values of oil from other samples as the temperature was increased.

The high peroxide values recorded in the oil from the sun dried tubers

samples could be attributed to prolong period of sun drying which must have

promoted hydrolytic rancidity in the tiger nut tuber. It was also discovered

from the result in table 2 that the oil form the brown variety tiger nut tuber

were thermally and hydrolytically more stable than the oil from the yellow

variety tiger nut tuber since all the oil samples from the yellow variety tiger

nut tuber had a peroxide values higher than the oil from the brown variety

tiger nut tuber. The low peroxide value recorded in oil samples from brown

variety tiger nut tubers as the temperature was increased also indicates slow

oxidation of the oil samples according to Damain (1990). It also suggests that

the oil will have a high induction period than the yellow variety. The

variance could be probably attributed to their differences in fatty acid

composition, vitamin E content (Tocopherol), soil type as well as agronomic

practices. Nevertheless, all the oil samples from the two variety tiger nut

tubers had peroxide values below the codex standard (10meq/kg) for freshly

refined vegetable oil. This suggests the edibility and freshness of tiger nut oil

even without refining (Tiger nut Traders, 2008). The result of the statistical

analysis revealed that there was no significant difference among the oil

samples (YD120, YD180 and BDs) at (P >0.05) while oil samples (YDS, YD60,

BD120 and BD180) differed significantly at (P < 0.05)

4.3.3 IODINE VALUE

This is the measure of the degree of unsaturation in oil and it is an

identity characteristic of native oil which is an indicatives of the degree of

unsaturation in the fatty acid of triacylglycerol which can be used to quantify

the amount of double bonds present in an oil and evaluate the susceptibility

of oil to oxidation (Nzikou et al; 2010 ). Result from table 2, indicates that

the iodine values of oil form the two varieties

tiger nut tuber varies from 124.024-131.299 wijs. The result from the two

varieties were comparable however, the oil from the brown variety tiger nut

tuber recorded higher iodine values than the oil from the yellow variety tiger

nut tuber. Also, there was a linear trend of decrease in the iodine value as the

temperature was increased. This suggests the loss of degree of unsaturation in

the fatty acids of the triacylglycerols (Nzikou 2010). According to Arawande

and Ademulegun (2009) report, the increase in Iodine value is always

accompanied with decrease in peroxide value owing to more C = C

unsaturated double bond that are present in the oil that is left to be oxidized

therefore leaving more C =C unsaturated double bond in the oil for iodination

reaction during Iodine value determination. The results in table 2, is not in

agreement with this report probably because oil from tiger nut tuber is

hydrolytically and thermally stable. The difference in the results of Iodine

values of tiger nut oil from the two varieties could be attributed to varietals

differences as well as difference in agronomic practices. From statistical

analysis, sample (YDs, BDs, YD180 and BD180) different significantly at (p <

0.05) while sample (YD60, YD120, BD60, and BD120) were significantly the

same at (P > 0.05).

4.3.4 PERCENTAGE OIL YIELD

Apart from the use of hydraulic pressing machine, use of solvent

extraction method which involves the process of leaching out soluble

constituent (non-polar) present as a solid or liquid from a solid or from a

liquid by means of a solvent (Richardson 1993). According to Mcclement

(2003), solvent extraction technique is one of the most commonly used

methods of isolating lipids from food samples and of determining the total

lipids content (percentage oil yield). Table 2 shows that the percentage oil

yield of oil from two varieties of tiger nut tuber ranges from 8.333-14.767%.

The sun dried samples from both variety (YDs and BDs) had the highest % oil

yield of (10.9000 and 14.767 %) respectively while oven dried samples

recorded a low % oil yield when the tubers were dried at 600C. However,

when the tubers were dried at 1200C, there was an increase in % oil yield

which later decreased again when the tubers were dried at 1800C. This

indicates that there was no linear trend in the percentage oil yield as the

temperature was increased. However, the result from the two varieties

followed the same pattern of rising and falling as the temperature was

increased. All the data generated from the two varieties tiger nut oil fell

below the codex alimentarius commission standard of 20% oil content

(percentage oil yield) for edible vegetable oil (Pearson 1976). The results also

fell below the values reported by Ezebor and co-worker (2005), Arubi (2009).

This could be attributed to the difference in methods of oil extraction used.

The results also indicate that cold extraction method is not a reliable method

of extracting oil from tiger nut tubers. Sample BDs was closer to the value

(15% oil content) reported by Tiger nut Traders (2008) for mechanically

pressed tiger nut oil. From statistical analysis, all the oil samples from the

two varieties were significantly different at (P < 0.05).

4.3.5 SPECIFC GRAVITY

Is one of the physical analyses used in predicting the quality of oil

extracted from an oil seed or nut. It has a linear relationship with the

saponification value of oil and can be used in predicting the suitability of an

oil for soap and shampoo manufacture (Karim 2009). Data obtained in table 2

revealed that the specific gravity of oil samples extracted from the two

varieties of tiger nut tubers varied from 0.853-0.883. the result of the specific

gravity of oil from the two varieties were comparable however there was no

specific pattern of increase or decreases as the temperature was increased

among the samples. Nevertheless, when the tiger nut tuber from the brown

variety was oven dried at 600C and 1200c, there was an increase in specific

gravity of the oil while sample from the yellow variety decrease when

subjected to the same temperatures. But when the temperature was increased

to 1800C sample from the brown variety decreased while sample from the

yellow variety increase in the specific gravity of their oil. Also, all the

specific gravities of all the oil samples from the two varieties did not fall

within the codex specification (0.919-9.25) for soybean (FAO/WHO, 1993) .

the differences could be attributed to temperature difference, geographical

location, as well as differences in agronomic practices.

However, the values were similar to the values (0.86) reported by Taiwo and

co-workers (2008) for water melon seed oil. Sample (YDs, YD60, YD120,

YD180 and BDs) and sample (BD60, BD120 and BD180) were significantly the

same at (P > 0.05).

4.3.6 SMOKE POINT

This is one of the factors used in the selection of oil for deep-frying

application. Oil smoke as a result of the decomposition of volatile

compounds from the oil followed by the production of a blue haze or smoke

and a characteristic burnt odour usually at a temperature above 2000C

(Gaman and sherrington, 1977). Table 2 shows the comparison of the smoke

points of oil extracted from the two varieties of tiger nut tubers subjected to

different drying temperatures. The result revealed that the smoke point of the

oil samples from the two varieties were within the ranges 240.000-263.0000C.

The values from the two varieties were comparable.

The data from the two varieties for smoke point also showed a linear

trend of decrease in their smoke points as the temperature was increased

which is in agreement with the report by Ezigbo (2009). This implies that the

smoke point of the oil samples from the two varieties tiger nut tubers varies

with their chain length of free fatty acid. The results were equally within the

range (215-3330C) reported by Onwuka (2005) for a good quality palm oil.

This suggests that the oil samples from the two varieties were thermally

stable and could be used for deep –frying operations (Gaman and Sherrington

1977). The difference among the smoke points of the oil from the two

varieties could be attributed to their differences in fatty acid composition,

Varietal differences, geographical difference, differences in soil types as well

as agronomic differences. Oil samples from (YDs, BDs, YD60 and BD60) were

significantly different at (P < 0.05) however, there was no significant

difference among sample (YD120, BD120, YD180 and BD180 at (P > 0.05).

CONCLUSION AND RECOMMENDATION

This study showed that oven drying tiger nut tubers especially at 1800C

is the best temperature for drying tiger nut tubers for oil extraction since the

results revealed that at this temperature, oil samples from the two variety

had the lowest value of peroxide value and free fatty acid which are

important variable in considering the quality of an oil because the lower the

values ( PV and FFA) the better the quality of the oil. The varietal differences

as well as differences in geographical locations had the least significant effect

on the quality of the oil samples from the two varieties at that temperature

also. The oil samples from the brown variety tiger nut tuber are preferred

because of its low PV and FFA values.

This implies generally, that the tiger nut oil from both varieties can be

rated as one of the best oil suitable for deep-trying, long term storage, soap

making and other industrial applications since they are hydrolytically and

thermally stable.

RECOMMENDATION

Based on findings from this work, the use of oven drying instead of sun

drying should be encouraged as a preparatory step in processing of tiger nut

tubers for oil extraction.

Further studies should be carried out to determine the effect of drying

temperatures and time on the induction time, chemical kinetics, fatty acid

composition and vitamin E content of tiger nut oil from tiger nut tubers so as

to evaluate the overall stability and behaviours of the oil at different

temperatures and times.

REFERENCES

.

, Abiodum O. A and Adeleke R. O. (2010) Comparative Studies on Nutritional Composition of four melon seed varieties. Pakistan Journal of Nutrition 9(9): 905-908.

Abitogun, A. S and Seyifunmi, O. E (2009) Physico-Chemical parameters of oil extracted from Lima Beans. Nigeria Institute of Food Science and Technology proceeding of the 33rd Annual Conference and AGM, Yola Oct, 12th -16th pp. 121-122.

Adejuyitan, J. A., E. T. Otunola, E. A. Akande, I. F Bolarinwa and F. M Oladokun, (2009) Some Physicochemical properties of flour obtained from fermentation of tiger nut (Cyperus esculentus) sourced from a market in gbomoso, Nigeria. African Journal of Food Science, 3: 51-55

Ajayi I. A., F. A. Dawodu, K. O. Adebowale and R. A oderinde, (2002). Chemical composition of pentaclethra Macrophylla seed and seed oil grown in Nigeria. Riv. Ital. Sostanze Grasse., 74: 183-185.

Akintayo, E.T., (2004). Characterization and composition of par-kia biaglobbosa and Jatropha curcas oil and seeds. Bioresour. Techno, 92 pp 307-310.

Alasela M. K. and Odumbaku L. A (2006) Acceptability of Tiger nut (Cyperus Esculentus) Oil in Human Diet. Nigerian Institute of Food Science and technology Proceedings of the 30th Annual Conference and AGM. Lagos, Oct 23rd -27th. Pp. 119-340.

Aluyor O. Emmanuel and Mudiakeoghene Ori – Jesu. (2008) the Use of antioxidants in Vegetable oils – A review African Journal of Biotechnology Vol. 7(25), pp. 4836 – 4842.

AOAC, (1980) official method of Analysis of the Association of official analytical chemistry.

13th edition by William Howitz, Washington D.C pg 437,441 Arubi, P.A (2009).

Applewhite T H (1978). Fats and fatty oils. In: Martin Grayson (Executive Editor) 1978, Kirk-othmer Encyclopedia of chemical Technology, Volume 9. 3rd Edition. John Wiley and Sons Inc., New York.

Arawande J. O (2008): Effects of storage container on shelf life of Refined Soybean oil, International Journal of Pure & Applied Sciences Vol. 1 No 1: 76-81.

Arawande J. O and Ademulegun T. I (2009). Effect of light and Dark Conditions on Some quality parameters of refined Palm Kernel oil stored in Different Containers, Journal of Science, Food and Hospitality, Vol. No 1: 18-22.

!

Nzikou J.M, Mvouula-tsieri, Ndangui C.B, Pambou-tobi, Kimbonguila A, Loumouamou B, Silou Th.and Desobry S. (2010) Characterization of seeds and oil of sesame (sesamum indicum L.) and the kinetics of Degradation of the oil During Heating. Research Journal of Applied Sciences, Engineering and Technology, 2(3): 227-232.

Bamgbose, A.M., Eruvbetin D, and Dada W., (2003) U.S National institutes of health. Washington D.C New York City.

Childers, N. F., (1992) fruit farming. In the new, Encyclopedia Britannica, marcopaedian Vol. 19(15th edn), P. 135-142. Encyclopedia Britannica, Chicago.

Ching Kuang Chow (2000) Fatty Acid in Foods and their Health Implications. Second Edition Marcel Decker Inc. New USA.

Codex Alimentarius Commission. (1983) Codex Standards for edible fat and oils. Supplement 1 to Codex Alimentarius volume XI, Rome, FAO/WHO.

De Bussay, J.H (1975) material used, in industry and commerce including food stuff and fuels volume 8, published in United States and the Philippings by Barness and Noble books. PP 16, 18, 25-26.

Djomdi, R.A.E and Ndjouenkeu, R. (2006). Characteristics of tigernut (cyperus esculentus) Tubers and their performance in the production of a milk drink. J. food presser PP 30, 145, 162.

Elain Morore, M.A., (1973). Vegetable oil and fats. A unilever educational booklet, revised ordinary series NO 2, unilever Limited, England.

Emmanuel, O. A and E. Edward, (1984). Nutritive value of a mixture of tiger nut tubers (cyperus esculentus L.) Journal Science Food Agriculture, 35: 80-85.

Etechola, E and A. C Otaedu, (1996). Fatty acid compositions of tiger nut tubers (cyperus esculentus L.) baobab seeds (Adansonia digitata L.) and their mixture. Journal of American oil Chemists’ Society, 73: 255-257.

Ezebor, F. Igwe, C.C., Owolabi, F.A.T. and Okoh, S.O., (2005). Omparison of physico-chemical characteristics, oxidative and hydrolytic stabilities of oil and fat of cyperus esculentus L. (yellow nut sedge) and Butyrospermum parkii (shea nut) from the middle belt states of Nigeria. Nigeria Food Journal, 23, 33-39.

Ezigbo, V. U. and Obasi, N. E. (2009): Effect of local processing methods on the quality of palm oil. Nigeria Institute of Food Science and Technology proceeding of 33rd Annual Conference and Alim. Yola Oct. 12th-17th. Pp: 336-337.

FAO/WHO. (1993) Fats, oils and related product Food Standard program. Codex Alimentarius Commission. Food and Agriculture Organization of the United Nations. World Health Organization Rome, 8: 33-35.

Fellows, P.J (2009) food processing technology, principal and practice second edition. CRC press Wood Head publishing Limited Cambridge England. PP. 153-154.

Frega N, Mozzon M, Lercker G. (1999). Effect of Free Fatty Acids on

Oxidative Stability of Vegetable oil. Journal of American oil chemists

society 76(3): 325-329.

Gaman, P.M., and Sherrington K.B (1977) the science of food, An introduction to food science, Nutrition and microbiology. Pergamon press, oxford, PP. 58-59.

Gertz C, Klostemanns S, and Kochhar S. P (2000). Testing and Comparing

Oxidative Stability of Vegetable oils and Fats at frying Temperature..

European Journal of Lipid Science and Technology, 102(8-9): 543-

541.

Gouveia A. De S., J. C. O. Livera Santo, M. M. Conceicae, M. C Dantas Silva

and S. Prasad, (2004) A Thermo analytic and Kinetic study of sun

flower oil. Brazilian Journal of chemical Engineering, 21(2): 265-

273.

Hawley; G.G. (1981) condensed chemical Engineering dictionary. 10th edition, Van Nostrand Reinhold company, New York pp 66-73.http://online.wsj.com/article/sb125051804649836945.html (accessed 5/02/2010).

Hui, Y. H. (1996). Bailey’s Industrial Oil and Fat products. Oil and Fat

Products: Oils and Oil seeds, 5th edition John Wiley and sons, Inc 2:

214. pp. 214-47.

Ihekoronye, A.I and Ngoddy; P.O. (1985) Integrated Food Science and Technology for the tropics. Macmillian Ltd Hong Kong pp. 296, 306, 311.Kajubi, S.W., Lewis L.J. and Taiwo, C.O. (eds). (1974). African Encydopedia. Oxford University press, London pp. 345-348.

Kowalki, B., (1995). Determination of Oxidative Stability of edible Vegetable

oil by Pressure differential scanning Calorimetry. Thermo chim.

Acta., 250: 197-205.

Linssen J., G Kielmen, L. Codijnsen and W. Pilmik, (1988). Comparison of

chuta and olive oils. Food chemistry, 28: 279-285.

Martinez, V., (2003) Scientific Analysis of effects of Tigernut on hear diseases and related aspects, Tigernut and health. African Journal of Food Science Vol. 3 (1) 263-268.

Mcclements D. J., (2003) Analysis of food products University of Massachusetts, Lecture Note Food Science, 581. pp. 50. pp. 50-61.

McDaniels, L.H. (1987). Nut crop culture. In McGraw-Hill Encyclopedia of science and Technology. McGraw-Hill Book Company, New York, Vol. 12: 251-252.

Morelte, E and R. Felt, (1998). Oils and Food Technology in Industrial Station

of purification. Sao Paulo, Varele.pp 457-466

Morris B. J. (1999). The chemical Analysis of Foods and food products. Third Edition. CBS publishers New Delhi-pp. 365-366; 370-375; 380-391.

Mowia G., Sheick N. M and Kamal, A. S. M. (1990) Hand Book on Edible Oils

and Fats with special Reference to Bangladesh 1st Edition, City press,

Dhaka- Bangladesh.

Ojeh; O.A. (1981) Effect of refining on the physical and chemical properties of cashew kernel oil. Journal of Food Technology Vol 16, No 1, 22.

Okaka J.C. Akobundu E.N.T. and Okaka A.N.C. (206) Food and Human Nutrition, An integrated Approach OJC Academic publishers Enugu pp. 92.

Okogeri Otu (2009). Fat and oil technology notes on Food Chemistry II (FST 457) EBSU) pp. 27-29.

Oladele A. K and Aina J. O. (2007). Chemical composition and functional properties of flour produced from two varieties of tigernut (cyperus esculentus) African Journal of Biotechnology. Vol 6 No21 pp. 2473-2476.

Oladele, A. K and J. O. Aina, (2007) chemical composition and

Functionalproperties of flour produced from two varieties of tigernut. African

Journal of Biotechnology, 6: 2473-2476.

Oladele, A.K., Osundahunsi, O.F. and Adebowale, Y.A. (2009). Effect of processing techniques on the nutrients and anti-nutrients of tigernut (cyperus esculentus I). Nigeria Food Journal, Vol. 27, No 2, 210.

Oluba M.O, Ogunlowo Y.R, Ojieh G.C, Adebisi K.E, EidangG.O and Isiosio I.O(2008).physicochemical properties and fatty acid composition of Citrullus lanatus(Egusi Melon) seed oil. Journal of Biological sciences 8(4):814-817, 2008.

Onwueme; I.C. and sinha T.D. (1991) field crop production in tropical Africa. CTA, Nether lands. Pp. 321.

Onwuka, G. I. (2005). Food Analysis and Instrumentation Theory and Practice.

Naphtali prints. , Lagos, Nigeria. 102-103.

Oresanya, M.O. and Aitzetmuller, K.. (2001), Comparative study of some common component of tigernut (cyperus) esculentus, L. cyperaceae). Proceeding of the 25thAnnual Conference of Nigerian Institute of Food science and Technology, Lagos, proceedings pp. 45-46.

Oyedeji F. O, Oderinde R. A (2006) characterization of Isopropanol Extracted

oils. Journal of Applied Science 6(11): 2510-2513.

Pearson, D. (1976). The chemical Analysis of Foods. 7th Edn. Churchill

Livingstone, Edinburgh Uk, pp: 200-205; 488-496.

Norman. P and Hotchkiss J.H. (2007) Food Science fifth edition. CBS publishers New Delhi, pp 158.

Ramos, A. M. andIbarz, A. (1998). Density of juice and fruit puree as a function of soluble solids content and temperature. J. Food engineering, 35: 5,7-63.

Robert C. (2001) Russian and sovient Economic performance and structure, 7 th

Edition, New York; Addition Wesley Longman. PP. 265.

Roseell, J. B (1991) Purity Criteria for edible vegetable oils and fats. Fat

Science and Technology, 93(4): 526-531.

Rossel, J. B. (1994): Measurements of rancidity, In J. C. Allen & R. J. Hamilton

(Eds), Rancidity in Foods (3rd Edn) Blackie Glasgow, Uk 22 – 53.

Shaker M Arafat, Ahmed M. Gafar, Amany M. Basuny and Shereen L. `Nassef

(2009) Chufa tubers (cyperus esculent: As a new source of food.

World Apllied Science Journal us L.) 7(2): 151-156.

SON, Standard organization of Nigeria (2000) Standard for Edible Refined

Palm Oil and its Processed form (Vol. B). Publisher, city/town,

country?

Swiff, H. W., (1989). Sedge in the Encyclopedia, Americana Vol. 24

(International ed.) P 513 Eroller, Danbury Connecticut.

Taiwo A.A, Agbotoba M.A, Oyedepo JA, Shobo O.A, Oluwadare I,

Oluwunmi M.O(2008). Effect of drying methods on properties of

water melon (Citrullus lanatus) seed oil. African journal of food

agriculture nutrition and development. Vol 8(4):492-501

Tak hata Jah, A., (1992) Angio sperms (the flowering plants) in the new

Encyclopedia Britannica, Marcropaedia, 13 (15th ed) pp: 596-610.

Encyclopedia Britannica, Chicago.

Thieme; J.G. (1968). Coconut oil processing. Food and Agricultural organization of the United Nation, FAO, pp 24-31.

Tiger nuts Traders, S. L. (2008). Tiger nuts oil profile. Plaza Pais Valenciano,

No 7. E46183 LD Eliana (VALENCIA) Spain. Pp: 2-10.

Toshiyuki C (1999). Prediction of Oxidative stability Based in Various

Chemical Properties for refined vegetable oils. Journal of Japan oil

Chemical Society 48(8): 781-786.

Umeri, S.C., E. P Okkafor and A. S. Uka (1997). Evaluation of the tubers and

oil of cyperus esculentus. Bioresource Technology, 16: 171-173.

Wesis;E.A(1983) oil seed crops. Longman Inc, New York; pp 1-2, 530.

Wikipedia (2000). The free encyclopedia, south province (Cameroon). GNU

free documentation license. Htt//en.wikipedia.org/wiki/south-province-

cameroon. Accessed 25/10/2010

www.tiger nut .com. Date Accessed 12/11/2010.

APPENDIX 1

Table 4: STATISTICAL ANALYSIS OF FREE FATTY ACID

Replica

t

YDs YD60 YD120 YD180 BDs BD60 BD120 BD180 Sum of

Sample

s

1 0.03

4

0.02

0

0.014 0.014 0.01

1

0.00

8

0.008 0.006 0.115

2 0.03

4

0.01

7

0.014 0.011 0.01

4

0.01

1

0.011 0.006 0.118

3 0.03

4

0.02

0

0.017 0.011 0.01

4

0.01

1

0.008 0.008 0.123

Total 0.10

2

0.05

7

0.045 0.036 0.03

9

0.03

0

0.027 0.020 0.356

Mean 0.03

4

0.01

9

0.015 0.012 0.01

3

0.01

0

0.009 0.007

SD 0.00

0

0.00

2

0.002 0.002 0.00

2

0.00

2

0.002 0.001

Correction factor (CF) = Grand total of sum of Samples

rt

where r = number of replication = 3

t = number of treatment/samples = 8

CF = 0.356 2 = 0.127

3X8 24

= 0.0052917

Sum of squares sample (SSS)

= 0.102 2 + 0.057 2 + 0.045 2 …+ 0.020 2 – CF

3

= 0.0205240 – 0.0052917

3

+-

= 0.0068413 – 0.0052917

= 0.0015496

Sum of Square Total (SST)

= 0.0342 x 3 + 0.0202 x 2 +0.0172 x 2 … + 0.0142 x 5 + 0.0062 x 2 – CF

= 0.0068800 – 0.0052917

= 0.0015883

Sum of Square Error (SSE) = SST – SSS

= 0.0015883 – 0.0015496

= 0.0000387

Total Degree of Freedom (TDF)

= Total number of samples (n) – Mean degree of freedom (1)

= n-1

= 24 – 1

= 23

Total degree of samples (TDS)

= Number of samples – Mean Degree of freedom

= 8-1

= 7

Error Degree of freedom (EDF) = TDF – TDS

= 23 – 7

= 16

Treatment Mean Square (TMS) = SSS

TDS

= 0.0000387

16

= 0.000024

Variance Ratio of the F-statistics

F-cal of sample i.e F-treatment

= TMS = 0.0002214

EMS 0.0000024

= 92.25

Variance Ratio table at 5% level distribution

F- tab for sample = Error degree of freedom under total degree of sample

= 16 under 7

= 2.59

Table 5: ANOVA TABLE

Sources

of

DF SS MS F-cal F-tab

variance

Sample 7 0.0015496 0.0002214 92.25D 2.59

Error 16 0.0000387 0.0000024

Total 23 0.0015883

Since F_cal > F-tab, there is significant difference among the sample at 5% level

of significance. Hence, mean separation.

Least significant Difference, LSD

= Error d.f X Sd

Error d.f from t-table, t05/2, 16 = 2.120

Sd = Standard Error =

Where S2 = M. S for Error = 0.0000024

r = number of replications = 3

2 = constant for equal replication

Sd = =

= 0.0012649

LSD = Error d.f X Sd

= 2.120 x 0.0012649

= 0.0027

2S 2 r

2 x 0.000024 3

0.0000016

Any 2 sample differing by 0.0027 or more is significantly different at 5%

level of probability.

Arranging the means in the order of magnitude

YDs YD60 YD120 BDs YD180

0.034 0.019 0.015 0.013 0.012

BD60 BD120 BD180

0.010 0.009 0.007

Mean Difference LSD

0.034 0.007 0.027 0.0027 D

0.034 0.009 0.025 0.0027 D

0.034 0.010 0.024 0.0027 D

0.034 0.012 0.022 0.0027 D

0.034 0.013 0.021 0.0027 D

0.034 0.015 0.019 0.0027 D

0.034 0.19 0.015 0.0027 D

0.019 0.007 0.012 0.0027 D

0.009 0.010 0.0027 D

0.010 0.009 0.0027 D

0.012 0.007 0.0027 D

0.013 0.006 0.0027 D

0.015 0.004 0.0027 D

Mean Difference LSD

0.015 0.007 0.008 0.0027 D

0.015 0.009 0.006 0.0027 D

0.015 0.010 0.005 0.0027 D

0.015 0.012 0.003 0.0027 D

0.015 0.013 0.002 0.0027 N.S

0.013 0.007 0.006 0.0027 D

0.009 0.004 0.0027 D

0.010 0.003 0.0027 D

0.012 0.001 0.0027 N.S

0.012 0.007 0.005 0.0027 D

0.009 0.003 0.0027 D

0.010 0.002 0.0027 N.S

0.010 0.007 0.003 0.0027 D

0.009 0.001 0.0027 N.S

0.009 0.007 0.002 0.0027 N.S

YDs YD60 YD120 BDs YD180

0.034a 0.019b 0.015c 0.013d 0.012c

BD60 BD120 BD180

0.010d 0.009e 0.007e

YDs = Difference BDs and YD180 = same

YD60 = Difference BD120 and BD180 = same

Statically, the free fatty Acid of the samples (YDs and YD60) differed

significantly at 5% level of significant. However, sample (YD120 and BD180)

were significantly the same.

Appendix 2

STATISTICAL ANALYSIS OF PEROXIDE VALUES

Table 6: ANOVA TABLE

Source of

variance

(SOV)

DF SS MS Fcal Ftab

Sample 7 11.056800 1.5795429 599.83D 2.59

Error 16 0.0421333 0.002633

Total 23 11.0989333

YDs YD60 BDs YD120 YD180

2.833a 2.267b 1.873e 1.867c 1.807cd

BD60 BD120 BD180

1.473e 0.793f 0.633g

YDs = diff BD60 = diff BD180 =

diff

YD60 = diff BD12 = diff BDs =

same

YD120=

same

YD180 = same

APPENDIX 3

STATISTICAL ANALYSIS OF IODINE VALUE

Table 7: ANOVA TABLE

Source of

variance

(SOV)

DF SS MS Fcal Ftab

Sample 7 120.153 17.1647143 62.07D 2.59

Error 16 4.4243060 0.2765191

Total 23 124.5773060

BDs YDs BD60 YD60 YD120

131.299a 129.861b 129.607bc 129.523cd 128.930de

BD120 BD180 YD180

128.846ef 125.716g 124.024h

BDs = diff

YDs, BD60 and YD60 = same

YD120 and BD120= same

BD180 = diffenernce

APPENDIX 4

STATISTICAL ANALYSIS OF PERCENTAGE OF OIL YIELD

TABLE 8: ANOVA TABLE

Source of

variance

(SOV)

DF SS MS Fcal Ftab

Sample 7 96.9762500 13.8537500 5541.50D 2.59

Error 16 0.0400000 0.002500

Total 23 97.0162500

BDs YDs YD120 YD180 YD60

14.767a 10.900b 10.767c 9.433d 9.267e

BD120 BD BD60

8.833f 8.333g 8.200h

BDs =diff YDs = diff YD120 =diff YD180 = diff

YD60 =diff BD120=diff BD180=diff BD60=diff

APPENDIX 5

STATISTICAL ANALYSIS OF SPECIFIC GRAVITY

Table 9: ANOVA TABLE

Sources of

variance

(SOV)

DF SS MS F-cal F-tab

Sample 7 0.0024666 0.0003524 8.46D 2.59

Error 16 0.0006667 0.0000417

Total 23 0.0031333

BD120 BD60 BD180 YDs YD180

0.883a 0.877ab 0.877ab 0.863c 0.863c

BDs YD60 YD120

0.860cd 0.857cd 0.853df

BD120, BD60 and BD180 = same

YDs, YD180 and BDs = same

YD60 and YD120 = same

APPENDIX 6

STATISTICAL ANALYSIS OF SMOKE POINT

Table 10: ANOVA TABLE

source of

variance

(SOV)

DF SS MS F-cal F-cal

Sample 7 1341.624667 191.6606667 176.92D 2.59

Error 16 17.3333330 1.0833333

Total 23 1358.958000

YDs BDs YDs BD60 YD120

263.000a 252.667b 247.333c 244.000d 241.667ef

BD120 BD180 YD180

241.333ef 240.333fg 240.000fg

YDs = diff YD60 = diff YD120 and BD120 = same

BDs = diff BD60 = diff BD60 and YD180 = same