CHAPTER ONE

1.0       INTRODUCTION

Groundnut (Arachis hypogaea) is a leguminous plant grown in Nigeria mainly for its seeds though farmers use its leaves and shells as organic mulch. The seeds are eaten raw, boiled, fried and roasted. In most Nigerian homes, women use the seed paste in soups and stews as a thickener. Like soyabean (Glycine max), groundnut (Arachis hypogaea) is an industrial crop used mainly as a source of oil . The cake or residue obtained after the oil is extracted has been reported to be high in protein and used as supplement in animal feed

Groundnut cake obtained after frying the cake in oil and which the Hausa people of Nigeria call Kulikuli is used as a delicious snack for humans and can be used as supplement in other dishes, and as a food, groundnut is very high in energy due to its high fat and protein content.

Dietary fats are nutrients needed for an overall healthful lifestyle.

Like carbohydrates and protein, dietary fats are an important source of energy for the body, they are the most concentrated source of energy in the diet, providing nine calories per gram compared with four calories per gram from either carbohydrates or protein.

 Dietary fats supply essential fatty acids, oleic and linolenic acids, which are especially important to children for proper growth. In addition, fats are required for maintenance of healthy skin, for regulation of cholesterol metabolism, they are also needed to carry and aid in absorption of fat-soluble vitamins A, D, E and K and carotenoids.

 Fats provide the fatty acids which form structural components of biological membranes. In addition fat impart taste and texture to foods.

 Oils are easily deteriorated by heat and/or oxygen, especially when they are composed of  unsaturated fatty acids, deteriorated oils give food speculiar smell or taste, and they have adverse effect on health. This is one of the main problems with processed foods because most of the food processes involve one or more thermal treatments in air at high temperatures. Under these thermal conditions, unavoidable denaturation of the oils occurs which deteriorates the quality of the food (Amatsubo et al., 2006).

Vegetable oils  are important because of their high content in mono- and poly-unsaturated fatty acids when compared to animal fats(Harwood et al., 1994).

Oxidation of unsaturated fatty acids is the main reaction responsible for the degradation of lipids. Also oxidation of oils not only produces rancid flavours but can also decrease the nutritional quality and safety by the formation of oxidation products, which may play a role in the development of diseases (Stapranus et al., 1996; Kanazawa et al., 2002). When food is cooked in heated fat many complex physical and chemical changes occur in the food as well as the fat (Wanasundara and Sahidi, 1998). Fats and oils are heated at high temperatures during baking, grilling, frying and other cooking practices. Cooking produces desirable food flavour, golden brown colour and crisp texture. Frying and other methods of cooking bring palatability but nutritionally the food gets destroyed. Thus lead to demoisturization, heat and fat transfer, crust formation and various structural, textural and chemical changes in the product and degradation of the cooking medium (Fillion and Henry, 1998).

Recently consumption of fried foods have become popular, and it is well known that frying lead to degradation of the fat and require large amount of oil, specially in case of repeated frying ,So to overcome these problems people used ovens for frying besides other uses. In all oven cooking methods oils or fat may be part of the food or even it may be used as lubricant to container of cooking; according to this facts there is a need to study the effect of oven heating on oil and fat.

1.1 STATEMENT OF RESEARCH PROBLEM

Many of our foods are fried example, fried yam, beans cake, fried meat. It was observed that commercial food sellers use the same oil for frying over and over again. This frying will certainly cause changes in the physicochemical properties of the oil. There could also be some decomposition of oil with its attendant problems caused upon consumption.

1.2     JUSTIFICATION

Deep frying is one of the most common methods  used for the preparation of food. Repeated frying causes several changes in the physicochemical properties of the oil.There is a decreasing trend in absorbance with increase in frying time, this trends however is not the same with boiling groundnut oil. There is possible breakdown in the structure during frying, the lesser number of ester bond suggest that the fat molecule is intact.

1.3       OBJECTIVES

1. To determine the effect of frying and boiling on  physicochemical properties of  oil.
2.  To determine the effect of frying on uv -visible spectrophotometer and FTIR(Fourier transform infrared)  spectra of the oil.
3. To determine the effect of boiling on uv-visible spectrophotometer and FTIR(Fourier transform infrared) spectra of the oil.

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