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58.2 GENERAL STRUCTURE OF FATS AND OILS

Fats and oils are triesters of glycerol with long chain fatty acids. Each molecule of fat is
composed of one molecule of glycerol and three molecules of fatty acids. A molecule of fat may be represented by the general formula,

Specific Objectives

After studying this unit, the students will be able to

  • identify sources and properties of fats and oils.
  • describe fats and oils as alkylakanaotes.
  • describe the extraction of fats and oils.
  • describe the preparation of soap from fats and oils.
  • compare soapy and soapless detergents.
  • Outline some uses of fats and oils.

These triesters of glycerol and fatty acids are known as triglycerides. If the triglyceride contains all the three same acid groups, it is known as simple glyceride and if the acid groups are different, it is called a mixed glyceride. Glycerides consisting predominantly of saturated fatty acids are solid at room temperature while those with a high proportion of unsaturated acids are usually liquid at room temperature and are called oils.

The fats containing saturated fatty acids are also called saturated fats and the fats containing unsaturated fatty acids are called unsaturated fats, Saturated fats have higher melting point than unsaturated fats. Saturated fatty acids occur in animal fats, margarine and butter. Unsaturated fatty acids occur in vegetable oils like ground-nut oil, palm kernel oil, olive oil, com oil, cotton seed oil, mustard oil, etc. Because of the presence of double bonds in them, unsaturated fats are
more reactive than the saturated fats. Saturated fats being more stable tend to accumulate and get stored under the skin. Therefore, persons consuming more amounts of saturated fat gain weight and become obese. Excessive use of saturated fats leads to many diseases such as hypertension.

Vegetable and marine oils can be hardened and turned into solid fats by hydrogenation in the presence of some appropriate catalyst such as nickel. This-process converts most of the unsaturated fatty acids into saturated fatty acids.

Among saturated fatty acids palmitic acid (C15H31COOH) is widely present in fats. Oleic acid (C17H33COOH), an unsaturated fatty acid, is the most widely distributed in nature. In most fats of animal as well as plant origin it forms 30 per cent or more of the total fatty acids.

 

ESSENTIAL FATTY ACIDS

Cells, in our body, can synthesize most of the fatty acids that it needs, from the carbohydrates. However, a few polyunsaturated fatty acids cannot be synthesized in the body. The fatty acids which cannot be synthesized in the body are known as essential fatty acids (EFA). Linoleic acid and linolenic acids are examples of essential fatty acids.

CH3(CH2)4-CH=CH-CH2-CH=CH-(CH2)7,COOH
Linoleic Acid

CH3CH2CH=CHCH2CH=CHCH2-CH=CH3CH2COOH
Linolenic Acid

Essential fatty acids are present in large amounts in many vegetable oils. A diet rich in essential fatty acids (linoleic acid and linolenic acid) can be obtained by eating plenty of vegetable seed oils. Essential fatty acids are drastically reduced during hydrogenation of oils. For example, hydrogenation of groundnut oil reduces essential fatty acids from 28 to 2 per cent.

Some common food items which are rich in fats and the type of fatty acids they contain are given in Table 58.1.