There are over 40 fatty acids found in nature. Fatty acids have the basic formula, CH3 (CH2) nCOOH; where n can be any number from 2 to 24, generally an even number.
Fatty acids occurring in nature can be classified into three types:
(i) Saturated fatty acids.
(ii) Unsaturated fatty acids with one double bond.
(iii) Polyunsaturated fatty acids with two or more double bonds. These are sometimes abbreviated as PUFA.
The degree of instauration in any fat plays an important role in determining the physical state of the fat. Fats consisting largely of saturated fatty acids are solid at room temperature while those with high proportion of unsaturated acids are generally liquid and are known as oils. For example, whale oil, cod-liver oil, groundnut oil, mustard oil and olive oil are liquids due to the high proportion of unsaturated fatty acids present in them. 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 percent 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 on 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. 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 vegetables seed oils. Essential fatty acids are drastically reduced during hydrogenation of oils. For example, hydrogenation of groundnut oils reduces essential fatty acids from 20 per cent to 2 per cent.
Distribution of fatty acids in Animal and Plant life
The composition of the natural’s fats is related to biological species from which they are derived.
Fats from all fresh-water life, whether plant or animal, contain largely unsaturated C16, C18, C20 and C22 fatty acids. They also contain C16 saturated acid that is palmitic acid.
Fats from marine life are rich in polyunsaturated C20 and C22 fatty acids.
Fats from land animals predominantly contain unsaturated fatty acid, oleic acid and saturated fatty acid, palmitic acid.
Plant seeds also contain mainly oleic acid and palmitic acid. In addition they also contain essential fatty acids, linoleic and linolenic acid, inconsiderable proportion. Coconut oil is an exception in that it is mostly made up of saturated fatty acids and contains very little unsaturated and polyunsaturated fatty acids (essential fatty acids).
Milk fats (butter) differ from other animal fats in containing small amounts of short chain fatty acids.