They are the basic structural unit of the fat molecule. They are the key refined fuel form of fat that the cell burns to yield energy. The type of fatty acid present in the oil determines its nature, flavor and other properties. Fatty acids are two types:
- Saturated fatty acids
- Unsaturated fatty acids
This differing state of saturation result from the ratio of hydrogen to carbon in the basic fatty acid structure. Saturated fatty acids (SFAs) -have two hydrogen atoms (the maximum number) attached to each carbon atom in the chain, i.e. ,there are no double bonds in the fatty acid chain. For example butyric, caproic, lauric, myristic, palmitic and stearic acids. Predominance of saturated fatty acids in fats makes it solid at room temperature. Saturated fatty acids may be envisaged as based on acetic acid (CH3-COOH) as the first member of the series in which -CH2- is progressively added between the terminal CH3- and -COOH groups. A few branched-chain fatty acids have also been isolated from both plant and animal sources. Saturated fatty acids are found in animal foods such as whole milk, cream ,ice-cream, butter, cheese made from whole milk, egg-yolk, meat (except poultry) , fish, pork, lard, margarine, vanaspati, chocolates, rich desserts, coconut and coconut oil. SFA intake are associated with causing hypercholesterolemia and atherosclerosis in humans. Some SFAs elevate serum LDL-cholesterol and HDL-cholesterol. Unsaturated fatty acids- have fewer number of maximum hydrogen atoms attached to the carbon chain . They contain one or more double bonds. A fat containing more of unsaturated fatty acids are liquid at room temperature.These may be further subdivided as follows:
- Monounsaturated (monoethenoid, monoenoic)- acids, containing one double bond.
- Polyunsaturated (polyethenoid, polyenoic)- acids, containing two or more double bonds.
Monounsaturated fatty acids (MUFA)- In MUFA, a single double bond is present between the two carbon atoms of the fatty acid chain, i.e. ,one hydrogen atom is missing from one of the two these two adjacent carbons. For example, palmitoleic and oleic acids. Foods which predominate in MUFA (oleic) are avocado, olives, olive oil, peanut butter, peanut oil, lard, regular margarine, vegetable shortenings, pork, poultry, eggs, cashew fruits.They lower serum total cholesterol, LDL-cholesterol without lowering HDL-cholesterol when substituted for saturated fatty acids in the diet. Polyunsaturated fatty acids (PUFAs)- In some fatty acids with 14 or more carbon atoms (long chain fatty acids) double bonds appear at two or more places and theses are called PUFAs. For example, lonoleic, linolenic and arachadonic acids. Foods which predominate in PUFA are corn, cottonseed, soybean, safflower , sunflower oil, walnuts, mayonnaise. French dressing if made with above oils , fish and fish oils. PUFAs are of omega-6 , omega-3 series.
- Omega-6 series PUFAs – the first double bond in the carbon chain occurs after the 6th carbon atom from the methyl end of the chain, e.g. , linoleic acid. They lower serum total cholesterol, LDL-cholesterol and HDL-cholesterol when substituted for saturated fatty acids in the diet.
- Omega-3 series PUFAs – The first double bind in the carbon chain occurs after the third carbon atom the methyl end of the chain, e.g. , eicosapentanoeic acid.
A nutritional classification of fatty acid is:
- Essential fatty acids- are those which cannot be synthesized by the body and need to be supplied through the diet. Linoleic, linolenic acid and arachidonic acid are three essential fatty acids. Primary source of linoleic acid in a diet are vegetable oils.
- Non-essential fatty acids- are those which can be synthesized by the body and need not to be suppiled through diet. Palmitic acid, oleic and butyric acid are examples of non-essential fatty acids