Fats in Nutrition:
Fats constitute approx. 34% of the energy in the human diet. It is energy rich and provides 9 Kcal/g of fat, that’s why humans are able to obtain adequate energy with a reasonable daily consumption of fat containing foods. Dietary fat is stored in the form of adipose fat cells in the body.
Fats are the most concentrated source of energy in foods. They constitute the body’s chief reserve of energy and are essential for diverse functions such as insulation, padding, integrity of cell membranes, synthesis of some hormones and carriers of fat soluble vitamins. Fats also helps to increase the palatability of food.
Characteristics of Fats:
1. Hardness: The hardness of a fat is determined by its fatty acid composition. It containing 12 carbon atoms or fewer and unsaturated fatty acids are liquid at room temperature. Saturated fatty acids containing 14 carbon atoms or more are solid at room temperature. Food and body fat contain mixture of short and long chain fatty acids and of saturated and unsaturated fatty acids. No natural fat is made up completely of either saturated or unsaturated fatty acids.
2. Hydrogenation: In the presence of a catalyst such as nickel. Liquid fats can be changed to solid fats by hydrogenation. This process consists of the addition of hydrogen at the double bonds of the carbon chain. In the manufacture of vegetable shortenings and margarine. Some, but not all of the double bonds in the oils are hydrogenated, thereby forming fats that are somewhat soft and plastic. Hydrogenation reduces the linoleic acid content of the fat.
3. Emulsification: Fats are capable of forming emulsions with liquids, that is the fats can be dispersed into minute globules, thereby increasing the surface area and reducing the surface tension so that there is less tendency for the globules to come together. Bile salts and lecithin are essential biochemical emulsifiers in digestion and absorption. The property of emulsification is also utilized in the homogenization of milk and in the preparation of mayonnaise. Lecithin and other emulsifiers are widely used by the food industry.
4. Saponification: The combination of a fatty acid with an action to form a soap is known as Saponification. In the alkaline medium of the intestine. for example, free fatty acid may combine with calcium to form an insoluble compound excreted in the faeces. In certain disease characterized by poor fat absorption like in spure, the fat is not absorbed by the body. It causes significant loss of calcium in this diseases.
5. Rancidity: Air at room temperature can induce oxidation of fat, resulting in the changes in odour and flavour commonly known as rancidity. These changes are accelerated upon exposure to light and in the presence of traces of certain minerals. The oxygen attacks the double bonds of fatty acids to form peroxides. Thus, per-oxidation occurs more readily in fats that have a high proportion of unsaturated fatty acids.
6. Effect of Heat: Excessive heating of fats leads to the breakdown of glycerol, producing a pungent compound (acrolein) that is especially irritating to the gastrointestinal mucosa. Fatty acids are also oxidized by prolonged heating at high temperature. Under ordinary conditions of home or commercial frying, few adverse effects on nutritional properties have been found.