Question

Among the following organic acids, the acid present in rancid butter is:
A. Pyruvic acid
B. Lactic acid
C. Butyric acid
D. Acetic acid

Answer 1

Hint: We know that the process in which the food containing oils and fats gets oxidised is known as rancidity. The food gets rancid when the oxidation reaction of oil and fat present in it occurs. Rancid food has an unpleasant smell and unpleasant taste.

Complete step by step solution:
Food becomes rancid when it is exposed to oxygen, heat and light. We know that butter contains lipase enzymes. When butter becomes rancid the breakdown of enzyme lipase occurs. Enzyme lipase breaks down to fatty acids and glycerol thus making butter rancid.
In rancid butter there is no physical change but there is a chemical change because oxidation reaction occurs. The oxidation of oils and fats produces a gas. The produced gas has an unpleasant smell. Thus, rancid butter has an unpleasant smell. Sometimes rancid butter becomes intense yellow in colour and also its texture changes. It is sour in taste.
When butter is exposed to air, the oils and fats in butter are converted to hydroperoxides. The hydroperoxides break down to compounds that have unpleasant odour. The hydrolysis of butter produces volatile butyric acid.
Thus, the acid present in rancid butter is butyric acid.

Thus, the correct option is (C) butyric acid.

Note:
Bacteria carrying out fermentation of butyric acid are anaerobic and spore-forming. We can fix rancid butter by the following process: To water add a little amount of liquor of chloride or lime. Wash butter in this solution. After washing let it stand and then wash with pure water.