Microbes In Human Welfare

Curd is produced from milk through the action of lactic acid bacteria (LAB) such as Lactobacillus, which multiply in warm milk and convert lactose into lactic acid, causing the milk proteins to coagulate. Apart from giving curd its characteristic taste and texture, these bacteria also increase the nutritional quality of the product by raising its content of vitamin B12, making curd a richer source of this vitamin than the original milk. Vitamin C is incorrect because lactic acid bacteria are not noted for enriching milk with ascorbic acid, and curd is not regarded as a vitamin C source. Vitamin K is wrong; although gut bacteria can synthesise vitamin K in the intestine, it is not the vitamin highlighted for LAB-mediated curd formation. Vitamin D is incorrect because it is mainly synthesised in skin upon sunlight exposure and is not added by curd-forming bacteria. As mentioned in NCERT Class 12, Chapter 10 (Microbes in Human Welfare), LAB also check disease-causing microbes in the stomach. As a consistency check, the only vitamin specifically associated with the nutritional enrichment of curd by lactic acid bacteria is vitamin B12, confirming it as the correct answer.