Question

Study the following statements regarding lactic acid bacteria (LAB) which are used to convert milk into curd.
(i) They produce and coagulate and partially digest the milk proteins.
(ii) A small amount of curd added to fresh milk as an inoculum contains millions of LAB, which at suitable temperature, multiply and convert milk into curd.
(iii) Conversion of milk into curd improves its nutritional quality by increasing vitamin B12.
(iv) LAB may result in acidity in the stomach of human beings.
Which of the given statements are correct?
A. (i) and (ii)
B. (ii) and (iii)
C. (i), (ii) and (iii)
D. (i), (ii), (iii) and (iv)

Answer 1

Bacteria are unicellular microscopic organisms living in a variety of natural habitats. They are important organisms used in the food and beverages industry. The different types of bacterial reactions and chemicals are used in the food especially in the dairy industry, to produce varied types of food.

Complete answer:
Different strains of bacteria are useful in the food and dairy industry. They are useful as they produce different end products mostly by their anaerobic sugar fermentation. Different strains of bacteria which are used in the food industry are the strains of Streptococcus, Lactobacillus etc. They are used to produce yogurt.
Lactic acid bacteria (LAB) are an important group of bacteria that are used in the decomposing of the milk and production of different types of dairy products. The lactic acid bacteria are an order of gram-positive bacteria with either rod or spherical shaped structure. They produce lactic acid as the important and prime metabolic end product of carbohydrate fermentation. The bacteria are tolerant to increased levels of acidity and protected from the lactic acid that is produced.
The lactic acid bacteria causes fermentation of milk sugar which is lactose and converts it into lactic acid. When the lactic acid bacteria are added into the milk, it uses enzymes to produce energy in the form of ATP from the lactose. As a result, the byproduct of the metabolic reaction lactic acid is formed. The lactic acid enzyme causes coagulation of the milk as a result the milk curdles. The culture of the lactic acid bacteria can be used in fresh milk to start the process of curdling. A small amount of the curd or the mixture containing lactic acid bacteria is known as the starter culture. It is mixed with fresh milk to start the process of fermentation of milk. At a suitable temperature, the culture causes production of curd. In this process, the nutritional quality of milk is enhanced as the important and significant nutritional element vitamin B12 increases considerably. The curd contains valuable amounts of vitamins.
Therefore, the correct option is option C.

Note: The lactic acid bacteria are important groups of microorganisms that are used in the dairy industry. The simple metabolism and the end product by the process of lactic acid fermentation make them useful as microbial cell factories that are employed for production of several food and dairy products.