[PPSC Principal, HM and BPEO, 2020]

32. In olden days when refrigerators did not exist, it was customary to boil milk twice or thrice in a day to prevent it from becoming sour, the reason being

1. Denaturation of the milk protein, casein

2. Killing lactobacilli that convert milk into curd

3. Pasteurization of milk

4. All of the above

Correct Answer :

Killing lactobacilli that convert milk into curd