Lactic acid fermentation by bacteria in cheese production

Steps:

• Milk is inoculated with bacteria like Lactobacillus during cheese-making.
• These bacteria perform anaerobic respiration, fermenting lactose into lactic acid.
• Lactic acid accumulates, decreasing the pH of milk.
• Lower pH causes casein proteins to coagulate, forming curds.

Why C is correct:

• Anaerobic respiration by bacteria produces lactic acid via fermentation (lactose → lactic acid + energy), directly lowering pH as per the biochemical pathway in dairy fermentation.

Why the others are wrong:

• A: Aerobic respiration by bacteria produces CO2 and water, not significant acid to lower pH in cheese-making.
• B: Yeast performs anaerobic respiration but is not primary in cheese; bacteria dominate acid production.
• D: Aerobic respiration by yeast yields minimal acid and is irrelevant to anaerobic cheese fermentation.

Final answer: C