Lactic acid fermentation — in situ neutralization: During lactic fermentations, which compound is commonly added to neutralize produced lactic acid and prevent growth inhibition of lactic acid bacteria?

Introduction / Context:
Lactic acid bacteria are sensitive to the falling pH that their own metabolism creates. Maintaining a favorable pH by neutralizing acid in situ sustains productivity and cell viability in batch and fed-batch processes.

Given Data / Assumptions:

• Neutralizing agent must be food/bioprocess compatible.
• It should buffer or neutralize without introducing toxicity.
• We are choosing among common salts and nutrients.

Concept / Approach:
Calcium carbonate (CaCO3) is widely used as a sparingly soluble base that reacts with lactic acid to form calcium lactate while buffering pH. Its slow dissolution provides gentle control and avoids rapid pH swings. Other salts listed serve as nutrients or inert ions but do not neutralize acid effectively.

Step-by-Step Solution:
Identify the need: counter acidity to prevent self-inhibition.Select a benign base and buffer: CaCO3 fits.Exclude nutrient salts ((NH4)2HPO4, MgSO4) and inert salts (Na2SO4, NaCl) as primary neutralizers.

Verification / Alternative check:
pH-stat systems using NaOH/Ca(OH)2 are also common, but solid CaCO3 remains a classic, economical choice especially in traditional fermentations.

Why Other Options Are Wrong:
They provide nitrogen, magnesium, or ionic strength but do not neutralize lactic acid efficiently under process conditions.

Common Pitfalls:
Allowing pH to drop below growth optima, causing early cessation of fermentation.

Final Answer:
CaCO3.