Food acids from microbes: Which major organic acid is widely produced by microbial fermentation and used in foods?

Introduction / Context:
Organic acids contribute flavor, preservation, and pH control in food systems. Several are produced at scale by microbes, with one being a global benchmark for volume and applications.

Given Data / Assumptions:

• We are choosing the acid most famously produced via fermentation and utilized in foods.
• Industrial organism: often Aspergillus niger.

Concept / Approach:
Citric acid is manufactured in multi-million-ton quantities using Aspergillus niger under controlled conditions (carbon source, trace metals, pH). It serves as an acidulant, chelator, and flavor modifier in beverages and foods. Other listed acids are either not produced microbially for food use at scale (sulfuric, uric) or are much less prominent (oxalic poses safety concerns).

Step-by-Step Solution:
Identify the dominant fermentation acid in foods → citric acid. Exclude strong mineral acids (sulfuric) and non-food metabolites (uric). Recognize oxalic acid’s limited and safety-constrained role. Choose citric acid.

Verification / Alternative check:
Food ingredient compendia and industrial microbiology texts identify citric acid as the top microbial food acid, with gluconic, lactic, and acetic following in other contexts.

Why Other Options Are Wrong:
They are either not typical food acids from fermentation or are not broadly used.

Common Pitfalls:
Confusing chemical synthesis with fermentation routes; for citric acid, fermentation dominates.

Final Answer:
Citric acid.