Microbial diversity and flavor formation in onion fermentation

Area of Science:

• Food Microbiology and Fermentation Science
• Applied Microbiology
• Food Chemistry

Background:

• Fermented onion products are globally popular, yet the specific microbial communities and biochemical changes driving their unique characteristics require detailed investigation.
• Understanding the role of salt in fermentation is crucial for optimizing flavor profiles and preserving desirable qualities in fermented foods.

Purpose of the Study:

• To identify the dominant microorganisms responsible for onion fermentation, both with and without salt.
• To elucidate the biochemical changes, including organic acid and amino acid profiles, that contribute to the unique flavor of fermented onions.
• To determine the specific effects of salt on the fermentation process and the resulting product characteristics.

Main Methods:

• Polymerase chain reaction-denaturing gradient gel electrophoresis (PCR-DGGE) was employed to profile microbial communities.
• Analysis of organic acids, amino acids, esters, alcohols, and aldehydes was conducted to assess biochemical transformations.
• Comparative analysis of fermentation with and without salt was performed.

Main Results:

• Dominant microorganisms identified include lactic acid bacteria, acetic acid bacteria, citric acid bacteria, and yeasts.
• Fermentation significantly increased lactic and acetic acid levels. Unique flavor compounds like esters, alcohols, and aldehydes also increased.
• Salt fermentation inhibited organic acid accumulation and reduced total amino acids but preserved the characteristic onion odor by limiting sulfur compound degradation.

Conclusions:

• A diverse microbial consortium, including bacteria and yeasts, drives onion fermentation.
• Fermentation generates key organic acids and volatile compounds responsible for the distinct flavor profile of fermented onions.
• Salt plays a critical role in modulating fermentation, influencing acid and amino acid profiles while maintaining desirable aromatic qualities.