Surface Film Formation in Static-Fermented Rice Vinegar: A Case Study

Area of Science:

• Food Microbiology
• Fermentation Science
• Bacterial Physiology

Background:

• Traditional static fermentation of rice vinegar can lead to undesirable surface film formation.
• Acetic acid is the primary organic acid in rice vinegar, with concentrations ranging from 3.0-8.7% at pH 3.0-3.3.

Purpose of the Study:

• To identify the microbial cause of surface film formation in rice vinegar.
• To elucidate the mechanism behind surface film development during traditional rice vinegar fermentation.

Main Methods:

• Isolation and identification of microorganisms from rice vinegar surface films using GYC medium and 16S rDNA sequencing.
• Microscopic analysis (field-emission scanning electron microscopy) of isolated bacterial cells.
• Assessment of bacterial adaptation to high acetic acid concentrations.

Main Results:

• Acetobacter pasteurianus was consistently isolated from the surface film of all rice vinegar samples.
• Bacterial cellulose production, forming fine threadlike structures, was observed in A. pasteurianus cells, likely as a survival mechanism.
• Surface film formation was attributed to bacterial cellulose production by A. pasteurianus, not external contamination.

Conclusions:

• Acetobacter pasteurianus is responsible for surface film formation in rice vinegar via bacterial cellulose production.
• Bacterial cellulose production is a survival strategy for A. pasteurianus in high-acetic acid environments.
• Preventing surface film formation requires modified fermentation processes to maintain rice vinegar quality.