Microbial communities in the fermentation of Meju, a Korean traditional soybean brick

Meju is a traditional Korean soybean brick characterized by diverse microbial communities. The microbial communities in Meju were identified at the phylum and genus levels using high-throughput sequencing. During Meju fermentation, diverse factors such as total bacterial cell numbers, moisture content, salinity, pH, enzyme activities, and free amino acids were monitored. After 30 days of fermentation, microbial adaptation and increased protease activity resulted in significant changes, including an increase in pH and alterations in free amino acid content by day 70. Bacterial community analysis revealed significant changes in Bacillus, Lactococcus, and Enterococcus levels as fermentation progressed. The decrease in pH during fermentation was influenced by lactic acid bacteria, which affected bacterial dynamics. At the end of fermentation, the fungal community was dominated by Monascus, Aspergillus, and Scopulariopsis, which affected the free amino acid levels. These results indicate that pH and moisture content may be significant factors in determining microbial communities.