Functional insights into microbial communities of Korean traditional rice wine (makgeolli) during fermentation

Makgeolli, a traditional Korean rice wine, produced by fermenting glutinous rice using a nuruk containing various microbes that can facilitate saccharification and alcoholic fermentation. The microbial communities in makgeolli determine its quality by metabolizing raw materials into physiologically active substances, such as volatile acids, ethanol, and amino acids. However, the microbial metabolic pathways associated with physicochemical properties remain poorly understood. Therefore, this study applied shotgun metagenomic sequencing to investigate the microbial communities of two makgeolli types, produced using Jinju gokja and Sansung nuruk as starters, during fermentation. Microbial structures differed depending on the starter type (nuruk), with Firmicutes and Proteobacteria dominating in the Jinju and Sansung makgeolli, respectively. Initially, the sugar content increased, displaying high level of alpha-glucosidase coding gene. Thereafter, the microbial genes encoding lactate dehydrogenase and alcohol dehydrogenase increased on day 3 of fermentation. Furthermore, lactic acid bacteria, such as Pediococcus acidilactici and Leuconostoc lactis, increased on day 3 of fermentation and were negatively correlated with pH. However, Leuconostoc sp. showed a positive correlation with acetic acid, an indicator of abnormal fermentation. These findings reveal interaction between makgeolli quality and different microbial strains related with various metabolic functions, providing insights for enhancing quality and optimizing fermentation conditions.