High-throughput sequencing of the microbial community associated with the physicochemical properties of meju (dried fermented soybean) and doenjang (traditional Korean fermented soybean paste)

Doenjang, a traditional Korean soybean paste consisting of fermented meju has been consumed for centuries as a protein source. In this study, the physicochemical factors and microbial communities of samples prepared from four batches of meju and doenjang were investigated to identify the factors that affect the food quality. The water content and salt concentration were higher in doenjang than in meju, and the acidity and amino-type nitrogen varied depending on the batch. After fermentation of doenjang, the pH, salt concentration, and amino-type nitrogen increased in all batches. Enterococcus and Bacillus were present in all meju samples, whereas Enterococcus, Tetragenococcus, and Bacillus were present in all doenjang samples. The dominant fungi in meju and doenjang was Aspergillus. The abundance of certain fungi, such as Debaryomyces, Candida, Mucor, and Gibberella, varied batch to batch. The amino-type nitrogen, which determines the quality of doenjang, was correlated with the relative abundance of Aspergillus in doenjang prior to fermentation. In addition, these strains had a negative correlation with the salt concentration. This study has elucidated the composition of microbial communities in meju and doenjang, which may lead to improved quality in the production of fermented food.