Exploring the changes in microorganisms and metabolites during the fermentation process of traditional Chinese watermelon–soybean paste

Watermelon–soybean paste (WSP) is a traditional Chinese fermented food item. Changes in the microbial community diversity affect the final product quality. However, the correlation between microorganisms and their metabolites in WSP is not clearly understood. In this study, seven bacterial and eight fungal genera were found to be dominant during WSP fermentation using 16S rRNA and ITS gene sequencing. A total of 838 metabolites were identified using UHPLC-TOF-MS; of which, 99 were identified as differential metabolites. Correlation analysis showed that the microbial metabolic activities of Bacillus sp., Candia sp., and Kodamaea sp. were associated with amino acid production. Bacillus sp. and Aspergillus sp. correlated with dipeptide production. Metabolic pathway analysis suggested that amino acid metabolism was the most significant differential metabolic pathway, which may be related to the fermentation quality of WSP. Our study provides a new theoretical basis for improving WSP quality from the perspective of metabolomic and microbial diversity.