Bacterial community succession and metabolite changes during sufu fermentation

Sufu, a traditional Chinese fermented soybean product, is obtained through solid-state fermentation of tofu followed by ripening in a dressing mixture. To explore the functionally important bacteria for sufu industrial production, the dynamics of bacterial community and metabolites during sufu fermentation were investigated and their relationships were elucidated here. The bacterial community was analyzed by both culture-dependent approach and high-throughput sequencing. Flavor compounds and non-volatile polar metabolites were identified and quantified by HS-SPME-GC-MS and H-1 NMR, respectively. The results showed that Enterobacteriaceae, Enterobacter, Acinetobacter, Lactococcus were predominant taxa during sufu fermentation. Thirty three non-volatile metabolites and 72 flavor compounds were detected. Correlation analysis revealed that the final characteristics of sufu were strongly influenced by Enterobacter and Lactococcus. Unclassified genera of Enterobacteriaceae and Enterobacter were correlated to sugars, such as glucose and fructose, and most of the amino acids. Enterococcus was linked to eight amino acids. Lactococcus is one of the major flavor producers, especially for ester and acids. Pseudomonas was correlated with biogenic amines which were undesirable in sufu, such as histamine and cadaverine. These findings will help to understand the biochemical processes and fermentation mechanism of sufu production.