High-throughput sequencing and culture-based approaches to analyze microbial diversity associated with chemical changes in naturally fermented tofu whey, a traditional Chinese tofu-coagulant.

Naturally fermented tofu whey (NFTW) has been used as traditional tofu coagulant in China for hundreds of years. In this study, the microbial diversity in NFTW was firstly analyzed with high-throughput sequencing and its effect on chemical contents of tofu whey (TW) was investigated. Lactobacillus with 95.31% was the predominant genus in the microbial community of NFTW while Picha, Enterococcus, Bacillus and Acetobacter occupied about only 0.90%, 0.04%, 0.02% and 0.09%, respectively. Besides, Lactobacillus amylolyticus were determined to be one of the dominated species with metagenomic analysis and culture method. Lactobacillus with α-galactosidase activities played leading role in metabolizing the soybean oligosaccharides of TW to produce lactic acid. And acetic acid produced by genus of Acetobacter was another main organic acid attributed to the acidification of TW except lactic acid. Meanwhile, the bioconversion of isoflavone glucosides into aglycones could also be promoted by Lactobacillus with the help of β-glucosidase activity. Moreover, the production of equol in NFTW was confirmed, which might be jointly converted from daidzein by several strains. Therefore, our results indicated that Lactobacillus was the dominated microorganism and mainly affected the chemical changes of NFTW. This study help provide basic theory and technical references for the production of tofu and its derivative products (like sufu) with NFTW as coagulator.