Effects of microbial community structure and its co-occurrence on the dynamic changes of physicochemical properties and free amino acids in the Cantonese soy sauce fermentation process

The soy sauce produced by Cantonese fermentation has a unique flavor, among which brine fermentation plays an important role. In this fermentation process, 61 volatile compounds, including 19 esters, 10 aldehydes, 9 alcohols, 5 phenols, and 18 others, were identified by headspace solid-phase microextraction–gas chromatography–mass spectrometry. Seventeen kinds of free amino acids were detected by high-performance liquid chromatography. Results showed that Touyou, which comprised 1.5 g/100 g total nitrogen, 1.0 g/100 mL amino acid nitrogen, 3.66 g/100 g reducing sugar, 1.44 g/100 mL total acid, 17.04 g/100 mL salt content, and 27.3% umami free amino acids, had excellent quality. High-throughput sequencing was used to identify microorganisms. The top 3 of bacteria were Weissella, Staphylococcus, and Lactobacillus, and the top 3 fungi were Aspergillus, Zygosaccharomyces, and Candida. The co-occurrence network analysis of microorganisms showed that the top-ranked microorganisms were Plectosphaerella, Aureobasidium, unidentified_Mortierellales_sp, Glutinomyces, Faecalibacterium, and Cladophialophora. Then, eight microorganisms (VIP[pred] > 1) were obtained by two-way orthogonal partial least squares model, namely, Staphylococcus, Candida, Weissella, Aspergillus, Zygosaccharomyces, Lactobacillus, Monilinia, and Clavispora. Correlation analysis showed that these microorganisms were strongly related to flavor metabolites. This study explored the dynamics of traditional Cantonese fermentation, which has positive implications for optimizing this traditional fermentation process.