Effects of Cold Post-Fermentation Process on Microbial Diversity and Biogenic Amines in Protease-Assisted Fermented sufu

This study investigated the effects of enzyme-assisted low-temperature cold fermentation on <i>sufu</i>'s microbial diversity, biogenic amine (BA) formation, and physicochemical properties. The results showed that the enzyme-assisted fermentations for both room- and low-temperature groups (RTEF30 and LTEF20, respectively) significantly increased total acid (TA), amino nitrogen (NH3-N), and enzyme activity compared to the non-enzyme fermentation at room-temperature post-fermentation (RTNF30). This indicated that enzyme-assisted fermentation effectively overcame challenges associated with low-temperature fermentation of <i>sufu</i>. BA analysis revealed that the LTEF20 group had the highest total BA (3.7 mg/g) and putrescine (1.8 mg/g) levels compared to other groups. Microbial analysis showed that the LTEF20 group exhibited higher microbial diversity compared to the RTEF30 group. They had the highest levels of Enterobacteriaceae (0.4131) and lactic acid bacteria in the early and late phases (0.5556) among the groups. Correlation analysis revealed significant links between <i>sufu</i>'s physicochemical properties and microbial communities. Notably, putrescine positively correlated with <i>Bifidobacterium</i>, while TA negatively correlated with <i>Enterococcus</i>. These findings suggest that microbial activity alterations, caused by low-temperature cold fermentation, influences <i>sufu</i>'s fermentation process and quality, guiding further studies on the regulation of biogenic amine formation.