Biogenic amines content and assessment of bacterial and fungal diversity in stinky tofu - A traditional fermented soy curd

•A large diversity of microbita was found in stinky tofu and the brine samples.•Streptococcus lutetiensis and Lactococcus lactis were the predominant LAB species.•Yarrowia lipolytica was the predominant species of fungi.•Contents of biogenic amines varied among samples of different regions.•Tyramine is the one of highest concentration in all stinky tofu and brine samples.

Microbial profiles of eighteen soy curd (stinky tofu) samples as well as their brines, collected from six different regions, were assessed. In addition, biogenic amines were also quantified using HPLC to determine their levels in Chinese fermented soy curd. A total of 444 bacteria, comprising 80 species, and 116 fungal isolates, comprising 26 species, were identified using 16 S rDNA gene and internal transcribed spacer (ITS) rDNA gene sequencing, respectively. In all samples, the average number of bacteria in tofu and brine was 7.00 log cfu/g and 6.99 log cfu/mL, respectively, while the average value of fungal cells in tofu and brine were 2.58 log cfu/g and 3.55 log cfu/mL, respectively. The results revealed the predominance of Streptococcus lutetiensis, Lactococcus lactis and Yarrowia lipolytica in the samples tested. In case of biogenic amines, tyramine was detected in all samples while spermine could not be detected. β-phenethylamine was only detected in the tofu of Xi'an. The microbial composition and biogenic amines content are the main factors affecting the safety of stinky tofu products. This study indicates that a large microbial diversity is associated with the fermentation of stinky tofu which may have a key role in the production of biogenic amines.