Abstract
In this study, Clostridium spp. was counted in 49 Chinese commercial sufu samples, and 25 samples were detected Clostridium in all samples: the detection rate was 51.02%. About 93.87% of the samples contained Clostridium at low levels (log CFU/g＜3.0) and one sample had over 4.12lg CFU/g indicating potential hazard to consumers. The 16S rDNA identification was carried out on the genus Clostridium, and the isolates were confirmed as Clostridium botulinum, Clostridium sporogenes, Clostridium beijerinckii and Clostridium bifermentans, while Clostridium butyricum, Clostridium botulinum, Clostridium perfringens and Clostridium bifermentans were the species detected in the sufu samples by high-throughput sequencing. Based on these results, the research on the number and distribution of clostridium and the possible risks of biotoxins in fermented food needs to be strengthened. To our knowledge, this is the first study to isolate and identify Clostridium spp. in sufu.
Highlights
Sufu is a kind of traditional fermented bean curd with more than 1000 years of history in China
The identification was performed by 16S rDNA sequencing, and high throughput sequencing was used to analyze the bacterial flora in sufu samples
The V1V3 variable regions of the bacterial 16S rRNA gene were amplified by the primer pair 27 F (5’AGAGTTTGAT CCTGGCTCAG-3’) and 515R (5’ATTACCGCGGCTGCTGG -3’), and the internal transcribed spacer 2 (ITS 2) region of fungi amplicons was amplified with forward primer ITS2F (5’GCATCGATGAAGAACGCAGC-3’) and reverse primer ITS2R (5’- TCCTCCGCTTATTGATATGC-3’) primers
Summary
Sufu is a kind of traditional fermented bean curd with more than 1000 years of history in China. It is a cheeselike, creamy, soft product made from tofu and fermented by microorganisms. Sufu may be contaminated with microbes from the air. We fund that the relative abundance of clostridium in one sufu sample was 7.12% by high-throughput sequencing[3].Clostridia are grampositive, spore-forming, anaerobic bacteria which are considered to be the principal organisms responsible for late blowing[4]. In 2017, a botulism outbreak was associated with by eating homemade stinky tofu and self-cured soybean products[5] and in 1998, a homemade sufu caused an outbreak[6]. The identification was performed by 16S rDNA sequencing, and high throughput sequencing was used to analyze the bacterial flora in sufu samples
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