Abstract:Chinese traditional vinegars are produced in open fermentation conditions involving various types of microorganisms, and improper control in the production process can lead to microbial contamination of the products. In this study, the differences in physicochemical properties and viable bacterial count between normal vinegar (NV) samples and abnormal vinegar (ANV) samples were compared. Additionally, the gas composition in ANV samples was analyzed, and the potential microbial contaminants were separated and identified. The results showed that in ANV samples the viable bacterial count exceeded the limit, the reducing sugar and total sugar contents decreased, and the lactic acid content increased. The main gas that resulted in the expansion of plastic bottles was CO2, whose concentration was more than 0.005 in the headspace of the ANV samples. Thirty strains were separated from the ANV samples, and 16 of them were identified as heat-resistant, gas-producing, or preservative-resistant strains that belonged to the genera Bacillus, Pseudomonas, Stenotrophomonas, Serratia, Clostridium, Aneurinibacillus, Brevibacillus, Sphingobacterium, and Delftia. Among them, strains PMB-9 and PMB-16 could produce white flocs that allowed the fermented liquid to become ropy, and these were the main potential microbial contaminants causing the ropy vinegar. Strains PMB-3, PMB-4, PMB-7, PMB-8, and PMB-14 could grow and produce gases in the vinegar, and were the main potential microbial contaminants causing the gas expansion.
