Abstract: This study investigated bgutyric acid contents in different types of sufu and the pattern of change in butyric acid content during grey sufu fermentation, and it also evaluated fermentation characteristics of butyric acid-producing bacteria isolated and identified from grey sufu. The results showed that the butyric acid content of grey sufu was 25.4 mg/g dry sample, much higher than that of other kinds. Butyric acid was mainly produced during the first 30 days of post-fermentation, which was closely related to specific microorganisms in the post-fermentation process. The lactic acid content of grey sufu was low and gradually decreased during post-fermentation, which could be converted into butyric acid by specific microorganisms. Clostridium butyricum BP01 quickly entered the logarithmic growth stage and then the stationary phase after 18 hours of cultivation. The pH of the final product was 5.8, and the strain could utilize lactic acid as a carbon source, and the butyric acid content of the final product increased significantly when glucose and lactic acid were used as a mixed carbon source. The strain had the strongest ability to inhibit Escherichia coli followed by Staphylococcus aureus and Bacillus cereus. It could tolerate a certain concentration of NaCl, and had certain temperature adaptability, indicating its potential to be applied in grey sufu fermentation. These results showed that grey sufu was rich in butyric acid, which was much higher than any other food resource reported so far.

Key words: grey sufu; butyric acid; short chain fatty acid; Clostridium butyricum; fermentation characteristics