Enhancing the quality of fermented sufu: synergistic effects of Staphylococcus sciuri and Bacillus toyonensis

Sufu, a traditional Chinese fermented soybean product, is renowned for its long history and distinctive taste. Despite its popularity, variability in quality due to conventional fermentation practices has been a persistent challenge. This study aimed to improve the quality of sufu by introducing Staphylococcus sciuri and Bacillus toyonensis, both of which were isolated from traditional Chinese fish sauce and exhibit strong protease activity.

Microbial inoculants accelerated the fermentation process and improved the sufu quality significantly, with the mixed-strain group (MF) showing the greatest improvement. After 15 days of fermentation, the protease activity of the MF group was 2.8 times that of the natural fermentation (NF) group. At 20 days of fermentation, compared with the NF group, the total volatile basic nitrogen (TVB-N) level in the MF group decreased by 33% (P < 0.05). The amino acid nitrogen (AAN) content was 1.47 times higher and the trichloroacetic acid-soluble (TCA-soluble) peptide content was 1.18 times higher (P < 0.05 in both cases). The production of key volatile flavor compounds such as 1-octen-3-ol, 4-methyl-1-pentanol, isoamyl alcohol, methyl palmitate, and 2-pentylfuran in the artificially fermented samples enhanced the overall flavor of the product. The microstructure of the inoculated samples was improved, leading to a better texture and mouthfeel in the final product.

Employing artificial inoculation with S. sciuri and B. toyonensis, especially in the MF group, significantly enhanced both the safety and quality of sufu. This study offers a theoretical basis for developing new varieties of sufu. © 2025 Society of Chemical Industry.