Elucidating the mechanisms of texture thinning in compound seasoning sauce: Microbial isolation, identification, and spoilage potential assessment

Compound seasoning sauce, a type of Chinese semi-solid condiment, is widely used in catering. However, it occasionally undergoes quality deterioration during storage, typically manifesting as thinning of the paste with reduction in viscosity. Existing studies regarding the seasoning sauce predominantly focused on quality deterioration in terms of gas production and flavor changes. The mechanisms underlying texture degradation for various sauces, particularly the role of microbial activity in this process, remain poorly understood. Thus, the commercially available samples with texture thinning were collected and analyzed for physicochemical and microbial characteristics. It was found that the liquefied sauce samples exhibited high levels of reducing sugar and TCA-soluble peptide. By employing selective medium cultivation and 16S rRNA sequencing, three predominant spoilage bacterial strains were successfully isolated and identified as B. amyloliquefaciens, B. velezensis, and B. haynesii. Metabolic phenotypic characterization demonstrated that all the three strains exhibited robust extracellular protease production capabilities. Notably, the amylase activities of B. amyloliquefaciens and B. haynesii were dramatically higher than that of B. velezensis (p < 0.05). Microbial inoculation experiments found that the three strains caused significant increase in reducing sugar and TCA-soluble peptide content, ultimately resulting in a 60 %–79 % reduction in sauce viscosity after 10 days of storage. This study identified the key microorganisms responsible for the texture thinning of compound seasoning sauce, providing critical guidance for the quality control of compound seasoning sauce.