Effects of the interaction between Aeromonas sobria and Macrococcus caseolyticus on protein degradation of refrigerated sturgeon fillets: Novel perspective on fish spoilage

This study aims to investigate the impact of nonspecific spoilage dominant bacteria on fish protein degradation and elucidate the effect of dominant bacteria interactions on the spoilage of sturgeon fillets during refrigeration. Macrococcus caseolyticus and Aeromonas sobria were individually inoculated and co-inoculated into sturgeon fillets, and their influence on protein degradation, oxidation, muscle structure changes, and spoilage indicators were examined using a sterilized fish fillet model. The results revealed that the nonspecific spoilage dominant bacteria M. caseolyticus disrupted the protein structure by secreting proteases and aminopeptidases (159.7 and 112.6 U/g respectively, at the end of storage), leading to the hydrolysis of protein into small peptide molecules and amino acids. Although M. caseolyticus exhibited a weak ability to produce spoilage metabolites, its presence in the co-culture group provided nutrients for the growth and metabolism of A. sobria. This synergistic interaction promoted muscle structure breakdown and protein degradation in sturgeon fillets during the late storage period, resulting in increased spoilage metabolites and accelerated oxidation. Peptidomics analysis revealed that A. sobria and M. caseolyticus influenced protein degradation by affecting molecular functions and altering biological processes, including interspecies interaction, molecular transduction activity, and regulation of molecular functions. This work unveils the mechanism of protein degradation in sturgeon fillets induced by spoilage bacteria during refrigerated storage, providing a foundation for quality control of aquatic products.