Effects of Pediococcus acidilactici and Rhizopus Oryzae on protein degradation and flavor formation in fermented mutton sausages

Protein degradation occurs during the fermenting of traditional mutton sausages, which influences on the flavor and quality of products. In this study, HS-SPME-GC-MS and Sodium dodecyl sulfate-polyacrylamide gel electrophoresis were used to study the degradation kinetics of myofibrillar protein (MP) and sarcoplasmic protein (SP) during fermentation and ripening of fermented sausages by single and mixed starters (Pediococcus acidilactici CICC 10344 and Rhizopus Oryzae ATCC 96382). It was shown that flavor formation and protein degradation are related. Adding mixed starters effectively reduced the loss of sulfhydryl content compared to single starter. Moreover, cathepsin B and cathepsin L activities were continuously enhanced during sausage fermentation. Analysis of SDS-PAGE showed processing affected protein degradation, and the degree of degradation was increased with increasing fermentation time. Meanwhile, the inoculation of mature sausage samples with mixed starters accelerated the production of water-soluble flavor compounds (e.g., free amino acids and TCA-soluble peptides). The mixed starters group had more amino acids presenting the umami-free amino acids. Based on the ROAV values for odor thresholds, we identified 12 key volatile flavor compounds. The correlation heat map showed higher concentrations of key volatile flavor compounds in the mixed starters. Overall, Pediococcus acidilactici and Rhizopus Oryzae addition may effectively improve the flavor quality of fermented sausage products during fermentation.