Effects of Lactobacillus curvatus SQ-425 and Staphylococcus simulans 65-4 as starter cultures on sensory characteristics, microbial communities and metabolites in fermented sausage.

Mixed starting cultures have been reported to perform better than commonly used single Lactic acid bacteria in meat fermentation. Lactobacillus curvatus SQ-425 and Staphylococcus simulans 65-4 were screened from 67 sausages collected from southwest regions in China to investigate the effects of single and combined inoculation (SF and CMF) on sausages quality, while natural fermentation (NF) was used as a control group. Inoculation of mixed cultures resulted in a continuous decrease in pH during fermentation, an increase in redness values of sausages and the highest sensory score. Inoculation of mixed starter cultures increased the richness of bacterial communities in sausages, but their diversity decreased. The diversity and richness of the fungal community were increased, and spoilage microorganisms such as Shigella and Fusarium were suppressed. The starting cultures did not obviously affect the fatty acid composition of the sausages, but significantly increased the diversity of volatiles, especially aldehydes and alcohols. The generation of unique flavor compounds such as 2-undecenal, p-methoxy benzaldehyde and 3, 5-octadien-2-ol was found in the CMF group. Metabolomics and correlation analyses showed that amino acid metabolism was significantly enhanced in the CMF group, with Aspergillus contributing significantly to amino acid production in the CMF group, in addition to Staphylococcus, Lactobacillus, and Sphingomonas being positively correlated with amino acid metabolites. It is further inferred that the production of amino acids and their derivatives is facilitated by the conversion of fumarate in the TCA cycle into the lysine biosynthetic pathway and the urea cycle.