Microbial interaction and metabolic profile of low-salinity doubanjiang fermentation with Staphylococcus carnosus and Zygosaccharomyces rouxii

Staphylococcus carnosus and Zygosaccharomyces rouxii are key microbial drivers in high-salinity doubanjiang fermentation. As sodium salt reduction is demanded recently, understanding the behavior of these core microbes under lower salinity is crucial. Therefore, this study aimed to elucidate the growth, metabolic characteristics and interaction between Z. rouxii Y-8 and S. carnosus M43 under 9%, 12% and 15% salinities. Through mono- and co-culture experiments, the interaction between Z. rouxii and S. carnosus was strongly influenced by salinity. A positive interaction was observed at 9% and 12% salinities while the interaction shifted from positive to negative at 15% salinity. Physically separated co-culture experiments confirmed that the interaction between these two strains was maintained via extracellular metabolites instead of direct physical contact. Moreover, differential metabolites in co-culture groups under different salinities were analyzed by untargeted metabolomics and OPLS-DA. 145 differential metabolites were identified and isovalerylglutamic acid, isoquinoline and vitamin K3 were found to be different among all three groups. Finally, Z. rouxii and S. carnosus were applied in doubanjiang fermentation under different salinities. The results showed that doubanjiang inoculated with Z. rouxii and S. carnosus under 9% and 12% salinities showed better sauce and fruity aroma while 15% salinity favored the formation of color and texture in doubanjiang. The results indicated that the positive interaction between Z. rouxii and S. carnosus under relatively low salinities was beneficial for shaping doubanjiang flavor.