Impact of Aspergillus Species on Microbial Community Dynamics and Their Associations with Fermentation Properties in Fermented Walnut-Based Soy Sauce

This study investigated microbial community dynamics and their links to fermentation traits in solid-state fermentation of walnut -based soy sauce (WSS) using walnut meal-soybean meal mixtures. Via 16S rRNA sequencing and molecular docking, it analyzed the effects of three distinct starter culture treatments—Aspergillus oryzae(AO),Aspergillus niger(AN), and mixed starter culture (A. oryzae+A. niger, ON)—as well as fermentation duration on microbial diversity and physicochemical properties, aiming to clarify microbial-driven quality mechanisms. Physicochemical analysis demonstrated superior fermentation performance in the AO group, showing significantly higher amino nitrogen (NH3-N) accumulation (0.23 g/100 mL) and protease activity (30.5 U/mL) compared to the AN group, with the mixed inoculation group (ON) exhibiting intermediate results, indicatingA. oryzae’s dominant role in mixed fermentation. Via PCA and Shannon index, microbial diversity analyses revealed starter cultures shaped microbial community structure:Enterococcusand Staphylococcaceae were enriched by AO starter, andKlebsielladominated in AN group. Additionally, temporal succession of the microbiota occurred during post-fermentation of WSS, with Lactobacillales,Staphylococcus, and special flavor-producing functional flora dominating early, middle, and later stages, respectively.Staphylococcuspositively correlated with protease activity and amino nitrogen, critical for quality. Molecular docking showed major walnut polyphenols significantly affected protease activity, aiding process optimization. This research provides theoretical foundations for improving WSS production and enriches understanding of solid-state fermentation microbial ecology.