Mixed solid-state fermentation and microbial consortium improved the nutritional value of mulberry leaves and distillers' grains.

The rapid expansion of the livestock sector has precipitated a substantial surge in animal feed demand, necessitating immediate exploration and development of alternative feed sources to ensure sustainable supply. Mulberry leaves (ML) and distillers' grains (DG) are by-products generated from agriculture and industry in Sichuan, China. Characterized by abundant output and favorable nutritional composition, two materials can be further processed to alleviate the shortage of feed resources. In this study, four strains including Bacillus subtilis, Saccharomyces cerevisiae, Levilactobacillus brevis and Lactiplantibacillus plantarum were mixed at three ratios: A (B. subtilis: S. cerevisiae: L. brevis = 1:1:1), B (B. subtilis: S. cerevisiae: L. plantarum = 1:1:1), and C (B. subtilis: S. cerevisiae: L. brevis: L. plantarum = 1:1:1:1). 10% inoculation rate was adopted for short-term anaerobic fermentation lasting 5 days using ML, DG and their mixed substrates (ML&DG) to optimize fermentation performance and modulate the microbial community structure. The results demonstrated that exogenous microbial inoculation effectively degraded tannin (50.81%) and phytic acid (52.66%), lowered the pH value below 4.77, and increased lactic acid content to 83.43 mg/g, which was 4.57 times higher than that of the control group. Meanwhile, the mixed fermentation of mulberry leaves and distillers' grains maintained a true protein retention rate of over 99% and retained antioxidant activity, with the ABTS radical scavenging capacity of the mixed substrates reaching 114.35% relative to the initial level. Microbial analysis confirmed Lactobacillus as the dominant genus correlating with quality enhancement. This study demonstrates the efficient bio-conversion of ML and DG into high-nutrient feed via solid-state fermentation using mixed fermentation and a designed microbial consortium. This waste-to-feed strategy establishes a sustainable model for circular agriculture by transforming low-value residues into functional feed resources.