Co-fermentation of hot-pressed rapeseed meal with multiple strains and cellulase: Evaluating changes in protein quality and metabolite profiles

Hot-pressed rapeseed meal (RSM) is rich in resources, but high fiber content and low protein utilization result from high temperature processing. This study aims to obtain a high-quality protein source through the fermentation of hot-pressed RSM. We used Plackett-Burman and Box-Behnken designs to optimize parameters for solid state fermentation with Bacillus subtilis strain 5, Saccharomyces cerevisiae , and Aspergillus niger . Under the optimum conditions, the synergistic fermentation with multiple strains and cellulase significantly reduced anti-nutritional factors in hot-pressed RSM, while also increasing protein solubility, digestibility and extraction rate by 466.80%, 45.56% and 816.44%, respectively. 77 enzymes secreted by fermentation strains were identified in fermented hot-pressed RSM, which were mainly involved in the metabolism of proteins, peptides and amino acids (28.6%), energy (28.5%), carbohydrates (13.0%) and lipids (5.2%). Non-targeted metabonomics identified 1245 differential metabolites, with the top five being peptides and amino acids, lipids, heterocyclic compounds, alkaloids, and organic acids. These differential metabolites enhanced the nutritional, functional and flavor properties of fermented hot-pressed RSM. Among them, 702 differential metabolites were enriched into metabolic pathways, with the largest number of pathways associated with amino acid metabolism. These results hold important implications for understanding the quality of fermented hot pressed RSM. • A novel strain of Bacillus subtilis 5 with high proteolytic capacity has been detected • A fermentation technique for improving hot-pressed rapeseed meal quality was developed. • Bio-enzymes and metabolites in fermented hot-pressed rapeseed meal were identified. • Metabolic network of fermentation strains was established based on bio-enzymes and metabolites.