Compound probiotics producing cellulase could replace cellulase preparations during solid-state fermentation of millet bran

[Display omitted] •The high cost of enzyme preparation limits its application in fermentation.•Probiotics producing cellulase replaced cellulase preparation during fermentation.•Found the dynamic changes of metabolites during the fermentation of millet bran.•Fermented millet bran with probiotics increased the anti-inflammatory levels.•Lactiplantibacillus and Issacchenkia exerted synergistic effects during fermentation. Low-value agricultural by-products can be converted into high-value biological products by fermentation with probiotic strains or by enzymatic hydrolysis. However, the high costs of enzyme preparations significantly limit their applications in fermentation. In this study, the solid-state fermentation of millet bran was performed using a cellulase preparation and compound probiotics producing cellulase (CPPC), respectively. The results showed that both factors effectively destroyed the fiber structure, reduced the crude fiber content by 23.78% and 28.32%, respectively, and significantly increased the contents of beneficial metabolites and microorganisms. Moreover, CPPC could more effectively reduce the anti-nutrient factors and increase the content of anti-inflammatory metabolites. The correlation analysis revealed that Lactiplantibacillus and Issatchenkia had synergistic growth during fermentation. Overall, these results suggested that CPPC could replace cellulase preparation and improve antioxidant properties while reducing anti-nutrient factors of millet bran, thus providing a theoretical reference for the efficient utilization of agricultural by-products.