Cooperative Fermentation Using Multiple Microorganisms and Enzymes Potentially Enhances the Nutritional Value of Spent Mushroom Substrate

Abstract

Large amounts of spent mushroom substrate (SMS) are produced globally, but their utilization efficiency is low, which leads to negative environmental impacts, such as water, soil, and air pollution. SMS contains nutrients, such as cell proteins, with a potential application in animal feed. However, the lignocellulose in SMS restricts animal digestion and absorption, thus hindering its application in animal nutrition. We investigated the potential of cellulase, xylanase, β-galactosidase, and a variety of microorganisms to optimize the conditions for reducing sugars’ (RS) production and the degradation rate of neutral detergent fibers. The results showed that the optimum proportion of multiple enzymes for glucose production of up to 210.89 mg/g were 10% cellulase, 10% xylanase, and 2% β -galactosidase, at 50 °C and 60% moisture for a 20 h hydrolysis duration. To enhance the optimal enzymolysis combination, co-fermentation experiments with multiple microorganisms and enzymes showed that inoculation with 10% Bacillus subtilis, 2% Pediococcus acidilactici, and 2% Saccharomyces cerevisiae, in combination with 10% cellulase, 10% xylanase, 2% β-galactosidase, and 1% urea, at 36.8°C and 59% moisture for 70 h hydrolysis, could lead to a 23.69% degradation rate of the neutral detergent fiber. This process significantly increased the degradation rate of the neutral detergent fiber and the nutrient content of Pleurotus eryngii compared to the initial fermentation conditions. Overall, our study generated optimal co-fermentation conditions for bacteria and enzymes and provides a practical reference for biological feed synthesis using P. eryngii spent mushroom substrate.