Co-ensiling maize straw with monk fruit extract residue: A sustainable strategy for agro-industrial waste valorization and silage improvement

Turning monk fruit ( Siraitia grosvenorii ) extract residue into value-added products is a sustainable direction for the development of the related agro-industry. One promising disposal is to ensile monk fruit residue with silage for ruminant and poultry feed. Here, we investigated the fermentation characteristics of co-ensiling monk fruit residue with maize straw. After 60 days of ensiling, we found that monk fruit residue increased crude protein contents in maize straw silage, while effectively reducing neutral detergent fiber and acid detergent fiber contents. In silages supplemented with 5% and 10% monk fruit residue without lactic acid bacteria (LAB) inoculant, crude protein content increased by 13.0% and 17.8%, respectively, whereas acid detergent fiber content decreased by 46.6% and 47.8%, and neutral detergent fiber content decreased by 4.8% and 7.9%, respectively. Besides, monk fruit residue significantly increased lactic acid and acetic acid concentrations, contributing to a decline in pH. Supplementation with a LAB inoculant further optimized the fermentation environment by increasing acetic acid concentrations in silages containing 5% and 10% monk fruit residue compared with the corresponding non-inoculated treatments (17.1 vs. 12.3 and 16.1 vs. 12.4 g·kg−1 DM, respectively; P < 0.05), while simultaneously reducing propionic acid production (0.41 vs. 0.64 and 0.48 vs. 1.45 g·kg−1 DM, respectively; P < 0.05). In addition, the ensiling process promoted the conversion of bound phenolics to free forms, resulting in a significant increase in total phenolic content and antioxidant capacity. Microbial community analysis revealed that 5% monk fruit residue and LAB inoculant act synergistically to increase the relative abundance of beneficial microbes, while suppressing harmful bacteria, and enhancing core fermentation functions related to carbohydrate metabolism and energy conversion. In conclusion, co-ensiling monk fruit residue with crop straw represents a promising strategy for the high-value utilization of this underexplored herbal medicine by-product.