Ligninolytic Enzyme Content of Mushroom Pleurotus ostreatus and Agaricus bisporus Extracts and In Vitro Rumen Fermentation of Fungal Extract-Treated Wheat Straw

Mushrooms get nutrients from the soil fibrous substrates by producing enzymes (mainly laccases and manganese peroxidases) via the radical apparatus to attack lignin and cellulose. In fungi cultivation, the spent mushroom substrate (SMS) is a mix of plant disintegrated lignocellulosic biomasses, residual fungal mycelium and other materials (e.g., straw, cereal grains, hays, livestock litter and manure, wood chip, sawdust, etc.) on which the mushrooms grow, whereas mushroom basal bodies (MBB) are parts discharged to remove the portion in contact with the SMS. The current lab-scale project aims to evaluate the ligninolytic enzyme content of mushroom extracts from SMS and MBB of Pleurotus ostreatus (PO) and Agaricus bisporus (AB), using two extraction solvents (acetate buffer solution or only water) for 3 h. The extracts were used to treat wheat straw and to measure the rumen fiber degradation and gas production by in vitro fermentation assays. All extracts have been acidic (pH 5.2–6.0), the acidity being more pronounced for the acetate solvents (p < 0.01). AB extracts had higher laccase activity than PO extracts (155 vs. 29 U L−1, p < 0.01). On the contrary, manganese peroxidases showed a significant interaction (p < 0.01) between mushroom species and type of solvent, being higher (p < 0.01) in PO-MBB extracts (35.2 U L−1) than in PO-SMS, AB-MBB and SMS (28.0, 20.1 and 26.1 U L−1, respectively). Wheat straw incubated in acetic solvent extracts showed significantly higher NDFD (p < 0.05) than untreated straw (CTRL) in both mushroom species and their byproducts. Wheat straw treated in acidic extracts from PO by products produced more gas (p < 0.05) than CTRL straw. On the contrary, extracts from AB reduced (p < 0.05) gas production compared to CTRL straw, except for the acidic AB-MBB extract. In conclusion, extracts from mushroom by-products, primarily those from SMS of Pleurotus, increase rumen in vitro fermentability of wheat straw.