Valorization of apple tree pruning residues via ozone micro-nano-bubble water pretreatment and Pleurotus ostreatus fermentation.

Lignocellulose recalcitrance and competition from indigenous microorganisms constrain the conversion of apple tree pruning residues (ATPR) into feed by Pleurotus ostreatus. This study compared ozone micro-nano-bubble water (O3-MNBW) and atmospheric intermittent steam sterilization (SS) as pretreatment routes for ATPR fermentation, assessing substrate conversion, lamb growth performance and modelled feed costs. Dry matter recovery reached 85 % under the O3-MNBW route, compared with 79 % under SS. The apparent increases of crude protein mass were 22 % under the O3-MNBW route. Cellulose and hemicellulose degradation reached 49 % and 46 %, respectively, whereas lignin was relatively enriched. Glucose, xylose and total free amino acid concentrations were 1863.34 mg kg-1, 252.87 mg kg-1 and 630.64 ng mg-1 on day 30, respectively. Under SS, lignin and hemicellulose degradation reached 45 % and 63 %, respectively, exceeding cellulose degradation. Metabolomic features assigned to central carbon metabolism and amino acid-related pathways varied with pretreatment route and fermentation time. Fermented ATPR replaced corn straw at 10 % of total dietary dry matter, with no significant differences in lamb growth performance over 45 days. Modelled feed costs per kilogram of body weight gain were 11 % and 9 % lower than in the control for O3-MNBW and SS, respectively. These findings support the use of O3-MNBW pretreatment followed by P. ostreatus fermentation to produce feed for partial replacement of corn straw in lamb diets.