Biotechnological Processing of Sugarcane Bagasse through Solid-State Fermentation with White Rot Fungi into Nutritionally Rich and Digestible Ruminant Feed

Sugarcane (<i>Saccharum officinarum</i>) bagasse (SCB) is one of the most widely produced lignocellulosic biomasses and has great potential to be recycled for sustainable food production as ruminant animal feed. However, due to severe lignification, i.e., lignin-(hemi)-cellulose complexes, ruminants can only ferment a minor fraction of the polysaccharides trapped in such recalcitrant lignocellulosic biomasses. This study was therefore designed to systematically evaluate the improvement in nutritional value, the in vitro dry matter digestibility (IVDMD), and the rate and extent of in vitro total gas (IVGP) and methane (CH₄) production during the 72 h in vitro ruminal fermentation of SCB, bioprocessed with <i>Agaricus bisporus</i>, <i>Pleurotus djamor</i>, <i>Calocybe indica</i> and <i>Pleurotus ostreatus</i> under solid-state fermentation (SSF) for 0, 21 and 56 days. The contents of neutral detergent fiber, lignin, hemicellulose and CH₄ production (% of IVGP) decreased (<i>p</i> < 0.05), whereas crude protein (CP), IVDMD and total IVGP increased (<i>p</i> < 0.05) after the treatment of SCB for 21 and 56 days with all white-rot fungi (WRF) species. The greatest (<i>p</i> < 0.05) improvement in CP (104.1%), IVDMD (38.8%) and IVGP (49.24%) and the greatest (<i>p</i> < 0.05) reduction in lignin (49.3%) and CH₄ (23.2%) fractions in total IVGP were recorded for SCB treated with <i>C. indica</i> for 56 days. Notably, <i>C. indica</i> degraded more than (<i>p</i> < 0.05) lignin and caused greater (<i>p</i> < 0.05) improvement in IVDMD than those recorded for other WRF species after 56 days. The increase in IVGP was strongly associated with lignin degradation (R² = 0.72) and a decrease in the lignin-to-cellulose ratio (R² = 0.95) during the bioprocessing of SCB. Our results demonstrated that treatment of SCB with (selective) lignin-degrading WRF can improve the nutritional value and digestibility of SCB, and <i>C. indica</i> presents excellent prospects for the rapid, selective and more extensive degradation of lignin and, as such, for the improvement in nutritional value and digestibility of SCB for ruminant nutrition.