Fungal Pretreatment of Sweet Sorghum Bagasse with Combined CuSO4-Gallic Acid Supplement for Improvement in Lignin Degradation, Selectivity, and Enzymatic Saccharification

Sweet sorghum (Sorghum sp.) has high biomass yield. Hydrolysis of lignocellulosic sweet sorghum bagasse (SSB) to fermentable sugar could be useful for manufacture of biofuel or other fermentation products. Pretreatment of lignocellulosic biomass to degrade lignin before enzymatic hydrolysis is a key step. Fungal pretreatment of SSB with combined CuSO4-gallic acid supplements in solid-state fermentation (SSF) to achieve higher lignin degradation, selectivity value (SV), and enzymatic hydrolysis to sugar was studied. Coriolus versicolor was selected due to high activities of ligninolytic enzymes laccase, lignin peroxidase (LiP), manganese peroxidase (MnP), polyphenol oxidase (PPO), and arylalcohol oxidase (AAO) and low activities of cellulolytic enzymes CMCase, FPase, and β-glucosidase with high lignin degradation and SV in 20 days. CuSO4/gallic acid increased the activities of ligninolytic enzymes resulting in enhanced lignin degradations and SVs. Cumulative/synergistic effect of combined supplements further increased the activities of laccase, LiP, MnP, PPO, and AAO by 7.6, 14.6, 2.67, 2.06, and 2.15-folds, respectively (than control), resulting in highest lignin degradation 31.1 ± 1.4% w/w (1.56-fold) and SV 2.33 (3.58-fold). Enzymatic hydrolysis of pretreated SSB yielded higher (~2.2 times) fermentable sugar. The study showed combined supplements can improve fungal pretreatment of lignocellulosic biomass. XRD, SEM, FTIR, and TGA/DTG of SSB confirmed the results.