Biological and Physicochemical Pretreatment of Sweet Sorghum Bagasse to Liberate Reducing Sugars

On screening for lignolytic microorganisms, 27 different isolates were obtained. Isolate GFCD1 showed maximum lignolytic activity. Pretreatment of sweet sorghum bagasse was carried out by GFCD1 along with reference lignocellulolytic fungi Phanerochaete chrysosporium. GFCD1 showed maximum lignolytic activity by degrading 56% lignin of sweet sorghum bagasse in mineral medium which increased to 65.27% on addition of 0.25% yeast extract and 0.5% glucose. Further increase to 70.95% in lignin hydrolysis was observed on optimization of process parameters that eventually led to 73.94% cellulose exposure. Physiochemical pretreatment of sweet sorghum bagasse using 0.5% sulphuric acid at 15 psi for 45 min resulted in 55.28% lignin hydrolysis which was found to be lesser in comparison with GFCD1 (70.95%), but gave a significantly higher cellulose enrichment of 125% in comparison to 73.94% enrichment by GFCD1. 1g of GFCD1 and physicochemically treated sweet sorghum bagasse on enzymatic hydrolysis using endoglucanase produced 0.134 g and 0.27 g reducing sugars, respectively. Microscopic examination revealed delignification of plant cells after pretreatment and FTIR analysis showed distortion of lignin structure. Though biological and physicochemical methods are equally efficient for lignin hydrolysis in sweet sorghum bagasse with 14.46 g and 11.33 g of lignin degradation in 15d, respectively; on biochemical hydrolysis of cellulose using endoglucanase, physicochemical pretreatment was found to be more effective and produced higher amount of reducing sugars in comparison with biological method. Thus biological pretreatment of lignocellulosic biomass using microorganisms appeared to be an ecofriendly way of making cellulose accessible for hydrolysis by cellulases to produce reducing sugars for microbial fermentation, thus removing recalcitrance waste using an environment friendly process.