Abstract
After chemical pretreatment, improved amenability of agrowaste biomass for enzymatic saccharification needs an understanding of the effect exerted by pretreatments on biomass for enzymatic deconstruction. In present studies, NaOH, NH4OH and H2SO4 pretreatments effectively changed visible morphology imparting distinct fibrous appearance to sugarcane bagasse (SCB). Filtrate analysis after NaOH, NH4OH and H2SO4 pretreatments yielded release of soluble reducing sugars (SRS) in range of ~0.17–0.44%, ~0.38–0.75% and ~2.9–8.4% respectively. Gravimetric analysis of pretreated SCB (PSCB) biomass also revealed dry weight loss in range of ~25.8–44.8%, ~11.1–16.0% and ~28.3–38.0% by the three pretreatments in the same order. Release of soluble components other than SRS, majorly reported to be soluble lignins, were observed highest for NaOH followed by H2SO4 and NH4OH pretreatments. Decrease or absence of peaks attributed to lignin and loosened fibrous appearance of biomass during FTIR and SEM studies respectively further corroborated with our observations of lignin removal. Application of commercial cellulase increased raw SCB saccharification from 1.93% to 38.84%, 25.56% and 9.61% after NaOH, H2SO4 and NH4OH pretreatments. Structural changes brought by cell wall degrading enzymes were first time shown visually confirming the cell wall disintegration under brightfield, darkfield and fluorescence microscopy. The microscopic evidence and saccharification results proved that the chemical treatment valorized the SCB by making it amenable for enzymatic saccharification.
Highlights
After chemical pretreatment, improved amenability of agrowaste biomass for enzymatic saccharification needs an understanding of the effect exerted by pretreatments on biomass for enzymatic deconstruction
The sugarcane bagasse (SCB) biomass was subjected to mechanical comminution followed by chemical pretreatments i.e., alkali (NaOH), acid (H2SO4) and liquid ammonia (NH4OH) for improving enzymatic digestibility (Strategy outlined in Supplementary Fig. 1)
When compared to raw untreated SCB biomass control, distinct separation of fibrous and stiff vascular bundles from the shattered, fluffy and soft parenchymatous pith mass were clearly visible from pretreated SCB biomass (Supplementary Fig. 2a–d)
Summary
After chemical pretreatment, improved amenability of agrowaste biomass for enzymatic saccharification needs an understanding of the effect exerted by pretreatments on biomass for enzymatic deconstruction. The biorefinery process demands partial fractionation of cell wall matrix and their utmost amenability towards enzymatic depolymerization[5] This can be achieved through applying different pretreatments to agro waste biomass before the enzymatic saccharification. Different chemical reagent loadings along with several modifications in physical factors like residence or holding time, temperature and pressure conditions during these pretreatments have been studied[10,11,12,13] Such combinations variedly affect biomass by altering the lignocellulosic structural components and improve the accessibility of glycosidic linkages to the PCWD enzymes and enhances their enzymatic saccharification activity, i.e., biomass deconstruction. Process should have low energy requirement, operational cost and capital investment[11]
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