Structural and Functional Characterization of Two Pennisetum sp Biomass during Ultrasono-Assisted Alkali Pretreatment and Enzymatic Hydrolysis for Understanding the Mechanism of Targeted Delignification and Enhanced Saccharification

The recalcitrance offered by lignocellulose to get converted into simple sugars makes its conversion process complicated, hence pretreatment is required prior to enzymatic hydrolysis and fermentation. Ultrasonication-assisted alkali pretreatment (UA-NaOH) was found to be an effective pretreatment for delignification and enzymatic hydrolysis of denanath grass (DG) and hybrid napier grasses (HNG) in terms of maximum delignification and reducing sugar production. To determine the mechanism of pretreatment and enzymatic hydrolysis, the structural and functional characterization of native and pretreated grass biomass were investigated using SEM (scanning electron microscope), FT-IR (Fourier transformation infrared) spectroscopy, TGA (thermal gravimetric analysis), DSC (differential scanning) spectroscopy, and solid state C-13 CP/MAS NMR (cross-polarization magic angle spinning nuclear magnetic resonance) spectroscopy. The surface erosions, distorted surface morphology and deconstruction of the cell wall components of the Pennisetum sp. were detected by SEM. The differences in the intra- and intermolecular hydrogen bonds that make the crystalline and amorphous regions in the cellulose were detected by FT-IR. While TGA studies revealed higher phenolic content in untreated grass biomass, DSC patterns indicated the formation of laevoglucose in DG pretreated samples. Interestingly, the NMR studies revealed the presence of maximum aliphatic lignin components with absence of the aromatic lignins in both DG and HNG samples. NMR results also showed the presence of maximum hexosans and xylans revealing that the presence of aliphatic lignin components could be a helpful way of retaining the monosaccharides.