Sonication-Induced Enhancement of Enzymatic Saccharification of Sugarcane Bagasse: Statistical Optimization and Mechanistic Investigation Using Molecular Simulations

Sugarcane bagasse (SCB), the solid residue produced by the sugar industry, is a potential substrate for the fermentative synthesis of value-added products. The present study has reported statistical optimization of the enzymatic saccharification of SCB and its intensification using 35 kHz ultrasound. Initial dilute acid and alkali pretreatment of 100 g of raw SCB yielded 43.7 g of cellulose-rich SCB (or ApSCB). Statistical optimization of enzymatic saccharification resulted in a total reducing sugar (TRS) yield of 388 mg/g ApSCB (16.9 g) with a glucose content of 330 mg/g ApSCB (14.4 g). In ultrasound-assisted saccharification with a 10% duty cycle, the TRS yield was enhanced by 1.7× to 660 mg/g ApSCB (28.9 g) with 85% (24.5 g) glucose content. Analysis of the changes induced by sonication in the secondary structure of enzymes revealed the unfolding of the enzyme structure with the rise in random coil content. The random coil content of enzymes increased from 35.72 to 45.16, with a reduction in the α-helix content from 43.71 to 34.16%. Simultaneously, the molecular docking of the enzyme–ligand complex was carried out for both enzymes, viz., the combinations of endoglucanase–cellulose (binding energy = −4.16 kcal/mol) and β-glucosidase–cellobiose (binding energy = −7.42 kcal/mol). The molecular docking revealed that residues involved in the cellulose and cellobiose binding sites were in random coil regions. Thus, sonication resulted in opening the binding sites of enzymes with easier access to the substrate, which enhanced the enzyme activities with a higher TRS yield.