Optimization of rice straw pretreatment using microwave-assisted tetrahydrofuran-water systems through response surface methodology for improved sugar recovery

A pretreatment process is indispensable for the reduction of biomass recalcitrance to enhance its hydrolytic bioconversion efficiency. A combination of Microwave heating and Tetrahydrofuran-water co-solvent systems was applied to Rice Straw (RS) to improve its sugar conversions. The current study employed a Central Composite Design-based Response Surface Methodology (CCD-RSM) to statistically optimize and study the interaction of different independent variables, like temperature, time, substrate ratio, and enzyme loading, on the total reducing sugar (TRS) yields on the RS pretreatment. At 100 °C and 40 min with 5.0 % (w/v) substrate concentration, the THF–water pretreatment system enabled the highest sugar recovery (76.60 %) from RS, achieved using an enzyme load of 200 U/g substrate. The significance of the pretreatment model was confirmed by ANOVA, with a p-value < 0.05 and an R² value of 0.97. The crystallinity indices calculated from FTIR and XRD were incorporated into a CCD-RSM model with three factors but were found to be non-significant. However, the reduction observed in the crystallinity indices of pretreated samples, concomitant with their higher sugar yields, indicates effective amorphization of cellulose. Furthermore, the detection of 12 distinct platform chemicals in the pretreatment hydrolysates also highlights the potential sustainability of this method for downstream bioconversions.