Optimization of organosolv pretreatment of starch waste from sugar palm trunk (Arenga pinnata) for the production of reducing sugar

Arenga pinnata is rich in hemicellulose (27.95 %) and lignin (36.98 %). In this study, it was processed in a three-step process to produce reducing sugar; lignocellulose pretreatment, optimization and enzymatic hydrolysis. A combination of acid and organosolv pretreatment was expected to remove a significant amount of lignin from the biomass, but not dissolve much hemicellulose. Response surface methodology (RSM) was employed to determine optimum operational conditions (ethanol concentration, pretreatment time and temperature) for the organosolv pretreatment, which minimized inhibition by lignin in the enzymatic hydrolysis process. Lignin content was analyzed using gravimetric method. Reducing sugar was analyzed using the 3.5-dinitrosalicylic acid (DNS method) and validated by high-performance liquid chromatography (HPLC). From the RSM results, it can be concluded that all the variables studied were significant (p<0.05), apart from the interaction between pretreatment time and temperature (p>0.05), which had an R2 of 99.38 %­. The optimum conditions for organosolv pretreatment were obtained at 30.35% (v/v) ethanol concentration, 107 °C, and 33 minutes pretreatment time. The enzymatic hydrolysis process was conducted with different combinations of enzymes, and with Tween 80 as a surfactant. The best yield of reducing sugar was 20.28 % by using the combination of cellulase-xylanase enzymes with Tween 80, while the combination of enzymes without Tween 80 resulted in a yield of 18.15 %.