An evaluation of chemical pretreatment methods for improving enzymatic saccharification of chili postharvest residue

Abstract

Residue of chili plants left in the field after harvesting is a major lignocellulosic resource that is underexploited. India has over 0.6 million tons of this residue available as surplus annually which projects it as a potent feedstock for conversion to bioethanol. The cellulose, hemicellulose and lignin content of the chili residues are subject to variations with type of cultivar, geographical region and the season of cultivation, and the composition is critical in developing strategies for its conversion to bioalcohol(s). As with any lignocellulosic biomass, this feedstock needs pretreatment to make it more susceptible to hydrolysis by enzymes which is the most efficient method for generating sugars which can, then, be fermented to alcohol. Pretreatment of chili postharvest residue (CPHR) is, therefore, important though very little study has addressed this challenge. Similarly, enzymatic saccharification of pretreated chili biomass is another area which needs dedicated R&D because the combination of enzyme preparations and the conditions for saccharification are different in different biomass types. The present study was undertaken to develop an optimal process for pretreatment and enzymatic saccharification of CPHR that will yield high amount of free sugars. Dilute acid and alkali pretreatment of the biomass was studied at high temperatures (120-180 A degrees C), with mixing (50-200 rpm) in a high pressure reactor. The holding time was adjusted between 15 and 60 min, and the resultant biomass was evaluated for its susceptibility to enzymatic hydrolysis. Similarly, the conditions for hydrolysis including biomass and enzyme loadings, mixing and incubation time were studied using a Taguchi method of experimentation and were optimized to obtain maximal yield of sugars. Efficiency of pretreatment was gauged by observing the changes in composition and the physicochemical properties of native and pretreated biomass which were analyzed by SEM and XRD analyses. The studies are expected to provide insights into the intricacies of biomass conversion leading to better processes that are simpler and more efficient