Immobilization of Scheffersomyces stipitis cells with calcium alginate beads: A sustainable method for hemicellulosic ethanol production from sugarcane bagasse hydrolysate

Abstract

Lignocellulosic ethanol has shown promising alternative to gasoline however expensive and cumbersome bioprocessing limits the commercialization of biofuels. The major impediment toward the economic ethanol production is the bioconversion of sugars into ethanol via microbial fermentation. Application of immobilized cells in fermentation of hemicellulosic hydrolysate could minimize the ethanol production cost. This study evaluated the conditions for cell immobilization for the yeast Scheffersomyces stipitis NRRL Y-7124 by the method of entrapment in calcium alginate gel. A full factorial design (23) was designed to investigate the effect of three process variables i.e. sodium alginate concentration (1.0, 1.5 and 2.0%), calcium chloride concentration (0.1, 0.15 and 0.2 M) and conditioning time (12, 18 and 24 h). Twelve numbers of experiments were performed with central points in quadruplicates. The range of ethanol production in all experiments was observed from 4.88 g/L (Yp/s, 0.16 g/g) to 9.9 g/L ethanol (Yp/s, 0.29 g/g). Statistical analysis revealed that immobilization conditions (2.0% sodium alginate concentration, 0.1M calcium chloride concentration and 12 h conditioning time) were responsible for high stability of immobilized cells which in-turn enabled the maximum ethanol production (7.2 g/L, Yp/s, 0.26 g/g) from hemicellulosic hydrolysate of sugarcane bagasse