Maximizing the enzymic saccharification of corn stover

Abstract

Lignocellulosic biomass (e.g. agricultural residues, wood, municipal solid waste, tree and yard t gs, sewage sludge, and waste paper) comprises three major components: cellulose, hemicellulose and lignin. It can contain as much as 75% polysaccharide; thus, biomass has considerable potential as a fermentation feedstock. Corn stover represents an especially important resource because it is the single largest source of agricultural residue in the United States. The best method to obtain fermentable sugars from biomass is by enzymic saccharification. Before biomass can be effectively saccharified, some pretreatment is required. Calcium hydroxide (Eme) is an effective pretreatment agent for corn stover and is less expensive and easier to recover than other alternatives. The reconunended process conditions for treating corn stover are 4 h at 120 'C using 0. 075 g Ca(OH)2/g dry biomass and 5 g H20/g dry biomass. The maximum sugar yield bv enzymic hydrolysis (25 FPU ceflulase/g dry biomass, 50 'C, 7 days) of pretreated corn stover is 88.0% of the glucose and 88.1% of the total sugars. The recommended enzyme loading is IO FPU ceUulase/g dry biomass. Tween 20 and Tween 80 are effective at improving the enzymic saccharification of corn stover. The recommended loading of Tween is 0. 15 g Tween/g dry biomass; the loading, rather than the concentration, is the critical parameter. Adding Tween to the hydrolytic medium increases the maximum sugar yield to I 00% and 94.8% of the glucose and 97.4% and 93.3 % of the total sugars for Tween 20 and Tween 80, respectively. Tween also reduces the recommended enzyme loading to 3 FPU ceflulase/g dry biomass. The action of Tween is three-fold: (1) Time profiles show that enzymes remain active at higher temperatures in the presence of Tween. (2) Kinetic analyses show that, although the theoretical maximum hydrolysis rate is unchanged by Tween, the adsorption and coverage parameters, a and c, in the HCH-1 model are reduced which results in higher effective hydrolysis rates. (3) The maximum enzymic digestion, which is independent of enzyme effects, is higher with Tween. Thus, the action of Tween is a combination of surfactant, enzyme effector, and fignoceflulose matrix disrupter.