Conversion of corn fiber into fuel ethanol

Abstract

Corn fiber due to its chemical composition (up to 20% starch, 50 - 60% non-starch polysaccharides) and availability has potential to serve as a substrate for manufacture of various products, including fuel ethanol. This paper deals with assessment of fiber-to-ethanol conversion. The water/dry fiber ratio in suspensions was 10/1. Enzyme liquefaction and saccharification of residual starch in corn fiber was carried out in two steps with thermostable α-amylase (20 min, 120°C) and mixture of pullulanase and glucomalyse (24 hours, 60°C). Procedures resulted in release of 57.7±1.6 mg of glucose per gram of dry fiber basis. It responds to the dextrose equivalent expression to 96.7±2.2%. By fermentation of the starch hydrolysates by yeasts Saccharomyces cerevisiae CCY-11-3 (5% v/v inoculum, 28°C, 72 hours) 0.48 g of ethanol per gram of glucose in hydrolysates was obtained. The solids after starch hydrolysis were separated by filtration and processed by acid pretreatment (0.1 g of conc. HCl/g of biomass/5 ml of water, 120°C, 20 min) with subsequent enzyme hydrolysis (24 hours, 60°C) by the multienzyme preparations containing cellulases and hemicellulases. Overall yield of reducing sugars after these two steps was 740.7±3.9 mg/gram of dry corn fiber basis. Fermentation of lignocellulosic hydrolysates by yeasts Pichia stipitis CCY-39-50-1 and Candida shehatea CCY-29-68-4 (in both cases 5% v/v inoculum, 28°C, 72 hours) resulted in 0.38 and 0.12 g of ethanol per gram of reducing sugars. The results indicate that applied pretreatment methods and used microorganisms are able to produce ethanol from corn fiber.