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A flux balance based approach of hemicellulose fermentation to ethanol by industrial yeast Saccharomyces cerevisiae

Published by the American Society of Agricultural and Biological Engineers, St. Joseph, Michigan www.asabe.org

Citation:  2010 Pittsburgh, Pennsylvania, June 20 - June 23, 2010  1009509.(doi:10.13031/2013.29921)
Authors:   Ragothaman Avanasi Narasimhan, Ganti S Murthy, Frank W.R Chaplen
Keywords:   Lignocellulosic ethanol, hemicellulose utilization, Saccharomyces cerevisiae, flux balance analysis, experimentally determined constraints

A major challenge in ethanol production using lignocellulosic feed stocks is the inefficient utilization of hemicellulose, which accounts for 30-40% of the lignocellulosic biomass. Xylose is the major product of the hydrolysis of hemicellulose of lignocellulosic feed stock, which is not fermented by industrial yeasts. So, utilization of this carbon source would significantly increase the ethanol yield from 60 gal/dry ton to 90 gal/dry ton. One strategy for the utilization of xylose is by fermenting xylulose, an isomer of xylose. A flux balance based model can be used to study the xylulose metabolism. This approach relies on the stoichiometry of the yeast reaction network and the constraints determined by steady state growth of the organism in a defined media. A media replicating the hemicellulose hydrolysate in composition was designed and isomerized. Sugars (glucose, xylose, xylulose), sugar alcohols (ethanol, xylitol and glycerol), yeast cell mass, was monitored during the growth. The data from fermentation experiments were used to conduct a flux balance analysis of the yeast using the Saccharomyces cerevisiae iND750 model. The model outputs were comparable to the experimental production rates of products. Under the experimental conditions, the model gives an increase of 1.047 mmol/hr.g biomass of ethanol production by the consumption of xylulose.

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