Ethanol production from corn cob hydrolysates by Escherichia coli KO11.

KATIA GIANNI DE CARVALHO LIMA; CAROLINE MAKI TAKAHASHI; FLAVIO ALTERTHUM

JOURNAL OF INDUSTRIAL MICROBIOLOGY & BIOTECHNOLOGY

SPRINGER HEIDELBERG

Año: 2002 vol. 29 p. 124 - 128

1367-5435

Corn cobs were evaluated as feedstock for production of ethanol by recombinant Escherichia coli KO11. Mild treatment of corn cob with dilute sulfuric acid at 121°C released 65.0-95.0 g/L of reducing sugars, with xylose as the dominant sugar.The hydrolysates were prepared for fermentation following overliming and neutralization, by adding yeast extract and tryptone. When inoculum was grown on LB medium containing glucose, fermentation of the hydrolysate was completed in 163 h and ethanol yield was 0.50 g ethanol/g sugar. When inoculum was grown on xylose, ethanol yield dropped, but fermentation was faster and substantially complete in 113 h. Rice bran also served as excellent nutrient. Hydrolysate containing 72.0 g/L of xylose and supplemented with 20.0 g/L of rice bran was readily fermented by recombinant E. coli, producing 36.0 g/L of ethanol within 70 h. Scale-up of inoculum concentration on LB medium was carried out using 250 mL erlenmeyers with chicanes and containing glass beads. Neverthless, maximum ethanol concentrations were not higher for fermentations using higher cellular concentration inocula. A second stage fermentation for ethanol production was performed by the addition of baker s yeast and sucrose (150.0 g/L) to the hydrolysed wine when fermentation by E. coli was finished. At the first step, E. coli fermented the hydrolysate containing 85.0 g/L of xylose and produced 40.0 g/L of ethanol in 94 h. At the second step, after 8 h of yeast fermentation, the ethanol concentration accumulated in the medium was 104.0 g/L. This two-stage fermentation can render the bioconversion of lignocellulose to ethanol more attractive due to increase in final alcohol concentration.