13-23: Influence of the enzyme and yeast concentrations in the simultaneous isomerization and fermentation of xylose with glucose isomerase immobilized in chitosan and co-immobilized with S.cerevisiae in alginate gel

Tuesday, May 1, 2012
Napoleon Ballroom C-D, 3rd fl (Sheraton New Orleans)
Raquel L. C. Giordano, Claudia R. Silva, Patricia M. Aquino, Joao P. Rodrigues, Guilherme S. Moraes, Teresa C. Zangirolami and Roberto C. Giordano, Chemical Engineering Department, Federal University of Sao Carlos, Sao Carlos, Brazil
The fermentation of the xylose, an abundant sugar present in lignocellulosic materials, may increase the Brazilian ethanol production. However, xylose can not be metabolized by the industrial yeast Saccharomyces cerevisiae. Its isomer, xylulose, obtained by action of glucose isomerase, can be fermented to ethanol by this yeast. An innovative biocatalyst was developed to allow the continuous production of ethanol from xylose. GI was covalently immobilized in chitosan and co immobilized with yeast in calcium alginate gel particles. The aim of the present work was to investigate the influence of enzyme and yeast concentrations on the productivity and selectivity of the ethanol production. The simultaneous isomerization and fermentation (SIF) experiments were carried out for 48 h, at pH 6.0 and 35°C, in a shaker, under stirring. The medium composition contained 60 g/L of xylose; nitrogen sources, salts and enzyme co-factors. The mass of alginate particles and medium volume were equals and kept constant in all the assays. The enzyme and yeast concentrations were varied by changing the IGI-Ch mass (chitosan containing immobilized GI), 5-38%, or the yeast mass, 2-16%, in the final particle. Xylose, xylulose, xylitol, ethanol, glycerol and acetic acid concentrations were analyzed by HPLC. A maximum ethanol concentration of 12 g/L was reached. The obtained results indicated that the higher the concentration of the intermediate product, xylulose, the higher is the selectivity between ethanol/xylitol. The maximum ethanol concentration reached was 12 g/L. Results also indicated need of pH control in the process to allow total conversion of xylose.
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