Tuesday, May 1, 2012
Napoleon Ballroom C-D, 3rd fl (Sheraton New Orleans)
The hydrolysis of lignocelulosic material for ethanol production release, besides glucose, high quantities of pentoses. Since the yeast Saccharomyces cannot ferment this sugar, the selection of yeasts strains with ability to produce ethanol from xylose is necessary. In this work, pentose-fermenting yeasts were isolated. Twenty-five strains belonging of the genera Aureobasidium, Candida, Hanseniaspora, Issatchenkia, Metschnikowia, Pichia, and Rhodotorula were studied. Strains were grown aerobically in basal nutrient medium containing xylose as sole carbon source in media with 30 g/L to evaluate the assimilation of this sugar and furthermore it was evaluated their ability to produce ethanol under anaerobic cultivations in media with 100 g/L of xylose or glucose. Samples were taken periodically to analyze the consumption of sugars and of cell growth. Ethanol production was evaluated by gas chromatography. All strains were able to assimilate xylose and glucose. The strains Candida shehatae BR6-2AY and BR6-2AI consumed 100% of the xylose in 24 hours of cultivation and the strains Pichia guilliermondii G1.2 and G4.2, Candida oleophila G10.1, Metchnikowia koreensis G18 and Pichia ofunaensis 1A-14 assimilated 100% of the xylose within 120 hours. Four strains were able to produce ethanol from xylose. Candida shehatae BR6-2AY and BR6-2AI attained yields of 0.3 g ethanol/g xylose, as Rhodotorula sp G10.2 and Pichia guilliermondii G1.2 achieved yields of 0.2 g ethanol/g xylose. The strains of C. shehatae and Rhodotorula sp G10.2 had ethanol production from glucose with yields of 0.2 and 0.4 g ethanol/g glucose, respectively.