XYLULOSE FERMENTATION BY SACCHAROMYCES-CEREVISIAE AND XYLOSE-FERMENTING YEAST STRAINS

Xylulose fermentation by four strains of Saccharomyces cerevisiae and two strains of xylose-fermenting yeasts, Pichia stipitis CBS 6054 and Candida shehatae NJ 23, was compared using a mineral medium at a cell concentration of 10 g (dry weight)/l. When xylulose was the sole carbo n source and fermentation was anaerobic, S. cerevisiae ATCC 24860 and CBS 8066 showed a substrate consumption rate of 0.035 g g cells(-1) h( -1) compared with 0.833 g g cells(-1) h(-1) for glucose. Bakers' yeast and S. cerevisiae isolate 3 consumed xylulose at a much lower rate al though they fermented glucose as rapidly as the ATCC and the CBS strai ns. While P. stipitis CBS 6054 consumed both xylulose and glucose very slowly under anaerobic conditions, C. shehatae NJ 23 fermented xylulo se at a rate of 0.345 g g cells(-1) h(-1), compared with 0.575 g g cel ls-lh-l for glucose. For all six strains, the addition of glucose to t he xylulose medium did not enhance the consumption of xylulose, but in creased the cell biomass concentrations. When fermentation was perform ed under oxygen-limited conditions, less xylulose was consumed by S. c erevisiae ATCC 24860 and C. shehatae NJ 23, and 50%-65% of the assimil ated carbon could not be accounted for in the products determined.