Effect of Acetic Acid on Growth and Ethanol Fermentation of Xylose Fermenting Yeast and Saccharomyces cerevisiae

Growth of some xylose fermenting yeasts, Candida shehatae, Pichia stipitis CBS5773, fusant F101 and fusant F198, was completely inhibited in xylose medium added with 0.5% v/v acetic acid which caused the reduction of pH to 4.1. Only one xylose fermenting strain, Pachysolen tannophilus NRRL-Y2460, showed relatively low growth and ethanol fermentation. However, in the medium added with 1.0% v/v acetic acid (pH 3.7) all of these strains were completely inhibited. When the medium was adjusted by hydrochloric acid to pH 4.1 and 3.7, all xylose fermenting strains showed almost the same growth as in the medium without pH adjustment (pH 6.2). In glucose medium added with 0.5% v/v acetic acid, various strains of Saccharomyces cerevisiae, M30, Sc90, N1, G/3, G/5, G/2, TJ3 and SH1089, grew with lower specific growth rate and provided lower maximal cell concentration rate than in medium without adding acetic acid (pH 6.2). All strains, except N1, produced slightly higher maximal ethanol concentration. However, all of them yielded lower ethanol production rate. Among S. cerevisiae, strain B120 was more sensitive to acetic acid than the others since its growth was completely inhibited by 0.5% v/v acetic acid. In glucose medium, 0.5% v/v acetic acid did the same role as in xylose medium to xylose fermenting strains. Hence, the xylose fermenting yeasts revealed higher sensitivity to acetic acid than S. cerevisiae.