Effects of initial pH value of the medium on the alcoholic fermentation performance of Saccharomyces cerevisiae cells immobilized on nipa leaf sheath pieces

Immobilized yeast on nipa leaf sheath pieces was applied to ethanol fermentation using the medium with different initial pH values (5.1, 4.5, 4.0, and 3.5). Control samples with the free yeast were also carried out under the same conditions. Low pH value of 4.0 or 3.5 significantly reduced yeast growth and increased the residual sugar level in the fermentation broths for both the immobilized and free cells. In all cases, the ethanol content produced and ethanol formation rate of the immobilized yeast were 13-33% and 35-69%, respectively, higher than those of the free yeast. In addition, the residual sugar content in the immobilized yeast cultures was 2.1-20.5 times lower than that in the free yeast cultures. The yeast immobilized on nipa leaf stem pieces exhibited higher alcoholic fermentation performance than the free yeast in medium with low pH value. This support was potential for further research for application in ethanol industry.