Effects of metal salt catalysts on yeast cell growth in ethanol conversion
The effects of the addition of metal salts and metal salt-catalyzed hydrolyzates on yeast cell growth in ethanol fermentation were investigated. Four yeast strains (Saccharomyces cerevisiae WT1, Saccharomyces cerevisiae MT81, Candida sp. 1779, and Klumaromyces fragilis), four metal salts (CuCl2, FeCl3, AgNO3, and I2), two metal salt-catalyzed hydrolyzates (CuCl2, and FeCl3), and a H2SO4-catalyzed hydrolyzate were evaluated in this study. Candida sp. 1779 was selected as the most suitable yeast strain to evaluate the effects of catalyst and hydrolyzate on this ethanol fermentation experiment. The addition of FeCl3 and I2 did not have any effects on the cell growth of the yeast. It is noted that addition of 0.1 g/L or less concentration of CuCl2 also showed no effect on yeast growth; but further increase of the concentration resulted in substantial decrease in yeast growth. In the case of AgNO3 addition, the inhibitory effect on the yeast growth covered the entire range of the concentration. Compared to the yeast cell growth of H2SO4-catalyzed hydrolyzate, FeCl3-catalyzed hydrolyzate had very similar early log-phase yeast cell growth; but the CuCl2-catalyzed hydrolyzate resulted in a much lower cell growth. These results strongly suggest that the FeCl3-catalyzed hydrolyzate is the superior catalyst among the metal salt catalysts in this study. The much less corrosiveness of the FeCl3 catalyst system, as compared to the H2SO4 system, makes it a strong candidate for further research and development.