Effects of Growth Media pH and Reaction Water Activity on the Conversion of Acetophenone to (S)-1-Phenylethanol by Saccharomyces cerevisiae Immobilized on Celite 635 and in Calcium Alginate

摘要

Biologically catalyzed reactions often produce enantiomers of the product; however, only one configuration is desired. Reaction conditions are known to affect enantiomer ratios and reaction kinetics, but little is known regarding the effect of processing conditions on whole-cell biocatalysis. Saccharomyces cerevisiae cells were grown in batch on glucose at pH = 4, 5, and 7, and then immobilized on Celite beads or in calcium alginate beads and used as the biocatalyst for the conversion of acetophenone in hexane to (S)-1-phenylethanol at water activities of 0.37, 0.61, and 0.80. S. cerevisiae was used as a model microorganism for the whole-cell catalyzed reaction. The initial reaction rate (IRR) and the final (S)-1-phenylethanol concentration were quantified for each treatment. The highest IRR value (94.9 µ mol/h) and the highest final concentration of (S)-1-phenylethanol (17.8 mM) were observed on Celite-immobilized cells grown at pH 5 or 7, with the main effect of growth medium pH highly statistically significant. The main effect of water activity and the interactions of the two were not statistically significant ( a = 0.05). The cells immobilized in calcium alginate beads favored a water activity of 0.61, resulting in an IRR of 916.2 µ mol/h/g dcw, averaged over pH. The highest final concentration of (S)-1-phenylethanol (4.8 mM) was achieved with cells grown at pH 5 or 7. Calcium alginate beads gave the highest initial reaction rate with a growth pH of 7 and a water activity of 0.61. However, pH of 5 and water activity of 0.61 resulted in the highest final concentration of (S)-1-phenylethanol