Effect of pH on cell viability and product yields in D-xylose fermentations by Candida shehatae

Candida shehatae were sequentially subjected to aerobic conditions for cellular growth, followed by anaerobic conditions for ethanol production from D-xylose at pH 2.5,4.5 and 6.0. Ethanol yields increased from 0.25 g/g to 0.37 g/g and xylitol yields decreased from 0.33 g/g to 0.1 g/g as the pH was increased from 2.5 to 6.0. Cell viability, measured by plate counts and methylene blue staining, decreased in all of the fermentations, following the switch from aerobic to anaerobic conditions. However, pH 6.0 was shown to extend cell viability and increase the final ethanol concentration from 45 g/l to 55 g/l, compared to the yield at pH 4.5.