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 product ion 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, measure d by plate counts and methylene blue staining, decreased in all of the fermentations, following the switch from aerobic to anaerobic conditi ons. However, pH 6.0 was shown to extend cell viability and increase t he final ethanol concentration from 45 g/l to 55 g/l, compared to the yield at pH 4.5.