Effect of pretreatment chemicals on xylose fermentation by Pichia stipitis.

Pretreatment of biomass with dilute H2SO4 results in residual acid which is neutralized with alkalis such as Ca(OH)2, NaOH and NH4OH. The salt produced after neutralization has an effect on the fermentation of Pichia stipitis. Synthetic media of xylose (60 g total sugar/l) was fermented to ethanol in the presence and absence of the salts using P. stipitis CBS 6054. CaSO4 enhanced growth and xylitol production, but produced the lowest ethanol concentration and yield after 140 h. Na2SO4 inhibited xylitol production, slightly enhanced growth towards the end of fermentation but had no significant effect on xylose consumption and ethanol concentration. (NH4)2SO4 inhibited growth, had no effect on xylitol production, and enhanced xylose consumption and ethanol production.