Abstract: The effects of chlorides and sulfates on co-fermentation of glucose and xylose by Pichia stipitis NLP31were investigated, and fluorescence polarization was used as the method to determine the effect of salts on membrane fluidity. The results showed that salt concentration had a significant negative impact on the fermentation performance of yeast. When the concentration of salt was 0.5 mol/L, after 24 h, the inhibition effect of NaCl was the most. The sugar utilization ratio, ethanol concentration and ethanol yield decreased by 52.00 %、65.10 % and 22.50 %, respectively, compared to that of the control. The inhibition effect of chlorides was Na+>NH4+>K+. Although cation concentrations in the sulfates were twice in the chlorides, the inhibition effect had not significant difference. So the inhibition effect of Cl- on ethanol fermentation by P. stipitis was more significant than that of SO42-. The membrane fluidity of yeast in high concentration of salts became higher, and the different salt ions had different effects on cell membrane fluidity. NH4+ showed the greatest impact on cell membrane fluidity. Increased membrane fluidity could increase cellular resistance to stress, and decrease cell loss.

Key words: salt, Pichia stipitis, ethanol fermentation, cell membrane fluidity