EFFECTS OF CULTURE CONDITIONS ON THE CO-FERMENTATION OF A GLUCOSE ANDXYLOSE MIXTURE TO ETHANOL BY A MUTANT OF SACCHAROMYCES-DIASTATICUS ASSOCIATED WITH PICHIA-STIPITIS

Substrates that contain hexose as well as pentose sugars can form an i nteresting substrate for the production of ethanol. Pichia stipitis an d a respiratory-deficient mutant of Saccharomyces diastaticus were use d to convert such a substrate into ethanol under continuous culture co nditions. With a sugar mixture (glucose 70%/xylose 30%) at 50 g/l, the xylose was entirely consumed when the dilution rate (D) did not excee d 0.006 h-1 whereas the glucose was entirely consumed whatever the D. The study of influence of initial substrate concentration (S0) was per formed at D=0.015 h-1. Under these conditions the substrate was entire ly consumed when its initial concentration did not exceed 20 g/l. With S0=80 g/l the residual xylose concentration reached 20.5 g/l. At low D or at low S0, P. stipitis was the dominant species in the fermentor. Increasing the D or S0 resulted in the wash-out of P. stipitis mainly because of its low ethanol tolerance.