Résumé
To investigate simultaneous alcoholic fermentation of glucose and xylose derived from lignocellulosic material by separate or co-culture processes, the effect of oxygen transfer rate (OTR) on the fermentation of 50 g/l xylose by Pichia stipitis NRRL Y 7124 and Candida shehatae ATCC 22984, and the fermentation of 50 g/l glucose by Saccharomyces cerevisiae CBS 1200 and Zymomonas mobilis ATCC 10988 was carried out in batch cultures. The kinetic parameters of the xylose-fermenting yeasts were greatly dependent on the OTR. The optimum OTR values were found to be 3.9 and 1.75 mmol·1–1·h–1 for C. shehatae and P. stipitis, respectively. By contrast the fermentative parameters of S. cerevisiae were poorly affected by the OTR range tested (0.0–3.5 mmol·l–1·h–1) Under these conditions the ethanol yields ranged from 0.41 g·g–1 to 0.45 g·g–1 and the specific ethanol productivity was around 0.70 g·g–1·h–1. Z. mobilis gave the highest fermentative performance under strictly anaerobic conditions (medium continually flushed with nitrogen): under these conditions, the ethanol yield was 0.43 g·g–1 and the average specific ethanol productivity was 2.3 g·g–1·h–1. Process considerations in relation to the effect of OTR on the fermentative performance of the tested strains are discussed.