A NEW METHOD FOR STUDYING MICROAEROBIC FERMENTATIONS .2. AN EXPERIMENTAL INVESTIGATION OF XYLOSE FERMENTATION

A new experimental technique, called oxygen programmed fermentation (O PF), was used to study microbial cultures of the yeasts Pichia stipiti s and Candida utilis growing on xylose as carbon and energy source. In the oxygen programmed fermentation, the inlet oxygen mole fraction wa s continuously changed to scan through a wide range of oxygen uptake r ates in a continuous culture. The largest ethanol yields and productiv ities for P. stipitis were found at oxygen transfer rates below 1.5 mm ol L(-1) h(-1). It was found that the ratio between the culture fluore scence and near-IR absorbance increased at oxygen transfer rates lower than 1.5 mmol L(-1) h(-1). Small amounts of ethanol were produced als o by C. utilis when the oxygen transfer rate was between 0 and 3 mmol L(-1) h(-1). It is suggested that OPF will form a nice complement to o rdinary, microaerobic chemostat experiments, by making the identificat ion of interesting regions of oxygen transfer rates possible in an eff icient and time-saving initial experiment. (C) 1994 John Wiley & Sons, Inc.