INVESTIGATION OF ETHANOL FORMATION BY PACHYSOLEN-TANNOPHILUS FROM XYLOSE AND GLUCOSE XYLOSE CO-SUBSTRATES

The batch, fed-batch and continuous cultivation of Pachysolen tannophi lus on various substrates (xylose, glucose, glucose/xylose and hydroly sate of cellulose/hemicellulose) was performed under aerobic, microaer obic and anaerobic conditions in stirred tank reactors equipped with p H-, redox potential-meter, microfluorometer, off-gas analyser, and for continuous cultivations with crossflow filter. The concentrations of ethanol, acetaldehyde, acetate, glucose, xylose, xylitol and the activ ities of the intracellular enzymes alcohol dehydrogenase, NADH-depende nt xylose dehydrogenase, NADPH-dependent xylose reductase, NAD(+)-depe ndent xlitol reductase and NADP(+)-dependent xylitol dehydrogenase wer e determined as a function of the cultivation time. Under anaerobic co nditions mainly cell mass and a low amount of ethanol were formed. The highest ethanol productivity was obtained under microaerobic conditio ns. Under anaerobic conditions xylitol was the main product. Glucose a nd xylose were consumed consecutively. Steady state operation of an in tegrated system consisting of a cellulose/hemicellulose enzymic hydrol yser reactor and a fermenter for glucose/xylose conversion to ethanol was maintained. However, the ethanol productivity was low due to the l ow sugar concentration, which was necessary because of the inhibition of the hydrolyses caused by high sugar concentration.