Effect of temperature on the microaerophilic metabolism of Pachysolen tannophilus

Xylitol production by Pachysolen tannophilus from detoxified hemicellulose hydrolysate was investigated under microaerophilic conditions at temperatur e ranging from 20 to 40 degreesC. A carbon balance previously proposed to s tudy the influence of pH was used in this work to evaluate the amounts of c arbon source (xylose) utilised in competitive metabolic ways: reductive pro duction of xylitol, ethanol fermentation and respiration. At pH = 5.5 more than 83% of xylose was reduced to xylitol at 25 < T < 30 degreesC, whereas respiration became the main process at low temperature (71.1% at 20 degrees C). At high temperature, on the other hand, all three processes took place at comparable rate, consuming at 40 degreesC nearly the same percentage of carbon source (33-35%). Finally, the maximum values of volumetric productiv ity calculated at variable temperature were used to estimate the main therm odynamic parameters of both xylitol production (Deltah* = 105.4 kJ mol(-1); Deltas* = -13.2 J mol(-1) K-1) and thermal deactivation (Deltah*(D) = 210. 5 kJ mol(-1); Deltas*(D) = 3.63 J mol(-1) K-1). (C) 2001 Elsevier Science I nc. All rights reserved.