Influence of temperature on the fermentation of D-xylose by Pachysolen tannophilus to produce ethanol and xylitol

The influence of temperature between 283 and 313 K on the fermentation of D-xylose with Pachysolen tannophilus ATTC 32691 to produce ethanol and xylitol was studied. All experiments were made in a batch-culture reactor keeping the aeration level constant and the pH of the culture medium at 4.5. In each experiments the maximum specific net growth rate (mu(m)), biomass productivity (b), the specific rates of xylose uptake (q(s)) and ethanol and xylitol production (q(E) and q(Xy)) and overall yields in biomass ethanol (Y-x/s(G)) and xylitol (Y-Xy/s(G)) were determined. A fitting of the. experimental values of mu(m) - T, within the wide temperature range studied lead to the equation, mu(m) = 2.2 x 10(9)e(-6839/T)-9.1 X 10(22)e(-16702/ T) which allows a determination of the apparent activation energies, - for cell growth (E-a=56.9 kJ/mol) and death (E-d=138.9 kJ/mol) and an optimum growth temperature of 306 K. The value of q(E) remained virtually constant during the linear growth phase whilst q(s) fell throughout the whole culture. The highest values for overall ethanol yield (Y-E/s(G)=0.39 kg/kg) and the specific ethanol-production rate (q(E)=0.06kg/kgh) were obtained for fermentations carried out at 303 K, which is also quite close to the optimum temperature for the formation of biomass. Maximum overall xylitol yield (Y-Xy/s(G)=0.14 kg/kg) occurred at 288 K. (C) 2003 Elsevier Ltd. All rights reserved.