Fermentation ofd-xylose,d-glucose andl-arabinose mixture byPichia stipitis Y 7124: sugar tolerance

Summary The effect of substrate concentration (S₀) on the fermentation parameters of a sugar mixture byPichia stipitis Y 7124 was investigated under anaerobic and microaerobic conditions. Under microaerobiosisP. stipitis maintained high ethanol yield and productivity when initial substrate concentration did not exceed 150 g/l; ethanol yield of about 0.40 g/g and volumetric productivity up to 0.39 g/l per hour were obtained. Optimal specific ethanol productivity (0.2 g/g per hour) was observed withS₀=110 g/l. Under anaerobic conditionsP. stipitis exhibited the highest fermentative performances atS₀=20 g/l; it produced ethanol with a yield of 0.42 g/g, with a specific rate of 1.1 g/g per day. When the initial substrate level increased, specific ethanol productivity declined gradually and ethanol yield was dependent on the degree of utilization of each sugar in the mixture.Abbreviations E_m maximum produced ethanol (g/l) - E₀ initial ethanol (g/l) - E_v evaporated ethanol (g/l) - Q_p volumetric productivity of ethanol (g ethanol/l per hour or g/l per day) - q_p specific productivity of ethanol (g ethanol/g cells per hour) - q_pm maximum specific productivity of ethanol (g/l per hour) - S₀ initial substrate concentration (g/l) - t_f time at which produced ethanol is maximum (h) - Y_p/s ethanol yield (g ethanol produced/g substrate utilized) - Y_x/s cell yeild (g cells produced/g substrate utilized) - Y_xo/xy xylitol yield (g xylitol produced/g xylose utilized) - probability coefficient - specific growth rate coefficient (h^-1 or d^-1)