Statistical investigation on the effects of starting xylose concentration and oxygen mass flowrate on xylitol production from rice straw hydrolyzate by response surface methodology Original Research Article

A 32 full-factorial design combined with response surface methodology was used to investigate the simultaneous effects of starting xylose concentration (S0) and oxygen mass flowrate (qO2) on xylitol production from rice straw hydrolyzate. Fermentations were performed at 30 °C, using Debaryomyces hansenii NRRL Y-7426 as xylitol producer and varying S0 between 50 and 150 g/l and qO2 between 2.5 and 5.9 mgO2/s. At the lowest starting xylose concentration and an oxygen mass flowrate of 4.2 mgO2/s, volumetric productivity and xylitol yield reached maximum values (Qp=0.70 gP/l h and YP/S=0.73 gP/gS, respectively), but xylitol concentration was quite low (35.9 gP/l). The results were in close agreement with the model prediction. The statistical model also allowed identifying the optimum operating conditions (S0=71 g/l and qO2=4.1 mgO2/s) able to simultaneously maximize volumetric productivity (0.53 gP/l h), xylitol yield (0.71 gP/gS) and final xylitol concentration (42.2 gP/l).