Rodrigues et al. [23] investigated the effects of the use of urea and ammonium sulfate as nitrogen sources on xylitol production by Pichia stipitis YS-30. The medium containing corn stover hydrolysate was supplemented with urea (5.0 g L−1) or ammoniumsulfate (5 g L−1) for comparison. It was observed that using urea as an alternative to (NH4)2SO4 increased xylose consumption and ethanol production rates by 25% and 34%, respectively. Mushtaqet al. [40] evaluated xylitol production from bean husk by C. tropicalis and tested various nitrogen sources (NH4Cl, urea, NH4NO3,(NH4)2SO4and NaNO3) for production optimization for this parameter, but the results were different from the ones observed in the present study, since all sources favored improvement of xylitol. There sults of these researchers have also led to an improvement in production of xylitol when urea was added to the medium. It was also noted that when yeast extract was added at concentrations above 2.5 g L−1, the xylitol production was reduced.