Nitrogen sources can have great influence on cell growth andxylitol accumulation. In many cases, organic nitrogen sourcesare more favorable than in organic sources, for both of the separameters [40]. It is known that, in many cases, is necessary to supplement the culture medium with nutritional compounds, suchas yeast extract, ammonium sulfate, urea, among others. For some yeasts, yeast extract is an important nutrient in xylitol production.For others, however, it has no significant effect, since the yeast growth is favored by the use of ammonia or urea and casamino