Other important topic in xylitol production is the supplementation of hydrolysates with factors that enable an optimization of productivity. Several nitrogen sources are being investigated in biotechnological studies to optimize the growth of microorganisms and the production of metabolites of interest, sincethese sources, in many bioprocesses, are essential for microbial growth [22]. Media of industrial fermentation usually contain nitro-gen sources in organic form, as urea or a complex mixture ofamino acids (yeast extract and peptone) and in inorganic form,such as ammonium sulfate. Ammonium ions, either supplemented to the medium or deriving from the catabolism of nitrogenous compounds, are actively transported and assimilated by yeasts for amino acids synthesis [23]. Nevertheless, just a few studies on the supplemental nitrogen sources are available insofaras xylitol production from hemicellulosic hydrolysates is concerned.