Bioenergetic aspects of xylitol production from lignocellulosic materials

With the aim of identifying the best experimental conditions able to optimize the industrial production of xylitol from lignocellulosic materials, this chapter pro-vides a review about the present knowledge on the use of material and bioenergetic balances implied in xylose-to-xylitol bioconversion by yeasts. To this purpose, xylose metabolism was investigated in three different pentose-metabolizing yeasts, namely Pachysolen tannophilus, Candida guilliermondii and Debaryomyces hansenii, using different lignocellulosic hydrolyzates as carbon and energy sources. The main hypotheses on which material and bioenergetic balances were based are a) fermentative assimilation of xylose, b) semi-aerobic xylose-to-xylitol bioconversion, c) biomass growth from pentoses, d) catabolic oxidation of xylose and e) NADH regeneration by the electron transport system. Similar approaches could be proposed to investigate and modeling other semi-aerobic processes.