TRANSPORT OF SUGARS IN YEASTS - IMPLICATIONS IN THE FERMENTATION OF LIGNOCELLULOSIC MATERIALS

Ethanol productivities in fermentation processes depend on a number of regulatory mechanisms, which may include the uptake of nutrients. Membrane transport has been considered to play an important role in the utilization of sugars present in hemicellulose and cellulose hydrolysates, and eventually limit the production of ethanol from lignocellulosic materials by yeast. Modes for the uptake of carbohydrates are briefly reviewed, with particular attention to cellobiose- and xylose-fermenting yeasts of potential industrial interest. The effects of different environmental conditions, such as oxygen availability, temperature, pH, mixed sugars, acetic acid and ethanol concentrations, on the transport rates and on the efficiency of the fermentation process are discussed.