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. Mem brane transport has been considered to play an important role in the u tilization of sugars present in hemicellulose and cellulose hydrolysat es, and eventually limit the production of ethanol from lignocellulosi c materials by yeast. Modes for the uptake of carbohydrates are briefl y reviewed, with particular attention to cellobiose- and xylose-fermen ting yeasts of potential industrial interest. The effects of different environmental conditions, such as oxygen availability, temperature, p H, mixed sugars, acetic acid and ethanol concentrations, on the transp ort rates and on the efficiency of the fermentation process are discus sed.