Ethanol fermentation of sugar beet thick juice diluted with crude cheese whey by the flex yeast Kluyveromyces marxianus KD-15

Kluyveromyces marxianus KD-15, called flex yeast, is a strain that is insensitive to catabolite repression and has the capacity to produce ethanol efficiently from a mixture of beet molasses and whey powder. When a fermentation test was conducted in 50 mL of a medium containing 200 mg mL(-1) of sugar as sugar beet thick juice diluted with an arbitrary amount of crude whey, strain KD-15 produced over 99 mg mL-1 ethanol in all the media tested, and ethanol formation decreased in proportion to the volume of whey by K. marxianus NBRC 1963, the parental strain of KD-15, and Saccharomyces cerevisiae NBRC 0224, the reference strain for conventional ethanol production. Fermentation of thick juice diluted with whey alone by strain KD-15 at 30 degrees C initially proceeded slower than that at 33 degrees C-37 degrees C but finally bore the highest level of ethanol. The maximum ethanol concentration obtained in 1.5 L of a medium using a 2-L fermentor was elevated by aeration of 15-50 mL min(-1) and reduced by that in excess of 100 mL min(-1). Under optimized conditions in 72 h, strain KD-15 converted all of the sugars derived from thick juice and whey to ethanol at 102 mg mL(-1), corresponding to 92.9% of the theoretical yield. (C) 2010 Elsevier Ltd. All rights reserved.