Metabolic heat evolution of Saccharomyces cerevisiae grown under very-high-gravity conditions

Metabolic heat evolution of Saccharomyces cerevisiae under conditions of various combinations of glucose level (low gravity, log glucose/l; very-high-gravity, 300 g glucose/l), temperature, and urea concentration was investigated. The measured overall metabolic heat evolution was 0.416 and 0.476 J/h, respectively, for 10 and 300 g glucose/l in the presence of urea. As glucose level was increased from low- to very-high-gravity when urea was supplemented, a lesser amount of heat evolved (66-43 kJ/mol glucose consumed; 54-32 kJ/mol ethanol produced at 25 degrees C), implying that a combined substrate and product inhibitory effect was exerted on yeast. When yeast was cultivated under 300 g glucose/l without urea addition, more metabolic heat was evolved at the elevation of fermentation temperature. Comparatively, when yeast was grown at a very-high-gravity condition with urea addition, an inverse relationship between temperature and metabolic heat evolution was recorded. (C) 2008 Elsevier Ltd. All rights reserved.