Resumo

The understanding of the biochemistry and physiology of yeast is crucial for improvements of fuel ethanol industrial process. In order to further understand the biochemistry and physiology of industrial fuel alcohol yeast strains including Brazilian yeasts), producing bioethanol yeasts Ethanol RedTM (from Lasaffre) and PE-2, SA-1, CAT-1 and BG (Brazilian) were grown in media containing sucrose, glucose, fructose, maltose and galactose, and evaluated by biomass accumulation (turbidimetryand dry weight), sugar consumption (DNS method) and secretion of invertase activity. It was also studied the yeasts response under fermentative conditions by following trehalose accumulation. The strains exhibit rapid and intense growth in presence of sucrose, glucose and fructose, but have differing behavior in media containing maltose and galactose. The industrial fuel strain Ethanol RedTM is more adapted for growing on maltose, and maltose fermenting and non-fermenting were found among Brazilian yeasts. All strains showed slower grown on galactose. Three categories of strains were identified concerning invertase activity: with high (Ethanol RedTM), intermediate (SA-1 and BG) and low level of enzyme activity (PE-2, CAT1), suggesting differing sensibility to sugar catabolite repression among strains. Industrial yeasts were able to respond to fermentative and ethanol stressing conditions, under 30 and 37°C, by producing higher levels of trehalose. It was also observed that Brazilian PE-2 and CAT-1 Brazilian strains accumulate higher amount of trehalose, suggesting their adequacy to sucrose fermentation. Besides academic value, the results obtained have industrial significance indicating that industrial ethanol fuel-producing strains exhibit different physiological characteristics that can be exploited to improve the fermentation processes. CAPES