Abstract:

To investigate the impact of peptone or yeast extract on yeast stress tolerance during very high gravity (VHG) ethanol fermentation, experiments were conducted using 300 g/L initial glucose. Results showed that the increase of peptone from 3 to 6 g/L, or yeast extract from 5 to 12 g/L, in the fermentation medium resulted in a noticeable increase in cell growth and glucose consumption compared with the control experiment using 3 g/L peptone plus 5 g/L yeast extract as nitrogen source. The final ethanol was increased from 13.1% to 14.4% and 14.7% (v/v) respectively. During the fermentation process, it was found that the cell growth in the increased level of peptone or yeast extract exhibited significantly higher plasma membrane ATPase activity and much more intracellular trehalose were accumulated than the control. Moreover, a close correlation was found in the enzyme activity and intracellular trehalose content with the fermentation parameters, such as cell growth, glucose utilization and final ethanol level, which suggested that both plasma membrane ATPase and intracellular trehalose contribute to the increased stress tolerance of yeast during VHG ethanol fermentation.