Ethanol production from sweet sorghum juice under very high gravity conditions: Batch, repeated-batch and scale up fermentation

Batch ethanol fermentations from sweet sorghum juice by Saccharomyces cerevisiae NP 01 were carried out in a 500 ml air-locked Erlenmeyer flask under very high gravity (VHG) and static conditions. The maximum ethanol production efficiency was obtained when 9 g l-1 of yeast extract was supplemented to the juice. The ethanol concentration (P), productivity (Qp) and yield (Yp/s) were 120.24 \ub1 1.35 g l-1, 3.01 \ub1 0.08 g l-1 h-1 and 0.49 \ub1 0.01, respectively. Scale up ethanol fermentation in a 5-litre bioreactor at an agitation rate of 100 rev min-1 revealed that P, Qp and Yp/s were 139.51 \ub1 0.11 g l-1, 3.49 \ub1 0.00 g l-1 h-1 and 0.49 \ub1 0.01, respectively, whereas lower P (119.53 \ub1 0.20 g l-1) and Qp (2.13 \ub1 0.01 g l-1 h-1) were obtained in a 50-litre bioreactor. In the repeated-batch fermentation in the 5-litre bioreactor with fill and drain volume of 50% of the working volume, lower P and Qp were observed in the subsequent batches. P in batch 2 to 8 ranged from 103.37 \ub1 0.28 to 109.53 \ub1 1.06 g l-1

Ethanol Production from Sweet Sorghum Juice at High Temperatures Using a Newly Isolated Thermotolerant Yeast Saccharomyces cerevisiae DBKKU Y-53

Ethanol production at elevated temperatures requires high potential thermotolerant ethanol-producing yeast. In this study, nine isolates of thermotolerant yeasts capable of growth and ethanol production at high temperatures were successfully isolated. Among these isolates, the newly isolated thermotolerant yeast strain, which was designated as Saccharomyces cerevisiae DBKKU Y-53, exhibited great potential for ethanol production from sweet sorghum juice (SSJ) at high temperatures. The maximum ethanol concentrations produced by this newly isolated thermotolerant yeast at 37 °C and 40 °C under the optimum cultural condition were 106.82 g·L−1 and 85.01 g·L−1, respectively, which are greater than values reported in the literatures. It should be noted from this study with SSJ at a sugar concentration of 250 g·L−1 and an initial pH of 5.5 without nitrogen supplementation can be used directly as substrate for ethanol production at high temperatures by thermotolerant yeast S. cerevisiae DBKKU Y-53. Gene expression analysis using real-time RT-PCR clearly indicated that growth and ethanol fermentation activities of the thermotolerant yeast S. cerevisiae DBKKU Y-53 at a high temperature (40 °C) were not only restricted to the expression of genes involved in the heat-shock response, but also to those genes involved in ATP production, trehalose and glycogen metabolism, and protein degradation processes were also involved

Ethanol production from sweet sorghum juice under very high gravity conditions: Batch, repeated-batch and scale up fermentation

Batch ethanol fermentations from sweet sorghum juice by Saccharomyces cerevisiae NP 01 were carried out in a 500 ml air-locked Erlenmeyer flask under very high gravity (VHG) and static conditions. The maximum ethanol production efficiency was obtained when 9 g l-1 of yeast extract was supplemented to the juice. The ethanol concentration (P), productivity (Qp) and yield (Yp/s) were 120.24 ± 1.35 g l-1, 3.01 ± 0.08 g l-1 h-1 and 0.49 ± 0.01, respectively. Scale up ethanol fermentation in a 5-litre bioreactor at an agitation rate of 100 rev min-1 revealed that P, Qp and Yp/s were 139.51 ± 0.11 g l-1, 3.49 ± 0.00 g l-1 h-1 and 0.49 ± 0.01, respectively, whereas lower P (119.53 ± 0.20 g l-1) and Qp (2.13 ± 0.01 g l-1 h-1) were obtained in a 50-litre bioreactor. In the repeated-batch fermentation in the 5-litre bioreactor with fill and drain volume of 50% of the working volume, lower P and Qp were observed in the subsequent batches. P in batch 2 to 8 ranged from 103.37 ± 0.28 to 109.53 ± 1.06 g l-1