Background: Fermentation process development has been very important for efficient ethanol production.
Improvement of ethanol production efficiency from sweet sorghum juice (SSJ) under normal gravity (NG,
160 g/L of sugar), high gravity (HG, 200 and 240 g/L of sugar) and very high gravity (VHG, 280 and 320 g/L of
sugar) conditions by nutrient supplementation and alternative feeding regimes (batch and fed-batch systems)
was investigated using a highly ethanol-tolerant strain,
Saccharomyces cerevisiae
NP01.
Results: In the batch fermentations without yeast extract, HG fermentation at 200 g/L of sugar showed the
highest ethanol concentration (
PE, 90.0 g/L) and ethanol productivity (
QE, 1.25 g/L·h). With yeast extract
supplementation (9 g/L), the ethanol production efficiency increased at all sugar concentrations. The highest
PE (112.5 g/L) and
QE (1.56 g/L·h) were observed with the VHG fermentation at 280 g/L of sugar. In the
fed-batch fermentations, two feeding regimes,
i.e., stepwise and continuous feedings, were studied at sugar
concentrations of 280 g/L. Continuous feeding gave better results with the highest
PE and
QE of 112.9 g/L and
2.35 g/L·h, respectively, at a feeding time of 9 h and feeding rate of 40 g sugar/h.
Conclusions: In the batch fermentation, nitrogen supplementation resulted in 4 to 32 g/L increases in ethanol
production, depending on the initial sugar level in the SSJ. Under the VHG condition, with sufficient nitrogen,
the fed-batch fermentation with continuous feeding resulted in a similar
PE and increased
QP by 51% compared
to those in the batch fermentation.
