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Improvement of ethanol production from sweet sorghum juice under batch and fed-batch fermentations: Effects of sugar levels, nitrogen supplementation, and feeding regimes

Phukoetphim, Niphaphat, Salakkam, Apilak, Laopaiboon, Pattana, Laopaiboon, Lakkana
Electronic Journal of Biotechnology 2017 v.26 pp. 84-92
Saccharomyces cerevisiae, batch fermentation, ethanol, ethanol production, gravity, juices, nitrogen, sugars, sweet sorghum, yeast extract
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, 160g/L of sugar), high gravity (HG, 200 and 240g/L of sugar) and very high gravity (VHG, 280 and 320g/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.In the batch fermentations without yeast extract, HG fermentation at 200g/L of sugar showed the highest ethanol concentration (PE, 90.0g/L) and ethanol productivity (QE, 1.25g/L·h). With yeast extract supplementation (9g/L), the ethanol production efficiency increased at all sugar concentrations. The highest PE (112.5g/L) and QE (1.56g/L·h) were observed with the VHG fermentation at 280g/L of sugar. In the fed-batch fermentations, two feeding regimes, i.e., stepwise and continuous feedings, were studied at sugar concentrations of 280g/L. Continuous feeding gave better results with the highest PE and QE of 112.9g/L and 2.35g/L·h, respectively, at a feeding time of 9h and feeding rate of 40gsugar/h.In the batch fermentation, nitrogen supplementation resulted in 4 to 32g/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.