Enhancement of ethanol production efficiency in repeated-batch fermentation from sweet sorghum stem juice: Effect of initial sugar, nitrogen and aeration

摘要

BackgroundEthanol concentration (PE), ethanol productivity (QP) and sugar consumption (SC) are important values in industrial ethanol production. In this study, initial sugar and nitrogen (urea) concentrations in sweet sorghum stem juice (SSJ) were optimized for highPE(≥10%,v/v),QP, (≥2.5?g/L·h) andSC(≥90%) bySaccharomyces cerevisiaeSSJKKU01. Then, repeated-batch fermentations under normal gravity (NG) and high gravity (HG) conditions were studied.ResultsThe initial sugar at 208?g/L and urea at 2.75?g/L were the optimum values to meet the criteria. At the initial yeast cell concentration of ~1?×?108?cells/mL, thePE,QPandSCwere 97.06?g/L, 3.24?g/L·h and 95.43%, respectively. Repeated-batch fermentations showed that the ethanol production efficiency of eight successive cycles with and without aeration were not significantly different when the initial sugar of cycles 2 to 8 was under NG conditions (~140?g/L). Positive effects of aeration were observed when the initial sugar from cycle 2 was under HG conditions (180–200?g/L). ThePEandQPunder no aeration were consecutively lower from cycle 1 to cycle 6. Additionally, aeration affected ergosterol formation in yeast cell membrane at high ethanol concentrations, whereas trehalose content under all conditions was not different.ConclusionInitial sugar, sufficient nitrogen and appropriated aeration are necessary for promoting yeast growth and ethanol fermentation. The SSJ was successfully used as an ethanol production medium for a high level of ethanol production. Aeration was not essential for repeated-batch fermentation under NG conditions, but it was beneficial under HG conditions.