Abstract Background Ethanol 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 high PE (≥ 10%, v/v), QP, (≥ 2.5 g/L·h) and SC (≥ 90%) by Saccharomyces cerevisiae SSJKKU01. Then, repeated-batch fermentations under normal gravity (NG) and high gravity (HG) conditions were studied. Results The 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, the PE, QP and SC were 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). The PE and QP under 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. Conclusion Initial 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. How to cite: Sriputorn B, Laopaiboon P, Phukoetphim N, et al. Enhancement of ethanol production efficiency in repeated-batch fermentation from sweet sorghum stem juice: Effect of initial sugar, nitrogen and aeration. Electron J Biotechnol 2020;46. https://doi.org/10.1016/j.ejbt.2020.06.001

中文翻译：

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提高甜高粱茎汁重复分批发酵乙醇生产效率：初始糖、氮和曝气的影响

摘要 背景乙醇浓度（PE）、乙醇生产率（QP）和糖消耗量（SC）是工业乙醇生产中的重要数值。在本研究中，甜高粱茎汁 (SSJ) 中的初始糖和氮 (尿素) 浓度针对高 PE (≥ 10%, v/v)、QP (≥ 2.5 g/L·h) 和 SC (≥ 90%) 由酿酒酵母 SSJKKU01 提供。然后，研究了在正常重力 (NG) 和高重力 (HG) 条件下的重复分批发酵。结果 208 g/L 的初始糖和 2.75 g/L 的尿素是满足标准的最佳值。在~ 1 × 108 个细胞/mL 的初始酵母细胞浓度下，PE、QP 和SC 分别为97.06 g/L、3.24 g/L·h 和95.43%。重复分批发酵表明，当循环 2 至 8 的初始糖在 NG 条件下 (~140 g/L) 时，连续 8 个循环的乙醇生产效率在通气和不通气的情况下没有显着差异。当循环 2 的初始糖处于 HG 条件 (180–200 g/L) 时，观察到曝气的积极影响。从第 1 次循环到第 6 次循环，未曝气下的 PE 和 QP 连续降低。此外，在高乙醇浓度下，曝气会影响酵母细胞膜中麦角甾醇的形成，而所有条件下的海藻糖含量没有差异。结论初始糖、充足的氮和适当的通气是促进酵母生长和乙醇发酵的必要条件。SSJ 成功地用作乙醇生产介质以实现高水平的乙醇生产。在 NG 条件下，曝气对于重复分批发酵不是必需的，但在 HG 条件下是有益的。如何引用：Sriputorn B、Laopaiboon P、Phukoetphim N 等。提高甜高粱茎汁重复分批发酵乙醇生产效率：初始糖、氮和通气的影响。电子 J 生物技术 2020；46。https://doi.org/10.1016/j.ejbt.2020.06.001