The simultaneous and effective conversion of both pentose and hexose in fermentation is a critical and challenging task toward the lignocellulosic economy. This study aims to investigate the feasibility of an innovative co-fermentation process featuring with a cell recycling unit (CF/CR) for mixed sugar utilization. A l-lactic acid-producing strain Enterococcus mundtii QU 25 was applied in the continuous fermentation process, and the mixed sugars were utilized at different productivities after the flowing conditions were changed. A mathematical model was constructed with the experiments to optimize the biological process and clarify the cell metabolism through kinetics analysis. The structured model, kinetic parameters, and achievement of the fermentation strategy shall provide new insights toward whole sugar fermentation via real-time monitoring for process control and optimization. Significant carbon catabolite repression in co-fermentation using a glucose/xylose mixture was overcome by replacing glucose with cellobiose, and the ratio of consumed pentose to consumed hexose increased significantly from 0.096 to 0.461 by mass. An outstanding product concentration of 65.2 g L−1 and productivity of 13.03 g L−1 h−1 were achieved with 50 g L−1 cellobiose and 30 g L−1 xylose at an optimized dilution rate of 0.2 h−1, and the cell retention time gradually increased. Among the total lactic acid production, xylose contributed to more than 34% of the mixed sugars, which was close to the related contents in agricultural residuals. The model successfully simulated the transition of sugar consumption, cell growth, and lactic acid production among the batch, continuous process, and CF/CR systems. Cell retention time played a critical role in balancing pentose and hexose consumption, cell decay, and lactic acid production in the CF/CR process. With increasing cell concentration, consumption of mixed sugars increased with the productivity of the final product; hence, the impact of substrate inhibition was reduced. With the validated parameters, the model showed the highest accuracy simulating the CF/CR process, and significantly longer cell retention times compared to hydraulic retention time were tested.

中文翻译：

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使用蒙蒂肠球菌 QU 25 进行乳酸生产的连续混合糖发酵与增加细胞保留时间的动态模拟。

在发酵过程中同时有效地转化戊糖和己糖是木质纤维素经济的一项关键且具有挑战性的任务。本研究旨在调查以细胞回收单元 (CF/CR) 为特征的用于混合糖利用的创新共发酵工艺的可行性。将一株L-乳酸产生菌株Enterococcus mundtii QU 25应用于连续发酵过程，改变流动条件后，混合糖以不同的产率进行利用。通过实验构建数学模型，优化生物过程，通过动力学分析阐明细胞代谢。结构化模型，动力学参数，发酵策略的实现将通过实时监控过程控制和优化为全糖发酵提供新的见解。通过用纤维二糖代替葡萄糖克服了在使用葡萄糖/木糖混合物的共发酵过程中对碳分解代谢物的显着抑制，消耗的戊糖与消耗的己糖的质量比从 0.096 显着增加至 0.461。在 0.2 h-1 的优化稀释率下，使用 50 g L-1 纤维二糖和 30 g L-1 木糖实现了 65.2 g L-1 的出色产品浓度和 13.03 g L-1 h-1 的生产率，并且细胞停留时间逐渐增加。在乳酸总产量中，木糖占混合糖的34%以上，与农业残渣中的相关含量接近。该模型成功地模拟了分批、连续过程和 CF/CR 系统之间的糖消耗、细胞生长和乳酸生产的转变。细胞保留时间在平衡 CF/CR 过程中的戊糖和己糖消耗、细胞衰变和乳酸产生方面发挥了关键作用。随着细胞浓度的增加，混合糖的消耗随着最终产品的生产力而增加；因此，底物抑制的影响降低了。使用经过验证的参数，该模型显示出模拟 CF/CR 过程的最高精度，并且测试了与水力保留时间相比显着更长的细胞保留时间。细胞保留时间在平衡 CF/CR 过程中的戊糖和己糖消耗、细胞衰变和乳酸产生方面发挥了关键作用。随着细胞浓度的增加，混合糖的消耗随着最终产品的生产力而增加；因此，底物抑制的影响降低了。使用经过验证的参数，该模型显示出模拟 CF/CR 过程的最高精度，并且测试了与水力保留时间相比显着更长的细胞保留时间。细胞保留时间在平衡 CF/CR 过程中的戊糖和己糖消耗、细胞衰变和乳酸产生方面发挥了关键作用。随着细胞浓度的增加，混合糖的消耗随着最终产品的生产力而增加；因此，底物抑制的影响降低了。使用经过验证的参数，该模型显示出模拟 CF/CR 过程的最高精度，并且测试了与水力保留时间相比显着更长的细胞保留时间。