The production of second-generation (2G) ethanol remains an interesting proposition for the implementation of sustainable and net carbon–neutral energy systems. To be economically viable, 2G biorefineries must make use of all processing streams, including the less desirable pentose (C5) sugar stream. In this work, a strategy of sequential dilute acid and alkaline pretreatment of the lignocellulosic feedstock, switchgrass, was implemented for improving the fermentable sugar yield. The hemicellulose-enriched hydrolysate obtained after dilute acid pretreatment was fermented by a newly isolated wild Scheffersomyces parashehatae strain—UFMG-HM-60.1b; the corresponding ethanol yield (Y_PS) and volumetric productivity (Q_P) were 0.19 g/g and 0.16 g/L h, respectively. The remaining switchgrass cellulignin fraction was subjected to optimized alkaline delignification at 152 ºC for 30 min. Then, the delignified solid fraction was subjected to contiguous enzymatic saccharification and fermentation releasing a glucose (C6) sugar stream. The control yeast strain, Saccharomyces cerevisiae 174, displayed an ethanol Y_PS of 0.46 g/g and Q_P of 0.70 g/L h for the C6 sugar stream, whereas the above-mentioned wild strain presented Y_PS and Q_P of 0.29 g/g and 0.38 g/L h, respectively. Upon combining the conversion of hemicellulose (37%) and cellulose-derived sugars (57%), the wild S. parashehatae strain provided higher yield (94%) than the generic S. cerevisiae (90%). Henceforth, our sequential two-stage pretreatment and fermentation of C5 and C6 sugar streams provides a pathway for maximum utilization of switchgrass carbohydrates for 2G ethanol production.

第二代 (2G) 乙醇的生产仍然是实施可持续和净碳中性能源系统的一个有趣提议。为了在经济上可行，2G 生物精炼厂必须利用所有加工流，包括不太理想的戊糖 (C5) 糖流。在这项工作中，实施了木质纤维素原料柳枝稷的连续稀酸和碱预处理策略，以提高可发酵糖产量。将稀酸预处理后得到的富含半纤维素的水解物用新分离的野生副乳杆菌菌株UFMG-HM-60.1b发酵；相应的乙醇产量 (Y _PS ) 和体积生产率 (Q _P) 分别为 0.19 g/g 和 0.16 g/L h。剩余的柳枝稷纤维素部分在 152 ºC 下进行优化的碱性脱木素 30 分钟。然后，对脱木质素的固体部分进行连续的酶糖化和发酵，释放出葡萄糖 (C6) 糖流。对照酵母菌株Saccharomyces cerevisiae 174 的乙醇 Y _PS为 0.46 g/g，Q _P为 0.70 g/L h，而上述野生菌株的 Y _PS和 Q _P为 0.29 g分别为 /g 和 0.38 g/L h。在结合半纤维素 (37%) 和纤维素衍生糖 (57%) 的转化后，野生S. parashehatae菌株提供了比一般酿酒酵母(90%)更高的产率 (94 %)。今后，我们对 C5 和 C6 糖流的连续两阶段预处理和发酵提供了最大限度利用柳枝稷碳水化合物生产 2G 乙醇的途径。