The high concentration of fructose in agave juice has been associated with reduced ethanol tolerance of commercial yeasts used for tequila production and low fermentation yields. The selection of autochthonous strains, which are better adapted to agave juice, could improve the process. In this study, a 2-step selection process of yeasts isolated from spontaneous fermentations for tequila production was carried out based on analysis of the growth dynamics in combined conditions of high fructose and ethanol. First, yeast isolates (605) were screened to identify strains tolerant to high fructose (20%) and to ethanol (10%), yielding 89 isolates able to grow in both conditions. From the 89 isolates, the growth curves under 8 treatments of combined fructose (from 20% to 5%) and ethanol (from 0% to 10%) were obtained, and the kinetic parameters were analyzed with principal component analysis and k-means clustering. The resulting yeast strain groups corresponded to the fast, medium and slow growers. A second clustering of only the fast growers led to the selection of 3 Saccharomyces strains (199, 230, 231) that were able to grow rapidly in 4 out of the 8 conditions evaluated. This methodology differentiated strains phenotypically and could be further used for strain selection in other processes. PRACTICAL APPLICATION A method to select yeast strains for fermentation taking into account the natural differences of yeast isolates. This methodology is based on the cell exposition to combinations of sugar and ethanol, which are the most important stress factors in fermentation. This strategy will help to identify the most tolerant strain that could improve ethanol yield and reduce fermentation time.

中文翻译：

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基于果糖和乙醇混合培养基中生长动力学的龙舌兰酒发酵酵母菌株选择

龙舌兰汁中高浓度的果糖与用于生产龙舌兰酒的商业酵母的乙醇耐受性降低和发酵产量低有关。选择更适合龙舌兰汁的本土菌株可以改善该过程。在这项研究中，基于对高果糖和乙醇组合条件下的生长动力学分析，从自发发酵中分离出的用于生产龙舌兰酒的酵母进行了两步选择过程。首先，筛选酵母分离物 (605) 以鉴定对高果糖 (20%) 和乙醇 (10%) 耐受的菌株，产生能够在两种条件下生长的 89 个分离物。从 89 株分离物中，获得了果糖（20% 到 5%）和乙醇（0% 到 10%）组合 8 个处理下的生长曲线，采用主成分分析和k-means聚类分析动力学参数。得到的酵母菌株组对应于快速、中等和慢速生长者。仅快速生长者的第二次聚类导致选择了 3 种酵母菌株（199、230、231），它们能够在评估的 8 个条件中的 4 个中快速生长。该方法在表型上区分菌株，并可进一步用于其他过程中的菌株选择。实际应用 考虑酵母分离物的天然差异，选择用于发酵的酵母菌株的方法。该方法基于细胞暴露于糖和乙醇的组合，这是发酵中最重要的压力因素。