Dept Tecnologia Agroindustrial e Socio-Economia Rural, Centro de Ciencias Agrarias, Universidade Federal de São Carlos, Via Anhanguera, Km 174, Araras, SP 13600-970, Brazil.
World J Microbiol Biotechnol. 2013 Sep;29(9):1661-76. doi: 10.1007/s11274-013-1329-x. Epub 2013 Mar 28.
The alcoholic fermentation in Brazil displays some peculiarities because the yeast used is recycled in a non-aseptic process. After centrifugation, the cells are treated with acid to control the bacterial growth. However, it is difficult to manage the indigenous yeasts without affecting the main culture of Saccharomyces cerevisiae. This work evaluated how the cell treatment could be modified to combat contaminant yeasts based on the differential sensitivities to low pH and high concentrations of ethanol displayed by an industrial strain of S. cerevisiae and three strains of Dekkera bruxellensis, which are common contaminant yeasts in Brazilian fermentation processes. The tests were initially performed in rich medium with a low pH or a high concentration of ethanol to analyse the yeast growth profile. Then, the single and combined effects of low pH and ethanol concentration on the yeast cell viability were evaluated under non-proliferative conditions. The effects on the fermentation parameters were also verified. S. cerevisiae grew best when not subjected to the stresses, but this yeast and D. bruxellensis had similar growth kinetics when exposed to a low pH or increased ethanol concentrations. However, the combined treatments of low pH (2.0) and ethanol (11 or 13 %) resulted in a decrease of D. bruxellensis cell viability almost three times higher than of S. cerevisiae, which was only slightly affected by all cell treatments. The initial viability of the treated cells was restored within 8 h of growth in sugar cane juice, with the exception of the combined treatment for D. bruxellensis. The ethanol-based cell treatment, in despite of slowing the fermentation, could decrease and maintain D. bruxellensis population under control while S. cerevisiae was taking over the fermentation along six fermentative cycles. These results indicate that it may be possible to control the growth of D. bruxellensis without major effects on S. cerevisiae. The cells could be treated between the fermentation cycles by the parcelled addition of 13 % ethanol to the tanks in which the yeast cream is treated with sulphuric acid at pH 2.0.
巴西的酒精发酵具有一些特点，因为所使用的酵母是在非无菌过程中回收的。离心后，细胞用酸处理以控制细菌生长。然而，在不影响主要酿酒酵母（Saccharomyces cerevisiae）培养的情况下，很难控制本土酵母。这项工作评估了如何修改细胞处理方法，以基于工业酿酒酵母（Saccharomyces cerevisiae）菌株和三种常见巴西发酵过程污染物德克酵母（Dekkera bruxellensis）菌株对低 pH 和高乙醇浓度的差异敏感性，来对抗污染酵母。在低 pH 或高乙醇浓度的丰富培养基中进行初始测试，以分析酵母生长曲线。然后，在非增殖条件下评估低 pH 和乙醇浓度对酵母细胞活力的单一和联合影响。还验证了对发酵参数的影响。在不受压力的情况下，酿酒酵母生长最好，但在暴露于低 pH 或增加乙醇浓度时，该酵母和德克酵母具有相似的生长动力学。然而，低 pH（2.0）和乙醇（11 或 13%）的联合处理导致德克酵母细胞活力下降近三倍，而酿酒酵母仅受到所有细胞处理的轻微影响。在甘蔗汁中生长 8 小时后，处理细胞的初始活力得到恢复，但德克酵母的联合处理除外。基于乙醇的细胞处理虽然会减缓发酵，但可以在六个发酵周期中降低并维持德克酵母的种群控制，同时酿酒酵母接管发酵。这些结果表明，在不对酿酒酵母产生重大影响的情况下，可能可以控制德克酵母的生长。可以通过在向装有硫酸（pH 2.0）的酵母膏的罐中分批添加 13%乙醇来处理细胞，从而在发酵周期之间进行处理。
