In the bioethanol industry, the acid washing applied to yeast cell mass after fermentation cycles is not always effective in removing the unwanted bacteria. In fact, it poses safety hazards due to the handling of large volumes of sulfuric acid. We explored whether sulfuric acid could be replaced, partially or completely, in the acid washing step to control bacterial growth. To achieve this, we evaluated: (1) the effect of ethanol and pH on growth of Lactobacillus fermentum in MRS medium; (2) ethanol as a substitute to or adjuvant of sulfuric acid in the cell treatment against L. fermentum; (3) acid treatments of cells with or without 5% ethanol in cell-recycled batch fermentation with an industrial strain of Saccharomyces cerevisiae and contaminated with L. fermentum. There was a total loss of L. fermentum viability in the following cell treatments: pH 2.0 with 5% ethanol, pH 3.0 with 20% ethanol, only 22% ethanol and pH 2.0 with 3 mg L–1 Kamoran®. Switching the treatment from pH 2.0 with 5% ethanol to pH 2.0 during the fermentative cycles was effective in non-sterile must samples that were not contaminated with L. fermentum, because the native bacteria did not survive the acid treatment (pH 2.0).

中文翻译：

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乙醇能否在生物乙醇生产的酸洗步骤中部分或完全替代硫酸以对抗发酵乳杆菌的污染？

在生物乙醇工业中，发酵循环后对酵母细胞团进行的酸洗在去除不需要的细菌方面并不总是有效。事实上，它会因为处理大量硫酸而造成安全隐患。我们探讨了在酸洗步骤中是否可以部分或完全替代硫酸以控制细菌生长。为此，我们评估了： (1) 乙醇和 pH 值对 MRS 培养基中发酵乳杆菌生长的影响；(2)乙醇作为硫酸的替代物或佐剂用于发酵乳杆菌的细胞处理；(3) 用或不加 5% 乙醇对细胞进行酸处理，在细胞循环分批发酵中用工业酿酒酵母菌和被发酵乳杆菌污染。L 全损。发酵液在以下细胞处理中的活力：pH 2.0，含 5% 乙醇，pH 3.0，含 20% 乙醇，仅含 22% 乙醇，pH 2.0，含 3 mg L–1 Kamoran®。在发酵循环期间将处理从使用 5% 乙醇的 pH 2.0 切换到 pH 2.0 对于未被发酵乳杆菌污染的非无菌葡萄汁样品是有效的，因为天然细菌无法在酸处理 (pH 2.0) 中存活。