Identification of the potential inhibitors of malolactic fermentation in wines

Abstract This exploratory work aims to identify the potential inhibitors of lactic bacterial growth and to propose enological practices to guarantee the occurrence of spontaneous malolactic fermentation (MLF) in wines from traditional and double-pruning management harvests in southeast Brazil. One white wine from a summer harvest and one red wine from a winter harvest that failed to complete MLF were utilized as comparative models to identify inhibitor compounds to lactic bacteria. Wine composition, alcoholic-fermentation temperature and bacterial strain contribute to the success or failure of MLF. Temperatures below 12 °C during alcoholic fermentation decrease lactic bacterial metabolism and may impair the bacteria’s growth after yeast cells lysis. A must pH below 3.2 in a summer harvest impairs bacterial growth, and the association of low pH with a free-SO2 concentration above 10 mg L-1 may inhibit MLF. For grapes with a high sugar content, harvested in the winter cycle, enologists should keep the alcohol content below 15% and control the alcoholic-fermentation temperature.

摘要 本探索性研究旨在筛选乳酸菌生长的潜在抑制剂，并提出酿酒学操作规范，以保障巴西东南部地区采用传统修剪与双修剪管理模式采收的葡萄酒能够顺利发生自发苹果酸-乳酸发酵（malolactic fermentation, MLF）。本研究选取两款未完成苹果酸-乳酸发酵的葡萄酒作为对比模型：一款为夏收白葡萄酒，另一款为冬收红葡萄酒，用于筛选乳酸菌生长抑制性化合物。葡萄酒酒体组成、酒精发酵温度以及乳酸菌菌株，均会影响苹果酸-乳酸发酵的成败。酒精发酵阶段温度低于12℃时，会抑制乳酸菌的代谢，并可能在酵母细胞裂解后阻碍乳酸菌的生长。夏收葡萄汁的pH值低于3.2时，会损害乳酸菌的生长；若低pH值与游离二氧化硫浓度高于10 mg·L⁻¹的条件同时存在，则可能抑制苹果酸-乳酸发酵。针对冬收高糖葡萄，酿酒师应将酒精度控制在15%以下，并严格管控酒精发酵阶段的温度。