Abstract
During alcoholic fermentation, Saccharomyces cerevisiae is subjected to several stresses, among which ethanol is of capital importance. Melatonin, a bioactive molecule synthesized by yeast during alcoholic fermentation, has an antioxidant role and is proposed to contribute to counteracting fermentation-associated stresses. The aim of this study was to unravel the protective effect of melatonin on yeast cells subjected to ethanol stress. For that purpose, the effect of ethanol concentrations (6 to 12%) on a wine strain and a lab strain of S. cerevisiae was evaluated, monitoring the viability, growth capacity, mortality, and several indicators of oxidative stress over time, such as reactive oxygen species (ROS) accumulation, lipid peroxidation, and the activity of catalase and superoxide dismutase enzymes. In general, ethanol exposure reduced the cell growth of S. cerevisiae and increased mortality, ROS accumulation, lipid peroxidation and antioxidant enzyme activity. Melatonin supplementation softened the effect of ethanol, enhancing cell growth and decreasing oxidative damage by lowering ROS accumulation, lipid peroxidation, and antioxidant enzyme activities. However, the effects of melatonin were dependent on strain, melatonin concentration, and growth phase. The results of this study indicate that melatonin has a protective role against mild ethanol stress, mainly by reducing the oxidative stress triggered by this alcohol.
Highlights
IntroductionYeasts face several stresses, such as osmotic, oxidative, and acidic stresses; nutrient starvation; and the presence of ethanol and other toxic molecules
Saccharomyces cerevisiae is the main yeast involved in alcoholic fermentation and is widely used in industrial fermentation of products such as wine, beer, and bread, and in the production of bioethanol, a sustainable and clean transportation fuel [1].During fermentation, yeasts face several stresses, such as osmotic, oxidative, and acidic stresses; nutrient starvation; and the presence of ethanol and other toxic molecules
For strain QA23, similar growth curves were obtained for stressed cells treated with or without melatonin, the values of area under the curve (AUC) and OD max were slightly increased by melatonin (Figure S4B, Table S5). These results suggest that melatonin could modulate the growth recovery of cells exposed to ethanol stress
Summary
Yeasts face several stresses, such as osmotic, oxidative, and acidic stresses; nutrient starvation; and the presence of ethanol and other toxic molecules. As these stresses can compromise fermentation performance, an increase in yeast tolerance is a way to enhance the process [2,3]. To cope with these fermentation-associated stresses, yeasts have developed specific responses to each stress as well as a general response, the environmental stress response (ESR) These responses are coordinated, and the mechanism triggered by one stress can induce a protective response against others, causing a phenomenon called cross-protection [3]. The accumulation of ethanol and its metabolite acetaldehyde in the cell inhibits its growth due to the inhibition of cell division and the intracellular acidification
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