Mechanism of Exogenous Melatonin to Alleviate the Fermentation Performance of Saccharomyces cerevisiae Under Copper Stress.

Melatonin is involved in biological adverse stress response and enhances the ability of yeast to adapt to adverse conditions. This study investigated the mechanism of exogenous melatonin addition to Saccharomyces cerevisiae (S. cerevisiae) under copper stress. The results indicated that the addition of excessive exogenous melatonin (100 mg/L) led to the accumulation of maltose and trehalose in S. cerevisiae, which slowed glucose metabolism and further suppressed the alcoholic fermentation process. The cell morphology, cell wall structure, and the organelle morphology of S. cerevisiae EC1118 under copper stress improved with the addition of 1 μg/mL of melatonin. The results of gas chromatography-mass spectrometry (GC-MS) indicated that melatonin induced more creamy and waxy flavors in the fermentation broth, whereas excessive melatonin led to the production of unpleasant fats with a coconut oil smell. The metabolomics results showed that melatonin promoted the synthesis of Cup1p and increased copper resistance by upregulating the sulfur-containing amino acids methionine and cysteine. Furthermore, lipid peroxidation and DNA damage were alleviated through the upregulation of AFMK, which protected the integrity of the cell membrane, thereby the physiological mechanism of alleviating copper stress was achieved. Overall, moderate amounts of melatonin reduced the contraction of cells caused by copper stress and promoted the production of flavor substances. This study holds theoretical and practical importance for wine making and industrial wine production under copper stress.