Curcumin Enhances Alcoholic Fermentation in Yeast by Promoting Osmotic Stress Adaptation
Spices contain diverse plant secondary metabolites with antimicrobial and antioxidant activities that can influence plant–microbe interactions. Among these metabolites, curcumin and piperine are major bioactive constituents of turmeric and black pepper, respectively. In this study, we demonstrate that curcumin and piperine enhance alcoholic fermentation in the budding yeast Saccharomyces cerevisiae. Curcumin significantly promoted alcoholic fermentation under high-glucose conditions (20–40% glucose), which impose substantial osmotic stress on yeast cells. Under these conditions, curcumin enhanced yeast growth, improved osmotic stress tolerance, and increased resistance to cell wall digestion, suggesting enhanced stress adaptation during fermentation. Furthermore, deletion of HOG1, which encodes the central MAP kinase of the High-Osmolarity Glycerol (HOG) pathway responsible for the osmotic stress response, abolished the fermentation-enhancing effect of curcumin, indicating that Hog1 function is required for this effect. Consistent with this result, transcriptomic and RT- qPCR analyses revealed increased expression of stress adaptation-related genes, including known HOG pathway-responsive genes. In contrast, the expression of genes involved in amino acid catabolism was decreased at 12 h after the initiation of fermentation, while metabolomic analysis revealed increased intracellular levels of amino acids, including glutamate and asparagine, at 24 h. These coordinated transcriptional and metabolic changes are consistent with reduced amino acid catabolism and a shift toward a metabolic state favorable for sustained fermentation. Together, these findings suggest that curcumin enhances alcoholic fermentation under osmotic stress by promoting stress adaptation that supports yeast growth and sustained fermentation. Importance Plant secondary metabolites are widely recognized for their roles in plant defense, whereas their beneficial effects on microbial physiology and metabolism remain poorly understood. This study demonstrates that the spice-derived compounds curcumin and piperine enhance alcoholic fermentation in the budding yeast Saccharomyces cerevisiae. Curcumin, in particular, improved yeast growth and stress tolerance under high-glucose conditions that impose substantial osmotic stress. Its fermentation-enhancing effect required Hog1 function and was accompanied by increased expression of HOG pathway- responsive genes and changes in amino acid metabolism. These findings demonstrate that plant-derived compounds can not only exert antimicrobial effects but also beneficially modulate yeast stress adaptation and fermentation performance. The use of natural bioactive compounds to improve fermentation robustness under high-sugar conditions may contribute to increased productivity and reduced costs in fermented food and bioethanol production.