Serine Improves Lactic Acid Stress Tolerance and Ethanol Production in Zygosaccharomyces bailiiin BaijiuFermentation

Lactic acid is the primary inhibitor of the growth and ethanol production of yeasts in Baijiufermentation. Certain amino acids have been found to be related to stress tolerance in yeasts. This study explored the effect of lactic acid stress on the ethanol-producing yeast Zygosaccharomyces bailiiand evaluated the ability of serine to increase the lactic acid tolerance of Z. bailiiin vitro. Serine significantly improved Z. bailiiviability by 16.5% and ethanol production by 226.6% under lactic acid stress. Under lactic acid stress, serine supplementation led to an increase of 41.9% in cell wall integrity, 31.9% in cell membrane integrity, 296.6% in intracellular adenosine triphosphate (ATP), and 18.4% in the mitochondrial membrane potential. Finally, field emission scanning electron microscopy (FESEM) indicated that serine supplementation maintained the cell shape and reduced cell leakage. This study revealed a novel lactic acid tolerance mechanism of core functional yeasts during Jiang-flavor Baijiufermentation.