Enhancing ethanol tolerance and metabolic activity of Saccharomyces cerevisiae during Rice fermentation by fixed-frequency ultrasound

Ultrasound pretreatment shows potential for enhancing microbial fermentation efficiency, but its mechanochemical impact on S. cerevisiae during rice fermentation, particularly regarding ethanol tolerance and metabolic activity, requires systematic investigation. Therefore, the multi-dimensional influence of ultrasound on S. cerevisiae was studied from the aspects of biomass dynamics under ethanol stress, membrane biophysics, metabolic markers, and oxidative stress response. Following the ultrasound treatment (logarithmic metaphase, 28 kHz, and 45 W/L), the growth rate of S. cerevisiae was faster and the tolerance to ethanol was significantly increased. Sonication increased the fluorescence intensity of cell membrane potential by 15.83 % over the untreated sample, notably at 100 min. The extracellular AKP enzyme activity gradually increased with the increase of ultrasound time. The highest Na⁺K⁺-ATPase and total ATPase activities (following ultrasonic treatment) were 7.41 and 13.76 U/mgprot, representing a respective 111.62 and 67.20 % increase over the control. Metabolic activity increased by 4.78 % at 80 min. The data suggest that low-intensity ultrasound could be used to improve the ethanol tolerance of S. cerevisiae, disperse cells, change permeability of cell membrane, accelerate transfer of materials inside and outside cells, and increase enzyme activity. Consequently, it promotes the growth and reproduction of strain, to accelerate fermentation process, and increase the production of metabolites.