Effects of microwave irradiation dose and time on Yeast ZSM-001 growth and cell membrane permeability

To obtain a theoretical reference for microwave control of yeast used in the fermented products, the effects of microwave irradiation dose and time on growth and cell membrane permeability of Yeast ZSM-001, Brettanomyces custersii isolated from spontaneously fermented rice paste, were evaluated. When treated at a microwave dose from 1.0 to 1.6 W/g for 90 s or at the optimal dose of 1.6 W/g for duration ≤ 120 s, the yeast growth was enhanced according to Gompertz equation, and the yeast cells were almost intact with smooth surfaces observed by SEM. Meanwhile, DNA, protein and electrolyte leakage, as well as the fluidity of H+ and Ca2+ increased within a reversible range as compared with the untreated control. At a microwave dose above 2.0 W/g or duration over 160 s, the yeast growth rate decreased, and the cells were collapsed and electroporated with rough surfaces. Therefore, low-intensity microwave (dose ≤ 1.6 W/g or duration ≤ 120 s) favors yeast growth and induces a repairable increase in cell membrane permeability without cell damage. High-intensity microwave results in the yeast cell death mainly due to an irreversible increase of electrolyte, Ca2+ and DNA leakage.