Abstract: We subjected Pichia membranifaciens to thermal and hydrogen peroxide pretreatments and added sodium chloride and calcium chloride to its culture medium in order to enhance its stress tolerance and hence improve the viability of vacuum-dried P. membranifaciens. The trehalose content of heat-adapted P. membranifaciens (40 ℃ for 40 min) was higher than that of the control; the survival of heat-adapted P. membranifaciens after vacuum-drying was higher than that of the control. The trehalose content of oxidative stress-adapted P. membranifaciens (40 min treatment with 5 mmol/L hydrogen peroxide) was higher than that of the control. Similarly, the survival of oxidative stress-adapted P. membranifaciens after vacuum-drying was higher than that of the control. The addition of 0.1–0.9 mol/L sodium chloride or 1–10 mmol/L calcium chloride to the culture medium induced a marked increase of the trehalose content, and P. membranifaciens cells showed the highest amount of trehalose upon adding 0.7 mol/L sodium chloride, followed by 0.9 mol/L sodium chloride; 5 mmol/L calcium chloride treated P. membranifaciens induced the highest amount of trehalose in yeast cells. The viability of vacuumdried P. membranifaciens without any protectant and with 0.7 or 0.9 mol/L sodium chloride added was higher than that of all other treatments and the control. The viability of vacuum-dried P. membranifaciens with a protectant and sodium chloride or calcium chloride at each concentration was not significantly different from that of the control, indicating that the effect of adding protectant on the viability of vacuum-dried P. membranifaciens is greater than that of pretreating the yeast with sodium chloride or calcium chloride.

Key words: Pichia membranifaciens, vacuum-drying, tolerance, thermal environment