Heat Resistance of Vegetative Cells and Asci of Two Zygosaccharomyces Yeasts in Broths at Different Water Activity Values

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Abstract
The heat resistance of vegetative cells and asci of two osmotolerant yeasts (Zygosaccharomyces rouxii and Z. bailii) was investigated in two different broths of aw 0.963 and 0.858, respectively. The highest heat resistance was observed with asci of Z. bailii LMZ 108, showing a decimal reduction time (D-value) at 60°C and aw 0.858 of 14.9 min. Asci of Z. rouxii LMZ 100 were less heat resistant (D60°C-value at aw 0.858 = 3.5 min). The heat resistance (D-values) of asci at aw 0.963 proved to be 20- to 50-fold and 5- to 8-fold higher than the D-valucs of the corresponding vegetative cells of Z. rouxii and Z. bailii, respectively. However, the lower the aw of the heating broth, the smaller the differences between heat resistance of asci and that of vegetative cells. Morever, different preparations of the same cell material were found to lead to different heat resistances.