Involvement of Two Specific Causes of Cell Mortality in Freeze-Thaw Cycles with Freezing to -196°C

• Published in: Applied and Environmental Microbiology 2006-02, Vol.72 (2), p.1330-1335
• Main Authors: Dumont, Frédéric, Marechal, Pierre-André, Gervais, Patrick
• Format: Article
• Language: English
• Subjects: Biological and medical sciences; Biotechnology; Chemical and Process Engineering; cooling rate; cryopreservation; Engineering Sciences; freeze-thaw cycles; freezing; Fundamental and applied biological sciences. Psychology; Life Sciences; Microbiology; mortality; osmotic pressure; Physiology and Biotechnology; Saccharomyces cerevisiae; starter cultures; thawing; thawing rate; yeasts
• ISSN: 0099-2240; 1098-5336
• DOI: 10.1128/AEM.72.2.1330-1335.2006

The purpose of this study was to examine cell viability after freezing. Two distinct ranges of temperature were identified as corresponding to stages at which yeast cell mortality occurred during freezing to -196°C. The upper temperature range was related to the temperature of crystallization of the medium, which was dependent on the solute concentration; in this range mortality was prevented by high solute concentrations, and the proportion of the medium in the vitreous state was greater than the proportion in the crystallized state. The lower temperature range was related to recrystallization that occurred during thawing. Mortality in this temperature range was increased by a high cooling rate and/or high solute concentration in the freezing medium and a low temperature (less than -70°C). However, a high rate of thawing prevented yeast mortality in this lower temperature range. Overall, it was found that cell viability could be conserved better under freezing conditions by increasing the osmotic pressure of the medium and by using an increased warming rate.