Japanese Journal of Freezing and Drying

Indicators presenting the total activity of cells of a preserved culture for growth and for enzyme productivity were proposed, which were assayed by the delayed time to attain a level of growth and the enzyme accumulation refered to the fresh culture. Frozen Bacillus amyloliquefaciens culture with 5% PVP or 5% soluble starch maintained the full α-amylase productivity of the fresh culture at -80℃ for 2 weeks.

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Cellular viability of various yeast strain were examined after freezing and thawing with or without cryoprotectant at -70℃. Sensitivity to the freeze-thawing, treatment was varied depending on the strains was modified by age of culture, growth media, protective solution and freezing conditions. Twenty-four hr culture was optimal for preservation by freezing. The optimum freezing rate depended on kind of protective agent, although protective effect of 10% dimethyl sulfoxide was observed at all of freezing rate and gave the highest survival among the agent tested. Polyvinylpyrrolidone failed to protect yeast cell subjected to freeze-thaw. Warming rate during thawing did not affect the viability of various Saccharomyces yeasts and unexpectedly high recoveries of them were obtained without cryoprotectant. Hodling period at an intermediate temperature was not necessary when cells were frozen at an optimum freezing rate. Some strains were very sensitive to the freezing-thawing process. However, in general more than 55% of survival rate was found when 10% dimethyl sulfoxide was used as a agent. Some of the yeast strains tested showed more than 90% of survival rate.

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A mechanism of freezing and thawing of aqueous solutions compartmentalized by a cross-link structure of a hydrophilic polymer was investigated by using low-temperature DSC. In an adequately small pore formed by a cross-linked dextran were aqueous solutions of glycerol, glucose, sucrose, sodium chloride and tetraalkylammoniumbromides (alkyl=methyl, ethyl, n-propyl and n-butyl), having been used in this experiment, confined by the compartmentalization, they remained unfrozen during freezing which was indicated by recrystallization phenomena during the subsequent thawing. Recrystallization can be ascribed to ice formation in some cases, and ice and eutectic formations in other cases according to the relative position of a recrystallization temperature and an eutectic point of each solution. Recrystallization due to clathrate hydrate formation was also observed when a tetra-n-butylammoniumbromide solution was compartmentalized.

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