Freezing of Listeria monocytogenes and Other Microorganisms: A Review

Abstract
When the temperature of microbes is lowered rapidly, some are injured through thermal shock. Frozen cells can be injured mechanically by intra- and extracellular ice crystals. During freezing, as water is removed, there is a concentration of cell solutes which can lead to dissociation of cellular lipoprotein. Warming of frozen cells can be accompanied by growth of ice crystals which then can physically affect cells. Freeze-thaw injury of microbes is manifested by an increase in fastidiousness and by changes in cellular morphology, release of materials from the micro- and macrostructure of cells, and denaturation of macromolecules. Given the proper environmental conditions, cells can repair such injury. Cryoprotectants minimize damage to cells during freezing and frozen storage. Death and injury of Listeria monocytogenes were greater when cells were frozen and stored at −18°C rather than −198°C. Tryptose broth was more protective of cells than a phosphate buffer solution when freezing and storage were at −...

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