Refrigeration at 5C slows the growth of microorganisms and keeps food fresh for a few days. Freezing at -10C stops microbial growth, but generally does not kill microorganisms, and keeps food fresh for several months. Lack of water inhibits the action of microbial enzymes. Dehydrated and freeze-dried foods, for example, do not require refrigeration because the absence of water inhibits microbial growth. The rigid cell walls of bacteria and fungi, however, prevent bursting or plasmoptysis .
Water flows equally in and out of the cell.
Hypotonic and isotonic environments are not usually harmful to microorganisms. Under this condition, water flows out of the cell , resulting in shrinkage of the cytoplasmic membrane or plasmolysis . Under such conditions, the cell becomes dehydrated and its growth is inhibited . The canning of jams or preserves with a high sugar concentration inhibits bacterial growth through hypertonicity. The same effect is obtained by salt-curing meats or placing foods in a salt brine.