Sodium chloride (NaCl), or common salt, is probably the oldest known food preservative. Few present-day foods are preserved directly by high concentrations of NaCl. Rather salt is used primarily as an adjunct to other processing methods such as canning or curing (3). In general, food-borne pathogenic bacteria are inhibited by a water activity of 0.92 or less (equivalent to a NaCl concentration of 13% w/v). The exception is Staphylococcus aureus, which has a minimum water activity for growth of 0.83 to 0.86. Another relatively salt-tolerant foodborne pathogen is Listeria monocytogenes, which can survive in saturated salt solutions at low temperatures. Fungi are more tolerant to low water activity than bacteria. The minimum for growth of xerotolerant fungi is 0.61 to 0.62, but most are inhibited by 0.85 or lower (4).
The antimicrobial activity of sodium chloride is related to its ability to reduce water activity (aw). As the water activity of the external medium is reduced, cells are sub jected to osmotic shock and rapidly lose water through plasmolysis. During plasmolysis, a cell ceases to grow and either dies or remains dormant. To resume growth, the cell must reduce its intracellular water activity (5). In addition to osmotic influence on growth, other possible mechanisms of sodium chloride inhibition include limiting oxygen solubility, alteration of pH, toxicity of sodium and chloride ions, and loss of magnesium ions (6).
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