Preservatives: Traditional Preservatives - Sodium Chloride

Sodium chloride commonly called table salt or salt is a viral part of human life and human evolution. Salt enhances the flavor of foods and plays a preservative as well as functional role in food processing. Apart from its use in the food industry, salt has uses in the agricultural and chemical industries as well as in water conditioning and transportation. The antimicrobial activity of salt can be both direct and indirect depending on the amount added and the purpose it serves. Since the amount of sodium chloride needed to be added to foods to prevent microbial growth is large and will cause an unacceptable taste, it usually is added in combination with other hurdles. The mechanism of inhibition of microorganisms by sodium chloride is mainly by lowering the water activity (a_w) of the substrate. Studies also have indicated that sodium chloride could also have a role in interfering with substrate utilization in microorganisms. The influence of sodium chloride alone as well as its interactive effects with other factors on various microorganisms such as Staphylococcus aureus, Escherichia coli O157:H7, Listeria monocytogenes, spore-formers, and so on in laboratory media as well as in foods have been studied in detail. Tolerance to sodium chloride has been observed in spoilage and pathogenic microorganisms and mechanisms of such tolerance have been described, and in some cases, attributed to synthesis of stress proteins and protective polyhydric alcohols. In some pathogens, such as E. coli O157:H7, salt tolerance is regulated by the rpoS sigma factor. Heat resistance of some microorganisms increases when sodium chloride is used to decrease a_w. Salt-induced microbial selection is useful in fermentations. Vegetables, dairy products, meats, and seafood are preserved using salt. Salt is also useful in inhibiting some undesirable enzymes and stabilizing some desirable enzymes used in the food industry. Excessive sodium intake in humans has been linked to hypertension and the related cardiovascular problems and stroke. Hence, there are many consumer concerns and the food industry is trying to minimize the salt content of food products.