Sodium Benzoate
Sodium benzoate is the sodium salt of benzoic acid. It is an aromatic compound denoted by the chemical formula C7 H5 NaO2 with a molecular weight of 144.11. In its refined form, sodium benzoate is a white, odorless compound that has a sweetish, astringent taste. It is soluble in water. Sodium benzoate has antimicrobial characteristics it is typically used as a preservative in food products.
Sodium benzoate is supplied as a white powder or flake. During use it is mixed dry in bulk liquids where it promptly dissolves. Approximately 1.75 oz (50 g) will readily dissolve in 3 fl oz (100 ml) of water. In contrast, benzoic acid has a significantly lower water solubility profile. When placed in water, sodium benzoate dissociates to form sodium ions and benzoic acid ions. It is a weak organic acid that contains a carboxyl group. Benzoic acid occurs naturally in some foods including cranberries, prunes, cinnamon, and cloves. It is also formed by most vertebrates during metabolism.
Sodium benzoate is an antimicrobial active against most yeast and bacterial strains. It works by dissociating in the system and producing an amount of benzoic acid. Benzoic acid is highly toxic to microbes however, it is less effective against molds. Overall, it has more effect as the pH of a system is reduced with the optimal functional range between pH 2.5-4.0. The antimicrobial effect is also enhanced by the presence of sodium chloride.
There are three methods for the commercial preparation of sodium benzoate. In one method, naphthalene is oxidized with vanadium pentoxide to give phthalic anhydride. This is decarboxylated to yield benzoic acid. In a second method, toluene is mixed with nitric acid and oxidized to produce benzoic acid. In a third method, benzotrichloride is hydrolyzed and then treated with a mineral acid to give benzoic acid. Benzotrichloride is formed by the reaction of chlorine and toluene. In all cases, the benzoic acid is further refined to produce sodium benzoate. One way this is done is by dissolving the acid in a sodium hydroxide solution. The resulting chemical reaction produces sodium benzoate plus water. The crystals are isolated by evaporating off the water.
Some toxicity testing has shown sodium benzoate to be poisonous at certain concentrations. However, research conducted by the U.S. Department of Agriculture (USDA) has found that in small doses and mixed with food, sodium benzoate is not deleterious to health. Similar conclusions were drawn about larger doses taken with food, although certain physiological changes were noted. Based on this research and subsequent years of safety data, the United States government has determined sodium benzoate to be generally recognized as safe (GRAS). It is allowed to be used in food products at all levels below 0.1%. Other countries allow higher levels, up to 1.25%.
Studies investigating the accumulation of sodium benzoate in the body have also been done. This led to the discovery of a natural metabolic process that combines sodium benzoate with glycine to produce hippuric acid, a material that is then excreted. This excretion mechanism accounts for nearly 95% of all the ingested sodium benzoate. The remainder is thought to be detoxified by conjugation with glycuronic acid.
Sodium benzoate has been used in a wide variety of products because of its antimicrobial and flavor characteristics. It is the most widely used food preservative in the world being incorporated into both food and soft drink products. It is used in margarines, salsas, maple syrups, pickles, preserves, jams, and jellies. Almost every diet soft drink contains sodium benzoate as do some wine coolers and fruit juices. It is also used in personal care products like toothpaste, dentifrice cleaners, and mouthwashes. As a preservative, sodium benzoate has the advantage of low cost. A drawback is its astringent taste which can be avoided by using lower levels with another preservative like potassium sorbate.
In addition to its use in food, it is used as an intermediate during the manufacture of dyes. It is an antiseptic medicine and a rust and mildew inhibitor. It is also used in tobacco and pharmaceutical preparations. In the free-acid form, it is used as a fungicide. A relatively recent use for sodium benzoate is as a corrosion inhibitor in engine coolant systems. Sodium benzoate has recently been incorporated into plastics, like polypropylene, where it has been found to improve clarity and strength.
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