Chemical preservatives are used for different purposes in many foods, and must be included in the ingredient list if present in a food. The U.S. Food and Drug Administration (FDA) requires that, when an approved chemical preservative is added to a food, the preservative's common name and function must be included in the ingredient list. Common functions for chemical preservatives in food include colour retention, flavour protection, mould inhibition, spoilage retardation, and general preservation.
Several acids are commonly used as chemical preservatives. Acetic acid (vinegar) is a traditional preservative used in pickling. Pickling foods in vinegar stops them from decaying; this is why pickled eggs stay safe and edible much longer than fresh eggs. Benzoic acid is another common chemical compound used as a preservative. It is found naturally in cranberries, prunes, cinnamon, apples, ripe cloves and greengage plums, and has antimicrobial properties. Ascorbic acid is another commonly used chemical preservative.
Benzoates are salt compounds which are often chosen over acid compounds because of their much greater solubility in water. Sodium benzoate is a commonly used chemical preservative in food, although it only works well in foods which are naturally acidic or which have been acidified. Sodium benzoate is most effective below pH 4.5. Lower pH levels require a smaller amount of sodium benzoate for effective food preservation. Sodium benzoate is commonly found in products containing fruit, beverages, salads, dressings, icings, sauerkraut and olives. The maximum level of sodium benzoate allowed in food is 0.1 per cent.
Sorbate compounds are salts based on sorbic acid, and like benzoates, are often chosen for their solubility in water. Potassium sorbate is the most commonly used food preservative in the world. It is most effective at lower pH levels but works well up to pH 6.5. Volume for volume, potassium sorbate is only about three-quarters as effective a preservative as sorbic acid, and therefore potassium sorbate has to be present in higher concentrations than sorbic acid to achieve the same preservative results. Potassium sorbate prevents food decay due to yeasts, mould and some bacteria, and is commonly used in mayonnaise and dairy products, bread, salads, olives, dressings, fruit products and smoked or salted fish. Sorbates and benzoates are often used together in foods with an acidic pH level.