Preservatives are substances that are added to food items in order to inhibit, retard or arrest growth of microorganisms thereby preventing spoilage. There are two types of preservatives used in foods – Natural or Class I preservatives and Synthetic or Class II preservatives.
Class I preservatives include natural agents like sugar, salt, vinegar, spices and alcohol that have been traditionally used to preserve food. These preservatives are safe to use in foods.
Synthetic, chemical or class II preservatives are chemicals that are added during food processing and act as antimicrobials, anti-oxidants or anti-enzymatic. Synthetic preservatives are Generally Recognized as Safe (GRAS), when used within the permissible limits as prescribed by the Food Regulatory bodies.
Here are some of the common food preservatives that are added to foods:
Antioxidants are substances that are added to fats or to foods with a high fat content and help retard or prevent oxidative deterioration thereby prolonging the wholesomeness, palatability and shelf life of foods. Antioxidants should not contribute to an objectionable odour, flavour or colour to the fat or to the food in which it is present and should be fat soluble, effective in low concentrations and not be harmful to health.
Both natural and synthetic compounds are used as antioxidants by the food industry. Natural antioxidants include ascorbic acid (vitamin C) and tocopherols (vitamin E). Ascorbic acid is used to prevent enzymatic browning in cut fruits and vegetables and the presence of citric acid and phosphoric acid increases the effectiveness of vitamin C in preventing this browning.
Chemicals such as Butylated Hydroxy Anisole (BHA), Butylated Hydroxy Toulene(BHT), Propyl Gallate (PG), Tetiary butyl hydroquinone (TBHQ), Thiodipropionic acid and Dilaurylthio dipropionate are now used as antioxidants in processed foods. The joint FAO/WHO expert committee on food additives has suggested an Acceptable Daily Intake (ADI) for BHA as 0.05 mg /kg body wt and BHT as 0.03 mg/kg body weight. Long term use of synthetic antioxidants above the levels of ADI can be carcinogenic.
Acetic acid in the form of vinegar has been traditionally used as a preservative along with sugar and salt. Acetic acid is added to foods such as mayonnaise, pickles, sauces, ketchups, salad dressings where it contributes to the flavour of the food and also acts as a preservative. Today acetates of sodium, potassium and calcium are used in the bakery industry to prevent ropiness and growth of moulds in bread and other baked foods.
Benzoic acid is used in the form of sodium salt and sodium benzoate. It is one of the most widely used chemical food preservatives in acidic foods such as fruit juices, squashes, fruit cocktails, jams, jellies, pickles, sauerkraut, etc. Sodium benzoate inhibits the growth of yeast to a larger extent than moulds and bacteria. Other chemical derivatives of benzoic acid used as food preservatives are alkyl esters of p-hydroxy benzoic acid commonly known as parabens. These are effective inhibitors of moulds and yeasts but are relatively ineffective against bacteria.
Sorbic acid is generally considered non-toxic and is used along with its salt – potassium sorbate as a preservative in cheese, baked products, fruit juices, wines, pickles, high moisture dehydrated fruits, etc. They inhibit the growth of moulds and yeasts.
Propionic acid and its salts, sodium and calcium propionates exert antimicrobial activity against moulds and some bacteria. They are used extensively in the bakery industry as they not only inhibit moulds effectively but are also active against the Bacillus mesentericus that causes ropiness in bread.
Epoxides are cyclic ethers that destroy all forms of microorganisms including spores and viruses. The epoxides used as preservatives are ethylene oxide and propylene oxide. Their use in food preservation is limited to dry items such as nuts and spices.
Sulphur dioxide gas has been used for many centuries as a fumigant and wine preservative. Today it is used as a chemical food preservative in gaseous form or in powder form as sulphite, bisulphite and metabisulphite salts of sodium and potassium in the preservation of a wide variety of foods. These chemicals inhibit the growth of yeasts, moulds and bacteria and are used to preserve dry fruits, vegetables and semi processed fruit products, etc. Sulphur dioxide is also used to prevent enzymatic and non-enzymatic browning reactions in foods. When used in recommended concentrations in food, sulfur dioxide, sulfites, bisulfites and metabisulfites are GRAS; however, a small number of individuals are sensitive and develop hives, nausea, diarrhoea, shortness of breath and asthma after consuming foods containing even tiny amounts of these substances.
(The writer is a consultant nutritionist with 19 years of experience, practicing at Panaji and can be contacted on firstname.lastname@example.org)