Alkyl esters ofp-hydroxybenzoic acid (parabens) have been known to possess antimicrobial activity since the 1920s. Esterification of the carboxyl group of benzoic acid allows the molecule to remain undissociated up to pH 8.5, giving the parabens an effective range of pH 3.0 to 8.0 (36). In most countries, the methyl, propyl, and heptyl parabens are allowed for direct addition to foods as antimicrobials while the ethyl and butyl esters are approved in a limited number of countries.
The antimicrobial activity of p-hydroxybenzoic acid esters is, in general, directly proportional to the chain length of the alkyl component (8,36). As the alkyl chain length of the parabens increases, inhibitory activity generally increases. Increasing activity with decreasing polarity is more evident against Gram-positive than against Gramnegative bacteria (8). Parabens are generally more active against molds and yeast than against bacteria (8).
To take advantage of their respective solubility and increased activity, methyl and propyl parabens are normally used in a combination of 2-3:1 (methyl:propyl). The compounds may be incorporated into foods by dissolving in water, ethanol, propylene glycol, or the food product itself. The re-heptyl ester is used in fermented malt beverages (beers) and noncarbonated soft drinks and fruit-based beverages. Parabens are used in a variety of foods including baked goods, beverages, fruit products, jams and jellies, fermented foods, syrups, salad dressings, and wine (8).
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