in the place of the polyphenols and when enough ascorbic acid is present, enzymatic activity will be inhibited. (Paul and Palmer, 1972) With insufficient amounts, however, it also can be destroyed with prolonged exposure to air, light, high pH levels, and heat. (McGee, 1984) In some foods, the acid may also lower pH enough to interfere with the browning enzyme. (Bennion, 1995)

Sodium bisulfite, and other sulfites, work to block the enzymatic browning reactions by combining with highly reactive o-quinones to produce less reactive diphenols. It also works as a chelating agent to complex with copper in PPO and inhibit browning by preventing participation in browning reactions. (Sapers, 1993) Caution is taken when using sulfites because many individuals have allergic reactions, especially asthmatics.

Citric acid creates highly acidic conditions; as enzymes are pH dependent and most effective at pH 5-7, anything that lowers the pH below 2.5-2.7 will effectively inhibit the enzyme. (Paul & Palmer, 1972) The problem with citric acid is that it may cause off-flavors in some fruits and vegetables.

Sodium chloride (table salt) interferes with enzyme activity. Chloride ions retard the browning reaction in such fruits as apples but is only temporary. The concentrations needed for permanent inhibitions would make the fruit inedible.

Sugars, syrups and gums may serve to inhibit browning by coating fruits and impenetrable by oxygen. Dipping in water may also inhibit browning temporarily this way.

Chilling fruits or vegetables below 40C, the optimum temperature for enzymatic activity, will retard browning. But freezing won't permanently inhibit browning and once the product returns to around 40C, browning rate will increase as freezing breaks cell structure and exposes more surfaces to air.

Blanching causes tissues to shrink and drive off oxygen so oxidation is less likely to occur. The enzyme is also destroyed this way. But flavor and texture can be affected adversely.

ENZYMATIC BROWNING INHIBITORS: FACTORS WHICH INTERFERE OR PREVENT POLYPHENOLOXIDASE FROM OXIDIZING PHENOLIC COMPOUNDS IN TISSUES AND CREATING BROWNISH POLYMERS. June 3, 1996 by Connie Robertson and Gina Christensen

Updated: Sunday, March 30, 2008.