text: *Acidification − Browning enzymes, as other enzymes, are active at a specific range of pH. For example, PPO shows optimal activity at pH 5-7 and is inhibited below pH 3. Acidifying agents and acidity regulators are widely used as food additives to maintain a desired pH in food products. Acidulants, such as citric acid, ascorbic acid, and glutathione, are used as anti-browning agents. Many of these agents also show other anti-browning effects, such as chelating and antioxidant activities.
  *Antioxidants − Many antioxidants are used in food industry as food additives. These compounds react with oxygen and suppress the initiation of the browning process. Also, they interfere with intermediate products of the following reactions and inhibit melanin formation. Ascorbic acid, N-acetylcysteine, L-cysteine, 4-hexylresorcinol, erythorbic acid, cysteine hydrochloride, glutathione are examples of antioxidants that have been studied for their anti-browning properties.
  *Chelating agents − Polyphenol oxidase requires copper as a cofactor for its functionality, thus copper-chelating agents inhibit the activity of this enzyme. Many agents possessing chelating activity have been studied and used in different fields of food industry, such as citric acid, sorbic acid, polyphosphates, hinokitiol, kojic acid, EDTA, porphyrins, polycarboxylic acids, different proteins. Some of these compounds also have other anti-browning effects, such as acidifying or antioxidant. Hinokitiol is used in coating materials for food packaging.