Even though enzymatic browning can make foods become browning when cut, the same chemical reaction also develops the colours and tastes of tea, coffee, and chocolate that many people love.
When these fruits and vegetables are cut or sliced and exposed to air, the polyphenol oxidase (a substrate from a family of chemicals called polyphenols, and oxygen) catalyse oxidation of phenolics compounds to ortho-quinone compounds, which then polymerize, forming brown pigments.
Enzymatic browning can be slowed or stopped by removing or changing the chemicals required for the browning reaction. Several types of chemicals are used in the control of browning:
*Acidulant. Higher acidity, such as a pH below 4.0, inhibits the activity of the polyphenol oxidase enzyme. The moist commonly used is citric acid.
*Reducing agent. Ascorbic acid is probably the most widely used anti-browning agent and in addition to its reducing properties, it also slightly lowers pH. The reducing agent, sulfate, and its derivatives act as irreversible inhibitors of polyphenol oxidase.
*Chelating agents: such as EDTA which is a metalloenzyme containing copper in the active site. Other important chelating agents are kojic acid, citric acid E330.
*Complexing agents: cyclodextrins
*Enzyme inhibitors: 4-hexylsorcinol
*Other anti-browning agents: sodium chloride, honey, proteases, aromatic carboxylic acids
Chemical used to control enzymatic browning reactions
