Anti-Browning

• Two types of browning are Non-Enzymatic Browning and Enzymatic browning
• Non-Enzymatic browning are Maillard reaction, Caramelisation and Oxidation of ascorbic acid
• Enzymic browning is oxidation reaction between; Phenols and the enzyme phenolase (polyphenol oxidase - PPO) are found in the cells of the apple, and when these are exposed to oxygen in the air.
• Phenol + PPO > oxidises the phenolic compound = orthokuinone will form a polymer and produce brown melanin
• PPO active in range pH 5-7
• Anti-browning agent; freezing, heat, container free-O2, sodium sulfite (remove O2 from water), Thiourea, Ascorbic acid (lower pH, reducing agent)
• Melanin is the pigment that gives human hair, skin and eyes their colour.
• Enzymes are special proteins which can speed up chemical reactions and act as biological catalysts
• Enzymes can cause fruit to ripen and over-ripen, which gives the fruit a brown colour.
• To stop the oxidative reaction, the phenolase enzymes need to be denatured.  This could be done by using heat and acids
• Lemon juice contains an acid which can stop enzymes working properly as enzymes often work best at a certain pH.
• oxidation can affect the nutrient content of a fruit or vegetable
• PPO is deactivated below pH3