Monitoring the apple polyphenol oxidase-modulated adduct formation of phenolic and amino compounds

Treatment of a Braeburn apple half with proline and 4-methylcatechol. A freshly cut apple was washed with distilled water and treated with 0.5 M l-proline solution followed by 25 mM 4-methylcatechol solution. After a few minutes the coloration changed to pink, documenting the formation of PPO mediated proline adducts.