Banana polyphenol oxidase: occurrence and change of polyphenol oxidase activity in some banana cultivars during fruit development

Occurrence of polyphenol oxidase (PPO, o-diphenol: oxygen oxidoreductase, EC.1.10.3.1) in the fruits of nine cultivars of banana (Musa spp.) commercially cultivated in China was investigated. All banana fruits peel and pulp tested had PPO activity, and all PPO strongly oxidized dopamine and 3-hydroxytyramine (tyramine). However, very weak and/or no oxidative activity was recognized on such trihydroxybenzenes as phloroglucinol and gallic acid. Similar substrate specificity of PPOs toward phenolic compounds was detected in the pulp and peel of all banana cultivars tested. The specific PPO activities toward dopamine for pulp were between 5.11 and 25.72, and those of peel were between 6.75 and 26.86 units/mg protein. However, PPO activities toward dopamine in the pulp and peel of AAA and AA genome group bananas were higher than those of ABB and AAB groups. The changes of pulp and peel PPO activities during fruit development were also determined in the three banana cultivars. During this development a remarkable decrement in pulp and peel PPO activities was found in all banana cultivars used.