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.Keywords: banana (Musa spp.) cultivars, polyphenol oxidase, tyrosynase, development period Polyphenol oxidase (PPO, o-diphenol: oxygen oxidoreductase, EC.1.10.3.1) is a copper-containing enzyme which oxidizes phenolic compounds to produce undesirable browning during storage and processing of fresh fruits and vegetables. PPO has been widely studied in many fruits and vegetables to prevent the browning which results in the loss of their marketability (Kahn, 1977;Park et al., 1980;Park & Luh, 1985;Augustin et al., 1985;Tono et al., 1986;Fujita & Tono, 1979;Fujita & Tono, 1988;Fujita et al., 1991;Murata et al., 1992;Chilaka et al., 1993;Fujita et al., 1995;Castaner et al., 1996;Fujita et al., 1997;Ding et al., 1998). The PPO in banana (Musa sapientum L.) had been characterized (Palmer, 1963; Galeazzi & Sgabieri, 1981;Thomas & Janave, 1986;Yang et al., 2000;Yang et al., 2001), because a remarkable browning occurred in the pulp section. Many banana cultivars which fall into several genome groups are being cultivated in the world, however, little is known about the occurrence of PPO in them or on the change of PPO activity during development of the fruit. In the present study, determinations were made on the occurrence of PPO in nine banana cultivars commercially cultivated in China, and on the change of PPO activity during fruit development. Materials and MethodsFruit materials Banana fruits of the nine cultivars at the maturate stage for marketing were harvested from the experimental orchard of Guangxi Agricultural Vocation-Technical College and from a local farm in Nanning, China, placed in a plastic bag, and kept at room temperature to ripen the fruits for 2 to 3 days. The fruits at the same yellow-green and/or yellow-red stage were used as materials for our study.The cultivars, scientific name and genomic groups of bananas used were: Brazil Jiao (Musa cavendishii L.; AAA genome group), Nalong Jiao ( To determine the changes of PPO...

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