engleski

Polyphenol oxidase from Croatian traditional apple varieties and its role in anthocyanins degradation during storage

The enzyme polyphenol oxidase (PPO) catalyses the oxidation of phenolic compounds into highly reactive quinones. Polymerization of PPO-derived quinones causes the postharvest browning of cut or bruised fruit. In this work, we investigate the activity of PPO and its role in anthocyanins degradation during the storage of Croatian traditional apple varieties. Polyphenol oxidase was extracted from five Croatian traditional apple varieties (‘Austrougarka’, ´Božićnica´, ´Čelenka´, Ílzer Rosenapfel´ and ´Kraljevčica´) after harvest and after three months of storage. Furthermore, the activity of polyphenol oxidase (POA) was determined with the substrate catechol by a continuous spectrophotometric test at 410 nm. The monomeric anthocyanin pigment content of extracts was determined using the pH-differential method. After harvest, the highest activity of polyphenol oxidase was determined in ´Božićnica´ (302%) and the lowest in ´Čelenka´ (172%). During storage, the activity of polyphenol oxidase was decreased in four apple varieties while in ´Ílzer Rosenapfel´ the activity of polyphenol oxidase was increased. After three months of storage, the highest activity of polyphenol oxidase had ´Ílzer Rosenapfel´ (349%) and the lowest had ´Čelenka´ (171%). Considering anthocyanins, the highest content of anthocyanins after the harvest had ´Čelenka´ (48.09 mg/L) and the lowest had ´Kraljevčica´ (3.0 mg/L). The highest content of anthocyanins after three months of storage had ´Čelenka´ (47.59 g/L) and the variety without anthocyanins after storage was ´Ílzer Rosenapfel´. The increase of polyphenol oxidase activity during storage caused degradation of anthocyanins in Ílzer Rosenapfel´ apple variety which leads to discolouration. This is due to the ability of polyphenol oxidase and polyphenol peroxidase to break covalent bonds between anthocyanin glycosides. In conclusion, varieties with the highest activity of polyphenol oxidase had the lowest content of anthocyanins and vice versa.

polyphenol oxidase ; storage ; anthocyanins

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