Polyphenol polymerisation involvement in apple superficial scald
M. V. Piretti, G. Gallerani and U. Brodnik
Postharvest Biology and Technology Vol: 8 Issue: 1 Pages: 11-18.
1996
บทคัดย่อ
In Granny Smith apples scald injury progression is accompanied by a progressive decrease of all types of oligomeric polyphenols, with complete disappearance in the brown skin patches where damage reaches a maximum intensity. To tentatively explain the disappearance of quercetin glycosides we proposed a connection between the oxidation of farnesene and the reduction of quercetin moieties to flavan-3,4-diols, followed by an oxidative coupling of the latter compounds to polymeric proanthocyanidins. The data we obtained in the course of the present investigation show that the extractable polymeric polyphenol fraction also decreases during scald progression, until it completely disappears when fruit damage reaches maximum intensity. We show that the latter finding is the consequence of a process through which the new polymeric polyphenols, probably formed as we supposed, are irreversibly bound to polymeric matrices, such as proteins, in brown apple skin. Thus we can confirm our previous hypothesis of the reduction of quercetin-aglycone to flavan-3,4-diol followed by a production of polymeric anthocyanidins. The interaction of the latter with the polyphenoloxidases when the tissue integrity is damaged produces brown patches on the skin, which are characteristic of scald damage. An irreversible covalent bond between the new polymeric proanthocyanidins and structural proteins of the apple skin inhibits the extraction of the former by methanol.