Oxidation and epimerization of epigallocatechin in banana fruits.

To examine the metabolism of proanthocyanidins in banana fruit, (-)-epigallocatechin was treated with the homogenate of the fruit flesh to yield (-)-gallocatechin and an oxidation product, 1-(3,4,5-trihydroxyphenyl)-3-(2,4,6-trihydroxyphenyl)-2-hydroxy-1-propan one. The latter product is a stable form of a key intermediate in the oxidative metabolism of flavan-3-ols, and is also related to the biogenesis of A-type proanthocyanidins. In addition, treatment of the reaction mixture with o-phenylenediamine afforded monomeric and dimeric phenazine derivatives generated by condensation with the o-quinone form of the oxidation product.