The Effect of Amino Acids and Other Several Substances on the Autoxidation of Catechins

Abstract

The aqueous solutions of catechins exhibited a remarkable peak at 270-280 mμ in ultraviolet area, but had not any adsorbance in visible area. These colorless solutions turned to yellowish or brownish on standing a long time by autoxidation. The rate of color development was very slow in general although there was considerable differences in attitude with each catechin. The colored solutions were classified approximately into two groups from the shape of spectra, which had not maximum and exhibited declining curve from 350 mμ to 500 mμ (A) (catechins containing pyrogallol group in molecule), and had maximum at 380-390 mμ (B) (catechins containing only catechol group).
Furthermore, (-)-epicatechin presented a different spectrum (λ max. 4300 mμ) (C) from above both spectra under addition of basic substances or amino acids in an earlier stage. And then it exhibited similar spectrum to (B) in a later stage.
The presence of amino acids during the autoxidation of catechins caused a gradual promoting effect generally with increasing of their basic nature. This promoting effect by adding amino acids was not observed under acidified condition. It was supposed that this enhancement was resulted mainly from alkalinity, but somewhat from the basic function of amino radical for reason of promoting effect by theanine or aspartic acid alone. Pyrogallol catechin was oxidized more speedy, but colored less than catechol catechin.