Structure of green pigment formed by the reaction of caffeic acid esters (or chlorogenic acid) with a primary amino compound

A marked greening observed in some foods such as sweet potato, burdock, and others during food processing was shown to be due to green pigment formati on by the condensation reaction of two molecules of chlorogenic acid or caf feic acid ester with one molecule of a primary amino compound under aeratio n in alkaline solution. Reduction of the green pigment by ascorbic acid or NaBH4 gave a yellow product, which readily turn green and then blue in air. The reduced and acetylated product of the green pigment was identified to be a novel trihydroxy benzacridine derivative, and the yellowish ethanol so lution of this product immediately turned green upon addition of butyl amin e or diluted alkali. Therefore, the green pigment was assumed to be an oxid ized quinone type product of trihydroxy benzacridine. This identification o f the structure was supported by the correspondence of the measured absorpt ion spectra with those calculated by the molecular orbital method. A possib le charge transfer complex between products of different oxidation steps in green solution was proposed.