Roles of o-quinones and their polymers in the enzymic browning of apples

• Published in: Phytochemistry (Oxford) Vol. 29; no. 2; pp. 435 - 440
• Main Authors: Rouet-Mayer, Marie-Aude, Ralambosoa, Justin, Philippon, Jean
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier Ltd 1990; Elsevier
• Subjects: apple fruit; ascorbic acid; Biological and medical sciences; catechol oxidase; enzymic browning; Fundamental and applied biological sciences. Psychology; HPLC; o-quinone; phenolic oxidation; Pirus malus; Plant physiology and development; polymerization; Rosaceae; enzymic browning; polymerization; Pirus malus; apple fruit; ascorbic acid; catechol oxidase; phenolic oxidation; Rosaceae; o-quinone; HPLC; Vegetals; Ascorbic acid; Enzyme; Quinone; HPLC chromatography; Polymerization; Catechol oxidase; Malus domestica; Browning; Dicotyledones; Angiospermae; Spermatophyta; Oxidation; Ultraviolet visible spectrometry
• ISSN: 0031-9422; 1873-3700
• DOI: 10.1016/0031-9422(90)85092-T

Enzymic browning and the bleaching produced by the addition of ascorbic acid have been studied simultaneously in crushed apple tissue and in pure solutions of (+)-catechin and chlorogenic acid. Spectrophotocolorimetry was used to study crushed apple tissue. The compounds formed by secondary reactions were darker than their source o-quinone in the case of (+)-catechin, and lighter in the cases of chlorogenic acid and crushed apples. The o-quinone of (+)-catechin was very unstable, and that of chlorogenic acid less so. Instability increased at higher pH. Gradual secondary bleaching followed the instantaneous bleaching brought about by addition of ascorbic acid to crushed apple and to an equimolar solution of chlorogenic acid and (+)-catechin. This phenomenon was not seen with pure solutions of o-diphenol. The o-quinone of chlorogenic acid was more intensely coloured than the quinones derived from (+)-catechin [ɛ (λ) = 2100 and 1300, respectively, at pH 4]. The oxidation products of (+)-catechin were separated by HPLC. o-Quinone was identified among the separated peaks. The area under the o-quinone peak rose and then fell as the peaks of the secondary products increased in size and number. The first polymerized products were partially reduced by ascorbic acid at the start of the reaction.