Proposed mechanism for the degradation of pelargonidin 3-glucoside by caffeic acid o-quinone

Caffeic acid o-quinone (CQ) was prepared by oxidation of caffeic acid with o-chloranil in organic media. The reaction between the purified CQ and pela rgonidin 3-glucoside (Pg 3-glc, non-o-diphenolic anthocyanin) was monitored by HPLC and spectrophotometric analysis. Quantitative analyses were perfor med to establish the stoichiometry of the reactions. The results showed tha t Pg 3-gic reacted with the hydroxycaffeic acid o-quinone formed by dismuta tion of CQ in aqueous media. This reaction led to the formation of condensa tion products with a stoichiometry close to 1:1. The degradation products w ere isolated by gel filtration on Sephadex G-25. The UV-vis spectra and che mical analysis of the degradation products suggested that they contained bo th caffeic acid (or secondary products of oxidation) and anthocyanin moieti es. HPLC analysis showed that the purified fractions contained several degr adation products. (C) 2001 Elsevier Science Ltd. All rights reserved.