Effect of polymerization on the antioxidant capacity of anthocyanins in Roselle

The aim of this study is to investigate how antioxidant capacity [1,1-diphenyl-2-picrylhydrazyl radical (DPPH) scavenging effect, ferric reducing ability of plasma (FRAP) and Trolox equivalent antioxidant capacity (TEAC)] changes during anthocyanin degradation and brown pigment formation. Roselle anthocyanin model system was used to compare changes of three patterns of anthocaynin (monomeric, co-pigmented and polymeric), colour density and degradation index (DI). After heating, Roselle anthocyanins were separated into three fractions by gel filtration to elucidate the contribution of each fraction to the antioxidant capacity. In the model system, colour density, FRAP activity, monomeric and co-pigmented anthocyanins decreased after heating, while DI, polymeric anthocyanins, and DPPH scavenging effect increased after heating. Statistical analysis showed polymeric or monomeric anthocyanins were positively related to DPPH scavenging effect or FRAP activity with respective coefficients of 0.97 and 0.84. Further purification using Sephadex G25 separate the pigment into three fractions, I, II and III, according to their decreasing molecular size. Results indicated that the contribution percentage of DPPH scavenging effect of fraction II increased after being heated, while the contribution in FRAP activity of fraction III dropped. This suggested that fractions II and III might be the major contributors for DPPH scavenging ability and FRAP activity, respectively. (C) 2004 Published by Elsevier Ltd.