Comparative Evaluation of the Antioxidant Capacities of Commonly Consumed Dietary Polyphenols

Dietary polyphenols are plant-derived secondary metabolites recognized as highly bioactive molecules. One of their most significant biological properties is their antioxidant potential. In the present study, the antioxidant capacities of commonly consumed dietary polyphenolic compounds were comparatively evaluated. Antioxidant activities were assessed using sing ferric reducing antioxidant power (FRAP) and 2,2-diphenyl-1-picrylhydrazy (DPPH) radical scavenging assays. Twenty-three polyphenol standards were classified into two primary groups, phenolic acids and flavonoids, each further divided into their respective subclasses, and their antioxidant capacities were examined in relation to structural features. Among the phenolic acids, gallic acid (11.29 ± 0.05 µmol Trolox equivalents/mg), protocatechuic acid (6.69 ± 0.04), syringic acid (5.76 ± 0.03), caffeic acid (4.76 ± 0.02), and ellagic acid (4.65 ± 0.07) exhibited the highest FRAP activities. Among the flavonoids, quercetin (5.98 ± 0.03), epicatechin (2.69 ± 0.02), and resveratrol (2.59 ± 0.01) were the most potent antioxidants. Compounds such as chlorogenic acid, ferulic acid, caffeic acid phenethyl ester (CAPE), rutin, and luteolin displayed moderate antioxidant activity, whereas p-hydroxybenzoic acid, pinocembrin, chrysin, daidzein, hesperetin, t-cinnamic acid, and myricetin showed markedly low activity. These results indicate that antioxidant capacity of polyphenols is strongly influenced by both the number and the positions of hydroxyl groups on their aromatic rings, highlighting the critical role of structural features in determining their redox potential.