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Background: Protocatechuic acid (PCA) is a natural phenolic acid widely distributed in plants and is considered as an active component of some traditional Chinese herbal medicines such as Cibotium barometz (L.) J.Sm, Stenoloma chusanum (L.) Ching, Ilex chinensis Sims. PCA was reported to possess various pharmacological effects which may be closely correlated with its antioxidant activities. However, the antioxidant of PCA has not been investigated systematically yet. Methods: In the study, the antioxidant activities of protocatechuic acid were measured in vitro using various antioxidant assays including 1,1-diphenyl-2-picryl-hydrazyl (DPPH•), 2,2’-azino-bis (3-ethylbenzthiazoline-6-sulfonic acid) (ABTS+•), superoxide anion radicals (•O2-) and hydroxyl radical (•OH) scavenging activity, ferric ions (Fe3+) and cupric ions (Cu2+) reducing power, ferrous ions (Fe2+) and cupric ions (Cu2+) chelating activity, compared with the positive controls Trolox or BHT.Results: In all assays, PCA along with positive controls exhibited dose-dependently antioxidant ability. Comparing to a standard antioxidant Trolox, the relative antioxidant activity of PCA (i.e. the ratio of IC50(Trolox)/IC50(PCA) ) was calculated as 2.8, 2.3, 3.7, 6.1, 4.2, 1.0, 2.7, 1.5, respectively, for DPPH, ABTS, reducing power (Fe3+), reducing power (Cu2+), superoxide anion radical-scavenging, hydroxyl radical-scavenging, chelating ability (Fe2+) and chelating ability (Cu2+). Conclusion: Comparing to Trolox, PCA shows much more effective antioxidant activity in vitro in both lipid and aqueous media. Hence, it could therefore be used in pharmacological or food industry as a natural antioxidant. It may exhibit antioxidant activity by both chelating metal transition ions as well as by scavenging free radicals via donating hydrogen atom (H•) or electron (e).Keywords: Protocatechuic acid, antioxidant, reducing power, free radical-scavenging, chelating ability.
Li et al. (Sun,) studied this question.