Antioxidant Activity of C -Glycosidic Ellagitannins from the Seeds and Peel of Camu-camu ( Myrciaria dubia )

C-Glycosidic ellagitannins grandinin (1), vescalagin (2), castalagin (3), methylvescalagin (4), stachyurin (5), and casuarinin (6) were isolated from the 50% acetone extract of camu-camu (Myrciaria dubia) seeds and peel. These tannins exhibited antioxidant activities measured by 1,1-diphenyl-2-picrylhydrazyl (DPPH) and 2,2'-azino-bis-(3-ethylbenzothiazoline-6-sulphonic acid) (ABTS) assays, and the oxygen radical absorbance capacity (ORAC) assay. In the DPPH and ABTS assays, stachyurin exhibited the strongest antioxidant activity among the tannins, and the activities were stronger for tannins containing two hexahydroxydiphenoyl (HHDP) groups and a galloyl group than for tannins containing a nonahydroxyterphenoyl group and a HHDP group. The activity of vescalagin was stronger than that of castalagin, and a similar relationship was observed for stachyurin and casuarinin. Thus, the antioxidant activities of these tannins may depend on the conformation of the hydroxyl group at C-1 of the open ring d-glucose. However, in the ORAC assay, casuarinin exhibited the strongest activity, and the respective activities could not be explained by the structural rigidity or conformation of the C-1 hydroxyl group.