Antioxidants of Purple and White Greater Yam (Dioscorea alata L.) Varieties from the Philippines


Angelo Josue M. Lubag, Jr.§, Antonio C. Laurena and Evelyn Mae Tecson-Mendoza*

Institute of Plant Breeding, Crop Science Cluster, College of Agriculture
University of the Philippines Los Baños, College, Laguna 4031 Philippines

*corresponding author: This email address is being protected from spambots. You need JavaScript enabled to view it./ This email address is being protected from spambots. You need JavaScript enabled to view it.

§Advanced Imaging Research Center, University of Texas Southwestern Medical Center
5323 Harry Hines Blvd. NE 4.2, Dallas, TX 75390-8568, USA



Aqueous methanolic (50% MeOH) extracts of the tubers (peel and flesh) of nine cultivars of greater yam (Dioscorea alata) were determined to have relatively high antioxidant activities among which two cultivars (Ubing upo, purple; LA 096, white) had activities as high as those of a-tocopherol and butylhydroxyanisole (BHA). The aqueous methanol extract of the purple variety was fractionated on XAD-2 column chromatography serially with water, 25% MeOH, 50% MeOH, 75% MeOH, 100% MeOH and acetone. High activities were found in the 50% and 75% MeOH fractions; these were dried and further subjected to semi- or preparative HPLC chromatography using Develosil column. Two major peaks were isolated with high antioxidant activities, P1 and P2. P1 was established to be a purple anthocyanidin with UV-Vis and 1H NMR spectral data that are very similar to alatanin C (Yoshida et al., Tetrahedron Lett. 32: 5579-80 (1991)). Initial results for P2 indicated its phenolic nature with a glucose moiety and a molecular weight of 306. Both P1 and P2 had antioxidant activities higher than those of butylated hydroxyanisole and a-tocopherol.



Antioxidants prevent oxidation and oxidative damage to cells by scavenging oxygen radicals or hydroxy radicals which have been implicated to attack polyunsaturated fatty acids in cell membranes giving rise to lipid peroxidation (Aust & Sringen 1982; Osawa et al.1990; Kaur & Perkins 1991; Ramarathnam et al. 1995). At high levels, this type of oxidation has been linked not only to aging but also to mutagenesis, carcinogenesis, atherosclerosis (Halliwell & Whiteman 2004; Addis & Warner 1991; Ramarathnam et al. 1995) and to diabetes (Mooradian et al. 1994; Wehmeier & Moorradian 1994).





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