Evaluation of antioxidant and DNA protection activities in the extracts of Oncidium flower

Oncidium is a tropical species of the family Orchidaceae. The Oncidium, also named as the Dancing Lady Orchids, is commercialized as cut flowers in Taiwan. The aim of the present study was to examine the antioxidant and DNA protection activities which could be applied for the anti-ageing cosmetic products.The aqueous extract from the Oncidium flower was used in this study. Antioxidant activities were measured by both 1, 1-diphenyl-2-picrylhydrazyl radical (DPPH·) scavenging and 2, 2-azino-bis (3-ethylbenz- thiazoline-6-sulfonic acid) (ABTS·+) decolourisation methods. To further evaluate the effect of Oncidium flower extracts on UV induced DNA damages, the DNA protection assay was employed. Oncidium flower extracts had effective DPPH bleaching activity and ABTS·+ radical scavenging activity in a concentration dependent manner. Furthermore, the Oncidium flower extracts to inhibit the oxidative DNA damages were assessed by measuring the conversion of supercoiled pUC119 plasmid DNA to the linear forms. UV irradiation of DNA with hydrogen peroxide resulted in the formation of linear forms of DNA, indicating double-strand DNA breaks. Addition of the Oncidium flower extracts to DNA resulted in a partial inhibition of the conversion of supercoiled DNA to linear forms, indicating that the Oncidium flower extract was able to protect plasmid DNA against hydroxyl radical induced oxidative damage. The inhibition of hydroxyl radical induced DNA strand breaks by Oncidium flower extracts exhibited a concentration dependent relationship.