Sulfur free radical reactivity with curcumin as reference for evaluating antioxidant properties of medicinal Zingiberales

Rhizome extracts of some members of the medicinal Zingiberales are widely used in dietary intake as well as in the traditional system of medicine. Curcumin, the chrome orange-yellow coloring compound present in turmeric rhizomes, has long been known to possess antioxidant property. Crude methanol extracts of the rhizomes of 11 species-Alpinia allugbas, A galanga, Curcuma amada, C. caesia, C leucorrbiza, Hedycbium coronarium, H. coccineum, H. flavescens, Kaempferia galanga, Zingiber cassumunar, and Z officinale-were evaluated for their antioxidant properties using sulfur free radical reactivity with curcumin as a reference indicator. Sulfur free radicals (GS) are generated by irradiating 15 mM glutathione (GSH) solution using a 5100 Ci cobalt-60 gamma irradiator. As reference indicator for the reactivity with sulfur free radicals, we used the depletion of pure curcumin sample in vitro as determined by a simple spectrophotometric method. The addition of the supernatant from crude rhizome extracts to the reaction mixture significantly decreased the depletion of curcumin, indicating that these crude extracts possessed antioxidant properties. The relative curcumin protection by different crude extracts against GS- showed that Z cassumunar gave the highest degree of radioprotection. Our results reveal the potential medicinal use of rhizomes of medicinal Zingiberales as dietary agents.