Antioxidant Activities and Antioxidative Components in Extracts of Alpinia galanga (L.) Sw.

Abstract

Galangal extracted using 50% ethanol in water was studied for its antioxidant activity and composition in comparison with two other samples based on a water extract and the essential oil. The antioxidant activities were determined using the 2,2-diphenyl-1-picrylhydrazyl (DPPH) and oxygen radical absorbance capacity (ORAC) methods. The ethanolic extract showed the highest DPPH free radical scavenging ability as well as the highest ORAC value when compared to the water extract and the essential oil. The IC50 values of the galangal ethanolic extract (10.66 mg/ml), water extract (55.48 mg/ml) and essential oil (455.43 mg/ml) were higher than those of α-tocopherol (1.45 mg/ml) and butylated hydroxyanisole (BHA; 0.41 mg/ml). The results indicated that the antioxidant activities of galangal extracts were lower than that of BHA, the commercial synthetic antioxidant generally used in food. The ethanolic extract contained the highest concentrations of total phenolic compounds (31.49 mgGAE/g) and flavonoids (13.78 mgCE/g). The water extract and the essential oil had a total phenolic content of 8.25 and 5.01 mgGAE/g and a total flavonoid content of 1.48 and 0.20 mgCE/g, respectively. Antioxidants in the galangal essential oil, namely, methyl eugenol (4,130.38 μg/g), chavicol (2,390.45 μg/g), and eugenol (728.30 μg/g) were found in its volatile fraction. The water extract contained mainly myricetin (14.60 mg/g extract) and an unknown phenolic compound. The major antioxidants in the ethanolic extract were 1´-acetoxycavichol acetate (10.56 mg/g extract), catechin (1.74 mg/g extract), and three unknown subtances. In addition to the phenolic compounds, 1´-acetoxycavichol acetate (ACA) could play an important role in the antioxidant activity of galangal. The ethanolic extract of galangal was also advantageous as an antioxidant in food due to its mild odor compared with the essential oil.