Influence of Polyphenolic Contents on the Antioxidant Properties of Hibiscus sabdariffa Extract (HSE), Aged Garlic Extract (AGE) and Garlic Tablet (GT) in Vitro

Abstract

This study compared the antioxidant properties of Hibiscus sabdariffa extract (HSE), commercial aged garlic extract (AGE, Kyolic) and garlic tablet (GT). The results indicate that HSE, AGE and GT are effective antioxidant as xanthine/xanthine oxidase generated superoxide ions are significantly inhibited in the presence of 20% (v/v) diethyl ether extract of HSE, AGE and GT by 100%, 66.39% and 18.61% respectively, while uric acid production is not affected by AGE and GT. However, at 2.5% and 5.0% (v/v) reaction volumes, HSE significantly inhibits uric acid production by 9.5% and 33.0% respectively, and this suggests that components of HSE inhibit xanthine oxidase activity while AGE and GT scavenge superoxide. In addition, it is also found that the three extracts scavenge ABTS radical cations in dose-dependent manner. In all cell free assays, HSE is found to be more effective as an antioxidant when compared with AGE and GT under the same experimental conditions. Chromatographic and colorimetric analyses suggest that HSE has numerous different types of phenolic compounds with higher amount of phenolic compounds (14.9 mg/g) when compared with AGE (2.8 mg/g) and GT (3.6 mg/g) catechin equivalent respectively. Therefore, the effectiveness of antioxidant activities of these three extracts may be related to their phenolic content.