Antioxidant activity of Bupleurum kaoi Liu (Chao et Chuang) fractions fractionated by supercritical CO2

Bupleurum kaoi Liu was mixed with ethanol at a ratio of 1:4 (v/w) for 24 h to yield ethanol extract. Extract was further fractionated using supercritical CO2 (SC-CO2) under the following operating conditions: 40°C and a pressure of 20, 15, 10 or 5 MPa into R, F1, F2 or F3 fractions, respectively. To assess the selectivity of the fractionation, four fractions were characterized in terms of total phenol contents, the antioxidant abilities and the antioxidant mechanisms. Experimental results indicated that fractionation altered the composition distributions and the antioxidant activities, including antioxidant ability, reducing power and the scavenging capacity of DPPH, superoxide, and hydroxyl radicals. The antioxidant activities increased with fraction concentrations. The scavenging effect on DPPH of B. kaoi L. fractions at 10 g/l was R (53%), F1 (65%), F2 (71%), and F3 (76%), respectively. At a concentration of 5 g/l, all fractions can inhibit the O2·-formation by over 50%. Fractions R, F2 and F3 at concentrations of 3 g/l can trap over 50% of the OH groups. Notably, this in vitro study of antioxidant effects demonstrated that antioxidant activities were correlated well with the contents of phenol compounds. F3 fraction, contained the highest levels of total phenol contents, was the best inhibitor of lipid peroxidation and scavengers of DPPH, O2·- and ·OH radicals.