Effect of drying processes on prenylflavonoid content and antioxidant activity of Epimedium koreanum Nakai

Abstract

Epimedium koreanum Nakai is a famous Chinese herbal medicine for the treatment of impotence, osteoporosis, immune suppression and cardiovascular diseases. Drying is the most common and fundamental procedure in post-harvest processing of E. koreanum, which contributes to the variations of flavonoid content, especially prenylflavonoids, the bioactive components. In present study, effect of drying processes on flavonoid content and antioxidant activity were investigated. High performance liquid chromatography coupled with diode-array detection and electrospray ionization quadrupole time-of-flight tandem mass spectrometry methods were employed. Twenty seven compounds were identified and 11 of them, including eight prenylflavonoids and three other types of flavonoids, were further quantified. The antioxidant activity of E. koreanum was evaluated by the 2,2-diphenyl-1-picrylhydrazyl free radical scavenging method. The results showed that content of the eight prenylflavonoids exhibited significant variations after different drying processes, especially icariin and baohuoside I. The variation tendency of antioxidant activity was positively correlated with the content of total flavonoid, afzelin and icariin.

Keywords: Antioxidant activity; Drying process; Epimedium koreanum Nakai; Prenylflavonoid; Quantitative analysis.

Fig. 1

Chemical structures of the 11 flavonoids. Compounds 1–8 are eight prenylflavonoids and compounds 9–11 are three other types of flavonoids.

Fig. 2

HPLC chromatograms of standard compounds (A) and sample extract (B). Fig. 2B was the HPLC chromatogram of the sample drying by method 12. The injection volumes of the standard mixture (A) and the sample extract (B) were both 10 μL. The concentrations of the standards (A) were as follows: epimedin A (1), 0.076; epimedin B (2), 0.107; epimedin C (3), 0.156; icariin (4), 0.236; baohuoside I (5), 0.057; korepimedoside C (6), 0.192; epimedokoreanoside I (7), 0.255; korepimedoside B (8), 0.177; hyperoside (9), 0.117; quercitrin (10), 0.149; afzelin (11), 0.0895 mg/mL. Concentration of the extract (B) was 2.0 mg/mL.

Fig. 3

Content of eight prenylflavonoids (A) and three other types of flavonoids (B). The results were presented as the mean value ± standard deviation of three separate experiments.

Fig. 4

Content of icariin and total flavonoid. The content of icariin was determined using an HPLC-DAD method. The total flavonoid content was measured on a Shimadzu UV-2401 spectrophotometer. The results were presented as the mean value ± standard deviation of three separate experiments.

Fig. 5

Base Peak Chromatogram (BPC) of the HPLC-MS analysis of the extract of E. koreanum. The BPC of the extract was the sample drying by method 10. Concentration of the extract was 1.0 mg/mL. The injection volume was 5 μL. Intens = Intensity.