Separation and Identification of the Active Ingredients in Piper nigrum L. Leaves and Analysis of Their Antioxidant Activity
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Abstract:
The leaves and fruit of Piper nigrum Linnaeus (black pepper)exhibit antioxidant activities; the leaves also possess anti-atherosclerotic properties, and the removal of black pepper leaves can increase the yield of pepper fruits. However, the active components in the leaves of Piper nigrum L. were not clear. In order to provide a theoretical basis for the exploitation of Piper nigrum leaves, the antioxidant activity was analyzed by oxygen radical absorbance capacity (ORAC). The results indicated that the ORAC value of the Piper nigrum leaves was 3639.05 μmol TE/g, which was greater than that of the Piper nigrum fruits (fresh, black, and white). Through serial solvent extractions, the ethanol extract of Piper nigrum leaves was determined to have the highest ORAC value. Using the ORAC detection method as the tracing method for the separation and identification of antioxidative components, the active target compounds were isolated after successive extractions of the ethanol extracts of Piper nigrum leaves, followed by silica gel chromatography (Sephadex LH-20 resin), gel-filtration chromatography, reversed-phase chromatography, thin-layer chromatography, and high-performance liquid chromatography. The identification and characterization experiments carried out using nuclear magnetic resonance spectroscopy (NMR) and mass spectrometry (MS) confirmed that hinokinin and rhoifolin-two active ingredients with high antioxidant activities-were separated from Piper nigrum leaves, and their ORAC values were 16070 μmol TE/g and 10823 μmol TE/g, respectively.
