Comparative antioxidant and antimicrobial activities of phenolic compounds extracted from five Hypericum species

Phenolic compounds were extracted from five Hypericum species (H perforatum, H oblongifolium, H. monogynum, H. choisianum and H. dyeri Redher) using ethanol. The crude extract (called fraction 1) was then fractionated using re-extraction to water (fraction 2), ethyl acetate (fraction 3), and acetone (fraction 4). The final residue was marked as fraction 5. The content of total phenolics in the fractions ranged from 21 mg of gallic acid equivalents per g (fraction 5 of H. dyeri) to 100 mg of gallic acid equivalents per g (fraction 5 of H. choisianum). Phenolic compounds present in the fractions showed antioxidant and antiradical properties investigated using DPPH radical scavenging activity, molybdate method, and reducing power. The strongest antiradical properties were noted for fraction 3 of H. choisianum ([EC.sub.50]=11.2 µg/mL), whereas the weakest was for fraction 5 of H. dyeri ([EC.sub.50]= 139.2 µg/mL). Fractions 1 and 5 of H. dyeri showed good antibacterial activity against Escherichia coli, while fractions 3-5 of H. perforatum were active against Staphylococcus aureus and Pseudomonas aeruginosa. Fractions 1-4 of H. perforatum were found most active against Helminthosporium maydis as determined by antifungal screening. Key words: Hypericum monogynum, H. oblongifolium, H. perforatum, H. choisianum, H. dyeri, phenolic compounds, antioxidant activity, antimicrobial activities