Hydrolyzable tannins as antioxidants in the leaf extract of eucalyptus globulus possessing tyrosinase and hyaluronidase inhibitory activities

Abstract

The aqueous ethanolic extract of Eucalyptus globulus leaves has been used as an antioxidant in food additives. From the extract, five ellagitannins and four gallotannins were isolated as the major antioxida- tive components. Heterophylliin A,l,3-di-O-galloyl-4, 6-hexahydroxydiphenoyl-β-D-glucose, 1,2,4-tri-O-galloyl-β-D-glucose, 1,2,3, 6-tetra-O-galloyI-β-D-glucose and l,2,4,6-tetra-0-galloyl-β-D-glucose are the first to be isolated from this plant. These hydrolyzable tannins exhibited more potent antioxidant activity (superoxide dismutase-Iike activity) than ascorbic acid, as well as inhibitory activities against tyrosinase and hyaluronidase. Thus, the eucalyptus leaf extract may be useful in food and cosmetics for not only an- tioxidation, but also anti-melanogenesis, anti-allergy and anti-inflammation.