ANTIOXIDANT PROPERTIES OF THE EXTRACT AND SUBFRACTIONS FROM OLD LEAVES OFTOONA SINENSISROEM (MELIACEAE)

Abstract

ABSTRACT The methanolic crude extract and four subfractions (hexane fraction, ethyl acetate fraction, n-butanol fraction and aqueous fraction) of old leaves of Toona sinensis (L.T.S.) were prepared by sequential partitioning, and their antioxidant activities were evaluated using 1,1-diphenyl-2-picrylhydrazyl (DPPH) free radical-scavenging assay, ferric reducing ability of plasma (FRAP) assay, β-carotene bleaching method and stabilizing soybean oil. The results indicated that old L.T.S. possess powerful antioxidant activity and could prevent oxidation of soybean oil. The ethyl acetate-soluble fraction had the strongest antioxidant activity, with high levels of total flavonoids content (108.57 ± 4.21 mg rutin equivalents/g), total phenol contents (262.09 ± 1.93 mg gallic acid equivalents/g), reductive activity (467.53 ± 6.75 mg ascorbic acid [Vc] equivalents/g), FRAP value (10578.71 ± 149.00 µM FRAP/g) and strong DPPH radical scavenging capacity, respectively. These results suggest that the extract of old L.T.S. is a promising natural alternative to synthetic antioxidants as functional food ingredient and a natural antioxidant in soybean oil. PRACTICAL APPLICATIONS Toona sinensis, the popular tree vegetable, is widely cultivated in China. The fresh young leaves and shoots of this plant are nutritious. Every year there are quite a lot of old leaves left and/or discarded after these shoots are consumed. Extracts from old leaves of T. sinensis showed strong antioxidant activity in this study. The strong antioxidant capacity is mainly contributed by the high contents of total flavonoids and total phenolic compounds. Therefore, the total flavonoids and total phenolic compounds could be developed into ingredients of functional foods with antioxidant capacity and as a natural antioxidant for soybean oil.