Antioxidant activity of extracts from the leaves of Smallanthus sonchifolius

Background & Aims: Yacon (Smallanthus sonchifolius, Asteraceae) is a native Andean plant, cultivated for its tubers throughout South America. The leaves are used in folk medicine as a medicinal tea for hypoglycemia. This paper describes the antioxidant activity of various extracts from S. sonchifolius leaves for their content of phenolic components. Methods: The dried leaves were extracted in several ways. Two fractions were selected for their high content of phenolic compounds and analyzed by RP-HPLC. The antioxidant activity of these fractions was tested in 1,1-diphenyl-2-picrylhydrazyl (DPPH) and xanthine/XOD superoxide radical scavenging assays, as inhibition of lipoperoxidation of subcellular membranes and as protective activity against oxidative injury of rat hepatocytes in primary cultures. Results and conclusions: The presence of protocatechuic (2.5 and 0.12 mg/g), chlorogenic (9.9 and 1.7 mg/g), caffeic (14.7 and 0.09 mg/g) and ferulic (traces) acids were determined in the two fractions. Both fractions showed potent antioxidant activity in DPPH (IC50 = 16.1 ± 3.4 and 24.3 ± 2.7 mg/ml) and xanthine/XOD superoxide radical scavenging (42.0 ± 20.3 and 34.3 ± 11.4 SOD equivalents (U/mg)) tests, they inhibited the lipoperoxidation of rat liver subcellular membranes and they protected rat hepatocytes against oxidative injury. Our results may predetermine the use of S. sonchifolius leaves in human diet as a potential remedy in the prevention of chronic diseases caused by radicals, e. g., arteriosclerosis.