Antioxidant activity of Stevia rebaudiana

The antioxidant activity against sardine oil and linoleic acid of hot water extract from Stevia rebaudiana was compared to DL-α-tocopherol (DL-α-Toc), butyl hydroxy anisol and green tea extract. The sardine oil oxidation was assessed from the formation of peroxides. The concentration of odor components was measured by a portable type odor concentration meter equipped with a metal oxide semiconductor. Linoleic acid oxidation was assessed by the ferric thiocyanate method. Stebia rebaudiana extract effectively inhibited hydroperoxide and volatile component formations in sardine oil. The oxidation was more effectively inhibited by the hot water extract from S. rebaudiana than DL-α-Toc or green tea extract at the same concentration in sardine oil. Additive effects were observed when the extract was mixed DL-α-Toc or citric acid. Some effective fractions were separated from the extract by dialysis, column chromatography and thin layer chromatography. Some of the antioxidant fractions were polyphenolic compounds. The component which showed the highest antioxidant activity contained large amounts of potassium.