Antioxidant activity of phenolic fractions of rapeseed

Extract of rapeseed in 80% methanol was prepared. Three fractions (I-III) were separated from the extract on a Sephadex LH-20 column using ethanol as the mobile phase. The antioxidant activity of fractions was investigated using a beta-carotene-linoleate model system and enhanced chemiluminescence (ECL) and photochemiluminescence (PCL) methods. Scavenging effect on DPPH radical and reducing power of the extract were examined, UV spectra recorded and the content of total phenolics determined. The highest content of total phenolics (176 mg/g) was present infraction III; the content of total phenolics found infraction I was the lowest (78.6 mg/g). UV spectra indicated that derivatives of phenolic acids were dominant in all fractions. Results of beta-carotene-linoleate model system indicated that antioxidant activities of separated fractions correlated well with their content of total phenolics and were in the order of III > II > I, similar to the scavenging effect on DPPH radical. The reducing powers of separated fractions was in the order of III > I > II, but differences were minor. Fractions II and III exhibited strong antioxidant activities as measured by the chemiluminescence (ECL and PCL) methods.