Antioxidant activity of phenolic compounds from canola (Brassica napus) seed

The antioxidant activities of various extracts from canola (Brassica napus) seed were investigated using the DPPH assay, ABTS radical assay, and reducing power. An 80% methanol extract from canola seed was sequentially fractionated and separated according to the solvent polarity and Sephadex LH-20 chromatography, respectively. The antioxidant activities of various extracts and their total phenolic content (TPC) and total flavonoid content (TFC) were closely correlated, resulting in correlation coefficient values higher than 0.87. Of all extracts, the sub-fraction 3 had the highest TPC (462.3 mu g/mg) and TFC (75.4 mu g/mg) while it showed the lowest EC50 value (183.1 mu g/mL). The EC50 value of sub-fraction 3 measured using the DPPH radical assay was 1.3 times lower than that of butylated hydroxytoluene (BHT). The major free phenolic compound was trans-sinapic acid (193.4 mu g/mg) and sinapic acid derivatives identified as 1-O-beta-d-glucopyranosyl sinapate and 1,2-di-O-sinapoyl-beta-d-glucose in sub-fraction 3.