Determination of Sinapic Acid Derivatives in Canola Extracts Using High-Performance Liquid Chromatography

A high-performance liquid chromatographic (HPLC) method with diode array detection (DAD) was used to determine the total phenolics, including sinapic acid derivatives in canola. Ten Western Canadian canola seeds, six other commodity canola seeds, their corresponding press cakes and meals were analyzed. Seeds of European 00 rapeseed and Brassica Juncea (Indian mustard) were included for comparison. Phenolic compounds were separated using a gradient elution system of water–methanol-ο-phosphoric acid solution with a flow rate of 0.8 ml/min. In addition to sinapine (SP) and sinapic acid (SA), sinapoyl glucose (SG) is reported in the methanolic extracts. The detection and quantification limits of these compounds were 0.20–0.40 and 0.50–0.80 μg/ml, respectively with recovery values over 98.0%. The content of total phenolics, SP, SA and SG in canola extracts ranged from 9.16 to 16.13, 6.39 to 12.28, 0.11 to 0.59 and 1.36 to 7.50 mg/g, respectively with significant differences among varieties

The Interactions Between Rapeseed Lipoxygenase and Native Polyphenolic Compounds in a Model System

The focus of the present research was to study inhibition of lipoxygenase activity by rapeseed native polyphenols and the interactions between those compounds and the enzyme. The enzyme and polyphenolic compounds (polyphenols, phenolic acids) were extracted from rapeseed (Brassica napus) varieties Aviso and PR45DO3. The total phenolic compounds concentration in tested rapeseed was 1,485–1,691 mg/100 g d.m. (dry matter) and the free phenolic acids content in both rapeseed varieties was about 76 μg/100 g d.m. The isolated proteins showed lipoxygenase activity. Prooxidant properties of phenolic compounds in the presence of lipoxygenase and linoleic acid were observed rather in the case of extracts containing a relatively high concentration of miscellaneous polyphenols. Antioxidant properties were recorded in the case of phenolic acid extracts which contain only 1.4–1.9% of phenolics present in raw phenolic extracts. We propose that the prooxidant effect of phenolic compounds comes from quinone and oxidized polyphenols formation. The observed antioxidant activity of phenolic acid extracts is probably due to their ability to scavenge free radicals formed from linoleic acid. However, reduction of lipoxygenase ferric to ferrous ions, which prevent the activation of the enzyme and inhibited its activity, was also observed