Radical scavenging activity of canola hull phenolics

Possible use of canola hulls as a source of natural anti-oxidants was explored. Cyclone canola hulls were extracted with methanol (30 to 80 %, vol/vol) and acetone (30 to 80 %, vol/vol). The free radical-scavenging activity of phenolic extracts so prepared was evaluated using the 2,2'-azinobis-(3-ethylbenzothiazoline-6-sulfonate) (ABTS) radical ion (ABTS degrees(-)),1,1-diphenyl-2-picrylhydrazyl DPPH) radical, and chemiluminescence assays. The total content of phenolics in prepared extracts from canola hulls ranged from 15 to 136 mg sinapic acid equivalents per gram of extract. Higher levels of condensed tannins were detected in the acetone extracts than in the corresponding methanolic counterparts. Seventy and 80 % (vol/vol) acetone extracts displayed markedly stronger antioxidant activity than any of the other extracts investigated. Statistically significant linear correlations were found between TEAC (Trolox equivalent antioxidant capacity) values (expressed in mM of Trolox equivalents per gram of extract) and total phenolics, TEAC and total condensed tannins (i.e., determined using the modified vanillin and proanthocyanidin assays), as well as TEAC and protein precipitation activity of phenolic extracts (i.e., measured using the dye-labeled assay). The antioxidant activities of extracts as determined by the ABTS degrees(-) radical ion assay correlated highly with those of the chemiluminescence and DPPH radical assays.