Radical scavenging activity of canola hull phenolics

Abstract

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°-), 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°-radical ion assay correlated highly with those of the chemiluminescence and DPPH radical assays.Paper no. J11016 in JAOCS 82, 255-260 (April 2005). d ACW, antioxidant activity of water-soluble constituents of extract; units are in mM ascorbic acid/g extract. e ACL, antioxidant activity of lipid (methanol)-soluble constituents of extracts; units are in mM Trolox/g extract. Values in each column sharing the same roman superscript letter are not significantly different (P > 0.05; t-test). DPPH, 1,1-diphenyl-2-picrylhydrazyl; C 50% , µg of extract required for 50% reduction of the DPPH radical present in the reaction mixture; ABTS, 2,2′-azinobis-(3-ethylbenzothiazoline-6-sulfonate); TEAC, Trolox (6-hydroxy-2,5,7,8-tetramethylchroman-2-carboxylic acid) equivalent antioxidant capacity.

PHOTOCHEM® for Determination of Antioxidant Capacity of Plant Extracts

“…This is reflected in the total phenolics content of canola hull extracts reported by Naczk et al (24): 70 and 80% acetonic extracts contained 94.3 and 104 compared to 36.5 and 40.4 mg sinapic acid eq/g extract for their methanolic extracts, respectively. The condensed tannins are oligomers and polymers of flavonoids, specifically flavan-3-ols such as (+)-catechin.…”

“…The TEAC values for the ethanol and acetone fractions were 2.24 and 3.94 mM Trolox eq/g extract, respectively. Naczk et al (24) reported that the TEAC values for 70 and 80% (v/v) acetonic extracts of canola hulls were ~ 2 to 3 times higher than those found for their methanolic counterparts. The difference in the TEAC values was possibly due to a higher level of both total phenolics and condensed tannins in the acetonic extracts compared to the methanolic preparations.…”

“…Moreover, PCL measurements are collected at nonphysiological pH values; hence, it is difficult to transfer the results of foodstuffs by this assay to the physiological environment of the human body. Naczk et al (24) found that ACL values of extracts from canola hulls correlated with TEAC values, but did not correlate with ACW measurements. Prior et ai (33) reported that data from Dr. Luke Howard's lab clearly showed that there is little relationship between ORAC and PHOTOCHEM® data across a variety of foods.…”

Phenolics and polyphenolics in foods, beverages and spices: Antioxidant activity and health effects – A review

“…Shahidi, Wanasundara, Amarowicz, and Naczk (1995) demonstrated that addition of canola flour to meat resulted in 73-97% inhibition of lipid oxidation, as determined by the 2-thiobarbituric acid (TBA) test. Use of canola hulls as a source of natural antioxidants was explored by Naczk, Pegg, Zadernowski, and Shahidi (2005). According to , the antioxidant activity of different rapeseed phenolic fractions was lower than the activity of crude ethanolic extract due to synergism between different phenolics in a β-carotene−linoleate model system.…”

Quantitative analysis and free-radical-scavenging activity of chlorophyll, phytic acid, and condensed tannins in canola

“…The isolated tannins exhibited high antioxidant activity as the scavenging effect, at a dose of 1 mg, on the DPPH radical ranged from 35.2% to 50.5%. Furthermore, Naczk, Pegg, Zadernowski, and Shahidi (2005) reported a significant linear correlation between TEAC (Trolox equivalent antioxidant capacity) values and the total condensed tannins of canola hull extract.…”