Canola phenolic compounds

Amarowicz et al. (1994) studied the phenolic compounds of flaxseed meal extracted into 80% ethanol (v/v) by chromatographic techniques. Both hydrophilic and hydrophobic phenolic compounds were present. The separated hydrophilic fractions had a UV maximum absorption between 270 and 290 nm which was different from that observed for phenolic acids. Meanwhile, the tannin content of flaxseed meal was very low (125 to 137 mg/100 g of defatted meal) when compared to that of high glucosinolate rapeseed and canola (Shahidi and Naczk 1988 Shahidi et al., 1988 Wanasundara and Shahidi, 1994a). 

Subsequent work by Zambiazi and Przybylski (1998) also showed that fatty acid composition could only explain half of the oxidative stability of vegetable oils including canola oil. The other half was attributed to the amount and composition of endogenous minor components which can shorten or extend the shelf-life of an oil. Such endogenous components were later discussed by Przybylski and Eskin (2006) and included tocopherols, mono- and diacylglycerols, free fatty acids, phospholipids, chlorophylls and derivatives, carotenoids, phytosterols, phenolic compounds and trace metals. In addition, the position that the fatty acid occupies in the triacylglyc-erol can also affect stability. For example, the location of linolenic and linoleic acids on the sn-2 position has been reported to cause faster oxidation and lower stability compared to the same fatty adds on ml- and sn-3 positions. In contrast oleic acid at the sn-2 position proved stabler compared to its location on sn-1 and sn-3 positions (Neffetal., 1994,1997). 

Sinapic acid, an important hydroxydnnamic acid is the most significant phenolic compound in rapeseed and forms 70.2-85.4% of free phenolic adds in defatted canola meals. Esterified forms of these phenolic acids constitnte abont 99% of total phenolics in rapeseed flour of which the sinapine, the choline ester of sinapic acid, is the main ester. A phenolic glucoside namely glucopyranosyl sinapate is also reported in canola (Amarowicz and Shahidi, 1994). Figure 2.1 shows the structures of sinapic acid, sinapine and glucopyranosyl sinapate. 

Naczk M, Amarowicz R, Zademowski R, Shahidi F. 2005. Antioxidant capacity of pheno-lics from canola hulls as affected by different solvents. Phenolic compounds in foods and natural health products, Chapter 6, 2005, pp. 57-66, ACS Symposium Series, Volume 909. 

Xu, L. and Diosady, L. L. 2002. Removal of phenolic compounds in the production of high-quality canola protein isolates. Food Res. Int. 35 23-30. 

Despite these negative attributes, there are opportunities for these phenolic compounds to be extracted using pure or aqueous solvents like ethanol to be further utilized as natural antioxidants. Studies showed that the extracts obtained from the oilseed residues displayed remarkable antioxidant activity, the extent of which depends on the type of residue and the solvent used for the extraction (Amarowicz et al 2000). Wanasundara et al. (1994) reported that the best antioxidant activity was exhibited by a fraction of canola meal phenolics that contained only 34 mg of phenolic compounds/g of sample. On the other hand, Amarowicz et al. (1996) observed that the antioxidant activity of ethanolic extracts of mustard correlated well with the total content of phenolic... 

While the main phenolic compounds of olive oil, hydroxytyrosol and oleuropein, give the oil its bitter and pungent taste, the major phenolic compounds in canola seeds are esterified phenolic acids. The main component of the latter is sinapine, the choline-ester of sinapic acid (3,5-dimethoxy-4-hydroxycinnamic acid) (Krygier et al., 1982). Some free phenolic compounds of about 15% are also present with... 

Seki, T., Morimura, S., Kida, K., Fang, J. and Maeda, M. 2006. Suppression of inflammatory cytokines including TNF-a, IL-12, antiNOS by a phenolic compound, obtained from crude canola oil. Nitric Oxide 14 A17-A19. 

Antioxidative compounds from oilseeds such as canola/rapeseed, mustard, flax, borage and evening primrose, soybean, cottonseed, peanut and sesame have been investigated. The antioxidative conq)onents present are diverse and may end up in the extracted oil or in their resultant meal after oil extraction. The antioxidative compounds present include tocopherols, sterols, phospholipids, phenolic acids and phenylpropanoids, flavonoids and isoflavonoids, hydrolyzable and condensed tannins, lignans, coumarins, amino acids, peptides and proteins as well as carotenoids (7). 

For example, the main phenol with antioxidative and antimutagenic activities that occurs in crude canola oil is 2,6-dimethoxy-4-vinylphenol known as canolol, which is produced from syringic acids. The major products of caffeic acid pyrolysis at 225 °C are pyrocatechol, 4-vinylpyrocatechol and 4-ethylpyrocatechol (see Section 8.3.4). A more complex mixture of products arises by pyrolysis of lignin, in the smoke condensates used in the meat industry, more than 150 different phenols, and dozens of aromatic alcohols, phenolic acids and hydroxylated heterocyclic compounds have been identified. 

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