Canola, phenolic antioxidants

Chapter 15 Rapeseed and Canola Phenolics Antioxidant Attributes... 

Figure 5. Chemical structures of selected phenolic antioxidants of canola, borage and evening primrose.

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. 

Rapeseed phenolics isolated by Vuorela et al. (2004) were tested for radical scavenging and for liposome and low-density lipoprotein (LDL) model systems. The inhibition of hexanal and conjugated diene hydroperoxides formation was reported (>90% and >80%, respectively). All isolates also exhibited inhibition of LDL particles oxidation by >90%. The antioxidant activity of methanol and acetone extracts of canola hulls in a P-carotene-linoleate model system was comparable to that displayed by butylated hydroxyanisole (Naczk et al., 2005). These extracts showed more than 95% scavenging effects (at 40 p/assay on DPPH radical). Vuorela et al. (2005a,b) indicated that rapeseed phenolics were excellent antioxidants towards oxidation of phosphatidylcholine membrane (liposomes) and rapeseed oil (crude) phenolics were effective radical scavengers (DPPH test). The authors suggested that these phenolic isolates from rapeseed are safe and bioactive for possible food applications including functional foods intended for health benefit. 

Amarowicz R, Naczk M, Shahidi F. 2000. Antioxidant activity of various fractions of nontannin phenolics of canola hulls. Journal of Agriculture and Food Chemistry, 48 2755-2759. 

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. 

Some of the minor components that remain in the refined oil may act as antioxidants within the body and thus may be beneficial for chronic disease prevention, inclnding metabolic syndrome, however, there are no data as to the levels of these componnds present in canola oil and their effects on health. For example, Siger et al. (2008) have documented a relatively high amount of phenolic componnds (256.6 + 0.73 pg/lOO g) and antioxidant activities in cold-pressed canola oil... 

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... 

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