Antioxidant Activity of Sinapine

In biological systems, an antioxidant can be defined as any substance that, in low concentration compared with the oxidizable substrate, significantly delays or prevents oxidation of that substrate. The substrate, that is, the oxidizable compound, is usually a lipid, but can also be a protein, DNA, or carbohydrate. In the case of lipid oxidation, the main mechanism of antioxidants is to act as radical chain-breakers. Another mechanism is to act as preventive antioxidant oxygen scavenging or blocking the pro-oxidant effects by binding proteins that contain catalytic metal sites (Frankel and Meyer, 2000). 

Amarowicz et al. (2000) and Matthaus (2002) investigated the effect of rapeseed phenolics on radical scavenging. The antioxidant activity of ethanolic (95%) extract of rapeseed meal towards the oxidation of rapeseed oil was better than that of some widely used synthetic antioxidants (Wanasundara and Shahidi, 1994). Phenolic compounds present in crude rapeseed oil have also shown antioxidant properties (Koski et al., 2003) in bulk and emulsified methyl linoleate and lecithin-liposome systems. Amarowics et al. (2003) investigated the antioxidant activity of phenolic fractions of rapeseed (total three fractions) using a P-carotene-linoleate model system and enhanced chemiluminescence and photochemiluminescence methods. A measure 

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. 

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