Antioxidants sinapine

Control (no-antioxidant) > sinapine > unfractionated extract > bound fraction > sinapic acid > free fraction. 

Sinapoyl esters are considered antinutritional compounds because they have a bitter and astringent taste, thus contributing to the bitter taste of rapeseed meal. The intensity of the bitter taste is comparable to the intensity of the bitter taste of caffeine. In the refining of rapeseed oil, sinapines form complexes with proteins. They show lower antioxidant activity than the corresponding phenolic acids and do not have antimicrobial effects. Sinapines present in the feed of some breeds of laying hens cause an off-flavour and fish-like odour of yolks. 

The antioxidant activities of standards of sinapoyl glucose, sinapine and sinapic acid, the major sinapic acid derivatives, were compared using the free radical scavenging activity. Under the tested concentrations (Figure 15.8), the free radical scavenging activity followed the order ... 

To scavenge 25 x 10 DPPH radicals, the required concentrations (mM) for sinapic acid, sinapoyl glucose and sinapine cation were 30.8, 35.8 and 47.5 mM, respectively, compared to 21.5 mM for Trolox, a water-soluble antioxidant. 

Results of the present stndy indicate that the bonnd and the non-fractionated extract could inhibit the hydroperoxides, propanal and hexanal in a similar manner to sinapine alone when compared with the control sample withont any added antioxidant. This was in contrast to the resnlts illustrated in the bnik rapeseed oil system, where these extracts and sinapine fnnctioned as a mild pro-oxidative or ineffective antioxidant. The non-fractionated extract and sinapine represented a comparable manner in inhibiting PV increase, whereas the bound fraction was more effective as compared with sinapine and nonfractionated extract. This means that in this case, the unidentified peaks of the hydrophilic compounds contributed to the enhanced activity of the bound-phenolic fraction. It was also observed that sinapic acid and the free-phenolic fraction functioned in a similar manner until the 18th day of incnbation. 

FIGURE 15.14 Effect of fractionated rapeseed meal extracts on the formation of hydroperoxides of rapeseed oil at 40°C in the dark. Control (no antioxidants), sinapic acid (SA), extract (non-fractionated 70% methanolic extract), free (free-phenolic fraction), bound (bound-phenolic fraction), sinapine (SP), all added to stripped rapeseed oil at a concentration of 500 0,mol/kg oil. 

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