Rapeseed meal extract fractionation

The main phenolic compounds of rapeseed meal are commonly sinapic acid (Figure 15.3a) and its derivatives—sinapine the choline ester of sinapic acid (Figure 15.3b), or as the glucosidic ester, glucopyranosyl sinapate. About 80-90% of all the phe-nolics in the meal are sinapic acid esters (SAEs) as discussed earlier. Thus, 70% methanolic rapeseed meal extracts of the meal have been classified into free-pheno-lics, esterifled phenolics and released-phenolics according to Krygier et al. (1982). Krygier et al. (1982) extracted free and esterified phenolics, which were methanol soluble and demonstrated that only a small fraction of the total phenolic compounds of rapeseed occurs as free sinapic acid (Koski et al., 2002 Vuorela et al., 2003). 

These results concurred with the findings of Thiyam et al. (2006a) that rapeseed meal extracts contained free sinapic acid, which was equivalent to just one-tenth of the content of sinapine. This was further illustrated by the Iree-phenolic fractions of the meal extracts that could recover the free sinapic acid safisfactorily. Usually in analysis, the phenofic extracts are hydrolysed with NaOH and the released-phenolics are extracted with diethyl ether, ethyl acetate or both. Comparisons between the aqueous fraction (rich in sinapine) before and after hydrolysis producing the released fraction (rich in sinapic acid) showed reasonable results with minimum hydrolysis losses affecting the accuracy of the process. Additionally, fiactionation of the 70% methanolic extract showed comparable extraction efficiency to the original extract before fractionation. 

Rapeseed meal extract was fractionated following the procedure of Krygier as described in Figure 15.4. Thus, 70% methanolic extract of rapeseed meal was fractionated to obtain fractions that were rich in free, esterified and released-pheno-lic compounds (Table 15.2). The fractionation of the 70% methanolic extract with an initial content of free sinapic aci 1.15-1.38 mg/g fat-free meal and sinapine 13.85 mg/g fat-free meal. 

FIGURE 15.4 Fractionation procedure of rapeseed meal extract. (Adapted from Krygier, K., Sosulski, F. and Hogge, L. 1982. J. Agric. Food Chem. 30 330-334.)... 

The fractionated and non-fractionated 70% methanolic rapeseed meal extract were also added to 10% o/w emulsion at a concentration of 500 pmol/kg oil. This set of experiments aimed at studying differences in effectiveness of the fractionated rape-seed meal extracts in bulk oils and emulsion using the rate of oxidation as monitored by the formation of hydroperoxides and secondary volatiles. Auto-oxidation was carried out at 40°C in the dark. The oil that was used for preparing the emulsion was purified. Purification of rapeseed oils was done to strip the rapeseed oils of natural... 

Evaluation of the fractionated and non-fractionated 70% methanolic rapeseed meal extract added to stripped rapeseed oil at a concentration that was equivalent to 500 pmol/kg oil of total phenolic compounds (as quantified by HPLC, 330 nm) was compared with sinapic acid. The fractionated free-phenolic compounds (free-phenolic fraction), which contain over 85% sinapic acid, showed a similar pattern with the sinapic acid standard with respect to the inhibition of both the hydroperoxides and propanal in the emulsion. This was observed for both the cases, that is, hydroperoxide inhibition and propanal inhibition. The effectiveness of the fractionated free-phenolic componnds (free-phenolic fraction) may be dne to the high concentration of sinapic acid in the extracts. These extracts, when added to a 10% o/w system at a concentration of 500 pmol/kg oil exhibited differences in the potencies with respect to inhibition of the primary and secondary prodncts of oxidation. 

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. 

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). 

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... 

To allow the use of seed cakes as animal feed, the extracted press cake is treated with steam to remove the remaining 2% of hexane in the cake. As a consequence, the digestibility of the deoiled meals is decreased. The price of rapeseed cake varied between 200 and 400 dollars per tons in 2012-2015. Efforts are also ongoing to valorize press cakes by conversion of various products from the cake such as the proteic fraction that can be used to produce chemicals. ... 

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