RESUMO
Canola meal, the by-product of canola oil refining, is a rich source of phenolic compounds and protein. The meal, however, is primarily utilized as animal feed but represents an invaluable source of nutraceuticals. Of particular interest are the sinapates, sinapine and sinapic acid, with the decarboxylation of the latter to form canolol. Extracting these phenolics has been carried out using a variety of different methods, although there is an urgent need for environmentally safe and sustainable methods. Microwave-assisted solvent extraction (MAE), as a green extraction method, is receiving considerable interest. Its ease of use makes MAE one of the best methods for studying multiple solvents. The formation of canolol, from sinapine and sinapic acid, is primarily dependent on temperature, which favors the decarboxylation reaction. The application of MAE, using the MultiwaveTM 500 microwave system with green extractants, was undertaken to assess its ability to enhance the yield of sinapates and canolol. This study examined the effects of different pre-treatment temperature-time combinations of 140, 150, 160, and 170 °C for 5, 10, 15, 20, and 30 min on the extraction of canolol and other canola endogenous phenolic compounds. Total phenolic content (TPC), total flavonoid content (TFC), as well as metal ion chelation (MIC) and DPPH radical activity of the different extracts were assessed. The results confirmed that extractability of canolol was optimized with methanol at 151 °C and with ethanol at 170 °C with pre-treatment times of 15.43 min and 19.31 min, respectively. Furthermore, there was a strong positive correlation between TPC and TFC (p < 0.05) and a negative correlation between TFC and DPPH radical activity. Interestingly, no significant correlation was observed between MIC and DPPH. These results confirmed the effectiveness of MAE, using the novel MultiwaveTM 500 microwave instrument, to enhance the yield of canolol. This was accompanied by substantial improvements in the antioxidant activity of the different extracts and further established the efficacy of the current MAE method for isolating important natural phenolic derivatives for utilization by the nutraceutical industry.
RESUMO
Mercury bioaccumulation models developed for fish provide insight into the sources and transfer of Hg within ecosystems. Mercury concentrations were assessed for 16 fish species of the western reach of Lake Diefenbaker, Saskatchewan, Canada. For top predators (northern pike, Esox Lucius; walleye, Sander vitreum), Hg concentrations were positively correlated to δ(15)N, and δ(15)N to fish age, suggesting that throughout life these fish fed on organisms with increasingly higher trophic values and Hg concentrations. However, fish mass and/or age were the principal parameters related to Hg concentrations for most species. For 9 common species combined, individual variation in Hg concentration was explained in declining order of importance by fish mass, trophic position (δ(15)N), and fish age. Delta (15)N value was not the leading variable related to Hg concentration for the assemblage, probably because of the longevity of lower--trophic-level species (3 species ≥ 20 yr), substantial overlap in Hg concentration and δ(15)N values for large-bodied fish up to 3000 g, and complex relationships between Hg concentration and δ(15)N among species. These results suggest that the quantity of food (and Hg) consumed each year and converted to fish mass, the quantity of Hg bioaccumulated over years and decades, and trophic position were significant determinants of Hg concentration in Lake Diefenbaker fish.
