AbstractThe present study compared the in vitro hydrolysis of two 18:3n-6-rich oils - evening primrose (EPO) and borage oil (BO) - and different synthetic 18:3n-6-containing triacylglycerols (TG), incubation of EPO and BO with pancreatic lipase lipolyzed 18:3n-6 from the TG species. The rate of lipolysis of TG species containing two or three molecules of 18:3n-6, which comprised 36% of total 18:3n-6 in BO and only 7% in EPO was significantly slower than those containing only one molecule of 18:3n-6. This was found especially in those with two molecules of linoleic acid, which constituted 20% of total 18:3n-6 in BO, whereas over 80% were present in EPO. In a separate study, various synthetic 18:3n-6-containing TG were also subjected to in vitro hydrolysis by pancreatic lipase. Results showed that release of 18:3n-6 from the sn-1/sn-3 positions was significantly slower when two other stereospecific positions in the same TG molecule were occupied by either palmitic acid (16:0) or monounsaturated (18:1 and 20:1) fatty acids than when occupied by 18:2n-6. The rate of hydrolysis of sn-2-gamma-linolenyl-sn-1(3)-diacylglyc erol to form sn-2-mono-gamma-linolenyl glycerol was also significantly slower when both the sn-1 and sn-3 positions in TG molecules were occupied by either saturated fatty acids (16:0 and 18:0) or long-chain monounsaturated fatty acids than when occupied by 18:2n-6. These findings suggest that the stereospecific position of 18:3n-6 in TG molecules and the constituent of its neighbouring fatty acids modulated availability of 18:3n-6 from 18:3n-6 containing TG or 18:3n-6-rich oils.
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