In vitro hydrolysis of natural and synthetic γ‐linolenic acid‐containing triacylglycerols by pancreatic lipase

The present study compared thein vitro hydrolysis of two 18:3n‐6‐rich oils—evening primrose oil (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 toin vitro hydrolysis by pancreatic lipase. Results showed that release of 18:3n‐6 from thesn‐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 ofsn‐2‐γ‐linolenyl‐sn‐1(3)‐diacylglycerol to formsn‐2‐mono‐γ‐linolenyl glycerol was also significantly slower when both thesn‐1 andsn‐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 neighboring fatty acids modulated availability of 18:3n‐6 from 18:3n‐6‐containing TG or 18:3n‐6‐rich oils.