In vitro gastrointestinal digestion of marine oil emulsions and liposomal solutions: fate of LC-PUFAs upon lipolysis

The bioaccessibility and bioavailability of dietary fatty acids depend on the lipid to which they are esterified, the organisation of theses lipids in water and their recognition by lipolytic enzymes. In this work, we studied the release of marine long-chain polyunsaturated fatty acids (LC-PUFA), depending on their presentation either in the form of phospholipids (PL) or triacylglycerol (TAG). Two formulations based on marine PL or TAG extracted from salmon heads (Salmo salar) were prepared. Lipolysis was first tested in vitro by using individual gastrointestinal lipases and phospholipases to identify the enzymes involved in the digestion. Second, the lipolysis of the prepared formulations by a combination of enzymes was tested under in vitro conditions mimicking the physiological conditions found in the GI tract, both in the stomach and in the upper small intestine, in order to evaluate digestibility of TAG and LC-PUFA-containing liposomes. The in vitro results showed that TAG emulsion was hydrolyzed by porcine pancreatic extracts (PPE) and pure pancreatic lipase (PPL) with its cofactor, colipase, and to a lesser extent by pancreatic-lipase-related protein 2 (PLRP2) and a gastric extract (RGE) containing gastric lipase while no hydrolysis was observed with purified pancreatic phospholipase A2 (PLA2) and carboxyl ester hydrolase (CEH). The PL substrate was found to be hydrolysed by PLA2, PPE and PLRP2. Their phospholipase activities on liposomes formulation was dependent on the presence of bile salts. Using a two-step in vitro digestion model, we measured the kinetics of fatty acid release from TAG and PL during the gastric and intestinal phases of digestion. The highest overall lipolysis level was obtained with liposomes (around 75%) during the intestinal phase while they were preserved during the gastric phase. The overall lipolysis level of TAG emulsion was lower (around 33%), while it started already in the gastric phase. In conclusion, liposomes appear as a better delivery system for intestinal absorption of LC-PUFA than TAG. In addition, their resistance to lipolysis under gastric condition can protect LC-PUFA and provide a gastric stable delivery system for other molecules.