Principles of Physiology of Lipid Digestion

Abstract

The processing of dietary lipids can be distinguished in several sequential steps, including their emulsification, hydrolysis and micellization, before they are absorbed by the enterocytes. Emulsification of lipids starts in the stomach and is mediated by physical forces and favoured by the partial lipolysis of the dietary lipids due to the activity of gastric lipase. The process of lipid digestion continues in the duodenum where pancreatic triacylglycerol lipase (PTL) releases 50 to 70% of dietary fatty acids. Bile salts at low concentrations stimulate PTL activity, but higher concentrations inhibit PTL activity. Pancreatic triacylglycerol lipase activity is regulated by colipase, that interacts with bile salts and PTL and can release bile salt mediated PTL inhibition. Without colipase, PTL is unable to hydrolyse fatty acids from dietary triacylglycerols, resulting in fat malabsorption with severe consequences on bioavailability of dietary lipids and fat-soluble vitamins. Furthermore, carboxyl ester lipase, a pancreatic enzyme that is bile salt-stimulated and displays wide substrate reactivities, is involved in lipid digestion. The products of lipolysis are removed from the water-oil interface by incorporation into mixed micelles that are formed spontaneously by the interaction of bile salts. Monoacylglycerols and phospholipids enhance the ability of bile salts to form mixed micelles. Formation of mixed micelles is necessary to move the non-polar lipids across the unstirred water layer adjacent to the mucosal cells, thereby facilitating absorption.

Effect of free thymol on differential gene expression in gastric mucosa of the young pig

“…In humans, the encoded protein can hydrolyze up to 17.5% of dietary triglycerides (Carrière et al, 1993). A preduodenal lipase has also been identified in pigs (Bauer et al, 2005). PNLIPRP2 is important for newborn and milk-fed mammals (Andersson et al, 2011).…”

In Vitro Gastrointestinal Digestibility of Soybean Oil-in-Water Emulsion Droplets Stabilized by Polyglycerol Esters of Fatty Acid

“…Therefore, the nature of the interfacial layer surrounding the lipid droplets is expected to play an important role in determining the rate and extent of lipid hydrolysis (Fillery-Travis et al, 1995). Additional surfaceactive substances may be produced during the hydrolysis of tri-, di-and mono-glycerides, as well as free fatty acids (FFA) (Bauer et al, 2005). In summary, the composition, structure, and physicochemical properties of the interfacial layer surrounding the lipid droplets should have a great influence on determining the extent of enzyme binding to the droplet surface and, therefore, the extent of lipolysis (Wickham et al, size of the dispersion significantly influences the transfer of β-carotene from dispersions into micelles.…”

“…Nevertheless, most fats are broken down into O/W emulsions in the mouth, stomach and/or small intestine due to the mechanical stresses they experience and the presence of various surface-active and stabilizing components (Armand et al, 1997;Bauer et al, 2005;Pafumi et al, 2002). Hence, the substrate for the digestion of dietary lipids is usually lipid droplets dispersed in an aqueous medium, with the surface of the droplets being coated by a complex layer of surface-active materials that may come from a variety of sources (Armand et al, 1997;Bauer et al, 2005).…”

Improving Nutrition Through the Design of Food Matrices

“…The emulsified lipids within the chyme are transferred from the stomach to the duodenum where they are mixed with sodium bicarbonate, BSs, phospholipids (PLs) and enzymes. The sodium bicarbonate secreted into the small intestine causes the pH to increase from highly acidic in the stomach to neutrality (pH 6.0-7.5) in the duodenum, where the pancreatic enzymes work most efficiently (Bauer et al, 2005). BSs and PLs are surface-active agents that can facilitate emulsification of the lipids by adsorbing to the droplet surfaces (Porter et al, 2007).…”