Explain the role of bile salts and lecithin in the emulsification of lipids (fats).

Answer 1

1. Fats or Lipids (Lecithin is the name of fat source from food) are insoluble in water and aggregate into large lipid droplets in the upper portion of the stomach → pancreatic lipase (which catalyzes the splitting of bonds linking fatty acids to the first and third carbon atoms of glycerol, producing two free fatty acids and a monoglyceride) is a water-soluble enzyme, its action in the small intestine can take place only at the surface all of the lipid droplet → therefore if most of the ingested fat remained in large lipid droplets, the rate of triglyceride digestion would be very slow because of the small surface area to volume ratio of these big droplets
2. Rate of digestion is substantially increased by division of large lipid droplets into very many small droplets →  emulsification
3. Requires: mechanical disruption (GI motility/grinding and mixing) of large lipid droplets into smaller droplets, and an emulsifying agent (phospholipids) that keeps them from Free aggregating into large droplets → Nonpolar portions of the phospholipids in bile salts associate with a non-polar interior of the lipid droplets leaving the polar portions exposed to water at the surface → they repel other lipid droplets that are similarly coated with these emulsifying agents
4. Emulsifying agents impair the accessibility of water-soluble pancreatic lipase to its lipid substrate → to overcome this problem the pancreas secretes a protein known as colipase→ which is amphipathic and lodges on the lipid droplet surface; it binds the lipase enzyme holding it on the surface of the lipid droplet