Question

Why may pancreatic lipase not have much effect on digesting milk fat? What else do we need to make the digestion of fats more efficient?

Answer 1

Pancreatic lipase has more specificity for fats with sn-1 and sn-3 ester bonds breaking them down to form 2-monoacylglycerols and free fatty acids. Pancreatic lipase cannot efficiently digest milk lipids in invitro conditions.

Human milk is composed of lipids present in milk fat globules. Milk also contains larger amounts of protein and phospholipids. The thick surface layer of protein and phospholipids impedes or reduces the action of pancreatic lipase. Pancreatic lipase requires a larger surface area for actions. Thus, pancreatic lipase has reduced ability to digest milk lipids.

Normally bile salts are added to increase the action of pancreatic lipases by emulsifying fats in order to provide a larger surface area for action of the lipase. However in milk, surface proteins and phospholipids, are present. Bile salts can inhibit pancreatic lipase by displacing them from the interfaces in milk. Colipase will anchor the pancreatic lipase to the interface thereby increasing its actions. Thus, colipase, a cofactor, will increase the actions of pancreatic lipase in presence of bile salts by opening the molecular lid on active site of the pancreatic lipase. If bile salts are not added, phospholipase A2 enzyme can be used. This enzyme can increase actions of pancreatic lipase in absence of bile salts. Phospholipase A2 can breaks down some phospholipids, thereby increasing the action of pancreatic lipase. Thus, actions of pancreatic lipase on milk can be enhanced by addition of colipase with bile salts or phospholipase A2 alone.