Introduction for the effect of bile concentration on the hydrolysis of lipids in milk

Lipids/lipase

Lipase is an enzyme which, through the process of hydrolysis, breaks the ester bond in the molecule triglyceride to produce 3 fatty acids and one glycerol. Lipase can be found in two places- the duodenum (secreted by the pancreatic juice from the pancreas) and the stomach (secreted from the gastric glands). The optimum pH for the lipase in the stomach is 4.0 – 5.0 and in the pancreas it is around 8. Lipase is water soluble; therefore it can increase the surface area of the lipids so that it can come to contact with the lipids.

Triglyceride

Triglycerides, a type of lipid, are made from three fatty acids and one glycerol molecule condensed together. It is insoluble in water but can be soluble in some certain solvents, such as ethanol and chloroform. This is due to the long hydrocarbon tails present on the fatty acids. The functions of triglycerides include acting as an insulator to the body to prevent heat loss. Also, it is used for storage in some parts of the body. These are stored in adipose tissues (a tissue in which each cell is filled with a large droplet of lipid). Triglycerides are split into fatty acids and glycerol inside the hepatocytes. Fatty acids and glycerol is lipid soluble, therefore they can diffuse easily through the phospholipid bilayer of the plasma membranes. When they are inside an epithelial cell, they are converted back to triglycerides on the smooth endoplasmic reticulum and transferred to the golgi apparatus where they are modified and then surrounded by a protein coat to form chylomicro, a type of lipoprotein [source mammalian physiology and behavior OCR, page 10]. Some of the fatty acids produced are acetyl coenzyme A, which is used in the Krebs Cycle to produce ATP and some of the glycerol is converted to glucose.

Below is a diagram of a triglyceride being broken down into fatty acids and glycerol [http://www.chemistryland.com/ElementarySchool/BuildingBlocks/BuildingOrganic.htm]

Fat structure

Enzymes

Enzymes can be described as biological catalysts. This means they ‘speed up the chemical reaction, but remains unchanged at the end of reaction’ [source- biology1, OCR]. Enzymes are globular proteins, which is coiled into a tertiary structure. The enzymes have a region called active site, in which a substrate molecule comes and binds into and is then released as two or more products. The joining of the substrate into the active site of the enzyme occurs through two methods, the induced fit theory and the lock and key theory. Induced fit theory is when the active site of the enzyme slightly changes its shape in order for the substrate to fit in. The lock and key theory is when both the substrate and the enzyme’s active site are specific. In the following page there are two diagrams of the lock and key theory and the induced fit theory. For the substrate to be converted to products it has to have energy, this energy is called activation energy. One way to increase the activation energy is by heating them. By this more kinetic energy is provided to the enzyme and the substrate