Isolation of Casein and Lactose from Milk

Experiment 5: Isolation of Casein and Lactose from Milk

Theoretical Background

Milk is the most nutritionally complete food found in nature. All kinds of milk, human or animal, contain vitamins (principally thiamine – VitB1, riboflavin – VitB2, pantothenic acid – VitB5, and vitamins A, B12, D), minerals (calcium,potassium, sodium, phosphorus, and trace metals), proteins(mostly casein), carbohydrates (principally lactose), and lipids (fats).

Whole milk is an oil-in-water emulsion, containing its 3.9% fat dispersed as micronsized globules. The fat emulsion is stabilized by complex phospholipids and proteins that are adsorbed on the surfaces of the globules. Because the fat in milk is so finely dispersed, it is digested more easily than fat from any other source. The globules are lighter than water, thus colesce on standing and eventually rise to the surface of the milk as cream. Vitamins A and D are fat-soluble substances and are thus concentrated in the cream. The fats in mil kare primarily triglycerides, which are esters of saturated and unsaturated carboxylic acids with glycerol, a tri-alcohol [1].

There are three kinds of proteins in milk: casein, lactalbumins, and lactoglobulins. All three are globular proteins, which tend to fold back on themselves into compact, nearly spheroidal units and are more easily solubilizied in water as collodial suspensions than fibrous proteins are. They are “complete proteins”, so called because they contain all the amino acids essential for building blood and tissue, and they can sustain life and provide normal growth even if they are the only proteins, but they can contain greater amounts of amino acids than the proteins in egg and meat [1].

Casein, the main protein in milk, is a phosphoprotein. The phosphate groups are attached to the hydroxyl groups of some of the amino acid side chains. Casein exists in milk as the calcium salt, calcium caseinate. It is actually a mixture of at least three similar proteins...