To study coagulable and non-coagulable milk
proteins.
1
Milk contains mainly two types of protein: whey and casein, both of which are
high quality proteins according to science-based rating scales. Both contain all
the essential amino acids in amounts sufficient to support the multiple roles of
protein in the human body. So, milk is considered an ideal food. It is also a rich
source of fats. It also contains Calcium and Phosphorus in sufficient quantities.
Therefore, milk is considered to be an important diet for the growing children
and pregnant and lactating women.
According to the Protein Digestibility Corrected Amino Acid Score (PDCAAS), a
method of measuring protein quality based on availability of essential amino
acids as well as digestibility, milk provides higher quality protein than meat,
soy or wheat. The milk of cow, buffalo and goat are commonly used for human
consumption. Because of its high quality, cow’s milk protein is used as a
standard reference protein to evaluate the nutritive value of food proteins.
2
The various constituents of milk and their percentages are given in the table
below:
COMPONENTS
1.
2.
3.
4.
5.
6.
Water
Butter fat
Casein (a protein)
Lactalbumin and globulin (other proteins)
Lactose (milk sugar)
Ash (minerals)
PERCENTAGE (in %)
87.3%
3.8%
2.5%
0.7%
5.0%
0.7%
Milk is slightly heavier than water (specific gravity = 1.305) and has a slightly
acidic pH (pH = 6.5 – 6.7). The principle type of protein present in the milk is
casein. It represents approximately about 80% protein nitrogen of the milk.
Also, α-lactalbumins and β-lactoglobulins are the other proteins of the milk.
Some antibodies called immunoglobulins present in the milk are also proteins.
Casein can be coagulated by acid, rennet and heating. It is a coagulable
protein. The other milk proteins i.e. the albumins and globulins are called noncoagulable proteins as they can be coagulated only by heating.
Casein
Casein is a family of related phosphoproteins (αS1, αS2, β, κ). These proteins
are commonly found in mammalian milk, the most common form of casein
is sodium caseinate. Casein contains a high number of proline residues, which
do not interact. It is relatively hydrophobic, making it poorly soluble in water. It
is found in milk as a suspension of particles, called casein micelles. Casein has a
wide variety of uses, from being a major component of cheese, to use as a
food additive. As a food source, casein supplies amino acids, carbohydrates,
and two essential elements, calcium and phosphorus.
3
Whey Protein
Whey protein is a mixture of proteins isolated from whey, the liquid material
created as a by-product of cheese production. The protein in cow's milk is 20%
whey and 80% casein. The protein in human milk is 60% whey and 40%
casein. The protein fraction in whey constitutes approximately 10% of the total
dry solids in whey. This protein is typically a mixture of
β-lactoglobulin (~65%), α-lactalbumin (~25%), and bovine serum albumin (~8%)
and immunoglobulins. These are soluble in their native forms, independent of
pH. Some clinical studies in rodents suggested that whey protein may possess
anti-inflammatory or anti-cancer properties, however human data is lacking.
The effects of whey protein on human health are of great interest and are
currently being investigated as a way of reducing disease risk, as well as a
possible supplementary treatment for several diseases. Although whey
proteins are responsible for some milk allergies, the major allergies in milk are
the caseins.
4






Milk
Test tubes
Rennin tablets
Millon’s reagent
Beaker
Burner
5
1. We have to first take about 20 mL of milk in a beaker. Then we have to
grind a rennin tablet and add it to the milk.
2. Next, we have to warm the milk.
The milk will coagulate
3. Then we have to filter the coagulated (solidified) milk.
The liquid filtrate is whey.
4. Lastly, we have to take a small amount of whey in separate test tube and
test it for the presence of presence by using Millon’s reagent.
6
The coagulated milk contains casein which gets coagulated by rennin.
The liquid filtrate, which is whey, gives positive test for protein, indicating the
presence of non-coagulating protein in whey.
7
Cow and buffalo milks contain both coagulable and non-coagulable proteins.
8
 Comprehensive Laboratory Manual In Biology Class XII
 www.google.com
 www.dairynutrition.ca/nutrients-in-milk-products/protein/milk-productssource-of-high-quality-protein
 en.wikipedia.org/wiki/Casein
 en.wikipedia.org/wiki/Whey_protein
 https://dairyprocessinghandbook.tetrapak.com/chapter/chemistry-milk
9