This story will focus on some of the proteins in milk, and in particular a protein called casein. Casein is the protein used to make cheese. You probably think of it as being the curds, whereas the whey contains all the other different proteins in milk.

Separation of casein

Casein can be easily separated from milk by making the milk more acidic. This can be done either by adding acid or by adding bacteria which produce lactic acid.

Get information sheet: Lactic acid fermentation to separate the casein in milk

The lumps that form when the milk is acidified are the casein proteins (curds). The rest of the solution is called the whey.

The casein can be collected, and then turned back into a solution by adding an alkali, e.g. sodium hydroxide. The re-dissolved casein solution is now called caseinate. It can be sold directly or it can be processed further.

Further processing of casein

Tatua Dairy Cooperative

At dairy companies like Tatua Co-operative Dairy Company, enzymes are used to modify some of the caseinate. Enzymes are proteins that speed up chemical reactions. In this case, hydrolysing enzymes are used. These enzymes break up (or hydrolyse) the casein protein into smaller parts. The bits of protein that are produced are called amino acids and peptides.

Get information sheet: Hydrolysis of protein

The solution containing the amino acids and peptides that are produced when the casein is broken down is called a casein hydrolysate.

Controlling enzyme activity

Enzymes are very specific. Different enzymes will break down the casein protein in different ways to produce different casein hydrolysate solutions. Enzyme activity is also affected by the time of the reaction, the pH and the temperature. By carefully controlling the enzyme reaction (the enzymes that are used, the time of the reaction, the pH of the reaction, the temperature of the reaction), a wide variety of hydrolysate solutions can be produced.

Uses of casein hydrolysates

Tatua scientist

Casein hydrolysates have many advantages when compared with the untreated casein. In particular, they are more easily absorbed by our bodies than whole proteins. (In our bodies, the proteins must first be broken down in our digestive system before they can be absorbed).

The broken up proteins (hydrolysates) have a wide range of potential uses. These include:

• providing the amino acids and peptides needed for liquid feeds for patients in hospital
• making infant formula
• making food products for people who might be allergic to whole milk proteins
• providing the amino acids and peptides needed for making solutions to grow up bacteria and cell cultures in laboratory or industrial settings.

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