Milk is a highly nutritional natural product that can be used for a wide range of different products. For example, casein protein can be separated and then broken down to provide a nitrogen source for infant formula, special diets for critically ill people and growth materials for bacteria.

This looks at 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.

The bacteria (e.g. Streptococcus thermophiles, Lactobacillus acidophilis and Lactobacillus bulgaricus) use a process called fermentation to get energy from the milk sugar (lactose). The lactic acid that is produced as a by-product makes the milk more acidic.

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

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.

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

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.

Quality control

Quality control procedures are vital for a company that is producing food and health products for the New Zealand and international market.

Meeting customer specifications

All products produced by Tatua Dairy Co-operative need to meet customer specifications. To check this, a certain percentage of the end-products are tested to verify that customer criteria have been met. Sampling and monitoring are also carried out at different steps in the process.

Health regulations

Health regulations are also very important within any industry making products that will be added to foods. Regulations are set by the New Zealand Food Safety Authority.

Sample swabs are taken from around the Tatua factory twice daily and tested for bacterial contamination.

Rodent and insect traps are placed at particular sites around the factory.

There is also a ‘foot exchange’ system, and anyone entering the factory is required to exchange their shoes for gumboots, which are always kept within the factory. This minimises the risk of contamination from footwear.

All workers within the factory are also required to wear laboratory coats and protective caps over their hair.

Other considerations

Other things to consider when developing a product are legal issues, environmental issues, feasibility and market analysis.

Where's the biotech?

Using bacteria to produce lactic acid

Casein (‘curds’) is separated from the rest of milk when the milk is acidified.

One way of doing this is using special bacteria, which produce lactic acid. This is what happens when yoghurt is made, and is an example of how living organisms can be used, in this case, to separate the casein from milk.

Using enzymes to break down proteins

Enzymes are able to break down the casein protein into peptides and amino acids (the same process that happens during human digestion). Enzymes are produced by living cells.

Tatua buys the enzymes from a biological supplier and then uses them to break the casein from milk into smaller peptides and free amino acids.

What a biotechnologist needs to consider

Biotechnologists need to provide the best conditions for growing the bacteria so that they produce just the right amount of lactic acid.

Usually the bacteria are grown in culture first to create large numbers, and then this culture is transferred to milk. When using enzymes, a biotechnologist must check what the optimum conditions are for the enzymes to work.

The biotechnologist must then monitor all stages of the production process to make sure that the correct operating conditions are being maintained. The quality and properties of the end product are very important, and need to meet the customer specifications.

Testing and monitoring is carried out at every stage of the process. Biotechnologists also need to consider the effect of carrying out the process on a large scale (upscaling) in order to produce larger amounts of product.

Published 1 December 2005