The Casein Family – Science of Cheese Proteins

There are so many different types of cheese: brie, fresh cheese, mozzarella, gruyere, parmezan, Gouda, paneer, emmentaler and I could go on for a lot longer. What’s interesting though is how they just about all depend on one type of protein in milk: the casein proteins. Thanks to these proteins the milk can be made to curdle and form cheese.

Therefore, it’s about time we discuss these proteins in more detail, they are fascinating from a science perspective. In previous posts we’ve discussed the process of making cheese. We discussed the casein proteins slightly, however, now it’s time to dive deeper into the science of these casein proteins.

It all starts with milk

Cheese is made from milk. Let’s do a quick recap of what milk is (see also the infographic). Milk is mostly water, but also contains fat, proteins and sugars as well as some other minor components such as vitamins and minerals. When making cheese a lot of this water is removed. The fats, some of the sugars as well as some of the proteins will form the cheese.

Proteins play a central role

In order to make this cheese and separate the water and whey from the milk, a split has to happen. Essentially, making cheese is nothing more than splitting these two phases from one another. Here is where the casein proteins come in. These proteins can be made to make the milk curdle and thus make cheese.

Proteins are highly complex molecules in food (catch up on the basics here). They are very long strands of amino acids. Because of their size and length, it is not really useful to draw out their chemical structures and bonds, they’ll be too long. And anyway, it is nothing more than a long chain of amino acids. It is not the chain that is interesting. It is how all these different amino acids interact.

Each amino acid has a different side chain and it is these side chains that determine the functionality of a protein. These side groups can interact with one another, but also with other molecules.These long chains can curl themselves up in a lot of different, complex ways. The structures that result from this are essential for life. Proteins can do highly complex processes. An example of a group of proteins are enzymes. Enzymes are proteins that can catalyze chemical reactions.

Whey & casein proteins

In milk the proteins can be split into two main groups: whey & casein proteins. Within each of these groups there exist a lot of different proteins. We will zoom in on the casein proteins below, but let’s quickly see what happens to the whey proteins. Whey proteins do not end up in the cheese, instead, they end up in the liquid that is separated from the cheese. Whey proteins dissolve in the water and do not curdle at the low pH that causes casein to curdle. The proteins are used for a lot of other applications in the industry, e.g. processed cheeses.

Casein proteins & micelles

This long chain of amino acids of a protein can fold themselves up in a variety of very complex 3D structures. These structures are very important for determining the functionality of the proteins. In the case of casein, researchers are still trying to understand the exact structures of the proteins. It is not completely clear how they fold up and arrange themselves.

It is known that there are four main types of casein molecules in milk, it is not just one type. These are αs1 , αs2, β and κ. Despite all being casein molecules they have different lengths and a different composition of the amino acids. This gives them all slightly different abilities.

Casein molecules have hydrophobic and hydrophilic regions in the molecules. This means that some parts like to sit in water, whereas other parts don’t. This caseus casein molecules to organize themselves in micelles. They form globular round structures which float around in milk. The different casein types each take up a different place within the micelles. Some will sit more towards the outside (the κ-casein) whereas others sit more on the inside.

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These micelles do not consist of solely casein molecules. Instead calcium phospohate plays and essential role in forming this stable micellar structure. Exactly how the casein micelles look like isn’t fully known yet it seems, there’s still discussion between several possible models (see sources at the bottom of this article for some interesting links to learn more).

Casein makes milk turn white

It is known that the micelles are small (50-500nm) and are able to reflect light. It is these micelles that contribute largely to the white colour of milk. During cheese making the casein micelles fall apart (more on that in the paragraph below) and casein molecules will aggregate in larger clusters than these small micelles. This causes the milk to lose its white colour and is a useful indication to determine whether the cheese making process is proceeding well.

Gouda cheese, all made possible by casein proteins.

Casein micelles falling apart

We know that casein micelles do not stay stable all the time. Casein proteins can handle heat very well (unlike most other proteins), but are sensitive to a change in pH (acidity). Also, the micelles depend on the casein proteins to stay intact. If some break down, this will instabilize the micelles. It’s these two properties that are used to make cheese. As discussed in other posts, there are roughly two ways to make cheese:

  1. Lower the pH (either by the addition of an acid or by the addition of micro organisms that make acids)
  2. Add an enzyme

Both methods will cause the stable micelles to lose stability and curdle into larger aggregates. The lower pH will destabilize the casein micelles and cause them to aggregate. They will form clumps which catch the fat and which will form the final cheese. Enzymes on the other hand come into play to change the size of the proteins.

Enzymes cut κ-casein

Within the micelles it is the κ-casein that plays a very important role in stabilizing the whole structure. It sits on the outside of the micelle and prevents the micelle from growing too large. The hydrophilic section that sits on the outside keeps it flowing around in the watery milk. When κ-casein is broken down somehow, it will lose its ability to stabilize these micelles.

When making cheese the enzyme chymosin can be used to cut the κ-casein in two parts. Let’s look at little deeper at this cut. As discussed before, the κ-casein protein is, just like any other protein, a long chain of amino acids. The κ-casein protein is 148 amino acids long.

As we discussed before as well, enzymes are proteins which are very good in catalyzing a specific reaction. When making cheese we use an enzyme called chymosin. This enzyme is very good in cutting up κ-casein at one specific spot, between the 105th and 106th amino acid. Thus that leaves us with two shorter chains, one of 105 amino acids and one of only 43. These shorter chains aren’t as good in stabilizing the casein micelles anymore, resulting in the proteins aggregating together.

And that leaves us with cheese. Without casein proteins we wouldn’t have brie, gruyere, Edam, Gouda, etc! It’s just one family of proteins, but has significantly contributed to diets around the world!

Sources

Review from 2005 on the theories of the different casein micelle structures. Another research article discussing the different possible structures of casein micelles (from 2006) as well as a whole book chapter.

Book: Cheesemaking practice, R.Scott, third edition, p.50

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8 Comments

  1. My son has a dairy protein intolerance and we are slowly trying to reintroduce it to see his reaction. I was told Mozzarella is a less strong cheese when it comes to the protein. Is this correct and if so cheeses are the least amount of dairy proteins and what cheeses are the strongest?

    • Hi Heidi,
      Thanks for your question! In general, all cheeses will contain a considerable amount of protein, however, in more moist cheeses that content is slightly lower per ounce or 100g of cheese since there is more moisture in there. I’m thinking that is one of the reasons people may have recommended Mozzarella. Mozarella and other fresh cheeses still contain a lot of moisture and may therefore contain slightly less protein per portion. Harder, drier cheeses will still contain the same protein but more moisture has evaporated, increasing the protein content. What you might also consider is a processed cheese type to start with, in various cases (e.g. cream cheese) the actual milk protein content isn’t as high because of the addition of other ingredients.
      That said, which type is best to start with when you have (had) an allergy I wouldn’t be able to say since I’m not a dietician nor an expert on food allergies. A dietician might be able to give you more specific advice.

    • Hi Jenny,

      Thanks for your questions but unfortunately I don’t have a good answer. All dairy made cheeses contain some amount of casein since it is what makes cheese a cheese. Without the casein, the milk wouldn’t set and form the cheese curds. The main variation in casein contents will likely be related to the amount of fat and moisture in cheeses. If there is a lot of fat and water in a cheese, almost automatically there is less protein (thus casein) in the cheese. That said, there still is casein in there.

      Hope that helps at least a bit!

  2. What cheese has the highest casein?

    I understand concept of driest but not being familiar with cheese variety can you give some names?

    When I search it seems to default to “least” for those with allergies but I’m trying to find highest casein to buy and try to make homemade.

    • Hi Lauren,

      If you’re making cheese from just milk and some enzymes or acids, the composition of your milk will determine the composition of your cheese (assuming you’re not adding any other protein sources etc.). The more water you remove from the milk, the higher the protein-% of the cheese (but the less overall weight of cheese) you’ll end up with. Also, a milk with a lower fat content will result in a cheese with a higher protein content (but less cheese in overall).
      To illustrate, let’s assume you have 1000g of milk that you’re making into cheese. We can assume that all the casein in the milk will end up in the cheese, let’s assume there’s 5%, that is 50g. If you make 500g of cheese out of this milk (not adding anything else except for enzymes), you’ll have 50g/500g*100=10% casein. However, if we dry the cheese for longer and press it more, you right end up with only 250g of cheese, now your casein content will be 50/250*100 = 20%. How much water gets expelled will impact casein content. So, if you’re making your own cheese, one that is drier (e.g a parmesan instead of a fresh mozzarella) will have a higher protein-%.

      A similar story goes up for fat. If you remove all the fat from your milk, and aim for a similar moisture-% at the end, you will also end up with more protein. An example, again you have 1000g of milk of which 5% is fat. In this case you’re removing all the fat, so you’ve only got 1000-(0.05*1000)=950g milk. Again, you’re removing 500g of moisture from the cheese (same as above where you made 500g of cheese from 1000g of milk, for simplicity we’re assuming you’re removing the exact same amount of water). The protein content will now be 50/(950-500)=11.1% protein. So your protein content is higher because there’s no fat left. (This calculation is a bit of a simplification of reality, but good enough for reality).

      When making cheese at home especially, all these factors are important since you might not be able to standardize as well as large scale manufacturers are. So knowing just how much fat your milk contains (this can differ per season) can be important.

      I know you’d like to know specific names of cheeses but since there are so many types of cheeses (hundreds, if not thousands) I want to make sure you understand the concepts so you can choose yourselves. Generally, going for a pretty dry cheese like a parmesan or a low-fat aged Gouda or cheddar. Personally, I would suggest you choose a type of cheese you’d like to make and within that realm find one that has the highest casein content.

      Good luck!

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