How is casein protein digested in humans

How exactly is casein digested?

  1. Casein proteins are soluble in milk, but once they reach the stomach they form insoluble curds, making it difficult for digestive enzymes to break them apart. Slower digestion is also associated with a delayed release of the protein's amino acids into the bloodstream.

These properties of milk caseins may have evolved to benefit infants in mammals, but slower digestion provides milk drinkers of all ages with the benefit of increased satiety. Eating foods like milk that are on the slow track can mean you are eating less overall.

Casein proteins in milk form small spheres, so-called micelles, with the hydrophilic (water-loving) parts of the protein on the outside of the sphere and the hydrophobic (water-accessible) parts on the inside. With structures that are hydrophilic on the outside, the micelles are water-soluble (or milk, mostly water) [1,2].

However, when the micelles reach the stomach, "one of the most ingenious events in nature takes place" [2]. The digestive enzyme chymosin cuts one of the bonds on the outer protein (known as the kappa subunit), leaving only the hydrophobic subunits inside [1]. Without their protective layer, the now insoluble proteins form a quark.

  1. It looks like various proteolytic enzymes digest the casein curd in the stomach and intestines. "Activated human proteolytic enzymes were obtained by collecting human gastric (HGJ) and duodenal (HDJ) juice." This is the article: In Vitro Digestion of Beef and Goat Milk by Human Gastric and Duodenal Enzymes

  2. It has been shown that dipeptidyl peptidase IV (DPP IV), a type of protease that breaks down proteins in gluten and casein. ›Diseases and Conditions

It's in our intestines:

  1. Brush Edge Enzymes & Casein [that gives me your question about the stack exchange!] This article: "Effect of diet on the enzymes of the brush edge of the small intestine and kidney of rats" says: "Diets with low starch and high casein content led to higher specific activity of leucine aminopeptidase in the Small intestine as high starch, low casein diets. "You can find out a bit more about this enzyme by reading the abstract of the article.

  2. 'Digestion of peptides in the small intestine' in Google states: "The brush edge of the small intestine is equipped with a family of peptidases. ... They promote the hydrolysis of lumen peptides and convert them into free amino acids around small peptides. These on the surface of the Enterocyte-formed end products of digestion are ready for absorption. "

[Note - these are Google searches with the occasional Scholar.Google search. ... Maybe I should go back to my own work and let you all do the search!]


Thanks for the answer! The problem is that after many hours of reading I was convinced that I could digest very aged cheeses like Parmesan because it was predigested by bacteria - the casein was supposed to be broken down into free amino acids - I tried 22 month old Parmesan - the result was a disaster. Also, I eat the cheese with ginger enzymes which should act as the DPP 4 enzyme - it just didn't work. So after reading your answer, there seems to be a ton of things that can go wrong with casein digestion, especially with concentrated foods like cheese.


PH has been a variable in a lot of research, but I haven't talked about that. I'm sorry about your cheese research - I think I have a slight increase in mucus with dairy products, so I don't tend to eat cheese at home. But it's only a minor problem.