Caseins represent the most abundant protein fraction of milk, whose nitrogen content is divided into four components:
- caseins: family of phosphoproteins which constitute the main protein fraction of milk (about 2/3 of the nitrogenous substances present in that of cow). They constitute the insoluble protein fraction of milk, which precipitates (coagulates) at pH 4.6 and / or due to the addition of rennet. They are therefore essential in the cheese-making processes (from which cheese is obtained). The casine boast a good biological value by virtue of the excellent composition of essential amino acids.
- Whey-proteins (or whey protein or whey protein): they abound in the whey residual from the cheese-making and are distinguished by their very high biological value. They constitute the soluble protein fraction of milk at pH 4.6 and represent 17% of the content total nitrogen of the cow's milk During the heating of the milk the whey proteins are denatured while the casein micelles undergo only small changes.
- Proteins with enzymatic activity (antibacterial such as lysozyme, immunological such as immunoglobulins and lactoperoxidase, trophic such as lactoferrin which favors the absorption of iron, digestive as protease and lipase ...). These proteins do not have a purely nutritional purpose, but for their actions contribute to improving the state of health.
- Non-protein nitrogen: urea is the main non-protein nitrogen compound in milk; its values depend on the state of health of the animal.
Good sources of caseins they are represented by aged cheeses, while whey proteins abound in dairy products produced with whey, such as ricotta. The two protein fractions are also present in many protein supplements.
Nutritional characteristics of caseins
DEEPENING
In milk, caseins are mostly found in the form of micelles, large spherical protein aggregates dispersed in the milk mass with the hydrophilic part facing outwards and the hydrophobic part concentrated in the internal "core". Knowing these aspects is important. to understand the different properties of casein supplements.
Casein micelles are the result of the association of other smaller spherical particles, the submicells.Each submicell is made up of many casein molecules, but they are not all the same. In fact, 4 different proteins are known: αs1-casein, αs2-casein, β-casein and k-casein. The first three are strongly hydrophobic and tend to precipitate in the presence of calcium; k-casein is instead made up of two different parts, one more hydrophobic and one more hydrophilic: the hydrophobic portion of k-casein integrates perfectly with the other caseins, while the hydrophilic part turns towards the outside of the micelle, in contact with the surrounding liquid environment; a sort of shield is thus formed which protects the other caseins from contact with calcium ions (which would cause them to precipitate). Furthermore, this shield is negatively charged and this causes the various micelles to repel each other.
Inside the micelle are incorporated small quantities of lactose and mineral salts such as calcium and phosphorus, which have the function of stabilizing the structure. On the outside we find instead the whey, containing lactose, whey-proteins and organic ions of small dimensions .
The size of the micelles varies according to the type of milk; in that of a woman, for example, they have a smaller diameter than that of cow's milk and this makes human casein more digestible. The stomach proteases, in fact, must break down these micelles before attacking and digesting the proteins concentrated inside them; in this sense, the increase of the specific surface (smaller micelles) facilitates the digestive action. Similarly, in the dairy industry smaller micelles mean faster, thicker curds.
With the addition of rennet (proteolytic enzymes), the k-casein is broken in two, its protective action is lost and the various caseins, instead of repelling each other, aggregate and form the curd. With acidification, however, the charge is lost. -negative of the micelles with consequent tendency to aggregation.
BIOLOGICAL VALUE
From the point of view of the amino acid composition, caseins are rich in proline and phosphorylated amino acids, while they are relatively poor in sulfur amino acids (especially cystine). For this reason, considered individually, they have a good but not optimal biological value. Instead, they contain greater amounts of glutamine, arginine and phenylalanine than whey. In this regard it is interesting to note once again the "wisdom" of nature, given that in the whole food the amino acids lacking in the caseins are compensated by the richness in sulfur amino acids of the whey proteins.
The athlete who takes casein protein supplements should not worry about the relative deficiency of sulfuric AAs, as it is necessary to consider the protein intake of the diet as a whole instead of focusing on the single carrier food. Sulfur amino acids are well represented in fish and meat, especially in the connective tissues, which generally abound in the sportsman's diet.
DIGESTIBILITY "
Due to their nature and tendency to form micelles (which are very resistant to heat and dehydration, so they can be found in protein supplements), caseins are known to represent a "slow-absorbing" protein source. Compared to whey proteins, therefore, caseins are digested and absorbed more slowly, ensuring a more delayed entry of amino acids into the bloodstream. For the same reason, at the same dosage, they have a lower insulin index and a greater satiating power.
From all these premises derives the advice to take casein supplements away from training and / or before going to bed for night rest, in order to stimulate protein synthesis and limit the catabolic phenomena induced by prolonged night fasting.
Compared to whey proteins, caseins tend to give more viscous and sticky solutions (lower solubility).
The graph shows the slower absorption rate of casein amino acids compared to whey protein. It was performed by measuring the circulating appearance of radiolabeled leucine (13C Leucine) after the administration of a meal of casein or radiolabeled whey protein. The horizontal bar shows the time intervals in which the differences between the two proteins are significant.
Source: Boirie Y, Dangin M et al. Slow and fast proteins differently modulate postprandial protein accretion. Proc Natl Acad Sci USA, 1997; 94: 14930-5.
CONTENT IN MINERALS
The calcium concentration is higher in caseins than in whey proteins. Much depends, however, on the extraction techniques adopted.
Calcium Caseinate (or Calcium Caseinate)
A caseinate is a casein made soluble (in water) by the addition of alkali; this solution is then dried using the spray-dry process or on cylinders.
At a neutral or acidic pH, caseins are relatively insoluble in water and therefore are easily separable from other milk proteins, lactose and minerals.
To produce the calcium caseinate supplements, the skim milk caseins are then precipitated with acids up to their isoelectric point (pH 4.6); A repeated washing with water and new acid precipitations are then carried out to eliminate the excess of lactose and salts. At this point, adding a calcium hydroxide solution and injecting steam, the precipitated casein is subjected to an increase in pH which transforms into a viscous solution of calcium caseinate, then dried on cylinders or through a process called spray-dry.
Similarly to the whey proteins obtained by ion exchange, calcium caseinate boasts a high degree of purity; in fact, it contains a higher protein percentage, greater solubility in water, less fat, less lactose and less sodium. For these characteristics it should therefore have a faster digestibility, while the negative aspects derive from the partial protein denaturation induced by chemical treatments.
Micellar Caseins
They are obtained through the use of physical, semi-permeable or ion-selective filters, the type of which influences the degree of "purity" of the casein supplement. Similarly to whey proteins, two main techniques are known, microfiltration and ultrafiltration. The selectivity of these filtration processes (favored by forces such as pressure, electrical potential or concentration) determines the degree of purity (intended as the residual percentage of fats, lactose and mineral salts); in general, micellar proteins represent a less pure protein source than calcium caseinate, characterized by higher percentages of fat, lactose and sodium. However, it should be noted that the improvement of production techniques will likely lead to a reduction in the gap with respect to calcium caseinate within a short time, reaching levels of purity that can be superimposed with the advantage of protein non-denaturation. The main value of micellar caseins derives in fact from the conservation of the original micellar structure, which preserves its biological function (instead altered by the chemical processes used to obtain calcium caseinate). The addition of soy lecithin can improve its solubility, resulting in products generally referred to as instant micellar caseins.
Hydrolyzed Caseins
These supplements are obtained by subjecting the caseins to enzymatic digestion, which breaks down the peptide bonds of the proteins, reducing them into more rapidly digestible and absorbable fragments. In this way, many of the distinctive characteristics of caseins are lost compared to whey proteins: digestion times are reduced (theoretically) and the insulin stimulus increases, therefore the only substantial difference remains the amino acid profile. Even if these statements do not seem to make a fold from the theoretical point of view, what seems obvious based on the physiology of protein metabolism is not always confirmed by scientific studies; for example, some studies have shown that both casein and whey protein hydrolyzates do not seem to present significant differences in terms of digestion / absorption times compared to intact proteins.
Hydrolyzed caseins have better solubility characteristics and a much higher cost.
To conclude, in the table we compare the nutritional values and the amino acid profile of calcium caseinate, micellar caseins and whey proteins.
Values extrapolated from the data sheets of some raw materials used for the production of the related casein and whey protein supplements: 1Calcium Caseinate 385 - NZMP Fronterra; 2 Calcium Caseinate 41638 DMV; 3 Micelles milk protein isolate powder MPI85 Benseng Foodsupplement BV; 4Carbery Isolac Instant.
