Classification of proteins

Classification of proteins

Classification of proteins

In general, in nature there are no food proteins that would be perfectly absorbed by the human body. Scientists believe that the essential amino acids tryptophan, methionine, lysine - in a conventionally ideal food protein should be related as 1.0: 3.5: 5.5.For proteins of freshwater fish - 0.9: 2.8: 10.1;for proteins of chicken eggs - 1.6: 3.3: 6.9;for proteins of fresh milk - 1.5: 2.1: 7.4;for proteins of unrefined wheat grain - 1,2: 1,2: 2,5;for soy proteins - 1.0: 1.6: 6.3.If the food and biological value of a theoretically ideal protein is taken as 100 units, the proteins of fresh cow's milk will score 72 points on this conditional scale, soy proteins - 67 and wheat proteins - 57 points.

In an effort to improve the classification of food proteins, some scientists propose to divide them into four classes. The first of these proteins consisted of proteins with alimentary specificity, in particular proteins of milk and eggs. Although they are inferior in biolog

ical value to, for example, fish proteins and even soybeans, but the human body is able to straighten the aminogram of these proteins due to the available at its disposal a fund of essential amino acids that are lacking in the proteins of these products. In addition, milk and eggs remove the activity of chemical reactions in the body, the result of which is the formation of simple substances from substances of more complex, that is, processes of catabolism. To proteins with alimentary specificity, the modern science of nutrition refers to proteins, the nature itself intended for performing alimentary function, so it is no accident that a chicken egg, sour and fresh milk are considered one of the most valuable products.

The second class includes fish, soybean, rapeseed and cotton seed proteins. These dietary proteins of animal and vegetable origin are distinguished by the best ratio of essential amino acids( aminogram), respectively, with the highest biological value. However, these proteins are also characterized by the so-called absence of a compensation phenomenon. In other words, the organism does not participate in straightening the nonideal aminogram of these proteins due to the fund of its own essential amino acids and does not provide a reduction in their catabolism. The third class of food proteins, according to the same theory, are proteins with a worse balance than in previous cases, a balance of essential amino acids;the worst biological value and even lower values ​​of the phenomenon of compensation. These are mainly proteins of cereals. Finally, in the fourth class of food proteins included proteins in the food ratio are defective, defective, i.e., not containing essential amino acids, with zero biological value. Such proteins are gelatin proteins and, as it may seem strange, proteins of hemoglobin.

The completeness of the breakdown of proteins largely depends on the nature and duration of the heat treatment of the product in which they are contained. For example, at high temperatures in milk, cottage cheese, not only lysine is destroyed, but also an amino acid, methionine, which is slightly heat-resistant.

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