Protein quality

The quality of any protein can be assessed using a classification system based on several variables:

BIOLOGICAL VALUE (VB or BV): represents the amount of nitrogen actually absorbed and used net of urinary, fecal, cutaneous losses, etc. A protein that has a perfect balance between absorbed amino acids and between believed amino acids has a biological value of 100. The reference protein is that of the egg that has a VB equal to 100%

NB: cooking food greatly decreases the biological value of proteins (for example, after cooking, chicken meat has a VB of 76 and beef meat even 50)

PROTEIN EFFICIENCY REPORT (PER) : indicates the weight increase in grams for each gram of ingested protein (3.1 for milk; 2.1 for soy)

DIGERIBILITY (D, PD) or digestive utilization coefficient (CUD): ratio between absorbed and ingested nitrogen (in descending order wheat, milk and soy)

NET PROTEIN USE (NPU): represents the amount of ingested nitrogen that is retained by the organism.

AMINO ACID LIMITING : Represents that essential amino acid that becomes limiting for protein synthesis because it is contained in reduced quantities compared to other amino acids. In proteins of plant origin this amino acid is generally not sufficient to guarantee the needs and must be introduced through the combination with other foods.

INDEX OR CHEMICAL SCORE (IPC) : it is the ratio between the quantity of a given essential amino acid in a gram of the protein under examination and the quantity of the same amino acid in a gram of the biological reference protein (of the egg). The higher this index, the greater the percentage of essential amino acids. For example, if the quantity of a limiting amino acid in a "test" protein is 2% and the amount of amino acid limiting in the reference protein (ALBUMIN) is 5%, the chemical score is 40%.

CONTENT IN ESSENTIAL AMINO ACIDS: those proteins containing all the essential AAs in quantity and in balanced relationships can be defined as complete or noble. In general, animal proteins are complete and plant proteins are incomplete. The noble wording associated with vegetable proteins is incorrect and was introduced to counter the saying that "legumes are the meat of the poor". In reality, taking a decent source of vegetable protein in the diet is very important and to further enhance this concept the term "noble" has been improperly introduced. In any case, these deficiencies can be overcome simply by using appropriate food associations such as PASTA and FAGIOLI. In this case we speak of mutual integration because the amino acids of which the pasta is lacking are supplied by the beans and vice versa.

PDCAAS ( Protein Digestibility Corrected Amino Acid Score or amino acid value corrected for protein digestibility ): this is a new method for measuring protein quality, based on the amino acid demands of the human organism. The PDCAAS, which was adopted by the FDA and the FAO / WHO as an ideal system to classify protein quality, takes into account both the amino acid content and the digestibility of proteins. It is therefore an index similar to the chemical score, which instead of considering the profile of egg proteins as ideal, uses as a reference the optimal amino acid supply of children aged 2-5 years; it also takes into account, very importantly, the digestibility of the considered protein. The age group examined (2-5 years) is the one in which the need for protein per kg, and therefore for single amino acids, is maximum.

The highest PDCAAS value is 1.0, the minimum 0; therefore every protein with a value of 1.0 is considered complete for humans (after its digestion it provides, per unit, 100% or more of the essential amino acids required).

When relying on PDCAAS to determine the quality of a protein, it must always be taken into account that the combination of two incomplete but complementary protein sources (eg wheat and legumes) brings the overall PDCAAS of the meal closer to unity.