As protein has prime importance in diet and its quality depend upon the Net Protein utilization that is the proportion of protein ingested and retained in the body under specified conditions. But its high level is important in order to proper growth and maintenance of the body.But a large group of the population protein is not of high quality as Net Protein utilization is found in 50-80%.in diet.
What property of protein differentiates utilizable, high-quality protein from non-utilizable protein? Is it the nature of the protein itself (structure, amino acid composition), the matrix in which the protein is found (vegetable matter, muscle tissue), the manner of preparation (raw, cooked, how cooked)?
There are two factors involved. (1). The amount of essential amino acids in the protein and (2) They ALL need to be present. Protein synthesis requires a full complement of the essential amino acids. If only one is missing, the protein cannot support protein synthesis and so is a poor quality protein. Note that if the 'missing or deficient' amino acid is supplied by another protein, which might also be imbalanced, the two together will supply a good amino acid mix, the net effect is that individually the two proteins are of poor quality, but when given together the overall quality is good and there is no problem.
T Peter Stein: Since not all the amino acids are essential in the diet, is it only necessary that the mixture of proteins contain all the essential amino acids?
T. Peter Stein. Just You need to know the essential amino acids content and the requirements for the population that you want the diet.
Proein quality is essentially a function of two variables,namely: the digestibility and the aminoacid composition of the dietary protein.There are different ways to quantify. These are: the Biological value (BV) ,the Protein Efficiency Ratio (PER), the Amino Acid Score (AAS),and the Protein Digestibility Corrected Amino Acid Score (PDCAAS).The PDCAAS has a maximum value of 1.0;milk, egg,and isolated soy proteins have this maximum value.It is interesting to note that combining wheat (PDCASS=0.4) or other grains (limited by lysine) with beans (PDCAAS 0.6-0.7, limited by methionine) yields a PDCAAS close to 1.0.
You may also find the following paper relevant:
Br J Nutr. 2012 Aug;108 Suppl 2:S183-211. doi: 10.1017/S0007114512002309.
the assumption the protein has PRIME importance in the diet needs qualification. ALL essential nutrients are of "prime importance" and in terms of utilisation of nitrogen, it will do a large extent depend not only on the balance of amino acids, but also on the balance with the other type II nutrients. Thus the utilistation of different amino acid mixes will depend upon an adequate intake and availability of zinc, phosphorus, mangensium, potassium, inorganic sulphate etc. they are all important. the most limiting nutrient in most populations health are not essential amino-acids but other elements that are not normally considered such as zinc and available (non-phytate) phosphorus etc. You question is much more complicated than commonly posed. By making sure that ALL type II nutrients are in adequate supply and balance we have shown remarkable improvements in the treatment of the malnourished child (see data on RUTF) - and years ago showed an improvement in lean body mass accretion and utilistation of nutrients with supplements of the limiting type II nutrients.
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