Protein Digestibility Corrected Amino Acid Score (PDCAAS) is a method of evaluating the protein quality based on the amino acid requirements of humans. The PDCAAS rating is a fairly recent evaluation method (it was adopted by the US Food and Drug Administration in 1993) and emerged due to weaknesses in earlier evaluations of protein quality, such as the Protein Efficiency Ratio (PER) and the Biological Value (BV).
A PDCAAS value of 1 is the highest, and 0 the lowest. Some ratings of commons foods include soy (1.0), egg white (1.0), casein (1.0), milk (1.0), whey (1.0), beef (0.92), kidney beans (0.68), lentils (0.52), peanuts (0.52), wheat (0.25).
Advantages
The PDCAAS is superior to both the PER and the BV. The PER was based upon the amino acid requirements of growing rats, which are noticeably different to that of humans. The BV uses nitrogen absorption as a basis. However, it does not take into account certain factors influencing the digestion of the protein.
Limitations
Amino acids that move beyond the terminal ileum in the body are less likely to be absorbed for use in protein synthesis. They may pass out of the body, or may be absorbed by bacteria, and thus will not be present in the faeces, and will appear to have been digested. The PDCAAS takes no account of where the amino acids have been digested.
Similarly, amino acids that are lost due to antinutritional factors present in many foods (such as tannins in soy) are assumed to be digested by the PDCAAS.
The PCDAAS method may also still be considered incomplete, since human diets, except in times of famine, almost never contain only one kind of protein