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Protein quality is the digestibility and quantity of essential amino acids for providing the proteins in correct ratios for human consumption. There are various methods that rank the quality of different types of protein, some of which are outdated and no longer in use, or not considered as useful as they once were thought to be. The Protein Digestibility Corrected Amino Acid Score (PDCAAS), which was recommended by the Food and Agriculture Organization of the United Nations (FAO), became the industry standard in 1993. FAO has recently recommended the newer Digestible Indispensable Amino Acid Score (DIAAS) to supersede PDCAAS. The dairy industry is in favor of this[citation needed], because while PDCAAS truncates all protein types that exceed the essential amino acid (EAA) requirements to 1.0, DIAAS allows a higher than 1.0 ranking: while for example both soy protein isolate and whey isolate are ranked 1.0 according to PDCAAS, in the DIAAS system, whey has a higher score than soy.

Contents

PDCAAS versus DIAASEdit

The main limitations of PDCAAS is that it does not take into account anti-nutrient factors like phytic acid and trypsin inhibitors, which limit the absorption of protein among other nutrients, and its use of fecal digestibility, whereas in the DIAAS system, ileal digestibility of the essential amino acids is emphasized as a more accurate measure of protein absorption.[1][2][3] For this reason, DIAAS is promoted as the superior method and preferable over the PDCAAS.[2][4] Due to not factoring in anti-nutritional content into the digestibility equation, the PDCAAS has consequently been criticized for overestimating protein quality.[5] Other older methods like BV, PER, NPU and nitrogen balance may not reveal much about the amino acid profile and digestibility of the protein source in question, but can still be considered useful in that they determine other aspects of protein quality not taken into account by PDCAAS and DIAAS.

Due to the difficulties of measuring amino acid digestion through the ileuem, a minimally invasive dual-tracer method has been developed for the DIAAS method.[6]

Protein sourcesEdit

Protein ranking methods and standards
Protein type PER NPU BV Protein
Digestibility
(PD)
Protein
absorption
rate
Amino
Acid
Score
(AAS)
PDCAAS DIAAS Limiting
amino
acid
Complete
protein
?
Cow's milk 2.5[1] 82%[1] 91[1] 3.5 g/h[7] 1.0[1] None Yes
Whey 3.2[1] 92%[1] 104[1] 8-10 g/h[7] 1.0[1] 0.973-1.09[2][4] Histidine[8] Yes
Casein 2.5[1] 76%[1] 77[1] 97.6%[9] 6.1 g/h[7] 1.19[10] 1.0[1] None Yes
Egg 3.9[1] 94%[1] 100[1] 97–98%[11] 1.3-2.8 g/h[7] 1.19[10] 1.0[1] None Yes
Beef 2.9[1] 73%[1] 80[1] 94–98%[11] 0.94[10] 0.92[1] Tryptophan No
Oat 72,[12] 91%[10] 0.63[10] 0.57[9] Lysine No
Wheat 0.8[1] 67%[1] 64[1] 96–99%[11] 0.26,[11] 0.44[10] 0.25-0.51[1][8] 0.45[8] Lysine[8] No
Maize 1.23[13] 85%,[12] 89%[14] 0.67[14] Lysine[14] No
Rice 2.2[13] 0.42[2] 0.37[2] Lysine No
Quinoa 75.7%[15] 82.6[15] 91.7%[15] 0.667[16] None Yes
Soy 2.2[1] 61%[1] 74[1] 95-98%[11] 3.9 g/h[7] 0.91-1.0[4][1][2] 0.90-0.91[2] Meth+Cyst[8] No
Black bean 0.75[1] Meth+Cyst No
Pea 88%[10][12] 2.4-3.4 g/h[7] 0.89[2] 0.82[2] Meth+Cyst Yes
Peanut 1.8[1] 94[12] 0.52[1] Lysine No
Hemp 87 94.9%[9] 0.64[9] 0.61[9] Lysine[9] No
Mycoprotein 86%[17] 0.996[17] Meth+Cyst No
Spirulina 1.8-2.6[13] 53-92%[13] 68[18] 83-90% Lysine Yes
Chlorella Meth+Cyst No

Amino acid profileEdit

The amino acid score is based on the prevalence of the essential amino acids and depends on if they reach sufficient quantity. PDCAAS scores do not take into account the quantity of the non-essential amino acids. Despite the insufficient essential amino acid profiles of most plant-based proteins, it is possible to combine low lysine with low methionine plant-based proteins, which would yield a more complete protein.[19][1]

Below follows a table that compares the complete amino acid profiles of various proteins.

  First limiting amino acid
  Second limiting amino acid, especially depending on certain age requirements and demanding conditions for EAAs
  Amino acid is technically complete, but might turn out incomplete anyway after digestibility has been factored in
Amino acid profiles and requirements
Essential Amino Acids Required
per 100 g
of protein DRI[20][21][22][23]
Human breast milk[24] Quinoa[25] Corn[26] Oat[27] Hemp
seeds
(shelled)
[28]
Green peas[29] Soybeans (Edamame)[30] Spirulina[31] Chlorella[32] Whey[33] Casein[34] Egg white[35]
Histidine 1.8 g 2.230 g 3.455 g 2.710 g 2.414 g 2.821 g 2.495 g 2.756 g 1.888 g 3.3 g 1.974 g 3.2 g 2.660 g
Isoleucine** 2.5 g 5.673 g 4.279 g 3.928 g 4.137 g 3.744 g 4.547 g 4.514 g 5.584 g 3.5 g 5.001 g 5.4 g 6.064 g
Leucine** 5.5 g 9.623 g 7.132 g 10.597 g 7.654 g 6.296 g 7.532 g 7.334 g 8.608 g 6.1 g 9.475 g 9.5 g 9.321 g
Lysine 5.1 g 6.888 g 6.503 g 4.172 g 4.179 g 3.714 g 7.392 g 6.138 g 5.264 g 10.2 g 8.554 g 8.5 g 7.394 g
Meth + Cyst 2.5 g 4.052 g 4.346 g 2.832 g 4.292 g 4.672 g 2.658 g 2.178 g 3.151 g 1.6 g 3.684 g 3.5 g 6.293 g
Phen + Tyr 4.7 g 10.029 g 7.302 g 8.132 g 8.751 g 7.889 g 7.332 g 8.316 g 9.328 g 5.6 g 5.790 g 11.1 g 10.486 g
Threonine 2.7 g 4.660 g 3.574 g 3.928 g 3.428 g 3.694 g 4.734 g 4.087 g 5.168 g 2.9 g 5.001 g 4.2 g 4.119 g
Tryptophan 0.7 g 1.722 g 1.418 g 0.700 g 1.395 g 1.074 g 0.863 g 1.243 g 1.616 g 2.1 g 2.106 g 1.4 g 1.147 g
Valine** 3.2 g 6.382 g 5.043 g 5.633 g 5.585 g 5.173 g 5.480 g 4.562 g 6.111 g 5.5 g 5.001 g 6.3 g 7.422 g
Total EAAs 28.7 g 51.259 g 43.052 g 42.632 g 46.014 g 39.077 g 43.033 g 41.128 g 46.718 g 40.8 g 46.586 g 53.1 g 54.906 g
Non-Essential Amino Acids Required? Human breast milk Quinoa Corn Oat Hemp
seeds
(shelled)
Green peas Soybeans (Edamame) Spirulina Chlorella Whey Casein Egg white
Alanine Varies 3.647 g 4.992 g 8.983 g 5.252 g 4.448 g 5.597 g 4.609 g 7.856 g 7.7 g 4.343 g N/A 6.458 g
Arginine* 4.356 9.263 g 3.989 g 7.106 g 13.245 g 9.981 g 8.253 g 7.216 g 15.8 g 2.764 g 3.7 g 5.945 g
Asparagine* N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A
Aspartic acid 8.307 g 9.628 g 7.430 g 8.632 g 10.660 g 11.567 g 11.943 g 10.080 g 6.4 g 9.738 g N/A 11.192 g
Cysteine* N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A
Glutamic acid 17.018 g 15.834 g 19.366 g 22.127 g 18.249 g 17.280 g 19.269 g 14.592 g 7.8 g 17.898 g N/A 14.220 g
Glutamine* N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A
Glycine* 2.634 g 5.892 g 3.867 g 5.013 g 4.690 g 4.291 g 4.269 g 5.392 g 6.2 g 1.842 g N/A 3.789 g
Proline* 8.307 g 6.563 g 8.891 g 5.568 g 4.649 g 4.034 g 4.807 g 4.145 7.2 g 5.922 g N/A 3.991 g
Selenocysteine N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A
Serine* 4.356 g 4.814 g 4.659 g 4.471 g 4.987 g 4.221 g 5.710 g 5.217 3.3 g 4.606 g N/A 7.321 g
Tyrosine* 5.369 g 2.267 g 3.745 g 3.409 g 3.677 g 2.658 g 3.675 g 4.496 g 2.8 g 2.500 g N/A 4.193 g
Total non-EAAs 53.994 g 58.257 g 60.93 g 61.578 g 64.605 g 59.629 g 62.535 g 58.994 g 57.2 g 49.613 g N/A 57.109 g
22nd Amino Acid Required? Human breast milk Quinoa Corn Oat Hemp
seeds
(shelled)
Green peas Soybeans (Edamame) Spirulina Chlorella Whey Casein Egg white
Pyrrolysine Not used
by humans
N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A

*Semi-essential, under certain conditions
**Branched-chain amino acid (BCAA)

Different essential amino acid requirements based on ageEdit

While the amino acid scores for PDCAAS and DIAAS are based on toddler requirements (1-3 year olds),[20] the essential amino acid requirements differ for adults and infants.[20] The most demanding essential amino acid requirements are for infants, and as children get older and transition into adulthood, the less proportions of essential amino acids they will need. This also means that many of the vegan protein sources that are limited in one or more essential amino acids, are actually less deficient in essential amino acids for adults, perhaps not deficient at all. The essential amino acid requirements for infants is based on the essential amino acid proportions in human breast milk.[20]

Essential amino acid requirements
Amino Acid required mg per g of protein Infants[20] 1-3 year olds[20] Adults (18+ y)[20]
Histidine 23 18 17
Isoleucine 57 25 23
Leucine 101 55 52
Lysine 69 51 47
Methionine + Cysteine 38 25 23
Phenylalanine + Tyrosine 87 47 41
Threonine 47 27 24
Tryptophan 18 7 6
Valine 56 32 29
Total mg of Essential Amino Acids per g of protein 496 287 262

ReferencesEdit

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