Protein quality

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 There are various methods that rank the quality of different types of protein, some of which are outdated and no longer in use, or not considered as useful as they once were thought to be.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 current protein ranking standard in use is the Protein Digestibility Corrected Amino Acid Score (PDCAAS), which was recommended by Food and Agriculture Organization (FAO), and became the industry standard in 1993, and FAO has recently recommended the newer Digestible Indispensable Amino Acid Score (DIAAS) to supersede PDCAAS, due to the limitations of PDCAAS. The dairy industry is in favor of this, 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, and as such, 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.

PDCAAS versus DIAAS

The main limitations of PDCAAS is that it doesn't take into account anti-nutrient factors like phytic acid and trypsin inhibitors, which limit the absorption of protein among other nutrients. For this reason, DIAAS is promoted as the superior method and preferable over the PDCAAS. 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.

Protein ranking

Below follows a table that compares various proteins based on their rankings. Some of these results may differ and vary significantly depending on if it is soybeans or soy protein isolate, and so on. For example, while soybeans have a PDCAAS score of 0.91, many soy protein isolates (though not all) typically get a PDCAAS score of 1.0, and as such, is a complete protein. Likewise, the amino acid profile may differ from crop to crop depending on the soil, and between different breeds of soy. Generally speaking, however, soybeans rarely outperform whey protein isolate in PDCAAS rankings.

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?
Whey 3.2 92% 104 N/A 8-10 g/h N/A 1.0 1.09[1] None Yes
Casein 2.5 85-92% 77[2] 95.1-97.6% 6.1 g/h 1.19 1.0 None Yes
Egg 3.9 94% 100 97%[3] 1.3-2.8 g/h[4] N/A 1.0 None Yes
Beef 2.9[5] 73% 80 N/A N/A N/A 0.92 N/A Tryptophan No
Soy 2.2 61% 74 86% 3.9 g/h N/A 0.91 0.898-0.906 Meth+Cyst Yes
Rice N/A N/A N/A N/A N/A 0.50 Lysine No
Pea N/A N/A N/A 2.4-3.4 g/h 0.70 Meth+Cyst No
Hemp N/A N/A 87[6] 94.9% N/A 0.64 0.61 Lysine No
Mycoprotein N/A N/A N/A 86% N/A N/A 0.996[7] Meth+Cyst No
Spirulina 1.8-2.6[8] 53-92% 68[9] 83-90% N/A N/A None Yes
Chlorella N/A N/A N/A N/A N/A N/A Meth+Cyst No

Amino Acid profile

Below follows a table that compares the complete amino acid profiles of various proteins. 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. The proteins deficient in an essential amino acid, are technically not complete proteins, but may still be considered as such if it is a slight deficiency in only one limiting amino acid (many vegan proteins are deficient in several EAAs).

Amino acid profiles and requirements
Essential Amino Acids Required per 100 g of protein[10][11] Human breast milk[12] Hemp seeds (shelled)[13] Hemp (hydrolyzed) Soybeans (Edamame)[14] Spirulina[15] Chlorella[16] Whey[17] Casein[18] Egg white[19]
Histidine 1.8 g 2.233 g 3.071 g 2.9 g 2.687 g 1.888 g 3.3 g 1.974 g 3.2 g 2.660 g
Isoleucine** 2.5 g 5.437 g 4.075 g 4.1 g 4.402 g 5.584 g 3.5 g 5.001 g 5.4 g 6.064 g
Leucine** 5.5 g 9.224 g 6.855 g 6.9 g 7.151 g 8.608 g 6.1 g 9.475 g 9.5 g 9.321 g
Lysine 5.1 g 6.602 g 4.044 g 4.2 g 5.985 g 5.264 g 10.2 g 8.554 g 8.5 g 7.394 g
Meth + Cyst 2.5 g 3.884 g 5.087 g 4.1 g 2.123 g 3.151 g 1.6 g 3.684 g 3.5 g 6.293 g
Phen + Tyr 4.7 g 9.612 g 8.588 g 8.2 g 8.108 g 9.328 g 5.6 g 5.790 g 11.1 g 10.486 g
Threonine 2.7 g 4.466 g 4.021 g 3.3 g 3.985 g 5.168 g 2.9 g 5.001 g 4.2 g 4.119 g
Tryptophan 0.7 g 1.651 g 1.169 g 0.8 g 1.212 g 1.616 g 2.1 g 2.106 g 1.4 g 1.147 g
Valine** 3.2 g 6.117 g 5.631 g 5.3 g 4.448 g 6.111 g 5.5 g 5.001 g 6.3 g 7.422 g
Total EAAs 28.7 g 49.226 g 42.541 g 39.8 40.101 g 46.718 g 40.8 g 46.586 g 53.1 g 54.906 g
Non-Essential Amino Acids Required? Human breast milk Hemp seeds (shelled) Hemp (hydrolyzed) Soybeans (Edamame) Spirulina Chlorella Whey Casein Egg white
Alanine Varies 3.495 g 4.842 g 5.2 g 4.494 g 7.856 g 7.7 g 4.343 g N/A 6.458 g
Arginine* Varies 4.175 g 14.419 g 12 g 8.046 g 7.216 g 15.8 g 2.764 g 3.7 g 5.945 g
Asparagine* Varies N/A N/A N/A N/A N/A N/A N/A N/A N/A
Aspartic acid Varies 7.961 g 11.605 g 10.9 g 11.645 g 10.080 g 6.4 g 9.738 g N/A 11.192 g
Cysteine* Varies N/A N/A N/A N/A N/A N/A N/A N/A N/A
Glutamic acid Varies 16.311 g 19.866 g 17.2 g 18.788 g 14.592 g 7.8 g 17.898 g N/A 14.220 g
Glutamine* Varies N/A N/A N/A N/A N/A N/A N/A N/A N/A
Glycine* Varies 2.524 g 5.105 g 4.9 g 4.162 g 5.392 g 6.2 g 1.842 g N/A 3.789 g
Proline* Varies 7.961 g 5.061 g 4.7 g 4.687 g 4.145 7.2 g 5.922 g N/A 3.991 g
Selenocysteine Varies N/A N/A N/A N/A N/A N/A N/A N/A N/A
Serine* Varies 4.175 g 5.428 g 5.3 g 5.568 g 5.217 3.3 g 4.606 g N/A 7.321 g
Tyrosine* Varies 5.146 g 4.002 g 3.5 g 3.583 g 4.496 g 2.8 g 2.500 g N/A 4.193 g
Total non-EAAs 51.208 g 70.328 g 63.7 g 60.973 g 58.994 g 57.2 g 49.613 g N/A 57.109 g
22nd Amino Acid Required? Human breast milk Hemp seeds (shelled) Hemp (hydrolyzed) 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

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

References

  1. ↑ http://jn.nutrition.org/content/early/2014/11/26/jn.114.195438.full.pdf
  2. ↑ http://www.jssm.org/vol3/n3/2/v3n3-2pdf.pdf
  3. ↑ http://www.blv.admin.ch/themen/04679/05108/05869/index.html?lang=de&download=NHzLpZeg7t,lnp6I0NTU042l2Z6ln1acy4Zn4Z2qZpnO2Yuq2Z6gpJCFfX1,fGym162epYbg2c_JjKbNoKSn6A--
  4. ↑ https://www.researchgate.net/profile/Neil_Mann/publication/7003706_A_review_of_issues_of_dietary_protein_intake_in_humans/links/0c960514d545ac59a2000000.pdf
  5. ↑ http://www.jssm.org/vol3/n3/2/v3n3-2pdf.pdf
  6. ↑ http://www.nutritionaloutlook.com/articles/plant-protein-versus-dairy-protein-muscle-building
  7. ↑ http://journals.cambridge.org/download.php?file=%2FPNS%2FPNS69_OCE4%2FS0029665110001400a.pdf&code=bee01b2804c41b400e7fa9d615b280fd
  8. ↑ http://www.researchgate.net/profile/M_Mozafari/publication/236095734_Nutritional_and_Medical_Applications_of_Spirulina_Microalgae/links/004635200924e5b75a000000.pdf
  9. ↑ http://www.researchgate.net/publication/16391549_Nutritional_quality_of_the_blue-green_alga_Spirulina_platensis_Geitler
  10. ↑ http://www.umich.edu/~exphysio/mvs.241/RI.macronutrients.pdf
  11. ↑ http://nutritiondata.self.com/help/analysis-help#protein-quality
  12. ↑ https://ndb.nal.usda.gov/ndb/foods/show/96?fg=&man=&lfacet=&count=&max=35&qlookup=human&offset=&sort=&format=Full&reportfmt=other&rptfrm=&ndbno=&nutrient1=&nutrient2=&nutrient3=&subset=&totCount=&measureby=&_action_show=Apply+Changes&Qv=97.09&Q300=1&Q301=1
  13. ↑ https://ndb.nal.usda.gov/ndb/foods/show/3614?man=&lfacet=&count=&max=&qlookup=&offset=&sort=&format=Full&reportfmt=other&rptfrm=&ndbno=&nutrient1=&nutrient2=&nutrient3=&subset=&totCount=&measureby=&_action_show=Apply+Changes&Qv=3.169&Q6777=3.0
  14. ↑ https://ndb.nal.usda.gov/ndb/foods/show/3162?man=&lfacet=&count=&max=&qlookup=&offset=&sort=&format=Full&reportfmt=other&rptfrm=&ndbno=&nutrient1=&nutrient2=&nutrient3=&subset=&totCount=&measureby=&_action_show=Apply+Changes&Qv=7.722&Q5983=1
  15. ↑ https://ndb.nal.usda.gov/ndb/foods/show/3306?man=&lfacet=&count=&max=35&qlookup=spirulina&offset=&sort=&format=Full&reportfmt=other&rptfrm=&ndbno=&nutrient1=&nutrient2=&nutrient3=&subset=&totCount=&measureby=&_action_show=Apply+Changes&Qv=1.74&Q6228=1&Q6229=1
  16. ↑ Fowden, L (1952). "The composition of the bulk proteins of Chlorella". Biochem. J. 50: 355–8. doi:10.1042/bj0500355. PMC 1197660Freely accessible. PMID 14915957.
  17. ↑ http://ndb.nal.usda.gov/ndb/foods/show/101?fg=&man=&lfacet=&count=&max=35&qlookup=whey&offset=&sort=&format=Full&reportfmt=other&rptfrm=&ndbno=&nutrient1=&nutrient2=&nutrient3=&subset=&totCount=&measureby=&_action_show=Apply+Changes&Qv=131.6&Q310=1&Q311=1
  18. ↑ http://www.fao.org/docrep/u5900t/u5900t07.htm
  19. ↑ https://ndb.nal.usda.gov/ndb/foods/show/113?fg=&man=&lfacet=&count=&max=35&qlookup=egg+white&offset=&sort=&format=Full&reportfmt=other&rptfrm=&ndbno=&nutrient1=&nutrient2=&nutrient3=&subset=&totCount=&measureby=&_action_show=Apply+Changes&Qv=9.174&Q352=1&Q353=1
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