Reference
Essential Amino Acid Index (EAAI)
**Essential Amino Acid Index (EAAI)** is a composite measure of protein quality calculated as the geometric mean of the ratios between each essential amino acid in a test protein and the corresponding amounts in a reference protein, traditionally whole egg.
How it is calculated
The EAAI evaluates all of the essential amino acids at once rather than only the single most deficient one. For each of the nine essential amino acids, the content in the test protein is divided by the content in the reference pattern, and the geometric mean of those ratios produces a single index value. A protein matching the reference across every essential amino acid yields an index near 1.0 (or 100%); a protein deficient in one or more essential amino acids yields a lower value.
This makes the EAAI distinct from the amino acid score, which is determined only by the limiting amino acid — the one in shortest supply relative to requirement. Because the index averages across all essential amino acids, a single shortfall lowers the EAAI less sharply than it lowers the amino acid score.
How EAAI relates to other quality scores
The EAAI is one of several chemical and biological methods used to rank proteins. It is closely associated with biological value (BV), since proteins with amino acid profiles near the reference tend to be retained efficiently. It differs from the PDCAAS and DIAAS systems, which combine an amino acid score with a digestibility correction. PDCAAS, developed in 1989 by a Joint FAO/WHO Expert Consultation, compares a food protein against a reference requirement pattern and corrects for digestibility, while DIAAS, proposed by the FAO in 2013 as its replacement, uses ileal digestibility and does not truncate scores at 1.0. The EAAI, by contrast, is a purely compositional index and applies no digestibility adjustment.
Relevance to potato protein
Potato protein isolate contains all nine essential amino acids and supplies about 37% essential amino acids by weight, compared with roughly 43% for whey protein isolate (Amino Acids, 2018, PMID:30167963). Its reported amino acid score is 65% (PMID:34507729), reflecting a limiting amino acid, yet its measured Digestible Indispensable Amino Acid Score has been reported as high as 100 (Food Science & Nutrition, Herreman et al., 2020, PMID:33133540), because digestibility-based scoring weights the surplus of well-absorbed amino acids differently from a strict limiting-amino-acid index. For readers comparing supplement labels, the best protein powder guide explains how these quality metrics translate into practical selection.
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