Amino acids and protein quality of milk
Proteins are bio-molecules that are made up of smaller building blocks called amino acids. There are twenty different amino acids in total, nine of which are essential. Milk has a high protein quality, as it contains all nine essential amino acids in relatively high quantities.
Essential and non-essential amino acids
Essential and non-essential amino acids form the basic material of all proteins found in the diet. The liver can make non-essential or dispensable amino acids if dietary intake is insufficient, but it cannot produce the nine essential amino acids. A sufficient dietary intake is therefore necessary to meet the body’s requirements.
Amino acid profile dairy versus other sources
All essential amino acids are present in milk proteins in relatively high amounts. Table 2 provides the amino acid profile of various animal and plant proteins, in comparison with the FAO requirement. Methionine and cysteine, the sulphur-containing amino acids, are often grouped together as they are metabolically close. The same is true for aromatic amino acids phenylalanine and tyrosine. This is reflected in the recommendations below.
|mg /g protein||milk||egg||beef||soy||wheat||rice||FAO requirements|
|SAA = methionine + cystein ; Aromatics = phenylalanine + tyrosine|
Protein and amino acid requirements
The FAO has defined amino acid requirements per age group. The amino acid requirements for children above the age of three, adolescents and adults are similar. However higher protein and amino acid recommendations are for instance given to pregnant and lactating women – together with the advice to obtain additional proteins from food sources rather than from supplements. There are currently ongoing discussions about higher protein requirements for the elderly.
FAO/WHO/UNU Expert Consultation (2007). Expert consultation on protein and energy requirements. Protein and amino acid requirements in human nutrition. WHO Technical Report Series nr. 935.