• Amino acid;
  • breast milk;
  • casein;
  • infant formula;
  • α-lactalbumin;
  • milk protein;
  • tryptophan;
  • whey protein

Summary Demineralized whey, whey protein concentrates and, to a lesser extent, some other whey protein fractions are key raw materials in infant formula manufacture. An estimate of the amount of whey protein used in infant formulae annually is in the order of 30–40 000 tons. Infant formula development has been a long lasting effort to approach the nutrient composition of human breast milk while using cow's milk as the raw material. This required extensive fractionation of the bovine milk followed by subsequent recombination of specific fractions. Criteria to judge protein quality and define adequate protein quantity in infant formulae have also evolved. Early criteria for protein adequacy were based on Protein Efficiency Ratio (PER) testing in rats and/or nitrogen balance studies. More recently, the approach of essential amino acid scores, based on the amino acid pattern of mature human milk has been put forward. Regulatory authorities such as CODEX, EC Commission and more recently LSRO in its suggestions to FDA in the USA, have issued reference amino acid profiles which are based on the average amino acid composition of human milk. The same authorities have also regulated protein density in infant formulae, accounting for an observed protein mean density of 1.5–1.6 g /100 kcal in mature breast milk. The minimum protein level of cow's milk based infant formulae was fixed at 1.8 g/100 kcal by these authorities. Current infant formulae have however protein densities significantly higher than the minimum of 1.8 g/100 kcal. The higher protein density compensates for the likeliness that the protein in the best of the formulae, is not as ideal for the infant as the protein from breast milk. Even if a complete equivalence may be difficult to reach, efforts continue in the direction of further optimizing the protein quality in terms of essential and semi-essential amino acid profiles. This is the only way to be able to lower the protein content in a formula to levels that are nearer to the low protein density of human milk. Among several possibilities, the increase in the mass proportion of bovine α-lactalbumin is a particularly promising way to achieve this goal.