Amino Acid Composition and Protein Content of Mature Human Milk from Nine Countries

Abstract

This study represents analysis of 220 human milk samples from nine cities in nine countries crossing five continents. Samples were collected from mothers from 18 to 40 years of age with a lactation range from 30 days to 188 days. Amino acids were analyzed using Waters Accq_Tag HPLC method. Total protein was calculated from the nitrogen content multiplied by a protein factor of 6.25. The nitrogen content was analyzed using FP‐528 nitrogen analyzer made by LECO Corporation. True protein was calculated from amino acid analysis and includes protein, free amino acids and peptides. Total protein, true protein, and the amino acid composition are not influenced by mother's age, and are statistically similar among locations, with the exception of samples from Chile, which had higher total protein and true protein. True protein is approximately 76% of total protein, is statistically similar among locations, and is not influenced by mother's age or days of lactation. Total protein, true protein, and individual amino acid concentrations in human milk steadily decline from 30 to 151 days of lactation, and are significantly higher in the second month than in the following four months. The amino acid profiles are statistically similar among locations. These results confirm higher protein and amino acid levels in early lactation and demonstrate consistency in the protein and amino acid composition of human milk across all locations.