Human milk nonprotein nitrogen components: changing patterns of free amino acids and urea in the course of early lactation

• Published in: The American journal of clinical nutrition Vol. 40; no. 2; pp. 303 - 309
• Main Authors: Harzer, G, Franzke, V, Bindels, J.G
• Format: Journal Article
• Language: English
• Published: United States Elsevier Inc 01.08.1984
• Subjects: ACIDE AMINE; Amino Acids - analysis; AMINOACIDOS; CONTENIDO DE NUTRIENTES; Female; FEMME; free amino acids; Glutamates - analysis; Glutamic Acid; Human milk; Humans; LACTACION; LACTATION; LAIT HUMAIN; LECHE HUMANA; Milk, Human - analysis; MUJERES; Nitrogen - analysis; nonprotein nitrogen; Pregnancy; TENEUR EN SUBSTANCES NUTRITIVES; Time Factors; urea; Urea - analysis; Human milk; nonprotein nitrogen; lactation; free amino acids; urea
• ISSN: 0002-9165; 1938-3207
• DOI: 10.1093/ajcn/40.2.303

Free amino acids and urea were analyzed in 78 human milk samples obtained during the first 5 wk of lactation from 10 mothers delivering at term. Significant differences (p &lt 0.05) in the concentrations between colostral and mature milk were found for glutamic acid, glutamine, alanine, glycine, cystine, and phosphoethanolamine which increased, and with serine, phosphoserine, aspartic acid + asparagine, arginine, lysine, isoleucine, phenylalanine, proline, methionine, tryptophan, and β-alanine which decreased. Some of these changes occurred within the first 5 days of lactation, so that differences between transitional and mature milk became negligible (glutamic acid, alanine, and serine, aspartic acid + asparagine, lysine, isoleucine, methionine, tryptophan, respectively). No significant differences between any of the three stages of lactation were found regarding the concentrations of total free amino acids, urea, taurine, threonine, valine, leucine, histidine, and tyrosine. Possible relevances for free amino acids, including nonprotein ones, in human milk are discussed.