Crude Protein Content and Amino Acid Composition in Taiwanese Human Milk.

Abstract

SummaryBreast milk provides the essential nutrients for infants in readily available form. The content of nitrogen in human milk is of great importance because it relates to the growth of infants in the early stage, and the composition of nitrogenated compounds varies according to the lactational stage. Three-hundred-and-three human milk specimens were obtained from 240 healthy mothers living in two different districts in Taiwan, and 264 specimens were used for the analysis. The crude protein content, total and free amino acid compositions as well as urea content were evaluated using pooled milk samples according to different lactational stages and geographical location. The crude protein content de creased sharply from colostrum (2.51g/100mL) to mature milk (1,25g/100mL), Total amino acids account for 80-85% of the crude protein throughout the whole lactation pe riod. Crude protein also contained 30 to 35mg/l00mL urea and 41 to 48mg/100mL free amino acids as non-protein nitrogen components. The ratio of essential to non-essential amino acids remained constant throughout the lactation period in spite of a decline in amino acid content. The amino acid composition per 1g of nitrogen varied during the lacta tion period. The differences of these lactational changing patterns of individual amino acids were probably reflected by variation of the protein composition during lactation. The sum of free amino acid content ranged from 43 to 50mg/100mL in Taipei and 40 to 45mg/100mL in Kaohsiung. Although the variations of free amino acids during the lacta tion period differed among amino acids, glutamic acid predominated in mature milk while phosphoethanolamine was predominant in colostrum.

A nine-country study of the protein content and amino acid composition of mature human milk

“…5) (5–19). The mean total protein and amino acid concentrations reported here are also consistent with previously reported data (6, 12, 14, 15, 17, 18, 20). …”

“…Enrolling mothers over a broad range of days, post-partum, permitted the assessment of amino acid and protein levels across several stages of lactation. It has been shown previously that the protein level and amino acid content in human milk decrease over the course of lactation (20), whereas maternal race/ethnicity, age, and maternal dietary protein intake appear to have little effect on the total protein in human milk (22). …”

Evaluation of a novel food composition database that includes glutamine and other amino acids derived from gene sequencing data

“…Likewise, free amino acids found in foods were not included in the final calculation of amino acids in food proteins because of their short half-life and small contribution to total nitrogen in food (Schloerb et al ., 2002). For example, free amino acids contribute to <2% of the total protein in yolk solids (Osuga and Feeney, 1977) and breast milk (Wu et al ., 2000). Finally, we used similar food proteins for missing food items.…”

Revised Reference Values for the Intake of Protein

“…After correction for the nonprotein nitrogen (NPN, estimated to 25%), the average protein content in breast milk is 1.36 g/100 mL in the first month after birth and 1.17 g/100 mL in the second and third month after birth. Taking into account a daily average breast milk intake [21] of 600 mL/day (0 to under 1 month), 694 mL/day (1 to under 2 months) and 723 mL/day (2 to under 4 months), respectively [22], the protein intake in all 3 age groups is 8 g/day. In consideration of the reference body weights, the estimated reference values (g/kg body weight per day) for protein intake are 2.5 for infants at the age of 0 to under 1 month, 1.8 for infants at the age of 1 to under 2 months, and 1.4 for infants at the age of 2 to under 4 months ( Table 1).…”