Crude protein content and amino acid composition in Taiwanese human milk.

Breast 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/100mL 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 1 g 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.