Crude protein content and amino acid composition in Taiwanese human milk

Breast milk provides the essential nutrients for infants in readily availab le form. The content of nitrogen in human milli is of great importance beca use it: relates to the growth of infants in the early stage, and the compos ition 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 wer e used for the analysis. The crude protein content, total and free amino ac id compositions as well as urea content were evaluated using pooled milk sa mples according to different lactational stages and geographical location. The crude protein content decreased sharply from colostrum (2.51 g/100 mL) to mature milk (1.25 g/100 mL). Total amino acids account for 80-85% of the crude protein throughout the whole lactation period. Crude protein also co ntained 30 to 35 mg/100 mt urea and 41 to 48 mg/100 mt free amino acids as non-protein nitrogen components. The ratio of essential to non-essential am ino acids remained constant throughout the lactation period in spite of a d ecline in amino acid content. The amino acid composition per 1 g of nitroge n varied during the lactation period. The differences of these lactational changing patterns of individual amino acids were probably reflected by vari ation of the protein composition during lactation. The sum of free amino ac id content ranged from 43 to 50mg/100mL in Taipei and 40 to 45 mg/100 mL in Kaohsiung, Although the variations of free amino acids during the lactatio n period differed among amino acids, glutamic acid predominated in mature m illi while phosphoethanolamine was predominant in colostrum.