Free amino acids in preterm and term milk from mothers delivering appropriate- or small-for-gestational-age infants.

Free amino acids were quantitated in human milk collected during the first month postpartum from mothers of appropriate preterm (26-32 and 33-36 wk gestation) and term (small or appropriate-for-gestational-age) infants. Glutamic acid and taurine were the most abundant amino acids in all four groups at all stages of lactation. The ratio of essential to nonessential amino acids was higher in colostrum than in mature milk although the total amino acid level of mature milk was double that of the colostrum. Nonprotein amino acids amount to approximately 40% of the free-amino acid pool in colostrum. Differences in the content and changes in free-amino acid levels during lactation among the groups were observed.