Characterization of d-amino acids in colostral, transitional, and mature preterm human milk

D -Amino acids are regulatory molecules that affect biological processes. Therefore, being able to accurately detect and quantify these compounds is important for understanding their impact on nutrition and health. There is a paucity of information regarding d -amino acids in human milk. We developed a fast method for simultaneous analysis of amino acid enantiomers in human milk using liquid chromatography with tandem mass spectrometry. The method enables the separation of 41 amino acids without chemical derivatization. Our results revealed that human milk from mothers of preterm infants contains concentrations of d -amino acids that range from 0.5 to 45% that of their l -counterparts and that levels of most d -amino acids decrease as the milk production matures. Moreover, we found that Holder pasteurization of milk does not cause racemization of l -amino acids. To our knowledge, this is the first study to describe percentages of d -amino acid levels in human milk; changes in d -amino acid concentration as the milk matures; and the effect of Holder pasteurization on d - and l -amino acid concentrations in human milk.