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Amino acid

Free amino acids (FAAs)

  • Analysis of free amino acids is important in determining the quality and quantity of milk proteins. FAAs in mother milk contribute not only to the overall protein quality but also to the supply of nutritional nitrogen and essential amino acids. The evaluation of FAA composition in human milk is valuable as a reference for protein quality for breast milk substitutes.


Seleno-amino acids (Se-AAs)

  • Selenium (Se) is an essential micronutrient for humans. The majority of selenium in milk is associated with protein, the remaining selenium is present in the water-soluble fraction of milk as free seleno-amino acids, which are almost completely absorbed (> 90%) via gut transporter. The supplement of nutrients like Se-AAs in milk can be of interest to human health.

In NFML, analytical methods of FAAs and Se-AAs including Seleno-methyl-selenocysteine (MetSeCys), Selenomethionine (SeMet), Selenocysteine (SeCys), Selenocystine (SeCys2) in the complex biological sample, i.e. human breast milk were applied through the combination of solid phase extraction with a HILIC-ESI-MS/MS

Research highlight


  • The analytical method for FAAs was established in a small volume (10 mL) of human milk.
  • This is the first report for FAAs analysis in breast milk through the integration of cation exchange extraction with a HILIC-UPLC-MS/MS.
  • A comparative analysis of FAAs in human milk from four Asian countries (China, Korea, Pakistan, Vietnam) was investigated. 
  •  A simple and rapid LC-MS/MS method was also developed and validated for analysis of four aforementioned Seleno-amino acids in breast milk matrix.
  • A quantitative analysis of MetSeCys was conducted in Asian milk samples using a triple quadrupole mass spectrometry under the MRM mode.

Relevant publications


  • Kambhampati, S., et al., Accurate and efficient amino acid analysis for protein quantification using hydrophilic interaction chromatography coupled tandem mass spectrometry. Plant Methods, 2019. 15(1): p. 1-12.
  • Baldeón, M.E., et al., Free amino acid content in human milk is associated with infant gender and weight gain during the first four months of lactation. Nutrients, 2019. 11(9): p. 2239.
  • Van Sadelhoff, J.H., et al., Longitudinal variation of amino acid levels in human milk and their associations with infant gender. Nutrients, 2018. 10(9): p. 1233.
  • Garcia-Rodenas, C.L., et al., Amino acid composition of breast milk from urban chinese mothers. Nutrients, 2016. 8(10): p. 606.
  • Ferchaud Roucher, V., et al., Use of UPLC-ESI-MS/MS to quantitate free amino acid concentrations in micro-samples of mammalian milk. SpringerPlus, 2013. 2(1): p. 1-11.
  • López R., et al., Green and simple extraction of free seleno-amino acids from powdered and lyophilized milk samples with natural deep eutectic solvents, Food chemistry, 2020. 326: 126965.
  • Gómez‐Ariza, J. L., et al., First approach of a methodological set‐up for selenomethionine chiral speciation in breast and formula milk using high‐performance liquid chromatography coupled to atomic fluorescence spectroscopy, Applied Organometallic Chemistry, 2007. 21(6): 434-440.