Abstract: For this experiment, we collected human and bovine milks at 30–40 days postpartum. Isobaric tags for relative and absolute quantification combined with high performance liquid chromatography-tandem mass spectrometry (iTRAQ-HPLCMS/ MS) was used to compare the composition of full-spectrum free and hydrolyzed amino acids in milk samples. The results indicated that total free amino acid content was 0.37 and 0.16 g/L in human and bovine milks, and total hydrolyzed amino acid content was 2.5 and 3.3 g/L, respectively. Among the full-spectrum free amino acids, 9 essential amino acids and 15 non-protein amino acids were detected in both milks, and 11 and 7 non-essential amino acids were detected in human and bovine milks, respectively. Moreover, 9 essential amino acids, 10 non-essential amino acids and 7 non-protein amino acids in human milk were significantly more abundant than in bovine milk (P < 0.05). Among the full-spectrum hydrolyzed amino acids, 8 essential amino acids, 10 non-essential amino acids and 12 non-protein amino acids were detected simultaneously in human and bovine milks. Moreover, the levels of γ-aminobutyric acid, taurine, α-amino-n-butyric acid and β-alanine in human milk were significantly higher than in bovine milk (P < 0.05). This study provides a theoretical basis for the development of milk formulaeand functional foods.

Key words: human milk, bovine milk, iTRAQ, HPLC-MS/MS, full-spectrum free amino acid, full-spectrum hydrolytic amino acid