Abstract: Dairy fan, milk pastry and milk residue as traditional ethnic dairy products in Yunnan have a long history, possess distinctive characteristics and are high in protein. This study was implemented to investigate the peptide profiles and free amino acid contents of dairy fan, milk pastry and milk residue by liquid chromatography-tandem mass spectrometry (LC-MS/MS) and an amino acid analyzer based on simulated gastrointestinal digestion, and to analyze potential biological peptides by peptide database searching. The results showed that a total of 221 peptides including five angiotensin converting enzyme inhibitory peptides, four immunoregulatory peptides, three antioxidant peptides, two antithrombotic peptides and one antibacterial peptide were identified from dairy fan, with molecular mass distribution in the range of 500–750 Da. In total 225 peptides including two potential antioxidant peptides were identified from milk pastry, with molecular mass distribution in the range of 750–1 000 Da. In total 222 peptides including two immunoregulatory peptides, two antioxidant peptides and one antithrombotic peptide were identified from milk residue with molecular mass distribution in the range of 750–1 000 Da. The peptides in the three dairy products were mainly derived from β- and α-casein. The contents of free amino acids in dairy fan, milk pastry and milk residue after simulated gastrointestinal digestion were 9.45, 10.7 and 9 g/100 g, respectively, with neutral amino acids being the most abundant, followed by basic and acidic amino acids. This study reveals the biological value of dairy fan, milk pastry and milk residue, and provides a scientific basis for the development of functional dairy products.

Key words: ethnic dairy products in Yunnan; simulated gastrointestinal digestion; proteomics; biological peptides; free amino acids