Abstract:This study aims to investigate the physicochemical properties and nutritional value of milk residue casein.To be specific，through alkali dissolution and acid precipitation，the fat and lactose in the milk residue were removed and then the casein was extracted.The physicochemical properties of the casein were determined by ultraviolet spectrophotometer and fluorescence probe，and the primary structure and potential active polypeptide fragments were identified by enzymolysis and mass spectrometry.The result showed that the protein content in the extract was up to 91.41%and the casein was soluble in alkali.Sodium dodecyl sulfatepolyacrylamide gel electrophoresis（SDS-PAGE）analysis indicated that the molecular weight of α-casein was 30 kDa and that of β-casein was 26 kDa.Compared with the α-casein and β-casein on the market，α-casein and β-casein from milk residue presented better emulsifying property and higher surface hydrophobicity and showed distinguished thermal stability and secondary structure stability，but the crosslinking ability was poor.Milk residue casein contained 17 amino acids，and the content of 6 essential amino acids was higher than that of commercial casein.Moreover，it contained 129 kinds of potentially active polypeptide fragments，which may have the functions of lowering blood glucose and pressure，antithrombus，and antisenility.