[Comparison of the function and conformation of human β-casein and bovine β-casein by spectroscopic study]

β-Casein was the main component of human milk casein, but the content of β-casein in the bovine milk was less. The difference in β-casein content of the two samples was one of the reasons why human milk is more digestible than bovine milk. Studying the differences of structure and function in human and bovine milk β-casein can help us develop a new human milk simulated infant formula which will be more suitable for the infant gut. The UV spectrophotometer was used to study the solubility, sulfhydryl and emulsification of human milk β-casein and bovine milk β-casein, Fluorescence spectroscopy and the infrared spectroscopy were used to study the structural characteristics of human milk β-casein and bovine milk β-casein. The two samples shared a similar isoelectric point (pH 4.0~5.0), the solubility of human milk β-casein (10.83%) was lower than which in bovine milk β-casein (11.83%) near the pI, while it was higher when it deviated the pI. The emulsion ability (110~140 m2 · g(-1)) of human milk β-casein was higher than that in bovine milk β-casein (70~130 m2 · g(-1)) and surface sulfhydryl group (SH) of two kinds of milk protein were similar [(18.47±0.08) μmol · g(-1) and (18.67±0.17) μmol · g(-1)]. The total sulfhydryl group [(47.46±0.23) μmol · g(-1)] in bovine milk β-casein was more than that in human milk β-casein [(26.17±0.12) μmol · g(-1)]. Functional groups in two samples were similar and they both contained beta sheet, human milk β-casein had less H-bond and internal hydrophobic than bovine milk β-casein. The results showed that the two samples had similar functional groups, while human milk β-casein had much less secondary structure such as α-helix and β-sheet, a looser tertiary structure and a better interfacial activity.