Enzymatical Dephosphorylation Of Milk Protein And The Effect On Digestibility

With the development of food-processing technology and the improvement of living standards, consumers have higher requirements for the nutritions and functions of infant food, such as formula milk powder. Dairy protein is the main ingredient of formula milk powder. However, there are great differences between bovine and human milk protein in overall compositions and molecular structure, which limit the application of bovine milk protein in infant food. β-casein from bovine and human milk are highly concerved in amino acid sequences, while human β-casein has a lower phosphorylation level. Currently, the research and industrialization of formula milk powder containing bovine milk mainly focus on simulating the overall composition of human protein. Hence, dephosphorylation of bovine milk protein would provide a better ingredient that simulates human milk protein for the production of infant food.Both sodium caseinate(SC) and milk protein concentrates(MPC) mainly contain casein and are widely used as protein ingredients. The natural structure of casein micelles is destroyed during the prodution of sodium caseinate and is well maintained in milk protein concentrates. In this study, sodium caseinate and milk protein concentrates were dephosphorylated by potato acid phosphatase(PAP) and calf intestinal alkaline phosphatase(CAP), respectively. Urae-PAGE, Microwave digestion-UV visible absorption spectrum and LC-MS were applied to investigate the dephosphorylation levels. Moreover, the digestibility of dephosphorylated proteins was also studied using the simulated infant’s gastric and intestinal fluid.Potato acid phosphatase dephosphorylated sodium caseinate and milk protein concentrates. The results showed that after 8 min in p H 6.8 and enzyme concentration 0.24U/m L, β-casein formed four phosphorylation levels, each molecular of β-casein containg 1, 2, 3 or 4 phosphorus, which was similar to that of human β-casein. After 5 h, the dephosphorylation rate of sodium caseinate and milk protein concentrates reached 87.8% and 85.8%, respectively.Calf intestinal alkaline phosphatase dephosphorylated sodium caseinate. The results showed that after 0.5h in p H 9.0 and enzyme concentration 0.8 U/m L, β-casein formed four phosphorylation levels. After 7 h, 71.5% phosphate groups in sodium caseinate were removed. As for milk protein concentrates, after 1h in p H 6.5 and enzyme concentration 1.5 U/m L, β-casein also formed four phosphorylation levels and 69.0% phosphate groups in milk protein concentrates were removed after 7 h.In simulated infant gastric fluid, sodium caseinate and milk protein concentrates formed dense floc; while partially dephosphorylated soudium caseinate and milk protein concentrates with phosphorylation levels similar to those of human milk formed loose floc, which were similar to that of human milk in infant gastric fluid. Howover, the highly dephosphoryled soudium caseinate and milk protein concentrates evenly dispersed in simulated infant gastric fluid without the formation of floc. As the phosphate groups in soudium caseinate and milk protein concentrates were removed, the corrponding digestibility in both the simulated infant gastric fluid and the following simulated infant intestinal fluid increased.