Influence Of Phosphorylation Treatment On Enzymatic Hydrolysis Characteristics Of Casein

The casein is the precipitation of the skim milk, when the pH was adjusted to4.6at20°C, and the casein is accounting for80%-82%of the total milk protein. The aim of this workwas to determine optimal conditions of phosphorylation treatment for casein by means oforthogonal test using sodium tripolyphosphate (STP). And then the phosphorylated caseinwas hydrolyzed with trypsin. Optimal conditions were as follows:5%of STP,30°C and pH=9.Phosphorylation degree is the largest (18.18mgP/g casein) after treatment for3h. Obviouschange was found for phosphorylated casein compared to the control according toSDS-PAGE. And the phosphorylation can break down the casein micelle, it was showed asthe molecular weight decreased gradually. And the greater degree of phosphorylation, themore obviously its molecular weight decreased.The casein was digested by trysin for the enzymatic properties, it was found thatphosphorlation processing can improve the degree of hydrolysis at different levels. And thegreater degree of phosphorylation, the more obviously the degree of hydrolysis increased. Thesoluble nitrogen content in hydrolysates of phosphorylated casein increased significantlycompared with the control group. There was no significant change in the peptide nitrigencontent between the experimental group and the control.The structure of hydrolysates was studied by Fourier transform infrared spectroscopyscan and UV scanning spectrum. The rate of α-helix and β-sheet of hydrosates ofphosphorlated casein increased significantly compared with the control. It was found that thedifferent phosphorylated casein has a common feature, namely the β-turn was dominant. Andas enzymolysis, the content of β-turn increased obviously. The UV scanning curves beforeand after phosphorlation was studed, found that the OD of the phosphorylated casein at themaximun absorption wavelength increased significantly. Maybe it is because thephosphorylated casein was hydrolyzed by STP, and found that phosphorylation helped morechromophore generated in the process of enzymolysis.The molecular weight distribution of different phosphorylated casein was studied bySDS-PAGE, gel exclusion chromatigraphy and amino acid analysis. From the gel exclusionchromatography, we could know that, there were mainly small peptides, whose molecularweight was less than20KDa in the hydrolysates of phosphorylated casein for30min. And wealso could see from the SDS-PAGE, when it was hydrolyzed for6h, the content of smallpeptides with2.05KDa was25.7%. The SDS-PAGE band of the hydrolysates of phosphorylated casein for2h was more than the control. And the hydrolysate contained moreuniform molecular weight peptides. From the gel exclusion chromatography, we can knowthat the content of the peptides, whose molecular weight was less than20KDa, was51.04%.While the electrophoresis bands of the hydrolysates of phosphorylated casein for3h has beenblurred. And it can be seen from the gel exclusion chromatography of the hydrolysates at10min, the peptides whose molecular weight was less than20KDa was accounting for49.05%,which can be proved that the treatment of phosphorylation could be helpful for enzymolysis,and the more degree of phosphorylation, the more improved greatly. While phosphorylationhad little influence in the amino acids content of hydrolysates of the different phosphorylatedcasein...