The studies on casein structure modification contribute to better understanding of the role of nonamino acid components in forming casein complexes and improving ways of protein functionality. The objective of the experiments was to explain the influence of bovine milk casein glycation on some physico-chemical properties and structural changes. From the the analysis of glycation rate curve the reaction of the first order range can be assumed during the first 24 h, turning to a mixed type afterwards. The isoelectric point and molecular weight of beta-casein increased after glycation and the electrophoretic mobility was slightly modified. The structural changes were also confirmed by different absorption spectra in UV and a better heat stability of the modified beta-casein. The findings showed higher solubility with modified beta-casein. The glycation caused changes in beta-casein, modifying its susceptibility to the trypsin hydrolysis.

A major bovine casein fraction, β-casein was chemically glycated and/or enzymatically dephosphorylated. Ten glucose and nine lactose moieties were attached while all phosphate groups were removed. Glycation shifted the pI to acidic pH range and decreased the solubility at acidic pHs while dephosphorylation shifted the pI to neutral pH range and increased the solubility at acidic pHs. Dephosphorylation led to longer retention time measured using the reversed-phase high-performance liquid chromatography and affected UV-spectra of β-casein which suggested structural changes. Glycation did not affect these properties. Both modifications decreased the calcium sensitivity of β-casein, making it to keep α S1 -casein in solution in the presence of Ca 2+ .

The aim of this work was to study the chymosin-catalysed hydrolysis of reconstituted casein systems containing s1 -casein, s2 -casein, -casein and -casein or -casein modified via chemical glucosylation and/or enzymatic dephosphorylation. The systems containing modified -casein instead of -casein were destabilised after release of peptides in trace amounts. The coagulation of the systems reconstituted using -casein required release of much more peptides than coagulation of those containing modified -casein. Proteolysis range in both classes of reconstituted systems was much smaller than proteolysis range in milk. The specificity of chymosin against reconstituted systems was typical. The major proteolysis products were para--casein and caseinomacropeptide in the systems reconstituted using -casein as well as fragment 1-23 of s1 -casein and fragment 193-209 of -casein in all the systems used. Only the systems containing -casein formed gel with a structure similar to this obtained via casein coagulation in milk.