Nature of water bonding in hydrated milk-protein systems

Introduction. The nature of the connection and the characteristics of the process of relaxation of clusters and water domains in milk and protein systems was investigated in order to predict their functional and technological properties. Materials and methods. The relaxation features of water clusters and domains in colloidal solutions of milk proteins were studied by the thermo-stimulated depolarization method (TSD). Electrophoretic analysis of the fractional composition of milk proteins was performed according to modified Laemmli method. Results. The peculiarities of water distribution in bulk protein matrices in milk and in hydrated milk protein concentrates by TSD were studied. On the basis of comparative analysis of TSD spectra of relaxation of dipole structures of water in low-temperature and high-temperature regions in samples of fresh skimmed milk, reconstituted skimmed milk powder and sodium caseinate solution, a significant difference in the nature of water cluster formation in these systems is proved. Milk protein concentrates with reduced energy of activation of depolarization of water in the hydrated state are found to form spatial grids with smaller cell sizes than proteins of natural milk. The revealed effect is explained by the fact that under the influence of heat treatment and drying there are significant conformational changes of protein compounds caused by the denaturation of the majority of serum proteins, in particular, immunoglobulins, serum albumin, beta-lactoglobulin and a-lactalbumin. It is relevant to use in composition of foods milk protein concentrates, whose protein matrices have spatial limitations and hold water clusters smaller than that of natural milk. The results of the research are of practical importance as they allow the purposeful formation and stabilization of the spatial structure of protein-containing food systems. Conclusions. The peculiarities of the nature of water bonding in hydrated milk-protein systems of different degrees of heat treatment have been established.