Biochemistry

Casein of milk can be considered as an emulsifier stabilizing a natural emulsion - milk. Protein denaturation Under the influence of various factors, the native spatial structure of a protein molecule can be violated: the quaternary, tertiary and secondary structures are destroyed (changes do not affect the primary structure). This phenomenon is called denaturation. Protein denaturation leads to a decrease or complete loss of solubility, loss of specific biological activity, a change in optical properties and viscosity, etc. During denaturation, bonds that stabilize the structure of the protein molecule are broken: ionic, hydrogen and disulfide, the hydrophobic interaction is disrupted. The polypeptide chain unwinds and is in solution in the unfolded state or in the form of a disordered ball. The degree of protein denaturation can be different depending on its physicochemical properties, the nature of the denaturing agent and its duration of action. The denaturation processes are shown schematically in Figure 2.7. For some proteins, denaturation is reversible (muscle proteins). In this case, both native conformation and biological activity of the protein can be restored (subject to certain conditions). Denaturing factors can be divided into physical and chemical. Physical agents include temperature, pressure, mechanical stress, ultrasonic and ionizing radiation. The most common factor is heating. Thermal denaturation of proteins is one of their characteristic features. Strengthening the thermal motion of atoms of the polypeptide chain leads to the breaking of weak non-covalent bonds. The rate of thermal denaturation substantially depends on the pH of the medium, the ionic strength of the solution. Thermal denaturation is accompanied by aggregation of proteins, their precipitation. The most complete and rapid deposition occurs at the isoelectric point. Proteins are denatured by grinding dry preparations, vigorously shaking solutions, heating, etc. When lyophilizing proteins (drying in a vacuum by sublimating moisture from a frozen state), most of them do not denature, which allows using this drying method for long-term storage of protein preparations. Chemical factors causing denaturation include acids, alkalis, organic solvents, surfactants, alkaloids, heavy metals, etc. 61