Effects of high hidrostatic pressure on the viscosity of β-lactoglobulin solution

In this research new experimental data for the pressure dependence of the viscosity of beta-lactoglobulin solution are presented. The experimental investigation is based on in-situ viscometric measurement technique which provides an observation of the high-pressure-induced changes of beta-lactoglobulin solution during the treatment. This method refers to a rolling ball viscometer that is adapted for the use at high pressures and has a variable inclination angle. The estimation of the viscosity has been done in order to detect reversible and irreversible conformational changes of beta-lactoglobulin. For investigation protein solutions concentration 0.01, 0.02, 0.03, 0.04, 0.05 and 0.06 g/g were used. The sample solutions are exposed to pressure of 0.1-600 MPa. The results showed that there is no significant effect of 100 MPa pressure on the viscosity of beta-lactoglobulin solutions. With increasing pressure, between 100 and 300 MPa, the viscosity of beta-lactoglobulin solutions increase. Pressure above 300 MPa causes further increase of the viscosity due to nonreversible and more extensive effects on protein, e.g. unfolding of monomeric proteins and aggregation. The structural changes of the beta-lactoglobulin under high pressure affect the hydration of the beta-lactoglobulin molecules. At pressure between 100 and 300 MPa there is a significant increase in relative hydration due to structural changes and increase in number of water molecules which are associated with protein molecules. Higher pressure cause protein aggregation due to formation of intermolecular disulfide bonds and irreversible denaturation and aggregation occurs. Because of that, there is no changes in protein hydration, moreover, the hydration of beta-lactoglobulin molecules have a small decreases at pressure between 400 and 600 MPa.