Induced structural change to beta-lactoglobulin by combined pressure and temperature

In this paper we report on the structural changes to the milk protein beta-lactoglobulin induced by the combined effects of pressure and temperature. A series of treatment combinations were studied using pressures up to 100 MPa, temperatures up to 75 degrees C and pH values of 5.6 and 7.0 as bring appropriate to milk. Examination of the pressure-temperature treated protein by circular dichroism, differential scanning calorimetry (DSC) and spectrofluorometry indicated that sufficient energy had been applied to disrupt irreversibly the molecular structure at both the secondary and tertiary level caused by both pressure and temperature. Pressure and temperature effects were observed most clearly to changes in the tertiary structure using circular dichroism and DSC for which complete loss of structure was observed following treatment at 100 MPa and 75 degrees C at pH 7.0 and 72% loss at pH 5.6. Combined pressure and temperature effects appeared to have less effect to the secondary structure and on the temperature of denaturation. The mechanism by which pressure and temperature function in combination, however, is not clear. (C) 2000 Elsevier Science S.A. All rights reserved.