Calorimetric studies of thermal denaturation of β-lactoglobulin in the presence of polysaccharides

The thermal denaturation of beta-lactoglobulin at pH 6 and 17 in the presence of polysaccharides was studied by differential scanning calorimetry. At neutral pH, the shape of differential scanning calorimetry curves was affected by polysaccharides and an increase of 2-3degreesC in the onset temperature of beta-lactoglobulin denaturation was observed. This tendency was magnified tip to 10 degreesC at low water contents. At pH 7, the apparent enthalpy changes and the activation energy (E-a) were larger for beta-lactoglobulin + polysaccharides mixtures than for pure beta-lactoglobulin. At pH 6 the transition temperatures, denaturation enthalpy and activation energy of pure beta-lactoglobulin were highly increased and slight changes were observed with further addition polysaccharides. The rate constants of conversion of native beta-lacroglobulin at pH 7 indicate a lower conversion of beta-lactoglobulin when heated in the presence of polysaccharides, in agreement with electrophoretic results. Nevertheless. the formation of larger protein aggregates is promoted, A general analysis of the calorimetric and kinetic data indicates that polysaccharides enhance the thermal stability of beta-lactoglobulin at neutral pH due to a limited thermodynamic incompatibility between the biopolymers. At pH 6 this effect is minimised because of the prevailing stabilizing of pH and a decreased incompatibility between beta-lactoglobulin and polysaccharides.