Thermotropic gelation of ovalbumin: 2. Boundary conditions on the formation and the concentration dependence of equilibrium elastic modulus for thermotropic ovalbumin gels

Abstract

Studies were made on the boundary conditions for thermotropic ovalbumin gelation at pH within the range 2.5 to 10.0. The pH dependence of the gelation threshold, C 0, and denaturation temperature, T d, were obtained. The dependence C 0(pH) has a sharp minimum close to the isoelectric point (pl). Over pH range 2.5 to 4.0 the dependence T d(pH) is linear; although above pI it shows unusual behaviour. T d increases smoothly, becoming a constant value ( T d=80°C) at pH 7. Analysis of the temperature dependence of Leu's line integral intensity in the p.m.r. spectrum of ovalbumin shows that the temperature threshold of thermotropic gelation closely approximates to T d. A diagram for the state of an ovalbumin -water system was constructed in temperature-concentration-pH coordinates. The dependences of the initial shear modulus for thermotropic ovalbumin gels on the concentration (0.06≤C≤0.25 g/ cm 3 were obtained at pH 4.0, 7.0, 8.5, 10.0. They are equivalent to the concentration dependence of the equilibrium elastic modulus E e(C). The dependences obtained may be reduced to the theoretical master dependence of Hermans, E e (rm C ̃ ) , where C ̃ = C/ C 0 is the reduced concentration. Hermans' theory, based o the model for random cross-linking of linear identical macromolecules without cyclization, adequately describes the equilibrium elastic properties of thermotropic ovalbumin gels.