Thermodynamic parameters for beta-lactoglobulin dissociation over a broad temperature range at pH 2.6 and 7.0

Abstract Thermodynamic parameters were determined for the dissociation of beta-lactoglobulin(β-Lg) at temperatures from −15 to 85°C. The effect of temperature on K d (equilibrium constant for dimer ⇌ monomer dissociation) was described by a second-order Van’t Hoff equation (ln  K d = AT −2 + BT −1 + C ) or Gibbs–Helmholtz equation. The Gibbs free energy (Δ G ), enthalpy (Δ H ), entropy (Δ S ) and thermal capacity (Δ C p ) for β-Lg dissociation were evaluated. At 25°C standard temperature thermodynamic parameters were Δ G 0 =24.8 (±0.35) kJ mol −1 , Δ H 0 =57 (±13) kJ mol −1 , Δ S 0 =92 (±30) J mol −1  K −1 and Δ C p =2383 J mol −1  K −1 at pH 2.6. For β-Lg dissociation at pH 7, Δ G 0 =28.6 (±2.7) kJ mol −1 , Δ H 0 =107.5 (±6.3) kJ mol −1 , Δ S 0 =265.7 (±39) J mol −1  K −1 and Δ C p =2383 J mol −1  K −1 . Simulated temperature–dissociation profiles of β-Lg show that the fraction of dissociated protein increases with increasing temperature, decreasing pH and with decreasing protein concentration.