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

Thermodynamic parameters were determined for the dissociation of beta-lactoglobulin(β-Lg) at temperatures from −15 to 85°C. The effect of temperature on Kd (equilibrium constant for dimer ⇌ monomer dissociation) was described by a second-order Van’t Hoff equation (ln Kd=AT−2+BT−1+C) or Gibbs–Helmholtz equation. The Gibbs free energy (ΔG), enthalpy (ΔH), entropy (ΔS) and thermal capacity (ΔCp) for β-Lg dissociation were evaluated. At 25°C standard temperature thermodynamic parameters were ΔG0=24.8 (±0.35) kJ mol−1, ΔH0=57 (±13) kJ mol−1, ΔS0=92 (±30) J mol−1 K−1 and ΔCp=2383 J mol−1 K−1 at pH 2.6. For β-Lg dissociation at pH 7, ΔG0=28.6 (±2.7) kJ mol−1, ΔH0=107.5 (±6.3) kJ mol−1, ΔS0=265.7 (±39) J mol−1 K−1 and ΔCp=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.