Impact of Preferential Interactions on Thermal Stability and Gelation of Bovine Serum Albumin in Aqueous Sucrose Solutions

Abstract

The influence of sucrose (0−40 wt %) on the thermal denaturation and gelation of bovine serum albumin (BSA) in aqueous solution has been studied. The effect of sucrose on heat denaturation of 1 wt % BSA solutions (pH 6.9) was measured using ultrasensitive differential scanning calorimetry. The unfolding process was irreversible and could be characterized by a denaturation temperature (T_m), activation energy (E_A), and pre-exponential factor (A). As the sucrose concentration increased from 0 to 40 wt %, T_m increased from 72.9 to 79.2 °C, E_A decreased from 314 to 289 kJ mol^-1, and ln(A/s^-1) decreased from 104 to 94. The rise in T_m was attributed to the increased thermal stability of the globular state of BSA relative to its native state because of differences in their preferential interactions with sucrose. The change in preferential interaction coefficient (ΔΓ_3,2) associated with the native-to-denatured transition was estimated. The dynamic shear rheology of 2 wt % BSA solutions (pH 6.9, 100 mM NaCl) was monitored as they were heated from 30 to 90 °C, held at 90 °C for either 15 or 120 min, and then cooled to 30 °C. Sucrose increased the gelation temperature due to thermal stabilization of the native state of the protein. The complex shear modulus (G*) of cooled gels decreased with sucrose concentration when they were held at 90 °C for 15 min because the fraction of irreversibly denatured protein decreased. On the other hand, G* of cooled gels increased with sucrose concentration when they were held at 90 °C for 120 min because a greater fraction of irreversibly denatured protein was formed and the strength of the protein−protein interactions increased. Keywords: BSA; heat denaturation; functionality; gelation; sucrose; preferential interactions