Impact of preferential interactions on thermal stability and gelation of bovine serum albumin in aqueous sucrose solutions

The influence of sucrose (0-40 wt %) on the thermal denaturation and gelati on 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 unfol ding 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 fr om 72.9 to 79.2 degreesC, 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 in creased thermal stability of the globular state of BSA relative to its nati ve state because of differences in their preferential interactions with suc rose. The change in preferential interaction coefficient (Delta Gamma (3,2) ) associated with the native-to-denatured transition was estimated. The dyn amic shear theology of 2 wt % BSA solutions (pH 6.9, 100 mM NaCl) was monit ored as they were heated from 30 to 90 degreesC, held at 90 degreesC for ei ther 15 or 120 min, and then cooled to 30 degreesC. Sucrose increased the g elation temperature due to thermal stabilization of the native state of the protein. The complex shear modulus (G*) of cooled gels decreased with sucr ose concentration when they were held at 90 degreesC 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 a t 90 degreesC for 120 min because a greater fraction of irreversibly denatu red protein was formed and the strength of the protein-protein interactions increased.