Interaction of selected cosolvents with bovine α-lactalbumin

α-Lactalbumin constitutes about 3% of bovine milk proteins. The preferential solvent interactions between selected cosolvents (sorbitol, sucrose and glycerol) and α-lactalbumin at pH 7.5 was determined using precision densitimetry. The preferential interaction parameter (ξ3) and other thermodynamic parameters were calculated at different solvent concentrations. The ξ3 parameter was maximum at 30%, 45% and 40% (w/v) concentrations with the values of −0.282 g/g, −0.171 g/g and −0.299 g/g for sorbitol, sucrose and glycerol, respectively. Thus the principal driving energy in the system being preferential hydration and mutual exclusion of bulk solvent. There was only a marginal change in the CD spectra of the protein with these cosolvents indicating the integrity of secondary structures. The results of thermal denaturation measurements indicated an increase in thermal stability of α-lactalbumin with these cosolvents. In the presence of 30% sorbitol there was an increase in the apparent thermal transition temperature (apparent Tm) from 65 to 71 °C. These results indicate that the selected cosolvents in this study stabilizes α-lactalbumin without altering the structure of the protein.