Thermal stability of a-Lactalbumin in the presence of various sugars as osmolytes

Thermal denaturation of a-Lactalbumin in the absence and presence of various concentrations of sucrose,sorbitol, glucose and galactose as sugar osmolytes were measured by monitoring changes in the absorptions thatcarried out in a Lambd 35 UV-Vis double beam spectrophotometer at pH 6.0. These measurements gave valuesof T., (midpoint of denaturation), AH., (enthalpy change at T.), and ACp (constant-pressure heat capacitychange) under a given solvent condition. Using these values of AH., T., and AC, AGD° (Gibbs energy change),was determined at a given concentration of each sugar. It has been observed that each sugar stabilizes the a-Lactalbumin in terms of T,„ and AGD°. The temperature that corresponds to maximum protein stability, Ts, isincreased in the presence of these osmolytes. The same trend was also observed for TM, the temperaturecorresponding to zero enthalpy change of denaturation