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

Abstract

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