Glass transition explanation for the effect of polyhydroxy compounds on protein denaturation in dehydrated solids

Dehydrated proteins are frequently subjected to thermal stress in the presence of other components. The effect such substances may have upon protein structure, and therefore function, has not been fully investigated. Thus, the effect of added polyhydroxy components on the denaturation of lyophilized beta-lactoglobulin, ovalbumin, and ribonuclease, as determined by differential scanning calorimetry, was evaluated. The denaturation temperature, T-m, of the globular proteins decreased in the dry state after the addition of sucrose, sorbitol, or glycerol. The thermal stability (based on T-m) of the dehydrated proteins appeared to correlate with the glass transition temperature (T-g) of the polyhydroxy component, which was assumed to be related to the T-g of the mixture. The lower the T-g of the component, the greater was the degree of protein destabilization. Thus, glass transition data may be used to predict the effect that a component would have on denaturation of dehydrated proteins at elevated temperatures.