Differential Scanning Calorimetry of Unfreezable Water in Water–Protein–Polyol Systems

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Abstract
The amount of unfreezable water in lysozyme and bovine serum albumin in aqueous solutions of xylitol, sorbitol, glucose and sucrose was estimated by a differential scanning calorimeter according to new analytical methods. The antemelting point of aqueous polyol solutions seemed to shift to a higher temperature upon addition of protein, but the incipient melting point was not affected by the coexisting protein. The amount of unfreezable water in both proteins, as well as the heat of fusion of ice, decreased with increasing polyol concentration, regardless of the kind of polyols added. On the basis of these results, the solvation structure of the protein in these three-component systems and the mechanism of the polyol-induced stabilization of protein were discussed assuming protein–polyol interactions.