Proteins embedded in glassy saccharide systems are protected against adverse environmental conditions [Croweet al. Annu. ReV. Physiol. 1998, 60, 73-103]. To further characterize this process, we studied the relationshipbetween the glass transition temperature of the protein-containing saccharide system (Tg) and the temperatureof thermal denaturation of the embedded protein (Tden). To this end, we studied by differential scanningcalorimetry the thermal denaturation of ferric myoglobin in water/disaccharide mixtures containing nonreducing(trehalose, sucrose) or reducing (maltose, lactose) disaccharides. All the samples studied are, at roomtemperature, liquid systems whose viscosity varies from very low to very large values, depending on thewater content. At a high water/saccharide mole ratio, homogeneous glass formation does not occur; regionsof glass form, whose Tg does not vary by varying the saccharide content, and the disaccharide barely affectsthe myoglobin denaturation temperature. At a suitably low water/saccharide mole ratio, by lowering thetemperature, the systems undergo transition to the glassy state whose Tg is determined by the water content;the Gordon-Taylor relationship between Tg and the water/disaccharide mole ratio is obeyed; and Tden increasesby decreasing the hydration regardless of the disaccharide, such effect being entropy-driven. The presence ofthe protein was found to lower the Tg. Furthermore, for nonreducing disaccharides, plots of Tden vs Tg givelinear correlations, whereas for reducing disaccharides, data exhibit an erratic behavior below a critical water/disaccharide ratio. We ascribe this behavior to the likelihood that in the latter samples, proteins have undergoneMaillard reaction before thermal denaturation.
|Numero di pagine||7|
|Rivista||JOURNAL OF PHYSICAL CHEMISTRY. B, CONDENSED MATTER, MATERIALS, SURFACES, INTERFACES & BIOPHYSICAL|
|Stato di pubblicazione||Published - 2009|
All Science Journal Classification (ASJC) codes
- Physical and Theoretical Chemistry
- Surfaces, Coatings and Films
- Materials Chemistry