Abstract: In order to provide the stability conditions of drying and freezing for whole egg, thermal transition temperatures of spray-dried whole egg powder containing unfreezable water and samples containing freezable water were determined by differential scanning calorimetry (DSC). The adsorption isotherm of whole egg was also established. Spray-dried whole egg powder containing unfrozen water showed two endothermic peaks, which corresponded to the denaturation of ovotransferrin and ovalbumin, respectively. The denaturation temperatures (Td) of ovotransferrin and ovalbumin decreased with the increase of water content. The relationship between freezing point (TF) and water content was modeled using the Clausius-Clapeyron equation. The content of unfreezable water was estimated as 0.18 g/g sample wet basis from the extrapolated enthalpy of ice melting (△Hm), and the corresponding end point of freezing (Tm’) was calculated as ?14.6 ℃ using the Clausius-Clapeyron equation. Only when water content was 0.22 g/g wet basis, was the glass transition temperature detected as ?46.3 ℃. In addition, the water adsorption isotherm of spray-dried whole egg powder was determined at 25 ℃ and the data were fitted to the GAB model. The absorption isotherm was classified as a type II isotherm. The content of monolayer water was found to be 0.043 g/g sample dry basis as the stability criterion based on water activity. These results provide a theoretical rationale for the optimal drying and freezing conditions of whole egg.

Key words: thermal transition, differential scanning calorimetry, sorption isotherms, water activity, whole egg powder