State diagram of whole milk for freeze-drying application
Résumé
The state diagram is a key parameter when optimizing a freeze-drying cycle, as it allows us to set the optimum processing temperature for a specific product. The purpose of this work is to provide some thermodynamic and physicochemical data for optimizing the freeze-drying cycle of whole milk. Freezing point measurements were determined using differential scanning calorimetry and cryoscopy methods, and glass transitions were evaluated by DSC. The endothermic peak was used as the equilibrium freezing point, a variation from 273.93 K to 264.92 K was detected when the dry matter content varied from 0 to 75%. Tg midpoint temperature was used as glass transition of dry mater. Furthermore, Fox and Gordon-Taylor equations were used to predict the glass transition curve to determine T'g, this temperature was used as an approximation of the critical temperature Tc. Collapse temperature was determined using the freeze-drying microscopy setup.
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