Direct Detection of Bound Water in Hydrated Powders of Lysozyme by Differential Scanning Calorimetry.

While exploring the behavior of lysozyme powders at different percentages of rehydration by differential scanning calorimetry, we noticed a small peak persistently on the left of the melting point of bulk water, which, when heating up the system, was always around -10 °C. The intensity of the transition was maximal at 160% rehydration and disappeared at higher values. By comparing the premelting peak properties in HO and DO, we attributed it to freezable water bound on the protein surface. This is the first time that such an observation has been reported.