Freeze-drying of ovalbumin-loaded carboxymethyl chitosan nanocapsules: Impact of freezing and annealing procedures on physicochemical properties of the formulation during dried storage

Nanocapsules were prepared from 6-O-carboxymethyl chitosan, ovalbumin, and calcium chloride as a cross-linker agent. Cryoprotectants were added to the formulation to protect these carriers during freezing and desiccation steps. The nanocapsules showed acceptable stability with regard to the residual humidity and cake appearance. Regarding the stability, particle diameter, and polydispersity index increased over the storage time, especially for formulations stored at room temperature. For all studied lyophilization protocols exclusively delta-mannitol was formed, and the addition of an annealing step maximized mannitol crystallization. The decrease of the pore surface area for annealed formulations resulted of structural changes other than Ostwald ripening.