Microencapsulation of oil droplets using freezing-induced gelatin–acacia complex coacervation

Abstract

A freezing process was applied to control the kinetics of a gelatin–acacia complex coacervation technique for encapsulating emulsified oil droplets. An oil-in-water emulsion was stabilized with a gelatin–acacia solution, and the pH of the solution was adjusted to a selected value with acetic acid. When the pH of the emulsion was adjusted to 4.7, the system was visibly stable at ambient temperature for up to 12h. Freezing the emulsion caused polymer phase separation (complex coacervation) in the cryoconcentrated phase and resulted in encapsulated oil droplets and the accumulation of a cream layer in the freeze-thawed solution. Observation by transmission electron microscopy clarified the formation of 50–4000nm core–shell nano-microparticles, the surfaces of which were surrounded by polymeric membranes. The membrane properties of the particulate systems were dependent on the cooling rate that was used during freezing. For example, when an emulsion with a pH of 4.7 was frozen, a cooling rate of −1.0°C/min maximized the encapsulation yield, whereas a rate of −2.0°C/min was effective in limiting the release rate of the ingredient (β-carotene) from the oil phase through the shell membrane. The results of this study suggest that the formation of nano-microparticles could be highly associated with the kinetics of freezing, so their resultant properties could be fine-tuned using a freezing operation. This is a potential concept providing a novel strategy for engineering core–shell nanoparticles.