In food flavoring, medical applications and similar processes where it is desirable to encapsulate a particle, or drop, with a shell to protect the interior contents of that particle, to provide controlled release or simply to mask the taste of the interior phase coacervation may be employed. It is common to use what is termed complex coacervation. In this case two hydrocolloids (gelatine, gum arabic, locust bean gum, etc.) are used, which can combine together to form a shell around the drop, where the shell may solidify to form the encapsulated particles.
The drop that forms the coacervate particle is often a liquid oil, e.g. vegetable oil, and the hydrocolloids are transported to the interface between the oil drop and the aqueous phase in which the hydrocolloids are dissolved.
Membrane emulsification is ideal as the process to form the oil drops, as it provides uniform drops on which the coacervation may take place. The drops will have a shell of the hydrocolloid mixture around them and, under the correct conditions, the colloids will set to form a solid (or semi-permeable) shell.
The process of setting the hydrocolloids can be slow and is very dependent on temperature and pH. A simple example of setting gelatine is the formation of jelly in the fridge. Conventionally, setting the coacervate shell is performed in the laboratory and industrially in stirred tanks, but the process is ideal for conversion to a continuous coacervation using drop generation followed by reactor system: after the drops are generated they can have the pH adjusted in the pipe transferring them to a plug flow reactor - the reactor provides sufficient residence time for them to set, and where temperature control can be exercised. The picture shows some very large coacervate particles formed by this process.
Coacervates can be produced using the process of membrane emulsification. The top picture on the right shows coacervate drops that have been produced continuously by a membrane process. The drops are a vegetable oil in which is dissolved a blue dye and flavoring. The hydrocolloids used to encapsulate the oil were gelatine and gum arabic. These are in the aqueous phase in to which the oil phase was injected, as illustrated by the picture at the lower right. Click on the upper right picture or this link to see a video (wmv format and 592 kB size)of the blue dyed oil coacervates leaving the droplet generation stage of the process and entering the plug flow reactor part of the process.
If you would like to see more information on the membranes used for this process of membrane emulsification, please see this explanation.