Polyelectrolyte nanocomplex from sodium caseinate and chitosan as potential vehicles for oil encapsulation by flash nanoprecipitation

A polyelectrolyte complex coacervation technique has been used for emulsion stabilization, nutraceutical encapsulation, and controlled delivery. However, traditional batch-mixing methods suffer from significant insufficiencies in scalability because of batch-to-batch variation and complicated multi-step preparation procedures resulting in uncontrollable size, wide size distribution, instability, and aggregation. This study used a flash nanocomplexation (FNC) method to continuously prepare protein (sodium caseinate) and polysaccharide (chitosan) nanocomplexes with narrow size distributions using a multi-inlet vortex mixer. The size distributions of nanocomplex can be controlled by volumetric flow rates of the inlet streams, the concentration, and the order/ratio of sodium caseinate to chitosan. Furthermore, a novel emulsion preparation method, flash-microemulsion (FME), was introduced. Under rapid mixing conditions, FME prepared emulsion in the presence of soybean or MCT oil by infusing aqueous solutions of sodium caseinate and chitosan in a single step. O/W emulsion prepared successfully by the FME method was confirmed with confocal microscopy. The emulsion droplet size ranged from 4.6 to 1.5 μm and showed elastic-like properties (G' > G″). Optical microscope, SEM, and TEM studies suggested that the FME method could form homogeneous and stable emulsions. The emulsions showed excellent stability over 30 days of storage. In addition, there were no noticeable differences in the size and size distribution of nanocomplex and emulsion prepared at different times, indicating excellent reproducibility. As a result of FNC and FME, other lipophilic bioactive compounds can be encapsulated/stabilized in the food, flavor, pharmaceutical, and cosmetic industries.