Fabrication and utilization of bifunctional protein/polysaccharide coprecipitates for the independent codelivery of two model actives from simple oil-in-water emulsions

Aside from single active microencapsulation, there is growing interest in designing structures for the co-encapsulation and co-delivery of multiple species. Although currently achievable within solid systems, significant challenges exist in realising such functionality in liquid formulations. The present study reports on a novel microstructural strategy that enables the co-encapsulation and co-release of two actives from oil-in-water emulsions. This is realised through the fabrication of sodium caseinate/chitosan (NaCAS/CS) complexes that in tandem function as encapsulants of one active (hydrophilic) but also as ('Pickering-like') stabilisers to emulsion droplets containing a secondary active (hydrophobic). Confocal microscopy confirmed that the two co-encapsulated actives occupied distinct emulsion microstructure regions; the hydrophilic active was associated with the NaCAS/CS complexes at the emulsion interface, while the hydrophobic active was present within the oil droplets. Aided by their segregated co-encapsulation, the two actives exhibited markedly different co-release behaviours. The hydrophilic active exhibited triggered-release that was promoted by changes to pH, which weakened the protein-polysaccharide electrostatic interactions resulting in particle swelling. The hydrophobic secondary active exhibited sustained release that was impervious to pH and instead controlled by passage across the interfacial barrier. The employed microstructural approach can therefore lead to the segregated co-encapsulation and independent co-release of two incompatible actives, thus offering promise for the development of liquid emulsion-based formulations containing multiple actives.