Emulsifiers of Pickering-like characteristics at fluid interfaces: Impact on oil-in-water emulsion stability and interfacial transfer rate kinetics for the release of a hydrophobic model active

The influence of interfacial layer composition on the release kinetics of a model hydrophobic active (dimethyl phthalate, DMP) from oil-in-water (o/w) emulsions relevant to foods is reported. The present study considers various food-relevant emulsifiers known to form colloidal particles in aqueous solutions. These range from a low molecular weight surfactant and protein polyelectrolytes, to biopolymer complexes and solid particles: sodium stearoyl lactylate (SSL); bovine serum albumin (BSA); sodium caseinate (NaCAS), chitosan (Ch); BSA/Ch or NaCAS/Ch complexes; and silica (Pickering) nanoparticles (A200), were all investigated. In all cases, DMP release from the oil droplets of the o/w emulsions was controlled by the interfacial transport of the active rather than by its diffusion through the globules’ interior. Release data followed first-order kinetics, where emulsions stabilised by soft (protein/polysaccharide complexes) colloidal structures were shown to provide similar (528 nm² s⁻¹) or even lower interfacial rate constants (241 nm² s⁻¹) to harder (silica) particulate entities (625 nm² s⁻¹). SSL (a lamellar-phase forming surfactant that has been previously suggested to stabilise o/w emulsions via a mechanism closely resembling that of Pickering particles) exhibited the lowest interfacial release rate (17 nm² s⁻¹). Overall, the present study contributes to current understanding on how emulsion interfacial architecture can be controlled to provide desirable molecular release performances.