Pickering emulsion stabilized by protein nanogel particles for delivery of curcumin: Effects of pH and ionic strength on curcumin retention

This study aimed to design whey protein nanogel particles (WPN)-stabilized Pickering emulsion as a delivery vehicle for curcumin (CUR). Firstly, the effectiveness of WPN to stabilize medium chain triglyceride (MCT) oil was assessed using droplet sizing, microscopy across scales, surface coverage calculations and interfacial viscosity measurements. Then, the ability of this delivery vehicle to encapsulate CUR and the effects of pH and ionic strengths on the retention of CUR were investigated in an in vitro release model at 37 ○C. Results demonstrate that 1.0 wt% WPN was sufficient to create a monolayer of particles at the droplet surface resulting in ultra-stable droplets that were resistant to coalescence over a year. Addition of 500 μg/ mL of CUR did not result in any change in the droplet size of the Pickering emulsion droplets. The CUR was fully retained within the Pickering emulsions, which might be attributed to the nanometric size of the gaps (≅30 nm) at the interface that did not allow CUR to diffuse out into the release media. The partitioning of CUR to the dispersed phase was influenced by pH of the media. Increased binding affinities between CUR and WPN at the interface (binding affinity constant, Ka = 1 × 104 M−1) existed at pH 3.0 as compared to that at pH 7.0 (Ka = 6.67 × 101 M−1) owing to the electrostatic interactions between CUR and interfacial WPN in the former. Such binding affinities between CUR and interfacial WPN at pH 7.0 was further influenced by presence of ions.