Background Curcumin has been widely acknowledged for its health-promoting effects. However, its application is often limited by its poor water solubility and biochemical/ structural degradation during physiological transit that restricts its bioavailability. Emulsion based approaches have attracted the most research attention to encapsulate curcumin and improve its stability, bioaccessibility and bioavailability. Scope and approach This review summarizes the recent advances in application of different oil-in-water emulsion-based approaches, such as, conventional emulsions (surfactants-, protein-and protein-polysaccharidestabilized emulsions), nanoemulsions, and Pickering emulsions that have been specifically used to deliver curcumin. Particular emphasis is given to factors affecting curcumin solubility, change in crystalline structure of curcumin upon dispersion and encapsulation efficiency. Changes in the droplet size and emulsion stability during in vitro oral-to-gastrointestinal digestion are discussed, with clear 34 focus on the bioaccessibility of the encapsulated curcumin. 35 36 Key findings and conclusions 37 Key factors that influence curcumin delivery include emulsion droplet size, oil composition, volume fraction, dispersion conditions of curcumin in the oil phase and the type of interfacial materials. Nanoemulsions have been the preferred choice for delivery of curcumin up to now. Although scarce in literature, emulsions stabilized by edible Pickering particles as shown by recent evidence are effective in protecting curcumin in an in vitro gastrointestinal setting due to their high coalescence stability. Further studies with emulsions stabilized by food-grade particles and accurate tracking of the physiological fate (in vitro to human trials) of different emulsion-based delivery vehicles are essential for rational designing of curcumin-rich functional foods with high bioaccessibility.

This is a repository copy of Pickering emulsion stabilized by protein nanogel particles for delivery of curcumin: Effects of pH and ionic strength on curcumin retention.

The aim of this study was to investigate the fate of curcumin (CUR)-loaded Pickering emulsions with complex interfaces during in vitro gastrointestinal transit and test the efficacy of such emulsions on improving the bioaccessibility and cellular uptake of CUR. CUR-loaded Pickering emulsions tested were whey protein nanogel particle-stabilized Pickering emulsions (CUR-E WPN ) and emulsions displaying complex interfaces included 1) layer-by-layer dextran sulphate-coated nanogel-stabilized Pickering emulsions (CUR-DxS+E WPN ) and 2) protein+dextran-conjugated microgel-stabilized Pickering emulsions (CUR-E WPDxM ). The hypothesis was that the presence of complex interfacial material at the droplet surface would provide better protection to the droplets against physiological degradation, particularly under gastric conditions and thus, improve the delivery of CUR to Caco-2 intestinal cells. The emulsions were characterized using droplet sizing, apparent viscosity, confocal and cryo-scanning electron microscopy, zeta-potential, lipid digestion kinetics, bioaccessibility of CUR as well as cell viability and uptake by Caco-2 cells. Emulsion droplets with modified to complex interfacial composition ( i.e. CUR-DxS+E WPN and CUR-E WPDxM ) provided enhanced kinetic stability to the Pickering emulsion droplets against coalescence in the gastric regime as compared to droplets having unmodified interface ( i.e. CUR-E WPN ), whereas droplet coalescence occurred in intestinal conditions irrespective of the initial interfacial materials. A similar rate and extent of free fatty acid release occurred in all the emulsions during intestinal digestion ( p > 0.05 ), which correlated with the bioaccessibility of CUR. Striking, CUR-DxS+E WPN and CUR-E WPDxM significantly improved cellular CUR uptake as compared to CUR-E WPN ( p < 0.05 ). These results highlight a promising new strategy of designing gastric-stable Pickering emulsions with complex interfaces to improve the delivery of lipophilic bioactive compounds to the cells for the future design of functional foods.

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This is a repository copy of Conjugate microgel-stabilized Pickering emulsions: Role in delaying gastric digestion.