Design of high-loading and high-stability viscoelastic emulsions for polymethoxyflavones

Polymethoxyflavones (PMFs), a class of highly lipophilic phytochemicals found in citrus peels, were documented to possess various potent biofunctionalities. The efficacies of PMFs are greatly limited by their low solubility in aqueous environment and rapid metabolic activities. Moreover, the incorporation of PMFs into pharmaceutical, nutraceutical, cosmetic, and food products has been hindered by the instability of their liquid formulates and crystalline sedimentation at application and storage temperatures. In this paper, a new method of forming highly stable viscoelastic emulsions was revealed to suspend and encapsulate high loadings of PMFs (>2.5%) for prolonged storage under ambient temperature. Without utilizing any potentially toxic organic solvent during processing, oil-in-water (O/W) viscoelastic emulsions were constituted solely by GRAS status food ingredients: medium chain triacylglycerol (MCT), lecithin, and water. The viscoelastic emulsion matrices were homogeneous mixtures of PMF crystals and saturated emulsion droplets with an average particle size of approximately 400nm. Depending on their lipophilicity, the sizes of PMF crystals entrapped in the viscoelastic emulsion matrix varied considerably, with 9.3±1.3μm and 3.8±0.6μm for tangeretin and 5-demethyl tangeretin respectively. The effectiveness of viscoelastic structures to prevent the sedimentation of crystalline PMFs was confirmed by studying dissolution kinetics at 0, 15, 30, and 60 times of the emulsion dilutions. With PMF concentrations remaining constant in undiluted emulsion samples during the investigation time frame, PMF dissolution concentrations decreased to (26.3±2.8)% and (52.7±2.6)% for tangeretin and 5-demethyl tangeretin, respectively. •The first successful delivery system with high PMF loading and stability.•PMF emulsions were effectively stabilized by their unique viscoelastic structure.•PMF emulsions use only food-grade materials but no organic solvents.