Encapsulation of hydrophobic capsaicin within the aqueous phase of water-in-oil high internal phase emulsions: Controlled release, reduced irritation, and enhanced bioaccessibility

Abstract Capsaicin (CAP) is a hydrophobic substance with various physiological effects in chili peppers that is responsible for their perceived heat. Nonetheless, its application as a nutraceutical is hugely hindered by its low bioaccessibility and mucosal irritation. In this study, capsaicin was entrapped in the water phase of water-in-oil (W/O) high internal phase emulsions (HIPEs) using a pH-driven method. Initially, the capsaicin was mixed with sodium alginate (SA) to form a water-dispersible form of the capsaicin and then used to form CAP-loaded W/O HIPEs. The influence of capsaicin concentration on the properties of W/O HIPEs was then investigated. Cryo-SEM observation demonstrated a thick lipid shell formed around the water droplets and a dense network in the aqueous core. The addition of capsaicin caused an increase in the viscoelasticity of the HIPEs. The CAP-loaded HIPEs exhibited good stability and the capsaicin was shown to remain within the aqueous core (rather that moving to the oil phase) during storage. Only a relatively small amount of capsaicin leaked out of the HIPEs under simulated oral and gastric conditions, but it was progressively released under simulated small intestine conditions as the external lipid phase was digested by lipase. The bioaccessibility of capsaicin was greatly enhanced after encapsulation. An animal experiment showed that the CAP-loaded HIPEs reduced the irritation of the gastric mucosa. Our results suggest that W/O HIPEs may be a useful delivery system for active ingredients with undesirable flavor profiles and low bioaccessibilities.