Capsaicin (CAP) demonstrates a potential for application in the food and pharmaceutical industries owing to its various attractive health benefits, including anti-cancer, anti-inflammatory, and antioxidant activities. However, the application of CAP is often limited by its low solubility in water, low bioavailability, and strong pungency. In this study, a simple one-step method for the stable encapsulation and dispersion of CAP in aqueous media was developed using polyelectrolyte complex particles formed by chitosan (CHI) and oleic acid (OA). Homogeneous particles with mean diameters below 1 μm were successfully prepared via spontaneous molecular complexation by mixing an aqueous solution of CHI with an ethanolic solution of OA and CAP. CAP was incorporated into the hydrophobic domains of the CHI–OA complex particles through hydrophobic interactions between the alkyl chains of OA and CAP. The factors affecting CAP encapsulation were investigated, and a maximum encapsulation yield of approximately 100% was obtained. The CHI–OA–CAP complex particles could be stored for more than 3 months at room temperature (22–26 °C) without resulting in macroscopic phase separation or degradation of CAP. We believe that our findings provide a useful alternative encapsulation technique for CAP and contribute to expanding its practical application.

We investigated the factors affecting preparation of water-in-oil (W/O) emulsions using olive oil as the continuous phase, based on direct observation of microchannel (MC) emulsification.Monodisperse droplets were produced using polyglycerin polycondensed ricinoleic acid ester (PGPR) as an emulsifier. The mean droplet diameter and the time required for droplet formation (droplet detachment time) increased with increased viscosity of the continuous phase. Emulsifier concentration affects droplet formation, and stable emulsification was observed at PGPR concentrations exceeding 1wt％. Adsorption of PGPR was analyzed based on interfacial tension measurement with different measurement time scales. Monodisperse droplets with mean droplet diameters of 24 µm to 90 µm and coefficients of variation below 7％ could be produced using MC plates having different MC geometries. Furthermore, we demonstrated that droplet formation behavior differed with the addition of milk components (skimmed milk powder and whey powder) to the dispersed phase, based on high-speed observation of individual droplet formation.