Loading natural emulsions with nutraceuticals by ultrasonication: Formation and digestion properties of curcumin-loaded soybean oil bodies

Curcumin is often used as a natural food additive because of its many drug functions and biological properties; however, its poor water solubility, chemical instability, ease of degradation, relatively high rate of metabolic degradation, and low bioavailability has limited its use in functional foods and medicines. In this study, we prepared curcumin oil body (COB) emulsions by loading curcumin into soybean slurry and explored the structural characteristics of emulsions prepared using different ultrasound sequences with the aim of enhancing the functionality and digestion properties of the oil bodies. The measured encapsulation efficiencies, particle sizes, ζ-potentials, Turbiscan stability indices, and other indicators reveal that the best COB encapsulation efficiency and stability are obtained using two ultrasound treatment methods and the addition of 10% oil. Structural analysis using infrared spectroscopy and sodium dodecyl sulfate–polyacrylamide gel electrophoresis revealed that the curcumin-loaded oil was mainly bound to the hydrophobic area of the protein on the surface of the oil body through hydrophobic interactions. COB stability was found to positively correlate with the amount of extrinsic protein adsorbed on the surfaces of the oil droplets. Digestion data showed that, compared with the method in which the oil body is prepared and then loaded with curcumin (COB–U), the COB prepared by direct ultrasonication in the soybean slurry (U–COB) realizes sustained oil release in the intestine. U–COB also exhibits higher bioavailability (67.42%), which is important for creating a more effective curcumin delivery system.