Physicochemical properties, photostability, and digestive characteristics of natural emulsion system fabricated by recombinant rice bran oil bodies for lutein ester delivery

Rice bran oil bodies (RBOBs), as natural oil-in-water emulsions, can be used as a good carrier for delivering hydrophobic functional ingredients. In this work, the lutein ester-loaded rice bran oil body (LRBOB) emulsions were successfully prepared by restructuring the RBOBs natural structure through heat treatment and high-pressure homogenization. The physicochemical properties, photostability, and in vitro digestion of LRBOB emulsions with different oil body concentrations were investigated. The LRBOB emulsion with 50% RBOBs had maximum lutein ester encapsulation efficiency (94%) with larger mean particle size (566.44±18.05 nm) and zeta potential (-43.87±0.8 mV), exhibiting good physical stability and an amorphous structure of lutein ester. Meanwhile, the emulsion droplets formed a network structure through mutual adsorption, as observed by CLSM. Moreover, the apparent viscosity of LRBOB emulsion was increased with the increase of RBOBs concentration, showing a shear thinning behavior. Within the linear viscoelastic range, the emulsions mainly displayed elastic rheological characteristics. Furthermore, the photooxidation studies showed that the LRBOB emulsion retained a maximum of 37% lutein ester after 96 h of UV irradiation, and the half-life was extended to 58.89 h. Meanwhile, a higher amount of RBOBs effectively reduced lipid and protein oxidation and minimized color difference, indicating that RBOBs could effectively improve the stability of lutein ester. Based on the results of in vitro simulated digestion, LRBOB emulsion showed higher free fatty acid release (32%) and lutein ester bioaccessibility (40.17%) in the adult model, but is not recommended for infant diets. This work will provide a new delivery vehicle for the utilization of raw lutein materials, expanding the potential applications of natural plant oil bodies.