Low-oil-phase emulsion gel with antioxidant properties prepared by soybean protein isolate and curcumin composite nanoparticles

Abstract

A low-oil-phase emulsion gel (Φ < 0.3) was prepared via high-pressure homogenization (HPH) of composite nanoparticles of soybean protein isolate (SPI) with different curcumin concentrations. Native-PAGE electrophoresis, fluorescence spectroscopy, and Fourier-transform infrared spectroscopy demonstrated that the SPI and curcumin were bound by hydrophobic interactions within the nanoparticles (SPI-Cur-NPs). The three-phase contact angle (θo/w) was altered by the addition of curcumin, and the particles exhibited outstanding wettability (θo/w = 80.6 ± 1°) at a curcumin concentration of 50 μM. According to the confocal laser scanning microscopy and cryo-scanning electron microscopy images, the network of emulsion gels with an oil phase of 30% was mainly composed of compact “aggregated” oil droplets, which were mainly formed due to inter-droplet hydrophobic interactions. The formation of such a gel network and the addition of curcumin avoided oxidative deterioration, and maintained a lower peroxide value, which was 1.8 times lower than that of the blank control group during the 30-day storage experiment. Moreover, the peroxide value of this gel was maintained at approximately 0.118 μmol/L during the 14-day accelerated oxidation experiment. Therefore, the low-oil-phase-emulsion gels stabilized by SPI-Cur50-NPs may be used to protect easily oxidized-lipid-soluble nutrients in a low-fat diet.