Ultrasound-Induced Changes in Physicochemical, Microstructural, and Antioxidative Properties of Whey-Protein-Concentrate-Encapsulated 3,3′-Diindolylmethane Nanoparticles

This study determined the impact of ultrasound duration on the encapsulation of 3,3'-diindolylmethane (DIM) using whey protein concentrate (WPC) nanoparticles. Whey-protein-concentrate-based DIM nanoparticles were prepared and treated with different ultrasound times (0-20 min) with 30% amplitude at 4 °C. The results showed that ultrasound treatment significantly decreased the mean particle size (from 265 nm to 218 nm) and the Polydispersity Index (PDI) value (from 0.49 to 0.43) as well as zeta potential values were notably increased. The encapsulation efficiency (EE%) increased with increasing sonication time (0-20 min) from 76% to 88%, respectively. The ultrasound treatment had a significant effect on the apparent viscosity, and a decrease in the viscosity as a function of shear rate was observed with increasing sonication time. The transmission electronic microscopy (TEM) micrographs demonstrated that all of the formulations treated with different sonication times had a smooth and uniform spherical shape and ultrasound treatment led to the reduction of particle size, especially after 20 min of ultrasound. The thermal stability of the WPC-DIM nanoparticles was enhanced with increasing sonication time by increasing peak denaturation temperature and enthalpy. The Fourier transform infrared spectroscopy (FT-IR) spectra analysis revealed that ultrasound treatment had a remarkable effect on the secondary structure of WPC-DIM nanoparticles; electrostatic interactions and hydrogen bonds between DIM and whey protein were strengthened. Moreover, the length of ultrasound treatment exhibited a significant effect on the DPPH (2,2-diphenyl-2-picrylhydrazyl) scavenging activity (from 56% to 62%) and ABTS(2,2'-azinobis(2 ethylbenzothiazoline-6-sulfonate) scavenging activity (from 47% to 68%). In conclusion, the ultrasound treatment successfully improved the physicochemical, microstructural, and antioxidative properties of WPC-DIM nanoparticles; therefore, it is considered an effective method to develop whey-protein-concentrate-based DIM nanoparticles for medical and nutritional applications.