Physicochemical and Microstructural Properties of Polymerized Whey Protein Encapsulated 3,3′-Diindolylmethane Nanoparticles

The fat-soluble antioxidant 3,3′-diindolylmethane (DIM), is a natural phytochemical found in Brassica vegetables, such as cabbage, broccoli, and Brussels sprouts. The stability of this compound is a major challenge for its applications. Polymerized whey protein (PWP)-based DIM nanoparticles were prepared at different mass ratios of protein and DIM by mixing PWP and DIM followed by ultrasound treatment for 4 min. All the nanoparticles were studied for particle size, zeta potential, rheological and microstructural properties, and storage stability. The mean particle size of the PWP-based nanoparticles was significantly increased (p < 0.05) by the addition of DIM at different mass ratios, ranging from 241.33 ± 14.82 to 270.57 ± 15.28 nm. Zeta potential values of all nanoparticles were highly negative (greater than ±30 mV), suggesting a stable solution due its electrostatic repulsive forces. All samples exhibited shear thinning behavior (n < 1), fitted with Sisko model (R(2) > 0.997). Fourier Transform Infrared (FTIR)spectra revealed that the secondary structure was changed and the absorption intensity for hydrogen bonding got stronger by further incorporating DIM into PWP. Transmission electronic microscopy (TEM) images showed spherical and smooth surface shape of the PWP-based nanoparticles. DIM encapsulated by PWP showed enhanced stability at 4, 37 and 55 °C for 15 days evidenced by changes in mean particle size and color (a*-value and b*-value) compared with control (DIM only). In conclusion, the polymerized whey protein based 3,3′-diindolylmethane nanoparticles are stable and the encapsulation may protect the core material from oxidation.