Tannic acid-fortified zein-pectin nanoparticles: Stability, properties, antioxidant activity, and in vitro digestion

Tannic acid was loaded into zein nanoparticles using antisolvent precipitation and then these particles were coated by anionic pectin using electrostatic deposition. The resulting core–shell nanoparticles were near spherical and had an average diameter of 166 nm, a particle yield of 95%, a tannic acid content of 5.4%, and a tannic acid loading efficiency of 89%. Circular dichroism revealed that the presence of tannic acid caused little change in the secondary structure of the zein within the nanoparticles. Fluorescence spectroscopy suggested the formation of a molecular complex between the zein and tannic acid molecules. Fourier transform infrared spectroscopy indicated that hydrogen bonding was the main force holding these complexes together. The core–shell nanoparticles remained resistant to flocculation from pH 2 to 8, when heated at 80 °C for 2 h, and when the NaCl concentration was below 30 mM. The encapsulated tannic acid preserved its high antioxidant capacity. The tannic acid was progressively released from the core–shell nanoparticles under simulated gastrointestinal conditions, with the majority of release occurring within the small intestine. Overall, this research suggests that pectin-coated zein nanoparticles may be effective encapsulation and delivery systems for hydrophilic polyphenols in nutraceutical, supplements, or pharmaceutical formulations.