Incidental Nanoparticles in Black Tea Infusion: Carriers of Bioactives Fortifying Protection on Intestinal Mucosal Cells Against Oxidative Stresses

The health benefits of black tea have been well recognized worldwide. However, the low bioavailability of major bioactive compounds from tea has compromised the molecule-based mechanism of tea’s function. Knowing tea infusion is rich in polymers and colloidal particles, a hypothesis is proposed here that tea bioactives may have self-assembled into colloidal nanoparticles to interact with mucosal cells in alimentary tract, regulating intestinal barrier function and mucosal immunity. The present study of colloidal nanoparticles (NPs) from a Chinese black tea infusion supports this new perspective. The NPs with hydrodynamic diameter of 180 nm and ζ-potential of -33.4 mV were efficiently isolated with size-exclusive chromatography. The NPs are mainly composed of protein and polysaccharides, together with caffeine, gallic acid and catechins. A hypothetic structure of the NPs was proposed according to FTIR spectra analysis and cryo-TEM images, in which the small molecular components were carried by the proteins-polysaccharides hybrid core. Possibly owing to enrichment of bioactives on the interfacial space of particles, the antioxidant activity of NPs was more potent than the tea bioactive compounds in free form at the same concentrations. The NPs elevated both extracellular and intracellular antioxidant activities, scavenging reactive oxygen species in human intestinal epithelial cells and murine peritoneal macrophages challenged by AAPH-derived peroxyl radicals, restoring macrophages’ cell membrane potential and mitochondrial oxygen respiration. It showcases the cell protective capacity of incidental nanoparticles in food, enlightens the future of employing food nanoparticles to boost the mucosal barrier function and immunity, ameliorating inflammations in alimentary tract.