Mediated by tea polypeptides: A green synthesis approach for selenium nanoparticles exhibiting potent antioxidant and antibacterial properties

This study presents an ecologically conscious methodology for synthesizing tea polypeptides-selenium nanoparticles (TP-SeNPs) exhibiting antioxidant and antibacterial properties, utilizing tea polypeptides (TP). Proteins were extracted from tea leaves using an alkali extraction-acid precipitation method, and response surface methodology (RSM) was employed to optimize the preparation processes for both TP and TP-SeNPs. The TP extract was obtained with the highest TP content of 28.12% at a pH of 6, temperature of 50°C, duration of 3 h, and enzyme concentration of 4%. TP-SeNPs with a minimum particle size of 98 nm were biosynthesized by adding 3% TP at pH 4 and reaction temperature of 55°C for 6 h. The UV spectrum of TP-SeNPs showed an absorption peak at 285 nm. The EDS peak at 1.37 keV confirmed the presence of selenium in TP-SeNPs. Electron microscopy revealed a thin layer coating on the surface of TP-SeNPs. Infrared analysis showed changes in the C=O, NH, and C-N bonds. XRD analysis indicated the formation of a crystalline structure in TP-SeNPs. The absorbance ratio of the peptide selenium nanoparticle colloidal solution remained stable over 7 days at 25°C and 4°C. TP-SeNPs exhibited higher antioxidant activity than SeNPs at high concentrations. TP-SeNPs contain selenium, carbon, oxygen, and nitrogen, and TP plays a role in stabilizing and encapsulating TP-SeNPs. This may involve physical adsorption, covalent interactions, and other unknown interactions, preventing aggregation or degradation. The crystalline structure of TP-SeNPs improves their material properties and enhances their antioxidant and antibacterial abilities.