Biosynthesis of Silver Nanoparticles from Fermented Bush Tea (Athrixia phylicoides DC) Leaf Extract and Evaluation of Their Antioxidant and Antimicrobial Properties

Green synthesis is a promising strategy for producing eco-friendly, non-toxic, and less expensive metallic nanoparticles from plants and microorganisms. This research synthesized silver nanoparticles (AgNPs) from fermented leaf extract of bush tea (Athrixia phylicoides DC). The physicochemical characterization of AgNPs was conducted by UV-vis spectroscopy, Fourier Transform Infrared Spectrometry (FTIR), and Differential Scanning Calorimetry (DSC). In addition, the total phenolic and flavonoid contents, antioxidant and antimicrobial activities of AgNPs were evaluated. The results indicated the successful formation of AgNPs by a visual change of color in fermented bush tea leaf extract from black to brown and in unfermented bush tea leaf crude extract from dark brown to light brown. The UV-vis spectrum of the reaction of the mixture of synthesized AgNPs with unfermented and fermented bush tea showed maximum absorbance at 457 nm and 450 nm, which confirmed the formation of AgNPs. FTIR revealed the functional groups of a leaf extract from bush tea that contributed to the reduction and capping process. The thermal properties suggest that low thermal stable compounds contributed to the reduction of Ag+ to Ag&deg: in the phyto compounds found in the extract. The total phenolic content was higher in fermented AgNPs (290.44 mg/g GAE) compared to unfermented AgNPs (171.34 mg/g GAE). On the other hand, the total flavonoid content was higher in unfermented AgNPs (17.87 mg/g CE) than in fermented AgNPs (9.98 mg/g CE). Regarding antioxidant activity values, unfermented AgNPs had the highest FRAP (535.30 TE/mL) and 47.58% for DPPH. Fermented AgNPs had more antimicrobial activity than unfermented AgNPs. The results show that bush tea leaf extract can be used in different industries such as food, cosmetics, and biomedical.