Evaluation of Antimicrobial and Antioxidant Properties in Green Synthesized Zinc Oxide Nanoparticles Using Morama (Tylosema esculentum) Seed Coat Extract

Abstract

This study explores the green synthesis of zinc oxide (ZnO) nanoparticles using a seed coat extract of morama (Tylosema esculentum), an underutilised leguminous oilseed indigenous to the Kalahari Desert. Green synthesis is a method that utilises biological entities such as plant extracts, offering a sustainable alternative to conventional chemical methods. The qualitative phytochemical screening of the morama seed coat in this study confirmed the presence of bioactive compounds such as saponins, tannins, terpenoids and flavonoids, which facilitate the encapsulation of ZnO nanoparticles and influence their stability. The synthesis process involved boiling the seed coat extract, followed by its reaction with a zinc nitrate precursor and pH adjustment to produce ZnO nanoparticles. The synthesised ZnO nanoparticles were characterised using UV-Vis spectroscopy, which showed peaks at 369 and 373 nm at different concentrations. Further characterisation of ZnO nanoparticles was performed using FT-IR spectroscopy and showed peaks at 854, 1035 and 1112 cm-1. The antioxidant activity was assessed by the DPPH assay, revealing higher antioxidant potential with increasing concentrations of ZnO nanoparticles. The antimicrobial activity was evaluated against different bacteria using the agar well diffusion method. The results revealed strong antimicrobial activity against Staphylococcus aureus, which exhibited the highest zone of inhibition. E. coli demonstrated a larger inhibition zone at a higher nanoparticle concentration than Salmonella. This research indicates the potential of morama seed coat extract as a cost-effective and environmentally friendly route for nanomaterial synthesis, with potential applications in food safety, medicine and food packaging industries.