Synthesis of ZnO nanoparticles using Theobroma cacao L. pod husks, and their antibacterial activities against foodborne pathogens

Abstract

Zinc oxide nanoparticles (ZnONPs) with antimicrobial properties have potential applications in the food industry. In the present work, the biosynthesis of ZnONPs was carried out using Theobroma cacao L. pod husk extract. UV-Vis spectroscopy confirmed NP formation by the presence of a peak in the range of 390 - 360 nm. Different parameters affecting the biosynthesis were assessed. A temperature of 28°C and pH of 7 were the best conditions for the formation of small-sized NPs. The antibacterial activity of ZnONPs was evaluated using the resazurin microtiter assay. The minimum inhibitory concentrations of ZnONPs for Escherichia coli and Staphylococcus aureus were 6.25 and 12.5 μg/mL, respectively. ZnONPs were more potent than chloramphenicol, suggesting that they are effective against chloramphenicol-resistant bacteria. Based on scanning electron microscopy and transmission electron microscopy, the ZnONPs were irregular in shape, with an average size of 81 nm. The results of the present work provide a simple, cost-effective, and eco-friendly method for the large-scale production of ZnONPs. Moreover, the study highlights the potential of ZnONPs as an antimicrobial agent that can be applied to food packaging systems, textiles, and medical devices.