Valorisation of pomegranate processing waste for the synthesis of ZnO nanoparticles: antioxidant and antimicrobial properties against food pathogens

The sustainable management of food waste is a pressing concern, with fruit waste valorisation emerging as a viable strategy to address this challenge. This study investigated the potential of pomegranate peel waste (PPW) and pomegranate seed waste (PSW) as mediating agents for the biosynthesis of zinc oxide (ZnO) nanoparticles (NPs); ZnO-PPW and ZnO-PSW, respectively, for potential utilization as additives in various polymer matrices for food packaging materials. The resulting physicochemical characteristics were ascertained using Ultraviolet visible spectroscopy (UV-vis), x-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), x-ray diffraction (XRD), Scanning electron microscope (SEM) and Energy Dispersive x-Ray Analysis (EDX). The obtained indexed diffractogram from the XRD analysis for both ZnO-PPW and ZnO-PSW confirmed the wurtzite crystalline structure of ZnO NPs. The observed morphology from the TEM and SEM analysis showed a similar spherical shaped structure, with agglomerations. However, ZnO-PSW, had a smaller size (58 nm) in comparison to ZnO-PPW (59 nm). Total phenolic content (TPC) for ZnO-PPW and ZnO-PSW ranged from 16.87-54.4 μg GAE/g DM, respectively. Also, the estimated minimum inhibitory concentration at 50% (IC₅₀) for both DPPH and ABTS are 2.97 and 2.57 mg ml⁻¹ for ZnO-PPW; and 3.43 and 3.33 mg ml⁻¹ for ZnO-PSW, respectively. Moreover, due to its smaller size, ZnO-PSW demonstrated superior antimicrobial activity against five foodborne microorganisms. These findings suggest that pomegranate waste derived ZnO NPs could be beneficial for developing active food packaging materials.