Abstract
Effective food waste management is essential for lessening its socio-economic and environmental impacts. Fruit and vegetable by-products, rich in valuable compounds, are often overlooked. Advancements in waste valorization, particularly through the synthesis of metal oxide nanoparticles using biowaste, offer promising solutions for enhancing food preservation. These nanoparticles have been successfully applied in active packaging materials, improving the functional characteristics of edible films and coatings and prolonging postharvest shelf life of perishable items by protecting against deterioration and microbial contamination. This approach aligns with circular economy principles and offers a sustainable method to extend the postharvest longevity of fresh produce in the South African fruit industry. This can be achieved through the following objectives: 1) synthesize zinc oxide nanoparticles using fruit waste 2) formulation and characterization of nanocomposite films with relevance to the preservation of minimally processed fruit; 3) evaluation of the efficacy of nanocomposite edible coatings
on minimally processed fruit and establishment of their mode of action.
Chapter 1 presented an overview of postharvest of fruit, green synthesis as a sustainable approach to addressing food security, edible films and coatings and the postharvest application. The literature review in Chapter 2 contextualizes the research within the broader framework of sustainable waste management, reviewing the applications of green-synthesized nanomaterials in packaging. It underscores their significance in achieving the Sustainable Development Goal of halving food waste by 2030. Chapter 3 focused on the utilization of pomegranate fruit peel waste (PPW) and pomegranate seed waste (PSW) as biosynthetic agents for zinc oxide (ZnO) nanoparticles, designated as ZnO-PPW and ZnO-PSW. X-ray diffraction (XRD) analysis confirmed the wurtzite crystalline structure for both types of nanoparticles. Transmission electron microscopy (TEM) and scanning electron microscopy (SEM) analyses revealed spherical structures with some agglomeration, with ZnO-PSW exhibiting a slightly smaller average size of 58 nm compared to ZnO-PPW (59 nm). Ultraviolet-visible spectroscopy showed absorption peaks at approximately 369 nm for ZnO-PPW and 372 nm for ZnO-PSW, indicating successful nanoparticles formation. Fourier-transform infrared (FT-IR) spectra displayed a band at 470 cm-1 indicating the presence of zinc to oxygen bonding vibrations. The synthesized nanomaterials demonstrated a good antioxidant activity, and they were effective antimicrobial
v
agents against five different foodborne pathogens, suggesting their applicability in enhancing food safety.
In a follow up study (chapter 4), edible packaging material was developed by blending banana powder (BP) with cellulose nanofiber (CNF), then enhancing it with zinc oxide nanoparticles (ZnO NPs from chapter 3 and prepared at various concentrations. These ZnO NPs were effectively incorporated into the BP/CNF matrix, as evidenced by significant (p < 0.05) improvements in film physical and mechanical properties of the films ensuring that nanocomposite films are strong enough for protecting food during shipping and marketing. Zinc oxide nanoparticles enhanced UV-visibility barrier properties crucial for preventing food from degrading due to photo-oxidation reactions and the photoprotective action. Films enriched with ZnO NPs improved water vapor permeability barrier properties and they exhibited excellent antioxidant and antimicrobial properties screened against five different foodborne pathogens. These results showcase the potential of using biowaste-mediated nanoparticles in creating more effective, sustainable packaging solutions for food applications.
In Chapter 5, the novel nanocomposite coating composed of banana powder (BP), cellulose nanofiber (CNF), and zinc oxide nanoparticles (ZnO NPs) from chapter 3 was assessed for its efficacy in extending the shelf life of pomegranate arils. The application of this ZnO NP-enriched coating reduced microbial growth and outperformed both the control and the BP/CNF-only treatments. The coatings mitigated color and texture degradation, reduced weight loss and respiration rates, and maintained the physio-chemical and antioxidant attributes better than control and the BP/CNF-only treatments. Thus, suggesting that such coatings can significantly improve the postharvest quality and shelf life of minimally processed fruits by 6 days.
The research established the feasibility of creating zinc oxide nanomaterials from pomegranate by-products, demonstrating their effective use as antioxidants in food preservation. Additionally, it illustrated the practical application of these green-synthesized nanoparticles in edible coatings and films enriched with ZnO NPs, which significantly extend the shelf life of pomegranate arils. This approach presented a novel application of nanotechnology as a practical solution to food waste, which offers tangible benefits for the fresh produce industry.