Abstract
The growing concern over food loss and environmental pollution caused by petroleum-based, nonbiodegradable
plastics highlights the urgent need for sustainable alternatives. This study explored
the upcycling of phytochemical-rich Opuntia ficus-indica (OFI) cladode wastes, particularly the
cladode peel and mucilage residue, as potential mediating agents for the biosynthesis of zinc oxide
nanoparticles (ZnO). By utilizing these agricultural by-products, the study aimed not only to
minimize environmental burdens linked with waste disposal but also to develop valuable
nanomaterials that can be infused into active food packaging materials to improve food safety,
quality, and prolong shelf life. This was achieved through these main objectives: 1)
Characterization of OFI cladode wastes based on phytochemical content, antimicrobial, and
antioxidant properties; 2) Use of OFI cladode wastes as green mediators to synthesize ZnO; and
3) Development and characterization of OFI mucilage-based films infused with biosynthesized
ZnO for food packaging applications.
Chapter 1 provided an overview of the research context, addressing global issues related to
postharvest losses and the environmental impact of conventional plastics, while highlighting the
importance of developing sustainable food packaging systems. Chapter 2 examined the role of
various metal-based nanoparticles as active agents in food packaging materials, including different
methods for incorporating them into polymer matrices. It also addressed safety and regulatory
considerations, emphasizing green synthesis as a sustainable strategy. Chapter 3 investigated the
use of OFI cladode peel waste (CPW) and mucilage residue waste (MRW) as mediating agents to
synthesize ZnO-NPs, denoted as ZnO-CPW and ZnO-MRW, respectively. Liquid
chromatography–tandem mass spectrometry (LC-MS/MS) revealed 38 bioactive compounds,
including flavonoids, terpenoids, phenylpropanoids, and amino acids, which acted as stabilizing
and capping agents. The nanoparticles were successfully synthesized, as confirmed by XRD
analysis, which indicated a wurtzite crystalline structure. SEM/TEM analysis revealed
predominantly spherical nanoparticles, with some exhibiting rod-like morphology, more
pronounced in ZnO-MRW. The particle sizes were 24.33 nm for ZnO-CPW and 32.23 nm for
ZnO-MRW. ZnO-CPW demonstrated superior antioxidant and antimicrobial properties compared
to ZnO-MRW, indicated by a lower IC50 and enhanced antimicrobial activity, attributed to its
v
smaller particle size, which facilitates penetration into pathogen cells. Therefore, in Chapter 4, OFI
mucilage-based films were incorporated with ZnO synthesized exclusively from cladode peel
wastes, along with the addition of cellulose nanofibers (CNF) to improve barrier and mechanical
properties, addressing the limitations imposed by the hydrophilic nature of the mucilage. The
mucilage-based films (3%) were formulated with ZnO at various concentrations (0.2%, 0.4%, and
0.6% relative to the base matrix) and CNF (1% relative to the base matrix). Characterization via
FTIR, SEM, and UV-Vis spectrophotometry revealed that the incorporation of ZnO and CNF
significantly enhanced the physicochemical properties (e.g., water vapor permeability, tensile
strength, UV-barrier) and biological properties (antioxidant and antimicrobial activities) of the
films, rendering them suitable for food packaging. Higher nanoparticle concentrations caused
agglomeration and microcracks, resulting in increased water vapor permeability. All films
exhibited biphasic ZnO release profiles, with the 0.4% formulation achieving the most balanced
and controlled release, making it the most promising material for cherry tomato preservation.
Postharvest treatments for cherry tomatoes included control (uncoated), OFIM, OFIM/CNF, and
OFIM/CNF/ZnO (0.4%). Coated tomatoes exhibited reduced weight loss and respiration rates
compared to uncoated fruits, with the OFIM/CNF/ZnO (0.4%) film showing the most significant
effect, attributed to the improved barrier properties resulting from the synergistic interaction of
CNF and ZnO. No significant differences in firmness were observed among all fruits, while coated
fruits maintained higher lightness (L*), stable pH levels, delayed accumulation of total soluble
solids, and preserved lycopene and ascorbic acid content, indicating enhanced physicochemical
and antioxidant stability. These findings highlight the potential of mucilage-based nanocomposite
coatings for maintaining tomato quality.