Response surface optimization of agro-waste-derived quaternary nanocomposite films for antimicrobial active packaging: Application in postharvest preservation of tomatoes

A quaternary biopolymer nanocomposite film combining chitosan, mango kernel starch (MKS), sugarcane bagasse cellulose (SBC) fibres, and green-synthesised silver nanoparticles (AgNPs) was developed and optimised for active food packaging using response surface methodology. FTIR confirmed intermolecular hydrogen bonding through characteristic shifts in O-H and N-H stretching bands, while XRD revealed increased structural ordering with a crystallinity index of 57.3% and AgNP diffraction peaks at 2θ = 38° and 44°. SEM showed a uniform distribution of nanoparticles across a dense, homogeneous surface and DSC analysis recorded an onset degradation temperature of 340°C, reflecting improved thermal stability. The optimised film achieved a tensile strength of 30.5 ± 1.4 MPa (66% increase over neat chitosan), water vapour permeability of 2.83 ± 0.52 × 10⁻¹² g·m⁻¹·s⁻¹·Pa⁻¹ (26% reduction relative to neat chitosan), and UV-blocking efficiency of 91.8%. Antibacterial assessment yielded inhibition zones of 17.6 ± 0.9 mm against S. aureus and 15.4 ± 0.8 mm against E. coli. In postharvest trials conducted over 30 days at 10°C, optimized formulation coated tomatoes exhibited significantly lower physiological weight loss (12.1% vs. 27.2%), reduced decay incidence (34.5% vs. 89%), superior firmness retention (23.1 vs 9.8 N), and higher ascorbic acid content (19.8 vs 14.6 mg/100 g) relative to uncoated controls. Pearson correlation analysis confirmed that moisture loss, softening, pigment transition, and microbial decay operate as interconnected senescence cascades, collectively attenuated by the film's barrier, antioxidant, and antimicrobial functions. This agro-waste-derived nanocomposite offers a multifunctional and scalable approach to extending the shelf life of fresh produce.