Microbial Diversity of Spoiled Fruits and Vegetables and Application of Chitosan–Cellulose–Green Tea Biocomposite Coating for Postharvest Preservation

Abstract

Objectives: To characterise the microbial diversity associated with spoiled fruits and vegetables and to design a multifunctional biocomposite coating based on chitosan, cellulose and green tea extract for postharvest preservation and shelf-life extension. Method: Spoiled samples of Tomato, Cucumber, banana, and Grape were gathered from Sulur Market, Coimbatore, Tamil Nadu, India during the winter season (December 2025). Microbial diversity was determined by serial dilution, selective culture medium, Gram staining and biochemical assays. Chitosan was isolated from the waste of prawn shells and characterised by FTIR spectroscopy. Antioxidant activity was assessed by DPPH assay. Antibacterial activity was evaluated by agar well diffusion method. Fresh fruits and vegetables were coated with a chitosan–cellulose (coir pith)–greentea extract biocomposite and compared with uncoated controls. Findings: Spoilage bacteria consisted of Bacillus, Staphylococcus, Pseudomonas, Enterobacter, Klebsiella, Escherichia coli, Salmonella, Vibrio and Enterococcus spp. The FTIR analysis showed successful chitosan extraction with typical peaks at 3348.78, 2919.70, and 1635.34 cm-1. Chitosan displayed concentration-dependent antioxidant activity with DPPH radical scavenging of 18.18 ± 1.29% to 90.91 ± 1.29% (100–1000 μg/mL). The results showed antibacterial activity with inhibition zones of 22.0 ± 0.6 mm against Staphylococcus aureus and 21.0 ± 0.7 mm against Escherichia coli. The biocomposite covering enhanced shelf life of grapes from 5-12 days, bananas from 6-14 days, tomatoes from 10-18 days and cucumbers from 7-13 days by cutting moisture loss, delaying ripening, retaining firmness and minimising microbiological deterioration. Novelty: The research provides a multifunctional biodegradable chitosan–cellulose–green tea extract coating with antibacterial, antioxidant, and barrier capabilities. Unlike previous studies that have been mainly conducted on chitosan alone or on a single fruit commodity, the present study couples microbial profiling with the effective use of a composite coating on multiple fruits and vegetables, showing sustainable alternative to synthetic preservatives and packaging materials. Keywords: Chitosan, Microbial diversity, Cellulose, Green tea extract, Postharvest, preservation