Biocompatible Nanopolymer Coating Based on Chitosan Nanoprecipitation Containing Guava Oil to Control Fruit Rot, Enhance Defense-Related Enzymes, and Quality of Chili Pepper

This study evaluates the efficacy of chitosan nanoprecipitation loaded with guava leaf essential oil as a sustainable alternative to synthetic preservatives for reducing postharvest deterioration in Capsicum frutescens (chili pepper). Essential oils extracted from Psidium guajava leaves via hydrodistillation were analyzed by GC-MS, identifying β-caryophyllene (22.44%) as the major constituent. Nanoparticles were synthesized via solvent displacement (NP with guava oil and NNP without oil) and nanoelaboration (NC with guava oil and NNC without oil), and characterized by DLS and TEM, confirming stable sizes and zeta potentials. Antifungal activity of NP and NC was tested against Colletotrichum gloeosporioides and Rhizopus stolonifer, both pathogenic to chili. Complete fungal inhibition occurred in vitro by Day 5, whereas in vivo application significantly reduced disease incidence and prolonged shelf life up to 28 days. Treated fruits showed reduced weight loss, better firmness, lower electrolyte leakage, enhanced antioxidant activity, higher phenolic content, and reduced enzymatic browning. Encapsulation and release studies demonstrated controlled diffusion of guava oil, enhancing antimicrobial efficacy. Elevated activities of β-1,3-glucanase, phenylalanine ammonia lyase, and polyphenol oxidase indicated improved resistance to oxidative stress and microbial attack. Toxicity assays using Artemia salina confirmed formulation safety. These findings highlight chitosan nanoencapsulated guava oil as a safe eco-friendly biopreservative for chili peppers.