Effects of fungal chitosan nanoparticles as eco-friendly edible coatings on the quality of postharvest table grapes

Chitosan edible coatings are a potential alternative for extending the postharvest life of fruit. The properties of chitosan can be enhanced when it is used in the form of nanoparticles. The aim of this study was to evaluate the in vitro antimicrobial activity and the effect of gel + fungal chitosan nanoparticles on some physicochemical properties (total soluble solids, pH, titratable acidity, reducing sugar content and moisture content) and sensory characteristics of grapes stored at 12 °C and 25 °C. The chitosan nanoparticles were prepared by ionic gelation and then underwent a heat treatment (50 °C/1200 × g/30 min). Characterization of the particles was carried out by dynamic light scattering and scanning electron microscopy. The microdilution test was used to determine the minimum inhibitory (MIC) and bactericidal concentration (MBC) of chitosan nanoparticles against food-borne pathogenic bacteria. To obtain the coatings to be tested, chitosan was solubilized in 1% acetic acid (20 g/L−1) and nanoparticles were subsequently added (MIC/2, MIC and 2MIC). The produced nanoparticles were spherical, had a medium size of 128.3 nm and showed an inhibitory effect against pathogenic foodborne bacteria with MIC values ranging from 2 to 3 g/L−1. The edible chitosan nanoparticle coatings were responsible for delaying the ripening process of the grapes resulting in decreased weight loss, soluble solids and reducing sugar contents as well as increased moisture retention and preservation of the titratable acidity values and sensory characteristics. Therefore, the use of edible coatings containing chitosan nanoparticles at different concentrations (MIC/2, MIC, 2MIC) can be a promising strategy to improve the post-harvest quality of grapes.