Volatile organic compounds released by chitosan formulations present diverse chemical composition and produce differential effects on postharvest pathogens

Chitosan is a natural biopolymer used as a sustainable alternative to synthetic pesticides in agriculture due to its antimicrobial activity against postharvest pathogens, its ability to enhance plant defensive responses, and the formation of a protective film on the plant surface. Little is known regarding the nature of volatile organic compounds (VOCs) in chitosan formulations and their antimicrobial potential. In this study, we evaluated the antifungal activity of VOCs from nine chitosan formulations against Botrytis cinerea, Monilinia fructicola, Monilinia laxa, Alternaria alternata, and Alternaria brassicicola. The VOC composition of the tested formulations was analyzed by gas chromatography coupled with mass spectrometry (GC-MS), and the relative abundance of the different compounds was correlated with the antifungal activity using a hierarchical cluster analysis (HCA). VOCs released by chitosan formulations presented diverse chemical composition and produced differential growth inhibitory effects on the tested fungi. This activity seems to be dose dependent, although not directly linked to chitosan concentration, its chemical nature, or source. HCAs indicated a strong correlation between dichloromethane and, especially, phenol, 2,5-di-tert-butyl with the antifungal activity observed against all five tested postharvest pathogens, while M. laxa inhibition correlated also with 3-hexanone, 2-hexanone, and 2-pentanone. This study opens a new road for further research and characterization of VOCs from chitosan formulations, their biological activities, and their potential use in postharvest disease management.