Photodynamic Inactivation of Botrytis cinerea Spores by Curcumin—Effect of Treatment Factors and Characterization of Photo-generated Reactive Oxygen Species

Abstract

Botrytiscinerea is the main cause of gray mold in a wide range of fresh produce, which causes huge losses in pre- and/or post-harvest stages and is therefore considered the second major plant pathogen globally. Since the application of synthetic fungicides is not allowed in postharvest conditions, alternative natural approaches are required to reduce the resulting spoilage. The aim of this study was to investigate the efficacy of photodynamic treatment in inactivating B. cinerea spores in vitro, for which the interactive effect of influential treatment parameters on curcumin phototoxicity was studied using an I-optimal design. Results showed that the antifungal activity of the treatment was significantly dependent on solvent, curcumin concentration, and irradiance, except for light dose. A complete photoinactivation of spores was obtained in an aqueous ethanolic environment (optimum condition: 13 μM, 31.75 mW cm−2, 19.05 J cm−2), compared to when curcumin was dissolved in medium-chain-triglyceride (MCT) oil. Furthermore, the photogeneration of superoxide anion and hydroxyl radicals was demonstrated by electron paramagnetic resonance spectroscopy, which indicates the occurrence of a type-I photodynamic reaction. These findings suggest that curcumin-based photosensitization can inhibit/reduce fungal infection, which can be employed in pre/post-harvest stages to reduce the waste caused by spoilage.