Effect of gum Arabic on antifungal photodynamic activity of curcumin against Botrytis cinerea spores

This study investigated the effect of gum Arabic on curcumin's phototoxicity against Botrytis cinerea, a significant cause of postharvest losses in horticultural produce. Curcumin-loaded nanoparticle suspensions and emulsions stabilized with gum Arabic were prepared and their absorbance, fluorescence emission, physicochemical properties, antimicrobial photodynamic activity (using response surface methodology (RSM)), and reactive oxygen species (ROS) generation (via electron paramagnetic resonance (EPR) spectroscopy) were evaluated. Fluorescence emission exhibited a blue shift (510-550 nm) in both formulations, with emulsions showing higher intensities due to a more hydrophobic environment. Gum Arabic concentration significantly influenced the physicochemical properties of both suspensions, with nanoparticle size decreasing from 572.80 nm to 202.80 nm as gum Arabic concentration increased from 0.5 % to 2.5 % (at 65 mu M curcumin). Nanoparticle suspensions demonstrated higher antimicrobial efficacy, reducing B. cinerea spores by 0.39-3.40 log10(CFU.ml- 1), compared to 0.00-0.46 log10(CFU.ml- 1) in emulsions. The phototoxic effect was dependent on curcumin concentration and light irradiance, as demonstrated by RSM. EPR confirmed the generation of superoxide anion and hydroxyl radicals in both formulations, which indicated a Type I photodynamic mechanism, with nanoparticle suspensions having a sustained ROS generation. Overall, gum Arabic did not impair curcumin's antifungal photodynamic activity, making it as a promising stabiliser for curcumin-based treatments.