Ag-zeolites as fungicidal material: Control of citrus green mold caused by Penicillium digitatum

- Ag-zeolites are suitable antifungal materials for treating citrus fruit diseases.
- Antifungal activity depends on silver content, Si/Al ratio and topology of zeolites.
- Zeolites with larger pores and higher Si/Al ratio are more active.
- High silver content in the zeolites induces phytotoxicity in the fruit.

One of the most economically important postharvest diseases of citrus fruit is green mold caused by the fungus Penicillium digitatum. In this investigation, the antifungal properties of silver FAU and silver LTA zeolites against P. digitatum either alone or incorporated into edible coatings were evaluated in citrus fruit. The Ag-zeolites were characterized by different techniques such as ICP, TPR, XRD and electronic microscopy. These techniques demonstrated that ion exchange was a suitable method for the incorporation of silver cations into zeolites without changing the structure of the matrix. It was observed that silver was present in the zeolite mainly as well dispersed Ag+ and that different silver species with different reduction properties were formed depending on the zeolite structure. It was found that the resulting materials had potential to control citrus green mold caused by P. digitatum. The results confirmed that incorporation of these zeolites into coatings provided an affordable and safe method to control decay of fresh oranges. The antifungal activity depended on the amount of silver contained in zeolites, but a high silver content induced phytotoxicity in the fruit surface. Nevertheless, Ag-zeolites with low silver content were also active without phytotoxic effects. The best results were obtained with the FAU zeolite, which had the largest pores and the highest Si/Al, showing the influence of the topology and composition of the zeolites on their antifungal properties.

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