In vitro and in vivo antifungal activity of chitosan, as continuous gel and nanoparticles suspension, against Alternaria alternata and Penicillium expansum.

Abstract

Abstract Formulations based on chitosan of medium molar mass, in the form of continuous gel and suspension of nanoparticles with average dimensions of 117 ± 20 nm, obtained by crosslinking with sodium tripolyphosphate, were evaluated with respect to the antimicrobial activity against the fungi Alternaria alternata and Penicillium expansum. When essayed in in vitro condition, using the sequential dilution method, the resultant minimum inhibitory concentration (MIC) was 7 gL− 1 for both fungi. In diffusion measurements on solid agar medium, the MIC of 7 gL− 1 was confirmed for the inhibition of A. alternata and 8 gL− 1 was found for P. expansum. Based on these results, the concentration of 9 gL− 1 was chosen for the in vivo tests in the form of coatings on previously inoculated apples and guavas. The coatings were prepared via nebulization, either from the continuous or the nanoparticulate formulation. Fungal counting (CFU) from inoculation day to fruit decay indicated a greater efficiency of the nanoparticulate coating, especially for guava, which is more perishable and susceptible to infestation. By comparison, on apples the coatings have similar initial inhibition. After 20 days of measurements however, the particulate system shows 13% higher efficiency than the continuous coating. For guava, the efficiency of the particulate suspension was even better, 33% higher than the continuous covering, having a significant effect on the extension of the shelf life, with an increase of one week under the experimental storage conditions evaluated (room temperature, RH 50–60%).