Síntese e caracterização de nanopartículas de quitosana-tripolifosfato e seu potencial como antifúngico natural para aplicação por aspersão em frutas frescas

Abstract

Contamination by pathogens is a problem that occurs on a global scale and is related to approximately 25% of total fruit and vegetables losses in the post-harvest condition. The synthetic antimicrobials usually applied in order to minimize these losses, if not used in a moderate way, might generate undesirable impacts on human health and to the environment. So, a growing awareness and preference for healthy foods, absent of chemical pesticides, is in course. An alternative to meet these demands is the development of natural fungicides, which can act satisfactorily and with low impact or side effects. In this context, chitosan has been considered as a suitable alternative for the development of antimicrobials, mainly due its natural source and biodegradability. In conventional diluted form, chitosan has already proved to have a broad antimicrobial activity. In the present study, the synthesis of nanoparticles from the Chitosan-Tripolyphosphate (NPQui-TPP) system and their antifungal potential, when in aqueous suspensions, were evaluated in topical applications on fruits via spray. The premise is that as larger the particulate area, the greater will be the surface interaction between chitosan molecules and pathogens. The NPQui-TPP were synthesized by the ionotropic gelation method, and several experimental parameters evaluated aiming at the optimization and standardization of the process, where the following conditions were defined: height of 8 cm between intercrossing (TPP) dropping and the chitosan gel surface, under agitation of 1500 rpm and additional ultrasonication with 30% of amplitude for 2 minutes.In these conditions NPQui-TPP with an average diameter of 117.3 nm were generated and assessed in vitro at concentrations of 8 and 9 g/L with effective activity in inhibiting the growth of Alternaria alternata and Penicillium expansum inoculated in BDA medium. Formulations for topical application with 9 g/L (particles in suspension) were prepared and sprinkled on apples and guavas, inoculated and non-inoculated with the analyzed fungi, for in vivo assessment. Coatings in non-nanoparticulated condition (dipping into chitosan gel), were also carried out for comparison. The results show superior activities of NPQui-TPP when compared to the continuous coatings. The nanoparticulated coatings promoted reductions of 55 % in the loss of firmness in guavas and 38.7 % concerning the apples. Additionally the nanoparticles provided a decrease in 24 % in the fungal growth on apples and of 28 % on guavas, with simultaneous colorimetric alterations around 13.7 % on apples, when compared to non-coated samples, along 14 days. Although the exact mechanisms by which chitosan antimicrobial activity occurs is not yet fully elucidated, it is evident that chitosan in nanoparticles form has superior antifungal activity and general preservative properties, what have been attributed to their high surface area and consequently the ability to perform larger interactions.