Síntese e caracterização de nanocompósitos quitosana/montmorilonita para revestimento de frutas

Abstract

The high percentage of loss in fruit production worldwide occurs, especially, due to their short useful life, which is related to many changes suffered during post-harvest. The conservation methods act in the sense of delaying and minimizing these changes in order to increase the consumption period of the fruits. The edible coating acts as a second barrier, protecting the fruits against external damages. Chitosan, obtained from chitin, presents appropriate characteristics for this end. However, it is highly permeable to water vapor. One of the ways to improve this property and, concomitantly, improve its mechanical tensile properties, is through the formation of nanocomposites. Thus, the aim of this work was to promote the synthesis of chitosan/montmorillonite (MMT) nanocomposite in order to improve the mechanical and permeability to water vapor properties of the chitosan film for application in fruit coatings. For this, different concentrations of sodium MMT were employed and the characterization of the films was performed. We used scanning electron microscopy, Fourier transform infrared spectroscopy, X-ray diffraction, thermogravimetric analysis, differential scanning calorimetry, solubility, water vapor permeability, traction test and spectroscopy in the visible range.Wettability and surface energy analysis were conducted on the surface of the films and peal of the investigated fruits. The coating was done in Williams pear and Pera Rio orange, by means of the immersion method. The fruits were stored in room temperature and, during this period, we measured the weight loss and the decay incidence. The results showed that the nanocomposites presented probable intercalated/exfoliated structure, with a few agglomerations in certain regions. The concentration of 0.5% w/w of MMT presented significant improvement in the elasticity module and water vapor permeability rate, with this treatment being selected for coating the fruits. The pear presented reduction in the weight loss from the 12 th day of storage, when the nanocomposite was employed, in comparison to the chitosan coating, and this last in comparison to the control. The deterioration incidence was also smaller for the treatment with chitosan/MMT. For the orange, no differences were observed during storage in any of the analyses. Thus, the use of MMT in chitosan films improved the required properties and, when used as coating for pear, provided possible improvements to its shelf-life.