Revestimentos bioativos a base de alginato e quitosana aditivados com nanoZnO para aplicação em goiabas (Psidium guajava L.)

Abstract

Alginate is a film-forming polysaccharide due to its non-toxicity, biodegradability, biocompatibility, and low cost. As well, chitosan is one of the most abundant biological materials in the world and is after cellulose and next to lignin, the most biosynthesized polymer. However, films or hydrogels made exclusively from biopolymers have reduced water vapor barrier properties and flexibility. In order to improve these properties, several methods have been used, such as the incorporation of ZnONPs in polymer matrices, than has been demonstrated their ability to improve the barrier properties, mechanical strength and stability of the packaging. Thus, in order to develop bioactive coatings capable of delaying fruit maturation, coatings with Chitosan (100% Q); Alginate (100% A) and three polymer blends in the proportions of 50% Q-50% A; 90% Q-10% A and 90% A-10% Q, added with nanoZnO (1% w/v) were made and applied to guavas (Psidium guajava L.). The fruits were in a green maturity stage and, after the coating application, were stored for 15 days at 21 ± 1 °C and relative humidity (RH) of 80 ± 2%. To determine the effect of the coatings on the ripening process, the fruits at regular intervals of 3 days were submitted to water loss, texture, color, rot index, pH, SST/ATT ratio). The results showed that the coatings avoid the appearance of rot, as a function of the antibacterial action of nanoZnO, and that coatings containing alginate (90%) did not delay the fruit maturation process. However, the coatings containing a higher proportion of chitosan in the matrix (100% and 90%) protected the fruits against excessive mass loss and the physico-chemical changes related to fruit maturation were also delayed. Thus, it is possible to extend guava shelf life with the chitosan coating (100%) or with chitosan and alginate blends (90% and 10%, respectively), added with nanoZnO.