Caracterização reológica de soluções filmogênicas e sua aplicação na qualidade pós-colheita de uvas

Abstract

The grape production in Brazil is a profitable activity, but post-harvest treatment are still necessary since grapes show dehydration and infections caused by pathogens susceptibility. These problems can be avoided by treatment with compounds such as curcumin from the Curcuma longa, which has antimicrobial activity recognized, and calcium propionate (CaP), widely used in baking and that can also prevent grapes premature ripening with Ca+ 2 replacement. In this study the effect of an edible coating composed of enzymatically cross-linked gelatin added of CaP and curcumin nanoencapsulated in zein was characterized on the rheological and textural properties as well as its effect as an edible coating on Benitaka grape quality characteristics. Zein nanoparticles containing curcumin were synthesized by nanoprecipitation and presented encapsulation efficiency of 96.0 ± 1.5%, average ntensity diameter of 585 ± 45 nm (Dynamic Light Scattering) and spherical geometry Transmission Electron Microscopy). Nanoparticles were also characterized by Differential Scanning Calorimetry and Fourier Transform Infrared Spectroscopy FTIR) confirming curcumin encapsulation. The influence of these nanoparticles and CaP addition on rheological and textural properties of gelatin hydrogels was evaluated to characterize the filmogenic solution to be applied at grapes surface. The heological properties showed that gelatin hydrogel has low activation energy and pseudoplastic behavior, confirmed by mathematical models (Power Law, Herschel-Bulkley and Casson). It was also observed that formulations added of antifungal agents presented an increase on pseudoplastic behavior with temperature elevation confirmed by the power law modell adjustment. A rheopectic behavior was obtained as well as an increase in mixture viscosity when crosslinking time was increased. Hydrogels added of CaP had higher compressive strength when compared to those with nanoparticles indicating that the Ca+2 also contributed to protein network. Finally, control formulation (gelatin), the hydrogel containing CaP as well as the one containing nanoparticles (1%w/w related to gelatin) were applied to Benitaka grapes as an edible coating. The quality of the grapes parameters (soluble solids, color, acidity, weight loss and analysis of the texture profile, TPA) were evaluated over 15 days of storage at 25 ± 1 °C. It was not possible to prevent weight loss after 15 days of storage. The tretments also did not present effect on grapes soluble solids and itratable acidity. The color was not affected by the coating with the exception of the reatment containing nanoparticles as a result of the characteristic color of zein and curcumin (yellowish). An increase on grapes firmness was observed in TPA analysis of grape coated samples. A standard for chewiness was maintained for the coated samples compared with control samples (without edible coating).