Chitosan coating surface and permeation properties as affected by plasticizer, surfactant and polymer concentration-application to vegetables

Abstract

Edible coatings can act as moisture, lipid, and gas barriers and can improve the textural properties of foods or serve as carriers of functional agents such as colors, flavors, antioxidants, nutrients and antimicrobials. The objectives of this work were to study the potentialities of chitosan (obtained from lobster of the cuban coasts) coating to extend the shelf life of fruits. To do so, the surface properties of tomato and carrot were characterized and the wettability properties of chitosan edible coatings were studied. In such coatings, parameters such as chitosan concentration and effects of type and concentration of hydrophilic plasticizer or surfactant on wettability of chitosan coatings were evaluated, as well as the respective barriers properties to gases. It was possible to determine the values of the polar and dispersive components of the superficial tension, that are 3.32 and 25.24 mN/m, respectively, for the tomato and 0.48 and 25.62 mN/m, respectively, for the carrot; being the superficial tensions of the tomato and carrot the sum of the two components (28.55 and 26.40 mN/m) respectively. Both are therefore, low energy surfaces. The results of wettability determinations allowed to adjust one factorial model that suggests an increase of the spreading coefficient as the chitosan concentration decreases and Tween concentration increases. The best values of wettability correspond to the following coating composition: 1.5 % (w/v) of chitosan and 0.1 % (w/w) of Tween 80. A correlation has been found between the water vapor, oxygen and carbon dioxide permeability coefficients, and glycerol concentration (while keeping Tween and chitosan concentrations constant). In the absence of glycerol, a decreased permeability to the gases was observed. An increase of the chitosan concentration decreases a lightness and increase yellow color of coatings. The chitosan coatings with glycerol showed high values lightness and were more transparent and yellowier than those without glycerol.