Wetting Behavior of Chitosan Solutions on Blueberry Epicarp With or Without Epicuticular Waxes

摘要

In this paper, the physical properties of fresh highbush blueberry epicarp were determined in order to increase the effectiveness of chitosan-based coatings. SFE of blueberry epicarp, with and without epicuticular wax, was a low-energy surface and presented an apolar character and a small polarity. Indeed, with wax γsv = 29.1 ±4.1 mJ/m~2, while after the wax removal, γsv was increased significantly to 38.3 ± 2.8 mJ/m~2. Various chitosan-based coating solutions were applied to the blueberry epicarp with or without epicuticular wax. The effects of glycerol [G] and Tween 20 [T] concentrations on the spreading coefficient S have been studied. For the glycerol/chitosan coating solutions, the results showed that the addition of glycerol to the chitosan solution diminished the wetting capacity of the blueberry by the solution, whereas at fixed glycerol concentration an increase of the chitosan concentration wet more the blueberry epicarp. For the Tween 20/chitosan coating solutions, S was only slightly dependent on the chitosan concentrations, whereas at fixed chitosan concentration, the addition of Tween 20 allowed enhancement of the adhesion of the coating solution. More specifically, the results showed that wax removal of the epicarp improved the wetting capacity and that Tween 20/chitosan coating solutions wet the blueberry epicarp more (with or without wax) than glycerol/chitosan solutions, since S ～30 and 80 mJ/m~2, respectively. Finally, solutions that better wet the blueberry with wax were [G] = 0.1 g/100 g [C] = 1.1 % and [T] = 20 % [C] = 1.4 % and without wax [G] = 20 % [C] = 1.8% and [T] = 20 % [C] = 1 %.