Wettability of chitosan coating solution on 'Fuji' apple skin

Wettability of chitosan coating solutions on 'Fuji' apple skin in different surfactant concentration (Tween 80: 0, 10, 100, 1000 ppm) was investigated using the Du Nouy ring method and the sessile-drop method. The surface property of 'Fuji' apple skin as a coated solid surface was characterized by the Zisman plot. The critical surface tension of 'Fuji' apple skin was 18.7 dyne/cm. The surface tension of the chitosan coating solution was too high (61.5 dyne/cm) to wet the apple skin. Tween 80 as surfactant in water-borne coatings reduced the surface tension of the coating solution and enhanced its wettability. Surface morphology of the coated film was observed by scanning electron microscope. Surfactant driven autophilicity improved the adhesive force between coating solution and associative apple skin, and decreased the contact angle of coating solution.