The behavior of hydrocolloid coatings on vegetative materials
Coating vegetative materials by gelling agents is a process characterized by four different time scales. After wetting and penetration of the vegetative skin by the gum solution, adhesion of the viscous solution to the outer layer (skin) of the coated material is possible. The gelled film (coating) collapses during further drying and adheres to the vegetative tissue. Critical surface tensions of the solid object to be coated, its apparent and real roughness, wettability of the surfaces by the gum solution, the composition and polarity of the films designed to coat the solid, and the surface tension of gum coating solutions are among the critical properties that need to be explored and changed for a successful coating process. The critical surface tensions of garlic peel and gellan and alginate films (coatings) were evaluated by Zisman plots. Garlic skin has a low surface tension compared with those of synthetic films such as polystyrene and polyethylene. A spreading technique was used to determine the surface tension of the dry film and the solid garlic skin. Surface tension was divided into dispersive and polar components. The similarity between the coating solution and the object to be coated in values of dispersive and polar components influences the spreadability of the coating gum solutions. Better compatibility between the coated object and the coating films can be achieved by incorporating surface-active agents within the coating gum solution. From the compatibility requirements detailed above, it can be concluded that tailor-made hydrocolloid coatings for different vegetative materials can only be achieved by further exploring the chemical and physical properties of the coating solutions and the coated objects.
Institute of Biochemistry, Food Science and Nutrition, The Hebrew University of Jerusalem, Faculty of Agricultural, Food and Environmental Quality Sciences, P.O. Box 12, Rehovot 76100, Israel.
V
Hershko
A
Nussinovitch