Surface properties of Acacia senegal vs Acacia seyal films and impact on specific functionalities

Abstract

The microstructure and surface properties of spin coated films were studied to determine the structuration of Acacia gum films depending on gum type and composition. The difference between A. seyal and A. senegal films was clearly evidenced by surface morphology (SEM and AFM) and through the contact angle measurement: A. senegal films having a smoother and more hydrophobic surface (θ = 62°) than A. seyal films (θ = 42°) characterized by aggregated structuration. The film hydrophobicity increased with glycerol addition for both gum films (A. senegal, θ = 68° and A. seyal,θ = 50°). This could be due to hydrogen-bonding between hydroxyl groups of plasticizer and polar groups of Acacia gums favoring their reduction on films surface. Both gum films behave as dual polar surface showing high disperse component of free energy compared to the polar component. Both gums showed strong affinity for apolar compounds (θ < 20°). The overall results indicated that the structuration of films depended on the protein content and accessibility. Similar surface properties were found with self-supported films: A. seyal cast films being still more hydrophilic than A. senegal ones, demonstrating that the former provides a more favorable environment for water interaction than the latter. The specific interactions pointed for each gum films with water and apolar compounds were reflected in functionality such as water vapor permeability and efficiency to retain limonene and linalool. The knowledge of these properties is recommended to design specific coatings anticipating water loss of the coated product and to evaluate antimicrobial efficiency when active agents as aroma compounds are incorporated in the film.