INFLUENCE OF AMYLOSE CONTENT ON STARCH FILMS AND FOAMS

After extraction of smooth pea starch and waxy maize starch from pure amylose and amylopectin fractions, films with various amylose contents were prepared by casting in the presence of water or water with glyce rol. For unplasticized films, a continuous increase in tensile strengt h (40-70 MPa) and elongation (4-6%) was observed as amylose increased from 0 to 100%. Discrepancies with values obtained for native starches with variable amylose content and different botanical origins were at tributable to variations in the molecular weights of components. Takin g cell wall properties into account, the values obtained in the labora tory were used to improve the relation between the flexural behavior o f extruded foams and the model of cellular solids with open cavities. The properties of plasticized films were not improved by the presence of glycerol and remained constant when amylose content was higher than 40%. Results are interpreted on the basis of topological differences between amylose and amylopectin.