Edible films made from gelatin, soluble starch and polyols, Part 3

The thermal and mechanical properties of edible films based on blends of gelatin with soluble starch plasticized with water, glycerol or sugars were investigated. Two different methods, known as ‘the high temperature’ and ‘the low temperature’ methods, consisting of casting aqueous solutions of blends at 60 and 20 °C, respectively, were employed for the preparation of films. With increasing water, glycerol or sorbitol content, a drop of elasticity modulus and tensile strength (up to 50% of the original values for 30% plasticizer) was observed. The tensile strength and percentage elongation increased with high gelatin contents (> 20% ww). The development of a higher percentage renaturation of gelatin (reaching 70% for 5% water content) by the ‘low temperature’ method caused a reduction in gas and water permeabilities. The former decreased by one or two orders of magnitude for O2 and CO2, respectively. The semi-empirical model for calculation of gas permeability and the semi empirical equations for upper and lower limits of tensile moduli of composites were applied with limited success and the obtained values were compared to those experimentally determined.