Physical characteristics of a composite film of soy protein isolate and propyleneglycol alginate

Different levels (5, 10, 15, 17.5 or 20% w/w of solid) of propyleneglycol alginate (PGA) were incorporated into soy protein isolate (SPI) films to form biodegradable composite films with modified physical properties. Color of the SPI films was affected (P<0.05) by the incorporation of PGA. Tensile strength increased (P<0.05) with addition of PGA up to 17.5%, while the percentage elongation at break decreased with incorporation of PGA of higher levels. Water vapor permeability and water solubility also decreased by adding PGA up to 10%, but further addition of PGA increased values for these properties. Results suggest that the site of reaction with PGA on the protein chain may become saturated with PGA at the 10% level.