Effect of Oxidized Potato Starch on the Physicochemical Properties of Soy Protein Isolate-Based Edible Films

The influence of oxidized starch on the physicochemical properties of cast soy protein isolate films is determined in this study. Films were cast from heated (70 degrees C for 20 min) alkaline (pH=10) aqueous solutions of 7 % soy protein isolate containing 50 % (by mass) glycerol as a plasticizer and different levels of added oxidized starch (0, 5, 10, 15, and 20 To, by mass). For all types of films, opacity, contact angle, tensile strength, elongation at break, water vapour permeability, measured at 25 degrees C for four relative humidity differentials (30-53, 30-75, 30-84 and 30-100 %), differential scanning calorimetry and microstructure were determined after conditioning film specimens at 25 degrees C and 30 % relative humidity for 48 h. Oxidized starch content significantly affected (p<0.05) tensile strength, from 0.95 to 1.51 MPa, temperature at maximum degradation rate from 64.8 to 74.2 degrees C and water vapour permeability from 1.08.10(-10) to 3.89.10(-10) g/(m.Pa.s) at relative humidity differentials of 30-50 and 30-100 respectively. Various internal arrangements were observed as a function of film composition (percentage of oxidized starch).