Whey protein isolate-based edible films as affected by protein concentration, glycerol ratio and pullulan addition in film formation

Edible films were prepared from whey protein isolate (WPI), and characterized in order to select a best combination of protein concentration and glycerol (Gly) ratio. 5%, 7% and 9% (w/v) WPI were used at three WPI:Gly ratios (3.6:1; 3:1; and 2:1). 5% WPI with a 3.6:1 WPI:Gly ratio showed the best combination with factors considered being thickness and water vapor permeability (WVP), while the 9% WPI with 3.6:1 WPI:Gly showed the best result as seen from the oxygen permeability (OP). Further studies were conducted by adding pullulan (PUL) at different WPI:PUL ratios (1:0; 1:1; 2:1; 3:1; 4:1; 5:1; 6:1; 8:1; 10:1) to a selected film in order to investigate the effect of pullulan on thickness, OP, WVP, moisture content (MC), film solubility (FS) and morphology using scanning electron microscopy (SEM). WPI–PUL film had a good appearance and 1:1 WPI:PUL resulted in films with greatest values of OP, WVP, MC, FS, and transmittance. The SEM micrographs showed many pinholes and a favorable structure for the low barrier ability. However, addition of PUL at low concentration was good enough to significantly modify these properties, hence improving the potential characteristics of WPI-based films for food applications.