Barrier and tensile properties of whey protein–candelilla wax film/sheet

Barrier and tensile properties were compared for whey protein isolate- (WPI-) based solution-cast films, extruded sheets and extruded sheets subsequently thinned into films by compression. Solution-cast films were made from mixtures of WPI and glycerol (GLY) in water. Sheets were made by feeding WPI, GLY, and water to a twin-screw co-rotating extruder. In each case, candelilla wax (CAN) was added at 0, 5 or 7.5 g CAN/100 g dry mix to determine the effect on the barrier and tensile properties. Compressed extruded films were made by thinning extruded sheets using a Carver Press equipped with heated platens. Water vapor permeability (WVP), oxygen permeability (OP) and tensile properties were measured. Scanning electron microscopy (SEM) images were also taken. Addition of the CAN had a smaller effect on barrier than on tensile properties. Compressed extruded films had WVP similar to solution-cast films and much smaller compared to the extruded sheets. SEM showed pores in the extruded sheet were closed by the compression process. OP for compressed extruded films was much smaller than for solution-cast films. Compressed extruded films also had increased strength and flexibility compared to solution-cast films. The more practical extrusion and compression processes produce films with better overall properties.