When used as packaging materials, composite edible films exhibit improved properties over those made from individual components alone. This study investigated whey protein isolate films containing 10 – 40 g xylan / 100 g whey protein isolate (WPI). Transglutaminase (TG) was used as a cross-linking agent in WPI-only and 40 g xylan / 100 g WPI films. Food packaging properties investigated were water vapor permeability (WVP), oxygen permeability (OP), tensile stress, and % elongation at break. Thermal properties were studied using differential scanning calorimetry and thermogravimetric analysis. Crystallinity and microstructure were assessed using X-ray diffraction (XRD) and scanning electron microscopy, respectively. Films containing 40 g xylan / 100 g WPI that were also treated with TG showed the greatest improvement over control films in properties important to food packaging. WVP decreased from 6.41 to 3.89 g mm/m^2 day kPa (p ≤ 0.05), OP decreased from 21.85 to 7.32 cc μm/m^2 day kPa (p ≤ 0.05), and tensile stress increased from 6.73 MPa to 15.96 MPa (p ≤ 0.05). The % elongation at break decreased significantly from 12.5% in WPI-only films to 5.8 – 1.4 % in all xylan and TG treated films (p ≤ 0.05). The temperature of melting increased from 121°C in control films to a maximum of 166°C in the 20 g xylan / 100 g WPI films, indicating increased intermolecular strength. Film microstructure showed organization of xylan within films. Crystallinity was identified with increasing xylan content through XRD analysis, indicating increased polymer packing.
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