Effect of gelatin bloom values on the physicochemical properties of starch/gelatin–beeswax composite films fabricated by extrusion blowing

The effects of various Bloom values (120, 160, 200, 230, and 250) of gelatins on the properties of starch/gelatin–beeswax (S/G-BW) films fabricated by extrusion blowing were investigated. The S/230G-BW blend exhibited the highest storage modulus and complex viscosity determined by rheological analysis. The results of dynamic mechanical analysis and scanning electron microscopy images demonstrated that starch granules could be more effectively melted and fractured in the composite films with higher Bloom values. Attenuated total reflectance–Fourier transform infrared and X-ray diffraction spectra revealed that gelatin Bloom values strongly affected the migration and crystalline properties of beeswax in the film matrix, while the S/230G-BW film had more triple helical structures, as shown by the results of circular dichroism analysis. In addition, lower water solubility and higher thermal stability of the produced films was obtained from the gelatins with higher Bloom values. The highest water contact angle (87°) of the outer film surface and lowest water vapor permeability (0.88 × 10−10 g m−1·s−1·Pa−1) were obtained for the S/200G-BW sample. The S/230G-BW film had the maximum values of tensile strength, elongation at break, and Young's modulus that exceeded those of the S/120G-BW film by 90.9%, 96.8%, and 102.4%, respectively. Finally, the extremely high Bloom values enhanced the interfacial interactions between the starch and gelatin components in the films, which negatively affected their performance. Hence, the gelatins with an appropriate Bloom values could be used to produce S/G-BW films with desirable physicochemical properties.