Extrusion processing and characterization of edible starch films with different amylose contents

Various edible starch films were prepared via extrusion, with a particular focus on the effects of the amylose content of starches from the same resource (corn) on film processibility and performances. Four corn starches with different amylose contents (4.3–77.4%) were used as model materials. The effects of various extrusion processing conditions, such as temperature, screw speed, feeding rate, and water content were systematically investigated. It was found that, while a higher amylose content increased the difficulty of extrusion processing, this could be overcome by increasing the processing temperature, moisture content, and equilibration time. On the other hand, mechanical testing, differential scanning calorimetry, dynamic mechanical analysis, and microscopy showed that films based on higher amylose starch had better mechanical and thermal properties. The reasons include not only the easy entanglement of long linear amylose chains, but also the retained granular structure in high-amylose films, which may act as self-reinforcement.