Abstract: A series of edible films were obtained using native potato starch (PS) or modified potato starches, including hydroxypropyl distarch phosphate (HDP), acetate starch (AS) and oxidized starch (OS) by the casting method. The effects of freeze-thaw (F-T) treatment on the physical, mechanical and barrier properties, microstructure and thermal stability of the films were studied. X-ray diffraction (XRD) indicated that potato starch granules displayed a typical B-type crystalline structure, the crystallinity was damaged during the film-forming process, and the peak intensity was decreased obviously after F-T treatment. F-T treatment damaged the microstructure of starch-based films as observed by scanning electron microscopy (SEM), and there appeared obvious cracks on PS film, and honeycomb-like and lamellar structures on AS film, while OS and HDP films maintained a more complete morphology. In the thermogravimetric curves of starch-based films, four stages of mass loss appeared as temperature increased, corresponding to water loss, volatilization of glycerol, and depolymerization and decomposition of starch, respectively. Nevertheless, F-T treatment had little effects on the thermostability. At room temperature, PS film had the best mechanical property with tensile strength (TS) of 2.29 MPa and elongation at break (EB) of 68.82%. After three F-T cycles, film TS increased at least twice and EB generally declined, while solubility and WVP changed only a little. HDP film displayed much better F-T stability considering the microstructure, mechanical property, water vapor permeability and water solubility collectively, indicating its potential applications in frozen low-moisture foods.

Key words: starch-based edible film; freeze-thaw stability; modified starch; physical property; structural characterization