Composite and nanocomposite films based on amaranth biopolymers

•Composite and nanocomposite films were prepared from amaranth biopolymers.•The effect of amaranth starch granules and nanocrystals as reinforcement is studied.•Starch nanocrystals improved the mechanical and barrier properties of amaranth protein films.•Composite films formed by starch granules dispersed in the protein matrix were prepared.•Starch granules did not modify significantly the functionality of protein films.

The use of amaranth starch granules and nanocrystals as possible reinforcement of amaranth proteins films was analyzed. Starch granules and protein isolates were extracted of amaranth grain, and nanocrystals were prepared by acidic hydrolysis from starch. Films were prepared by casting aqueous dispersions containing amaranth protein isolate (API, 5% w/v), glycerol (1.25% w/v) and different concentrations of starch granules (0-30 wt% relative to API) and nanocrystals (0-12 wt% relative to API). All films were homogeneous, translucent and slightly brownish, with a general visual appearance similar to the control amaranth protein film. While it was possible to prepare films in which the starch granules retain their native structure after being processed, the presence of these particles did not improve the film properties. Only the addition of starch nanocrystals improved their tensile strength and water vapor permeability as well as their water susceptibility, probably due to their nanosize, uniform distribution and the strong interactions that developed with protein matrix.

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