Characterization of chitosan–whey protein films at acid pH

The capability to produce blend chitosan–whey protein films at acidic pH, carrying a high amount of protein, is demonstrated, even though under these conditions a pure whey protein film could not be obtained. The films are biphasic and characterized by a compositional gradient, with the downward film surface containing a lower amount of protein than the upward surface. The surface richer in protein was more hydrophobic than that richer in chitosan. The difference in composition and hydrophilicity between both surfaces increases with the amount of protein incorporated in the film. Increasing the protein amount decreased elongation at break and tensile strength but, in general, had little effect on water vapor permeability. Although some of the film functionality might be compromised due to the incompatibility between the polysaccharide and protein components within the film matrix, the blended films, especially those with intermediated protein amount, may have useful applications on those food systems where the edible films should break up during the cooking or mastication process.