Development and characterization of edible and/or degradable films from wheat proteins

A new procedure for making degradable films was developed which resulted in the issue of U.S. patent No. 5,472,511 (issued December 5, 1995). This procedure consisted of bringing the proteins into solution using wheat flour as raw material. A centrifugation step yielded a supernatant, containing the solubilized wheat proteins, called the film-forming solution (FFS). Several films were produced by casting the FFS on a flat inert surface. Depending on the FFS characteristics (e.g., pH and cross-linker), films with different properties were fabricated.; Analyses of the films were performed with different techniques involving mass transfer, rheological, chemical, and physical studies. Mass transfer was studied by oxygen permeability, showing low values, similar to those of nylons, and influenced mainly by temperature and type of flour used to make the films. Rheological methods included tensile stress and tensile creep: Tensile stress demonstrated the effect of a cross-linker on the mechanical properties and tensile creep showed the importance of the environmental conditions on long-term behavior. Chemical studies involved the analysis of the films by Fourier-Transformed Infrared Spectrometry (FTIR) and swelling behavior. FTIR showed important chemical groups or bonds present in the films. Swelling behavior was used to determine a solubility parameter for the protein films. Physical studies included the color analysis by the Commission Internationale de l'Eclairage Laboratory (CIE-Lab) technique. An increase in the yellow and red values upon cross-linking with glutaraldehyde was found while a reduction in the yellowness was observed when the films were cross-linked with cysteine or formaldehyde.