CONICET | Buscador de Institutos y Recursos Humanos

The structure-function relationship of composite films obtained from soy protein isolate (SPI) and cod gelatin was studied. Films with different ratios of SPI:gelatin (0, 25, 50, 75, 100% w/w) plasticized by a mixture of glycerol and sorbitol, were prepared by casting. Regardless of the soy protein concentration used, the thickness and water vapor permeability of composite films diminished significantly relative to films obtained with gelatin alone. The formulation containing 25% SPI: 75% cod skin gelatin was found to increase the maximum force at the breaking point as compared to the 100% gelatin and the 100% SPI films by 1.8-fold and 2.8-fold, respectively. Moreover, this formulation offered high percent deformation values as the 100% gelatin film and a relatively low water vapor permeability as the 100% SPI film. While all the films exhibited a high water solubility, a slight reduction of the protein content of the soluble fraction was observed with increasing soy contents, reaching values even lower than those corresponding to 100% soy films (in agreement with the SDS-PAGE profiles). DSC analyses revealed that gelatin was completely denatured in all the films, while the soy proteins maintained most of their native conformation. The FTIR analysis of films revealed the existence of soy protein-gelatin interactions, with a specially marked increase of C=C and C=N double bonds and diminution of free OH and NH groups in the 25S-75G film. Regarding appearance, all the films were translucent, but the yellowish color (b*) increased with increasing proportions of soy proteins.