Structural and functional properties of soy protein isolate and cod gelatin films

DENAVI G.A; PEREZ-MATEOS M.; AÑÓN M.C.; MONTERO M.P.; MAURI A.N.; GOMEZ-GUILLÉN C.

FOOD HYDROCOLLOIDS

Elsevier Ltd.

Año: 2009 vol. 90 p. 341 - 349

0268-005X

The structure-function relationship of composite films obtained from soybean-protein isolate (SPI) and cod gelatin was studied. Films with different ratios of SPI:gelatin (0, 25, 50, 75, 100% [w/w]) and plasticized by a mixture of glycerol and sorbitol were prepared by casting. Regardless of the soybean-protein concentration, the thickness and water-vapor permeability of the composite films diminished significantly as compared to pure-gelatin films. The formulation containing 25% SPI: 75% cod-skin gelatin had the maximum force at the breaking point, which was 1.8-fold and 2.8-fold greater than those of 100% gelatin and 100% SPI films, respectively. Moreover, this formulation offered high percent-deformation values lower than those of gelatin but higher than all other films containing SPI-, and the same relatively low water-vapor permeability as the 100% SPI film. While all the films exhibited high water solubility, a slight reduction in film solubility and soluble protein was observed with increasing SPI concentration. Differential-scanning calorimetry analyses revealed that gelatin was completely denatured in all films, while soy proteins largely maintained their native conformation. Analysis by fourier-transform–infrared revealed that the presence of 25% SPI produced gelatin conformational changes, selfaggregation of gelatin chains, and intermolecular associations via C]O bonds between gelatin and SPI proteins. All films were translucent in appearance, but the yellowish color increased with increasing proportions of the soybean proteins.