Films based on castor bean (Ricinus communis L.) proteins crosslinked with glutaraldehyde and glyoxal

Protein has been highlighted among the biopolymers used in the technology of biodegradable films, however much study remains to be done with less conventional protein sources, such as castor bean cake. The objective of this study was to evaluate the effect of the concentration of proteins extracted from castor bean cake and type of cross linker (GT: glutaraldehyde and GX: glyoxal) on the properties of the films produced with these proteins. Proteins were extracted from castor bean cake by solubilization in alkaline medium (pH 12 with NaOH) at 50 °C and freeze-dried, obtaining a material with 69% protein. The films were produced by dehydration of film-forming solutions (FFS) containing 2, 4, 6, 8, and 10 g protein/100 g FFS, 1 g GX or GT/100 g protein and 25 g glycerol/100 g protein. Films were characterized for thickness, humidity, solubility in water, microstructure, color, opacity, gloss, and mechanical properties by puncture and tensile tests. The protein concentration influenced positively the solubility and mechanical properties of the films, being that the film produced with 6 g protein/100 g FFS showed the best properties. With respect to the cross linking agent, the films produced with glyoxal presented improved mechanical properties and lower film solubility than those produced using glutaraldehyde. These results are consistent with the amino acid composition of proteins extracted from the castor bean cake.