Protein extracted from castor bean (Ricinus communis L.) cake in high pH results in films with improved physical properties

• Extraction of proteins from castor bean cake had no deleterious effect on amino acid composition.
• Extracted proteins at different pH produced films with different mechanical properties.
• Films produced with proteins extracted in pH = 12 showed better mechanical properties, without prejudice on others physical properties.

Castor bean plant (Ricinus communis L.) is a very important crop worldwide because it can be produced under severe climate conditions. Also, it gained importance last year because of the increasing industrial demand of biodiesel. The objective of this study was to study the effect of the pH (10, 11 and 12) of extraction of proteins from castor bean cake on some physical properties of films based on these proteins modified by tannin. Increasing pH improved the protein extraction yield without affecting their amino acid profile. The films prepared using these proteins by casting process showed a structural matrix sufficiently cohesive, intense total color difference (ΔE* = 83–85) and relatively high opacity (8–15%). The values of tensile strength, elongation at break, Young Modulus, water vapor permeability and hydrophobicity of films were affected by the protein extraction pH. The protein extraction in pH = 12 resulted in more rigid, more resistant, with enhanced extensibility, a lower rate of water diffusion and less hydrophilic films. The films showed homogeneous surfaces and dense internal microstructure. FT-IR spectra of all films showed characteristic bands and peaks typical of proteins with no differences in positions and intensity due to pH variations. It is possible to produce films from proteins extracted from castor bean cake by casting process. These films may be used in agriculture, specifically for planting seedlings.

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