Influence of plasticizers and treatments on the properties of films from pea proteins

Films were prepared, by a casting technique, from an industrial pea protein isolate, formulated in an alkaline medium in the presence of a plasticizer. The aim of the present work was to improve the hydrophobic character and mechanical properties of the film, mainly the tensile strength. The influence of plasticizer type on these film properties (mechanical behaviour, hydrophobicity, water permeability), and on the protein structure was investigated. Using glycols as plasticizers, the increasing of the chain length failed to improve the characteristics of the films. The comparison of infrared spectra of protein (11S glycinin) in aqueous solution and in film state, showed that conformational changes which accompanied the formation of films were significant. The amide I band of the protein sample in film state reveals that, in addition to beta-turn and random coil structures, the protein presents a large amount of intermolecular beta-sheet, probably due to polypeptide chains interactions. Besides, the significance of physical and chemical treatments was studied, either on film-forming solutions or on the protein film itself. The use of hydroxyethylacrylate as plasticizer, coupled to an ultra violet treatment, was also investigated and was found to correlate well with increased tensile strength and hydrophobicity. Formaldehyde added in the film-forming solution did not alter significantly the film behaviour, whereas treatment by immersion of the protein films in an ethanol-formaldehyde mixture markedly increased both their tensile strength and hydrophobic character. (C) 1998 Elsevier Science B.V.