Characterization of soybean protein concentrate-stearic acid/palmitic acid blend edible films

Abstract

The effect of incorporating commercial stearic acid/palmitic acid blend (SA/PA, 63/37 wt %) into hydrophilic soybean protein concentrate (SPC) film-forming solutions at neutral and alkaline pH on some selected properties of edible cast films was investigated. SA/PA-added SPC film exhibited a significant increase in translucency, being more relevant for films obtained at pH 7. This was associated with the more heterogeneous morphology of such films as observed by scanning electron microscopy. Calorimetric measurements and X-ray diffraction studies confirmed the presence of crystalline fatty acids in films at pH 7 and new crystalline structures at pH 10 due to interactions or reactions between SPC and SA/PA blend. Fourier Transform infrared spectroscopy results confirmed the incorporation of fatty acids into SPC and revealed the occurrence of interactions between both components, depending on the film-forming emulsion pH. Moisture absorption isotherms at high relative humidity (RH) were determined and experimental data were adequately fitted by Peleg's empirical equation. Control SPC films produced at pH 7 were distinctly more moisture resistant than those at pH 10 owing to the more charged protein molecules at alkaline pH. The increased moisture resistance of SA/PA-added-SPC film at pH 10 was related to the more homogeneous dispersion of fatty acid particles within the protein matrix.