Structure-modifying alkaline and acidic pH-shifting processes promote film formation of soy proteins

• Published in: Food chemistry 2012-06, Vol.132 (4), p.1944-1950
• Main Authors: Jiang, Jiang, Xiong, Youling L., Newman, Melissa C., Rentfrow, Gregg K.
• Format: Article
• Language: English
• Subjects: Animal, plant, fungal and microbial proteins, edible seaweeds and food yeasts; Biological and medical sciences; Edible film; Food industries; Fundamental and applied biological sciences. Psychology; General aspects; Handling, storage, packaging, transport; Microstructure; pH-shifting; Soy protein
• ISSN: 0308-8146; 1873-7072
• DOI: 10.1016/j.foodchem.2011.12.030

► Films are prepared from pH-shifting-treated soy proteins. ► Soy protein isolate treated at pH 12 spontaneously forms a film. ► Disulphide bonds are the major force in pH-shifting-treated protein films. ► pH-shifting treatment improves the elasticity of soy protein films. The effect of pH-shifting, a process that induces the molten globule state in proteins, on the film-forming potential of soy protein isolate (SPI) at different temperatures was investigated. Partial unfolding at pH 1.5 or 12, followed by refolding at pH 7.0, was performed to alter the protein structure. Glycerin-plasticised films were prepared from pH-treated SPI at ambient temperature (20°C), or by heating at 50, 60, 70, or 80°C (30min). Tensile strength (TS), elongation at break (EAB), water vapour permeability (WVP), protein solubility (pH 3–7), and non-participating proteins of films were analysed, and the film microstructures were examined. The pH12-treated SPI spontaneously formed a transparent, slightly yellowish film at 20°C, which had the greatest EAB, while pH1.5-treated and native SPIs required preheating at 50 and 70°C, respectively, to form a film. Heating generally decreased solubility and WVP but increased TS. Films formed from both pH12- and pH1.5-treated SPIs were more elastic (up to 2-fold greater in EAB, P