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

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Abstract

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 (30 min). 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 pH 12-treated SPI spontaneously formed a transparent, slightly yellowish film at 20°C, which had the greatest EAB, while pH 1.5-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 pH 12- and pH 1.5-treated SPIs were more elastic (up to 2-fold greater in EAB, P < 0.05) than the film formed from untreated SPI despite slightly reduced TS and WVP. Electrophoresis revealed disulphide bonds between A and B subunits of glycinin being a dominant force in pH 12- and pH 1.5-treated SPI films, while noncovalent forces were abundant in untreated SPI films. The pH 12-treated SPI film consisted of more interactive protein strands than other SPI films, which seemed to explain its superior elastic properties.

Original languageEnglish
Pages (from-to)1944-1950
Number of pages7
JournalFood Chemistry
Volume132
Issue number4
DOIs
StatePublished - Jun 15 2012

Bibliographical note

Funding Information:
Funding provided by the US Department of Agriculture, NRI/CSREES (Grant 20083550318790 ) and the US Department of Homeland Security, Science & Technology Directorate, through a technology development and deployment program managed by The National Institute for Hometown Security (Grant 200902160810 ).

Keywords

  • Edible film
  • Microstructure
  • Soy protein
  • pH-shifting

ASJC Scopus subject areas

  • Analytical Chemistry
  • Food Science

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