Effect of pH and temperature on protein unfolding and thiol/disulfide interchange reactions during heat-induced gelation of whey proteins

Frank J. Monahan, J. Bruce German, John E. Kinsella

Research output: Contribution to journalArticlepeer-review

260 Scopus citations

Abstract

In heat-induced whey protein isolate (WPI) gels, polymerization of the constituent whey proteins, via intermolecular disulfide (S-S) bonding, was dependent on both the pH of the WPI solution and the temperature to which the solution was heated. At pH 9 and 11, polymerization as determined by SDS-PAGE occurred at room temperature (22°C), while at pH 3, 5, and 7, polymerization was only evident after heating to 85, 75, and 70°C, respectively. Measurement of total sulfhydryl (SH) group content of gelling WPI solutions at each pH and temperature revealed that in the WPI solutions at pH 9 and 11 significant SH-SH oxidation to S-S occurred even at room temperature. In contrast, the total SH content of WPI solutions at pH 3 and 5 did not change with heating, indicating that polymerization reactions involving SH/S-S interchange rather than SH/SH oxidation predominated. Estimation of the degree of unfolding of the whey proteins by measuring the exposure of hydrophobic amino acid residues showed that at pH 9 and 11 extensive irreversible unfolding of the protein molecules had occurred at room temperature.

Original languageEnglish (US)
Pages (from-to)46-52
Number of pages7
JournalJournal of Agricultural and Food Chemistry
Volume43
Issue number1
StatePublished - 1995

Keywords

  • Gelation
  • pH
  • Protein unfolding
  • Temperature
  • Thiol oxidation
  • Thiol/disulfide interchange
  • Whey protein isolate

ASJC Scopus subject areas

  • Agricultural and Biological Sciences (miscellaneous)
  • Food Science
  • Chemistry (miscellaneous)

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