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 language | English (US) |
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Pages (from-to) | 46-52 |
Number of pages | 7 |
Journal | Journal of Agricultural and Food Chemistry |
Volume | 43 |
Issue number | 1 |
State | Published - 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)