29C-25 |
Effect of heating rate on gelation of whey protein |
J. LI1, M. Ould Eleya2, and S. Gunasekaran1. (1) Dept. of Biological Systems Engineering, Univ. of Wisconsin, Madison, 460 Henry Mall, 115 Agricultural Engineering Bldg., Madison, WI 53706-1561, (2) School of Business, Univ. of Wisconsin, Madison, 975 University Ave., 2250 Grainger Hall of Business Administration, Madison, WI 53706-1324 Whey proteins are widely used as functional ingredients due to their ability to form heat-induced gels. Factors that are known to influence gelation of whey protein include protein concentration, pH, ionic strength, presence of other substances, and heating conditions (e.g., temperature, heating rate). Unlike pH, temperature and ionic strength, the influence of heating rate on the gelation of whey protein is less understood. Our objective was to investigate the effect of heating rate on rheological properties of whey protein isolate (WPI) gel. WPI was dissolved in a 0.1M phosphate buffer (pH 7) to prepare 15% WPI solution. The WPI solution was heated from 25 °C to 90 °C at different constant heating rates (0.1, 1, 5, 10, and 20 °C/min) using a dynamic rheometer. WPI gel was then cooled at a constant rate of -5 °C/min to 25 °C and held for 60 min. Frequency sweep experiments in the range of 0.01 Hz to100 Hz and stress sweep tests in the range of 1 Pa to 100000 Pa were conducted. Similar experiments were performed using a mixture of 15% WPI + 1% xanthan gum. The results show that the gelation temperature (Tgel) of WPI increased from 56 °C at the heating rate of 0.1 °C/min to 87 °C at the heating rate of 20 °C /min. A similar trend of increasing Tgel with heating rate was observed for the gelation of WPI-xanthan mixture. At a given heating rate the Tgel of the WPI-xanthan mixture was lower than that of the WPI. Frequency spectra of WPI gels indicated that G’ increased inversely with the heating rate. Stress sweep test results showed that the linear viscoelastic region (critical stress) varied with the heating rate. These results suggest that protein aggregation occurs slowly relative to the heating rate when the heating rate is too fast. This may allow a way of modifying gel structure and texture.
Session 29C, Food Engineering: Rheology and texture
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