A rheological characterization of heat-induced protein gels

Abstract

The purpose of this study was to develop and utilize models for assessing viscosity, elasticity and gel strength of heat-induced gels from bovine plasma protein and egg albumen and to characterize the rheological response of these proteins when subjected to heat treatments and adjustments in pH and salt concentration. The counter-flow back-extrusion method, and the developed equations, sensitively measured rheological differences occurring between 8% protein suspensions of heat-induced (80(DEGREES)C) gels of bovine plasma protein and egg albumen. Bovine plasma protein consistently produced significantly greater rheological responses than egg albumen. Interactions between NaCl concentration, pH and heating temperature on the rheological properties of 8 and 10% bovine plasma protein gels heated for 60 min were not significant. The main effects, temperature and pH, were consistently significant and seemed to have an additive effect on the rheological properties. Sodium chloride concentration was not a significant effect. pH changes during storage of egg albumen produced a marked effect on the heat-induced rheological properties of this protein system. Egg albumen stored as whole eggs increased in pH to a value of 9.0 in 5 days of storage at 15(DEGREES)C, whereas semipermeable membrane stored eggs never attained a pH of 9.0. Egg albumen stored as whole eggs reached a much higher elasticity level and gel strength than eggs stored in semipermeable membranes. Viscosity levels remained the same in egg albumen stored in the two methods. Thin albumen produced significantly greater viscosity than thick albumen at the 0 day of storage, but this effect was masked at the longer storage periods because of pH changes.