Rheological properties of heat-induced gels from egg albumen and. bovine plasma proteins were measured using a mechanical loading device. Each protein was tested at 8% protein concentration and heated for 0-120 min at 80°C in an agitating water bath. After heating, the viscosity index, apparent elasticity and initial penetration force of the gels were evaluated. Bovine plasma protein dispersions exhibited a substantially higher viscosity index, apparent elasticity and initial penetration force than egg albumen gels. Bovine plasma proteins produced a gel structure which was strong and elastic. By comparison, heat-induced gels of egg albumen proteins were fragile and somewhat brittle. ~
The heat-induced gel strength in suspensions of two types of plasma protein isolates and egg albumen were compared to investigate the use of bovine blood plasma in food systems as a replacement for egg albumen and other proteins. A viscosity index, based on a counter-flow back-extrusion model, was used to measure gel strength. The optimum pH for gel formation was 7.0 for phosphated and nonphosphated plasma protein suspensions and 9.0 for egg albumen. The protein gel strengths were compared at 8% protein concentrations and at their respective pH optima. The gel strength of heated bovine plasma protein suspensions was greater (P < .01) than that of egg albumen, indicating that blood plasma exhibited a binding ability superior to that of egg albumen. The addition of controlled low levels of sodium and calcium increased (P < .05) the binding ability of both plasma protein isolates, while egg albumen showed no changes (P > .05). Greater concentrations substantially decreased (P < .01) the gel strength in both types of heated plasma protein suspensions and egg albumen, revealing that all three protein types exhibited an ionic strength dependency.
TWO groups of eggs were stored at 15°C for 0, 5 and 10 days. One group was stored, with the shell removed, in sterile Whirl-Pak bags. A second group was stored as intact whole -eggs. Viscosity index, apparent elasticity, and initial penetration force were determined for heat-induced (8O"C, 80 min) gels of the thick, thin and mixed albumens from each group. The rheological parameters increased with storage time, with the greater increase exhibited by the gels of the albumens that were stored as shell eggs. Solution pH was a major factor controlling these rheological properties of heated egg albumen.
A protein isolate was prepared from edible beef plasma by complexing the proteins with sodium hexametaphosphate. The isolate contained 82% protein which was completely soluble within the pH range 5.0-8.0. Foam volumes of solutions of the phosphated protein was greater than those observed in egg albumen or in plasma proteins prepared by the ultrafiltration process. Electrophoretic resolution revealed small differences in the protein species in phosphated plasma isolates and that prepared by ultrafiltration. Ammo acid analyses revealed no major difference between the two plasma protein isolates; the major difference was a reduced tryptophan content in the phosphated protein.
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