Rheological characterization of rhea (Rhea americana) eggs subjected to different storage periods

Abstract

Eggs are used as food industry ingredients due to their functional properties. Eggs from different bird species are used in industrial processing; therefore, rheological experiments were carried out at steady state to obtain the flow curves and also at a dynamic state to study the rheological properties of greater rhea eggs. The viscoelastic behavior of the fluids as a function of the coagulation temperatures for albumen and yolk and of the oscillatory shear frequency was studied. Fifteen rhea eggs stored for up to 28 days at 10 °C were analyzed at 1, 7, 14, 21, and 28 days. The albumen and yolk fractions showed pseudoplastic rheological behavior with small initial flow shear and dependence on shear time, with albumen demonstrating thixotropy and the yolk showing rheopexy. In low shear rheological tests, thermal gelation of albumen was observed, presenting a first change in the elastic modulus around 56 °C, and a second from 78 °C. In the yolk, a change was observed from 66 °C, with more structural variations in the development of the gel at higher temperatures. For rhea eggs, the gel structuring (gelation) temperature of albumen (80 °C) and egg yolk (69 °C) did not undergo variations during the storage periods. Compared to commercial eggs, the higher viscosity and gelation temperatures presented by the rhea eggs can help determine the size of the industrial processing system as they can be submitted to higher temperatures without modifying protein structures and hindering the process. Keywords: birds; denaturation temperature; flow; functional properties; protein