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.

摘要
鉴于蛋类具备优异的功能特性，其被广泛用作食品工业原料。不同鸟类的蛋类均可应用于工业加工场景，为此本研究针对大美洲鸵蛋（greater rhea eggs）开展了稳态流变实验（steady-state rheological experiments）以获取流动曲线，同时开展动态流变实验以探究其流变特性（rheological properties）。本研究分析了蛋清（albumen）与蛋黄（yolk）的黏弹性行为（viscoelastic behavior）随凝固温度以及振荡剪切频率的变化规律。本研究选取15枚于10℃下储存、储存时长不超过28天的大美洲鸵蛋，分别在储存第1、7、14、21及28天进行检测分析。蛋清与蛋黄组分均表现出假塑性流变行为（pseudoplastic rheological behavior），初始流动剪切应力较低且受剪切时间影响；其中蛋清表现出触变性（thixotropy），而蛋黄则表现出震凝性（rheopexy）。在低剪切流变实验中，研究人员观测到蛋清发生热凝胶化（thermal gelation）：其弹性模量（elastic modulus）首次出现跃变的温度约为56℃，第二次跃变则始于78℃。对于蛋黄而言，其弹性模量于66℃时出现变化，且在更高温度下凝胶形成过程中会发生更多的结构演变。对于大美洲鸵蛋而言，蛋清的凝胶形成（gel structuring / gelation）温度（80℃）与蛋黄的凝胶形成温度（69℃）在整个储存周期内均未发生显著变化。相较于市售鸡蛋，大美洲鸵蛋具备更高的黏度与凝胶化温度，这一特性可用于辅助确定食品工业加工系统的规模——因为大美洲鸵蛋可在更高温度下进行处理，且不会发生蛋白质结构改变或阻碍加工进程。