Functional and cake-baking properties of egg white, bovine blood plasma and their protein fractions
Heat denaturation, foaming, emulsification, and cake-baking properties of egg white, blood plasma, and their protein components were characterized and compared. Prior to evaluating the baking properties of small quantities of all these proteins, a micro method for cake-baking was developed using a high-ratio white layer cake formulation. All blood plasma proteins denatured at lower temperatures than ovalbumin and globulins of egg white. Denaturation temperature of ovalbumin, the major protein of egg white, was about 9°C higher than that of albumin which is the predominant protein in blood plasma. Fibrinogen was the most heat sensitive, and [gamma]-globulins were the most heat stable proteins in blood plasma with denaturation temperatures of 57 and 83.5°C, respectively. Plasma had similar foam capacity as egg white, but the foam stability of plasma was significantly less than that of egg white. Contrary to whole blood plasma, some of its constituent proteins, such as albumin, Cohn fraction IV-1 (predominantly [alpha]-globulins), and fibrinogen, exhibited good foaming capacities and stabilities. Globulins were the only protein fractions in egg white that had good foaming properties. Blood plasma and its component proteins were better emulsifiers than egg white and its component proteins;Cake volumes and denaturation temperatures of proteins were significantly correlated (r = 0.944, P = 0.001). Proteins that had higher denaturation temperatures produced cakes with larger volumes. Among egg white proteins, globulins produced cakes with the highest volume, the finest texture, and the most crowned profile. Cakes prepared with fibrinogen and albumin had smaller volumes than those prepared with blood plasma, whereas, cakes prepared with [gamma]-globulins had larger volumes and finer textures than those made with blood plasma.