Understanding the composition of foods will help us understand the changes that occur within foods when we process them. The contents of the egg is shown in PIC 5.1. Temperature is one of the primary causes of protein denaturation during cooking. As temperature increases, the energy of the protein molecules also increases and noncovalent interactions in the protein structure are weakened. At some temperature, the protein structure unfolds. The unfolded protein molecules interact (reassociate) with each other to form a new three-dimensional network. During the reassociation of protein molecules, water is entrapped within the network and a gel-like structure is formed (Figure 5.6). The temperature at which this process occurs is known as the protein denaturation temperature. Semisoft, semisolid precipitates are formed when denatured proteins are processed further. This process is called coagulation. Denaturation is the first stage of coagulation. Denaturation and coagulation of proteins are usually desirable in food processing. Differences between raw and cooked eggs are largely a result of protein coagulation that occurs during cooking. The egg white is liquid and translucent in its raw state. Upon cooking, albumen coagulation occurs; the texture gradually changes from liquid to solid. Simultaneously, the color turns white. If heating and denaturation continue, the interactions between proteins become very strong. The network collapses as water is removed from the network. The food becomes rubbery and dry as observed in the experiments when the egg white is overcooked.ALBUMEN (White) is the largest part of the egg. It makes up 2/3 of the egg mass. The total mass of egg white is 88% water and 12% protein. YOLK makes up 1/3 of the egg mass. The total mass of egg yolk is 48% water, 35% lipid, and 17% protein.
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