Food & Cooking (Q&A)

Answer:

Eggs are composed of a chain of amino acids which are known as Proteins. Egg contain 67 per cent proteins (in egg white) and 33 per cent fats and proteins (in egg yolk). Egg white protein is mostly albumin (ovalbumin and Conalbumin) All proteins have primary,secondary and tertiary structures. Tertiary structure of egg white protein is due to hydrophobic interactions and hydrogen bonding. They also contain Cysteine amino acid, which has sulfhydryl group (SH). The amino-acid strings fold back on themselves (the way the strings fold determines the protein's chemical and biological properties). The proteins are held in place by weak bonds (non-covalent) between different parts of the amino-acid string.

When we heat an egg, the proteins gain energy and they literally shake apart the bonds between the parts of the amino-acid strings, causing the proteins to unfold. As the temperature increases, the proteins gain enough energy to form new, stronger bonds (covalent) with other protein molecules. During boiling the heat first breaks (unfolds) the proteins, and then allows the proteins to link to other proteins. As the proteins form these new, strong bonds, the water that surrounded each protein molecule when the egg was liquid is forced out. That's why the egg turns hard.

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