At same boiling temperature of water potato gets softens but egg gets harder. Why?

Why does the same boiling water that softens the potato hardens the egg?

 

Potato and egg both are edible items. But each has different structure and stuff inside them. And when heat applied to them reacts differently by its structure and the nature of existence. 

Earlier to know the answer to the above question, we need to know two processes.

1. Starch Gelatinization

First we've to know that what is the starch? Starch or Amylum is an odourless, tasteless white substance occurring widely in plant tissue and obtained chiefly from cereals and potatoes. It is a polysaccharide which functions as a carbohydrate store and an important constituent of human diet. Usually we can see starch in the form of powder such as maize flour, corn flour, etc,.

Starch Gelatinization is a process of breaking down the intermolecular bonds of starch molecules, in the presence of water and heat.

There are three main processes will occur during heating the starch granules in the presence of water: Granule Swelling, crystallite or double helical melting and amylose leaching.

During heating, water is first absorbed in the amorphous space of starch, which leads to a swelling phenomenon.

 

Water then enters via amorphous regions into the tightly bound areas of double helical structures of amylopectin. At ambient temperatures these crystalline regions do not allow water to enter. Heat causes such regions to become diffuse, the amylose chains begin to dissolve, to separate into an amorphous form and the number and size of crystalline regions decreases. Under the microscope in polarized light starch loses its birefringence and its extinction cross. 

Penetration of water thus increases the randomness in the starch granule structure, and causes swelling; eventually amylose molecules leach into the surrounding water and the granule structure disintegrates.

The gelatinization temperature of starch depends upon plant type and the amount of water present, pH, types and concentration of salt, sugar, fat and protein in the recipe, as well as starch derivatisation technology are used.

Denaturation

The process that changes the physical and biological properties of proteins without affecting the chemical composition of a protein is called denaturation.

What are the changes will occur during boiling of potato and egg?

During the boiling of potato and egg, definitely changes will occur by the virtue of their structure and above processes.

Fig.1

Potato contains maximum of starch. So by the virtue of starch gelatinization, the starch granules will swell and absorb the water become very soft. And egg, egg has albumin protein in egg white. So by the virtue of denaturation of proteins, the protein albumin in the egg white undergoes denaturation and loss of solubility when the egg is cooked.

This is the reason why potato will become soft and egg gets hard when cooked.

I'm not comparing, but trying to reveal the fact behind this curious question.

References:

 Wikipedia

 YouTube