Eggs!
Wonderful things. Scrambled, boiled, fried, curried….
Also, very useful to demonstrate the difference in the Arrhenius Parameters with different proteins. Eggs contain at least two sets of proteins – the yoke (also including some fat, vitamins, lecithin and minerals) and albumen (about 40 different proteins in the white).
When we cook eggs we are applying heat for a certain length of time. This application of thermal energy causes the proteins to break down. How, and when, they break down is determined by their inherent Arrhenius Parameters….
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So I decided to try a wee experiment to see if this was the case. I chose four eggs and put them into a pan of boiling water. |
| After one minute I chose an egg, at random, and cut it open. As you can see, the white is beginning to coagulate (or denature). The proteins have sustained some thermal damage, but not much.
The yoke still appears to be liquid. |
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After another minute I chose another egg and cut it open. More of the white has been coagulated. This is simply because those proteins have been exposed to a longer period of heating (at the same temperature). |
| Finally, I sent in the military!!
A brave soldier valiantly jumped into the yoke to test if it was still runny (or, in a liquid phase as we physicists say!) Clearly, the yoke has not coagulated nearly as much as the surrounding white, which is relatively solid.
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So, what is going on here?
Well, the different proteins have intrinsic parameters which determines how they react to heat energy. Using the Arrhenius Equation, we can see that these parameters are E and A. Both of these determine when and how quickly the proteins break down.
k = A exp (-E / RT)
The Arrhenius Equation where A and E are the important parameters discussed
here. ‘A‘ determines the rate at which denaturation occurs while ‘E‘ determines
when the process begins.
In eggs, it is clear that the ‘white’ starts the coagulation (denaturation) process before the yoke proteins. Hence it changes from a transparent liquid into a white solid, due to the heating effect.
This is exactly what happens in skin too. Different parts of blood vessels and hair follicles denature at different times and rates leading to a variation in coagulated tissue. The trick is to coagulate the tissue which will prevent further growth (hair) or destroy the vessel (blood). In these cases the various constituents of hair and blood have their own intrinsic Arrhenius Parameters.
This can be achieved successfully with the proper application of light and heat in the skin, using lasers and IPL systems.
Mike.
Mike Murphy's Blog 