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E4 - How long does tissue take to be damaged by heat?
I often read about human tissue ‘denaturing’ or ‘coagulating’ at some temperature – usually 60 or 70°C. However, these claims are inaccurate. They rarely state the time over which the denaturation process occurs.
Denaturation is when the proteins in cells or tissues ‘unravel’. For example, collagen is made up of three amino acid chains, intertwined and linked by hydrogen bonds, to form a strong molecule. When sufficient heat energy is applied for a sufficient time, the hydrogen bonds break down which causes the amino acid chains to ‘slip’. With enough energy and time, these acid chains will disassociate completely, leaving the collagen molecules non-viable.
Once the tissue denatures past a certain point, it cannot recover – it is dead! Before this point, there is a possibility the acid chains may reform correctly (this is a function of the heat shock proteins, whose job is to fix heat-damaged tissue, when possible). As more heat is applied, the chances of passing this point of no return, increases. If a certain heat is applied for a long enough time, the same will occur.
So, the probability of any tissue denaturing to a point where it becomes non-viable depends on the combination of temperature and time.
This can be calculated, in a first approximation, using the Arrhenius Damage Integral. Svante Arrhenius (1859-1927) was a Swedish physicist/chemist who won the Nobel Prize for Chemistry in 1903. He is credited with first working out how species of chemicals react at various temperatures, and their corresponding time-dependence.
Using his famous equation, we can calculate when a tissue will reach 100% denaturation for any given combination of temperature and time. The table below shows some of these calculations.
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