How to tenderize meat④

One way to tenderize meat is to boil it.
We often have the image that meat becomes tender when it is slowly simmered, but this does not apply to all meat.

As shown in the figure above, meat has a structure in which cells called muscle fibers are bundled with a membrane of collagen.
The muscle fibers are composed of long fibrous myofibrillar proteins and water-soluble globular sarcoplasmic proteins, and have a structure in which the sarcoplasmic proteins are packed between the myofibrillar proteins.

● Myofibrillar proteins are coagulated by heat at around 45-50℃.
●At around 56-62°C, sarcoplasmic proteins are coagulated by heat.
●At around 65℃, collagen shrinks to about 1/3 of its original length.
●Collagen is decomposed and gelatinized at around 75℃.

In other words, the three types of proteins that make up muscle have different temperatures at which heat denatures them.

(1) When the meat begins to heat up and the temperature rises, the myofibrillar protein first hardens due to the heat. At this time, the water-soluble sarcoplasmic proteins that fill the gaps between the myofibrillar proteins are not solidified, so they feel soft.
(2) Myofibrillar proteins harden by heat coagulation. Furthermore, the rapid shrinkage of collagen makes it even harder.
(3) When the temperature exceeds 75℃, collagen decomposes and gelatinization progresses rapidly, making the meat tender.
In other words, no matter how much you boil it, meat with little collagen will not become tender.

From here on it's subjective.

“Why do you simmer slowly over low heat instead of high heat?”
I tried to find out the reason for this, but I couldn't find a solid scientific reason.
The reason it is commonly said
(1)Because the pan will burn.
(2)Because the soup becomes cloudy (scum is mixed in the soup).
(3) If you put meat in a hot liquid, it will shrink rapidly and the meat will harden (not soften).