One method of tenderizing meat is adding salt (*brining). This is a method of tenderizing meat by increasing its water holding capacity. *Blining is a method of tenderizing meat by soaking it in salt water (actually, it often contains sugar in addition to salt). In the meat industry, it is sometimes added by injection. 
In general, the pH of meat provided for human consumption is around 5.5, so the use of salt as a pretreatment for meat cooking is said to soften the cooked meat by improving water retention and solubilizing myofibrillar proteins. .
Meat that is suitable for brining 1) lacks flavor, 2) has almost no fat, and 3) tends to become dry when heated. For example, chicken breast or lean pork.
【reason】
① Flavorful meat loses flavor in salt water
② If there is a lot of fat, there is little protein, so the water retention capacity does not increase much
③ Meat with plenty of moisture is difficult to penetrate
From here on it's subjective.
When I checked the appropriate concentration of salt water for brine, it was quite different from 5 to 30%. There is no general answer to this question, as the type, size, temperature, soaking time, etc. of meat are not standardized. However, if you do it at home, poke holes in the meat with a fork, add 5g each of sugar and salt to 100g of water, and marinate for 1 hour.