A more credible usage is that it can be used to preserve food, such as meat. Boil the soy sauce and let it cool. Soak the meat in it. There is no refrigerator to try. I think this is feasible, because soy sauce contains salt, but you may get some delicious and unique soy sauce bacon!
In fact, there is a recipe that many westerners may not know, but it is very common in China. For me, this is not a hidden use, but you may find it an eye-opener.
This is boiled eggs with tea. Easy to make.
The basic ingredients are loose tea (ordinary green tea), soy sauce, star anise, cinnamon, bay leaf, salt and eggs.
Put all solid ingredients except eggs into seasoning bags (small reusable bags with ropes). Put the bag in a pot of water. Add soy sauce and salt to the pot and bring to a boil.
At the same time, you can cook some eggs separately, and cook them and shell them. Let the water in the seasoning bag boil for about 5 minutes before turning off the heat.
Take the boiled eggs out of the water and cool them with water so that you can touch them. Gently roll the eggs onto the chopping block or baking tray, so that the eggshell will crack. But don't take the shell off.
Soak eggs with shells in soy sauce and tea soup. Leave it for at least one night, or put it in the refrigerator 1-2 days. You will eat some beautiful tea eggs with beautiful marbles on them. As far as I know, there is no ulterior motive or conspiracy theory in using soy sauce made in China.
The purpose of using soy sauce is to add what the Japanese call umami flavor when preparing food. Soy sauce comes from Maillard reaction during soybean fermentation. Enzymes in yeast/mold/bacterial starter were added to hydrolyze the complex molecules of starch and protein stored in soybean cotyledons into simple molecules of monosaccharides and disaccharides in starch and amino acids in protein in the presence of high salt solution.
Another purpose of soy sauce is to increase the salty taste of cooked food, rather than simply using salt.
I hope I can help you, friend.