Why salt is added when boiling spinach

Cookbooks often say that when boiling greens, add a pinch of salt to prevent spinach from losing color.

Scientifically, the green color of greens when boiled in saline can suppress discoloration with a salt concentration of 2% or more.
* If the concentration is lower than this, there is no change that can be recognized in appearance.

In addition, when boiled at a salt concentration of 2% or less, it can be expected to have the effect of suppressing the outflow of water-soluble components such as vitamin C rather than retaining the green color. (When boiled for 3 minutes, the outflow of 10~15% vitamin C can be suppressed)
However, the outflow of minerals such as magnesium and calcium is accelerated.


On the other hand, there is also a technique of adding a pinch of baking soda to boiled soup (0.3%) to make the color beautiful.
This is a technique to make the boiled juice alkaline (pH 8.6) to preserve the color, remove the scum and soften it.
However, it is necessary to use it properly because water-soluble vitamins are greatly destroyed and baking soda has a unique taste.