Answer: The resistance is because MSG acts as a buffer, it accepts and donates H+ ions.
Explanation:
Monosodium glutamate (MSG) is a non-essential amino acid that acts as a water-soluble buffer, and it found in food such as meat as a sodium salt of glutamic acid.
A buffer is a solution that affects the concentration of hydrogen ions (also called hydrons) in water, because it can resist pH changes when other components are added, by increasing or decreasing the concentration of the hydrogen ions present. Remember, the pH is a measure of the acidity or alkalinity of a solution that indicates the amount of hydrogen ions present, and an acid is a substance that donate hydrogen ions in a solution, while a base is a substance that accepts hydrogen ions.
So, a buffer can neutralize small amounts of acid or base that is added, and maintain the pH relatively stable. The resistance of the MSG molecule to pH change, is because this molecule acts as a buffer and acepts the hydrogen ions when an acid is added. And it also acts as a buffer and donates hydrogen ions when a base is added. Thereby the hydrogens are not found free in the solution and are not able to change the pH.
For example, if HCl is added (a strong acid because it dissociates completely) on a solution which has MSG, there will be no big changes in the pH since the MSG acts as a buffer, accepting those hydrogen ions that the acid releases. So they will not be left in the solution and when you measure the pH, you will not detect them. However, if you add a large amount of acid, the molecule will no longer be able to accept all the hydrogens ions and you will begin to notice changes in the pH.