What is the numb sensation in the mouth caused by some fruits called?

Solution 1:

Astringency or Puckering

From Wikipedia

Some foods, such as unripe fruits, contain tannins or calcium oxalate that cause an astringent or puckering sensation of the mucous membrane of the mouth. Examples include tea, red wine, rhubarb, and unripe persimmons and bananas.

Less exact terms for the astringent sensation are "dry", "rough", "harsh" (especially for wine), "tart" (normally referring to sourness), "rubbery", "hard" or "styptic"

From Education.com (emphasis mine):

Unripe persimmons are inedible because of the tannins that are diffused throughout the fruit. This tannins cause proteins in the saliva and tongue to coagulate. This coagulation of proteins produces the puckery, furry taste in the mouth that we refer to as astringency. This also happens with unripe bananas, some red wine and tea.

Solution 2:

Desensitization generic term

The effect of certain chemicals such as capsaicin (active component of chili peppers; capsicum) on possible suppression of the sense of taste has been studied and it has been found that oral capsaicin reduces certain but not all taste sensations. There doesn't seem to be a specific name to such desensitization of the taste buds.

Certain foods (e.g. fats/ proteins) may leave a waxy residue on the tongue, also causing a suppression of the taste buds.