What does it mean when food does not react to iodine?

Answer 1

This is a classic Biology experiment known as the "Iodine Test".

Basically, by adding iodine (in the form of potassium iodide, KI) to something we can tell whether that something contains starch or not.

If it turns dark blue (it's a very striking and obvious change, actually) then starch is present.

So if there's no reaction, the food contains no starch. Coincidentally, it contains no Glycogen, either (as that would produce a brownish colour, albeit not the goal of the test).

When doing this test, it's important to mulch up the food so any starches hidden on the inside (like in vegetable cells) is well exposed to give a perfectly reliable result.