there aren't many enzymes in food, mainly in fruits, the enzymes in friuts are very similar to ptylin found in the mouth that help break down sugar, they do not need to be ingested before they activate, a proof of this is the apple test, buy an apple, take a bite and leave it without covering it for a few minutes, you'll notice that the bitten part starts turning yellowish brown because the enzymes in the apple are already breaking it down.
In summary, they do not need to be ingested before activation, and the major characteristic of an enzyme is that they do not change after they react with (breakdown) food, so they are in the same form before and after they finish breaking down the food.
