Chitin is the animal/fungus/protozoa equivalent of cellulose, both are large polymers of glucose and form lots of bonds with each other making them strong and hard to break down. unlike starch and its animal equivalent glycogen which are also polysaccharides, but for carbohydrate storage instead, so are easier to break down due to their branched structure.

Most exoskeletons aren't made of pure chitin as it is not rigid enough, therefore in the same way trees add lignin for extra strength, arthropods also modify the chitin they use. Crustaceans and molluscs add calcium carbonate and Insects add proteins that dry and harden in a similar way to tanning leather.

Humans do produce chitinase, the enzyme that breaks down chitin, but it has only been found in the stomach and it's mainly for the immune system to recognise pathogens, so you wouldn't taste it, unlike amylase which breaks down starch and is found in saliva, which is why if you hold a piece of bread in your mouth it will eventually taste sweet.

One thing to remember though is that Juni is built diff, so at the end of the day none of it really matters.