The fungal cell wall of Flammulina velutipes contains a large number of fungi called. Chitin? Flammulina velutipes is difficult to be digested by gastric juice because its fungal cell wall contains a lot of chitin, which is a kind of polysaccharide, but its texture is equivalent to shrimp shell and crab shell. There is no enzyme in our stomach to digest this substance, and even if the acidity of gastric acid is very strong, we can't digest chitin, and Flammulina velutipes contains a lot of this substance, which makes Flammulina velutipes unable to be completely digested.