Ficain
Ficain is an enzyme that is derived from figs latex. It is of a family of proteases known as the cysteine endopeptidases, a group that also includes papain derived from papaya latex, bromelase extracted from pineapple stem, calpain, caspases, cathepsin B, and chymopapain. It is one of the most commonly used for differentiating many blood group antigens: For example, it destroys M, N, S, Duffy a, and Duffy b, and enhances some other antigens including antigens from the Rh, Kidd, Lewis, I, and P1 systems.
It is a common occurrence when eating the skins or the white pulp directly inside the skin of a fig to get a burning or itching sensation. This is due to the ficin in the latex of the fruit, particularly if it is unripened.
