Hydrolyzes the N-acetamido groups of N-acetyl-D-glucosamine polymers in chitin to form chitosan and acetate (PubMed:27901067). May play a role in evasion of the host immune response; plant chitinases liberate chitin molecules from the fungal cell wall which act as elicitors of the plant immune response, deacetylation of the liberated chitin neutralizes elicitor activity (PubMed:27901067). [(1->4)-N-acetyl-beta-D-glucosaminyl](n) + n H2O = n acetate + chitosan Inhibited by Fe(2+) and to a lesser extent by Mn(2+). Optimum pH is 8. Optimum temperature is 55 degrees Celsius. Belongs to the polysaccharide deacetylase family.