Interconverts D-mannitol and D-fructose. Not active with fructose 6-phosphate or NADH. D-mannitol + NADP(+) = D-fructose + H(+) + NADPH Exists as monomer, dimer and tetramer. Causes an allergic reaction in human. Binds to IgE in 57% of 21 C.herbarum-allergic patients tested. Belongs to the short-chain dehydrogenases/reductases (SDR) family.