Low concentrations of chitosan coating reduce water spot incidence and delay peel pigmentation of Clementine mandarin fruit

The effect on fruit ripening and on water spot incidence in Clemenules mandarin fruit of preharvest (86 days before harvesting) or postharvest application of a low concentration (12.5-125 mg 1(-1)) of chitosan was investigated. Chitosan delayed the natural and ethylene-induced peel pigmentation without affecting the internal maturation, and reduced the softness and the water absorption capacity of the fruit at maturity irrespective of the concentration applied. In association with these antisenescence effects, chitosan reduced the water spot incidence, and this effect increased with increasing concentration. Best results were achieved with 125 mg 1(-1) chitosan, which reduced water spot incidence by 65%. It is unlikely that chitosan produces a coating film on the fruit surface, which would modify its gas exchange with the atmosphere and its internal gas composition. At these concentrations chitosan is probably absorbed by the peel cells and acts inside them, having a dual effect, antisenescent and antifungal. (c) 2005 Society of Chemical Industry.