Plant materials
Mature yellow fruits of longan (D. longan Lour.) cv Shixia were harvested from a commercial orchard in Guangzhou. Fruits were selected for uniformity, shape, colour, and size, and any blemished or diseased fruits were discarded. The fruits were randomly distributed into groups of 18 fruit. For each treatment, three replicates were used. To prepare 500 ml of 0.5, 1.0 or 2.0% chitosan solution, 2.5, 5.0 or 10.0 g of chitosan (Crab20 shell chitosan, Sigma Chemicals) were dispersed in 400 ml of distilled water to which 25 ml of glacial acetic acid was added to dissolve the chitosan. The pH of the solution was adjusted to pH 5.0 with 1 mol/l NaOH and the solution made up to 500 ml. Fruit were allowed to dry for 4 h at 25°C after dipping. Fruits dipped in the acid solution without chitosan, pH 5.0, were used as control. They were placed in punnets (18 fruit/punnet) and stored at 2±1°C and 90% relative humidity for progressive assessments.