| Longan(Dimocarpus Longan Lour.) is a famous fruit species and is planted mainly in south China. Since Longan fruit mature in the hot and humid condition from August to September in China, the fruit deteriorate rapidly due to its vehemence respiration. Pericarp will brown completely after storaged 3~4 days at room temperature. The short postharvest period limits its storage, transportation and marketing. It affects its marketability and price at the same time. Therefore, postharvest research has become a key problem in the development of Longan production. In order to get the mechanism of the konjac coating in Longan storage and the viable method of Longan storage at room temperature, the changes of healthy fruit rate, pericarp browing index, respiration, the MDA contents, flavonoid contents, chlorophyll contents, anthocyanin contents total phenolics contents, and the PPO activity, POD activity, SOD activity et al, were studied in this paper. The results are showed as follows:(1) Through observing the Longan pericarp surface ultrastructure and transverse section ultrastructure by scanning electron microscope, a white-continual transparent coating was formed on the longan exocarp. It overlaied exocarp surface lenticels and permeates mesocarp partly, which reduced the area of cell interstics significantly. Therefore, compared with the control, coating could significantly reduce water loss rate, membrane permeability, the loss of total phenolics contents and inhibit respiration, the PPO activity by partitioning O2. So the coating could inhibit Longan pericarp browing to some extent. On the contrary, with a high concentration, Longan fruit deteriorated quickly. After analysised from experiment, a conclusion could be obtained that 2.0g/L Konjac coating could reduce the physiologic activity, avoid aerobatil and could prolong the Longan storage.(2) Three dominant strain fungis were seperated from "Fuyan" Longan fruit which was deteriorated at room temperature. Through authenticating, three fungi were Mucro,Gibberella SP. and Penicillium respectively. Using coating fixing antiseptic agent could inhibit the Mucro, Gibberella SP growth, so it could avoid Longan being infected by fungi at room temperature. Compared with 2.0g/L Konjac mannan coating, composite coating could form a layer white-continual tighter transparent coating. It overlaied exocarp lenticels significantly and' penetrated mesocarp. Therefore, composite coating could reduce Longan fruit's water loss more effectively and had a longer storage than 2.0g/L Konjac mannan coating.(3) Through the orthogonal experiment, the best coating formation was got, which was 2.0g/L Konjac mannan, 4.0g/L Chitosan, 1.5 g/L sucrose ester. By repetitious experiments, composite coating could reduce water loss rate the index pericarp browing the MDA contents, and inhibit PPO activity significantly. The healthy fruit was 82% for 7 days at room temperature.(4) Composite coating added thiourea, could significantly reduce the pericarp browing index, inhibit the PPO, POD activity, decelerate the descent of SOD activity, reserve more total phenolics contents, flavonoid contents and improve Longan heathy rate.Under the condition of 29~33 , the healthy rate was 94% for 9 days.Compared with composite coating with thiourea, Composite coating with enzyme inhibitor could significantly postpone the increase of cell membrane permeability and MDA contents. Composite coating could also reserve the most of the nutrition effectively. Compared with control, the healthy rates were improved significantly by composite coating adding enzyme inhibition Under the condition of 29~33, the healthy rates was 85% for 8 days.Compared with control, composite coating adding thiourea, composite coating with inhibiting enzyme could significantly reserve more water contents, chlorphyll contents, flavonoid contents, lower carotenoid pigment contents,and had a lower pH of pericarp. Therefore, Longan could retain the original color (yellow-green color) for a longer time and had... |
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