Physiological-Biochemical Mechanism Of Section-drying Citrus Fruit During Storage

Citrus fruit Section-drying,a physiological disease widely appeared in citrus fruit ripeness and storage process,is not only the major limiting factor of fruit quality but also the important factor affecting on the further development of China's citrus industry.This disease in citrus fruit is especially common in sweet orange and mandarine which can greatly decrease the commodity value of citrus fruit products such as a significant reduction in nutrients and juice,less sweet and color flavor reduction,poor quality and so on.At present,many studies on the mechanism of citrus fruit section-drying mainly were focused on Physiological-Biochemical characters changes.The consensus has not been achieved yet.The section-drying of citrus fruit in post-harvest can not be controlled effectively so far.Therefore,there is a vital theoretical and practical significance to probe the section-drying mechanism for predicting and preventing citrus fruit section-drying.In order to further prove up the mechanism of citrus fruit section-drying,the relationships between the change trend of Physiological-Biochemical characters and fruit section-drying of Satsuma Mandarin and Ponkan as well as Jincheng was probed here.Meanwhile the changes of morphology and histological structure of the three cultivars of citrus fruit before and after the section-drying also have been investigated.The main results are as follows:1.The morphology and histological structure of Satsuma mandarin,Ponkan and Jincheng tended to senescence with occurrence of section-drying.The section-drying type of the citrus fruit of this three cultivars was granulation.2.It was significant positive correlation between index of section-drying and POD activity of the pericarp of Satsuma mandarin,Ponkan and Jincheng.POD activity of the pericarp affected the occurrence of section-drying which was one of the significant features of senescence of Satsuma mandarin,Ponkan and Jincheng after harvested.In addition,it was also significant positive correlation between index of section-drying and POD activity of the Satsuma mandarin pulp.A high level of POD activity of the pericarp and the pulp would accelerate the occurrence of section-drying fruits.POD activity of the pericarp and the pulp of Satsuma mandarin influenced the occurrence of section-drying which was the salient feature of Satsuma mandarin being different from Ponkan and Jincheng in the aspect of senescence after harvested.3.AAO activity of the pericarp and the pulp of Satsuma mandarin,Ponkan and Jincheng was one of the factors affecting the occurrence of section-drying.However,the mechanism of AAO influencing section-drying is not clear yet which needs to be further researched.AAO activities of the pericarp and the pulp of three citrus varieties all were lower and which was negatively correlated with the occurrence of section-drying.It indicated that the low activity of AAO was one of the characteristics in the aspect of postharvest physiology of Satsuma mandarin,Ponkan and Jincheng.4.The CAT activity variation in the pericarp of Satsuma mandarin,Ponkan and Jincheng was another factor to affect the section-drying of the citrus fruit.The interaction of CAT in the pericarp and the pulp affected section-drying of Satsuma mandarin.And it was another feature that the postharvest senescence physiology of Satsuma mandarin different from that of Ponkan and Jincheng.5.Significant correlation was observed among pectin methylesterase(PME) activity in the pericarp and the pulp with index of fruit section-drying of Satsuma mandarin,Ponkan,Jinchen.It was found that the second peak of PME activity associated with the occurrence of fruit section-drying.6.There was a significant positive correlation between index of fruit section-drying and relative electrical conductivity(REC) of Satsuma mandarin,Ponkan and Jinchen,which was one important expression of Section-drying citrus fruit.7.The fruit respiratory rate of Satsuma mandarin,Ponkan and Jinchen had a significant positive correlation with fruit index of section-drying.The fruit respiratory rate was one of the most important factors affecting the occurrence of section-drying.8.The citrus fruit is an organic whole.There was correlation among the physiological-biochemical characters in the pericarp and the pulp.They had synergistic effect on section-drying occurrence of Satsuma mandarin,Ponkan and Jinchen fruit.9.It was clear that the variation trend of POD,AAO,CAT,PME,REC and respiratory rate of citrus fruit during the storage was corresponded with the senescence characters of citrus fruit.So,it was suggested that the basic reason of the fruit section-drying occurrence should be contributed to the fruit senescence.This is in accordance with the hypothesis of fruit senescence.