Physiological-Biochemical Mechanism On Citrus Peel Pitting Fruit During Storage

Citrus peel-pitting,a storage disease,the incidence of which come to 20%-50%,up to 90% when seriously,which damage lot in the long-term storage.Fruit commercializations are more vulnerable to brown spot after Post-harvest.Circle light-borwn leathered dots can be found at the beginning of peel-pitting,then developed into bronze,brown and black.Mild browning spot affected the outlook of fruit,and malignant one would cause drying and shrinking on fruit peel,even cause damage to the cortex and sarcocyte of fruit.Penicillium digitatum,Penicillium expansum and some anthracnose may invade into and cause fruit decay at the end of browning spot.The smoothness of the skin and fruit flavor have been affected greatly by peel-pitting,which reduced the competitiveness of products in the market and the passing rate of exports and became as the obstacle of the citrus industry in China.Peel-pitting is widespread in sweet orange and Mandarin,especially in sweet orange.Many researches have been focused on the mechanics of browning spot in the late decades.The results turned out was that peel-pitting was the reaction of enviromental and physiological stress of fruit which had been resulted from many factors and hardly contribute to certain factor.While the exact cause and physiological mechanism are still not clear.Researches mainly focused on litchi,pear,strawberry and sweet cherry and partly on citrus for the mechanics of browning spot,just researched on some physiological-biochemical characters in Jinchen and naval orange.Less research on the disease mechanism of citrus fruit peel pitting.The unperfect corresponding control technique has become the key factor of restricting commercial production of citrus fruit.Therefore,there is a vital theoretical and practical significance to probe the peel-pitting mechanism for predicting and preventing citrus fruit peel-pitting.In order to further probe the browning spot development mechanism,the post-harvest fruit shape,the changes of peel structure, the change tendency of physiological and biochemical characteristics and the relationship research of browning spot of Beibei 447,Ponkan and Satsuma mandarin have been studied in this paper.The main achievements of our studies are as following.Not only fruit peel shrinking,drying and developing dark brown area,but also oil gland cutting down and breaking down.Distorted cells was observed in peel-pitting Jingcheng,Ponkan and Satsuma mandarin.The activity of soluble CAT in Ponkan and Satsuma mandarin fruit peel decreased after ripening and senescence while not correlated with peel-pitting in Jinchen.Significant positive correlation was observed between CAT activity and the total phenol content in the second phase of Phenol metabolism in Jinchen,Ponkan and Satsuma mandarin fruit peels.CAT activity is one of the significant factor effected on total phenol content.The activity of soluble POD in fruit peel increased in the course of after ripening and senescence, which positively correlated with peel-pitting.Peel-pitting development was stimulated by higher activity of soluble POD in Jinchen,Ponkan and Satsuma mandarin fruits.PPO activety was negatively correlated with peel-piting rate during the storing time.Lower PPO activity was the significant feature of post-harvest physiology of Jinchen,Ponkan and Satsuma mandarin fruits.Significant positive correlation was observed between relative electrical conductivity(REC) and peel-pitting rate of Jinchen,Ponkan and Satsuma mandarin.REC was one important index of peel-pitting proof test in citrus fruit.There was correlation among the physiological-biochemical characters such as REC,POD and PPO in the pericarp.They cooperated each other and together effected on peel-pitting occurrence of Satsuma mandarin,Ponkan and Jinchen fruit.Post-harvest storage period can be divided into two stages based on the metabolism of total phenols. In the first stage,the amount of total phenol increased and the POD was the key enzyme of this course.In the second stage,POD cooperated with REC,PPO,CAT to reduce the level of total phenol.