Study On The Mechanism Of Decreasing Chilling Injury With Cold And Heat Treatments In Nai Plum Fruit

Nai plum fruit (Prunus salicina Lind1. var cordata J. Y. Zhang et al) was one of the most favorite fruits on the market nowadays due to its high quality. Unfortunately, it was not easy to extend the shelf life of the fresh fruit on the market since that the temperature was very high during the harvest season and the common storage method could hardly solve the problems of limited shelf life for Nai plum fruit. Low temperature storage could extend storage time of the fresh fruit efficiently. Nevertheless, to keep the fruit at low temperature for too long period of time may result in chilling injury. In order to prolong the shelf life of the fruit and to increase the preservation efficiency, it was essential to adopt the cold chain techniques and to develop the technique to deal with the chilling injury. This paper reveals related mechanisms of chilling injury by studying the effects of different treatments, such as different storage temperature, altering temperature storage, cold shock and heat shock on fresh fruit before or during the storage period.The effects of above mentioned treatments on the forming of heat shock proteins (HSPs), the endogenetic hormone level, the cell structure and the quality of preserve freshness were carefully studied so as to decrease the chilling injury during low temperature storage and to provide necessary theory for preserve freshness during storage and transportation of Nai plum fruit. The study includes following components: the effects of treatments on the formation of HSPs and its changing level, the effects on the IAA, GA₃, ABA and ZR levels of the fruit, and last but not least the effects on the cell structure and preservation efficiency including preservation period, rotting rate, the chilling injury rate, etc. of the Nai plum fruit stored at 3℃. These treatments include two storage temperatures (3℃ and 5℃) , altering temperature treatments during storage (one was stored at 3℃ for 30 days, then 1 day at normal temperature, finally at 3 ℃ again. Another 2 was stored at 3℃ for 40 days, then 1 day at normal temperature, lastly at 3℃ again ) , cold shock (soaked in water at 0°C for lh 2h, 3h and 4h, separately) and heat shock (36℃ for 4h or 8h 40℃for 4hor 8h ; 44℃ for 0.5h, lh,4h and 8h, respectively ) .The fresh Nai plum fruit were stored at 3 ℃, and randomly sampled 30 fruits and packed in a PE plastic bag with thickness of 0.04mm, three replications for the test. The HSPs were analyzed with SDS-PAGE, endogenetic hormone level was tested by HPLC. The texture was observed with Olympus BH-2 Microscope. All data were processed by using Excel and SPSS. Main points of the study might be concluded as follows:1. The different temperature storage shows (1) By storing at 3℃ for 30 days, the rate of chilling injury was 5.57%, whilethat of chilling injury does not occur at all by stored at 5 for 70 days. At the same time, the decomposition rate of 14 different kinds of protein in Nai plum stored at 5 was slower than that at 3 . This phenomenon pointed that the happening of chilling injury might be restrained by storing Nai plum fruit at 5, and the possible explanation for it might be due to the relatively slower decomposition rate of HSPs.(2) During the low temperature storage period at 3 or 5, the GA3 of Nai plum fruit was accumulated, and the peak of GA3 for group at 3 occurs obviously more early than that at 5. Further, there was a strong positive correlation between the content of IAA and GA3 during the whole storage period, so that GA3 might inhibit the decomposition of IAA. For ABA, there was also an accumulation during the low temperature storage at 3 and 5, but the accumulated concentration of ABA at 5 was higher than that at 3, so the rate of chilling injury for the fruit was lower than that at 3, and the rate of chilling injury at 5 was less severe. The ZR content of Nai plum fruit at 3 fluctuates and reaches the peak level while that of Nai plum fruit at 5 maintains relatively stable.(3) Comparing with the storage at 3, storage at 5 may decrease the penetra...