Research On Mechanism Of Mealiness Of Apricot Fruit During The Cold Storage

Xinjiang apricot fruit(Saimaiti) were taken as the test materials in this article, beginning with the controlled of postharvest mealiness at low temperature storaged. The effect of apricot fruit harvest maturity on cold storage quality,cell wall metabolism, ethylene metabolism, the organizational structure and ultrastructure were researched. The improving mechanisms of postharvest cold resistance of apricot fruit on different maturity were discussed, which provided some theoretical basis for the control of postharvest apricot fruit mealiness.(1) They were divided intoⅠ(colored area < 50%),Ⅱ(colored area 50%~80%) and Ⅲ(colored area>80%) three different fruit maturity according to the turn yellow rate and were divided into three parts according to the same amount, then respectively storaged at 25℃, 4℃, 0℃ RH 90% ~ 95%. The chilling injury incidence, chilling injury index, firmness, total soluble solids, titratable acidity, chlorophyll, ASA content, membrane permeability, juice rate, weight loss rate, respiration rate and MDA content of apricot fruit were determined, The results showed that at 4℃ of apricot fruit chilling injury mainly occurred in mealiness,the fruits of mealiness deduced fruit hardness, TSS, chlorophyll, ASA, the juice yield, increase the incidence of chilling injury, membrane permeability and MDA content, and the maturity Ⅲ of apricot fruit mealiness occurred earliest and seriously. At 0℃,leathereness was the main chilling symptom,the higher maturity, the later lestheriness. Thus, the low temperature of 4℃ storage of the fruit with the extension of storage time, the apricot fruit mealiness will occurs, high maturity of apricot fruit was the most significant.(2) The changes in cell wall pectins and lignin in normally ripening and in mealy or leathery apricot fruit was investigated. The water soluble pectin, CDTA soluble pectin(CSF), Na2CO3 soluble pectin(NSF1) and Na OH soluble pectin(NSF2) content, the activities of galacturonic acid(PG) and the activities of pectinesterase(PME).The process of fruit ripening and softening storaged at room temperature, the activities of PG increased and the activities of PME decreased, NSF1 and CSF for the degradation of water soluble pectin, so the fruit ripening and softening. The fruits of 4℃ PG was lower than the fruit at 25℃, the activities of PME was higher than the fruit at room temperature. CSF, NSF1 content were higher than the normal mature fruit, inducing mealiness symptom. The activities of PG of apricot fruit at 0℃ stored was lower than that at 4 ℃, the activities of PME kept higher level, pectic substances cannot degradation normally.(3) Research on the changes of different maturity apricot fruit ethylene production, ACC content, the activities of ACO and ACS at three kinds of storage temperatures. The ethylene production, ACC content, the activities of ACO and ACS of apricot fruit at 25℃ stored drops rapidly after rising to the peak, and maturity Ⅲ apricot fruit was the earliest rise to the peak. The fruits ethylene production increased, the ACC content and the activities of ACO increased at 4 ℃, the fruit can be ripening, but occurs mealiness symptoms, and the peak was smaller compared with that at 25℃. In the last stage at 0℃, ACC content, ACO activity and ethylene production decreased,fruit lost ripening ability and manifested as leatheriness. The results showed that the fruit changes of the gap of ethylene metabolism at 25℃ and mealiness was not big, Ethylene physiological metabolism was not main factors affecting the formation of mealiness, maturity Ⅲ apricot fruit was always the earliest appears abnormal than others, maturity Ⅰ fruit the was not significant.(4) The changes of microscope and cell ultrastructure in apricot fruit harvest and stored at 25℃ for 24 h, 72 h, 144 h, the 7th day of cold storage, 21 st day of cold storage and the 35 th day of cold storage of apricot fruits at 4℃ and 0℃ were observed by paraffin section and transmission electron microscope. Stored in the 7th day at 4℃, three different kinds of apricot fruit maturity have not significant differences based on cells arrangement in neat rows and the integrity of the cell wall structure and the cell organells, and just have no obvious difference when harvested. The ultrastructure of apricot fruit changed obviously after 21 d, which exhibited that cell organelles was deformable or dissolved, gap junctional intercellular enlarged, cell contents decreased, cell empty was cavity, the phenomena of maturity Ⅲ was the most serious. Compared with the fruit at room temperature, the cellular structure of the fruit was damaged a little lighter at 4℃. And at 0℃, three kinds of maturity apricot fruit cell wall integrity organelles and membrane systems better. The results showed that the higher maturity of the fruit under 4℃, the larger damage to cells, the fruits of mealiness in defeat organizational structure damage was serious.