| Nanguo pear is the local specialty fruit in Liaoning Province due to its red color, thin skin, few stone cells and rich aroma. It is listed as one kind of the special pears with the key development during the major area agriculture development plan of the agriculture department. Its harvest time is almost in early-September or mid-September. It is softened quickly, aroma increased, then become soft quickly, the core browning, even the flesh browning and loss of the peculia commodity quality when it is stored at room temperature for10-15days after harvesting. Although can the cold storage keep the pear quality well, the aroma was lightened and it can not soften properly during the shelf life at room temperature after cold storage. The serious core and flesh browning has greatly hampered the promotion and application of the Nanguo pear cold storage technology, which has become the bottleneck problem of the Nanguo pear industry development. The study of the Nanguo pear browning mechanism after room temperature storage and cold storage can provide a basis for the approaches and methods how to control the Nanguo pear postharvest browning and will be great importance of promoting the development of the characteristic Nanguo pear industry in Liaoning Province.The inside mechanism of the flesh browning after room temperature storage and cold storage was studied in two aspects involved energy and membrane lipid metabolism. The energy and membrane lipid metabolism to clarify the browning mechanism during browning after the room temperature storage and cold storage with the1-MCP, SA and CO2treatment before harvesting, providing a basis for the further evidence of the Nanguo pear browning and the controls of the pear browning after the room temperature storage and the cold storage.1) At the room temperature condition, browning occurrence had a highly correlation with the preharvest average sunshine time (R2=0.9058). effective accumulated temperature (R2=0.6876) during growth period) and the conten of SSC (R2=0.7524)during the storage at room temperature. And the degree of browning occurrence had a Extremely correlation with the growth time (harvest date), the correlation was as high as94.71%. With the harvest delays, the soluble solids content and ethylene production of late harvested fruit (period of harvest3) were significantly higher than early harvest fruit, and its contents were2.2times to1.27times than the early harvested fruit. Browning occurrence at the room temperature condition after cold storage had a high negative correlation with the fruit firmness, and the correlation was as high as92.54%.2) The browning of Nanguo pear occurred mainly in core at the room temperature condition. The later of the fruit harvest date, the higher of fruit maturity degree. Compared with the early harvest fruit, ATP content and energy charge ahead of time7d peak appears in late picking fruit, In the Storage section7d, the ATP content and energy charge values were significantly (P<0.01) higher than the other two harvest period in the3rd harvest period. Mitochondrial proteins and respiratory control ratio was also significantly (P<0.05) higher than other harvesting period in the late harvest fruit. The results shown that mitochondrial structure and energy generating were maintained at a high level. There was also higher Phospholipase activity in late harvested fruits(the activity of late harvest fruit is1.53times than early harvested fruit, so the degradation rate of membrane lipids were accelerated. Result in the membrane permeability and MDA content in late harvest fruits were increased by48%and114%than early harvest fruits). Damage of membrane structure and function and total phenol content of in core were higher than in peel and pulp, respectively,12%and60%. Therefore, there were the first place in the core there browning occurrence.3) The fruits browning occurrence mainly in peel and core during shelf life at room temperature after cold storage. Browning index and browning degree in late harvest fruit were higher than in earlier harvested fruit, regardless of the peel, pulp or core. During the shelf life of5th days after cold storage, Respiratory control ratio and ATP content in late harvest fruit were1.37times to1.5times respectively than in early harvest fruits. At the same days the fruits of all harvest period had a peak of mitochondrial protein content, and the later the harvest, the peak is higher, the peak of3rd harvest period was1.2times, the peak of SDH and CCO (sugar invertase) activity appeared ahead of10d in late harvest fruits than early harvest fruits, and the peak is also higher than early harvested. This promoted carbohydrate utilization and decomposition. MDA and membrane permeability in the3rd harvest period were higher than other two harvest harvest periods during the entire sheld life. Duiring the5tn days of shelf life, the later the harvest, the higher of the phospholipase activity in mitochondria and microsomes. That can accelerated intracellular degradation rate of unsaturated fatty acids and further exacerbating the structural damage of cell membranes. All these result in browning occurrence. Extend the cold storage time very significantly (P<0.01) increased the occurrence degree of browning after cold storage.4)1-MCP treatment could significantly inhibit browning occurs at room temperature, because1-MCP could significantly inhibited postharvest respiration rate and ethylene production, delay ripening and senescence process, and extend the Nanguo pear storage time21d above;1-MCP treatment can contain the higher levels of mitochondrial protein content (higher46.5%than the control treatment) and ATPase activity in order to maintain the stability of ATP content. At the14th days during the storage, LOX activity treated by1-MCP decreased31%in order to delaying the content of unsaturated fatty acids in membrane decreased rate. CO2treatment has the similar effects with1-MCP, but the effect treated by CO2is not as good as1-MCP. At the21th during the storage, the fruit browning degree treated by1-MCP and C02is19.2%and51.9%respectively than control.1-MCP and CO2treatment may be sufficient to keep the cell by means of a stable energy supply and suppressing the degradation of cell structures play a role. SA treatment at room temperature on the Nanguo pear fruit browning effect is not obvious.1-MCP and CO2treatment were also reducing occurrence of browning degree during the Nanguo pear shelf life after cold storage, but the suppressing effect not as good as room storage effect. During the15th days of shelf life, fruit browning index treated by1-MCP and CO2were the69%and95%compared to the control. The browning index treated by SA was80.1%.1-MCP and CO2treatment mainly through inhibition of Nanguo pear ripening and senescence process maintain higher energy supply level and delayed the degradation of membrane lipid. SA treatment mainly through inhibiting phospholipase (at the5th days during the shelf life, phospholipase activity in fruit treated by SA is the70%compared to the control) and LOX enzyme activity, thus maintaining a high phospholipid content (26%higher in fruit treated by SA than the control) and lower proline content (62%of the control fruits), indicating that SA could kept the membrane lipid structure and function, improve low temperature flexibility, thereby inhibiting browning occurrence during the shelf life at room temperature after cold storage. |
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