Storage and Fresh-keeping Technology of Apples Treated with "1-MCP" Preservative

l Apple varieties and storage characteristics:

Apple is a typical respiration climacteric type fruit. After harvest, there is a clear post-ripening process. The starch in the fruit will gradually be converted into sugar, the acidity will decrease, the fruit will turn green to yellow, and the hardness will decrease, fully showing the unique color, flavor and the aroma of this variety and achieving the best edible quality of this variety. Further storage will result in a soft texture, loss of brittleness, and little juice due to the large consumption of nutrients in the fruit, which will decay, deteriorate, and rot.
There are many varieties of apples in China, which can be divided into three types: early maturity, middle maturity and late maturity according to different maturity periods.

1. Early maturing varieties: the maturity period is from June to early July. The  main varieties are Liaofu, Fushuai, Tianhuangkui, Huangkui, Hongkui, Zhuguang, Danding, Fuhuapi and so on. Due to the short growth period, the flesh tissue is not dense enough, the flesh is soft, the taste is weak, it is easy to rot, and it is not resistant to storage. It is generally sold directly on the market or short-term refrigerated.

2. Medium-maturing varieties: the maturity period is from August to September. The main varieties are Jinshuai, Yuanshuai, Red Star, Shouhong, Kuihong, Huaguan, Fujin, New gala, Hongyu, etc. Its storage characteristics are better than early maturing varieties, but under general simple storage conditions, it is not suitable for long-term storage. The cold storage and air-conditioned storage using mechanical refrigeration can extend the storage period, from January to March of the following year.

3. Late maturing varieties: the maturity period is from October to early November. The main varieties are Guoguang, Green Banana, Wajin, Fuji, Changfu No. 2, Qiufu No. 1, Cockscomb and so on. These varieties have high yields and are shelf-stable. Late maturing varieties are the main varieties stored.

l Harvesting and precautions:

The harvest of apples directly affects the yield, quality and storage. If the harvest is too early, the fruit is not fully developed, the fruit is light, the appearance and color are poor, the sugar content is low, and the quality is poor; if the harvest is too late, the pulp is fast and the disease resistance is low, and it is not resistant to storage. Only when harvested in a timely manner can the fruit have the best edible quality and the longest storage life, so as to obtain higher income.

1. The appropriate harvest period is mainly determined according to the following aspects:
(1) All of the external properties including fruit size, shape, color, etc. achieve the inherent traits of the variety. The seeds turn black and the fruit powder becomes mature.
(2) The internal indicators of fruit hardness are generally 5.4~6.8kg/m2, the earlier the maturity is, the lower the hardness is, the stored fruit is slightly harder than the fresh food; the solid content is 12%~15%. As the maturity of the variety is postponed, the solid content gradually increases.
(3) During the fruit growing period, each variety has a relatively stable number of days from the flowering period to the mature period. Generally, the early-maturing varieties are 100-110 days, the medium-maturing varieties are 120-140 days, and the late-maturing varieties are 140-175 days. As the accumulated temperature of fruit growing period is different in different regions, the harvesting period will be different. It is best to harvest in different regions around 10 days before and after the harvesting period.

2. Notes on harvesting operations:
(1) During the operation, hold the fruit with your hand, and gently lift the index finger against the end of the fruit stalk. The fruit stalk will be separated from the fruit table. Do not pull hard. Actions should be as gentle as possible to prevent mechanical damage and prevent microbes from invading the wound and infecting the disease.
(2) The order of picking is to pick the outer and lower parts of the canopy first, then the inner bore and the upper part.
(3) No water should be poured into the garden within 5 days before harvesting, no nitrogen fertilizer should be applied within 20 days, and no picking should be made within 3 days after rain or when there is dew or fog in the morning. Fruit should be picked in clear weather. It’s suitable for picking when the dew in the morning is dry and the temperature is low or after 4 pm. The fruits after picking should be placed in shade.

l Preparation before storage:

1. Pre-cooling Apple should be pre-cooled before low temperature storage, otherwise it will seriously affect the storage. Apples often maintains a high "field heat" during harvesting, and has strong physiological activities such as respiration and metabolism, so it is easy to spontaneously ripen. At the same time, if it is directly sent to the cold storage without pre-cooling, the temperature difference of about 20 ℃ inside and outside will cause disturbance of fruit physiological activities and excessive freezing injury and condensate on the fruit surface, which is easy to heat and rot, affect the quality, and shorten the storage period. Therefore, pre-cooling is necessary. The method is to put the freshly harvested fruits in a well-ventilated, dry ground, low temperature room or under the shade of trees, cover them during the day, and uncover them at night to cool down.

2. Warehouse management Eliminate the odor in the warehouse and eliminate the debris in the warehouse. Wash the ground with saturated potassium permanganate solution or bleaching powder, and close the door for 24 hours, or use 5 to 15 grams of sulfur per cubic meter to mix and dry the sawdust for 48 hours, and then turn it on to cool down. Reduce the temperature of the sterilized cold storage to 0°C two days in advance, and then put the pre-cooled fruits into the storage. There should be a gap between the box, the stack and the circumference of the apple stack to facilitate ventilation. After all storage is completed, adjust the temperature in the storage. In addition, try to fill the warehouse in about a week and carry out fresh-keeping treatment in time.

l "1-MCP" preservation treatment:
After the storage is full, use "1-MCP" preservatives for fumigation treatment in time to prevent the arrival of the peak of apple breathing, reduce the breathing intensity, and inhibit the release of large amounts of ethylene, so as to effectively extend the storage period and shelf life of apples. Our "1-MCP" preservative can also effectively prevent the occurrence of tiger skin disease during apple storage.

l Storage management:

1. Suitable storage conditions: temperature: -1 ℃～1℃
Relative humidity: 85%～95%
Modified atmosphere condition: O₂: 2%～4% CO₂: 1%～5%
Periodically check the temperature and humidity in the warehouse during storage and adjust it in time. The temperature and humidity are required to be stable. Frequent temperature and humidity changes are harmful to apples. Humidity should not be too low, so as not to cause dehydration and wilting and affect fruit quality. If the humidity in the warehouse is not enough, you can sprinkle water properly. Defrost in time and maintain constant temperature.

2. Sterilization: It should be sterilized regularly during storage, preferably   every half a month. If the fungicide is used alternately, the effect is better.

3. Ventilation: During storage, ventilation and ventilation must be carried out in time to eliminate bad gases and avoid other physiological diseases. Change the air every 15 days or so. The ventilation time should be controlled at about half an hour. Choose a sunny day when the outside temperature is low.

4. Listed on the market: The apple should be gradually warmed up before leaving the warehouse, otherwise there will be condensate on the apple after leaving the warehouse, which will accelerate the decay.

l The trial effect analysis of 1-methylcyclopropene on different apple varieties

"Red Fuji" Apple
"Red Fuji" apples have the advantages of late ripening, high quality, delicious taste and storability, and are the most famous late ripening apple varieties in the world. My country began to introduce Fuji apples in 1966. Today, Fuji apples have developed nearly one million hectares in China, and have replaced the late-growing variety "Guoguang" in Liaoning, Shandong, Hebei, Beijing, Shanxi, Shaanxi, Tianjin, Henan, Jiangsu, Anhui, and Gansu.
Studies have shown that 1-MCP has a significant effect on physiological changes such as sugar content and hardness of "Red Fuji" apples. The results of random inspection showed that after 1-MCP treatment, the fruit hardness decreased slowly and had little effect on the change of sugar content. This shows that the "Red Fuji" apples treated with 1-MCP, whether it is cold storage in ordinary storage or cold storage in modified atmosphere storage, have largely delayed the senescence of the fruit. Fuji Apple's "tiger skin disease" is essentially sign of fruit aging. While 1-MCP suppresses Fuji's aging, it also suppresses the occurrence of "tiger skin disease" and slows down the soft of the pulp, thereby extending the shelf life of the fruit.

"Gala" Apple
"Gala" apples are native to New Zealand and bred by New Zealand fruit tree breeder Kidd. The fruit is medium and large, with a single fruit weighing 180-200 g, short conical shape, golden yellow surface, thin peel and shiny. The flesh is light yellow, and the flesh is compact, crisp, juicy, sweet and slightly sour, and very palatable.
Treating “Gala” apples with 300 nL / L and 600 nL / L 1-MCP for 24 h, and the results significantly inhibited the respiration rate and ethylene production rate of the fruit during storage, and significantly inhibited the shelf life after storage The fruit respiration rate and ethylene production rate were not significantly different between the two concentration treatments, indicating that 300 nL / L concentration of 1-MCP treatment had the same effect as 600 nL / L in inhibiting "Gala" apple respiration and ethylene production. Similarly, 1-MCP treatment is also conducive to the maintenance of fruit firmness and titratable acid content. After 120 days of storage, the 1-MCP-treated fruit had higher hardness and titratable acid content than the control fruit. Studies have shown that 1-MCP preferentially binds to ethylene receptors, on the one hand prevents ethylene from binding to its receptor and inhibits the physiological effect of ethylene, on the other hand it can inhibit the genes expression of ACO (ACC oxidase) and ACS (ACC synthase) and reduce the synthesis and release of ethylene, which indicates that ethylene is closely related to the expression of specific proteins during apple ripening. 1-MCP may inhibit the production of ethylene, thereby inhibiting the expression of senescence-related proteins (enzymes) and genes inside the fruit, which in turn delays the aging of the fruit after ripening.

"Jonagold" Apple
"Jonagold" is an American variety. The fruit is large, oblate to round, and the single fruit weighs about 250 g. The flesh is light yellow, fine and crunchy. The taste is sweet, slightly sour, and has a special aromatic quality. It is durable and can be stored until around the Spring Festival. The fruit ripens in the first and middle of October. The surface of the fruit is easy to "return sugar", and it is easy to secrete waxy substances during storage.
The study found that treatment with 1-MCP can significantly reduce the respiration intensity of "Jonagold" apple fruit, delay the appearance of respiratory peaks, and reduce the peak of respiratory peaks; and can significantly slow down the decline of fruit hardness. Fruits treated with 1-MCP had a slow decline in hardness. The fruits in the control group began to become soft 2 weeks after harvest, and by the 4th week they had lost their commercial value; At the same time, studies have shown that 1-MCP can not only significantly inhibit the decomposition of chlorophyll in the peel of "Jonagold" apples, but also have a significant effect on the soluble solid content of "Jonagold" fruits. For the control fruit, the soluble solids were gradually consumed due to the greater respiration intensity, and the sweetness decreased. Fruits treated with 1-MCP had slower metabolism of respiration and higher levels of soluble solids. The titratable acid content of all treated fruits gradually decreased with the extension of shelf life, but the decrease rate of control fruits was significantly higher than that of 1-MCP-treated fruits.

"America NO. 8" Apple
"America NO. 8" Apple is a new apple variety introduced from the United States. This variety has large and neat fruits and the rate of high-quality fruit is up to 90%; It has features of early ripening and beautiful appearance. Around August 10th, the fruit surface is all red and smooth and rust-free, filling the off-season of the fruit; It has unique flavor, good palatability, good performance and long shelf life. Placed on the market shelf for 30 days, the apple’s color is unchanged and the flesh is not soft. It is early fruits with high yield. Fruits are seen in the second year after planting, and the yield is high in the third year. It is especially resistant to anthracnose and ring rot, and the fruit surface is clean. It does not require bagging cultivation and requires less investment.
Taking "America NO. 8" apple as the test material, the effect of 1-MCP treatment on post-harvest physiology of fruits under 0 ℃ storage conditions was studied. The results show that treatment with 1 nL / L 1-MCP can significantly inhibit the release of ethylene during storage, delay the emergence of its jump peak, inhibit the increase of ACO activity and respiration rate in the early post-harvest period; slow down the decrease of pulp hardness; at the same time reduce the activity of lipoxygenase (LOX) and delay the appearance of its peak, delay the increase of MDA content and relative membrane permeability, thereby reducing the degree of membrane lipid peroxidation, which states that 1-MCP can significantly improve its storage quality. The test results also show that 1-MCP treatment can significantly inhibit the decrease of pulp hardness during post-harvest storage. It has a very good effect on maintaining the flavor and quality of the fruit, prolonging the storage period and shelf life of the fruit, and delaying the ripening and senescence process of the fruit after harvest.

"Pink Lady" Apple
"Pink Lady" is a small fruit with yellow-green fruit background, full pink or bright red. The fruit surface is clean and bright and no rust. It has beautiful appearance. When the fruit was just harvested, the flesh was milky white, crisp, hard and juicy. After being stored at room temperature for 2 months, the flesh becomes light yellow, with moderate sweetness, rich aroma and excellent flavor.
Taking the "Pink Lady" apple as the test material, the effect of 500 nL/L concentration of 1-MCP on the fruit hardness, titratable acid content and soluble solids content of the Pink Lady apple during storage and at room temperature was studied. The results showed that the hardness, titratable acid content and soluble solids content of the treated fruits decreased significantly after 150 days of storage compared with the control fruits. It can be seen that 1-MCP treatment can significantly inhibit the decrease in the fruit hardness, titratable acid content and soluble solids content of the “pink lady” apples during storage and at room temperature. The inhibitory effect is related to the decrease in respiration rate and the reduction of ethylene production. “Pink lady” apples can be stored for 5 months at 0℃. 1-MCP treatment can significantly improve the storage quality.