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Litchi preservation principle and technology
The lychee fruit that has just been harvested has a "color change on one day, a fragrant change on the second day, a fragrant change on the third day, and a color, aroma, and flavour on the fourth and fifth days." With the development of production, litchi transport sales have increased year by year. Therefore, it is imperative to master the principle of preservation of litchi and adopt advanced preservation techniques. 1 Principles and conditions for storage and preservation of litchi 1.1 Storage physiological characteristics Litchi is a non-respiratory peak fruit, mature fruit during mature period without obvious respiratory transition period [1], but its respiratory intensity is 1 to 4 times larger than that of apple, banana and citrus. 〔2〕. The invertase and polyphenol oxidase in litchi fruit were very active at 30°C [2,3]. Because the peel is thin and has cracked pieces, the loose connection between the peel and the pulp causes the moisture in the pulp to be easily lost, and the skin is rich in tannins (about 7%), so the peel is prone to browning.[4] ~ 6〕, leading to a rapid decline in fruit disease resistance, color, smell and taste decline, and then infected with bacteria and rot. Inhibition of dehydration and browning can effectively preserve lychee and inhibit decay and decay. 1.2 Storage conditions Litchi preservation practices in ancient and modern times have proven that small packages under low temperature conditions have the best gas storage properties [2, 6, 7, 8]. 1.2.1 Temperature and humidity Low temperature is an important condition for reducing the respiration rate of Litchi and prolonging its storage period. At 1～5°C, litchi can be stored for one month, and the color, aroma, and taste are basically unchanged [2, 7]. Litchi storage conditions vary due to different varieties, but the general temperature at low temperature storage is 2 ~ 4 °C, relative humidity 90% ~ 95%. Cold is easy to cause if the temperature is too low, and worse if it is too high. Low humidity can easily lead to browning and dehydration. 1.2.2 Atmosphere storage of the gas components can maintain the humidity and inhibit the activity of polyphenol oxidase, which has a significant effect on maintaining the color, aroma and taste [1,9,10]. However, under controlled atmosphere storage, its optimum temperature is slightly higher than ordinary low temperature storage by 1~2°C. Litchi adapts to a wide range of gas conditions, as long as the carbon dioxide concentration does not exceed 10%, that is, no physiological damage occurs. Appropriate conditioning conditions are: temperature 4°C, carbon dioxide 3% to 5%, oxygen 3% to 5%. Under this condition, it can be stored for about 40 days. 1.2.3 Antisepsis Sterilization Litchi fruits are susceptible to browning and mildew, post infection, Phytophthora capsici, acid rot, penicillium and anthracnose, so no matter what kind of preservation method is used, high-efficiency and low-toxicity agents are required to sterilize the fruits. . Available 25010-6 benzene, carbendazim, imazalil or Tecdo soaked fruit, can also be used 50010-6 sec butylamine, chlorhexidine, sodium o-phenylphenol leaching fruit [2]. 2 Key to Litchi Fresh-keeping Technology 2.1 Selecting suitable varieties Although Litchi fruits have poor storage stability, there are still some differences between varieties, so it is better to choose Huaizhi, Guiwei, Baizhuzi, Shangshuhuai. , Litchi twigs and other storage. 2.2 Timely Non-injury Harvesting Grasping appropriate harvesting maturity is one of the key technologies for storage of litchi. The optimal harvesting maturity required for different storage methods is different. General low-temperature storage, should be harvested when the litchi is fully mature, the redder the more red the better its preservation effect. However, if spontaneous storage under low temperature (eg, film packaging, film formation, etc.) is used, then 2/3 of the fruit surface is colored, with a little cyan (about 8 mature) harvest is better [2,6, 9〕. Harvest time should be selected before sunrise in the morning on sunny days, without plucking whole leaves. Pay attention to avoid the sun and rain, so as to avoid cracking fruit or field bacteria. 2.3 Timely post-harvest treatment Litchi should be quickly moved to a cool place after harvest to carry out pre-cooling and heat dissipation, and to promptly remove rot fruit, diseased fruit and brown fruit. The whole process should be carefully handled and handled gently. Avoid all mechanical damage and take care to prevent the spread of germs. Air-conditioned storage of litchi fruit should enter the atmosphere as soon as possible. Long-distance and low-temperature storage of litchi, after pre-cooling and post-harvest sterilization treatment, when the fruit temperature is reduced, dried fruit surface liquid and then packaged storage and transportation. Practice has proved that the use of small packaging (0.25 ~ 0.5kg) storage and litchi than large packaging (15 ~ 25kg) effect is good [2,8]. The more timely the packaging and storage, the better the preservation effect, from the harvest received into the storage is generally completed in 12 to 24 hours is better [3]. 2.4 Maintaining stable storage and transportation conditions Maintaining a stable and appropriate temperature, humidity, and gas composition in the storage and transportation environment is the key to determining the success or failure of storage and transportation of litchi. Should pay attention to cold and heat, moisture and gas, to prevent excessive changes in temperature and humidity and gas composition, so as to avoid injury, chilling, cold injury, water loss, dry brown and so on. Even in the sales process, it is not advisable to open small packages in order to extend the shelf life of litchi. 3 Litchi Preservation Technology 3.1 Low-temperature storage 3.1.1 Natural low-temperature storage method Litchi fruit is harvested at the ripening stage. The day is soaked with 52°C, 50010-6 benfluther solution for 2 minutes. The potion is drained and put into a hard plastic box. Each box of 10 to 15, and then covered with 0.01mm thick polyethylene film, can be stored at a natural low temperature for 7 days, basically keep the color and flavor unchanged. Mature fresh litchi can also be soaked in 0.5% copper sulfate solution for 3 minutes, then packed in perforated polyethylene bags and stored at room temperature for 6 days to maintain a bright red appearance. 3.1.2 Low-temperature refrigeration method Use 2% sodium hypochlorite to dip fruit for 3 minutes. After draining the syrup, store the litchi in a 7°C environment for 40 days or so. The color and flavor are still good (11). 3.2 Cryogenic Air-conditioning 3.2.1 Pouch Packaging Method Litchi fruit is harvested at 8 days of maturity, using 50010-6 benzalkonium at 52°C on that day, 100010-6 carbendazim or thiophanate-methyl, or 50010-6 to 100010-6 betonite. Add B-Phosphorus Alkaline for 20 seconds. Leach off the liquid, dry it and put it in a polyethylene plastic pouch or box. The thickness of the bag is 0.02-0.04mm, 0.2-0.5kg per bag, and after adding a certain amount of ethylene absorbent (potassium permanganate or activated carbon) seal. Placed in the loading container for storage and transportation. It can be stored at 2～4°C for 45 days, and can be stored at 25°C for 7 days. 3.2.2 Large bag packaging method According to the above-mentioned pouch packaging method for harvesting and fruit soaking, drain it and dry it, then select the good fruit and put it in a container lined with plastic film bags or baskets, each containing 15 to 25 kg of fruit. , And add a certain amount of potassium permanganate or activated carbon, the film bag is basically sealed, at 3 ~ 5 °C can be preserved for about 30 days. If the oxygen content of the gas in the bag is 5% and carbon dioxide is 3% to 5%, it can be kept fresh for 30 to 40 days, and the color and flavor are better.