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Longan storage and preservation method
Longan is a famous subtropical fruit, mature in hot and humid season. The fruit has high water content and sugar content, strong respiratory activity, and is easy to infect various pathogenic bacteria. Under normal temperature conditions, browning, sour rot, and metamorphism occur after 3-4 days after harvest, which is one of the fruits that are difficult to store and keep fresh. The use of longan storage and preservation technology for preservation can relieve the sales pressure of fresh fruit, extend the supply period, and increase economic efficiency. First, pre-harvest, post-harvest treatment of longan storage preservation, first of all to do a good job of pre-harvest treatment, timely harvesting and color protection and other work. The longan tree can be sprayed with 500-750 times of emulsified promethazine or 0.02% 2,4-D solution, or a mixture of the two, usually about 2 weeks before picking, which can prolong the postharvest storage time of longan . The longan that is sold or processed for near-field use should be harvested at a maturity of 8.5-9.5, and harvested at a distance for early harvest. Should choose to be sunny or cloudy at 10 o'clock in the morning or in the evening. It should not be harvested in rainy, foggy and dew-free seasons. When harvesting, it is advisable to cut 2 pieces of compound leaves at the base of the ear with 3 to 6 centimeters, cut neatly, gently and gently, to avoid mechanical damage. After harvesting, fruit selection and grading are carried out to remove rotten fruit, cracked fruit, wounded fruit, and pests and fruits. According to need, choose one of the following methods to protect the color: 12% sodium sulfite, 1% citric acid, 2% saline solution soaked for 2 minutes. 20.5% citric acid plus 0.03% vitamin C solution, or 1% citric acid solution soaked for 2 minutes. Second, commonly used longan storage preservation method Normal temperature storage: The use of anti-corrosion preservatives dissolved in water can quickly form a transparent film on the surface of longan fruit, effectively closed the stomata, reduce the respiratory intensity, delay the aging of the fruit, and can play a role in antisepsis and sterilization mechanism for fruit preservation, and then use Polyethylene film or ethylene-vinyl acetate film packaging, tie tight film bag, stored at 302 °C for 5-8 days, good fruit rate of 96%, than the fresh fruit without drug treatment more fresh 4-5 days. Common anti-corrosion preservatives include sec-butylamine, tetoxyl, imazalil, carbendazim, thiophanate-methyl and others. However, the normal temperature storage and fresh-keeping technology adapted to the longan fruit with long production, storage and transportation time is not yet mature. 2. Low-temperature controlled atmosphere storage: Appropriate low temperature can reduce the respiratory intensity of the fruit, effectively inhibit the activity of polyphenol oxidase and microbial activity. After longan harvest, it is pre-cooled, packed with plastic film or film, and combined with drug preservation and cryopreservation. This is an effective method for longan storage. This method can exert spontaneous atmosphere modification and change the content of CO2 and O2. Inhibits the impregnation of microorganisms and reduces decay loss. After 4 years of trial and error, Fujian Agriculture and Forestry University used a thin film account with 0.1% sec-butylamine to cool fruit at low temperatures. It was preserved at 41°C for 40 days, and the good fruit rate was 96%. The fruit appearance and flesh quality were comparable. it is good. This preservation technology is simple and effective, with significant results. 3. Sulfur-preserving and fresh-keeping: Longan exported from Thailand is mostly used for sulphur dioxide fumigation and cold preservation. Because sulfur dioxide can effectively prevent skin browning and inhibit the spread of pathogenic microorganisms. With the concentration of 1% -2% of sulfur dioxide fumigation fruit, combined with cold storage, smoked sulphur-treated fruit in the cold storage at 3-5 °C, with 260-380 grams of sulfur per ton of fruit, smoke for a time of 20 minutes, storage In 35 days, the good fruit rate was 96%. The disadvantage is that if the amount of sulphur is not controlled properly, the fruit has a sulphur taste and affects the quality. 4. Modified atmosphere preservation: After longan harvest, it is pre-cooled, and it is sterilized by antiseptic and then bagged, pumped, and filled with nitrogen, and stored under low temperature conditions. Pay attention to adjusting the proportion of O2 and CO2 in the storage environment during storage (note that high CO2 concentration is prone to poisoning). After 3040 days of storage, the fresh state can still be maintained. With regard to gas storage technology, the overseas development has been rapid, and there has not been systematic and in-depth study on the long-term storage of longan in China. 5. Hot-keeping: This method is traditional folk preservation. The fruit of the whole panicle will be immersed in boiling water for 30-40 seconds. It will not scald the flesh. After blanching, it shall be hung in a cool, ventilated place. After the treated fruits were placed for 15 to 25 days, the flesh remained fresh and the taste was sweeter. 6. Quick-frozen storage: After selecting good fresh fruits and crack prevention treatment, the center temperature of the fruit is reduced to -30°C (usually no more than 1 hour), then stored in a cold storage at -18°C for a long time, and can be stored for one year or longer. time. The quick-freezing longan was removed from the low temperature of -18°C and treated with 0.5% citric acid plus 0.03% vitamin C solution or 1% citric acid solution, and the peel remained unchanged for 48 hours. However, the use of quick-frozen storage defects is long after the removal of longan at room temperature cracking more serious.