How to keep fresh longan and how to keep fresh longan for a long time.

1. Storage at room temperature: When the preservative is dissolved in water, it can quickly form a transparent film on the surface of longan, which can effectively seal the stomata, reduce the respiratory intensity, prolong the senescence of the fruit, and play the role of antisepsis and sterilization. Then the fruit is packed with polyethylene film or ethylene-vinyl acetate film bag, and the film bag is tightly tied. After storage at 28 ~ 32℃ for 5 ~ 8 days, the good fruit rate can reach 96. Commonly used preservatives are sec-butylamine, tektor, imazalil, carbendazim, azoxystrobin and so on. However, the storage and preservation technology of longan fruit at room temperature, which is suitable for large-scale production and long storage and transportation time, is not yet mature.

2. Low temperature controlled atmosphere storage: Appropriate temperature can reduce the respiratory intensity of fruits and effectively inhibit the activity of polyphenol oxidase and microbial activities. After harvesting, longan is precooled, packed in plastic film or stored in film shed, and combined with drug preservation and low temperature preservation; This is an effective method for longan storage, which can play the role of spontaneous controlled atmosphere and change the contents of carbon dioxide and oxygen, thus inhibiting microbial infection and reducing corruption losses.

3. Sulfur fumigation for preservation: In recent years, longan exported from Thailand has been fumigated with sulfur. The method is to burn100g of 90% sulfur powder for 20-30 minutes per cubic meter. Sulfur dioxide releasing agent was prepared by sodium dithionite, and the dosage per 2 kg longan was 16 ~ 22 g, which achieved good results at room temperature. Soaking longan with sulfite solution has no fresh-keeping effect, and it is better to release sulfur slowly with 6 ~ 8 grams of sodium bisulfite per kilogram of longan. In the sulfur fumigation treatment, every 10 kg longan was fumigated with 20 g sulfur for 20 minutes and stored at low temperature for 35 days. The good fruit rate reached 96%, while the control was 0. Sulfur dioxide can effectively prevent skin browning and inhibit microbial infection. When the sulfur smoked longan fruit is at 10 or 5 degrees Celsius, the pericarp can remain brown and disease-free 1 1 month (the pericarp has shrunk).

4. Modified atmosphere preservation: the longan is precooled for 2 days after harvesting, and then the fruit is sorted. After the bad fruit is cut into pieces, the ear of the fruit is cleaned, sterilized and disinfected with 0. 1% thiophanate methyl, and directly put into a polyethylene film bag with a thickness of 0.04 mm, or put into a plastic turnover box first, and then put on a plastic bag with a thickness of 0.04 mm.. The humidity is about 85%. After precooling, it was packed in plastic bags, and then pumped with nitrogen. The preservation effect was very good at 0 ~ 5℃ or 6 ~ 10℃, and the good fruit rate was still about 93% after 40 days storage. Pay attention to adjust the ratio of carbon dioxide and oxygen in the storage environment when storing. Oxygen 6% ~ 8% and carbon dioxide 4% ~ 6% are suitable gas indicators in the bag.

5, blanching preservation: this method is a traditional folk preservation method. Folk people soak the whole ear of fruit in boiling water for 30 ~ 40 seconds to avoid burning the pulp, and then lift it up and hang it in the air to dry. After the treated fruit was stored 15 ~ 25 days, the pulp remained fresh and the taste was sweeter. This method combines modern preservation technology, that is, blanched, dried and boxed fruits are stored in 2 1℃ cold storage for 22 days, and the good fruit rate reaches 100%. The appearance color of fruit is similar to that of fresh fruit, the endocarp is evenly browned, and the flavor of pulp is normal.

6. Quick-freezing and fresh-keeping: After fresh longan fruits are selected and treated with anti-cracking, the central temperature drops to -30℃ within 1 hour, and then stored in the cold storage at-18℃ for a long time, which can be stored for one year or longer. The quick-frozen longan was taken out at-18℃ and treated with 0.5% citric acid and 0.03% vitamin C solution or 1% citric acid solution, which could keep the peel unchanged for 48 hours.