What methods are there to extend the storage and freshness period of fresh-eating jujubes?
Jujubes contain a variety of trace elements and abundant nutrients, and have unique nutritional and medicinal value. However, after fresh jujubes are harvested and stored under natural conditions, they have only a few days of crisp freshness, and the flesh quickly turns brown and softens. After several years of experimental research, the author believes that to extend the storage and freshness period of fresh-eating jujubes, the following key techniques must be grasped:
1. Select storage-tolerant varieties
Generally speaking, late-maturing varieties are more storage-tolerant than early-maturing varieties, and dual-purpose varieties have better storage tolerance than fresh-eating varieties. At present, the quality and storage tolerance of Dongzao among fresh-eating jujubes enjoy the reputation of "king of jujube fruits" (Dongzao is generally considered to be a late-maturing variety with a fruit growth period of more than 120 days, usually maturing in mid-to-late October). The relatively storage-tolerant Dongzao varieties include the following: Zhanhua Dongzao, Daxuezao, Xuecheng Dongzao, Chengwu Dongzao, Jiuyueqing.
2. Do a good job of pre-harvest management
Soil, fertilizer and water management in the jujube orchard and the prevention and control of pests and diseases must be done well to enhance the storage tolerance of the jujube fruits themselves. Half a month before harvest, spray the tree canopy and jujube fruits with 0.2% calcium chloride solution and 1000-fold thiophanate-methyl solution to increase the calcium content of the jujube fruits and prevent mold infection.
3. Grasp the appropriate harvest period
Within a certain range (from the white-to-red stage to fully red), the lower the maturity, the more storage-tolerant. Experiments have shown that early-red fruits (more than 25% colored) are the most storage-tolerant, so fresh jujubes for storage should mainly be red fruits.
4. Control the storage environment well
Practice has shown that the suitable storage environment conditions are as follows: ① The freezing point of jujube fruits is lower than that of ordinary fruits. Within the temperature range above the freezing point of Dongzao, the lower the temperature, the better the storage effect. The freezing point temperature differs with different degrees of maturity, so Dongzao at different maturity stages should be treated separately, and it is generally best to keep it at 0°C to 1°C. Under refrigerated conditions, the suitable relative humidity for Dongzao storage is 90% to 95%. ② Under refrigerated conditions, the oxygen content should be controlled at 3% to 6%. Dongzao is a variety that is very sensitive to carbon dioxide, and the suitable carbon dioxide content should be 2% to 4%.
5. Use reasonable storage equipment
On the one hand, jujube storage requires certain low-temperature sealed conditions to reduce water loss and appropriately lower respiration intensity; on the other hand, it must maintain appropriate air permeability to prevent ethanol accumulation. Therefore, during storage, 0.05 mm thick perforated PVC bags are generally used for packaging, which can prevent carbon dioxide poisoning and also maintain humidity inside the bag to ensure the fresh state of the fruit. To store fresh jujubes under low-temperature conditions, generally plastic small bags that can hold 0.5 to 1 kg are used for packaging (2 to 3 small holes each with a diameter of 3 to 4 mm are made on each side of the bag). Jujube fruits that are 25% colored, undamaged, and free of pests and diseases are first soaked in 2% calcium chloride solution for 30 minutes, then pre-cooled at 5°C to 6°C for 1 to 2 days. After the jujube temperature drops to 6°C to 7°C, bag them, tie the bag openings tightly, and place them in a cold storage at a temperature of 0°C to 1°C and a relative humidity of 90% to 95% for storage.
In addition, storage management work must be done well, mainly including the regulation of temperature, humidity, and gas composition. At the same time, conduct sampling inspections every 7 to 10 days, and promptly deal with jujube fruits that are no longer suitable for storage.