A Detailed Guide to Jujube Fruit Storage Methods: Easily Extend the Fresh-Keeping Period

I. Timely Harvesting

Jujube fruit maturity is one of the important factors affecting the fresh-keeping effect of fresh jujube storage. Many studies have shown that jujube fruit maturity is negatively correlated with storage performance: the lower the maturity, the more storage-tolerant it is, and its storage tolerance declines with jujube fruit maturity. White-ripe fruit is better than early-red fruit, early-red fruit is better than half-red fruit, and the storage tolerance of fully red jujube fruit declines noticeably. In 1985, the storage performance at different harvest times at the Fruit Tree Research Institute of the Shanxi Academy of Agricultural Sciences showed that for pointed jujubes picked from the same tree at different maturity stages and stored in a cold store at 0°C±1°C for 90 days, the sound fruit rate of half-red fruit reached over 90%, while the sound fruit rate of fully red fruit was only 43.87%, a very obvious difference. For fresh jujube storage and preservation, most cultivars are best harvested at the half-red stage when about 50% of the fruit has colored. Harvesting too early gives poor quality, while harvesting too late is also problematic; for example, for Lubei winter jujube, the sugar content at the white-ripe stage already exceeds 20% and the taste is already very good, so it can be harvested somewhat earlier.

II. Storage Conditions

Temperature Temperature is the most important factor affecting the storage effect of fresh jujube. Within a certain range, the lower the temperature, the better the storage effect, but it must not fall below the freezing point, otherwise freezing injury is likely to occur. Relevant research has found that the freezing points of jujube fruit differ among cultivars and maturity stages. According to measurements, the freezing point of half-red Lang jujube is -2.4 to 3.8°C. Some cultivars, such as Linyi pear jujube, when stored for a long time at 0°C to -2°C, tend to develop sunken spot chilling injury symptoms on the fruit surface. During storage, attention should be paid to monitoring temperature. For most cultivars, the storage temperature for fresh jujube should be controlled between -0.5°C and 1°C, so that jujube fruit respiration is in a very weak dormant state.

Humidity Fresh jujube is a fruit prone to water loss. According to experiments, after harvest, jujube fruit stored in a single layer indoors at normal temperature loses more than 5% of its water in 24 hours. The taste is no longer fresh. According to tests, under conditions of a storage temperature of 6 to 10°C and relative humidity of 70% to 80%, the water loss rates of Lang jujube, apple and hawthorn stored for 14 days were 22.2%, 1.2% and 11.2% respectively. From this it can be seen that temperature has a very large effect on fresh jujube storage. Research has found that for fresh jujube storage, relative humidity should be controlled between 90% and 95%, and packaging with 0.03 to 0.06 mm non-toxic polyethylene perforated plastic bags gives a good moisture-retention effect.

Gas Composition Different cultivars react differently to gas composition. Many studies have shown that fresh jujube is relatively sensitive to CO2, and CO2 above 2% will accelerate softening and browning inside the fruit. For most cultivars, the suitable gas composition for fresh jujube storage is O2 3% to 5% and CO2 below 2%.

III. Storage Methods

After jujube fruit is harvested, it is packed into special fruit boxes. During transport, be sure to handle it gently, load and unload gently, and prevent bruising damage. Before storage, jujube fruit should be selected, graded, cleaned, disinfected and pre-cooled, and the above procedures should be completed within 1 day. Then the fruit is put into 0.01 to 0.02 mm non-toxic polyethylene or polyvinyl chloride plastic film bags, with each bag holding less than 5 kg. The bag opening is tied tightly, and two small holes with a diameter of 1 cm are made on both sides of the middle part of the bag to facilitate ventilation and remove harmful gases. The bags are placed on multi-layer storage racks, and inspection should be noted during storage. Jujube fruit can also be packed into special storage boxes lined with 0.02 to 0.03 mm non-toxic polyethylene or polyvinyl chloride film, with the film bag opening folded and tied but not sealed dead, and stored in stacks. In recent years, the special fresh-keeping bags for fresh jujube storage developed by the Agricultural Product Storage and Fresh-Keeping Research Institute of the Shanxi Academy of Agricultural Sciences can promptly remove harmful gases inside the bag, require no perforation, and hold about 10 kg per bag.

For the above several storage methods, the warehouse should be disinfected before loading, and the warehouse temperature should be adjusted to a suitable temperature. According to China's current management system, for storage at the production area, it is advisable to choose the 5 to 10 t or 20 t hanging-unit automatic cold storage developed and promoted by the Shandong Institute of Pomology, or the FACA flexible controlled-atmosphere storage, which are relatively economical and practical. Building a small storage with a capacity of 5 t requires an investment of about 20,000 yuan; a storage with a capacity of 10 t requires an investment of about 30,000 yuan; a storage with a capacity of 20 t requires an investment of about 40,000 yuan. Ordinary farmers can generally afford this, and with good management, the cost of building the storage can be recovered in 2 years of storage, or even leave a surplus. On the basis of small cold storages, gradually transition to small controlled-atmosphere storages. Small cold storages are flexible and mobile, and convenient for loading and unloading. If the storage volume is large, a group of small cold storages or a group of small controlled-atmosphere storages can also be built.

IV. Prevention and Control of Storage Diseases

During the fruit growth period before harvest, spraying the trees with 0.2% calcium chloride deep solution and 0.2% to 0.3% potassium dihydrogen phosphate can improve the storage tolerance of jujube fruit and reduce the incidence of physiological diseases. After harvest, treating jujube with fungicides such as TB2 can effectively kill pathogens and pathogenic microorganisms on the surface of jujube fruit, reduce the incidence of fungal diseases, and improve the storage quality of jujube fruit.