Key points of storage and fresh-keeping technology of jujube

Jujube is one of the unique fruits in China, which is rich in nutrition and contains more sugar, protein, fat, iron, calcium, phosphorus and other substances. At the same time, the content of vitamin C and cyclic phosphate gland (CAMP) is also very high, so it has preventive and therapeutic effects on antioxidation and increasing myocardial nutrition in clinical medicine, so it is favored by consumers. However, jujube fruit is a kind of fruit which is not tolerant to storage, it will lose its original quality in about 20 days at room temperature, and it can only be stored for 40 days at low temperature, so the storage and fresh-keeping technology of jujube fruit is very important.

The main results are as follows: (1) the storage characteristics of jujube fruit and the main symptoms of fresh jujube during storage, such as soft wine, flesh browning, rot and so on. Generally, with the extension of the storage period of jujube fruit, the pulp gradually softens, the nutritional composition of the fruit will change greatly, the content of vitamin C and total sugar will decrease obviously, the content of ethanol will increase obviously, and the taste of alcohol can be obviously felt when eating jujube fruit; the appearance of jujube fruit is characterized by water loss and shrinkage, the color of the pericarp deepens, and the pulp turns yellow, brown and even mildew from near the core.

There are many varieties of jujube fruit in China, and the storability of each variety is quite different. Late-maturing varieties are more resistant to storage than early-maturing varieties, dry-fresh varieties are more resistant to storage than fresh varieties, cracking-resistant varieties are more resistant to storage, and large-fruit varieties are usually not resistant to storage.

(2) the harvest maturity of jujube fruit has a significant effect on the storage life of fresh jujube. The jujube fruits picked on a tree at the same time were all red (coloured 100%), semi-red (about 50%) and early red (less than 25%). When stored at 0 ℃, the early red fruit was the most resistant to storage, and the whole red fruit was the worst, so the early red fruit should be selected for long-term storage.

The harvesting methods of jujube fruit often use pole shaking and picking jujube, these methods are more labor-intensive, and the jujube fruit is easy to be damaged during harvest, which affects the storage effect, so it is better to pick the fruit by hand for long-term storage.

(3) Storage of jujube fruit

① simple storage method is suitable for the northern region where the temperature of jujube fruit is low during the ripening season. The mature varieties that can endure storage are selected, and the fruit with semi-red peel is the best. During storage, in order to reduce water evaporation, it should be packed in a perforated polyethylene film bag 0.04 to 0.07 mm thick, sealed, and then stored on a layered storage shelf in a shade shed (or cave).

After the jujube fruit is harvested by ② cold storage method, it should be carefully selected as soon as possible, bagged and stored in cold storage. The method of fruit selection and bagging is the same as the simple storage method. During the storage of jujube fruit, the temperature in the library must be kept stable at (0-1) ℃, the relative humidity should be maintained at 90%-95%, and timely ventilation should be carried out. Prevent the high concentration of carbon dioxide in the air and affect the quality of jujube fruit.

③ modified atmosphere method jujube fruit can not tolerate more than 5% carbon dioxide in the environment, so fresh jujube is not suitable for spontaneous controlled atmosphere storage under closed plastic bags. However, some recent studies have shown that the effect of controlled atmosphere storage of some varieties is better than that of cold storage, such as Liang Xiaoe's study on Junzao jujube shows that the effect of controlled atmosphere storage with 5% oxygen and 0 carbon dioxide is obviously better than that of perforated bags. In addition, Yuanling jujube has a good storage effect under controlled atmosphere with 3% oxygen and 2% carbon dioxide, so whether different varieties of jujube fruits can be applied to controlled atmosphere depends on the variety.

In recent years, some physical and chemical methods, such as coating film, pre-harvest hormone treatment, 60Co radiation treatment, vacuum preservation, heat treatment and so on, have been discussed. Some methods have a certain effect on jujube fruit storage, but no breakthrough has been made, and new methods and techniques are still being explored.