Storage conditions and methods of walnut

  Compared with fruits, walnut kernel has relatively stable physiological metabolism and composition changes, which makes walnut have a relatively long storage period. However, under the condition that walnut is not sold or processed immediately, it is necessary to provide a suitable storage condition for walnut and adopt reasonable storage methods to ensure the quality of walnut kernel.

  1. Storage conditions The length of walnut storage period and the quality of storage effect are determined by two aspects: their own conditions and external conditions. Self-conditions include walnut variety characteristics, nut damage degree, kernel water content, etc. Generally, paper-covered walnut is the least storable, thick-shelled walnut is the most storable; the higher the damage degree, the shorter the storage period, and the longest storage period of intact stone fruit. In contrast, the kernel moisture content is a more important determinant, and the water content of walnut stored for a long time should not exceed 7%.

  ( 1) Temperature of storage environment Low temperature environment is the best condition for walnut long-term storage. The results showed that the storage time of walnut nuts and kernels was prolonged with the decrease of temperature. Some researchers have confirmed that walnut kernel at 10℃, shelf life can reach 1 year, its physical, chemical, sensory and other quality indicators are within the specified range. Another researcher recommended that the best storage temperature of walnut is 0~2℃. Studies have shown that walnut nuts sealed in polyethylene bags can be preserved in good quality for more than 2 years under freezing conditions.

  (2)The control of relative humidity of storage environment is of great significance to whether walnut kernel can maintain color, aroma and texture. Generally, it is appropriate to control relative humidity at 50%~60%. If the relative humidity is less than 40%, the kernel will lose water and dry, reducing the quality of nuts; if the relative humidity of storage environment reaches 70% or more, there will be a large number of molds produced, and the moisture content of the kernel will also increase, which will inevitably affect the storage effect.

  (3)The gas composition of storage environment was similar to that of other fruits, and walnut storage also needed low oxygen and high carbon dioxide environment. Walnut fat content is very high, pay special attention to the oxygen content. In general, the oxygen content of its storage environment should be less than 1. 5%, carbon dioxide or nitrogen concentration of more than 70%, in such an environment, can inhibit respiration, reduce consumption, prevent oxidation, at the same time can inhibit mold activities, prevent mildew, and can effectively reduce pests, rats.

  (4)Management during storage During the storage period of walnuts, regular observation and monitoring should be carried out to remove bad fruits and rotten fruits in time. During storage, the most likely to occur are mildew, pests and the occurrence of odor. The main reason for walnut rot during storage is caused by microbial contamination, some of these microorganisms are infected in the orchard field, and then latent damage, but most of them are infected in the post-harvest treatment process. Walnut fragrant fragrance, rich in protein and fat, easy to attract insects harm. Hala occurs because walnut kernel contains more fat, fat in high temperature, moisture and oxygen when sufficient oxidation occurs easily and produce Hala flavor. During storage, attention should be paid to preventing and handling the above phenomena.

  2. Storage method

  (1)Common storage is divided into dry storage and wet storage two methods. Edible walnuts are generally dry stored, and wet stored for seeding. Before storage, make sure that the walnut nuts have been completely dried. When drying, put the walnuts into bags or sacks and baskets, and put them in ventilated, cool and dry places. Just in case, hang it for storage. During storage, check and flip regularly to prevent rat damage, mildew and fever.

  (2)Walnuts that need to be stored for a long time must have a low temperature storage environment. For small storage quantities, nuts can be enclosed in polyethylene bags and stored in refrigerators at 0~ 5℃. Where there are conditions, a large number of storage can be packed in sacks, stored in low-temperature air-conditioned refrigerators (temperature-1 ° C, relative humidity 50%~60%, oxygen concentration below 1%), the effect is better.

  (3)The principle of plastic film tent storage is similar to that of controlled atmosphere storage. Walnuts harvested and processed in due time are bagged and stacked, stored in a low-temperature place, covered with plastic film, and carbon dioxide gas is charged into the account (nitrogen can also be charged) to reduce oxygen concentration. The content of carbon dioxide can reach more than 50% in the early stage of storage, and then keep about 20%, oxygen is 1. About 5%, the use of plastic tents sealed storage should be carried out in low temperature, dry season, in order to maintain low humidity in the tent. The results showed that after 4 weeks storage at 24℃ with carbon dioxide, its color and flavor were obviously different from those stored in air, and it still had good quality after 25 weeks, but it appeared oil return and deterioration phenomenon when stored in air.