1 Cold storage
Preservation of cold storage means mechanical refrigeration storage. The common cold storage can be divided into three categories according to the nature of their use: productive cold storage, distributed cold storage and retail cold storage. The production cold storage is generally built in the production area where the supply is relatively concentrated for the frozen processing and storage after the products are concentrated. Such cold storage requires a large cooling capacity and a certain turnover capacity. Distribution cold storage is generally built in large and medium-sized cities or transportation hubs and industrial and mining areas where population is more concentrated, and is used as the market for transit and storage of goods. This type of cold storage also needs a large capacity for refrigeration, and is suitable for storage of multiple varieties. Therefore, it is usually compartmentalized into several storage rooms, which can maintain different storage temperatures, transport within the warehouse to be smooth, and throughput should be rapid. Retail cold storage is generally a type of cold storage used by the retail sector. Its library capacity is small, the storage period is short, and the storage temperature can be changed as needed. At present, most of the cold storage areas in China belong to productive or distributive pools, and they are often used together. Raspberry berries are soft and juicy, and should not be stored at room temperature. It is best to sell them on the day of harvest or send them to a processing plant for processing. At present, almost all of the fruit berry fruits in Shangzhi City of Heilongjiang Province are sent to local quick-frozen processing plants for quick freezing and then exported. The so-called quick freezing means that in the time of freezing, the temperature of the center of the fruit falls from -1°C to -5°C within 30 minutes; or in terms of speed, the freezing speed is greater than or equal to 5 to 20 cm/hour. Raspberry berry quick-frozen maximizes its inherent color, aroma, and texture, thawed berries are close to the texture of fresh fruit, and cellular fluids do not escape in large quantities. Raspberry berries have a long shelf life after quick freezing and can provide processing materials for processing plants for a longer period of time, or they are exported to foreign countries.
2 Atmosphere Storage and Plastic Film Packaging
Fresh-keeping storage is the method of putting fruits in a relatively tight storage environment, and at the same time changing and adjusting the ratio of gas components such as oxygen, carbon dioxide and nitrogen in the storage environment and stabilizing them within a certain concentration range. The controlled atmosphere storage is carried out while maintaining a low temperature. Therefore, in addition to the storage facilities, there must be high airtightness in the storage area, and the warehouse should be able to withstand a certain pressure. Atmosphere storage can be divided into controlled atmosphere storage and spontaneous atmosphere storage.
2.1 Air-conditioning In addition to the features of ordinary cold-storage, the air-conditioned cold-storage cold storage should have high air-tightness to maintain the gas concentration required by the air-conditioning warehouse. The structure and equipment of the air-conditioning refrigerator in terms of heat insulation, cooling, and maintenance are the same as those of the conventional refrigerator, except that the former requires a certain degree of airtightness, and the library must be able to withstand a certain pressure when the air pressure changes. For this purpose, an airtight layer is usually added inside the insulation. Technically speaking, air tightness is considered good when objects stored in the library consume more oxygen than leaked oxygen. The general rule of thumb is that a positive or negative pressure of 10 mm water column is caused by inflating or pumping the warehouse. It does not return to zero within 30 minutes.
2.2 The plastic film is packaged in a small package. The plastic film is pressed into a bag and the fruit is packed in a bag. The bag is tightly closed and becomes a sealed storage place. Plastic bags can be stacked directly on shelves in a freezer or ventilated storage, or they can be placed in baskets (boxes). The fruit baskets (boxes) are stacked in stacks and stored. Some of the fruit baskets are packed in plastic bags, which are then tied tightly and then stored in the storage room. According to their management methods, they can be divided into the following three types:
2.2.1 Regular adjustment or air release: Sealed bags are mostly made of 0.05 to 0.07mm thick polyethylene plastic film bags with a length of 100cm and a width of 80cm. Each bag of fruit 15 ~ 20kg. Because of the respiration of the fruit inside the bag, the oxygen in the bag is reduced and carbon dioxide gradually increases. When the gas composition exceeds the required specifications, the bag opening is released, fresh air is replaced, and the bag is closed again.
2.2.2 Do not adjust gas: The thickness of the plastic film bag is 0.025~0.03mm. The film is thin and breathable, and it is possible to maintain proper low oxygen and high carbon dioxide levels without harmful effects for a long period of time. Therefore, it is not necessary to perform air conditioning or air release. This method is suitable for short-term storage, long-distance transportation or retail sales.
2.2.3 Silicon window bag storage method: The silicone rubber film is embedded in a plastic film bag. Using the special permeability of silicone rubber, the high carbon dioxide inside the bag penetrates through the silicone rubber window and the external oxygen penetrates inside. Its penetration ratio is 6:1, so that it plays an automatic adjustment role. 3 Other methods for storage and preservation 3.1 Electromagnetic treatment 3.1.1 High-frequency magnetic field treatment: The product is placed directly in or through the magnetic field of the electromagnetic coil and is directly affected by the magnetic field lines.
3.1.2 High voltage electric field treatment: The product is placed in or through a high voltage electric field consisting of metal plates. There may be such effects: the direct action of the electric field; the formation of ion air effect by the high-voltage discharge; the effect of the odor produced by the discharge, and so on.
3.1.3 Ion air and ozone treatment: The product is not directly in the electric field, but ionized air and ozone treatment products formed by high-voltage discharge. It has been reported that negative ion air has the effect of inhibiting physiological activity on some fruits. Positive ion air often plays a promoting role. Ozone is a strong oxidant, and there may be other physiological effects besides the disinfection and preservation. Electromagnetic treatment is used for fruit storage and is still in the experimental stage. Some devices are still indeterminate, and the mechanism of action needs to be further explored.
3.2 Storage under reduced pressure
Decompression storage of fruits is one of modern storage methods. The technical point of decompression storage is that the product is placed in a closed room, some air is drawn from the sealed room, the internal pressure is reduced to a certain degree, and a constant low pressure is maintained during storage. Decompression storage can also be said to be a special atmosphere storage method. In decompression storage, the control of the amount of oxygen and relative humidity is more accurate than ordinary controlled atmosphere storage.
3.3 Radiation treatment
Radiation storage technology mainly uses gamma (γ) rays generated by 60 Co (60Co) or 137 铯 (137CS), or electron flow generated by an electron accelerator having an energy of 10 MeV (million electron volts) or less. Gamma ray is a kind of ray with strong penetrating power. When it passes through biological organisms, it will ionize water and other substances, generate free radicals or ions, which will affect the body's metabolism, and when serious, it will kill the cells. . The penetrating power of the electron flow is weak, but it can also play an ionizing role. From the perspective of food preservation, radiation treatment is the use of ionizing radiation to cause insecticidal, bactericidal, fungicidal, and physiological and biochemical effects.
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