Cold chain storage method for fresh-keeping storage of fruits and vegetables

Vegetables and fruits are one of the main food and nutrient sources for people to survive. During the preservation and storage process, their nutritional components and color will undergo various changes. The shelf life will be shortened and the corruption caused by unfavorable factors will be controlled. The effects of deterioration, loss of nutrients, deterioration of flavor and color, and deterioration of texture require the establishment of a cold chain storage environment suitable for fresh-keeping storage of fruits and vegetables.

Cold chain storage is a low temperature storage process based on refrigeration technology and using refrigeration technology as a means. The cold chain storage environment suitable for fresh-keeping storage of fruits and vegetables mainly refers to soft and hard systems such as temperature, humidity and gas composition and its control elements. We hope to improve the packaging and storage forms, storage and transportation management methods, temperature and humidity monitoring and unit operation control system, cold chain data management in the cold chain storage process by researching and analyzing the fresh-keeping process of fruits and vegetables, cold chain storage process and its control factors. Efficient operation mode such as platform, effectively improve and optimize the cold chain warehouse management process, and make it comply with relevant regulations and standards, so that enterprises can find the best balance between operating cost and quality control to fully guarantee the quality of fruits and vegetables and ensure food safety. , adjust production and sales, balance the market, reduce circulation loss.

In combination with the characteristics of fruit and vegetable products, there are mainly four methods for fresh-keeping storage of fruits and vegetables at this stage: ordinary refrigeration, modified atmosphere storage, decompression storage and ice temperature storage, and then we introduce them one by one.

1. Temperature characteristics

Temperature is the most important factor in the storage of cold and chain storage of fruits and vegetables, which affects the various physical and chemical processes of fruits and vegetables and affects the activities of microorganisms. The quality change of frozen fruit and vegetable products mainly depends on the control range of temperature and humidity, the temperature change of fruits and vegetables, and even the temperature gradient between the surface temperature and the internal temperature of fruit and vegetable products will affect its quality.

Generally speaking, when the temperature rises, the respiration, transpiration, hydrolysis, and post-aging aging effects of fruits and vegetables will increase, and the proportion of hypoxic respiration will increase, and the peaks of some fruits and vegetables will appear early, for the peak of breathing. Fruits and vegetables can inhibit post-ripening and prolong the storage period by inhibiting or delaying the peak period; under the conditions of appropriate low temperature conditions, cooling methods and unit packaging requirements, the original coordination of various metabolic links between fruits and vegetables remains. Balance, the most reasonable storage and preservation environment conditions can be obtained; the temperature changes frequently, which is harmful to the preservation of fruits and vegetables, and has a stimulating effect on the metabolism of fruits, vegetables and microorganisms. The temperature change will cause fluctuations in air humidity, so Fruits and vegetables should be kept at a low temperature and relatively stable when stored and stored.

Ordinary refrigeration, also known as cryopreservation, refers to a method of storage under ambient conditions between 0 °C and 10 °C. This method relies on the low temperature action to inhibit the proliferation of microorganisms, and weakens the physiological activities of fruits and vegetables, so as to slow down the purpose of breathing. The cold storage is the most common low-temperature storage facility. It is suitable for storage of many kinds of fruits and vegetables. It has the advantages of being free from natural conditions, simple and easy to store, and long-term storage.

2. Humidity characteristics

In the storage environment of fresh-keeping cold chain of fruits and vegetables, the relative humidity level affects the transpiration of fruits and vegetables on the one hand, and also affects the activity of microorganisms on the other hand, thereby reducing transpiration. To prevent the wrinkles of fruits and vegetables, high humidity should be maintained. However, the higher the air humidity, the more favorable it is for microbial activity, and the more likely it is to cause the decay of fruits and vegetables. Therefore, in the actual control of the storage conditions of fresh-chain cold storage of fruits and vegetables, it is necessary to comprehensively consider the system, taking into account the influence of temperature and humidity, and maintaining the humidity in one. The appropriate level. Moreover, in order to prevent sweating of fruits and vegetables, it is necessary to reduce or eliminate the temperature difference and obtain a relatively stable cold chain storage temperature.

3. Gas composition characteristics

Changing the composition of air in the cold chain storage environment, appropriately reducing the partial pressure of O2 or appropriately increasing the partial pressure of CO2, all have the effects of inhibiting the respiration rate of plants, delaying the post-aging aging process, preventing evaporation of water, inhibiting microbial activity, etc. Loss and prolong the storage period.

The optimal composition of the gas varies depending on the type and variety of the fruit and vegetable, and also varies with the developmental stage, physiological state and storage temperature of the fruit. For general fruits and vegetables, it is appropriate to maintain an O2 concentration of 2% to 5%, and the CO2 and O2 concentrations are equivalent or slightly higher. For the release of volatiles from fruits and vegetables, appropriate air purification measures should be established to reduce their harmful concentrations and adverse effects. The combination of air conditioning and refrigeration is one of the main methods for the storage of fruits and vegetables at home and abroad.

Atmospheric storage, on the basis of low temperature storage, by controlling and changing the air composition, concentration and temperature in the storage, it can effectively inhibit the breathing of fruits and vegetables and prevent the generation of harmful gases (such as ethylene), to some extent reduce evaporation and The growth of microorganisms has the effect of delaying the start of respiratory jump on the climacteric fruits and vegetables, so that the fruits and vegetables maintain the minimum life activities, in order to prolong the fresh state of fruits and vegetables, and to ensure the hardening effect of fruits and vegetables, thereby achieving the purpose of prolonging the storage period.

Vacuum storage, also known as low pressure storage, negative pressure storage or vacuum storage, is a special atmosphere storage method developed on the basis of refrigeration and controlled atmosphere storage. Under low pressure conditions, it can inhibit the respiration of fruits and vegetables, reduce the oxygen content in the air, prevent the accumulation of harmful gases such as ethylene and ethanol during storage of fruits and vegetables, thereby prolonging the shelf life of fruits and vegetables.

4. Ice temperature storage and cell characteristics

The ice temperature refers to the temperature range from 0 ° C to the freezing temperature of the organism (ie, the freezing point). The biological cells dissolve many components such as sugar, acid, salt, polysaccharide, amino acid, peptide, soluble protein, etc., and the freezing point is lower than pure water, and it is in the range of -0.5 ° C to -3.5 ° C. In the temperature zone, the average temperature fluctuation in the library is less than 1 °C, the maximum temperature difference in the library is less than 1 °C, and even the specific temperature zone for storing fruits and vegetables can be precisely controlled. This is still very high for the ice temperature control technology. . The various natural high-molecular substances and their complexes in the cells exist in a spatial network structure, so that the movement and proximity of the water molecules are hindered by a certain hindrance.

Therefore, fruits and vegetables can maintain cell activity in a narrow temperature band between 0 ° C and freezing point, and their respiratory metabolism is inhibited and aging is also slowed down. Preserving stored fruits and vegetables in this temperature range allows it to maintain freshness just after harvest. Therefore, this technology has become the third generation preservation technology after refrigeration and freezing.

Reprinted from the network