Hypobaric storage and preservation technology

Hypobaric storage and preservation technology

Shanghai Shanrushui Freshness Preservation Technology Co., Ltd. Zheng Xianzhang

（2023.4.12）

Catalogue

1.Introduction

2.Application Fields

3.Product types

4.Product Usage

1）Decompression treatment

2） Reduced pressure storage

3） Reduced pressure storage and transportation

4） Building a vacuum cold fresh chain

5.Technical Sources

6.Technical Types

1） intermittent air extraction type

2） continuous extraction type

7.Basic Principles

8.Research and Application Status

1） Domestic hypobaric storage equipment

2） Products related to preservation research or commercial use

9.So-called existence problems

10.Application Prospects

1.Introduction

Reduced pressure storage refers to the technical method of continuously extracting mixed air from a closed container, delivering fresh air to the outside, maintaining a certain humidity and/or temperature inside the container, and maintaining a set pressure level. It is a modern cutting-edge preservation technology that differs significantly from technologies such as Controlled Atmosphere Storage (CA), Vacuum Precooling, Modified Atmosphere Packaging (MAP), and Vacuum Packaging.

Hypobaric storage and preservation technology is a collective term for the set of preservation process parameters that are matched with hypobaric storage equipment, just like computer hardware and matching software are collectively referred to as computer technology. The commonly used hypobaric storage and preservation technology can refer to both equipment and process parameters.

Chinese name: hypobaric storage

English name Hypobaric Storage, LP

Physical preservation technology with pollution-free properties

Invented by American scientist Stanley P. Burg from 1966 to 1967

2. Application Fields

Fresh products are not frozen for preservation, and food is not frozen for safe storage. Fresh logistics, fresh e-commerce, fresh home accessories. Land, sea. Logistics support supply for troops. Scientific research and commercial use.

3.Product types

Decompression processor, Decompression refrigeration warehouse, Decompression refrigeration car, Decompression refrigeration container, Decompression refrigeration shelter, Decompression refrigeration display cabinet (vacuum refrigeration display cabinet), Decompression refrigeration refrigerator (vacuum refrigerator).

4.Product Usage

Fresh agricultural products and pre made vegetables for preservation; Preservation of cooked food and cultural relics; Antibacterial and insecticidal properties of items; Building a vacuum cold fresh chain, etc. The main uses are in the following four aspects.

1)Decompression treatment

Fresh horticultural products are stored for several hours to several tens of hours in a timely manner after harvesting for short-term processing, either under reduced pressure refrigeration for short-term treatment or only under reduced pressure for short-term treatment, collectively referred to as reduced pressure treatment. Postharvest processing of horticultural products such as fresh vegetables and fruits in their place of origin (similar to pre cooling but different from pre cooling, with better effectiveness and applicability than pre cooling. Cold chain 'first one kilometer' processing equipment can extend the cold chain 'last one kilometer' preservation after this treatment). Its function:

① Quickly and effectively inhibit respiratory heat and ethylene production, reducing both production rates to below 90% within 1 hour;

② Reduce field heat;

③ Inhibiting the growth of pathogenic bacteria, including molds;

④ Kill insects;

⑤ Inhibiting the increase or decrease in the activity of several enzymes that affect the maturation and aging of fresh horticultural products, such as PAL, PPO, POD, SOD, CAT, etc;

⑥ Suppress water loss. After this treatment, the water loss rate in the subsequent circulation process is generally lower by more than 20% compared to those without this treatment;

⑦ Delaying the decay rate of original quality (appearance, nutrients, taste, taste, etc.) or improving certain qualities, including after cooking;

⑧ Tropical fruits such as peach, banana, and guava can be ripened later;

⑨ Reduce or delay the occurrence of cold damage to fresh horticultural products.

The low-pressure acclimation effect during the post harvest decompression treatment of fresh horticultural products can have a "5-day" subsequent preservation effect after leaving the decompression environment:

(1) Extend the refrigeration and preservation period.

For example, the good mushroom rate of Morchella esculenta produced in Yunnan for 11 days is about 40% compared to the cold storage control. After being treated with O3 concentration of 3g/h, time of 15 minutes and cold storage, it is about 30%, and after being treated with reduced pressure cold storage for 2.5 hours and cold storage, it is about 90%; The occurrence period of chilling injury of Mount Taishan No. 1 kiwifruit was extended from 4.5h of decompression and cold storage to 80d of cold storage control, that is, the cold storage period was extended by 20d (Shandong Fruit Research Institute, provided by Dr. Zhang Xuedan).

(2) Extend the cold chain break (so-called room temperature) preservation period in high or low temperature environments.

For example, fresh cut concanavali beans do not undergo browning at room temperature of 18-33 ℃, after being treated under reduced pressure for 23 hours and room temperature for 54 hours, while browning occurs at room temperature control for 23 hours; The suitable storage temperature for mangoes is 12-13 ℃. After decompression treatment, they will be stored in a natural environment in Shanghai for 36 days from January to February. Among them, the temperature will be below 0 ℃ for 5 days, the lowest temperature will be 6 ℃ and below for 30 days, and the highest temperature will be 13 ℃ and above for 10 days. The cut surface will have no obvious cold damage, no frostbite, and all are edible. The cut surface will have severe frostbite and almost no edible food compared to the 32 day cut surface.

(3) Delaying the decay rate of original quality and even improving certain qualities.

For example, the anthocyanins of the brilliant blueberry produced in Northeast China increased by about 90% after 14 days of refrigeration compared to before the experiment; After 1-MCP treatment and refrigeration, about 103%; Reduced pressure refrigeration treatment for 12 hours+refrigeration for about 161%; The chlorophyll content of fresh cut vegetables processed after 46 hours of reduced pressure refrigeration treatment and 5 days of refrigeration is 28.3% higher than that of the refrigerated control (provided by researcher Zhao Botao from Nanjing Institute of Wildlife Comprehensive Utilization of the All China Federation of Supply and Marketing Cooperatives); The loss rate of Vc content in Yunnan produced red peppers before and after cooking was 15.9% after vacuum refrigeration treatment for 24 hours+refrigeration for 12 days+room temperature for 3 days+cooking, and 18.1% for refrigeration control (provided by Associate Professor Kan Ankang of Shanghai Maritime University).

(4) Delaying the onset of pathogenic bacteria.

For example, the incidence of tiger skin disease in green banana apples decreased from 10.4% to 2.9% compared to the control group treated with reduced pressure refrigeration for 4.5 hours and 90 days (provided by Dr. Zhang Xuedan from Shandong Fruit Tree Research Institute).

(5) Delaying the occurrence of surface and internal browning.

For example, the occurrence time of browning on the cut surface, fresh cut beans, refrigerated control for 102 hours, decompression treatment for 23 hours+refrigerated for 171 hours; Freshly cut vegetables and yams, refrigerated for 24 hours, reduced pressure refrigerated for 29 hours+refrigerated for 24 hours+ 2.25h@36 ℃+14h。

Fresh cut vegetables. Fresh vegetables, fruits, and edible mushrooms that are processed by washing, cutting, and other processes after being harvested are called fresh cut vegetables. The procedure for reducing pressure treatment of fresh cut vegetables mentioned in this article must be: reducing pressure treatment of the original vegetables+processing. If inverted, the preservation effect is poor. Freshly cut vegetables treated with reduced pressure also have a "5 delay" subsequent preservation effect.

2）Hypobaric Storage（Similar to refrigeration, the effect is better than refrigeration）

Reduced pressure storage refers to the long-term unfrozen storage of fresh horticultural products (vegetables, fruits, edible fungi, flowers, traditional Chinese medicine), meat and poultry products, aquatic products, prefabricated vegetables, as well as the preservation of cooked food, grains, fabrics, leather, calligraphy and painting, archives, dried traditional Chinese medicine, animal carcasses and their internal organs.

Storage has all the effects of the "origin treatment" or decompression treatment mentioned above, but the subsequent "5 extensions" have better preservation effects, better antibacterial and insecticidal effects during storage, and better preservation or preservation effects. Compared with refrigeration technology, the main advantages are as follows.

① Extend the refrigerated storage and transportation period by 2-9 times.

For example, bananas can be refrigerated for about 14-21 days, controlled atmosphere refrigeration for about 42-56 days, and reduced pressure refrigeration for up to 150 days, and can naturally ripen (after ripening); Roche's marsh shrimp has a peeling, turning around, and foul odor when refrigerated for 6 days, and is intact and odorless when refrigerated under reduced pressure for 20 days.

② After leaving the decompression environment, the refrigerated shelf life and/or room temperature shelf life can be extended.

For example, beef is refrigerated for about 12 days, with a shelf life of 0, reduced pressure for about 41 days, and refrigerated shelf life of 8-9 days; Double spore mushrooms (white mushrooms) are refrigerated under reduced pressure for 505 hours 25h@22 -32 ℃, without browning or canopy opening, with a shelf life of up to 41 hours at room temperature of 22-32 ℃.

③ Fresh cut vegetables have a refrigerated shelf life of more than 3 days, and a normal temperature shelf life of more than 4 hours in summer.

For example, fresh cut vegetables processed under reduced pressure refrigeration in an uncontrolled temperature and bacteria free environment have a shelf life of (a) 60 days for West Blue Flower; Rice scallions, sweet peppers, and spinach for 18 days; 5 days for small green vegetables, green beans, white mushrooms, apricot mushrooms, water spinach, etc; Lotus root, yam, thin skin green pepper, etc. for 4 days. (b) Shelf life at room temperature in summer: Green vegetables refrigerated for 6 days+room temperature for 24 hours; Chill water bamboo for 3 days+room temperature for 53 hours.

④ The original quality of the item is maintained well.

For example, green asparagus still shows its original green color, tender and sweet taste, and has not undergone fibrosis after being refrigerated for more than 50 days under reduced pressure; White mushrooms are refrigerated under reduced pressure for 402 hours: 1)+refrigerated for 104 hours, with an opening rate of only about 10%. 2)+30 hours @ 27~29 ℃ during the shelf life, the overall white color is clean without browning spots, and the opening rate is only about 3.3%; Before the experiment, there were 7 volatile compounds in Tricholoma matsutake, and 8 compounds (2 of which disappeared and 3 new compounds were added) and 6 compounds (3 of which disappeared and 2 new compounds were added) under reduced pressure refrigeration for 20 days or reduced pressure refrigeration treatment+refrigeration for 20 days, respectively. There were 15 compounds in refrigerator refrigeration control (3 of which disappeared and 11 new compounds were added compared to before the experiment). This indicates that fresh Tricholoma matsutake has maintained its original aroma well through reduced pressure refrigeration or short-term treatment followed by refrigeration. After 56 days of reduced pressure refrigeration of celery, the loss of protein, Vc, and chlorophyll was less than half of that of the refrigerated control. Protein loss rate: 44.4% during refrigeration, 19.4% during reduced pressure refrigeration; Vc loss rate: refrigerated 64.5%, reduced pressure refrigerated 27.1%; Chlorophyll loss rate: 63.2% during refrigeration and 10.5% during reduced pressure refrigeration.

⑤ Effectively inhibit the decay of nutrient content.

For example, when white cauliflower is treated with reduced pressure refrigeration, modified atmosphere packaging (MAP), and refrigerated for 104 days, the overall white and edible rate is 95% on average, and the Vc content is 37.8mg/100g on average. The refrigerated control is black, rotten, and non edible; Broccoli was cut, cleaned, and packaged in a temperature and bacteria free environment after being refrigerated under reduced pressure. After being refrigerated for 49 days, it showed no mold, rot, and an average Vc content of 45.8mg/100g. The average content of gray mold, black rot, and Vc in the refrigerated control was 3.4mg/100g, which was 13.47 times higher than that in the refrigerated control.

⑥ Fruits that are left under pressure and refrigerated can naturally ripen (after ripening).

For example, the peach produced in Changzhou, Jiangsu, still has a peach flavor after being processed under reduced pressure and refrigerated for 20 days+5 days at room temperature @ 25 ℃. So far, only hypobaric storage or hypobaric treatment techniques can ripen peaches, and no other techniques have been found to accelerate their ripening. Bananas and other fruits can also ripen naturally after leaving the vacuum storage.

⑦ Inhibiting the growth of pathogenic bacteria such as fungi, molds, and yeast.

For example, unpackaged tofu and dried tofu purchased from the vegetable market are stored naked for 20 days and 27 days under reduced pressure, respectively, without mold, odor, or stickiness; Bean paste buns, meat buns, and vegetable buns purchased from the vegetable market are refrigerated under reduced pressure for 70 days without mold, odor, and elasticity; The black bone chicken was slaughtered in the vegetable market, and from pre experiment to reduced pressure refrigeration for 16 days, Salmonella was detected to not detected, the total number of colonies increased from 6.6 * 105cfu/g to 5.5 * 105cfu/g, and the volatile base nitrogen increased from 3.5mg/100g to 3.3mg/100g; The total bacterial count of pork purchased from the vegetable market during reduced pressure refrigeration for 6 days, 15 days, and 26 days is 49 * 105cfu/g, 19 * 105cfu/g, and 12 * 105cfu/g, respectively.

⑧ Kill adults, larvae, pupae, and eggs inside and outside the storage.

For example, peach aphids, waxberry fruit flies (white rice like insects), fruit flies from tropical fruits, mung bean weevils from mung beans, corn residue insects, etc.

⑨ Low water loss rate of storage.

For example, bayberry and lychee aged 37 days, pork and beef aged 26 days showed no weight loss; The weight loss rate of vegetables stored under reduced pressure for 41 days is less than 2%; The weight loss rate of meat buns stored under reduced pressure for 70 days is 0.61%; The weight loss rate of honey peaches produced in Changzhou, Jiangsu Province during reduced pressure refrigeration for 20 days+5 days @ 25 ℃ at room temperature is 5.7%. The weight loss rate of peaches after 12 hours of reduced pressure refrigeration and 20 days+5 days @ 25 ℃ at room temperature is 7.10%, and the weight loss rate of peaches after 5 days @ 25 ℃ in refrigerator refrigeration is 9.48%. The weight loss rate of peach under reduced pressure refrigeration is only 60% of that of the refrigeration control.

⑩ Different items can be mixed and stored without any odor, and can be opened at any time.

For example, meat, fish, shrimp, strawberries and bean products (tofu, shutter, baked bran, dried tofu, Oily bean curd fruit) are stored in the same vacuum room for dozens of days without flavor.

3）Reduced pressure storage and transportation（Similar to refrigerated transportation, but different from refrigerated transportation, the effect is better than refrigerated transportation）

The above stored items are all transportable. The transportation process is mobile storage.

4) Building a vacuum cold fresh chain（Similar to cold chain, compatible with cold chain, with better preservation effect and economy than cold chain）

There are two basic modes of vacuum cold fresh chain. 1) Decompression treatment+cold chain; 2) The vacuum storage series equipment is composed of its own components. Due to the "5 extension" subsequent preservation effect of decompression refrigeration and decompression treatment, it provides a foundation for "decompression treatment+cold chain". The solution to the problem of cold chain breakage, also known as room temperature preservation, has provided a breakthrough solution to the limitation of the word "cold". It is expected to provide some fresh horticultural products, including fresh cut vegetables, with circulation requirements even when their cold chain deviates from the appropriate temperature or even at room temperature. See 'Application Prospects'.

5.Technical Sources

The universally recognized theory of hypobaric storage was founded by Dr. Stanley P. Burg, an American scientist, and the technology was also invented by him. The world's first invention patent, "Method for Storing Fruit," was applied for by Burg in 1963 and approved by the US Patent Office in 1967 (1967,33333967). It has since received multiple patents. Burg's representative monographs include: 1) Postharvest Physiology and Hypobaric Storage of Fresh Product (hereinafter referred to as the 2004 monograph) published in 2004; 2) The "Hypobaric Storage in Food Industry: Advances in Application and Theory" (hereinafter referred to as the 2008 monograph) was published in 2014.

Regarding origin. According to the textbook "Horticultural Product Storage and Transportation" (edited by Rao Jingping and published by Science Press, 2009) for the 11th Five Year Plan of ordinary higher education institutions, "In 1957, Workman and Hummel found that some fruits and vegetables can further reduce respiration rate and ethylene production by reducing air pressure on the basis of refrigeration, thereby significantly extending their storage life (Edited by Qin Wen and Wang Mingli, Science Press, 2012) also said, "In 1957, Workman and Hummel discovered... simultaneously. In 1957, Workman et al. noticed that the respiratory heat of fresh tomatoes slightly decreased when the ambient temperature was 20 ℃ and the pressure increased by 88mm Hg. Hummel et al.'s report pointed out that the lifespan of several fresh garden products was extended by 20-90% when the pressure was maintained at 658-709mm Hg in a household refrigerator. In fact, the decompression storage and preservation technology was jointly discovered by Stanley P. Burg and his wife (1966) Burg invented it alone (1967).

American scientist Stanley P. Burg, born in 1933, devoted his life to reducing stress storage. From laboratory experimental research to the commercial application research of intermodal containers for highway rail sea intermodal transportation, from the technology of decompression storage equipment to the research on the technical parameters of decompression storage process, we have been persistent for decades to this day. He is a world-renowned postharvest physiologist for fresh horticultural products and the first person to use instruments to detect ethylene. Ethylene (C2H4) gas was discovered by Russian scientist Nel Jubow in 1901 or 1902 and was only detected in apples by Burg and Thimmann, K.V. using a gas chromatograph in 1959. In 1965, under the proposal of Burg, ethylene was recognized as a natural plant hormone, and the international community agreed to Burg's naming of ethylene, which has been used to this day. The 2004 monograph is a 16 volume, 654 pages, weighing 1.64kg, with over 2200 references, summarizing the research achievements of Western scientists over decades. The concepts, theories, and techniques discussed in the two national level university textbooks and other university textbooks, monographs, and commentary papers are often inconsistent with the 2004 monographs. See the Discussion on the Mainstream Viewpoints of Hypobaric Storage Technology and Theory (Zheng Xianzhang, Journal of agricultural engineering, 2017,33 (14): 1-10).

6.Technical Types

At the beginning of this century, some people proposed that hypobaric storage technology can be divided into two types: regular extraction (static) and continuous extraction (airflow). Please refer to "Research Progress in Theory and Technology of Hypobaric Preservation of Fruits and Vegetables" (Wang Li, Zhang Ping, Wang Shijun, Preservation and Processing, 2001, (5): 3-6). It has had a profound impact and has been cited as a classic to this day. The author, under the guidance of Burg, studied the 2004 monograph, developed and sold a series of equipment, and conducted in-depth analysis of several preservation test results. It is believed that there are actually two types of intermittent and continuous extraction types. The former has a technical core of "low pressure", while the latter has a technical core of continuous and uninterrupted "low pressure+high humidity+ventilation". Burg has always been, and only is, a continuous extraction type pressure reducing technology, The 2004 monograph "2 Origin of LP Concept" describes the concept of hypobaric storage as follows: "The 'wet' LP method (Figure 2.1) A vacuum tank is needed to store items. A vacuum pump continuously draws air from the tank, a pressure regulator leaks air into the tank at a certain rate and maintains the set pressure, a humidifier sprays enough moisture to saturate the low-pressure air entering the tank, and a refrigerator controls the temperature of the items‘ The dry type 'decompression method uses the same equipment, replacing the humidifier with a device that controls the extraction speed LP is the abbreviation for hypobaric storage.

1) Regular suction type

The working mode of the regular air extraction type is that the vacuum pump extracts air from the storage room. When the vacuum degree inside reaches the set lower limit value, such as 15kPa, the vacuum pump stops. Due to leakage, the pressure rises to the set upper limit value, such as when the vacuum pump runs again at 20kPa, and so on, the vacuum pump operates repeatedly and intermittently. The pressure difference between upper and lower is the range of pressure fluctuations, which is set by the operator. The humidification and ventilation of the vacuum chamber are also intermittently repeated. It can be seen that it cannot be pumped regularly or "stationary", but only intermittently. A significant feature of using this technology is that the minimum working pressure is ≥ 10kPa and the fluctuation range is ≥ 2kPa. The source of this technology is unknown.

2) Continuous extraction type

The working mode of the continuous pumping type is that the vacuum pump continuously vacuums, humidifies, and exchanges air, that is, continuously operates the technology of "pumping, humidification, and exchange" and "three consecutive" simultaneously. It can be seen that it is not simply a "airflow". Continuous "air extraction, ventilation, humidification, and low temperature" results in better results. The concept of "three consecutive" simultaneous operation technology did not directly appear in Burg's monographs, papers, and patents, but was recognized by Burg - since February 2005, the author has been in contact with Burg. The pressure fluctuation value of the continuous suction type is designed by the designer and controlled by the PLC, and cannot be changed by the operator. The continuous suction type of Shanru Water Company's products can have a minimum working pressure as low as 0.5kPa, and the average pressure fluctuation value can be no more than ± 0.03kPa. On page 2 of the 2004 monograph, it is described as follows: "35 years ago, in order to avoid low O2 injury, the earliest experiments were conducted at a pressure of 25-42kPa (O2 concentration of 3.9-6.6%). Later, it was tentatively reduced to 5.33-10.66kPa (O2 concentration of 0.8-1.9%). Finally, it was found that 1.33-2.67kPa (O2 concentration of 0.15-0.3%) was more effective, and now it seems that lower pressure is easy to achieve and may be better." In the past 10 years, research in China has shown that cherry vacuum refrigeration for 30 days The working pressure was 600Pa, the Cuiguan pear was refrigerated under reduced pressure for 60 days, and the working pressure was 500Pa, all of which did not cause low O2 concentration injury.

The continuous pumping type has a much better preservation effect than the intermittent pumping type. The main technical defects of the intermittent air extraction type include inability to kill insects, high water loss rate, poor antibacterial effect, poor quality degradation inhibition effect, and short shelf life.

7.Basic Principles

When a closed container (vacuum chamber) continuously extracts air while continuously delivering fresh air that is close to saturation, namely continuous extraction, continuous humidification, and continuous air exchange, the air entering the vacuum chamber will undergo rapid expansion. When the working pressure is below 1330Pa, the concentration of O2, CO2, C2H4, NH3, ethanol, acetaldehyde, etc. in the air will decrease by about 99%; The respiratory heat, ethylene production, and heat transfer capacity of fresh garden products are suppressed by over 90%. Continuous and uninterrupted "low pressure, high humidity, ventilation" or "low pressure, high humidity, ventilation, low temperature" create a good storage environment for items: effectively inhibit the activity changes of several enzymes that affect the maturity and aging of fresh horticultural products; Effectively inhibit the loss of nutrients such as ascorbic acid Vc, soluble solids and titratable acid, and prevent C2H4 from forming enzymes; Effectively reducing convective heat transfer, effectively suppressing the generation of respiratory heat, and high relative humidity to effectively reduce the water loss rate of storage; Extremely low concentrations of O2 and CO2 effectively inhibit the proliferation of fungi, molds, bacteria, and yeast, as well as effectively kill insects; The extremely low CO2 concentration causes plant stomata to open in the dark, as continuous ventilation can reduce the O2 concentration that horticultural products can tolerate to less than 0.1% without causing hypoxia damage; Due to dynamic continuous low pressure and ventilation, volatile harmful metabolites such as ethylene, ethanol, and acetaldehyde in the product tissue in the vacuum chamber are promptly discharged outside the vacuum chamber.

The most important preservation measures for fresh products are to suppress respiratory intensity, inhibit ethylene production, reduce water loss, inhibit bacteria and preservatives, and kill insects. The simultaneous operation of "3 consecutive" and "4 consecutive" conditions creates such a storage environment. Fresh agricultural products are in a dormant state in a vacuum refrigeration equipment or after leaving for a period of time. Therefore, vacuum refrigeration technology is the most effective physical technology for preserving fresh products.

At an O2 concentration of 0.13%, the average growth rates of R. Stolonifer, A. tenuis, B. cinerea, and C. herbarum were inhibited to 17%, 12%, 10%, and 4%, respectively. Under a pressure of 2kPa and 9.4 ± 0.1d, all eggs and larvae of the Caribbean fruit fly (Anasterpha suspensa Loeu) were killed.

Bacteria and bacterial toxins, mold and fungal toxins, viruses, parasites and insect eggs, insects, and natural toxins from animals and plants cause biological pollution to food. Agricultural chemicals, food additives, and packaging materials may contain polychlorinated biphenyls, which can cause chemical pollution. The above pollution can cause diseases. E. carotovora, Pseudomonas aeruginosa, and other bacteria can cause soft, rotten, and unpleasant odors in vegetables; However, B. cinerea and G. candidum can cause vegetable acid rot and root rot; Mold, yeast, etc. can cause fruit to become soft, sour, rotten, brown, etc; Mold, yeast, etc. can cause meat to become sticky, discolored, moldy, and foul smelling; Pseudomonas, fungi, etc. can cause sticky and unpleasant odors in poultry; Pseudomonas and other bacteria can cause sticky and unpleasant odors in fish and shellfish. Reduced pressure refrigeration technology can greatly reduce the concentration of volatile pollutants in the storage environment while effectively inhibiting microbial growth and killing insects. Therefore, vacuum refrigeration technology is also an effective physical technology for food safety preservation.

From the above "technical sources, types, and basic principles", it can be seen that the vacuum storage and preservation technology was not developed by lowering the air pressure on the basis of refrigeration, nor was it a special type of controlled atmosphere technology further developed on the basis of controlled atmosphere. It has no origin with controlled atmosphere, and the initial discoverers were not Workman and Hummel, but Stanley P. Burg and his wife.

8.Research and Application Status

1）Hypobaric Storage Equipment

① At the end of the last century, the Baotou Agricultural New Technology Research Institute (formerly known as the Baotou Agricultural Machinery Research Institute of the Ministry of Agriculture) received funding from the Ministry of Science and Technology of the People's Republic of China to research pressure reducing refrigerated containers. However, the prototype that came out was a vacuum chamber with a volume of 2000m3, which belonged to the intermittent pumping type according to its invention patent. The cylindrical vacuum chamber structure was very similar to the Grumman pressure reducing refrigerated warehouse in the 2004 monograph, and no sales information was found. The author, who was then the Chief Engineer of Yangzhou Tongli Refrigerated Container Co., Ltd., was invited to send relevant department heads to Baotou to discuss technical cooperation with him, but it was not resolved. Later, there was no information about the release of his reduced pressure refrigerated container. The vacuum chamber of a 2000m3 vacuum refrigerated storage needs to be equipped with a cold storage facility.

② At the beginning of this century, Shanghai Fresh Green Vacuum Preservation Equipment Co., Ltd. (hereinafter referred to as Fresh Green Company) sold plastic cylindrical vacuum chambers, multi vacuum chamber vacuum refrigeration experimental machines with a capacity of about 20L, as well as rectangular steel vacuum chambers, and reduced pressure refrigeration warehouses with a capacity of 6 and 12.5m3. Subsequently, a small and simple vacuum storage device (with unknown vacuum chamber volume) developed and produced by the National Agricultural Products Preservation Engineering Technology Research Center (Tianjin), consisting of metal or non-metallic pipes and plastic films, entered the market. Both products belong to the intermittent air extraction type and require cold storage support. After a few years, both products were withdrawn from the market and no subsequent products were released. The Fresh Green Company closed around 2010.

③ In 2008, Shanrushui Company, founded by the author, successfully developed the JYL2 vacuum refrigeration warehouse with a continuous pumping type, steel rectangular body, and a vacuum chamber volume of 2m3. It was certified as a high-tech achievement transformation project in Shanghai, and later successfully developed a series of products, including intermittent pumping type and continuous pumping type, including experimental machines and commercial warehouses. The vacuum chamber volumes were 0.03, 0.1, 0.2, 0.5, 0.85, 2, 5, 20, 23, and 50m3, respectively, Most of them have entered both military and civilian markets. At present, for continuous air extraction products, under the operating conditions of "3 consecutive" or "4 consecutive" simultaneously, the minimum pressure value is 500Pa, the average pressure fluctuation value is not more than ± 30Pa, and the RH can be close to saturation. The minimum temperature is 0.5 ℃, and the average fluctuation value is about ± 1 ℃. The preservation process technical parameters such as pressure, RH, temperature, etc. can be set and displayed on the touch screen, and can be viewed by mobile phones. The product comes with its own insulation enclosure, without the need for cold storage support. Furthermore, the project funded by the Shanghai Municipal Science and Technology Commission and the Ministry of Science and Technology regarding the technological innovation of vacuum storage equipment by Shanru Water Company was included in Burg's 2014 monograph "Chapter 1: History of Vacuum Storage"

④ In 2010, SIEMENS vacuum refrigerated refrigerators were seen in the Shanghai market, with a vacuum chamber capacity of about 10L and an unknown type of air extraction.

2) Products involving preservation research or commercial use

In the 2004 monograph, 27 types of fruits, 25 types of vegetables, 37 types of flowers, 20 types of meat, poultry, and aquatic products were listed as experimental data or commercial operation data for vacuum refrigeration. In the 1970s and 1980s, 40 foot reduced pressure refrigerated containers transported avocados from Mexico to Stockholm, cherries from Washington State to Stockholm, lemons from Brussels to Rotterdam, papayas from Hawaii to the West Coast of the United States, pineapples from Taiwan to Japan, and tomatoes from the Dominican Republic to New York; Over a decade, millions of fresh cut roses were transported from Colombia and the Dominican Republic to the United States, and from California to Chicago; Transportation of beef, pork and veal; Transport lamb produced in Australia to Arab countries, Iran, or the west coast of the United States, with a storage and transportation shelf life of up to 55 days. Since 2009, the United States has been using vacuum refrigerated warehouses for commercial storage and preservation of fresh flowers, mangoes, etc.

Since the end of the last century, more than 60 types of fresh agricultural products and cooked food have been preserved and insecticidal in China, and experimental research has been conducted in the laboratory or commercial large-scale operation research has been conducted in the production area.

Fruits such as winter jujube, pear jujube, peach, yellow peach, kiwifruit, loquat, bayberry, strawberry, blueberry, raspberry, mulberry, plum, apricot, persimmon, lychee, cherry, jujube, pear, grape, mango, pomegranate, watermelon, etc; Vegetables such as green vegetables, celery, spinach, lettuce, Chinese cabbage, cabbage, scallions, Malantou, broccoli, cauliflower, water bamboo, cucumber, garlic, ginger, lotus root, oil beans, winter bamboo shoots, lettuce, green asparagus, lotus seeds, Chinese toon, etc; Edible mushrooms such as Tremella fuciformis, Agaricus bisporus, Matsutake, etc; Livestock and poultry products such as pigs, cows, chickens, ducks, geese, etc; Aquatic products such as crucian carp, silver carp, bream, pomfret bream, yellow croaker, sea shrimp, Roche's marsh shrimp, etc; Cooked food such as Mantou, bean paste buns, meat buns, vegetable buns, shredded radish buns, pancakes, etc; Semi finished products such as tofu, shutter, Oily bean curd fruit, baked bran, etc; Red roses and lilies; Antibacterial and insecticidal. The research on the commercialization and large-scale operation of reduced pressure refrigeration in production areas is ongoing.

Research on decompression treatment has only appeared in China to this day. Since the beginning of 2011, over 90 fresh horticultural products and over 40 fresh cut products have been tested and studied in the laboratory or commercialized for large-scale operation in the production area.

Raw materials. Fruits such as peaches, pomegranates, cherries, apples, winter jujubes, flat peaches, kiwifruit, blueberries, bayberries, lychees, mangoes, goji berries, jiabao fruit, bananas, sugar oranges, pineapples, yellow peel, banana, etc; Vegetables such as green cabbage, small green cabbage, chicken hair cabbage, Chinese cabbage, Hangzhou cabbage, lettuce, beef heart cabbage, cabbage, coriander, ball lettuce, cattail, thin stem mustard, thick stem mustard, olive, spinach, water spinach, watercress, black cabbage, oilseed, leek, Malan head, pea tip, goji leaf, lettuce leaf, chrysanthemum, Artemisia annua, green onion, red onion, white onion, white cauliflower, broccoli, okra, kidney beans, jar beans, sweet peas Garlic seedlings, tomatoes, winter bamboo shoots, lotus seeds, white eggplants, purple eggplants, bitter melons, cucumbers, watermelons, luffa, lettuce stems, yams, white radishes, ginger, garlic, sweet potatoes, etc; Edible mushrooms such as Tricholoma matsutake, Boletus, Morchella, Agaricus bisporus, shiitake mushroom, mushroom, mushroom, white mushroom, white jade mushroom, etc; Fresh cut flowers such as red roses, pink lilies, chrysanthemums, violets, pink roses, pink plums, etc; Corn with and without wrapped leaves; Malt; Sliced bread; pork.

Freshly cut vegetables. Such as green vegetables, small green vegetables, chicken hair vegetables, lettuce, Hangzhou cabbage, Chinese cabbage, cabbage, oil wheat, beef heart vegetables, celery, spinach, leek, coriander, large leaf water spinach, bamboo leaf water spinach, amaranth, Malantou, Wuta Cai, lettuce leaves, lettuce stems, broccoli, white cauliflower, concanavalis, potatoes, jar beans, sweet potatoes, yams, yams, water bamboo shoots, watermelons, cucumbers, bitter gourds, luffa, sweet peppers, thin skin green peppers, red peppers, scallions Vegetables such as lotus root, white eggplant, purple eggplant, carrot, white radish, and edible mushrooms such as apricot mushroom, tea tree mushroom, white mushroom, agaricus blazei, and white mushroom; Apple.

9.So-called existence problems

Extremely prone to dehydration and wilting, poor ripening, loss of original aroma and flavor, may cause new physiological disorders and new growth

The long-standing and widespread spread of so-called defects in hypobaric storage technology, such as physical diseases, being in the laboratory stage, not accumulating high CO2 like CA, pressure resistance, and cost, have become key factors hindering the development of hypobaric storage and preservation technology. Because none of the above viewpoints can hold true! The Discussion on the Technology and Theoretical Mainstream of Hypobaric Storage (Zheng Xianzhang, Journal of agricultural engineering, 2017,33 (14): 1-10), from theory to practice, uses solid data to comprehensively and deeply explain that the above-mentioned so-called technical defects do not exist. So far, there is no refutation article or challenge information. This article has caused a relatively enthusiastic response both domestically and internationally. Among the 41 articles in this issue, this article has consistently ranked second in click through rate. The American Engineering Index (EI) includes the full English abstract of the article and edited the keywords, with an Access number of 20174104263189. The Korean journal International Journal of Applied Agricultural Sciences sent 10 emails to Zheng Xianzhang from 2018 to 2019, suggesting translation into English for submission to the journal and solicitation of contributions. The American Journal of Plant Sciences and other agricultural journals in the United States have sent emails for submissions, while some universities in Japan, Italy, Norway and other countries have invited them to give presentations.

10.Application Prospects

The hypobaric storage and preservation technology, including equipment and preservation process parameters, has matured in China, similar to the refrigeration equipment and preservation process parameters. At present, the technical level of the continuous extraction type of decompression storage in China is: "3 consecutive" or "4 consecutive" simultaneous operation; Working pressure of 3 kPa to 0.5 kPa; The average value of pressure fluctuation is ≤ ± 0.03kPa; Relative humidity can approach saturation; The hourly air exchange rate is 30% -100% of the vacuum chamber volume; Not frozen. The vacuum chamber volume series of commercial vacuum refrigerated warehouses include 2, 5, 10, 15, 20, 30, 40, and 50m3.

From the above, it can be seen that the vacuum storage preservation technology has unique, superior, and irreplaceable advantages compared to the current commercial non freezing preservation technology methods. Among them, the unique highlight is the "5-year follow-up preservation effect+antibacterial+insecticidal", especially the vacuum cold fresh chain constructed with decompression storage technology as the core, which has broader prospects.

There are two basic modes of vacuum cold fresh chain. 1) Decompression treatment+cold chain; 2) The vacuum storage series equipment is composed of its own components. In the basic model, several business models can be derived. In addition to the advantages mentioned above, each business model also highlights:

1) Break the game

① The classic view that breaking through the cold chain must always be at a suitable low temperature and breaking through the habitual thinking of the word "cold" provides a new direction for the development and innovation of existing cold chains, which can be considered a substantial leap in fresh supply chain theory and technology.

② Breaking through the traditional concept of 'fresh and nutritious vegetables and fruits of the season'. Open up the "mind" for the public to be willing to access nutritious and diverse ingredients all year round.

③ Solve the two dilemmas of the existing cold chain: the "first kilometer" and the "last kilometer". The former has a better technology besides pre cooling, namely decompression treatment; The latter, there is no need to force the courier guy to run for his life due to the concept of "seamless connection of the cold chain".

2) Economic benefits

① The overall energy consumption of the vacuum cold fresh chain is lower than that of the cold chain, and the equipment investment and operating costs are lower than those of the cold chain. For example, the requirement for suitable low temperature can be reduced, and short-term "cooling" can be achieved without being trapped in "seamless connection of the cold chain" at room temperature. Insecticidal equipment or facilities can be eliminated, and the ripening process of tropical fruits such as bananas can be avoided. Pre cooling equipment can be appropriately discarded, packaging requirements can be reduced, and refrigerated transportation can be changed to insulation or even temperature controlled transportation. However, insulation boxes can be discarded, and the effective loading capacity per unit volume of storage and transportation equipment can be increased, It can reduce floor space, equipment, operation and maintenance personnel, etc.

② Reduce the circulation loss of fresh products. One reason is low water loss rate, and the other reason is long shelf life.

③ Provide assistance for the export of certain perishable and high value-added fresh horticultural products to domestic and foreign markets.

3) Social benefits

① To play a supporting role in the national development strategy of the "Healthy China 2030" Plan, which is currently being implemented in China. The nutrients in vegetables and fruits that have been preserved under reduced pressure are well maintained.

② Reduce transportation vehicles and alleviate transportation pressure.

③ Reduce the pollution of food waste and packaging waste, as well as the associated wastewater and exhaust gas, to the city.

④ The fresh cut or clean vegetable production workshop (modern fresh central kitchen) can be moved to the county or even adjacent planting areas, which is conducive to the development of rural economy.

⑤ The vacuum cold fresh chain is compatible with existing cold chains and can integrate other non freezing preservation technologies to play new roles. For example, research has shown that some fresh horticultural products, including their fresh cut products, are particularly effective when subjected to "decompression treatment+MAP". It can be seen that the creation of several industrial chain operation models for the fresh product supply chain is likely to play a catalytic role.

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Main References

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Zheng Xianzhang, Xiong Weiyong Experiment on Vacuum Precooling and Reduced Pressure Refrigeration Preservation of Agaricus bisporus [J]. Edible and Medicinal Fungi, 2017,25 (1): 46-50 (Received the third prize of the 2017 Excellent Paper Award from the magazine).

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Zheng Xianzhang, Zheng Xi. An irreplaceable technology for non freezing, preservation, storage and transportation of fresh products - hypobaric storage technology [C]

Proceedings of the 6th National Food Refrigeration Chain Conference, 2008,10. (In 2009, won the Second Prize for Excellent Paper by the Chinese Refrigeration Society)