1. Overview of the development of vacuum packaging technology

1.1. Progress in foreign vacuum packaging technology

Vacuum packaging technology originated in the 1940s. Since the plastic film was successfully applied to commodity packaging in the 1950s, vacuum packaging technology has been rapidly developed. Vacuum packaging in the 1960s and 1970s was mainly used for meat products. Germany is one of the most developed countries in the world's packaging industry, and its vacuum packaging machine and vacuum packaging technology enjoys a good reputation. Kramer Grebe Machinery Manufacturing Co., Ltd. began to produce thermoformed vacuum packaging machines in 1965. It has carried out a lot of research on vacuum packaging of meat, and has achieved many results, such as packaging of barbecue products, adding appropriate amount after vacuuming. Oxygen; for sausages containing 40% fat, add appropriate amount of carbon dioxide after vacuuming; vacuum the bread, peanuts, nitrogen and appropriate carbon dioxide, etc. [8]. In 1962, Ordal proposed that oxygen-impermeable membranes can inhibit the growth of pathogenic microorganisms, and packaging fresh meat can prolong its shelf life [1]; Baltzer [2] believes that fresh-packed fresh meat has a longer shelf life than aerobic packaged fresh meat. The reasons are: (1) the total number of microorganisms increases slowly under anaerobic conditions; (2) the decay and mucus decrease; (3) after storage, the number of final microorganisms in the vacuum package is less than that of aerobic packaging. This shows that the oxygen-free membrane vacuum-packages the fresh meat. When the oxygen is converted into carbon dioxide, the oxygen-impermeable membrane can block the outside oxygen and enter the package, so the vacuum packaging can prolong the shelf life of the fresh meat. In 1970, Pierson et al. [3] proposed vacuum packaging to create an "ecosystem" that selects the type and level of microbes. In 1974, SCOPA of France first applied MAP (Modified Atmosphere Package, a package that first vacuumed and then filled with a certain proportion of mixed gas) to package meat products.

The emergence of various advanced vacuum packaging machines has accelerated the development of vacuum packaging technology. Vacuum packaging technologies in some developed countries such as Japan, Germany, and the United States are in a leading position. There are dozens of companies producing various types of vacuum packaging machines in Japan, and there are many varieties and specifications. At present, there are many high-efficiency, automatic and fully functional vacuum packaging machines, vacuum packaging machines filled with mixed gas, and some special vacuum packaging systems. The advanced models of foreign vacuum packaging machines mainly include: (1) Breathing vacuum packaging Machine, its working principle is to reduce the residual amount of oxygen by repeated pumping and inflating; (2) Thermoforming vacuum packaging machine, which is a combination of thermoforming-filling-sealing and vacuum air-packing High-efficiency packaging machine; (3) Rotary vacuum chamber packaging machine, which is a highly automated multi-station packaging machine named after multiple vacuum chambers on the turntable; (4) Anti-fabric vacuum packaging Systems, vacuum packaging has many unique advantages, such as reduced volume, easy storage, transportation and storage.

With the continuous advancement of science and technology, the vacuum packaging machine is constantly updated, and the vacuum packaging technology is developing in the direction of high efficiency and automation. There are three ways to increase the speed of vacuum packaging: (1) to improve the working speed of existing models; (2) to change the working principle and explore new design solutions; the former is limited by many conditions, sometimes it is difficult to make a big breakthrough; the latter However, there is a big development prospect. For example, the thermoforming vacuum packaging machine adopts a multi-column parallel operation scheme to greatly improve the production efficiency; (3) reduce the downtime, which requires the machine to increase the reliability of the machine, and also adds some such as fault display, rapid maintenance, Features such as automatic replacement of packaging materials to reduce downtime and increase productivity. Automation is closely related to high productivity, and high productivity is not achieved by human work. In industrially developed countries, high labor costs have accelerated the development of vacuum packaging technology toward automation. For example, Japan's rotary vacuum chamber packaging makes vacuum packaging highly automated, which can greatly reduce labor. In the future, vacuum-filled gas packaging will be greatly developed, and vacuum-inflated packaging can solve the packaging of some items that are not suitable for vacuum packaging. In addition, due to the strengthening of people's protection of the environment and the introduction of green food, the competition in the packaging market is becoming more and more fierce, and the requirements for vacuum packaging are getting higher and higher. In developed countries of Western Europe, once popular plastic food packaging has been eliminated, replaced by new paper packaging and edible packaging bags. Italy, the world's largest food exporter, has clearly announced that it will completely ban the use of plastic food packaging for food packaging in 1991. Since 1991, the United Kingdom has used an edible, thin and transparent film to preserve fruit [10]. In the United States, 50% of traditional plastic food packaging bags have been replaced by new paper packaging bags [7]. The replacement of plastic food packaging bags with new paper or other edible packaging bags is inevitable for the development of modern society and technology.

1.2, the status quo of domestic vacuum packaging technology

The level of packaging reflects to a certain extent the level of science and technology and the level of affluence in a country. The research and application of vacuum packaging technology in China is still in its infancy. However, China is a big agricultural country. At present, the processing and preservation of grain, oilseeds, fruits, vegetables, poultry and aquatic products are still in a low-level and extensive state, and the refrigeration conditions in China cannot be compared with the developed countries such as the United States and Japan. This leads to a large loss of agricultural products and waste of resources. According to the data, the current losses of China's grain and oil products are as high as 9% and 25%, respectively, while those in the United States and other developed countries are below 1% and 5% respectively. Since the 1980s, with the improvement of living standards, people's requirements for food have become higher and higher. The grain structure of the rural population has changed from the past rations to the fine grains. Urban residents not only pursue nutrition, but also pay more attention to health. Convenient and resistant to storage, and the demand for fruits and vegetables is also growing, but the fruit storage and storage technology is relatively backward. According to conservative estimates, post-harvest losses of horticultural crops can almost meet the basic nutritional requirements of 200 million people. Although there are some chemical preservation methods, people have some concerns about the safety of chemical preservatives, so the physical and pollution-free atmosphere preservation method has become a research hotspot. Pesis et al. (1986) [4] proposed that vacuum packaging is the best preservation method for maintaining the quality and hardness of persimmon fruit. It can be seen that the development and popularization of storage and preservation technology are increasingly valued by producers, operators and consumers.

In the late 1970s, China's higher agricultural institutions successively resumed the teaching and research work on the storage, preservation and processing of agricultural products. In the 1980s and 1990s, vacuum packaging technology developed rapidly. In 1996, Zhang Dejun and others applied vacuum technology to facilitate the processing and preservation of food. He believed that the food was processed under vacuum, not only retaining the original flavor and nutrients, but also being hygienic and fresh, easy to store and carry. Fu Xiguang et al [11] (1999) obtained a good storage effect by packing the food in a vacuum bag. He believed that the vacuum storage was used to store the rice in the summer, and the quality preservation effect was obvious. Due to the effect of the vacuum, the respiration intensity of the rice and the reproduction of the mold are suppressed, and the quality of the rice is maintained. Vacuum packaging storage is an advanced method of storing grain that is easy to use to ensure rice. Although in recent years, China's vacuum packaging technology has developed rapidly, but compared with developed countries, it is still a short distance. To reach the world's advanced level, we must improve the performance of vacuum packaging machines. China has introduced Italy

LEYDOLD-HETAEUS's three-dimensional pillow-shaped vacuum packaging production line for granular materials, Swedish Tree Hong Co., Ltd. and the Swedish Anti-Weaving Research Institute's anti-fabric vacuum packaging system [8]. At the same time as the introduction of foreign advanced technology, the state has a special department to carry out research. In 1996, Ma Jiayu developed the first rotary vacuum packaging machine in China, namely XZD-500/2S rotary vacuum packaging machine [12]. In 1997, Zhang Cong designed a large chamber vacuum inflatable packaging machine, which is especially suitable for vacuum sealing of large packaged items, and is applied to the fresh-keeping packaging of fresh pork. It can be used in a plastic film bag set of 1000×700 (mm). Fresh pork is subjected to suction sealing [13]. The development of vacuum packaging machines will certainly promote the improvement of vacuum packaging technology. The development of vacuum packaging machines and vacuum packaging technology complement each other and promote each other. We must pay attention to the development of both at the same time, in order to make vacuum packaging technology into the world's advanced ranks.

2. Characteristics, basic principles and main application areas of vacuum packaging

2.1, the characteristics and basic principles of vacuum packaging

At present, vacuum packaging and vacuum inflation packaging are often used for food preservation. In order to preserve food, in addition to controlling the external temperature and sterility, it is more important to control the proper gas environment of the food. If the appropriate packaging materials are selected, the vacuum packaging can achieve the expected preservation target. Vacuum packaging should first be pumped and then sealed. The methods for realizing vacuum packaging include: (1) mechanical extrusion; (2) suction pipe degassing; (3) chamber method. The so-called chamber method is to place the package containing the article in the chamber to open the valve, pump it by a vacuum pump, and then heat seal. Generally, plastic bags are vacuum-packed in this way.

The characteristics of vacuum packaging are as follows: (1) For meat foods, vacuum packaging can remove oxygen, which can inhibit the growth and development of mold and aerobic bacteria, inhibit the oxidation of oil components, control food deterioration, and achieve the purpose of preservation and quality preservation. Johnson (1974) [5] and Ingram (1962) [6] reported vacuum-packed fresh meat, which converts oxygen into carbon dioxide due to respiration and microbial activity of meat tissue, and accumulated carbon dioxide can inhibit Pseudomonas spp. (2) In terms of fruit thinning, vacuum packaging reduces the oxygen content in the bag, and produces carbon dioxide through anaerobic respiration, while maintaining a certain humidity, this low oxygen, high carbon dioxide, high humidity Environment, can effectively reduce fruit transpiration, reduce fruit and respiration, reduce ethylene production and nutrient consumption, and ultimately achieve the purpose of preservation; (3) In addition to other foods, vacuum packaging can reduce water evaporation, control due to food loss (8) In addition to the above-mentioned effects, vacuum packaging also has the advantages of resisting mechanical pressure, mitigating vibration, and facilitating long-distance transportation. Therefore, it can more effectively maintain the original color, fragrance, and Taste, shape and nutritional value.

2.2, the main application range of vacuum packaging

Although vacuum packaging has many advantages, it is not suitable for the preservation of all foods. Its scope of application: (1) pickled products: sausage, ham and some pickled vegetables, such as mustard, dried radish, kimchi, etc.; (2) fresh meat: beef, lamb, pork and so on. (3) Bean products: dried bean curd, bean paste, etc.; (4) cooked products: beef jerky, roast chicken, etc.; (5) convenience food: rice, vegetables, canned food, etc.; (6) fruits and vegetables; (7) in addition to In addition to the above foods, vacuum packaging is also suitable for the preservation of pharmaceuticals, chemical raw materials, metal products, electronic components, textiles, medical appliances and cultural relics. Vacuum packaging combined with some physical methods such as refrigeration and quick freezing will have better preservation effect. Vacuum packaging is not suitable for the packaging and preservation of fragile foods, plastic bags with sharp edges and corners, and soft and volatile foods.

3. Equipment and characteristics required for vacuum packaging

The equipment required for vacuum packaging consists of a vacuum packaging machine and a packaging container. Since the plastic film was used for vacuum packaging in the 1950s, there are many kinds of special machines for vacuum packaging of plastic films. For example, according to their structure, they can be divided into the following [7]:

(1) Mechanical squeeze vacuum packaging machine (Fig. 1) Before the bag is sealed, the air inside the bag is removed from the sides of the bag with a sponge-like article, and then the bag mouth is heat sealed. This mechanical vacuuming method is simple, but the degree of vacuum is low.

(2) The vacuum type packaging machine (Fig. 2) is inserted into the exhaust pipe from the opening of the bag, the valve 1 is opened, the vacuum pump is used to evacuate, and then the valve is sealed. To inflate, fill the required gas through valve 2 after pumping, and then seal. This mechanical structure is simple, but the vacuum is not too high. If you use breathing, you can achieve better results.

(3) The chamber vacuum packaging machine (Fig. 3) puts the plastic bag containing the articles into the vacuum chamber during packaging, and closes the suction air. After the predetermined vacuum degree is reached, the heat sealing device is closed and the bag mouth is sealed. To vacuum-pack, vacuum the gas before sealing. The vacuum packaging machine has a high degree of vacuum and can adjust the degree of vacuum according to needs, and is currently one of many applications.

(4) Thermoforming vacuum packaging machine (Fig. 4) is also known as continuous or deep drawing vacuum packaging machine. It is a method of thermoforming a sheet in a model, and the packaging container is self-made on the packaging, and then the steps of filling, capping, vacuuming, inflating, cross-cutting, slitting, etc. are completed until the finished product is output.

Another part of the equipment required for vacuum packaging is the packaging container. There are many types of packaging containers. There are composite materials such as plastic, plastic and paper, aluminum foil and other composite materials, glass bottles, metal containers and hard plastics. It should be determined according to the nature of vacuum-packed foods. For canned foods, glass bottles or metal cans are used. For example, Chinese medicines are made of aluminum foil or plastic. Although vacuum-packed containers are of a variety of materials, the most common is plastic film.

There are two kinds of plastic films for vacuum packaging: single film and composite film. The film used should have good barrier properties, safety, chemical stability, mechanical toughness, high and low temperature resistance and convenient printing, and some also require a certain degree of transparency, certain shading. Commonly used plastic single films are: polyethylene (PE), polypropylene (PP), nylon (NY), cellophane (PT), polyvinyl chloride (PVC), etc. [8]. Among them, the polyethylene film has good chemical stability, low price, easy processing, stable performance, freeze resistance, certain gas permeability, and is mostly used for vacuum packaging. If there is a certain respiration, the small amount of oxygen in the bag can be converted into carbon dioxide by its own breathing. The released carbon dioxide exchanges gas with the outside air through the permeability of the plastic, and finally reaches equilibrium and maintains a certain gas ratio. To the role of preservation and quality.

Plastic composite films for vacuum packaging vary depending on the combination, thickness, and composite method, such as polyvinyl alcohol (PVA), polyvinylidene chloride (PVDC), and polyester (PET). The polyvinyl alcohol (PVA) composite film is prepared by coating a PVA solution on a polypropylene biaxially oriented film (BOPP) film, and then hydroformylating it, and then compounding the PE film on the coating. The film is inexpensive, has excellent barrier properties, high strength, good heat sealability and non-toxicity, and has similar barrier properties to PVDC composite film, but has lower heat resistance. It can be used in the packaging of various pickled products, soy products and dried nuts. PVDC

The composite film is prepared by coating a PVDC latex on a BOPP film, and then compounding the PE film on the coating layer and curing at a certain temperature for 48 hours. The film is relatively cheap, has good oxygen barrier property, can withstand 110 ° C hot water sterilization treatment, good heat sealing performance, good chemical stability, non-toxic, and can meet various food packaging requirements.

In summary, the choice of vacuum packaging materials varies according to the nature of the food. For foods with low vacuum requirements, PE film, NY film and other low cost single film packaging can be used. For foods with high vacuum requirements, composite film packaging with better oxygen barrier properties, such as PVA. Membrane, PVDC film, etc.

4. Application of vacuum packaging technology in the dislocation and preservation of persimmon fruit

Persimmon fruit is nutritious and has important medical value and health care functions. With the gradual saturation of the production and supply of bulk fruit, persimmon production will play a more important role in China's fruit industry. Persimmon (Diospyroskaki L.f.) is native to China, but almost all of the traditional persimmon producing areas in China are cultivated in persimmon, and the representative variety is Mopan persimmon. The content of soluble tannin in the persimmon fruit is high, and the food has a strong astringent taste. It must be eaten after dislocation treatment, and the persimmon fruit after dislocation is easy to soften and cannot be exported and exported, resulting in backlog of fruit in the producing area. The price is low, but the persimmon fruit is not sold in the producing area. This contradiction between production and marketing has seriously hindered the sustainable development of China's persimmon industry. Therefore, it is imperative to explore the technology of persimmon fruit dislocation and preservation.

Previous studies have shown that low-density polyethylene (LDPE) plastic film vacuum packaging technology is used to treat persimmon, and persimmon fruit is subjected to anaerobic respiration in an anaerobic environment with low oxygen and high carbon dioxide to produce ethanol and acetaldehyde, acetaldehyde and The soluble tannin in the persimmon fruit undergoes a coagulation reaction, which can transform the soluble tannin into incompatible tannin and achieve the purpose of dislocation. Because LDPE has a certain gas permeability, and persimmon fruit produces carbon dioxide during anaerobic respiration, gas exchange between the carbon dioxide in the bag and the outside air will occur. When the gas exchange between the inside and the outside reaches equilibrium, the gas in the bag will maintain a certain proportion. By selecting the packaging materials, the ratio of the gas can be adapted to both the disintegration of the persimmon fruit and the preservation (preservation).

Through two consecutive years of research, Huazhong Agricultural University has further confirmed the good effect of vacuum packaging technology in the removal and preservation of persimmon fruit. The equipment and techniques for vacuum packaging of persimmon fruit are as follows:

(1) Vacuum packaging equipment: chamber vacuum packaging machine, 0.1mm LDPE;

(2) Test material: Mopan persimmon;

(3) Harvesting and grading: Fruit harvesting should be taken lightly; ensure that the sputum is intact, because scorpion is an important respiratory organ of persimmon fruit; the requirements for maturity are the same, about eight or nine mature, different maturity, persimmon fruit Inconsistent with fresh and fresh; remove pests and diseases, fruit, and oversized and undersized fruits;

(4) Single fruit packaging: pay attention to the size of the packaging bag, because the size of the packaging bag directly relates to the area of ​​gas permeation, affecting the final gas ratio in the bag, which is related to the shelf life of the persimmon fruit;

(5) Vacuum degree: The degree of vacuum determines the initial oxygen content in the bag, affecting the degree of anaerobic respiration of persimmon fruit, and thus affecting the length of time required for persimmon fruit dislocation.

The disc persimmon is vacuum-packed with 0.1mm LDPE single fruit. It takes 7 days to dislocate at room temperature, and it can be kept crisp for 50 days without softening. There was no change in the content of Vc, the color of the fruit surface, and the flavor of the fruit during storage, and no odor was produced. However, when the persimmon fruit is completely softened, the Vc content in the persimmon fruit is reduced, and ethanol is produced in the package, and the alcohol is slightly consumed at this time. The control persimmon fruit which was left untreated at room temperature was completely softened after 20 days, and the persimmon fruit was still not completely dislocated after softening. It can be seen that the vacuum packaging technology plays a role in double-cutting the dislocation and crispness of the persimmon fruit.

5. Application prospects and promotion value of vacuum packaging technology

With the development of food technology and industry, and the acceleration of China's accession to the World Trade Organization (WTO), the competition in the food packaging industry will become increasingly fierce, and vacuum packaging technology will become increasingly popular. Although vacuum packaging is still in the initial stage of popularization in China, under the condition that China's cold storage conditions are poor and refrigeration technology is not yet popular, the application of vacuum packaging technology can greatly reduce the loss of fruit and oil, grain and oil in China during storage and transportation. Moreover, vacuum packaging is easy to use, easy to automate and batch processing, and low cost, and will occupy a more important position in China's food preservation and packaging industry. With the development and application of high-efficiency, multi-functional vacuum packaging machines and packaging materials with excellent barrier properties, as well as vacuum packaging combined with physical and chemical treatments such as aeration, radiation, freezing, oxygen absorbers, and ethylene absorbents, Better storage and preservation effect.

references

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4. EdnaPesis, AhronLevl, etal.Deastringencyofpersimmonfruitsbycreatingamodifiedatmosphereinpolyethylenebags.J.FoodScience,1986,51(4):1014-1016

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Known as Goji (Lycium Barbarum L), Wolfberry, or Chinese Matrimony Vines. They are native to China.

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