Fish has the characteristics of high protein content and high water activity, and is highly susceptible to contamination by microorganisms such as spoilage bacteria and pathogenic bacteria, resulting in food waste and economic losses due to spoilage. It is therefore crucial to use the right packaging techniques to extend the shelf life of fish. Correct packaging can keep the fish in a relatively good hygienic condition, reduce fat oxidation caused by air, avoid dust pollution, dry consumption and weight loss after long-term storage, etc. Commercial value and consumer desire to buy. At present, the commonly used fish packaging solutions include Tray Cling Film Wrapping Packaging, Modified atmosphere Packaging (MAP), Vacuum Packaging (VP), vacuum skin packaging (VSP) and so on.
Fish tray cling film wrapping packaging
Cling film wrapping of fish products in premade trays is a kind of packaging method that uses premade trays made of polystyrene (PS) to contain the products, and uses polyvinyl chloride (PVC) or polyethylene (Polyethylene, PE) to wrap the tray and product. This packaging method is one of the most common packaging types for retail fish and meat products in supermarkets, grocery stores, etc. This package is not airtight, and the myoglobin (Mb) in the food can fully contact with oxygen to generate oxymyoglobin (MbO2), which makes the meat and fish in the package bright red. The storage time of tray-packed fish is usually 1 to 3 days. In order to prolong the shelf life of fish products in cling film wrapping packaging, researchers often add natural preservatives. Treatment of rainbow trout fillets with natural bacteriocins extends the shelf life of rainbow trout fillets by 2 days. The application of radish seed protein extract to sturgeon fillets can effectively inhibit the reproduction of spoilage bacteria.
Fish vacuum packaging
In order to meet market requirements, in the 1970s, the United States and the United Kingdom have applied vacuum packaging to meat packaging in bulk. In the past few decades, the use of vacuum packaging for fish storage has achieved great innovation, especially When it is combined with refrigeration and freezing preservation technologies, the shelf life of fish can be significantly prolonged.
Vacuum packaging is a preservation method that prolongs the shelf life of the product by evacuate the air in the package and seal the package afterwards, thus isolate the product from direct contact with air, water and dust outside of the package. In a low oxygen environment, the number of aerobic bacteria can be reduced, and the rate of protein degradation and fat oxidation can be slowed down. The physiological activity of lactic acid bacteria is strengthened in an anaerobic environment, which can produce organic acids to reduce the pH in the packaging and further inhibit the growth of other microorganisms. This packaging method can achieve better preservation purposes.
The shelf life of fish under vacuum packaging depends on the interaction of variables such as storage temperature and microbial status. By storing vacuum packed and non-vacuum-packed carp at 3°C to 15°C, it was found that the storage period of vacuum packed carp at 3°C was 4 to 5 days longer than that of non-vacuum-packed carp; when stored at low temperature, the content of biogenic amines in carp was lower, so the quality of carp is better. Although vacuum packaging can inhibit the growth of most aerobic microorganisms, even if the oxygen content in the package is reduced to 0.8%, it still cannot inhibit the growth of some aerobic bacteria, especially the growth and reproduction of Pseudomonas; under low temperature conditions, As the storage time increases, the lactic acid bacteria will gradually replace the Pseudomonas. Studies have also shown that the degree of microbial contamination of vacuum apcked fish is related to the oxygen transmission rate (OTR) of the packaging film and storage temperature; Vacuum packed smoked rainbow trout fillets (initial botulinum toxin type E 102 spores/g)4 When refrigerated at ℃, no botulinum toxin was detected during the entire storage period, and the toxin was detected on the 28th day when stored at 8 ℃; when rainbow trout were packaged in film with a higher OTR, the toxin was detected earlier in the vacuum package. Handling storage temperature and initial temperature will affect the quality of VP-packed fish, and VP-packaging itself also has deficiencies, which have an impact on fish color and water holding capacity. In addition, Vacuum packaging is easy to cause the loss of fish juice. After a long storage time, the water holding capacity of the fish is weakened, and the juice is lost to the vacuum packaging bag, which affects the consumer’s desire to buy.
Fish VSP vacuum skin packaging
Vacuum skin packaging originated in the 1960s. Developed countries used its packaging of hardware products to protect products from dust and to display products intuitively. With the wide application and rapid development of vacuum packaging in meat in the 1970s, in order to improve the visual presentation of vacuum packages, researchers proposed to apply Vacuum Skin Packaging (VSP) to food packaging.
VSP vacuum skin packaging is an advanced form of vacuum packaging. It covers a layer of heat-sealed plastic film on the product. With the negative pressure generated by vacuuming, the plastic film is closely attached to the product and the tray/cardboard that holds the product, which offers an attractive 3D presentation of the product. Vacuum skin packaging is an improved packaging method for the drawbacks of traditional vacuum packaging and modified atmosphere packaging.
Vacuum skin packaging of fish products has certain advantages in maintaining quality, extending shelf life, and increasing packaging aesthetics of food products. Compared with ordinary vacuum packaging, vacuum skin packaging can prolong the shelf life of fish products, slow down the growth of microorganisms, and slow down the generation speed of undesirable substances during the storage process of fish. The shelf life of Atlantic pomfret in three different packages of VSP vacuum skin packaging, VP vacuum packaging and TP tray cling film wrapping is 12 days, 7 days and 5 days respectively. Vacuum skin packaging can better maintain the sensory, biochemical and microbial indicators of Atlantic pomfret, and improve the quality of Atlantic pomfret under the same storage time. fish quality and extended shelf life. The shelf life of barracuda in vacuum skin packaging is 9 days under the condition of (2±2) ℃. Compared with the control group vacuum packagedbarracuda, the volatile basic nitrogen, trimethylamine and thiobarbituric acid in vacuum skin packaging are relatively low. It is stable, so the vacuum body packaging is more suitable for the packaging and preservation of jade barracuda. Some studies have compared VSP vacuum skin packaging, ordinary VP vacuum packagging and MAP modified atmosphere packaging, and found that the color stability of VSP is better than that of ordinary VP, which can be similar to the effect achieved by modified atmosphere packaging.
Fish modified atmosphere packaging
MAP modified atmosphere packaging is a fresh-keeping method that packs food into airtight materials, injects a special single gas or mixed gas, and then seals the packaging, so that the product is filled with special gas and isolated from the outside world. The original rationale was to exclude oxygen to limit oxidative rancidity due to oxygen, limiting microbial growth.
With the development of modified atmosphere packaging, the common injection packaging gases mainly include CO2, N2, O2, and CO is sometimes used. One gas or multiple gases are mixed and used in a certain proportion to replace the original air in the product packaging. Once the packaging is sealed, the gas composition in the packaging is no longer adjusted. In the storage process, the MAP preservation technology is often combined with the low-temperature preservation technology to inhibit the growth of microorganisms, maintain the color, slow down the degradation of nutrients, and prolong the shelf life. MAP packaging typically extends shelf life by 0.5 to 4 times, enabling long-distance transportation of products and helping to maintain quality. However, the cost of this packaging is high, and the gas mixture in each product packaging needs to be standardized; at the same time, the packaging equipment, technicians, and safety requirements are high.
The use of gas conditioning in meat storage to prolong shelf life is not a new concept. As early as 1882, scholars discovered that CO2 has a preservative effect on meat. In the 1930s, in order to meet the large-scale long-distance transoceanic transportation of fresh meat from Australia and New Zealand to the United Kingdom, research on meat storage in anaerobic and CO2 environments was carried out, providing that CO2 can inhibit microbial growth and reduce metabolic capacity. The scientific basis of CO2 is also found to have bacteriostatic effect on Gram-negative bacteria. When using different concentrations of CO2 for packaging, the high concentration of CO2 has a significant antibacterial effect; the increase of gas concentration, the more serious the loss of fish juice. Initially, the high concentration of CO2 will change the color of the fish meat, and the recommended maximum concentration is 25%, but it was later found that 100% concentration can inhibit the growth of aerobic dominant microorganisms; The shelf life at 2℃ can be extended to 42 days, which is twice that of VP vacuum packaging. CO2 dissolves in water and oil, which can change the pH and interfere with the growth of microorganisms. However, when the CO2 in the package is absorbed by the tissues containing moisture and oil, the change of air pressure in the package causes the packaging bag to collapse.
The mixed use of CO2 and inert gas N2 can maintain the air pressure to prevent the collapse of the packaging bag, and at the same time can maintain the reduced state of meat myoglobin to achieve the effect of meat color, fat stability and inhibition of microbial growth. When using CO2 and N2 combined modified atmosphere packaging, the low-fat sea bream (Sparus aurata) should use 40%CO2+30%N2+30%O2, and the high-fat seabream should use 60%CO2+40%N2. CO2, N2 and O2 can be used at the same time, O2 can inhibit the formation of Metmyoglobin (MetMb) to keep fish meat attractive. Taking air packaging as the control group, the storage of halibut in 50%CO2+50%N2 and 50%CO2+50%O2 modified atmosphere packaging was studied. The air packaging storage period was 10 to 13 days; Up to 13 days to 20 days, the modified atmosphere packaging containing O2 has the best preservation effect. CO maintains color; the use of CO in modified atmosphere packaging can improve the color of fish, such as colored meats such as tuna.
Fish packaging samples
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Fish packaging machines
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