Application of Modified Atmosphere Packaging Technology in Aquatic Product Packaging
Modified atmosphere packaging (MAP) is a packaging method that replaces the air in the food packaging containers with one or more mixed gases, inhibits the spoilage of the product, and prolongs the preservation period of the food. For food packaged by modified atmosphere, the initial proportion of gas in the packaging container will change spontaneously or be controlled to remain unchanged. MAP is suitable for both retail packaging and food preservation in large quantities. The MAP technology began commercial use in the 1930s, transporting fresh frozen beef from Australia to the UK in a CO2 environment. With the continuous development of MAP technology, it began to be widely used in European and American commercial markets in the 1970s and 1980s. Currently MAP modified atmosphere packaging technology has been developed for fresh meat, aquatic products, curds, fresh cheese, vegetables, fruits and ready meals.
Modified atmosphere packaging is widely used for various aquatic products, including fish fillets and nuggets, shrimp, and shellfish.
Gas composition of aquatic products’ modified atmosphere packaging
The mixed gas in modified atmosphere packaging is usually composed of three or two of CO2, O2, and N2. The gas in modified atmosphere packaging maintains its freshness and prolongs its shelf life by inhibiting the growth and reproduction of microorganisms in aquatic products and reducing fatty acid rancidity. The preservation effect of MAP on aquatic products is better than that of air packaging and vacuum packaging under the same conditions. For example, under the condition of modified atmosphere packaging (60% CO2: 40% N2), the growth of microorganisms in sardines is more inhibited. The shelf life of sardines under MAP, vacuum and air-packed conditions is 12 days, 9 days and 3 days, respectively.
CO2 is the main gas that plays a role in keeping freshness in the MAP modified atmosphere packaging of aquatic products. It has inhibitory effects on bacteria and fungi polluted on the surface of fish, and can inhibit or affect the growth of spoilage microorganisms. CO2 is soluble in water and fat, and its solubility in water increases rapidly with decreasing temperature. CO2 dissolves in food and combines with water to form a weak acid. The resulting acidic conditions have an inhibitory effect on the growth of microorganisms due to a decrease in pH in the food material or in the microorganisms. Studies have shown that 25% to 100% of CO2 can inhibit the activity of microorganisms in aquatic products, which is conducive to maintaining the quality of aquatic products. Within a certain range, the higher the CO2 content in the modified atmosphere packaging, the better the bacteriostatic effect. Some studies believe that the inhibitory effect of CO2 on microorganisms depends on the concentration of CO2 dissolved in the product; while Farber believes that the overall effect of CO2 on microorganisms is to prolong the lag phase of microbial growth and reduce the growth rate of microorganisms in the logarithmic growth phase; At present, the preservation mechanism of CO2 is still not fully understood.
O2: Oxygen is a key factor in many deterioration reactions during food storage. In the modified atmosphere packaging of aquatic products, O2 can inhibit the growth of anaerobic bacteria and reduce the reduction of trimethylamine oxide (TMAO) in fresh fish to trimethylamine (TMA). However, the presence of O2 is beneficial to the growth of aerobic microorganisms and the acceleration of enzymatic reactions, and also causes oxidative rancidity of high-fat fish fat. O2-free modified atmosphere packaging can better maintain the color of the northern long-fronted shrimp, prevent its fat oxidation and rancidity, maintain its toughness, and prolong its shelf life. Some studies have found that isolation of O2 can effectively slow down the denaturation and decomposition of oyster protein, the change of pH value, the generation and decomposition of free amino acids, and the increase of volatile base nitrogen content, and prolong the storage period of oysters. Recent studies have shown that the use of oxygen scavengers to remove all oxygen in air packaging can reduce the production of biogenic amines (histamine, putrescine and cadaverine) during the refrigeration of Conch’s mackerel compared to pure air packaging, and can reduce its shelf life from 12 days extended to 20 days. O2-free modified atmosphere packaging of aquatic products inhibits the growth of aerobic microorganisms, but creates the risk of promoting the growth of anaerobic microorganisms, such as Clostridium botulinum.
N2: Nitrogen is an odorless gas that is poorly soluble in water and fat. Due to the stability, insolubility and the property of N2 not easily permeable through the packaging film, it is mainly used as filling gas in the modified atmosphere packaging system to prevent the collapse of the packaging bag and make the packaging appear full; at the same time, it is used to replace the packaging The air and O2 in the bag can prevent the oxidative rancidity of high-fat fish and shellfish fat and inhibit the growth and reproduction of aerobic microorganisms.
Key factors effect the quality of modified atmosphere packaging for aquatic products
Aquatic products are perishable, and their shelf life is affected by many factors. Most of the aquatic products used for MAP modified atmosphere packaging need to undergo pretreatment such as gutting, slicing, shelling, and freezing. Each link in the process may affect the preservation effect and quality of MAP packed aquatic products. In MAP packging for aquatic products, packaging quality, food safety and food shelf life are greatly impacted by the following factors: product storage temperature, raw material freshness, product processing technology, composition and ratio of packaging gas, volume of gas in packaging container to material mass ratio (V/W), packaging materials, etc.
The processing and storage temperature of aquatic products determines the speed and degree of deterioration of their quality. Storage temperature is the most critical factor affecting the modified atmosphere packaging quality of aquatic products, and has a direct impact on the shelf life of MAP aquatic products. According to the British Advisory Committee on the Microbiology Safety of Food (ACMSF), when refrigeration is the only control factor for modified atmosphere packaged products, the shelf life should be limited to 5 days when stored at 5-10 °C. The shelf life can be extended to 10 days when stored below 5°C. There are large differences in temperature parameters in different studies, and the temperature range from -2 °C to 26 °C has been reported. The combination of low temperature and modified atmosphere preservation has a good preservation effect. Low temperature is necessary to control the spoilage of food and prevent the growth of potential pathogenic bacteria in the product. This is because the functions of microorganisms and enzymes are inhibited at low temperature, and it may also be due to the increased bacteriostatic effect of CO2 at low temperature. Elevated temperature will shorten the shelf life of MAP aquatic products.
For example, the total number of colonies of herring in modified atmosphere packaging (30% CO2:70% N2) reaches 106 CFU/g when stored at 4 °C for about 11 days, while the total number of colonies stored at 10 °C reaches this amount in 4 days; Bøknæs et al. studied the shelf life of cod in modified atmosphere packaging (40%CO2∶40%N2∶20%O2, V∶W=2∶1) at different temperatures, store cods at -20 ℃ environment for 12 months, the quality of cod has not changed significantly, and its shelf life can reach 14 days at 2℃. Moreover, different temperature treatments and temperature fluctuations have a great impact on the quality of MAP aquatic products. The shelf life of MAP packed cod fillets made from thawed cod at 2 ℃ (more than 20 days) was longer than that of MAP cod fillets made directly from fresh cod (11-12 days). This may be due to the fact that the cod has been frozen for 4-8 days After weeks, its specific spoilage bacteria Photobacillus was inhibited or destroyed, and the low temperature environment reduced the production of TMA. An important feature of MAP cod spoilage is the high content of TMA, which will rot and produce H2S odor under oxygen-containing packaging conditions, but 60% CO2 at 6°C can inhibit the growth of H2S-producing bacteria and TMA-producing bacteria in cod, and improve the growth of cod. The quality of the tablet extends its shelf life.
In addition, the combination of ice temperature technology and MAP technology can better extend the shelf life of fresh aquatic products. Under the same conditions, the shelf life of fresh aquatic products under ice temperature is longer than that under refrigerated conditions. The good quality of salmon can be maintained for up to 3 weeks under the conditions of ice temperature combined with high CO2 concentration in modified atmosphere. Studies have shown that controlled atmosphere storage at ice temperature can significantly prolong the shelf life of fish balls. Under ice temperature conditions, the fresh-keeping period of air-packed samples is 40 days, which is 5 times that of the fresh-keeping period (8 days) at 5 °C. Fish balls packed in 75% CO2:25% N2 have a shelf life of up to 50 days.
The shelf life of aquatic products in modified atmosphere packaging is closely related to the gas mixture composition. Different aquatic products should use different gas.
The corresponding shelf life of mackerel in modified atmosphere packaging under (2±0.5) ℃, 70% CO2:30% N2 gas and air-packed are 20-21 days and 11 days, respectively. The composition of gas not only affects the chemical quality of aquatic products, but also affects the changes of microorganisms in aquatic products. CO2 is the main component of modified atmosphere packaging, in most cases its proportion is 50% to 100%. Usually 30% to 80% CO2 is used to prolong the shelf life of fresh fish, because MAP with a high CO2 ratio will increase the juice loss rate of the package and cause package collapse due to the dissolution of CO2.
Modified atmosphere packaging with CO2 concentration greater than or equal to 50% can extend the shelf life of fresh herring blocks from 6 days to 12 days in air packaging under refrigeration conditions (2-4 ℃), and maintain good product quality; Davies’ research shows that , MAP with high CO2 concentration (80% CO2: 20% N2, trout; 60% CO2: 40% N2, cod) has better inhibitory effect on various pathogenic bacteria than MAP with low CO2 concentration. This may be because the increase in CO2 content inhibited the increase in the number of aerobic and psychrophilic bacteria. At the same time, the presence and increase of CO2 may reduce the growth rate of related microorganisms, such as: 20% or 60% CO2 at 0 ℃ can reduce the maximum growth rate of Shewanella spoilage by 40%; with the increase of CO2 concentration, the logarithmic growth phase of L. monocytogenes is prolonged, The maximum growth rate is also reduced. However, high CO2 MAP will cause the pH value of the material to decrease and increase the juice loss of the package. If the concentration of CO2 is reduced, the juice loss rate of the package will decrease. Studies have shown that when the concentration of CO2 is reduced from 70% to 50% , the sap loss of MAP perch was reduced by 50%.
Sometimes adding a certain amount of O2 to modified atmosphere packaging can better extend the shelf life of aquatic products. The suitable gas ratio of MAP hairtail (medium-fat fish) is: 60% CO2: 30% N2: 10% O2. Although the presence of O2 will accelerate the oxidation of fat, it inhibits the reproduction and growth of anaerobic bacteria, and reduces the Trimethylamine oxide is decomposed to generate trimethylamine, and the overall effect is better than that of anaerobic packaging. In the study of aerobic MAP, the proportion of O2 varies greatly. Although high oxygen MAP can easily lead to the deterioration of unsaturated fatty acids in aquatic products, there are still many research results showing that some aquatic products with high oxygen MAP have better quality. . A study on MAP halibut by Hovda et al. found that hyperoxic conditions of 50% CO2:50% O2 (23 days shelf life at 4°C) were superior to 50% CO2:50% N2 (20 days shelf life) and air-packed ( 10-day shelf life) gas conditions. It is possible that hyperoxia MAP can reduce the production of histamine in aquatic products and prolong the shelf life of aquatic products. The study of tuna by Jette et al. found that the histamine content in MAP tuna under the gas composition of 60% CO2: 40% N2 reached more than 5 000 mg/kg after being stored at 1.7 ℃ for 24 days; The histamine content was undetectable even after 28 days of storage at 1°C. López Caballero et al. studied MAP hake (1°C) with different gas combinations such as 60%CO2: 15% O2: 25% N2 and 40% CO2: 60% O2. The results show that: 40%CO2:60%O2 Shewanella had the strongest inhibition, and the contents of putrescine and histamine were the lowest; the air-packed group had a strong putrid smell when stored for 15 days, and the Shewanella putrefaction in the air-packed after storage for 3 weeks (109 CFU/mL ) and TMA (45 mg TMA-N/100 mL) were the highest. This may be because Shewanella spoilage is a CO2-intolerant species. For most aquatic products, MAP with low O2 is more suitable, and high O2 packaging can reduce the production of histamine, which may be more suitable for aquatic products such as tuna.
In the study, although different mixed gases have different effects on the quality of aquatic products in modified atmosphere packaging, most of the gas components in the MAP technology act on the packaging or microorganisms alone. The fresh-keeping effect of different mixed gases seems to be the superposition of the individual effects of several gases. The optimal mixed gas composition in the fresh-keeping of aquatic products is mostly the result of the comprehensive optimization of each gas composition. There are few studies on the interactions between different gases or between intermediates produced by different gases. The fresh-keeping mechanism of different mixed gases and the optimal fresh-keeping gas combination of different aquatic products need to be further studied. In addition, the composition of the gas in the modified atmosphere packaging aquatic products is related to the precision of the modified atmosphere packaging machine, the initial gas ratio, the properties of the raw materials, the air permeability of the packaging materials, and the microbial metabolism. The changes of CO2 and O2 in the packaging bag and the dissolved amount of CO2 during storage are less studied, which should be strengthened.
Gas volume and package weight ratio (V/W)
Due to the air permeability of the packaging material and the solubility of CO2, it is very important to make the volume of the gas charged into the packaging container larger than the volume of the packaging material, which can not only ensure the effect of modified atmosphere preservation, but also prevent the collapse of the packaging container. Usually, the volume of the gas is 2 to 3 times the weight of the food (V/W = 2～3) is ideal, but some studies on modified atmosphere packaging do not specify the ratio of V/W, nor do they involve the dissolution rate of CO2, which is an important index to study the mechanism of modified atmosphere preservation. Without the two, it is impossible to explain the mechanism of modified atmosphere preservation more scientifically. The research on the modified atmosphere packaging of grass carp segments shows that the suitable gas ratio is: 50% CO2: 40% N2: 10% O2, and the ratio of gas volume to grass carp weight is 2:1 or 3:1.
Raw material quality and initial conditions
The effect of modified atmosphere packaging has an important relationship with the degree of contamination before food packaging. The initial quality of raw materials has a direct impact on the shelf life of aquatic products in modified atmosphere packaging. The lower the degree of contamination of the material by spoilage microorganisms before packaging, the longer the shelf life of the modified atmosphere food. The number of microorganisms directly limits the shelf life of MAP aquatic products.
When the number of microorganisms exceeded the standard, the volatile basic nitrogen, TBA value and color in MAP salmon were still in the acceptable range. When the initial microbial number of MAP northern long-fronted shrimp increases by 10-100 times, the species and number of spoilage microorganisms will increase rapidly, and its shelf life will be significantly shortened; at the same time, the longer its exposure to air and light, its fat Oxidation is more pronounced.
Similarly, the freshness of cod has a significant impact on the quality of modified atmosphere packaged cod fillets, and only fresh cod can produce high-quality modified atmosphere cod fillets. Therefore, in the processing of MAP aquatic products, the processing conditions before air-packing are very important. In this process, the exposure time of aquatic products in adverse environments such as high temperature and microbial contamination should be minimized, and the number of microorganisms and quality deterioration such as fat oxidation before modified atmosphere packaging should be reduced. When aquatic products have good initial quality, MAP technology can better extend their shelf life.
Specification of packaging materials
The air permeability of modified atmosphere packaging materials has a great influence on the MAP packaging quality, and it determines whether the gas ratio in the packaging container is stable or balanced. Different packaging materials have different barrier rates for different gases, and are also affected by ambient temperature and humidity. Packaging materials with excellent barrier properties can not only prevent the overflow of various gases in the MAP package, but also prevent the entry of external gases. The research on modified atmosphere packaging materials with different barrier rates shows that their fresh-keeping effects under MAP (50%O2:50%CO2) are in the following order: high-barrier material (BOPP/AL/PET/CP composite film)>good-barrier packaging material (BOPP/PA/CP composite film)>Medium barrier packaging material (PET/CP composite film)>Low barrier material (BOPP/CPP composite film).
The use of modified atmosphere packaging in combination with acid leaching, salting, smoking, preservatives and bacteriostatic agents can better extend the shelf life of aquatic products, which will be the main trend in the development of MAP technology. Such as acetate (0.5% or 1%) combined with 50% CO2: 50% N2 packaged cod at 4 ℃ for 25 days in which the growth of Shewanella was completely inhibited. This may be due to the fact that the acidic conditions formed by CO2 inhibited the growth of Shewanella spoilage and slowed down the reduction of TMAO to TMA, extending the shelf life of cod. The shelf life of smoked salmon in vacuum packaging is 4 weeks, and the combination of 60%CO2:40%N2 and Nisin can extend its shelf life to 5 to 6 weeks.
Study also shows that peppermint essential oil, thyme essential oil and oxygen absorber are also playing positive role on the shelf life of MAP aquatic products.
Specified spoilage bacteria (SSOs) in modified atmosphere packaging of aquatic products
The spoilage of aquatic products is mainly due to the growth and metabolism of certain microorganisms to generate amines, sulfides, alcohols, aldehydes, ketones, organic acids, etc., resulting in unpleasant odors and odors, sensory unacceptable, and quality changes. Generally, aquatic products contain a variety of microbial populations. These microorganisms change dynamically during storage. However, most microbial populations do not cause spoilage of aquatic products. Only one or several specific spoilage bacteria (SSOs) Mass reproduction during storage of aquatic products leads to spoilage and deterioration of aquatic products. Different or the same aquatic product has different specific spoilage bacteria under different conditions. The specific spoilage bacteria may not have a small initial number under these conditions, but have strong endurance, advantages and activity, which will eventually lead to the spoilage of the aquatic product. main flora.
The specific spoilage bacteria in fresh fish in modified atmosphere packaging include luminobacterium, lactic acid bacteria, and Soxella thermophila, but different fish species, different storage temperatures, different MAP gas ratios, and different processing and storage conditions will affect the species and growth of specific spoilage bacteria. Hovda et al. used the PCR-DGGE method to identify the microorganisms in the cod in MAP modified atmosphere packaging, and found that under the high oxygen condition of 50%CO2:50%O2, Pseudomonas was the dominant flora; while in 50%CO2 : Under 50% N2 or air-packed gas conditions, Luminobacteria, Shewanella spoilage and Pseudomonas are all dominant flora; but compared with air-packed, modified atmosphere packaging significantly inhibits psychrophilic bacteria and the growth of H2S-producing bacteria. Hovda et al. also identified microorganisms in MAP-controlled atmosphere halibut and found that Luminobacter and Pseudomonas were the dominant flora. In the fresh fish packaged with CO2, the growth of Shewanella and many microorganisms are inhibited, but the photobacterial bacteria are highly resistant to CO2, and it is considered to be a specific spoilage bacteria of various modified atmosphere aquatic products (cod, etc.). , Dalgaard et al. believed that luminobacterium can be a good indicator of the freshness and quality changes of MAP aquatic products, and established a shelf-life model for predicting MAP packaged cod fish with luminobacter as indicator bacteria. Usually there may be more than one species of spoilage bacteria in MAP aquatic products. The microbial populations of MAP mackerel (50%CO2∶50%N2) at 3 ℃ or 6 ℃ were Lactobacillus and Thermonecrophila, followed by Shewanella spoilage and Enterobacteriaceae. The main spoilage bacteria of the oxygen-modified eel (40%CO2∶30%N2∶30%O2) stored at 0℃ were lactic acid bacteria, followed by Shewanella spoilage and Pseudomonas.
Food safety of aquatic products in modified atmosphere packaging
At present, there are many studies on spoilage microorganisms in aquatic products in modified atmosphere packaging, but there are relatively few studies on pathogenic bacteria. However, ignoring the growth of pathogenic bacteria in MAP aquatic products may lead to the fact that aquatic products have good sensory properties. , but it is not safe to eat, so research in this area should be strengthened.
The safety of fish and seafood products in modified atmosphere packaging is higher than that of vacuum packaging under the same conditions. MAP can reduce food safety problems caused by bacteria such as Salmonella, Staphylococcus, Clostridium perfringens, Campylobacter, Vibrio parahaemolyticus, and Enterococcus that appear in air packaging, and is similar to Shiga Bacteria were almost completely inhibited in modified atmosphere packaging. However, pathogenic bacteria such as Clostridium botulinum, Listeria monocytogenes, Yersinia, and Aeromonas hydrophila can grow in low-temperature MAP aquatic products, and they all have a negative impact on the safety of MAP products. potential threat.
Studies have shown that the inhibition of these pathogenic bacteria by modified atmosphere packaging is better than that of the control vacuum packaging, that is, its safety is higher than that of vacuum packaging. Modified atmosphere packaging also has an inhibitory effect on psychrophilic (0-2 ℃) Listeria monocytogenes. Under anaerobic MAP, the detection rate of Listeria, Yarrowia colon and other pathogens is significantly lower than that of aerobic Under MAP conditions, the activity of Listeria at each growth stage was reduced in the presence of 40% CO2: 60% N2 or 100% CO2. And the combination of modified atmosphere packaging and low temperature, adding inhibitor, acid treatment or salt treatment can better inhibit the growth of pathogenic bacteria. Delayed period and reduction of Escherichia coli O157 can improve its food safety. Salt leaching and acid (benzoic acid + sorbic acid + citric acid) combination inhibited the growth of Listeria monocytogenes in northern long-fronted shrimp for more than 40 days under storage conditions at 7 °C.
In order to ensure the safety of MAP aquatic products, a mathematical model for predicting the safety of aquatic products can be established by using pathogenic bacteria as indicator bacteria. In addition, histamine is also a potential unsafe factor for modified atmosphere packaged aquatic products. Photobacillus in marine aquatic products can produce histamine at 1 to 5 °C. Some studies have found that Morganella morganii can produce histamine in tuna kept fresh at low temperature, and high oxygen modified atmosphere packaging can inhibit the production of histamine by Morganella morganii and luminobacterium. This is also what needs to be paid attention to when studying the safety of aquatic products in modified atmosphere packaging.
Effects of modified atmosphere packaging on physical and chemical quality of aquatic products
Modified atmosphere packaging has no obvious adverse effect on the quality of most aquatic products. MAP controls black speckle in crustaceans and reduces histamine formation in storage in Scombroid fish. MAP has no effect on the odor and acceptability of cod, mackerel and salmon fillets, but has a certain effect on its color, elasticity, juice loss, volatile base nitrogen, etc. For example, high-pressure CO2 modified atmosphere packaging can cause aquatic products produce a sour and carbonated taste. Most aquatic products in modified atmosphere packaging have the problem of juice loss. The rate of juice loss can be reduced by the treatment of water-retaining agent and the reduction of CO2 concentration. Some people have studied the content of free amino acids in Norwegian lobster muscle. During storage under the composition of mixed gas CO2:O2:N2 of 60:15:25 and 40:40:20, threonine, valine, lysine and The content of arginine decreased significantly, and this change was greater in the samples under the CO2-enriched packaging than in the samples enriched in O2; the contents of ornithine and tryptophan in the storage period There is a significant increase in the time, which may have an impact on its flavor and umami.
Aquatic products modified atmosphere packaging machines
According to the packaging productivity and automatic-grade requirement, there are 4-6 types of modified atmosphere packaging machines can be used for aquatic products packaging. From tabletop MAP tray sealer machine to fully automatic thermoforming modified atmosphere packaging, the price ranges from a few thousand US dollars to around 50 thousand US dollars. The features and specificaitons of the machines are very different, make sure to contact us for suggestions..
Modified atmosphere packaging technology has been widely used in meat, fruits and vegetables, aquatic products, poultry products, and cheese products. In the future, MAP technology will develop in the direction of intelligence, safety and portability, and it will be mainly reflected in active packaging and intelligent Package. Active packaging can control the stability of packaging systems by absorbing or releasing gases such as CO2 and O2; smart packaging can monitor food quality changes through Time-Temperature Indicators (TTIs), freshness indicators, CO2 or O2 change indicators, etc. . The safety research of aquatic product MAP technology will also continue to develop in the aspects of identification of SSOs in aquatic products, establishment of predictive microbial shelf life model, research on pathogenic bacteria, the combined effect of various fence technologies and the use of molecular biotechnology. At the same time, with the development of packaging technology and packaging materials, MAP technology will develop in a portable direction that is conducive to production, storage, transportation and consumption convenience.