Fresh-keeping effect test and influence factors analysis of fish packaging

[Chinese Packaging News] For fresh fish, the greatest loss of freshness is characterized by spoilage. For freshness problems, fresh-keeping technology is especially important. For fresh fish, it is difficult to obtain the best preservation effect with a single preservation technique. Therefore, it is necessary to pay more attention to the synergies between packaging technology and preservation technology, and to combine the advantages of both parties to obtain the best preservation effect.

As the largest fishery country in the world, China accounts for one-third of the world's total output of aquatic products. The huge production capacity has made the demand for preservation of aquatic products increasingly urgent. After the death of a fish, various enzymatic reactions, redox reactions, and the action of microorganisms in the body cause a loss of freshness, and preservation is taking place.

Freshness loss analysis

For fresh fish, the greatest loss of freshness is characterized by spoilage. During the storage and transportation of fish, microorganisms invade the perishable parts of the fish or the mechanical wound tissue and multiply in the fish, decomposing nitrogenous substances such as proteins and amino acids, causing the fish to spoil and generate toxic substances. In addition to being affected by microorganisms, oxidation of oils is also a major cause of fish spoilage. Fresh fish is rich in protein, fat and other nutrients, including oil, light, heat, oxygen, rancidity reaction, decomposition of aldehydes, acids, ketones, resulting in changes in fish quality and body surface color.

Fish packaging preservation effect test

Faced with the above-mentioned problems of freshness loss, preservation technology is particularly important. At present, the mainstream preservation technologies include chemical preservation, preservation of natural additives, cryogenic preservation, ozone preservation, decompression and preservation. For fresh fish meat, it is difficult to obtain the best preservation effect with a single preservation technique. Therefore, related companies pay more attention to the synergy between packaging technology and preservation technology, and combine the advantages of both parties to obtain the best preservation effect. The variety of packaging, from the antibacterial and sterilizing mechanism point of view, vacuum packaging and modified atmosphere packaging is the best choice for fresh fish packaging. Vacuum packaging uses a vacuum to place the fish in a highly decompressed, low-oxygen environment. On the one hand, it inhibits the growth and reproduction of most aerobic microorganisms and delays the process of corruption. On the other hand, it can effectively prevent the oxidative deterioration of fish and extend the shelf life of the product. period. Modified atmosphere packaging is filled with different proportions of CO2, N2, and O2 in a sealed package. CO2 can penetrate the cells of microorganisms, so that the intracellular pH value decreases and the activity of the enzyme decreases, thus inhibiting the proliferation of cells; although O2 is the cause of microbial reproduction and lipid oxidation, it can be combined with the myoglobin of fish. Oxygenated myoglobin makes the meat red and fresh. Therefore, the filling ratio of CO2 should be higher than that of O2, and the dual effects of bacteriostatic and color retention are achieved.

The authors combined several different fresh-keeping technologies with the packaging technology for long-term storage at 4°C in cold storage and performed sensory scores on days 4d, 8d, 12d, 16d, and 20d respectively. The score is based on the sensory requirement level in GB/T 18108-2008 "Fresh Saltwater Fish" standard, 8 to 10 is divided into 1 grade, 6 to 8 is divided into 2 grades, and 6 or less is not fresh, and the score results are shown in Table 1.

It can be seen from Table 1 that the different combinations of packaging technology and preservation technology have a very different effect on the preservation of fish meat. Comparing the 1#, 2#, and 3# sample groups, the 1# fish showed a state of partial scale disengagement, poor elasticity, and slight odor, etc. on the 4th day, and on the 8th day it was completely corrupted. In contrast, 2 # and #3 fish did not become corrupt until the 20th day. It can be seen that the vacuum packaging and modified atmosphere packaging is twice as long as air packaging. The 4# and 5# sample groups are based on the 1# sample air package format, adding “chemical preservation technology for soaking fish meat with 2.5% potassium sorbate solution” and “utilizing 1.9% chitosan. Coating natural preservation technology." The preservation effect is very obvious, and the time of complete corruption is delayed until the 16th day. It can be seen that when the packaging technology and the preservation technology are combined, the preservation effect is significantly enhanced.

The 3#, 6#, 7#, and 8# sample groups all use modified atmosphere packaging. In comparison, the 3# sample group without additional preservation technology has the shortest decay time of 16 days, followed by 6# and 8#. The sample group was 20 days, while the 7# sample group was only kept fresh for 20 days without spoilage. Because the 6#~8# sample groups all use the same preservation technology, the difference in preservation effect mainly comes from packaging technology.

Analysis of Factors Affecting Preservation Effect of Fish Packaging

Fish fresh-keeping packaging is mainly based on two forms of modified atmosphere packaging and vacuum packaging. The characteristics of its packaging materials and many differences in molding process will affect its preservation effect.

1. Analysis of Factors Affecting Preservation Effect of Modified Atmosphere Packaging of Fish

For fresh fish, the role of CO2 in modified atmosphere packaging is to inhibit the proliferation of microorganisms. Studies have shown that increasing the proportion of CO2 can enhance the inhibition of microbial reproduction, and as the proportion of content increases, the inhibitory effect will gradually increase. This is also the reason why the shelf life of the 7# sample group is longer than the 6# sample group. However, when the CO2 content reaches more than 50%, the antibacterial enhancement effect is no longer significant. At the same time, the proportion of CO2 should be determined based on the initial microbial species and quantity of fish. If the initial microorganisms of the contents are dominated by anaerobic bacteria or facultative anaerobic bacteria, the high proportion of CO2 content will promote its growth and reproduction. This explains to a certain extent why, although the CO2 content of the 8# sample group in Table 1 is higher, the preservation effect is not as good as that of the 7# sample group.

After determining the proper gas composition and content ratio, how to maintain its stability during the shelf life is the key to ensure the fresh-keeping effect of modified atmosphere packaging. I took 9 KPET/PE modified atmosphere packages (60%CO2+10O2+30%N2) of fish meat products, and tested the O2 content of the three modified atmosphere packages using HGA-02 headspace gas analyzer at regular intervals. ,take the average. The test results showed that the initial O2 content was 10.02%, after 2 days it was 10.07%, after 4 days 11.39%, and after 6 days it was 12.87%. It can be seen that the atmosphere inside the modified atmosphere package is constantly changing. This is because there is a concentration difference between the “low O2 high CO2” atmosphere in the modified atmosphere packaging and the “high O2 and low CO2” atmosphere in the packaging atmosphere. The O2 and CO2 molecules inside and outside the packaging penetrate and diffuse each other through the packaging materials, along with storage. As time increases, the proportion of gas in modified atmosphere packaging will change to some extent. In this regard, packaging materials with high barrier properties to O2 and CO2 are generally used to maintain the atmosphere of the modified atmosphere packaging. Using the VAC-V2 differential pressure method gas permeation instrument of the Languang Packaging Safety Inspection Center, the authors tested the permeability of commonly used packaged materials such as PET, KPET, and BOPP for CO2 permeability, which were 493.621 cm 3 /(m 2 · 24 h·0.1 MPa), 10.637 cm 3 /(m 2 ·24h·0.1 MPa) and 2417.853 cm 3 /(m 2 ·24h·0.1 MPa). Among them, KPET has the lowest CO2 transmission rate and the best barrier property. This is because KPET is made by coating a PVDC layer on a PET substrate. PVDC has strong intermolecular cohesion and high crystallinity. Chlorine atoms are hydrophobic and do not form hydrogen bonds. Oxygen molecules, water molecules and carbon dioxide molecules are difficult to move in PVDC organic macromolecules. Therefore, KPET is an ideal material for modified atmosphere packaging.

2. Analysis of influencing factors of preservation effect of fish vacuum packaging

According to the principle of vacuum packaging, the effectiveness of vacuum packaging depends largely on the effect of vacuum packaging. However, during the storage process, the phenomenon of "loosening and loosening" often occurs in the vacuum packaging of fish, which seriously affects the shelf life of food. The shelf life effect.

I took 20 pieces of KPET/PE vacuum-packed filleted fish products, and used the RGT-01 vacuum-packed residual oxygen meter to perform gas residue testing. The author selected four typical samples among them, and the data results are shown in Table 2.

The test results showed that during the storage period, the residual gas in the vacuum packaged filleted fish showed an increasing trend. Among them, the three groups B, C, and D showed a gentle increase. After 16 days, the residual gas volume was controlled below 3 mL. The vacuum retention effect was satisfactory. . However, the initial gas residue in Group B was higher than that in Group C and D, which may be due to the limitations of vacuum operation accuracy and time. After storage in group A to 8 days, the test found that the internal gas content suddenly increased significantly, showing a very clear loosening state, which indicates that the bag body may have a more serious leakage problem, resulting in a large amount of gas into the bag.

“Loose packs” are due to factors such as poor gas barrier properties of the packaging materials, poor packing seals, gas-carrying microorganisms in the fish itself, and the adsorption of gases and gas in the packaging and contents. In particular, the last point is worth noting that in addition to metal and glass, other materials have a certain gas adsorption function. When the package is evacuated, the concentration of gas decreases so that the gas previously adsorbed on the surface of the package is slowly released again. For this problem, with the extension of storage time, the residual gas content of vacuum packaging should be tested multiple times and the gas concentration curve should be plotted for comprehensive analysis.

Fresh fish, tender and nutritious, nutritious and affordable, is the main source of high quality protein. However, the perishable nature of fish requires producers to enhance the preservation effect of storage and sales. Different forms of fish fresh-keeping packaging, there are great differences in the preservation effect, in the final analysis is due to the impact of packaging materials and packaging processes. It is recommended to strengthen the daily inspection of packaging materials and the research of packaging technology to further improve the preservation of fish packaging.