Method of modified atmosphere packaging to extend shelf life of cured beef

Abstract

This invention discloses a method for extending the shelf life of braised beef using modified atmosphere packaging, comprising the following steps: Step 1: The finished braised beef, obtained through thawing, marinating, and cooking processes, is trimmed and cut in a sterile workshop at a temperature below 12°C; Step 2: A high-barrier composite packaging box and a matching sealing film are selected, wherein both the packaging box and the film are made of a multi-layer co-extruded high-barrier structure of PET / PP / EVOH / PE; By precisely controlling the dynamic gas balance inside the packaging, 20%~80% high-concentration CO2 is used to dissolve on the surface of the meat to form carbonic acid, actively controlling and stably reducing the pH value of the meat surface to a critical threshold range below 6.0; Thus, modified atmosphere packaging can maintain water retention, inhibit microbial growth, and simultaneously inhibit myofibrillar protein and lipid oxidation.

Description

Technical Field

[0001] This invention relates to a method for extending the shelf life of braised beef using modified atmosphere packaging, and belongs to the field of beef processing. Background Technology

[0002] Beef holds a significant place in global meat consumption due to its high protein, low fat, rich minerals, and unique flavor. Currently, common packaging and preservation methods for braised beef include ordinary air packaging, vacuum packaging, and traditional modified atmosphere packaging.

[0003] However, these existing packaging technologies have the following significant technical defects and limitations in practical applications: Conventional air packaging: This packaging method directly exposes the meat to the air. The abundant oxygen in the air leads to the rapid proliferation of aerobic psychrophilic bacteria such as Pseudomonas aeruginosa; usually, after only 3 to 5 days, the surface of the meat will become sticky, slimy, develop an off-odor, and suffer from severe rancidity and spoilage, resulting in an extremely short shelf life and making it unsuitable for long-distance logistics transportation.

[0004] Vacuum packaging: The negative pressure created by vacuum packaging will strongly compress the muscle tissue of beef, causing a large amount of juice to seep out of the muscle (the juice loss rate is usually as high as 5% to 8%). After opening, the meat will be dry and the flavor will be damaged. In addition, a large amount of free blood water can easily cause the local anaerobic bacteria to multiply. Summary of the Invention

[0005] In view of the shortcomings of the existing technology, the purpose of this invention is to provide a method for extending the shelf life of braised beef through modified atmosphere packaging, so as to solve the problem.

[0006] To achieve the above objectives, the present invention provides a method for extending the shelf life of braised beef using modified atmosphere packaging, comprising the following steps: Step 1: The finished braised beef, which has been thawed, marinated and cooked, is trimmed and cut in a sterile workshop at a temperature below 12℃. Step 2: Select a high-barrier composite packaging box and a matching sealing film. Both the packaging box and the film are made of PET / PP / EVOH / PE multilayer co-extruded high-barrier structure. Step 3: Place the drained beef chunks flat in the packaging box and send them into the sealed vacuum chamber of the modified atmosphere packaging machine. First, a vacuum is drawn to a vacuum degree of -0.095MPa or higher and maintained for 3-5 seconds. Then, a pre-mixed composite protective gas is injected into the packaging box. The composition and volume percentage of the composite protective gas are as follows: carbon dioxide accounts for 20% to 80%, and the remainder is made up by nitrogen. Immediately after the gas is injected, the box is heat-sealed at a sealing temperature of 140-160℃, a sealing pressure of 0.3-0.5MPa, and a pressure holding time of 1.5-2.5 seconds to form a completely sealed modified atmosphere package. Step 4: After heat sealing, the modified atmosphere packaging will undergo online air tightness and leakage screening. Packaging that fails the sealing test will be removed. The qualified modified atmosphere packaging will be immediately transferred to a constant temperature cold storage at 11℃ and relative humidity of 80%~90% for light protection.

[0007] Preferably, the total bacterial count of the braised beef is less than 4.90 lg CFU / g when the beef is refrigerated for 24 days.

[0008] Preferably, the method results in the volatile basic nitrogen (TVB-N) value of the braised beef being less than 20 mg / 100g after 24 days of refrigerated storage. Preferably, the method controls the thiobarbituric acid reactant value of the braised beef to a mild oxidation level of less than 0.5 mg / 100g when the beef is refrigerated for 24 days.

[0009] Preferably, the composite preservative gas actively regulates and reduces the pH value of the meat surface to a threshold range below 6.0 by dissolving carbonic acid on the surface of the meat, thereby inhibiting the protease and lipase activities of Pseudomonas and Enterobacteriaceae.

[0010] Preferably, in step three, before placing the beef chunks into the packaging box, an absorbent pad is placed at the bottom of the packaging box. The absorbent pad has a saturation water absorption rate of ≥15 times and is used to absorb the blood water discharged by the beef during storage in real time, thereby reducing water activity.

[0011] Beneficial effects This invention precisely controls the dynamic gas balance inside the packaging, utilizing 20% ​​to 80% high concentration CO2 to dissolve on the surface of the meat to form carbonic acid, thereby actively regulating and stably reducing the pH value of the meat surface to a key threshold range below 6.0. Attached Figure Description

[0012] Other features, objects, and advantages of the present invention will become more apparent from the following detailed description of non-limiting embodiments with reference to the accompanying drawings: Figure 1This invention describes the change in thiol content during refrigeration of MAP-braised beef. Figure 2 This invention describes the change in carbonyl content of myofibrillar protein during refrigeration of MAP-braised beef. Figure 3 This invention relates to the change in myofibrillar protein solubility during refrigeration of MAP-braised beef. Figure 4 This invention relates to the change in surface hydrophobicity of MAP-braised beef during refrigeration. Detailed Implementation

[0013] To make the technical means, creative features, objectives and effects of this invention easier to understand, the invention will be further described below in conjunction with specific embodiments.

[0014] See Figure 1-4 This embodiment provides a method for extending the shelf life of braised beef using modified atmosphere packaging. The specific process steps are as follows: Includes the following steps: Step 1: The finished braised beef, which has been thawed, marinated and cooked, is trimmed and cut in a sterile workshop at a temperature below 12℃. Step 2: Select a high-barrier composite packaging box and a matching sealing film. Both the packaging box and the film are made of PET / PP / EVOH / PE multilayer co-extruded high-barrier structure. Step 3: Place the drained beef chunks flat in the packaging box and send them into the sealed vacuum chamber of the modified atmosphere packaging machine. First, a vacuum is drawn to a vacuum degree of -0.095MPa or higher and maintained for 3-5 seconds. Then, a pre-mixed composite protective gas is injected into the packaging box. The composition and volume percentage of the composite protective gas are as follows: carbon dioxide accounts for 20% to 80%, and the remainder is made up by nitrogen. Immediately after the gas is injected, the box is heat-sealed at a sealing temperature of 140-160℃, a sealing pressure of 0.3-0.5MPa, and a pressure holding time of 1.5-2.5 seconds to form a completely sealed modified atmosphere package. Step 4: After heat sealing, the modified atmosphere packaging will undergo online air tightness and leakage screening. Packaging that fails the sealing test will be removed. The qualified modified atmosphere packaging will be immediately transferred to a constant temperature cold storage at 11℃ and relative humidity of 80%~90% for light protection.

[0015] The method resulted in a total bacterial count of less than 4.90 lg CFU / g in braised beef after 24 days of refrigerated storage.

[0016] The method described above resulted in braised beef with a volatile basic nitrogen (TVB-N) value below 20 mg / 100g after 24 days of refrigerated storage. The method controls the thiobarbituric acid reactant value of braised beef to a mild oxidation level of less than 0.5 mg / 100g when refrigerated for 24 days.

[0017] The composite preservative gas actively regulates and lowers the pH value of the meat surface to a threshold range below 6.0 by dissolving carbonic acid on the surface of the meat, thereby inhibiting the protease and lipase activities of Pseudomonas and Enterobacteriaceae.

[0018] In step three, during the 24th day of refrigerated storage, the centrifugal loss and juice loss rate of the braised beef are controlled to be within 15% and 3.5%, respectively.

[0019] Example 1 The experimental material was finished braised beef, which was made from beef shank through thawing, marinating, and cooking processes. Under aseptic conditions, the finished braised beef was cut into blocks weighing (100±5)g.

[0020] Modified atmosphere packaging group setup: Place the block sample in a packaging tray container, use a modified atmosphere packaging machine to replace the air inside the container, and set up one control group and four experimental groups according to different carbon dioxide concentrations. The specific gas ratios (volume percentages) are as follows: Control group (CK): Traditional pallet packaging (air packaging).

[0021] Experimental Group 1 (20% CO2): Filled with a composite preservative gas of 20% CO2 + 80% N2.

[0022] Experimental Group 2 (40% CO2): Filled with a composite preservative gas of 40% CO2 + 60% N2.

[0023] Experimental Group 3 (60% CO2): Filled with a composite preservative gas of 60% CO2 + 40% N2.

[0024] Experimental Group 4 (80% CO2): Filled with a composite preservative gas of 80% CO2 + 20% N2.

[0025] All sealed beef samples from each group were stored at a constant temperature below 12°C. Samples were taken out on days 0, 4, 8, 12, 16, 20, 24, 28, and 32 of storage for subsequent parallel determination of various indicators.

[0026] Weigh 2g of each group of braised beef samples and add 20mL of protein dissolving solution (including 8mol / L urea, 2% SDS, and 20mmol / L Tris-HCl). Homogenize for 60s in an ice-water bath. Filter the homogenate and allow it to stand to obtain the MP solution. Pipette 5g of the obtained MP solution into a 50mL centrifuge tube, dilute it 10-fold with the protein dissolving solution, and centrifuge at 11℃ and 8500×g for 10min. Determine the protein concentration of the solution using the biuret method.

[0027] Dilute the known concentration of the stock protein solution with distilled water to a sample solution of 2 mg / mL. Take 0.5 mL of the sample solution and add 2.5 mL of Tris-glycine urea and 20 μL of DTNB solution. Add DTNB dropwise at 2-3 min intervals between each sample, and perform the entire process in a dark room for 25 min. Measure the absorbance at 412 nm and record it as A412. Take 0.1 mL of the mixture and mix it with 0.9 mL of distilled water, add 5 mL of Coomassie Brilliant Blue solution, and measure the protein concentration at 595 nm, recording it as C. The blank group uses distilled water instead of the sample solution. The total thiol content (nmol / mg) is calculated using the formula: Total thiol content =

[0028] In the formula, 1.36 × 10⁴ is the molar absorptivity and 10⁶ is the unit conversion factor.

[0029] Adjust the MP concentration to 25 mg / mL, and place two 0.1 mL aliquots into plastic centrifuge tubes. Add 2 mL of 10 mmol / L DNPH to one tube and 2 mL of 2 mol / L hydrochloric acid to the other as a control. Incubate at 11°C for 1 h (vortexing once every 15 min). Then add 2 mL of 20% TCA to each tube and centrifuge at 11000×g at 11°C for 3 min. Discard the supernatant, and wash the precipitate three times with a mixture of 4 mL of ethanol and ethyl acetate (1:1 volume ratio). After air drying, add 3 mL of 6 mol / L guanidine hydrochloride and incubate at 50°C for 45 min to dissolve the precipitate. Measure the absorbance (A370) at 370 nm. The protein concentration was determined using the bovine serum albumin standard curve and the absorbance at 280 nm (guanidine hydrochloride blank), and denoted as C1. The carbonyl content (nmol / mg) was calculated using the formula: Carbonyl content =

[0030] In the formula, 2.2 × 10⁴ M⁻¹·cm⁻¹ is the molar absorptivity.

[0031] MP was dissolved in a specific protein lysate at pH 6.2 (containing 0.6 mol / L NaCl, 2 mmol / L MgCl2, 10 mmol / L sodium pyrophosphate, and 10 mmol / L PHPES) to achieve a final protein concentration of 5 mg / mL. The solution was incubated at 11°C for 4 hours, with shaking every 20 minutes. Subsequently, it was centrifuged at 5000 × g for 15 minutes at 11°C, and the supernatant was collected. The protein concentration in the supernatant was determined using the biuret method, and the ratio of this concentration to the protein concentration before centrifugation was used to obtain the protein solubility.

[0032] The protein stock solution was diluted to 5 mg / mL using phosphate buffer solution at pH 7.0. 1 mL of the diluted solution was added to 200 μL of bromophenol blue (BPB) solution at a concentration of 1 mg / mL. After shaking at room temperature for 10 min, the solution was centrifuged at 11000 rpm for 15 min. 1 mL of the supernatant was collected and 9 mL of phosphate buffer was added. The absorbance was measured at 595 nm (denoted as sample A). A control group (denoted as blank A) was used with buffer and BPB. The results are expressed as the amount of hydrophobic amino acid residues bound by bromophenol blue (μg), calculated using the formula: Bromophenol blue binding amount (μg) = 200 × (A sample - A blank) / A blank Total bacterial count (TVC) determination: The samples were aseptically diluted, plated, and counted according to the national standard GB4789.2—2022.

[0033] pH value determination: Refer to the national standard GB5009.237—2016, and use a pH meter to periodically and in parallel determine the pH value inside the meat sample.

[0034] Thiobarbituric acid (TBARS) value determination: Take 5.0 g of minced sample, add 25 mL of 7.5% trichloroacetic acid (TCA) containing 0.1% EDTA, shake for 30 min, centrifuge at 5000 r / min, 2°C for 10 min, and filter. Take 5 mL of filtrate and add 5 mL of 0.02 mol / L TBA solution, react in a 100°C water bath for 40 min. After cooling for 1 h, centrifuge (5000 r / min, 5 min), take the supernatant, add 5 mL of chloroform, vortex mix, and allow to stand for separation. Measure the absorbance of the supernatant at 532 nm (A532) and 600 nm (A600), and calculate according to the formula: TBARS (mg / 100g) =

[0035] In the formula, 72.06 is the molar mass of malondialdehyde, and 155 is the absorptivity.

[0036] Determination of volatile basic nitrogen (TVB-N): The content of alkaline nitrogenous substances produced by protein decomposition during refrigeration was determined by the micro-diffusion method in the national standard GB5009.228—2016.

[0037] Centrifugation loss rate: Wrap 5.0g of meat sample (denoted as m0) in filter paper, centrifuge at 3500r / min for 15min, and accurately weigh the sample mass after centrifugation (denoted as m1). Centrifugation loss rate = .

[0038] Juice loss rate: Accurately weigh the initial mass of the sample taken at a specific storage time point (denoted as m2), blot dry the surface exudate with sterile filter paper, and weigh again (denoted as m3). Juice loss rate = = .

[0039] Color difference test: Using a spectrophotometer (8mm aperture, 2° field of view, 2% C light source), after calibration with a white board, measure the luminance L value, red-green value A value, and yellow-blue value B value of the product surface.

[0040] The testing method successfully captured the oxidative degradation pattern of myofibrillar proteins during refrigeration: with prolonged storage time, the total thiol content in each group showed a significant decreasing trend, while the carbonyl content continued to increase, leading to decreased protein solubility and increased surface hydrophobicity. Data showed that the 40%, 60%, and 80% CO2 groups effectively slowed down thiol oxidation and carbonyl formation.

[0041] This method clearly indicates the critical point of shelf life by dynamically measuring total bacterial count (TVC) and TVB-N.

[0042] The control group had a TVC level of 7.381g CFU / g and a TVB-N level of 23.47mg / 100g on day 12, both of which significantly exceeded the food safety limits, indicating that its shelf life was only 8 days.

[0043] In the 20%~80% CO2 group, TVC was successfully controlled below 4.901g CFU / g within the first 24 days of storage, TVB-N was consistently below 20mg / 100g, TBARS value was maintained at a mild oxidation level (<0.5mg / 100g), and water loss was extremely low (low juice loss rate at 32 days). Scientific predictions indicate that the shelf life can be extended to 24 days.

[0044] While the 80% CO2 group offers slight advantages in protein protection, excessive carbon dioxide accumulation can lead to a darker product color, a slightly astringent flavor, and excessively high industrial costs. In contrast, the 40% CO2 + 60% N2 packaging group perfectly maintains the characteristic reddish-brown color and sensory flavor of braised meat without introducing oxygen. This demonstrates that modified atmosphere packaging can effectively maintain moisture retention, inhibit microbial growth, and suppress myofibrillar protein and lipid oxidation.

[0045] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. It will be apparent to those skilled in the art that the invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from its spirit or essential characteristics. Therefore, the embodiments should be considered illustrative and non-limiting in all respects, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, all variations falling within the meaning and scope of equivalents of the claims are intended to be included within the scope of the invention. No reference numerals in the claims should be construed as limiting the scope of the claims. Furthermore, it should be understood that although this specification describes embodiments, not every embodiment contains only one independent technical solution. This narrative style is merely for clarity. Those skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. A method for extending the shelf life of braised beef using modified atmosphere packaging, characterized in that: Includes the following steps: Step 1: The finished braised beef, which has been thawed, marinated and cooked, is trimmed and cut in a sterile workshop at a temperature below 12℃. Step 2: Select a high-barrier composite packaging box and a matching sealing film. Both the packaging box and the film are made of PET / PP / EVOH / PE multilayer co-extruded high-barrier structure. Step 3: Place the drained beef chunks flat in the packaging box and send them into the sealed vacuum chamber of the modified atmosphere packaging machine. First, a vacuum is drawn to a vacuum degree of -0.095MPa or higher and maintained for 3-5 seconds. Then, a pre-mixed composite protective gas is injected into the packaging box. The composition and volume percentage of the composite protective gas are as follows: carbon dioxide accounts for 20% to 80%, and the remainder is made up by nitrogen. Immediately after the gas is injected, the box is heat-sealed at a temperature of 140-160℃, a sealing pressure of 0.3-0.5MPa, and a pressure holding time of 1.5-2.5 seconds to form a completely sealed modified atmosphere package. Step 4: After heat sealing, the modified atmosphere packaging will undergo online air tightness and leakage screening. Packaging that fails the sealing test will be removed. The qualified modified atmosphere packaging will be immediately transferred to a constant temperature cold storage at 11℃ and relative humidity of 80%~90% for light protection.

2. The method for extending the shelf life of braised beef using modified atmosphere packaging according to claim 1, characterized in that: The method resulted in a total bacterial count of less than 4.90 lg CFU / g in braised beef after 24 days of refrigerated storage.

3. The method for extending the shelf life of braised beef using modified atmosphere packaging according to claim 1, characterized in that: The method, when the beef is refrigerated for 24 days, results in a volatile basic nitrogen value of less than 20 mg / 100g for the braised beef.

4. The method for extending the shelf life of braised beef using modified atmosphere packaging according to claim 1, characterized in that: The method controls the thiobarbituric acid reactant value of braised beef to a mild oxidation level of less than 0.2 mg / 100g when refrigerated for 24 days.

5. The method for extending the shelf life of braised beef using modified atmosphere packaging according to claim 1, characterized in that: The composite preservative gas actively regulates and lowers the pH value of the meat surface to a threshold range below 6.0 by dissolving carbonic acid on the surface of the meat, thereby inhibiting the protease and lipase activities of Pseudomonas and Enterobacteriaceae.

6. The method for extending the shelf life of braised beef using modified atmosphere packaging according to claim 1, characterized in that: The method controls the centrifugal loss and juice loss rate of braised beef to within 15% and 3.5% respectively when it is refrigerated and stored for 24 days.

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