A thawing method for delaying the spoilage of frozen fresh beef

Abstract

The application discloses a thawing method for delaying corruption of frozen fresh beef, and relates to the technical field of frozen beef thawing, which is thawed by means of oregano essential oil fumigation and low-frequency alternating magnetic field combination. Compared with the traditional air thawing at 4 DEG C, the composite thawing process of oregano essential oil fumigation and low-frequency alternating magnetic field combination can reduce the recovery rate of sublethal cells of the common rotting bacteria Pseudomonas syringae by 20-100%, and reduce the total number of colonies by 0.7-1.6 orders of magnitude, and meanwhile, the thawed beef quality can be effectively improved.

Description

Technical Field

[0001] The invention relates to the technical field of frozen beef thawing, and more particularly to a thawing method for delaying the corruption of frozen fresh beef. Background Art

[0002] Meat, as one of the primary food sources for humans, is rich in nutrients such as lipids, protein, minerals, and vitamins, making it an excellent food for promoting human growth and development and maintaining functional metabolism. Freezing, as the most common and widespread method for long-term food preservation, plays a vital role in the food industry, effectively inhibiting microbial growth and reproduction and extending shelf life. It is a key product form for the import and export trade and interregional circulation of animal and plant products.

[0003] The processing, transportation, and storage of frozen foods are generally carried out at -18°C or lower. The extracellular ice crystals formed in the low temperature environment can easily inactivate microorganisms, so the microbial safety of thawed meat is easily overlooked. In fact, some cold-loving and cold-resistant pathogens (such as Escherichia coli, Staphylococcus aureus, Pseudomonas, etc.) can still survive in low-temperature refrigeration or even freezing environments. They may resist environmental stress by reducing metabolic levels or entering a dormant state. Once the cold chain is interrupted or the temperature rises and fluctuates, such as the subsequent thawing of frozen meat, the remaining microorganisms in the frozen food may quickly resume their growth, reproduction, and pathogenicity. For example, studies have found that after several days of freezing stress, the putrefactive and pathogenic properties of Pseudomonas fluorescens are significantly enhanced during the recovery process to a suitable temperature, which can pose a serious food safety risk.

[0004] Traditional thawing methods for meat include air thawing and water thawing. Air thawing is less expensive, but suffers from poor thermal conductivity and slow thawing speeds. Water thawing, while time-consuming, can lead to microbial contamination and proliferation due to prolonged immersion in water, and can also cause quality deterioration, such as juice loss, lipid oxidation, and myofibrillar protein denaturation. Studies have confirmed that frozen meat can have high levels of microbial contamination after air thawing and running water thawing. Frozen pork stored at -18°C for five days and then air-thawed for three hours showed contamination levels exceeding 4.0 lg CFU / g for Pseudomonas, Thermocytosporin, and Enterobacteriaceae, posing a high safety risk.

[0005] Therefore, developing a new meat thawing process that can improve the microbial safety of thawed meat and extend the shelf life of the product while ensuring the quality of the thawed meat is a technical problem that needs to be solved urgently by those skilled in the art. Summary of the Invention

[0006] In view of this, the present invention provides a thawing method for delaying the spoilage of frozen fresh beef. Compared with traditional air thawing at 4°C, the composite thawing process of low-frequency alternating magnetic field combined with oregano essential oil vapor fumigation can reduce the recovery rate of sublethal cells of Pseudomonas fragrans, a common spoilage fungus in beef, by 20-100% after thawing, and reduce the total colony count by 0.7-1.6 orders of magnitude, while effectively improving the quality of thawed beef.

[0007] In order to achieve the above object, the present invention adopts the following technical solutions:

[0008] A thawing method for delaying the spoilage of frozen fresh beef uses oregano essential oil fumigation combined with a low-frequency alternating magnetic field to thaw the frozen beef.

[0009] Preferably, the oregano essential oil fumigation combined with a low-frequency alternating magnetic field is used to thaw frozen beef as follows: the frozen beef is transferred to a closed low-frequency alternating magnetic field environment with a magnetic field frequency of 50 Hz and a magnetic field strength of 5 mT; oregano essential oil is placed in the magnetic field, and the oregano essential oil is dripped into a sterile polyurethane sponge.

[0010] Preferably, the oregano essential oil is dissolved and diluted with propylene glycol to a final concentration of 15.8 to 250 μL / L.

[0011] Preferably, the thawing temperature is 4°C, and the temperature of the meat sample core is monitored every 15 minutes. When the temperature rises to 2.0±0.5°C, the thawing process is completed.

[0012] Through the above technical solution, it can be seen that compared with the existing technology, the present invention targets the problems of the repair, growth and reproduction of dormant microorganisms in the traditional thawing process of frozen meat, as well as the high cost of low-frequency alternating magnetic field equipment. It combines a low-frequency alternating magnetic field with oregano essential oil vapor fumigation for beef thawing, which can effectively reduce the risk of microbial contamination caused by the existing thawing process and extend the shelf life of meat. Compared with traditional air thawing, the composite thawing process of low-frequency alternating magnetic field combined with oregano essential oil vapor fumigation can reduce the recovery rate of sublethal cells of Pseudomonas fragrans, a common spoilage fungus in beef, by 20 to 100% after thawing, and reduce the total colony count by 0.7 to 1.6 orders of magnitude, thereby extending the shelf life of beef by 2 to 5 days. This combined technology helps to reduce the intensity of the magnetic field, save process costs, and provide technical support for the healthy and high-quality production and sales of thawed meat. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are merely embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the provided drawings without paying any creative work.

[0014] Figure 1 The accompanying figure shows the thawing loss rate of beef under different thawing methods;

[0015] Figure 2 The accompanying figures show the recovery rate (A) of sublethal Pseudomonas fragariae in beef under different thawing methods and the radius of the transparent ring formed in the skim milk plate (B);

[0016] Figure 3 The attached figure shows the effect of different oregano essential oil concentrations on the recovery rate of sublethal Pseudomonas fragrans in composite thawed beef. DETAILED DESCRIPTION

[0017] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0018] Example 1

[0019] Fresh beef tenderloin purchased from the market was washed with sterile water and cut into 4 × 4 × 2 cm (20 ± 0.05 g) blocks in a laminar flow hood. The beef samples were then frozen and stored at -18°C for 70 days. The prepared frozen beef was transferred to a sealable sterile polypropylene box and sealed with parafilm. The sealed box was thawed in a low-frequency alternating magnetic field at a temperature of 4°C, a frequency of 50 Hz, and magnetic field intensities of 1, 3, 5, 7, and 9 mT. An air thaw control was used at 4°C. The core temperature of the meat sample was monitored every 15 minutes using a thermometer. Thawing was completed when the temperature reached 2.0 ± 0.5°C. The meat samples were accurately weighed before and after thawing, and the thawing loss rate was calculated.

[0020] The results of beef thawing loss rate are as follows Figure 1 The results are shown in Figure 2. The thawing loss of beef tenderloin after conventional air thawing was 5.9%. After thawing with a low-frequency alternating magnetic field (1-9 mT), the thawing loss of beef tenderloin was 4.2-5%, both lower than the conventional thawing group. The thawing loss rate was lowest when the magnetic field strength was 5 mT, a 29% decrease compared to air thawing. Therefore, a 5 mT magnetic field strength was used in the subsequent combined thawing process with essential oil vapor fumigation.

[0021] Example 2

[0022] Pseudomonas fragrans was inoculated into 50 mL of fresh sterile broth medium (TSB) and cultured in a shaking incubator at 37°C for 12 h. 15 mL of the culture solution was taken from the culture and centrifuged at 5000 rpm for 5 min in a 50 mL sterile centrifuge tube. The supernatant was discarded and the resulting cells were washed three times with sterile saline (0.85% NaCl). The cells were then suspended in an equal volume of sterile saline to obtain a concentration of 10 7 CFU / mL of bacterial solution.

[0023] Fresh beef tenderloin purchased from the market was washed with sterile water and cut into blocks of 4 × 4 × 2 cm (20 ± 0.05 g) in a clean bench. The blocks were washed with 75% alcohol to remove residual microorganisms on the surface of the blocks, and then washed three times with sterile water to remove residual alcohol on the surface. The blocks were then placed on a sterile culture dish and irradiated on both sides under ultraviolet light in the clean bench for 15 min each.

[0024] Inoculate 100 μL of the bacterial solution onto the surface of a beef sample and allow it to rest in a laminar flow hood for 30 minutes. After 70 days of refrigerated storage at -18°C, transfer the beef sample to a sterile polypropylene box with a sterile polyurethane sponge secured to the inside of the lid. Prepare a 125 μL / L oregano essential oil solution using propylene glycol and drip it onto the sterile polyurethane sponge. Seal the box with parafilm.

[0025] Thaw the sealed box in a low-frequency alternating magnetic field at 4°C, 50 Hz, and 5 mT. Monitor the core temperature of the meat sample every 15 minutes using a thermometer. Thawing is complete when the temperature reaches 2.0 ± 0.5°C.

[0026] The control groups were air thawing at 4°C, low-frequency alternating magnetic field (50 Hz, 5 mT), and oregano essential oil vapor fumigation (125 μL / L).

[0027] Thawed beef samples were prepared into homogenates and spread on non-selective culture medium (TSA) and selective culture medium (CFC), respectively. After 48 h of culture, colonies were counted, the sublethal cell count of Pseudomonas fragrans was determined, and the recovery rate was calculated.

[0028] Skim milk containing 10% (w / v) skim milk powder was sterilized by autoclaving to prepare 1.5% sterilized TSA. 10 mL of the aforementioned skim milk was added and mixed thoroughly to prepare skim milk plates. 1 μL of the homogenate, before and after thawing, was spotted onto the plates. The plates were then incubated at 30°C for 24 hours. The radius of the clearing zone on the skim milk plates was measured to assess changes in extracellular protease secretion by Pseudomonas fragariae before and after thawing.

[0029] The results of the recovery of Pseudomonas fragrans after thawing are as follows Figure 2 As shown in Figure A. After air thawing, the recovery rate of sublethal Pseudomonas fragrans was 100%. After thawing assisted by a low-frequency alternating magnetic field or oregano essential oil vapor fumigation, the recovery rates of sublethal Pseudomonas fragrans were reduced to 89.2% and 62.6%, respectively. However, when the beef was thawed using a combined magnetic field and oregano essential oil vapor fumigation, the recovery rate of sublethal Pseudomonas fragrans was as low as 22.5%, significantly lower than that of the air thawing group and the low-frequency alternating magnetic field or oregano essential oil vapor fumigation-assisted thawing group. This combined thawing process of low-frequency alternating magnetic field and vapor fumigation can effectively reduce the recovery rate of sublethal damaged cells of Pseudomonas fragrans, a common spoilage fungus in meat, thereby extending the shelf life of thawed meat.

[0030] The results of extracellular protease secretion of Pseudomonas fragrans before and after thawing are as follows Figure 2 Figure B shows the radius of the transparent ring formed by Pseudomonas fragrans in a skim milk plate before freezing. Before freezing, the radius of the transparent ring increased to 4.2 mm after air thawing. After thawing with the aid of a low-frequency alternating magnetic field, the radius of the transparent ring was 3.9 mm. Magnetic field-assisted thawing had little effect on the secretion of extracellular proteases by Pseudomonas fragrans. After thawing with the aid of oregano essential oil vapor fumigation, the radius of the transparent ring remained unchanged compared to before freezing. However, after thawing with the aid of a low-frequency alternating magnetic field combined with oregano essential oil vapor fumigation, the radius of the transparent ring decreased to 2.8 mm. This indicates that the combined thawing process can effectively reduce the secretion of extracellular proteases by Pseudomonas fragrans. Specifically, the putrefactive properties of Pseudomonas fragrans did not increase after the combined thawing process, and even showed a slight decrease. This is of great significance for extending the shelf life of frozen fresh meat products.

[0031] Example 3

[0032] Beef samples were prepared according to the method of Example 2. The prepared frozen beef was transferred to a sterile polypropylene box with a sterile polyurethane sponge fixed on the inner side of the lid. Oregano essential oil of different concentrations was prepared using propylene glycol to a final concentration of 15.8, 31.5, 62.5, 125 and 250 μL / L, respectively. The oregano essential oil solution was added dropwise to the sterile polyurethane sponge, and an equal volume of propylene glycol was added as the control group. The box was sealed with a sealing film. The box was then placed in a low-frequency alternating magnetic field environment for thawing, with the thawing temperature set at 4°C, the magnetic field frequency at 50Hz, and the magnetic field strength at 5mT. A thermometer was used to monitor the temperature of the meat sample core every 15 minutes. The thawing process was completed when the temperature rose to 2.0±0.5°C. Air thawing at 4°C and thawing in a low-frequency alternating magnetic field (50Hz, 5mT) were used as controls. The recovery rate of sublethal Pseudomonas fragariae in thawed beef was detected according to the method of Example 1.

[0033] The results of the recovery rate of sublethal Pseudomonas fragariae in thawed beef using low-frequency alternating magnetic field combined with different concentrations of essential oils are shown in the figure. Figure 3As shown in Figure 2 , the recovery rate of Pseudomonas gradually decreased with increasing essential oil concentration. At oregano essential oil concentrations of 15.8, 31.5, 62.5, and 125 μL / L, the recovery rates of sublethal Pseudomonas in composite thawed beef were 79.8%, 56.2%, 30.6%, and 22.5%, respectively. When the oregano essential oil concentration was increased to 250 μL / L, the recovery of sublethal Pseudomonas fragrans during composite thawing was completely inhibited.

[0034] Example 4

[0035] Fresh beef tenderloin purchased from the market was washed with sterile water and cut into 4 × 4 × 2 cm (20 ± 0.05 g) blocks in a laminar flow hood. The beef samples were then frozen and stored at -18°C for 70 days. The frozen beef was transferred to a sterile polypropylene box with a sterile polyurethane sponge fixed to the inner lid. A 250 μL / L solution of oregano essential oil prepared with propylene glycol was dripped onto the sterile polyurethane sponge, and the box was sealed with parafilm. The sealed box was thawed in a low-frequency alternating magnetic field at 4°C, 50 Hz, and 5 mT. Controls were performed using air thawing at 4°C, a low-frequency alternating magnetic field (50 Hz, 5 mT), and oregano essential oil vapor fumigation (250 μL / L). The core temperature of the meat sample was monitored every 15 minutes using a thermometer. Thawing was considered complete when the temperature reached 2.0 ± 0.5°C. The total colony count, juice loss rate, thiobarbituric acid reactive substances (TBARS) value, color and other indicators of the thawed beef were determined.

[0036] The results of the quality indicators of beef after thawing are shown in Table 1. The total number of colonies in beef before freezing was 3.6 log 10 CFU / mL. After air thawing, the total colony count of beef increased slightly to 3.8log 10 CFU / mL. After thawing with the aid of low-frequency alternating magnetic field or oregano essential oil vapor fumigation, the total number of colonies in beef was slightly lower than that in the air thawing treatment group. After thawing with the aid of low-frequency alternating magnetic field combined with oregano essential oil vapor fumigation, the total number of colonies in beef was reduced to 2.2log 10 The CFU / mL was 1.6 orders of magnitude lower than that of air thawing. Compared with traditional air thawing, the thawing loss rate of beef was reduced by 29% and the increase in TBARS value was reduced by 67% after thawing assisted by magnetic field combined with essential oil vapor fumigation. This effectively delayed lipid oxidation of beef during the thawing process. In addition, the brightness value (L*) and redness value (a*) of the beef thawed by the combined assisted thawing were also the closest to those before freezing. This shows that the composite thawing process can effectively improve the quality of thawed meat while ensuring microbial safety and delaying microbial spoilage of meat.

[0037] Table 1 Quality indicators of beef after thawing in different ways

[0038] Before freezing Air magnetic field fumigation Magnetic field + fumigation <![CDATA[Total number of colonies (log 10 CFU / mL)]]> 3.6 3.8 3.1 2.7 2.2 Thawing loss rate (%) - 5.9 4.3 5.8 4.2 TBARS (mg / 100g) 0.028 0.034 0.033 0.030 0.030 L* 41.3 36.2 40.2 39.5 40.9 a* 25.8 21.9 24.5 22.8 24.9

[0039] The various embodiments in this specification are described in a progressive manner, and each embodiment focuses on the differences from other embodiments. The same or similar parts between the various embodiments can be referenced to each other.

[0040] The above description of the disclosed embodiments is intended to enable one skilled in the art to implement or use the present invention. Various modifications to these embodiments will be readily apparent to one skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention is not limited to the embodiments shown herein but is intended to conform to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A thawing method for delaying the spoilage of frozen fresh beef, characterized in that: Frozen beef was thawed by fumigation with oregano essential oil combined with a low-frequency alternating magnetic field. The specific operation was as follows: the frozen beef was transferred to a closed low-frequency alternating magnetic field environment with a magnetic field frequency of 50 Hz and a magnetic field intensity of 5 mT; oregano essential oil was placed in the magnetic field and dropped into a sterile polyurethane sponge.

2. A thawing method for delaying the spoilage of frozen fresh beef according to claim 1, characterized in that: The oregano essential oil was dissolved and diluted with propylene glycol to a final concentration of 15.8-250 μL / L.

3. A thawing method for delaying the corruption of frozen fresh beef according to claim 2, characterized in that: The thawing temperature was 4°C, and the temperature of the meat sample core was monitored every 15 min. The thawing process was completed when the temperature rose to 2.0 ± 0.5°C.

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