A sauce marinating beef preservation method based on cold plasma activated halogen liquid circulation treatment

Abstract

The application provides a sauce marinated beef preservation method based on cold plasma activated brine circulation treatment, and belongs to the technical field of food preservation. The method is as follows: brine pretreatment: taking old brine liquid used in the sauce marinating process, filtering, adjusting the water activity, and obtaining pretreated brine liquid; the pretreated brine liquid is placed in a cold plasma reactor for treatment and activation; sauce marinating processing: after the beef raw material is cut into pieces, the activated brine liquid is used as a heating medium for sauce marinating processing; the activated brine liquid is atomized and sprayed on the surface of the meat pieces; vacuum packaging and cold storage. The application generates nitrite in situ by using cold plasma, and generates flavor compensation substances in situ by means of the controllable Maillard reaction of endogenous components in the brine under the action of plasma active species, the residual amount of nitrite in the final product is as low as 15-25 mg / kg, the total number of colonies can be controlled below 5.01 log CFU / g after 28 days of storage, the retention rate of characteristic flavor is greater than or equal to 70%, and long preservation period storage of sauce marinated beef under low nitrite residue is realized.

Description

Technical Field

[0001] This invention relates to the field of food preservation technology, specifically to a method for preserving braised beef based on cold plasma-activated brine circulation treatment. Background Technology

[0002] Braised beef is a traditional Chinese specialty meat product, beloved by consumers for its unique flavor and rich nutritional value. However, due to its high water activity and rich nutrients, braised beef is highly susceptible to quality deterioration during storage due to microbial growth and fat oxidation, resulting in a generally short shelf life.

[0003] Existing preservation technologies mainly include: (1) High temperature and high pressure sterilization (121℃), which can extend the shelf life to more than 90 days, but seriously damages the taste, flavor and nutrition of the product; (2) Adding chemical preservatives (such as potassium sorbate and nisin), which has a certain antibacterial effect, but may mask the characteristic flavor and does not conform to the trend of clean labeling; (3) Vacuum packaging combined with refrigeration can only delay deterioration, but cannot fundamentally solve the problems of flavor loss and texture softening; (4) Cold plasma directly treats the surface of meat products. Due to the extremely short half-life of active oxygen (ROS) (millisecond level), it can only act on the surface layer of a few millimeters and cannot penetrate into the core, resulting in the phenomenon of "good outside and bad inside" in the later stage of storage.

[0004] The simmering liquid used in braising and stewing is rich in reaction substrates and flavor precursors such as amino acids, peptides, and reducing sugars. However, in traditional processes, it is only used as a heating medium, and its chemical potential remains unactivated. If the simmering liquid could be used as a plasma reaction medium, utilizing its abundant endogenous components to generate antibacterial active substances that can then penetrate into the meat through the braising and stewing process, it would be possible to overcome the current technological bottlenecks. Summary of the Invention

[0005] The technical problems to be solved: In existing technologies, the penetration depth of surface active species in meat products by direct cold plasma treatment is insufficient, chemical preservatives affect characteristic flavors, flavor deterioration during storage is coupled with microbial proliferation, and traditional nitrite addition methods have low consumer acceptance. The purpose of this invention is to provide a method for preserving braised beef based on cold plasma-activated brine circulation treatment. This method uses old brine as the plasma reaction medium, utilizes cold plasma to generate nitrite in situ to exert antibacterial and color-protecting effects, and utilizes the endogenous components of the brine to generate flavor-compensating substances such as pyrazines and sulfur-containing heterocyclic compounds under the induction of plasma active species, thus simultaneously solving the problems of antibacterial, color protection and flavor preservation, while significantly reducing the nitrite residue in the final product.

[0006] Technical solution: A method for preserving braised beef based on cold plasma-activated brine circulation treatment, comprising the following steps: (1) Pretreatment of brine: Take the old brine that is recycled in the braising process, filter it through a 200-mesh filter to remove solid impurities, and adjust the water activity to 0.92-0.95 to obtain the pretreated brine; (2) Cold plasma activation: The pretreated brine is placed in a cold plasma reactor and a gas-liquid two-phase medium barrier discharge method is adopted. The high-voltage electrode is fixed in the gas phase region 1-5 cm above the brine surface. The auxiliary electrode set in the brine body or its interior serves as the grounding electrode. The gas phase region between the high-voltage electrode and the brine surface forms the discharge gap. The discharge voltage is 12-22 kV, the processing time is 1-8 min, the gas source is air or nitrogen-oxygen mixture, and the reactor jacket is circulated with cooling water to control the brine temperature to not exceed 40℃, thus obtaining the activated brine. (3) Activation endpoint determination: After activation, the concentration of nitrite generated in situ in the brine reaches 50-100 mg / L. Nitrite (NO2-) is generated by cold plasma fixing gaseous nitrogen (N2 in air or nitrogen-oxygen mixture) in gas-liquid two-phase medium barrier discharge to generate active nitrogen species (RNS, mainly NO and NO2), which are dissolved and oxidized in the brine to nitrite and nitrate. The endogenous components of the brine participate in the reduction, complexation and subsequent Maillard reaction of active nitrogen under the action of plasma active species. (4) Braised processing: After cutting the beef raw material into pieces, the activated brine is used as the heating medium for braising. The ratio of brine to meat mass is 2:1-4:1. The braising temperature is 85-92℃, the braising time is 60-120min, and the simmering time is 30-60min. (During the simmering stage, when the brine temperature naturally drops to 50-60℃, the amino acid oxidation condensation products generated by the plasma permeate into the intermuscular spaces with the brine reflux. Typical representatives of the above amino acid oxidation condensation products include pyrazines and sulfur-containing heterocyclic compounds.) (5) Surface spraying: After the meat is braised and cooled to 40-60℃, the activated brine is atomized and sprayed onto the surface of the meat. The amount of spraying is calculated as 3%-8% of the meat weight. (6) Vacuum packaging and refrigeration: After spraying, the surface is cooled to room temperature by sterile cold air to form an antibacterial film. After vacuum packaging, it is refrigerated at 0-4℃.

[0007] Furthermore, the old brine mentioned in step (1) is the old brine that has been recycled from the 2nd to the 6th batch; if the sodium chloride content of the brine is >8%, add pure water to dilute it to the sodium chloride content ≤8%, or use electrodialysis desalination treatment to the sodium chloride content ≤8%.

[0008] Furthermore, in step (2), the surface of the high-voltage electrode is coated with a zirconia ceramic insulating layer or fitted with a quartz dielectric tube, the dielectric layer thickness is 0.5-2mm; the discharge voltage is 15-20kV, the frequency is 50Hz-50kHz, the processing time is 2-5min, and the reactor jacket is circulated with cooling water to control the brine temperature at 25-30℃.

[0009] Furthermore, in step (2), the N2:O2 ratio in the nitrogen-oxygen mixture is 4:1-1:1.

[0010] Furthermore, the activation endpoint determination in step (3) also includes an oxidation-reduction potential ≥350mV and a pH decrease of 0.3-0.8 units compared to before activation.

[0011] Furthermore, the beef raw material mentioned in step (4) is beef shank or beef brisket, cut into pieces with a thickness of 3-5cm; the braising process also includes a 90-95℃ initial boiling and blanching step for shaping.

[0012] Furthermore, the nozzle diameter for atomizing spraying in step (5) is 0.3-0.8 mm, and the air pressure is 0.2-0.5 MPa.

[0013] Furthermore, the sterile cold air temperature in step (6) is 10-15℃.

[0014] Furthermore, the vacuum packaging in step (6) uses a vacuum packaging bag with an oxygen permeability ≤1cm. 3 / (m 2 ·24h·atm), evacuate until residual oxygen content ≤1%.

[0015] The present invention provides a braised beef product prepared by the above method, wherein the residual nitrite content in the product is 15-25 mg / kg. Beneficial effects

[0016] (1) This invention uses old brine as a cold plasma reaction medium and adopts a gas-liquid two-phase medium barrier discharge method. The high-voltage electrode is located in the gas phase region above the liquid surface, which avoids corrosion and metal dissolution problems caused by direct contact between the electrode and the brine. It utilizes amino acids and peptides in the brine to generate antibacterial active ingredients such as nitrogen-containing heterocyclic compounds and oxidized polymers. Through the heat penetration and concentration gradient drive in the brine processing, it achieves uniform protection from the surface to the inside, overcoming the defect of direct treatment that only acts on the surface.

[0017] (2) In this invention, the water activity is controlled at 0.92-0.95, which can ensure that the brine has sufficient free water content to facilitate the generation and dissolution diffusion of active species during plasma discharge, and can also avoid excessive water activity (>0.95) causing the meat pieces to absorb too much water and affect the texture during subsequent braising.

[0018] (3) The present invention precisely controls the concentration of nitrite generated in situ in the activated brine to 50-100 mg / L, and the residual amount of the final product is only 15-25 mg / kg, which is lower than the nitrite residue limit of 30 mg / kg for braised meat products specified in the national standard GB 2760 (for example, the residual amount of Comparative Example 4 reached 39 mg / kg due to excessive activation voltage, which exceeded the national standard). Moreover, all of them are converted from plasma-fixed gas phase nitrogen in situ. The endogenous components of the brine participate in the reduction and complexation of active nitrogen. No exogenous sodium nitrite is added to the brine during the preparation process, which achieves low residue while ensuring antibacterial effect.

[0019] (4) This invention induces a controlled, mild Maillard reaction between reducing sugars and amino acids in the brine via plasma, generating in situ flavor-compensating substances such as pyrazines and sulfur-containing heterocyclic compounds. The characteristic flavor retention rate of Example 1 reached 81%, significantly better than that of Comparative Example 8 (57.9%). This demonstrates that in addition to antibacterial and color-protecting effects, this invention also has a unique flavor compensation and enhancement effect, solving the problem of continuous decay of characteristic flavors during storage in the prior art.

[0020] (5) The present invention was tested for N-nitrosamines (GB 5009.26-2023, LC-MS / MS). The N-nitrosamine (calculated as NDMA) residues in each embodiment were lower than the limits of GB 2762 and related meat product standards. It can be seen that no risk of nitrosamine enrichment was observed under the low nitrite residue process. Compared with the traditional braising process with exogenous sodium nitrite, the present invention significantly reduces potential nitrosamine exposure, and the claims of clean labeling and food safety are valid. Detailed Implementation

[0021] This invention proposes a method for preserving braised beef based on cold plasma-activated brine circulation treatment. To make the objectives, technical solutions, and effects of this invention clearer and more explicit, the following will provide a more detailed description of the invention with reference to specific embodiments. It should be understood that the specific embodiments described herein are only for explaining the invention and are not intended to limit the invention.

[0022] Example 1 A method for preserving braised beef based on cold plasma-activated brine circulation treatment includes the following steps: (1) Take 100L of the fourth batch of old brine from a certain braised meat workshop, filter it through 200 mesh gauze to remove the residue, and measure the pH 5.8, Aw 0.90, amino acid nitrogen 1.2g / 100mL and sodium chloride content 8.4%. Add pure water to dilute until the sodium chloride content drops below 8.0%, and adjust Aw to 0.93 at the same time. (2) The brine is transferred to a gas-liquid two-phase dielectric barrier discharge reactor. The high-voltage electrode is a stainless steel disc electrode (8cm in diameter) with a zirconia ceramic insulating layer (1mm thick dielectric layer) on the surface. It is fixed in the gas phase region 2.5cm above the brine surface. A stainless steel auxiliary electrode is set at the bottom of the brine body as a grounding electrode. The gas phase region between the high-voltage electrode and the brine surface forms a discharge gap. An air source is used, with a discharge voltage of 17kV, a frequency of 50Hz, and a processing time of 3.5min. Cooling water is circulated through the reactor jacket to control the brine temperature at 28℃. (3) Detection after activation: The concentration of nitrite generated in situ was 78 mg / L, ORP 395 mV, pH 5.4, which is the activated brine; (4) Take 20kg of beef shank and cut it into 4cm cubes. Blanch it in boiling water for 3 minutes to set its shape. Add 60L of activated brine according to the ratio of brine to meat = 3:1. Heat the brine to 90℃ and simmer for 90 minutes. Turn off the heat and let it sit for 45 minutes. (5) Remove the meat pieces and drain for 5 minutes. Cool to 50°C. Take 1.2L of activated brine (6% of the meat weight) and spray it evenly onto the surface of the meat pieces through a pneumatic atomizing nozzle (0.5mm nozzle diameter, 0.3MPa air pressure). Place it in a sterile environment at 12°C and cool to 25°C. (6) Pack into a vacuum bag (oxygen permeability 0.8cm) 3 / (m 2 During 24 hours atm, the vacuum was evacuated until the residual oxygen content was 0.5%, and then heat-sealed and refrigerated at 4°C.

[0023] Example 2 The only difference from Example 1 is that the discharge voltage is 15kV, the processing time is 2.5min, and the high-voltage electrode is located 2cm above the liquid surface; all other conditions are the same.

[0024] Post-activation assay: In-situ nitrite concentration was 62 mg / L, ORP was 365 mV, and pH was 5.6.

[0025] Example 3 The only difference from Example 1 is that the discharge voltage is 20kV, the processing time is 4min, and the high-voltage electrode is located 3cm above the liquid surface; all other conditions are the same.

[0026] Post-activation assay: In-situ generated nitrite concentration 95 mg / L, ORP 430 mV, pH 5.2.

[0027] Example 4 The only difference from Example 1 is that the plasma treatment time is 2 minutes and the high-voltage electrode is located 2 cm above the liquid surface; all other conditions are the same.

[0028] Post-activation assay: In-situ nitrite concentration was 52 mg / L, ORP was 355 mV, and pH was 5.7.

[0029] Example 5 The only difference from Example 1 is that the plasma treatment time is 5 minutes and the high-voltage electrode is located 3 cm above the liquid surface; all other conditions are the same.

[0030] Post-activation assay: In-situ nitrite concentration was 98 mg / L, ORP was 460 mV, and pH was 4.9.

[0031] Example 6 The only difference from Example 1 is that the surface coating amount is 3% of the meat weight, while the other conditions are the same.

[0032] Example 7 The only difference from Example 1 is that the surface coating amount is 8% of the meat weight, while the other conditions are the same.

[0033] Example 8 The only difference from Example 1 is that the gas source is a nitrogen-oxygen mixture (N2:O2=4:1), the high-voltage electrode is located 2.5cm above the liquid surface, the discharge voltage is 17kV, and the processing time is 3.5min. All other conditions are the same.

[0034] Post-activation detection: In-situ generated nitrite concentration 69 mg / L, ORP 380 mV.

[0035] Comparative Example 1 (Conventional brine without plasma activation) The difference from Example 1 is that the brine is not subjected to cold plasma activation treatment (the background nitrite concentration of the brine is 12 mg / L, and there is no plasma-induced in-situ generation process).

[0036] Comparative Example 2 (Cold plasma directly treats the surface of meat blocks) The difference from Example 1 is that the brine is not activated. Instead, the meat pieces that have been braised and cooled to 50°C are placed directly in the plasma reactor for surface treatment (direct discharge method, high voltage electrode 2.5cm away from the surface of the meat piece, 17kV, 3.5min, the meat pieces are drained of surface juice).

[0037] Comparative Example 3 (only surface spraying with activated brine, without cooking with activated brine) The difference from Example 1 is that conventional unactivated brine is used during the braising process, and activated brine is only sprayed on after the food is removed from the pot (spraying amount 6%).

[0038] Comparative Example 4 (Discharge voltage 25kV, processing time 6min) The difference from Example 1 is that the discharge voltage is 25kV, the processing time is 6min, and the high-voltage electrode is located 4cm above the liquid surface.

[0039] Post-activation detection: In-situ generated nitrite concentration was 168 mg / L.

[0040] Comparative Example 5 (Discharge Voltage 10kV) The difference from Example 1 is that the discharge voltage is 10kV, the processing time is 3.5min, and the high-voltage electrode is located 2cm above the liquid surface.

[0041] Post-activation detection: The concentration of in-situ generated nitrite was only 28 mg / L, and the ORP was 280 mV.

[0042] Comparative Example 6 (using the 10th batch of aged brine) The difference from Example 1 is that the 10th batch of old brine (amino acid nitrogen 0.8g / 100mL, Aw 0.88, salt content 9.5%) was used, the high-voltage electrode was located 2.5cm above the liquid surface, the discharge voltage was 17kV, and the treatment time was 3.5min.

[0043] Post-activation testing: The concentration of nitrite generated in situ was 55 mg / L, but the brine was dark brown in color and had high viscosity.

[0044] Comparative Example 7 (Spraying with the chemical preservative nisin) The difference from Example 1 is that: no activated brine is used, and after braising, a 0.3% nisin solution (6% of the meat weight) is sprayed on.

[0045] Comparative Example 8 (exogenous sodium nitrite added to the same concentration) The difference from Example 1 is that the brine was not activated, and sodium nitrite was directly added to a final concentration of 78 mg / L (the same concentration as after activation in Example 1).

[0046] Comparative Example 9 (without surface coating step) The difference from Example 1 is that: after the braising is completed, it is directly vacuum packaged without the step of activating the braising liquid spraying.

[0047] Test method: (1) Determination of nitrite residue The procedure was performed in accordance with the National Food Safety Standard for the Determination of Nitrites and Nitrates in Food (GB 5009.33-2025). 5.0 g (accurate to 0.01 g) of braised beef sample was accurately weighed. After protein precipitation and fat removal, nitrite was diazotized with p-aminobenzenesulfonic acid under weakly acidic conditions, and then coupled with naphthylethylenediamine hydrochloride to form a purple-red dye. The absorbance was measured at 538 nm using visible spectrophotometry, and quantification was performed using the external standard method. Three parallel samples were prepared for each sample, and the results are expressed as an average value in mg / kg.

[0048] (2) Total bacterial count determination The procedure was performed according to the National Food Safety Standard for Microbiological Examination of Food: Determination of Total Colony Count (GB 4789.2-2022). Under aseptic conditions, 25g of braised beef sample was weighed and placed in 225mL of sterile phosphate buffer or 0.85% sterile physiological saline. After homogenization, a 1:10 sample homogenate was prepared and serially diluted 10-fold. 1mL of each of 2-3 suitable dilutions was injected into sterile Petri dishes, followed by approximately 15-20mL of plate counting agar (PCA). After mixing and solidification, the dishes were incubated at 36℃±1℃ for 48h±2h. Plates with colony counts between 30-300 CFU were used for counting, and the results are expressed as logCFU / g. Two replicates were performed for each sample, and the results are expressed as the average.

[0049] The results are shown in Table 1 below: Table 1. Nitrite Residue and Total Bacterial Count During Storage

[0050] Note: Since the total bacterial count of Comparative Example 1 exceeded 6.0 log CFU / g on day 14, and Comparative Examples 5 and 7 exceeded 6.0 log CFU / g on day 21, and Comparative Example 6 showed severe deterioration in sensory quality (overall acceptability score of 5.6) on day 26, the above samples no longer met the conditions for continued storage evaluation. Therefore, the data of the longest evaluable storage days were included in the comparison.

[0051] As can be seen from Table 1, the residual nitrite content of the final products in each embodiment of the present invention is 15-25 mg / kg. Among them, the residual nitrite content of Example 1 (19 mg / kg), Example 2 (16 mg / kg), and Example 4 (15 mg / kg) are significantly lower than the national limit standard (30 mg / kg). Moreover, all of them are generated in situ by cold plasma fixation of gaseous nitrogen, and no exogenous sodium nitrite is added to the brine during the preparation process.

[0052] Regarding the antibacterial effect, the total bacterial count of Examples 1-3, 5, and 8 after 28 days of storage was controlled below 4.68 log CFU / g, with Example 1 (3.50 log CFU / g) showing the best antibacterial effect. Comparative Example 1, without plasma activation, reached a total bacterial count of 6.83 log CFU / g after 14 days of storage, indicating significant spoilage and making further storage for 28 days impossible. Comparative Example 5, due to excessively low activation voltage and insufficient nitrite production (28 mg / L), reached a total bacterial count of 6.45 log CFU / g after 21 days of storage, indicating severely inadequate preservation.

[0053] Although Comparative Example 4 had a low total bacterial count (4.02 log CFU / g), the final product contained 39 mg / kg of residual nitrite, exceeding the national standard limit. This indicates that while excessively high activation voltage can generate more nitrite, it also poses a risk of exceeding the standard. Comparative Examples 2 and 3 had core bacterial counts as high as 6.08 and 5.75 log CFU / g, respectively. This demonstrates that only by using activated brine as the cooking medium can uniform protection be achieved from the surface to the core, overcoming the limitation of existing technologies where preservatives only act on the surface.

[0054] (3) Determination of textural properties (hardness) Texture Profile Analysis (TPA) was used for determination. Braised beef samples were cut into uniform cubes (1.5cm × 1.5cm × 1.0cm) perpendicular to the muscle fibers. A texture analyzer (such as the TA.XT Plus or equivalent) equipped with a P / 36R cylindrical probe (36mm diameter) was used. The measurement parameters were set as follows: pre-test speed 2.0mm / s, test speed 1.0mm / s, post-test return speed 2.0mm / s, compression set 40%, interval between two compressions 5s, trigger force 5.0g. Six to eight parallel samples were measured for each sample, and the average hardness index was taken, in Newtons (N).

[0055] The results are shown in Table 2 below: Table 2 Hardness during storage

[0056] Note: Comparative Example 1 was stored for 14 days, and Comparative Examples 5 and 7 were stored for 21 days and showed obvious spoilage, so subsequent indicators were no longer meaningful for measurement. Therefore, the data were calculated based on the data from 14 and 21 days, respectively. Comparative Example 6 was stored for 26 days and showed severe deterioration in sensory quality (overall acceptability score was only 5.6 points), so the data were calculated based on the data from 26 days. The data for the remaining samples were calculated based on the data from 28 days.

[0057] As shown in Table 2, the hardness of each embodiment of the present invention ranges from 38.7 to 42.8 N, with Example 1 (42.5 N) and Example 3 (42.8 N) exhibiting the best texture retention. Comparative Example 1, without plasma activation, showed a hardness drop to 28.5 N after 14 days of storage, indicating significant softening. The hardness of Comparative Examples 2 and 3 was also significantly lower than that of the embodiments, demonstrating that the myofibril structure of samples that were not cooked in activated brine or only surface-treated underwent severe degradation during storage.

[0058] (4) Sensory evaluation The sensory evaluation was conducted in accordance with the "Sensory Evaluation Standard for Meat and Meat Products" (GB / T 22210-2008). A professional sensory evaluation team of 10 people (5 men and 5 women, aged 25-45) was formed. All evaluators were trained and familiar with the sensory characteristics of braised beef products. The evaluation was conducted in a dedicated sensory evaluation room with the room temperature controlled at 22-25℃. White ceramic plates were used to hold the samples, and the samples were randomly numbered. The evaluation indicators included three dimensions: color, flavor, and texture, using a 10-point scoring system (1-3 points: unacceptable; 4-6 points: fair; 7-8 points: good; 9-10 points: excellent). The scoring criteria for each indicator are as follows: Color: Assess whether the cut surface of the product exhibits the characteristic reddish-brown or pink color of braised beef, whether the color is uniform, and whether there is any fading or abnormal discoloration.

[0059] Flavor: Assess whether the product has the unique complex flavor of braised beef, including soy sauce aroma, roasted aroma, and meat aroma, and whether it has any rancid, oxidized, or other unpleasant odors.

[0060] Texture: Assess the product's firmness, elasticity, and mouthfeel when chewed to see if it is appropriate, or if it is too soft, too hard, or dry.

[0061] After each sample evaluation, the evaluators rinsed their mouths with purified water and waited 2 minutes before evaluating the next sample. The average scores for each indicator and the overall average acceptability score were calculated.

[0062] The results are shown in Table 3 below: Table 3 Sensory evaluation results

[0063] Note: Comparative Example 1 uses 14 days of data, Comparative Examples 5 and 7 use 21 days of data, Comparative Example 6 uses 26 days of data, and the rest use 28 days of data.

[0064] As shown in Table 3, the overall acceptability scores of all embodiments of the present invention are ≥7.0 points, with Embodiment 1 (8.2 points) and Embodiment 3 (8.0 points) exhibiting the best sensory quality. Embodiment 1 performed best in all three indicators: color (8.5 points), flavor (8.1 points), and texture (8.0 points). The overall acceptability scores of Comparative Examples 1-7 are all below 6.8 points, with Comparative Example 1 scoring only 4.2 points at 14 days, Comparative Example 5 only 4.9 points, and Comparative Example 4 only 5.8 points. The overall acceptability score of Comparative Example 8 is 6.8 points, higher than the other comparative examples, but still significantly lower than that of Embodiment 1 (8.2 points). The difference between the two is mainly reflected in the flavor score, indicating that plasma-activated brine is crucial for flavor compensation. The overall acceptability score of Comparative Example 9 is 6.5 points, but its color score is only 6.0 points, significantly lower than that of Embodiment 1, indicating that surface-sprayed activated brine plays a key role in maintaining the color of the product during storage.

[0065] (5) Analysis of volatile flavor components The determination was performed using headspace solid-phase microextraction-gas chromatography-mass spectrometry (HS-SPME-GC-MS).

[0066] Sample pretreatment: Take 5.0g of braised beef sample, chop it and place it in a 20mL headspace vial, add internal standard (such as 2-octanol, 50μL, 1mg / L), and seal immediately.

[0067] Solid-phase microextraction (SPME): A 50 / 30 μm DVB / CAR / PDMS extraction fiber was used. The headspace vial was equilibrated in a 60 °C water bath for 15 min, and then the aged extraction fiber was inserted into the headspace vial, and extraction and adsorption were performed at 60 °C for 30 min. After adsorption was complete, the fiber was inserted into the GC-MS inlet, and desorption was performed at 250 °C for 5 min.

[0068] Gas chromatography conditions: The column was a DB-5MS capillary column (30m × 0.25mm × 0.25μm) or equivalent. The carrier gas was high-purity helium (purity ≥99.999%), with a flow rate of 1.0 mL / min. Temperature program: Initial temperature 40℃, hold for 3 min, increase to 200℃ at 5℃ / min, then increase to 250℃ at 10℃ / min and hold for 5 min. Injector temperature 250℃, splitless injection.

[0069] Mass spectrometry conditions: Electron impact ion source (EI), ion source temperature 230℃, quadrupole temperature 150℃, transfer line temperature 250℃. Electron energy 70 eV, mass scan range m / z 35-550, full scan mode.

[0070] Qualitative and quantitative analysis: Compounds were qualitatively identified by searching the NIST mass spectrometry library (match ≥80%), and confirmed by comparison with retention indices and standards. The relative content (%) of each compound was calculated using the peak area normalization method, i.e., the percentage of the peak area of ​​each compound relative to the total peak area of ​​all identified compounds.

[0071] Table 4 Comparison of characteristic flavor components of braised beef in Example 1 and Comparative Example 8

[0072] As shown in Table 4, the total relative content of pyrazine compounds in Example 1 was 17.93%, while that in Comparative Example 8 was only 4.71%. Specifically, 2,3,5-trimethylpyrazine (characteristic of roasted and meaty aroma) in Example 1 was 4.06 times higher than that in Comparative Example 8 (4.18% vs 1.03%); and 2,5-dimethylpyrazine (characteristic of roasted and nutty aroma) was 3.08 times higher (3.82% vs 1.24%). Pyrazine compounds are the most important contributors to the characteristic roasted and meaty flavor of braised beef, and their content differences directly determine the richness and typicality of the flavor. The total amount of sulfur-containing heterocyclic compounds in Example 1 was 7.96%, while that in Comparative Example 8 was only 1.29%. In Example 1, 2-methyl-3-furanthiol (with a strong meaty and roasted aroma) was 5.56 times higher than in Comparative Example 8 (3.45% vs 0.62%); 2-acetylthiazole (with roasted and nutty aroma) was 6.29 times higher (1.76% vs 0.28%). Sulfur-containing compounds are essential key components for the characteristic meaty aroma of meat products. The content of furans and pyrans in Example 1 was significantly higher than in Comparative Example 8. The differences in furfural (2.89% vs 1.56%), 5-methylfurfural (1.98% vs 0.87%), and 4-hydroxy-2,5-dimethyl-3(2H)-furanone (2.23% vs 0.89%) were mostly more than 2 times, and these substances give the product a richer caramel sweetness and roasted flavor profile. Ethanoin (3-hydroxy-2-butanone) was 2.34% in Example 1 and 1.12% in Comparative Example 8; diacetyl (2,3-butanedione) was 1.78% in Example 1 and 0.87% in Comparative Example 8. These two compounds impart a rounded, buttery aroma to the product, making the flavor fuller. 4-Ethylguaiacol (0.78% vs 0.34%) and 4-vinylguaiacol (0.56% vs 0.21%) were both higher in Example 1 than in Comparative Example 8, giving the product a more pronounced smoky and spicy background. Common components derived from lipid oxidation (nonanal, 2-nonenal, etc.) and spices (D-limonene, β-caryophyllene, linalool, etc.) showed little difference between the two groups (difference ≤25%), indicating that the basic braising process and spice formulation were the same for both groups, and the flavor differences mainly stemmed from Maillard reaction products induced by plasma-activated braising liquid.

[0073] (6) Determination of flavor retention Flavor retention rate is used to evaluate the degree to which characteristic volatile flavor compounds are retained in braised beef during storage. The calculation method is as follows: ① Using freshly cooked braised beef samples (stored for 0 days) as a control, the types and relative contents of volatile flavor substances were determined according to the above-mentioned “(5) volatile flavor component analysis” method (peak area normalization method).

[0074] ② Determine the types and relative contents of volatile flavor compounds in the samples to be tested for storage period (e.g., 21 days or 28 days of storage) using the same method.

[0075] ③ Flavor retention rate is calculated using the following formula: Flavor retention rate (%) = C t / C0×100%; Among them, C t Ct represents the total relative content of characteristic flavor compounds in the sample stored for t days (peak area normalization method), and C0 represents the total relative content of the corresponding characteristic flavor compounds in the fresh sample (stored for 0 days).

[0076] "Characteristic flavor compounds" refer to volatile flavor compounds such as pyrazines, sulfur-containing heterocyclic compounds, furans, pyrans, aldehydes, alcohols, ketones, esters, acids, phenols, terpenes, and heterocyclic compounds, identified by gas chromatography-mass spectrometry (GC-MS) with a matching degree ≥80%. Alternatively, key flavor active substances of braised beef (such as 2,3,5-trimethylpyrazine and 2-methyl-3-furanthiol, determined by odor activity value OAV ≥ 1) can be selected for targeted calculation.

[0077] ④ Each sample is prepared in triplicate, and the results are expressed as the average value, rounded to the nearest integer.

[0078] Table 5 Flavor Retention Rate During Storage

[0079] Note: Comparative Example 1 was not measured because it was stored for 14 days, Comparative Examples 5 and 7 were stored for 21 days, and Comparative Example 6 was stored for 26 days and showed obvious spoilage, so subsequent indicators were no longer meaningful for measurement. The remaining groups were measured after 28 days.

[0080] As shown in Table 5 above, in terms of flavor retention, Example 1 achieved a characteristic flavor retention rate of 81.1%, while Example 3 achieved 79.3%, significantly better than all comparative examples. The flavor retention rates of Comparative Example 2 (49.9%) were all less than 50%, indicating severe loss of characteristic flavor substances during storage. Particularly noteworthy is that the flavor retention rate of Comparative Example 8 (exogenous addition of sodium nitrite to the same concentration) was only 57.9%, significantly lower than that of Example 1 (81.1%). This demonstrates that plasma-activated brine not only provides the antibacterial and color-protecting effects of nitrite, but the additional pyrazines and sulfur-containing heterocyclic compounds induced by it can also effectively compensate for flavor loss during storage. This synergistic effect cannot be achieved by simply adding exogenous sodium nitrite.

[0081] Security testing: Referring to GB 5009.26-2023, "National Food Safety Standard - Determination of N-nitrosamines in Food," 5.0 g (accurate to 0.01 g) of braised beef sample was accurately weighed, extracted and concentrated with organic solvent, and then qualitatively and quantitatively analyzed using liquid chromatography-tandem mass spectrometry (LC-MS / MS). N-dimethyldeuterated amine (NDMA-d6) was used as an internal standard for calibration, and quantification was performed using a matrix-matched standard curve method. The limit of detection was 1.0 μg / kg, and the limit of quantitation was 2.0 μg / kg. Three parallel samples were prepared for each sample, and the results are expressed as an average value in μg / kg.

[0082] The residual NDMA in the final product is shown in Table 6 below: Table 6. Residues of N-nitrosamines (calculated as NDMA)

[0083] As shown in Table 6, the NDMA residue levels in each embodiment ranged from 1.8 to 2.6 μg / kg, all lower than the limit for N-nitrosodimethylamine in meat products specified in GB 2762 (≤3.0 μg / kg). The NDMA residue in Comparative Example 1 was 1.6 μg / kg, which is the background level of the brine; the NDMA residue in Example 1 was 2.2 μg / kg, only slightly higher than the background level. Comparative Example 8, with the addition of exogenous sodium nitrite to the same nitrite concentration, had an NDMA residue of 8.3 μg / kg, 3.8 times that of Example 1, and exceeded the limit specified in GB 2762. This is because the nitrite in the plasma-activated brine of this invention is generated gradually in situ, and is partially consumed and converted during the braising process. Furthermore, the Maillard reaction products induced by plasma in the brine competitively consume some of the nitrite, reducing the substrate for nitrosamine reaction and thus significantly reducing NDMA formation. Comparative Example 4 showed that excessively high discharge voltage resulted in nitrite residue reaching 39 mg / kg, and its NDMA residue correspondingly increased to 12.7 μg / kg, also exceeding the limit of GB 2762, further confirming the importance of controlling plasma activation parameters. These results demonstrate that the present invention achieves low nitrite residue while maintaining NDMA residue well below the national standard limit, and is significantly superior to traditional exogenous sodium nitrite addition processes, indicating good food safety.

[0084] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Any person skilled in the art can make many possible variations and modifications to the technical solutions of the present invention, or modify them into equivalent embodiments, without departing from the spirit and technical essence of the present invention. Therefore, any simple modifications, equivalent substitutions, equivalent changes, and modifications made to the above embodiments based on the technical essence of the present invention, without departing from the content of the technical solutions of the present invention, shall still fall within the scope of protection of the technical solutions of the present invention.

Claims

1. A method for preserving braised beef based on cold plasma-activated brine circulation treatment, characterized in that, Includes the following steps: (1) Pretreatment of brine: Take the old brine that is recycled in the braising process, filter to remove solid impurities, and adjust the water activity to 0.92-0.95 to obtain the pretreated brine; (2) Cold plasma activation: The pretreated brine is placed in a cold plasma reactor and a gas-liquid two-phase medium barrier discharge method is adopted. The high-voltage electrode is fixed in the gas phase region 1-5 cm above the brine surface. The auxiliary electrode set in the brine body or its interior serves as the grounding electrode. The gas phase region between the high-voltage electrode and the brine surface forms the discharge gap. The discharge voltage is 12-22 kV, the processing time is 1-8 min, the gas source is air or nitrogen-oxygen mixture, and the reactor jacket is circulated with cooling water to control the brine temperature to not exceed 40℃, thus obtaining the activated brine. (3) Activation endpoint determination: The concentration of nitrite generated in situ in the brine after activation reaches 50-100 mg / L; (4) Braised processing: After cutting the beef raw material into pieces, the activated brine is used as the heating medium for braising. The ratio of brine to meat mass is 2:1-4:

1. The braising temperature is 85-92℃, the braising time is 60-120min, and the simmering time is 30-60min. (5) Surface spraying: After the meat is braised and cooled to 40-60℃, the activated brine is atomized and sprayed onto the surface of the meat. The amount of spraying is calculated as 3%-8% of the meat weight. (6) Vacuum packaging and refrigeration: After spraying, use sterile cold air to cool to room temperature, vacuum package and refrigerate at 0-4℃.

2. The method according to claim 1, characterized in that, The old brine mentioned in step (1) is the old brine that has been recycled from the 2nd to the 6th batch; if the sodium chloride content of the brine is >8%, add pure water to dilute it to the sodium chloride content ≤8%, or use electrodialysis desalination treatment to the sodium chloride content ≤8%.

3. The method according to claim 1, characterized in that, In step (2), the surface of the high-voltage electrode is coated with a zirconia ceramic insulating layer or fitted with a quartz dielectric tube, with a dielectric layer thickness of 0.5-2mm; the discharge voltage is 15-20kV, the frequency is 50Hz-50kHz, the processing time is 2-5min, and the reactor jacket is circulated with cooling water to control the brine temperature at 25-30℃.

4. The method according to claim 1, characterized in that, In step (2), the nitrogen-oxygen mixture has a ratio of N2:O2 = 4:1-1:

1.

5. The method according to claim 1, characterized in that, The activation endpoint determination in step (3) also includes an oxidation-reduction potential ≥350mV and a pH decrease of 0.3-0.8 units compared to before activation.

6. The method according to claim 1, characterized in that, The beef raw material mentioned in step (4) is beef shank or beef brisket, cut into pieces with a thickness of 3-5cm; the braising process also includes a 90-95℃ initial boiling and blanching step for shaping.

7. The method according to claim 1, characterized in that, The nozzle diameter for atomizing spraying in step (5) is 0.3-0.8 mm, and the air pressure is 0.2-0.5 MPa.

8. The method according to claim 1, characterized in that, The sterile cold air temperature mentioned in step (6) is 10-15℃.

9. The method according to claim 1, characterized in that, The vacuum packaging described in step (6) uses vacuum packaging bags with an oxygen permeability ≤1cm. 3 / (m 2 ·24h·atm), evacuate until residual oxygen content ≤1%.

10. The braised beef product prepared by the method according to any one of claims 1-9, characterized in that, The residual nitrite content in the product is 15-25 mg / kg.

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