Preparation method of low-nitrite salted pork in jelly by using natural preservative

Abstract

The invention discloses a preparation method of low-nitrite salted pork in jelly by using a natural preservative, and belongs to the technical field of food processing. The preparation method comprises the following steps: mixing natural preservatives such as a tea polyphenol solution, an epsilon-polylysine solution, a ginger essential oil solution and an illicium verum essential oil solution to prepare a composite antibacterial solution; and dipping the salted pork in jelly, carrying out modified atmosphere packaging on the product, and carrying out radio frequency sterilization and ultrahigh-voltage electric field sterilization, so that the quality guarantee period of the product is prolonged, and the nitrite content is remarkably reduced. The method provided by the invention is simple and convenient in preparation process, obvious in effect, safe and non-toxic. By adopting the method to treat the salted pork in jelly, the shelf life of the salted pork in jelly at 0-4 DEG C is prolonged by 8-20 days. Compared with an untreated salted pork sample, the salted pork sample has the advantages that the nitrite residue is reduced by 68-88%, and no adverse effect is caused on the flavor of the product.

Description

Technical Field

[0001] The present invention discloses a preparation method of low-nitrite crystal cured meat using natural preservatives, belonging to the technical field of food processing. Background Art

[0002] Crystal cured meat, also known as crystal cured pig's trotters, is a traditional famous dish in Huaiyang cuisine, with a history of more than 300 years. It is a typical Chinese traditional sauce-braised low-temperature meat product, often eaten with shredded ginger and rice vinegar. It is deeply loved by consumers for its advantages such as white skin, red meat, transparent brine jelly, rich fragrance, and rich nutrition. The raw and auxiliary materials of crystal cured meat are various and rich in nutrition; the finished product contains a large amount of high-nutrition components such as protein and fat, with a high water activity and a moderate pH value, which are very suitable for the growth and reproduction of spoilage microorganisms. In addition, the brine jelly of crystal cured meat will be damaged under high-temperature conditions, so high-temperature sterilization cannot be used in the processing of this product, resulting in the difficult complete solution of the microbial problem. To ensure product quality, crystal cured meat needs to be transported, stored, and sold under the condition of 0-4°C, using low temperature to inhibit the activities of microorganisms. However, during this process, bacteria, especially psychrophilic bacteria, will still grow and reproduce, resulting in a decline in product quality, such as loss of luster, change in meat color, generation of peculiar smell, and even liquefaction and dripping of soup. Therefore, the shelf life of crystal cured meat is short, the factory pass rate is low, the requirements for storage and transportation conditions are high, its sales radius is limited, and the storage and transportation costs and food safety risks are relatively high. At the same time, crystal cured meat needs to use nitrite for color development and preservation. Nitrite can form strongly carcinogenic nitrosamines in the processing of meat products, posing a food safety hazard. In this regard, natural preservatives can be used to reduce the usage amount of nitrite and block the formation of nitrosamines.

[0003] Natural preservatives refer to substances secreted by organisms or existing in organisms that have antibacterial effects. After being artificially extracted or processed, they become food preservatives, with advantages such as high safety and biodegradability. As an antioxidant, tea polyphenols show good effects in inhibiting the spoilage of meat products. This substance is mainly composed of polyhydroxy phenolic compounds. Among them, catechin substances are the main active ingredients, accounting for 60-80%, and the remaining components are mostly flavonoids and anthocyanins. The good antioxidant property of tea polyphenols can effectively reduce the nitrite residue during the storage of crystal-cured meat. And ε-polylysine belongs to the preservative for cooked meat products and also shows good antibacterial properties for crystal-cured meat. This substance has a wide antibacterial spectrum and has a significant inhibitory effect on Gram-positive bacteria such as Staphylococcus aureus, etc., and can play a good antibacterial effect. In life, plants such as ginger, star anise, fennel, and garlic are often used for flavoring, antibacterial, and aroma enhancement of meat products. The essential oils prepared from these plants are rich in reducing substances and can also play good antioxidant, nitrite-reducing, and antibacterial effects. Plant essential oils belong to mixtures and contain compounds such as terpenoids, alcohols, ketones, and acids. Therefore, the ability of plant essential oils to scavenge nitrite is the result of the combined action of various compounds. The antioxidant components in plant essential oils can neutralize free radicals and inhibit lipid peroxidation; some active components can also hinder the synthesis of nitrosamines and catalyze the degradation of nitrite. In addition, plant essential oils have a broad-spectrum antibacterial effect and can inhibit the growth and reproduction of microorganisms by destroying the basic structure of bacteria, interfering with the genetic function of bacteria, affecting energy production and the synthesis of cell metabolites. In a low-temperature environment, plant essential oils can also form a relatively stable protective film on the surface of objects, which can not only maintain the appearance and texture of meat products but also increase the duration of the action of antibacterial substances. Traditional vacuum packaging cannot completely remove oxygen, and its oxygen residue is about 0.5-2%; while modified atmosphere packaging can accurately adjust the content of each gas, can achieve zero oxygen, and completely inhibit aerobic bacteria and lipid oxidation. At the same time, modified atmosphere packaging has good flexibility in adjusting the gas composition. The carbon dioxide content of the product environment can be increased by using modified atmosphere packaging, so as to have an excellent inhibitory effect on bacteria, especially spoilage bacteria including Pseudomonas. In addition, vacuum packaging will inevitably cause crystal-cured meat to be deformed by extrusion, while modified atmosphere packaging can avoid this point, maintain the integrity and crystal-clear texture of the product, and is more attractive to consumers. Radio frequency sterilization technology has deep penetration, and the penetration depth can reach more than 10 cm, far better than traditional steam sterilization and water bath sterilization, and is suitable for low-temperature meat products with a certain thickness such as crystal-cured meat. At the same time, radio frequency sterilization technology uses high-frequency electromagnetic fields to make molecules vibrate, and can raise the central temperature of the product to the target value in a short time, saving the processing time of the product. Radio frequency sterilization technology has a greater impact on areas with high water content (such as microbial enrichment areas), can specifically inactivate microorganisms, and also has an inhibitory effect on spores, while having less impact on the gel-state components in the product, and can maintain the transparent texture and elasticity of crystal-cured meat.Ultra-high pressure sterilization technology can uniformly penetrate the entire product without slicing the product or adding a conductive medium. The ultra-high pressure sterilization process is a non-thermal process and will not destroy the volatile flavor substances of the product. This technology can achieve an inactivation rate of more than 99.9% for Gram-negative bacteria, molds, and yeasts, will not damage the collagen network, and can maintain the unique shape and texture of crystal cured meat. Among them, the gel structure retention rate can reach more than 95%. However, ultra-high pressure sterilization can only inhibit some spores. Therefore, it is necessary to cooperate with radio frequency sterilization to reduce the initial microbial content of the product, and then combine with subsequent refrigeration treatment to significantly extend the shelf life of crystal cured meat.

[0004] Pan Daodong (2022) et al. disclosed a preparation method of low-biogenic amine and nitrite-free marinated duck (Publication No.: CN114081139A). After preparing ordinary marinated duck, it is necessary to soak the marinated duck in a grape seed extract solution (100 - 300 mg / kg) prepared with 10% brine for 30 - 40 s. The process also requires covering with plastic wrap. Then, the marinated duck is drained and vacuum-packed. The grape seed extract used in this method will affect the meat color of the product due to its inherent color, deepening the natural color of the duck meat and reducing its glossiness.

[0005] Xi Yimin (2016) disclosed a meat processing method to replace nitrite (Publication No.: 106071907A), and its nitrite substitutes include monascus red, betanin, potassium sorbate, D-isoascorbic acid sodium, lactococcus lactis streptocin, natamycin, natural vitamin E, rosemary extract, sage essential oil, tea polyphenols, L-sodium glutamate and other substances. The nitrite substitutes used in this method have a complex composition and a relatively high production cost.

[0006] Xiao Xiang et al. (2013) disclosed a compound bacteriostatic agent for extending the shelf life of vacuum-packed low-temperature meat products and its preparation method (Publication No.: 103315045A). The bacteriostatic agent is composed of the following substances: 3 - 6 parts of tea polyphenol solution A, 3 - 6 parts of garlic extract B, 0 - 3 parts of nutmeg extract C, and 0 - 3 parts of cinnamon extract D. In this method, the raw materials and ethanol are subjected to ultrasonic extraction for 30 - 40 min according to a certain material-liquid ratio. After filtering through 8 layers of sterile gauze, ethanol needs to be removed by rotary evaporation and the original volume is restored with sterile water. The whole operation process is time-consuming and laborious. In addition, the compounded extract solutions cannot be used directly and need to be diluted 100 - 1000 times.

[0007] Li Feng (2008) disclosed a natural film-forming preservative for crystal cured meat (Publication No.: CN 1723803A). The natural preservative contains 0.025 - 0.05% nisin, 0.5 - 1.0% tea polyphenols, 0.5 - 1.0% lysozyme and an appropriate amount of film-forming agent. The film-forming agent is glacial acetic acid-chitosan mixture, collagen or pullulan polysaccharide, with a mass fraction of 1 - 3%. In this method, collagen and pullulan polysaccharide as film-forming aids are also good carbon and nitrogen sources for most spoilage bacteria, which may lead to an increase in the total number of bacteria. In addition, the chitosan-glacial acetic acid solution has a certain viscosity, making it inconvenient to spray on the product.

[0008] Chang Zhongyi et al. (2006) disclosed a method for preserving crystal cured meat (Publication No.: CN 1806569A). This method sprays or drenches crystal cured meat with a transglutaminase solution to extend the shelf life of the product. This method uses a single bacteriostatic agent to treat crystal cured meat, and the effect of extending the shelf life is relatively ordinary. In addition, this method requires multiple sprays or drenches of crystal cured meat, resulting in a large loss of preservative.

[0009] Chang Zhongyi et al. (2006) disclosed a natural preservative film-forming solution for crystal cured meat (Publication No.: CN 1806567A). This film-forming solution is composed of 0.8 - 1.2% lactic acid, 0.8 - 1.2% chitosan, 0.008 - 0.012% nisin and the balance of water. The added lactic acid in this method may affect the product flavor. In addition, when the dosages of lactic acid, chitosan and nisin are all increased, the effect of extending the shelf life of the product does not change. Summary of the Invention

[0010] The object of the present invention is to provide a method for preparing low-nitrite crystal cured meat using natural preservatives. By compounding tea polyphenols, ε-polylysine and appropriate plant essential oils, and combining technologies such as modified atmosphere packaging, radio frequency sterilization, and ultra-high voltage electric field sterilization, while extending the shelf life of the product, the nitrite content is significantly reduced.

[0011] The technical solution of the present invention is as follows:

[0012] A method for preparing low-nitrite crystal cured meat using natural preservatives, the main steps are as follows:

[0013] (1) Preparation of natural preservative solution: Prepare a tea polyphenol solution and an ε-polylysine solution with a mass fraction of 0.5 - 1% using sterile water; prepare an absolute ethanol solution with a volume fraction of 20% using sterile water, and then prepare a ginger essential oil solution and an anise essential oil solution with a mass fraction of 0.6 - 1% using the absolute ethanol solution;

[0014] (2) Preparation of the composite antibacterial solution: Mix the tea polyphenol solution, ε-polylysine solution, ginger essential oil solution, and star anise essential oil solution, add soy protein isolate and lecithin as emulsifiers, and thoroughly mix these substances with a high-speed homogenizer to obtain the composite antibacterial solution;

[0015] (3) Immersion: Immerse the crystal cured meat samples in the composite antibacterial solution prepared in step (2). After 1 minute of immersion, take them out and let them air-dry naturally in the air for 1 minute;

[0016] (4) Modified atmosphere packaging: Use low-density polyethylene film to carry out modified atmosphere packaging on the immersed crystal cured meat samples; the gas filled in the modified atmosphere packaging is a mixed gas of nitrogen and carbon dioxide;

[0017] (5) Sterilization: Use radio frequency and ultra-high voltage electric field to sterilize the packaged crystal cured meat samples;

[0018] (6) Storage: Store the sterilized crystal cured meat samples in an environment of 0 - 4 °C.

[0019] In the above step (1), the mass fractions of each natural preservative solution are as follows: the tea polyphenol solution is 1%, the ε-polylysine solution is 1%, the ginger essential oil solution is 0.6%, and the star anise essential oil solution is 0.6%.

[0020] In the above step (2), the mass concentration of soy protein isolate is 0.5%, and the mass concentration of lecithin is 0.05%.

[0021] In the above step (4), the density value of the polyethylene film is 0.89 - 0.92 g / cm 3 .

[0022] In the above step (4), the gas composition of the modified atmosphere packaging is 30% carbon dioxide and 70% nitrogen.

[0023] In the above step (5), the radio frequency is 27.12 MHz, the electric field strength is 10 - 15 kV / cm, the plate spacing is 180 mm, and it is treated at 55 °C for 8 minutes; the pressure of the ultra-high voltage electric field sterilization is 500 MPa, and the treatment duration is 10 minutes.

[0024] The beneficial effects of the present invention compared with the prior art are as follows:

[0025] (1) The preparation method of the present invention is simple to operate, and the obtained product is convenient to use, safe and reliable, and has a broad market application space. The crystal cured meat samples are treated with the composite antibacterial solution, then subjected to modified atmosphere packaging, and then radio frequency sterilization and ultra-high voltage electric field sterilization. From the determination of the total number of colonies, the shelf life of the crystal cured meat under the storage condition of 0 - 4 °C is extended by more than 8 days. During storage, the nitrite content is significantly reduced, and the clearance rate can reach more than 68%.

[0026] (2) The present invention uses natural preservatives to reduce the residual nitrite in crystal braised pork and extend the shelf life of the product. The advantages are that the natural preservatives used are biodegradable, safe and non-toxic, water-soluble, and have a wide range of effects. In addition, the addition of the composite antibacterial liquid will not deteriorate the flavor of the crystal braised pork, thereby protecting the commercial value of the product to a large extent. The tea polyphenols used in the present invention can enhance the stability of protein through complexation, avoid protein corruption and produce biogenic amines; and can also reduce the content of microorganisms by destroying the cell structure of bacteria and inhibiting bacterial protein expression. In addition, the catechins rich in tea polyphenols have strong antioxidant properties and can significantly inhibit and remove free radicals, thereby reducing the formation of nitrite. ε-polylysine has a wide antibacterial spectrum and can destroy the cell membranes of microorganisms such as Escherichia coli and Staphylococcus aureus, causing the microorganisms to lose vitality or even die. The ginger essential oil used in the present invention has terpene compounds as its main chemical components, such as zingiberene, β-sesquiphellandrene, and α-curcumene. The antibacterial mechanism of ginger essential oil is to destroy the cell membrane structure of bacteria, causing leakage of intracellular substances, resulting in fatal damage to the bacteria. The main components of star anise essential oil include anisaldehyde, limonene, and trans-anethole, which damage the bacterial tissue structure and thus achieve the purpose of antibacterial. In addition, plant essential oils are mixtures containing terpenes, alcohols, ketones, acids and other compounds. Its ability to scavenge nitrite is the result of the combined effects of various compounds. The antioxidant components in plant essential oils can neutralize free radicals and inhibit lipid peroxidation; some active ingredients can also hinder the synthesis of nitrosamines and catalyze the degradation of nitrite.

[0027] (3) In the present invention, the compounding of the natural preservatives uses soy protein isolate and lecithin as emulsifiers, and is homogenized by a high-speed homogenizer, which can effectively mix the water-soluble natural preservatives (tea polyphenols, ε-polylysine) and the oil-soluble natural preservatives (ginger essential oil, star anise essential oil) fully. This avoids the stratification of natural preservatives of different phases, which makes the antibacterial effect and nitrite-reducing effect of the composite antibacterial liquid worse. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 It is a comparison chart of the residual nitrite of Examples 1, 2, 3 of the present invention and Comparative Examples 1, 2, 3, 4.

[0029] Figure 2 It is a comparison chart of the total number of colonies of crystal braised pork treated by radio frequency sterilization, ultra-high voltage electric field sterilization and their coordinated treatment.

[0030] Figure 3 It is a graph showing the total colony count results of Comparative Examples 1, 2, 3 and 4 of the present invention.

[0031] Figure 4 It is the comparison chart of the total number of colonies of Example 1, 2, 3 of the present invention and Comparative Examples 5, 6, 7. Specific embodiments

[0032] In order to make the objectives, technical solutions and advantages of the present invention more clear and understandable, the present invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0033] In the following embodiments of the present invention, the weight of the crystal cured meat sample used is about 100 g. The sample needs to be fully immersed in the compound bacteriostatic solution.

[0034] Example 1

[0035] A preparation method of low-nitrite crystal cured meat using natural bacteriostatic agents, the steps are as follows:

[0036] (1) Preparation of natural preservative solution: Prepare a tea polyphenol solution with a mass fraction of 0.5% and an ε-polylysine solution with sterile water; prepare an absolute ethanol solution with a volume fraction of 20% with sterile water, and then use it to prepare a ginger essential oil solution and an anise essential oil solution with a mass fraction of 0.6%;

[0037] (2) Preparation of compound bacteriostatic solution: Mix the tea polyphenol solution, ε-polylysine solution, ginger essential oil solution, and anise essential oil solution, and add soy protein isolate and lecithin as emulsifiers, the former with a mass concentration of 0.5% and the latter with a mass concentration of 0.05%. Mix these substances thoroughly with a high-speed homogenizer to obtain a compound bacteriostatic solution;

[0038] (3) Impregnation: Immerse the crystal cured meat sample in the compound bacteriostatic solution prepared in step (2). After 1 minute of impregnation, take it out and air-dry it naturally in the air for 1 minute;

[0039] (4) Modified atmosphere packaging: Use low-density polyethylene film (0.89 - 0.92 g / cm 3 ) to carry out modified atmosphere packaging on the impregnated crystal cured meat sample; the gas filled in the modified atmosphere packaging is a mixed gas of 30% nitrogen and 70% carbon dioxide;

[0040] (5) Sterilization: Use radio frequency and ultra-high voltage electric field to sterilize the packaged crystal cured meat sample. The radio frequency is 27.12 MHz, the electric field strength is 10 - 15 kV / cm, the plate spacing is 180 mm, and it is treated at 55 °C for 8 minutes. The pressure of ultra-high voltage electric field sterilization is 500 MPa, and the treatment duration is 10 minutes;

[0041] (6) Storage: Store the sterilized crystal cured meat sample in an environment of 0 - 4 °C.

[0042] For the crystal cured meat samples prepared above, measure their nitrite residue content and total number of colonies, and determine whether the crystal cured meat samples are spoiled based on the total number of colonies. After being treated through the steps of Example 1, the nitrite residue content of the crystal cured meat samples is less than half of the previous amount, the nitrite clearance rate reaches 68.54%, and the storage time is extended by 8 days.

[0043] Example 2

[0044] A method for preparing low-nitrite crystal cured meat using natural bacteriostatic agents, the steps are as follows:

[0045] (1) Preparation of natural preservative solution: Prepare a tea polyphenol solution with a mass fraction of 1% and an ε-polylysine solution using sterile water; prepare an absolute ethanol solution with a volume fraction of 20% using sterile water, and then use it to prepare a ginger essential oil solution and an anise essential oil solution with a mass fraction of 0.6%;

[0046] (2) Preparation of compound bacteriostatic liquid: Mix the tea polyphenol solution, ε-polylysine solution, ginger essential oil solution, and anise essential oil solution, and add soy protein isolate and lecithin as emulsifiers, with the former having a mass concentration of 0.5% and the latter having a mass concentration of 0.05%. Mix these substances thoroughly using a high-speed homogenizer to obtain a compound bacteriostatic liquid;

[0047] (3) Impregnation: Immerse the crystal cured meat samples in the compound bacteriostatic liquid prepared in step (2). After 1 minute of impregnation, take them out and let them air-dry naturally in the air for 1 minute;

[0048] (4) Modified atmosphere packaging: Use low-density polyethylene film (0.89 - 0.92 g / cm 3 ) to carry out modified atmosphere packaging on the impregnated crystal cured meat samples; the gas filled in the modified atmosphere packaging is a mixed gas of 30% nitrogen and 70% carbon dioxide;

[0049] (5) Sterilization: Use radio frequency and ultra-high voltage electric field to sterilize the packaged crystal cured meat samples. The radio frequency is 27.12 MHz, the electric field strength is 10 - 15 kV / cm, the plate spacing is 180 mm, and it is treated at 55 °C for 8 minutes. The pressure for ultra-high voltage electric field sterilization is 500 MPa, and the treatment duration is 10 minutes;

[0050] (6) Storage: Store the sterilized crystal cured meat samples in an environment of 0 - 4 °C.

[0051] For the crystal cured meat samples prepared above, measure their nitrite residue content and total number of colonies, and determine whether the crystal cured meat samples are spoiled based on the total number of colonies. After being treated through the steps in Example 2, the nitrite residue content of the crystal cured meat samples is greatly reduced, the nitrite clearance rate is 76.22%, and the storage time is extended by 12 days.

[0052] Example 3

[0053] A method for preparing low-nitrite crystal cured meat using natural bacteriostatic agents, the steps are as follows:

[0054] (1) Preparation of natural preservative solution: Prepare a tea polyphenol solution with a mass fraction of 1% and an ε-polylysine solution with sterile water; prepare an absolute ethanol solution with a volume fraction of 20% with sterile water, and then prepare a ginger essential oil solution and an anise essential oil solution with a mass fraction of 1% with it;

[0055] (2) Preparation of compound bacteriostatic liquid: Mix the tea polyphenol solution, ε-polylysine solution, ginger essential oil solution, and anise essential oil solution, and add soy protein isolate and lecithin as emulsifiers. The former has a mass concentration of 0.5%, and the latter has a mass concentration of 0.05%. Mix these substances thoroughly with a high-speed homogenizer to obtain a compound bacteriostatic liquid;

[0056] (3) Impregnation: Immerse the crystal cured meat sample in the compound bacteriostatic liquid prepared in step (2). After immersing for 1 min, take it out and air-dry it naturally in the air for 1 min;

[0057] (4) Modified atmosphere packaging: Use low-density polyethylene film (0.89 - 0.92 g / cm 3 ) to carry out modified atmosphere packaging on the impregnated crystal cured meat sample; the gas filled in the modified atmosphere packaging is a mixed gas of 30% nitrogen and 70% carbon dioxide;

[0058] (5) Sterilization: Use radio frequency and ultra-high voltage electric field to sterilize the packaged crystal cured meat sample. The radio frequency is 27.12 MHz, the electric field strength is 10 - 15 kV / cm, the plate spacing is 180 mm, and it is treated at 55 °C for 8 min. The pressure of ultra-high voltage electric field sterilization is 500 MPa, and the treatment duration is 10 min;

[0059] (6) Storage: Store the sterilized crystal cured meat sample in an environment of 0 - 4 °C.

[0060] For the crystal cured meat sample prepared above, measure its nitrite residue amount and total number of colonies, and judge whether the crystal cured meat sample is spoiled from the total number of colonies. After being treated by each step in Example 3, the crystal cured meat sample achieved the best nitrite reduction effect, the nitrite clearance rate reached 88.02%, and the storage time was extended by 20 d.

[0061] Experimental method:

[0062] 1. Nitrite residue amount and clearance rate

[0063] The spectrophotometric method in GB 5009.33-2016 was used to determine the nitrite content in crystal cured meat. After making the crystal cured meat into a homogenate, 5 g of the homogenate was taken and placed in a conical flask, and mixed thoroughly with 12.5 mL of saturated borax solution (50 g / L) and 150 mL of deionized water at 70 °C. The mixed solution was heated in a boiling water bath for 15 minutes and cooled to room temperature with a cold water bath. Then, 5 mL of K4Fe(CN)6·3H2O (106 g / L) and 5 mL of Zn(CH3COO)2 (220 g / L) were used to remove proteins and fats in the mixed solution. The mixed solution was filtered and the first 30 mL of the filtrate was discarded, and the remaining filtrate was reserved. 40 mL of the filtrate was taken and placed in a 50 mL stoppered colorimetric tube, 2 mL of sulfanilic acid solution (4 g / L) was added, mixed well and allowed to stand for 3 - 5 min, then 1 mL of N-(1-Naphthyl)ethylenediamine dihydrochloride solution (2 g / L) was added, and after volume fixing, it was mixed well and allowed to stand for 15 min. Finally, the absorbance of the sample solution was measured at 538 nm with a spectrophotometer. 0 mL, 0.2 mL, 0.4 mL, 0.6 mL, 0.8 mL, 1.0 mL, 1.5 mL, 2.0 mL and 2.5 mL of nitrite standard solutions were taken and placed in 50 mL stoppered colorimetric tubes respectively. Equal amounts and equal concentrations of sulfanilic acid solution and N-(1-Naphthyl)ethylenediamine dihydrochloride solution were added to each colorimetric tube. After volume fixing, the absorbance was measured at 538 nm, and a standard curve of sodium nitrite was constructed therefrom. The samples of each experimental group were measured three times and the average value was taken. According to the absorbance values (A values) measured in the blank control group and each treatment group, the nitrite scavenging rates of each pair ratio and example can be obtained by combining the following formula. The greater the nitrite scavenging rate, the better the nitrite-reducing effect of the treatment method adopted by this group.

[0064]

[0065] 2. Total number of colonies

[0066] The total number of colonies in crystal cured meat was determined according to GB 4789.2-2022. 25.0 g of crystal cured meat sample was taken and placed in 225 mL of 0.85% sodium chloride solution. After homogenization, 1 mL of the sample solution was taken for gradient dilution. 1 mL of the diluted solution was pipetted into a sterile culture medium, and 15 - 20 mL of plate count agar was added. After the agar solidified, the culture medium was placed in a constant temperature incubator at 37 °C for 48 h, and the total number of colonies was counted. According to GB 2726-2016, the limit of the total number of colonies in cooked meat products is 10 4 CFU / g, that is, it can be considered that the crystal cured meat sample exceeding this limit is in an inedible state.

[0067] Experimental results:

[0068] 1. Experimental results of nitrite scavenging rate

[0069] In the experiment for the determination of nitrite residue, the nitrite scavenging rates of the blank control (stored only at 0 - 4°C), Comparative Example 1 (Steps (1) and (2) of Example 1 were changed to prepare a tea polyphenol solution with a mass fraction of 1%, and the remaining steps were the same), Comparative Example 2 (Steps (1) and (2) of Example 1 were changed to prepare an ε-polylysine solution with a mass fraction of 1%, and the remaining steps were the same), Comparative Example 3 (Steps (1) and (2) of Example 1 were changed to prepare a ginger essential oil solution with a mass fraction of 1%, and the remaining steps were the same), Comparative Example 4 (Steps (1) and (2) of Example 1 were changed to prepare a tea polyphenol solution with a mass fraction of 1%, and the remaining steps were the same), and 3 groups of examples were measured respectively.

[0070] The measurement results are shown in Figure 1 , and the results show that each experimental group has a certain nitrite-reducing effect. Among the comparative examples, Comparative Example 1 (tea polyphenol group) has the best nitrite-reducing effect. Among the examples, Example 3 has the best nitrite-reducing effect. This is because compared with Example 1 and Example 2, the concentration of the active ingredients in the compound antibacterial solution increases, the content of antioxidant substances increases, and the nitrite-reducing effect is enhanced. Moreover, although individual natural antibacterial substances can reduce the nitrite content during the storage of crystal cured meat, the nitrite-reducing effect is not as good as that of the compound natural antibacterial substances. This is because under refrigeration conditions, plant essential oils can form a protective film on the surface of the sample, thereby protecting the tea polyphenols that are easily oxidized and discolored and then become ineffective. At the same time, there is a certain synergistic effect between the compound antibacterial substances, which can exert a better nitrite-reducing effect.

[0071] 2. Experimental results of total colony count

[0072] In the synergistic verification experiment of radio frequency sterilization and ultra-high pressure sterilization, the colony counts of the blank control (stored only at 0 - 4°C) during the storage period, the ultra-high pressure sterilization treatment example (Step (5) in Example 1 was changed to only perform ultra-high pressure sterilization, and the remaining steps were the same), the radio frequency sterilization treatment example (Step (5) in Example 1 was changed to only perform radio frequency sterilization, and the remaining steps were the same), and the radio frequency sterilization combined with ultra-high pressure sterilization treatment example (Example 1) were compared. In the experiment for the determination of total colony count, the colony counts of the vacuum packaging experimental groups (Comparative Examples 5, 6, and 7, in which the modified atmosphere packaging in Steps (4) of Examples 1, 2, and 3 was changed to vacuum packaging respectively, and the remaining steps were the same) and the modified atmosphere packaging groups (Examples 1, 2, and 3) were compared. The results show that modified atmosphere packaging can better slow down the growth and reproduction rate of spoilage microorganisms and extend the product quality guarantee period.

[0073] From Figure 2 , Figure 3 and Figure 4It can be seen that as the storage time increases, the total amount of microorganisms in the blank control group and each experimental group shows an upward trend. At the same time point, the total amount of microorganisms in each experimental group is lower than that in the blank control group, indicating that the additives have a certain anti-corrosion and antibacterial effect. During the period of 12 - 16d, the total amount of microorganisms in each experimental group increased rapidly, indicating that the microorganisms in the crystal cured meat were multiplying in large numbers, causing the product to gradually deteriorate. Figure 3 In it, the mass fraction of the antibacterial liquid used was 1% in all cases, but only the crystal cured meat of Comparative Example 4 (ε - polylysine group) remained in a suitable edible state on the 16th day, indicating that this substance has good antibacterial properties. From Figure 2 It can be obtained that the total colony counts of the single sterilization technology groups are all higher than those of the combined sterilization technology groups. This shows that there is a certain synergistic effect between ultra - high - voltage electric field sterilization and radio - frequency sterilization. If the single - technology groups want to achieve the same results as the combined group, then the radio - frequency sterilization group may have problems such as longer sterilization time or overheating caused by higher frequencies; the ultra - high - pressure sterilization group will face higher energy consumption, increasing the product cost. However, the combination of the two technologies can avoid these drawbacks and extend the product quality guarantee in a green and efficient manner. As Figure 4 shown, the total colony counts of the examples at the same time point are lower than those of the comparative examples. This indicates that modified atmosphere packaging can effectively inhibit the growth of microorganisms and help extend the shelf life of the product. This preservation effect is particularly evident in the comparison between Example 3 and Comparative Example 7. According to the Hygiene Standard for Cooked Meat Products GB 2726 - 2016, when the logarithm of the total colony count exceeds 4, the product is considered unfit for consumption. Comparative Example 7 extended the shelf life by 16 days, while Example 3 extended the product quality guarantee by 20 days, which fully demonstrates the superiority of modified atmosphere packaging. From Figure 4 and Figure 3 Comparing, it can be seen that after adding the composite antibacterial liquid, the growth rate of the total colony count further slows down, and the total colony count of the compound group is lower than that of the single antibacterial agent group and the blank control group, indicating that the composite antibacterial liquid has a better antibacterial effect. In Example 3, the concentration of each natural preservative reached 1%, and the antibacterial liquid prepared therefrom had the best antibacterial effect. From Figure 4 It can be seen that in Examples 1, 2, and 3, the shelf life of the crystal cured meat was extended by 8 days, 12 days, and 20 days respectively.

Claims

1. A preparation method of low-nitrite crystal cured meat using natural preservatives, characterized in that, The main steps are as follows: (1) Preparation of natural preservative solutions: Prepare a tea polyphenol solution and an ε-polylysine solution with a mass fraction of 0.5 - 1% using sterile water; prepare an absolute ethanol solution with a volume fraction of 20% using sterile water, and then prepare a ginger essential oil solution and an anise essential oil solution with a mass fraction of 0.6 - 1% using the absolute ethanol solution; (2) Preparation of compound antibacterial liquid: Mix the tea polyphenol solution, ε-polylysine solution, ginger essential oil solution, and anise essential oil solution, add soy protein isolate and lecithin as emulsifiers, and thoroughly mix these substances with a high-speed homogenizer to obtain a compound antibacterial liquid; (3) Immersion: Immerse the crystal cured meat samples in the compound antibacterial liquid prepared in step (2). After 1 minute of immersion, take them out and let them air-dry naturally in the air for 1 minute; (4) Modified atmosphere packaging: Use a low-density polyethylene film to perform modified atmosphere packaging on the immersed crystal cured meat samples; the gas filled in the modified atmosphere packaging is a mixed gas of nitrogen and carbon dioxide; (5) Sterilization: Use radio frequency and ultra-high voltage electric field to sterilize the packaged crystal cured meat samples; (6) Storage: Store the sterilized crystal cured meat samples in an environment of 0 - 4°C.

2. The preparation method of low-nitrite crystal cured meat using natural preservatives according to claim 1, characterized in that, In step (1), the mass fractions of the natural preservative solutions are: 1% for the tea polyphenol solution, 1% for the ε-polylysine solution, 0.6% for the ginger essential oil solution, and 0.6% for the anise essential oil solution.

3. A preparation method of low-nitrite crystal cured meat using natural preservatives according to claim 1, characterized in that, In step (2), the mass concentration of the soy protein isolate is 0.5%, and the mass concentration of the lecithin is 0.05%.

4. A method for preparing low-nitrite crystal cured meat using natural preservatives according to claim 1, characterized in that, In step (4), the density value of the polyethylene film is 0.89 to 0.92 g / cm 3 .

5. A preparation method of low-nitrite crystal cured meat using natural preservatives according to claim 1, characterized in that, In step (4), the gas composition of the modified atmosphere packaging is 30% carbon dioxide and 70% nitrogen.

6. A preparation method of low-nitrite crystal cured meat using natural preservatives according to claim 1, characterized in that, In step (5), the radio frequency is 27.12 MHz, the electric field strength is 10 - 15 kV / cm, the plate spacing is 180 mm, and it is treated at 55°C for 8 minutes; the pressure of the ultra-high voltage electric field sterilization is 500 MPa, and the treatment duration is 10 minutes.

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