A cured meat curing process that removes nitrite

Abstract

This invention relates to the field of cured meat processing technology and discloses a curing process for removing nitrites. The process includes: immersing the meat to be cured in a curing solution containing lactic acid bacteria fermentation broth, natural antioxidant extracts, chitosan / montmorillonite composite adsorbent, salt, sucrose, and spice extracts; performing a first-stage curing under low-temperature conditions using pulsed vacuum circulation combined with ultrasound; draining excess liquid from the surface; inoculating with a composite microbial fermentation agent composed of *Lactobacillus sakei*, *Staphylococcus xylose*, and *Hansellech. d'Ambrosia* for a second-stage fermentation and maturation; and finally, low-temperature drying to obtain the finished product. This invention, through enhanced mass transfer, adsorption removal, antioxidant inhibition, and the synergistic effect of composite fermentation, can reduce the residual nitrite and total nitrosamine compounds in cured meat products, and improve product maturity, quality stability, and edibility. It is suitable for the processing and preparation of low-nitrite cured meat products.

Description

Technical Field

[0001] This invention belongs to the field of food processing technology, specifically relating to a curing process for removing nitrites from cured meat. Background Technology

[0002] Cured meat products typically undergo curing, maturation, and drying processes during processing and storage. The flavor, color, and texture of these products are closely related to salt migration, protein changes, lipid oxidation, and microbial metabolism. In current cured meat processing, the use or control of nitrite formation is often involved to maintain color development, inhibit the growth of unwanted microorganisms, and stabilize product quality. High levels of residual nitrite in the system, or further nitrosation reactions during processing, can easily pose food safety risks and negatively impact the product's market acceptance.

[0003] Chinese patent application CN114098013A discloses a curing process for reducing the nitrite content in meat products. This process involves curing and fermenting a mixture of celery powder, beetroot red, and lactic acid bacteria to reduce the nitrite content and improve food safety. Chinese patent CN105309928B discloses a production process for low-salt cured meat with no nitrite residue. This method aims to eliminate the nitrite residue problem that may occur during traditional curing processes and improve food safety through process improvements.

[0004] These existing technologies mainly rely on the marinade formula and fermentation process itself to reduce nitrite content. Their treatment mechanisms are mainly focused on the combination of materials or fermentation conditions, while paying insufficient attention to the mass transfer efficiency of substances inside the meat during the marinating process, nitrite adsorption and removal, and the synergistic effect of acidification and maturation. This results in limited marinating effect, and it is difficult to take into account product maturity, flavor and texture stability while reducing nitrite residue.

[0005] Therefore, it is necessary to provide a curing process for meat that combines low-temperature intensified curing, compound adsorption removal, natural antioxidant inhibition, and compound microbial fermentation and maturation to solve the problems of high nitrite residue, limited control of nitrosamine compounds, and insufficient product maturity and quality stability in existing cured meat products. Summary of the Invention

[0006] This invention addresses the aforementioned deficiencies by providing a curing process for removing nitrites from cured meat. In the first stage, a low-temperature pulsed vacuum circulation combined with ultrasonic treatment enhances the penetration and distribution of effective components in the curing solution into the meat. After curing, a second stage of fermentation and maturation is carried out by inoculating with a compound microbial fermentation agent. This, combined with the effects of natural antioxidant extracts and chitosan / montmorillonite composite adsorbents, effectively reduces the content of nitrite residues and nitrosamines in the meat, while simultaneously maintaining product maturity, flavor, and textural stability. This process achieves the goal of improving both safety and quality, which is difficult to achieve simultaneously with existing technologies, through the synergistic effects of enhanced mass transfer, adsorption removal, antioxidant inhibition, and compound fermentation.

[0007] This invention provides the following technical solution: a curing process for removing nitrites from cured meat, comprising the following steps: S1: Immerse the meat to be cured in the pre-prepared curing solution and perform the first stage of curing at 4-10°C. The first stage of curing is carried out using pulsed vacuum circulation treatment, and ultrasound is applied in conjunction with the pulsed vacuum circulation process. The ultrasonic power is 200-400W, and the pulsed vacuum circulation conditions are a vacuum degree of -0.06 to -0.09MPa, maintained for 5-15 minutes and then restored to normal pressure for 5-10 minutes. The vacuuming and restoration to normal pressure are repeated in the above manner, and the total processing time is 2-6 hours. Ultrasound is applied continuously or intermittently during the pulsed vacuum circulation treatment. S2: After step S1, drain off the excess liquid on the surface, inoculate the surface of the meat with compound microbial fermentation agent, and ferment for 12 to 24 hours at a temperature of 15 to 25°C and a relative humidity of 75 to 85% to carry out the second stage of fermentation and maturation. S3: Dry the meat obtained in step S2 at a low temperature of 35-50℃ and a wind speed of 0.5-1.5m / s until the water activity Aw≤0.90 to obtain the cured meat product.

[0008] Furthermore, the pickling liquid comprises, by weight: 100-150 parts of lactic acid bacteria fermentation liquid, 5-15 parts of natural antioxidant extract, 1-5 parts of chitosan / montmorillonite composite adsorbent material, 8-12 parts of salt, 2-5 parts of sucrose, 0.5-2 parts of spice extract, and the remainder is purified water.

[0009] Further, the lactic acid bacteria fermentation broth is prepared by mixing *Lactobacillus plantarum* and *Pediococcus pentosaceus* at a viable count ratio of 1:0.5-1, and anaerobically culturing at 30-37°C for 24-36 hours in MRS medium containing 2-4% glucose and 0.5-1% peptone. After centrifugation at 6000-8000×g for 10-20 minutes at 4°C, the supernatant is filtered through a 0.22μm microporous membrane for sterilization to obtain the lactic acid bacteria fermentation broth. The pH of the lactic acid bacteria fermentation broth is 3.8-4.5, and the lactic acid content is ≥12g / L. That is, the glucose and peptone contents are adjusted to the above range based on conventional MRS medium.

[0010] Furthermore, both *Lactobacillus plantarum* and *Pediococcus pentosaceus* can be obtained commercially from strain preservation institutions, biological resource supply platforms, or fermentation agent suppliers within China; *Lactobacillus plantarum* strains corresponding to CGMCC No. 18980, CGMCC No. 14492, or CGMCC No. 21750 are selected, and *Pediococcus pentosaceus* strains corresponding to CGMCC No. 15957 are selected.

[0011] Further, the natural antioxidant extract is one or more selected from tea polyphenols, rosemary extract, bamboo leaf antioxidants, licorice antioxidants, and grape seed proanthocyanidin extract; wherein, the catechin content in the tea polyphenols is not less than 60%, the total antioxidant components in the rosemary extract (calculated as caryopsisic acid and caryopsisol) are not less than 10%, the bamboo leaf antioxidants contain not less than 20% bamboo leaf carbon glycoside flavonoids, and the grape seed proanthocyanidin extract contains not less than 70% proanthocyanidins. Further, the licorice antioxidant uses glycyrrhizic acid as a quality control indicator component, and its quality specifications meet the requirements of GB 1886.89-2015 <National Food Safety Standard for Food Additives: Licorice Antioxidants>.

[0012] Furthermore, the preparation method of the chitosan / montmorillonite composite adsorbent material is as follows: 1) Add montmorillonite to a sodium carbonate aqueous solution with a mass fraction of 2-8%, so that the amount of sodium carbonate is 3-6% of the mass of montmorillonite. Stir and react at 50-80℃ for 1-4 hours, let stand and age for 12-48 hours, wash until neutral, dry at 60-90℃ for 4-12 hours, crush and sieve to obtain sodium-modified montmorillonite. 2) Disperse the sodium-modified montmorillonite in acetic acid solution at an addition rate of 2-10 g / 100 mL, then add chitosan to make the mass ratio of chitosan to montmorillonite 1:2-5, and ultrasonically disperse for 10-40 minutes under ultrasonic power of 200-500 W and frequency of 20-40 kHz. 3) Then add the crosslinking agent and carry out the crosslinking reaction at 35-50℃ for 1-6 hours; 4) After cross-linking, wash with deionized water and anhydrous ethanol 2 to 5 times alternately, dry, grind and pass through a 300 to 800 mesh sieve to make the average particle size of the obtained composite adsorbent material no greater than 500 nm, thus obtaining the chitosan / montmorillonite composite adsorbent material.

[0013] Further, the crosslinking agent is one of sodium tripolyphosphate or glutaraldehyde; when sodium tripolyphosphate is used as the crosslinking agent, the amount of sodium tripolyphosphate added is 5 to 20% of the mass of chitosan; when glutaraldehyde is used as the crosslinking agent, the amount of glutaraldehyde added is 0.5 to 3% of the mass of chitosan.

[0014] Furthermore, the acetic acid solution used in step 2) is a mixed solution of acetic acid and water containing 1-2% acetic acid by volume.

[0015] Further, the drying in step 4) is carried out at 40-70°C for 8-24 hours.

[0016] Furthermore, the compound microbial fermentation agent comprises *Lactobacillus sakei*, *Staphylococcus xylosus*, and *Debaryomyces hansenii*, with a viable cell ratio of (3-5):(2-3):1. The compound microbial fermentation agent is a freeze-dried powder type compound fermentation agent with a total effective viable cell count ≥1×10⁻⁶. 9 CFU / g; the inoculation amount of the compound microbial fermentation agent is 0.05-0.2% based on the weight of the meat to be fermented.

[0017] Furthermore, the *Lactobacillus sakei* strain used was CGMCC No. 23702; *Staphylococcus xylose* strain used was CGMCC No. 3474; and *Hansordebali* strain used was CGMCC No. 22507.

[0018] Furthermore, the low-temperature drying in step S3 includes two stages: first drying at 38–42°C until the water activity Aw ≤ 0.93, and then drying at 45–50°C until the water activity Aw ≤ 0.90.

[0019] The advantages of this invention are that it can reduce the residual amount of nitrite and the total amount of nitrosamine compounds in cured meat products, and improve the maturity and edibility of the products.

[0020] In this invention, lactic acid bacteria fermentation broth, natural antioxidant extracts, and chitosan / montmorillonite composite adsorbent are added together to the pickling liquid. The lactic acid bacteria fermentation broth helps to create an acidic environment, the natural antioxidant extracts help to inhibit oxidation and nitrosation side reactions, and the chitosan / montmorillonite composite adsorbent helps to adsorb and remove nitrite, thereby improving the removal efficiency.

[0021] In the first stage of the marinating process, the present invention uses pulsed vacuum circulation combined with ultrasonic treatment, which can improve the penetration and uniform distribution of the effective components in the marinating solution into the meat, and make the migration and removal of nitrite more complete.

[0022] This invention involves inoculating a compound microbial fermentation agent after the first stage of pickling for a second stage of fermentation and maturation. This helps to further reduce the pH value of the system, promote product maturation and flavor formation, and enable cured meat products to maintain good quality while reducing harmful residues.

[0023] The present invention employs low-temperature drying after fermentation and maturation, which can gradually dehydrate and stabilize the product, reduce quality fluctuations, and thus improve the product's textural stability and storage stability. Detailed Implementation

[0024] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0025] In the specific embodiments of this application, the product standard for tea polyphenols is GB 1886.211-2016 National Food Safety Standard for Food Additives: Tea Polyphenols (also known as Vitamin Polyphenols); the product standard for rosemary extract is GB 1886.172-2016 National Food Safety Standard for Food Additives: Rosemary Extract; the product standard for bamboo leaf antioxidants is GB 30615-2014 National Food Safety Standard for Food Additives: Bamboo Leaf Antioxidants; and the product standard for licorice antioxidants is GB 1886.89-2015 National Food Safety Standard for Food Additives: Licorice Antioxidants. Furthermore, tea polyphenols, rosemary extract, bamboo leaf antioxidants, and licorice antioxidants all fall within the scope of antioxidants permitted under GB 2760-2024 National Food Safety Standard for Food Additives.

[0026] The natural antioxidant extracts used in the following embodiments of this application are food-grade natural plant extracts, which can be selected from one or more of tea polyphenols, rosemary extract, bamboo leaf antioxidants, licorice antioxidants, and grape seed proanthocyanidin extract. Preferably, the tea polyphenols are domestically available food-grade products, such as those from domestic suppliers like Zhejiang Tiancao Biotechnology Co., Ltd., and their quality specifications can be controlled according to GB 1886.211-2016 <National Food Safety Standard for Food Additives: Tea Polyphenols (also known as Vitamin Polyphenols)>, and the relevant content detection can be performed according to GB / T 8313-2018 <Detection Methods for Tea Polyphenols and Catechins in Tea>. The rosemary extract, bamboo leaf antioxidants, and licorice antioxidants are also preferably domestically available food-grade products, and their quality specifications can be respectively referenced to GB 1886.172-2016 <National Food Safety Standard for Food Additives: Rosemary Extract>, GB 30615-2014 <National Food Safety Standard for Food Additives: Bamboo Leaf Antioxidants>, and ... The content of proanthocyanidins in grape seeds is controlled according to the national food safety standard 1886.89-2015, "Food Additives: Licorice Antioxidants". The grape seed proanthocyanidin extract is preferably domestically available food-grade grape seed extract or food-grade grape seed proanthocyanidin extract, for example, from domestic suppliers such as Zhejiang Tiancao Biotechnology Co., Ltd. The content of proanthocyanidins, heavy metals, and solvent residues are preferably controlled according to the supplier's quality inspection report, enterprise standards, or delivered technical specifications. The use of the above-mentioned natural antioxidant extracts may also be carried out in accordance with the relevant provisions of the current version of GB 2760.

[0027] Example 1 This embodiment provides a curing process for removing nitrites in cured meat. The lactic acid bacteria fermentation broth used in this embodiment is prepared according to the following steps: Lactobacillus plantarum and Pediococcus pentosaceus are mixed at a live cell ratio of 1:1 and inoculated into MRS medium containing 2% glucose and 1% peptone, and anaerobically cultured at 34°C for 24 hours; after the culture is completed, the mixture is centrifuged at 8000×g for 10 minutes at 4°C, and the supernatant is filtered through a 0.22μm microporous membrane to remove bacteria, thus obtaining the lactic acid bacteria fermentation broth; the pH value of the obtained lactic acid bacteria fermentation broth is 3.8, and the lactic acid content is 14g / L.

[0028] The preparation steps of the chitosan / montmorillonite composite adsorbent material used in this embodiment are as follows: 1) Add montmorillonite to a 2% sodium carbonate aqueous solution, with the amount of sodium carbonate being 6% of the mass of montmorillonite. Stir and react at 65°C for 1 hour, let stand and age for 48 hours, wash until neutral, dry at 60°C for 4 hours, pulverize and sieve to obtain sodium-modified montmorillonite. 2) The sodium-modified montmorillonite was dispersed in a 1% (v / v) mixed solution of acetic acid and water at an addition rate of 10 g / 100 mL, and then chitosan was added to make the mass ratio of chitosan to montmorillonite 1:5. The mixture was ultrasonically dispersed for 40 minutes at an ultrasonic power of 350 W and a frequency of 20 kHz. 3) Then add sodium tripolyphosphate at 5% of the chitosan mass and carry out a cross-linking reaction at 35°C for 6 hours; 4) After cross-linking, the material is washed twice with deionized water and anhydrous ethanol, dried at 70°C for 8 hours, then ground and passed through a 300-mesh sieve to obtain a composite adsorbent material with an average particle size of 480 nm.

[0029] The pickling solution used in this embodiment is prepared as follows: by weight, take 150 parts of the above-mentioned lactic acid bacteria fermentation liquid, 10 parts of natural antioxidant extract, 1 part of the above-mentioned chitosan / montmorillonite composite adsorbent material, 12 parts of salt, 2 parts of sucrose, 1 part of spice extract and 824 parts of purified water, and mix them evenly to obtain the pickling solution; wherein, the natural antioxidant extract is composed of 6 parts of tea polyphenols and 4 parts of rosemary extract, the catechin content in the tea polyphenols is 65%, and the total antioxidant components in the rosemary extract, calculated as caryopsisic acid and caryopsisol, are 12%.

[0030] This embodiment provides a meat curing process for removing nitrites, including the following steps: S1: First stage of marinating: Take 1000g of fresh pork hind leg meat and completely immerse it in 1500g of the above marinating solution. Marinate in the first stage at 4℃. The first stage of marinating is carried out by pulsed vacuum circulation treatment, and ultrasound is continuously applied during the pulsed vacuum circulation. The ultrasound power is 320W, and the pulsed vacuum circulation conditions are vacuum degree of -0.09MPa, maintained for 10 minutes and then restored to normal pressure for 5 minutes. The vacuuming and restoration to normal pressure are repeated in the above manner. The total processing time is 4 hours. S2: Second stage fermentation and maturation: After step 4, drain excess liquid from the surface of the meat; inoculate the surface of the meat with a freeze-dried powder-type compound fermentation agent, which contains Lactobacillus sakei, Staphylococcus xylose, and Saccharomyces hansøe dubarry, with a viable cell ratio of 5:2:1 and a total effective viable cell count of 3×10^9 CFU / g; the inoculation amount is 0.05% of the weight of the meat to be fermented, i.e., 0.5g; then ferment for 12 hours at 25℃ and 75% relative humidity; S3: Low-temperature drying: The meat obtained in step 5 is subjected to two-stage low-temperature drying at an air velocity of 1.5 m / s. First, it is dried at 42℃ until the water activity Aw is 0.93, and then dried at 45℃ until the water activity Aw is 0.90, to obtain the cured meat product.

[0031] Example 2 This embodiment provides a curing process for removing nitrites in cured meat. The lactic acid bacteria fermentation broth used in this embodiment is prepared according to the following steps: Lactobacillus plantarum and Pediococcus pentosaceus are mixed at a live count ratio of 1:0.5 and inoculated into MRS medium containing 4% glucose and 0.5% peptone, and anaerobically cultured at 37°C for 30 hours; after the culture is completed, the mixture is centrifuged at 7000×g for 20 minutes at 4°C, and the supernatant is filtered through a 0.22μm microporous membrane to remove bacteria, thus obtaining the lactic acid bacteria fermentation broth; the pH value of the obtained lactic acid bacteria fermentation broth is 4.5, and the lactic acid content is 12g / L.

[0032] The preparation steps of the chitosan / montmorillonite composite adsorbent material used in this embodiment are as follows: 1) Montmorillonite was added to an 8% sodium carbonate aqueous solution (sodium carbonate was 3% of the mass of montmorillonite), stirred at 80°C for 2 hours, allowed to stand and age for 12 hours, washed until neutral, dried at 75°C for 12 hours, pulverized and sieved to obtain sodium-modified montmorillonite. The sodium-modified montmorillonite was dispersed in a 2% acetic acid and water mixed solution at a dosage of 2 g / 100 mL, and chitosan was added to make the mass ratio of chitosan to montmorillonite 1:2. The mixture was ultrasonically dispersed for 10 minutes at an ultrasonic power of 200 W and a frequency of 30 kHz. Glutaraldehyde was then added at a dosage of 1.5% of the chitosan mass, and crosslinking was carried out at 50°C for 3 hours. After crosslinking, the mixture was washed 5 times alternately with deionized water and anhydrous ethanol, dried at 40°C for 24 hours, ground, and sieved through an 800-mesh sieve to obtain a composite adsorbent material with an average particle size of 450 nm.

[0033] The pickling solution used in this embodiment is prepared as follows: by weight, take 100 parts of the above-mentioned lactic acid bacteria fermentation liquid, 15 parts of natural antioxidant extract, 3 parts of the above-mentioned chitosan / montmorillonite composite adsorbent material, 9 parts of salt, 5 parts of sucrose, 0.5 parts of spice extract, and 867.5 parts of purified water, and mix them evenly to obtain the pickling solution; wherein, the natural antioxidant extract is composed of 8 parts of bamboo leaf antioxidant and 7 parts of grape seed proanthocyanidin extract, the bamboo leaf antioxidant contains 22% bamboo leaf carbon glycoside flavonoids, and the grape seed proanthocyanidin extract contains 75% proanthocyanidins.

[0034] This embodiment provides a meat curing process for removing nitrites, including the following steps: S1: First stage of marinating: Take 1000g of fresh pork hind leg meat and completely immerse it in 1500g of the above marinating solution. Marinate at 7℃ for the first stage. The first stage of marinating is carried out by pulsed vacuum circulation treatment, and ultrasound is applied intermittently during the pulsed vacuum circulation. The ultrasound power is 200W, and the pulsed vacuum circulation conditions are vacuum degree of -0.06MPa, maintained for 15 minutes and then restored to normal pressure for 8 minutes. The vacuuming and restoration to normal pressure are repeated in the above manner. The total processing time is 6 hours. S2: Second stage fermentation and maturation: After step 4, drain excess liquid from the surface of the meat; inoculate the surface of the meat with a freeze-dried powder-type compound fermentation agent, which contains Lactobacillus sakei, Staphylococcus xylose, and Saccharomyces hansøe dubarry, with a viable cell ratio of 3:3:1 and a total effective viable cell count of 1×10^9 CFU / g; the inoculation amount is 0.2% of the weight of the meat to be fermented, i.e., 2.0g; then ferment for 24 hours at 20℃ and 85% relative humidity; S3: Low-temperature drying: The meat obtained in step 5 is subjected to two-stage low-temperature drying at an air velocity of 0.5 m / s. First, it is dried at 38°C until the water activity Aw is 0.93, and then dried at 50°C until the water activity Aw is 0.90, to obtain the cured meat product.

[0035] Example 3 This embodiment provides a curing process for removing nitrites in cured meat. The lactic acid bacteria fermentation broth used in this embodiment is prepared according to the following steps: Lactobacillus plantarum and Pediococcus pentosaceus are mixed at a live count ratio of 1:0.8 and inoculated into MRS medium containing 3% glucose and 0.8% peptone, and anaerobically cultured at 30°C for 36 hours; after the culture is completed, the mixture is centrifuged at 6000×g for 15 minutes at 4°C, and the supernatant is filtered through a 0.22μm microporous membrane to remove bacteria, thus obtaining the lactic acid bacteria fermentation broth; the pH value of the obtained lactic acid bacteria fermentation broth is 4.1, and the lactic acid content is 16g / L.

[0036] The preparation steps of the chitosan / montmorillonite composite adsorbent material used in this embodiment are as follows: 1) Add montmorillonite to a 5% sodium carbonate aqueous solution, with the amount of sodium carbonate being 4.5% of the mass of montmorillonite. Stir and react at 50°C for 4 hours, let stand and age for 24 hours, wash until neutral, dry at 90°C for 8 hours, pulverize and sieve to obtain sodium-modified montmorillonite. 2) The sodium-modified montmorillonite was dispersed in a mixed solution of acetic acid and water with a volume fraction of 1.5% at a dosage of 6 g / 100 mL, and then chitosan was added to make the mass ratio of chitosan to montmorillonite 1:3.5. The mixture was ultrasonically dispersed for 25 minutes under ultrasonic power of 500 W and frequency of 40 kHz. 3) Then sodium tripolyphosphate was added, the amount of which was 20% of the mass of chitosan, and the cross-linking reaction was carried out at 42°C for 1 hour. After the cross-linking was completed, it was washed 3 times with deionized water and anhydrous ethanol alternately, dried at 55°C for 16 hours, and then ground and passed through a 500-mesh sieve to make the average particle size of the obtained composite adsorbent material 320nm.

[0037] The pickling solution used in this embodiment is prepared as follows: by weight, take 125 parts of the above-mentioned lactic acid bacteria fermentation liquid, 5 parts of natural antioxidant extract, 5 parts of the above-mentioned chitosan / montmorillonite composite adsorbent material, 8 parts of salt, 3.5 parts of sucrose, 2 parts of spice extract, and 851.5 parts of purified water, and mix them evenly to obtain the pickling solution; wherein, the natural antioxidant extract is composed of 3 parts of tea polyphenols and 2 parts of grape seed proanthocyanidin extract, the catechin content in the tea polyphenols is 60%, and the proanthocyanidin content in the grape seed proanthocyanidin extract is 70%.

[0038] This embodiment provides a meat curing process for removing nitrites, including the following steps: S1: First stage of marinating: Take 1000g of fresh pork hind leg meat and completely immerse it in 1500g of the above marinating solution. Marinate in the first stage at 10℃. The first stage of marinating is carried out by pulsed vacuum circulation treatment, and ultrasound is applied intermittently during the pulsed vacuum circulation. The ultrasound power is 400W, and the pulsed vacuum circulation conditions are vacuum degree of -0.08MPa, maintained for 5 minutes and then restored to normal pressure for 10 minutes. The vacuuming and restoration to normal pressure are repeated in the above manner. The total processing time is 2 hours. S2: Second stage fermentation and maturation: After step 4, drain excess liquid from the surface of the meat; inoculate the surface of the meat with a freeze-dried powder-type compound fermentation agent, which contains Lactobacillus sakei, Staphylococcus xylose, and Saccharomyces hansenbergii, with a viable cell ratio of 4:2.5:1 and a total effective viable cell count of 2×10^9 CFU / g; the inoculation amount is 0.1% of the weight of the meat to be fermented, i.e., 1.0g; then ferment for 18 hours at 15℃ and 80% relative humidity; S3: Low-temperature drying: The meat obtained in step 5 is subjected to two-stage low-temperature drying at an air velocity of 1.0 m / s. First, it is dried at 40°C until the water activity Aw is 0.93, and then dried at 47°C until the water activity Aw is 0.90, to obtain the cured meat product.

[0039] Comparative Example 1 This comparative example illustrates the effect of conventional static curing as an alternative to pulsed vacuum and ultrasound on nitrite removal. 1000g of fresh pork hind leg meat was used. The preparation conditions for the lactic acid bacteria fermentation broth, the chitosan / montmorillonite composite adsorbent, the curing solution formula, the composition and inoculation amount of the composite microbial fermentation agent, the second-stage fermentation and maturation conditions, and the two-stage low-temperature drying conditions were all the same as in Example 2. The difference was that in the first stage of curing, the meat was completely immersed in 1500g of curing solution and statically cured at 7°C for 6 hours without pulsed vacuum circulation or ultrasound. Subsequent steps were then performed to obtain the finished cured meat product.

[0040] Comparative Example 2 This comparative example illustrates the effect of using only pulsed vacuum without ultrasound on the removal of nitrite. 1000g of fresh pork hind leg meat was used. The preparation conditions for the lactic acid bacteria fermentation broth, the chitosan / montmorillonite composite adsorbent, the marinating solution formula, the composition and inoculation amount of the composite microbial fermentation agent, the second-stage fermentation and maturation conditions, and the two-stage low-temperature drying conditions were all the same as in Example 2. The difference was that during the first-stage marinating, the meat was completely immersed in 1500g of marinating solution and subjected to pulsed vacuum circulation treatment at 7°C. The pulsed vacuum circulation conditions were -0.06MPa, maintained for 15 minutes, and then restored to normal pressure for 8 minutes. This vacuuming and restoration to normal pressure was repeated, with a total processing time of 6 hours. However, ultrasound was not applied during the entire first-stage marinating process. Subsequent steps were then performed to obtain the finished cured meat product.

[0041] Comparative Example 3 This comparative example illustrates the effect of removing chitosan / montmorillonite composite adsorbent on the removal of nitrite. 1000g of fresh pork hind leg meat was used. The preparation conditions of the lactic acid bacteria fermentation broth, the composition and inoculation amount of the composite microbial fermentation agent, the first-stage marinating conditions, the second-stage fermentation and maturation conditions, and the two-stage low-temperature drying conditions were all the same as in Example 2. The difference was that no chitosan / montmorillonite composite adsorbent was added to the marinating broth. The marinating broth, by weight, consisted of 100 parts lactic acid bacteria fermentation broth, 15 parts natural antioxidant extract, 9 parts salt, 5 parts sucrose, 0.5 parts spice extract, and 870.5 parts purified water. The meat was completely immersed in 1500g of this marinating broth for subsequent processing to obtain the finished cured meat product.

[0042] Comparative Example 4 This comparative example illustrates the effect of not inoculating with the compound microbial fermentation agent on the removal of nitrite. 1000g of fresh pork hind leg meat was used. The preparation conditions for the lactic acid bacteria fermentation broth, the chitosan / montmorillonite composite adsorbent, the curing solution formula, the first-stage curing conditions, and the two-stage low-temperature drying conditions were all the same as in Example 2. The difference was that after step S1, only excess liquid on the surface of the meat was drained, and the compound microbial fermentation agent was not inoculated. Instead, the meat was directly placed at 20°C and 85% relative humidity for 24 hours for maturation, followed by drying under the two-stage low-temperature drying conditions of Example 2 to obtain the cured meat product.

[0043] The residual nitrite, total nitrosamines, pH, water activity (Aw), and sensory scores of the cured meat products obtained in Examples 1-3 and Comparative Examples 1-4 were tested. The residual nitrite was determined by spectrophotometry, the total nitrosamines were determined by liquid chromatography-tandem mass spectrometry, the pH was determined by a pH meter, the water activity (Aw) was determined by a water activity meter, and the sensory scores were comprehensively evaluated by trained evaluators. The results are shown in Table 1.

[0044] Table 1. Test results of nitrite removal performance and product quality. As shown in Table 1, the residual nitrite and total amount of nitrosamines in the cured meat products obtained in Examples 1 to 3 were significantly lower than those in Comparative Examples 1 to 4, and all met the requirements for low residue levels, with Example 1 showing the best removal effect. The reason for this result is that this application employs a first-stage low-temperature curing process combined with pulsed vacuum circulation and ultrasonic treatment, which allows the lactic acid bacteria fermentation liquid, natural antioxidant extracts, and chitosan / montmorillonite composite adsorbent in the curing solution to be more fully transferred to the surface and interior of the meat, promoting the migration of existing nitrites from the meat into the curing system. Simultaneously, the second-stage inoculation with composite microbial fermentation agents further accelerates the acidification and maturation process, lowers the pH value of the system, and inhibits the nitrosation side reaction. Comparisons of different control ratios show that removing pulsed vacuum and ultrasound resulted in the most significant increases in nitrite residue and total nitrosamine content. While retaining only pulsed vacuum without ultrasound improved the removal effect compared to static curing, it was still lower than in the previous example. Removing the chitosan / montmorillonite composite adsorbent or failing to inoculate with the composite microbial fermentation agent also increased the nitrite residue and total nitrosamine content in the product. This indicates that this application does not rely on a single component or step to control nitrite, but rather achieves a simultaneous reduction in nitrite residue and total nitrosamine content in cured meat products through enhanced mass transfer, adsorption removal, antioxidant inhibition, and fermentation acidification.

[0045] Test Example 2 Referring to relevant food physicochemical and textural testing methods, the lactic acid content, overall color difference ΔE, elasticity, chewiness, and total bacterial count of the cured meat products obtained in Examples 1-3 and Comparative Examples 1-4 were tested. The lactic acid content was determined by high performance liquid chromatography, the overall color difference ΔE was determined by a colorimeter, the elasticity and chewiness were determined by a texture analyzer, and the total bacterial count was determined by plate counting. The results are shown in Table 2.

[0046] Table 2. Results of tests related to fermentation maturity and storage stability. As shown in Table 2, the cured meat products obtained in Examples 1 to 3 are superior to the comparative examples in terms of lactic acid content, color retention, elasticity, chewiness, and total bacterial count control. Example 1 shows better overall color and texture, while Example 3 exhibits superior maturity and tissue uniformity. This is because the lactic acid bacteria fermentation broth and the compound microbial fermentation agent in this application work together to create a more stable acidified environment in the meat during the ripening process, promoting the establishment of flavor precursors and mature tissue structures. Natural antioxidant extracts can slow down lipid oxidation and color deterioration, while the chitosan / montmorillonite composite adsorbent helps reduce the residue of adverse reactants, thereby mitigating quality fluctuations during ripening. Simultaneously, pulsed vacuum circulation combined with ultrasonic treatment improves the uniformity of the curing system's distribution in the meat, making subsequent fermentation and drying processes more coordinated. Therefore, the examples exhibit better elasticity and chewiness retention, smaller overall color difference, and a lower total bacterial count. In contrast, Comparative Examples 1 to 4, due to the lack of key enhanced pickling steps, adsorption materials, or compound fermentation agents, had their maturation and quality formation processes affected to varying degrees, ultimately resulting in lower lactic acid content, decreased color stability, poorer texture, and higher total bacterial count.

[0047] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A curing process for removing nitrites from cured meat, characterized in that, Includes the following steps: S1: Immerse the meat to be marinated in the pre-prepared marinating solution and perform the first stage of marinating at 4-10°C. The first stage of marinating is carried out using pulsed vacuum circulation, and ultrasound is applied in conjunction with the pulsed vacuum circulation. The ultrasonic power is 200-400W, and the pulsed vacuum circulation conditions are a vacuum degree of -0.06 to -0.09MPa, maintained for 5-15 minutes and then restored to normal pressure for 5-10 minutes. The process of vacuuming and restoring normal pressure is repeated, and the total processing time is 2-6 hours. S2: After step S1, drain off the excess liquid on the surface, inoculate the surface of the meat with compound microbial fermentation agent, and ferment for 12 to 24 hours at a temperature of 15 to 25°C and a relative humidity of 75 to 85% to carry out the second stage of fermentation and maturation. S3: Dry the meat obtained in step S2 at a low temperature of 35-50℃ and a wind speed of 0.5-1.5m / s until the water activity Aw≤0.90 to obtain the cured meat product.

2. The process according to claim 1, characterized in that, The pickling liquid comprises, by weight: 100-150 parts of lactic acid bacteria fermentation liquid, 5-15 parts of natural antioxidant extract, 1-5 parts of chitosan / montmorillonite composite adsorbent, 8-12 parts of salt, 2-5 parts of sucrose, 0.5-2 parts of spice extract, and the remainder is purified water.

3. The process according to claim 2, characterized in that, The lactic acid bacteria fermentation broth is prepared by mixing *Lactobacillus plantarum* and *Pediococcus pentosaceus* at a live count ratio of 1:0.5–1, and anaerobically culturing the mixture in MRS medium containing 2–4% glucose and 0.5–1% peptone at 30–37°C for 24–36 hours. After centrifugation at 6000–8000 × g for 10–20 minutes at 4°C, the supernatant is filtered through a 0.22 μm microporous membrane to remove bacteria, yielding the lactic acid bacteria fermentation broth. The pH of the lactic acid bacteria fermentation broth is 3.8–4.5, and the lactic acid content is ≥12 g / L.

4. The process according to claim 2, characterized in that, The natural antioxidant extract is one or more of tea polyphenols, rosemary extract, bamboo leaf antioxidants, licorice antioxidants, and grape seed proanthocyanidin extract; wherein, the catechin content in the tea polyphenols is not less than 60%, the total antioxidant components in the rosemary extract (calculated as carnosic acid and carnosine) are not less than 10%, the content of bamboo leaf carbon glycoside flavonoids in the bamboo leaf antioxidants is not less than 20%, and the proanthocyanidin content in the grape seed proanthocyanidin extract is not less than 70%.

5. The process according to claim 2, characterized in that, The preparation method of the chitosan / montmorillonite composite adsorbent material is as follows: 1) Add montmorillonite to a sodium carbonate aqueous solution with a mass fraction of 2-8%, so that the amount of sodium carbonate is 3-6% of the mass of montmorillonite. Stir and react at 50-80℃ for 1-4 hours, let stand and age for 12-48 hours, wash until neutral, dry at 60-90℃ for 4-12 hours, crush and sieve to obtain sodium-modified montmorillonite. 2) Disperse the sodium-modified montmorillonite in acetic acid solution at an addition rate of 2-10 g / 100 mL, then add chitosan to make the mass ratio of chitosan to montmorillonite 1:2-5, and ultrasonically disperse for 10-40 minutes under ultrasonic power of 200-500 W and frequency of 20-40 kHz. 3) Then add the crosslinking agent and carry out the crosslinking reaction at 35-50℃ for 1-6 hours; 4) After cross-linking, wash with deionized water and anhydrous ethanol 2 to 5 times alternately, dry, grind and pass through a 300 to 800 mesh sieve to make the average particle size of the obtained composite adsorbent material no greater than 500 nm, thus obtaining the chitosan / montmorillonite composite adsorbent material.

6. The process according to claim 5, characterized in that, The crosslinking agent is either sodium tripolyphosphate or glutaraldehyde; when sodium tripolyphosphate is used as the crosslinking agent, the amount of sodium tripolyphosphate added is 5-20% of the mass of chitosan; when glutaraldehyde is used as the crosslinking agent, the amount of glutaraldehyde added is 0.5-3% of the mass of chitosan.

7. The process according to claim 5, characterized in that, Step 2) The acetic acid solution used is a mixed solution of acetic acid and water with a volume fraction of 1-2% acetic acid.

8. The process according to claim 5, characterized in that, Step 4) involves drying at 40–70°C for 8–24 hours.

9. The process according to claim 1, characterized in that, The compound microbial fermentation agent contains *Lactobacillus sakei*, *Staphylococcus xylose*, and *Hanseloidomyces hansenoside*, with a viable cell ratio of (3-5):(2-3):

1. The compound microbial fermentation agent is a freeze-dried powder type compound fermentation agent with a total effective viable cell count ≥1×10⁻⁶. 9 CFU / g; the inoculation amount of the compound microbial fermentation agent is 0.05-0.2% based on the weight of the meat to be fermented.

10. The process according to claim 1, characterized in that, The low-temperature drying in step S3 includes two stages: first drying at 38–42°C until the water activity Aw ≤ 0.93, and then drying at 45–50°C until the water activity Aw ≤ 0.90.

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