Post-generation cooked food fresh-keeping process based on lactic acid bacteria in-situ conversion

Abstract

The invention discloses a post-generation cooked food fresh-keeping process based on lactic acid bacteria in-situ conversion. The process comprises the following steps: soaking raw materials in a 0.5-1.5% sodium chloride solution for 40-90 minutes, and then pre-cooling; inoculating lactic acid bacteria which are directionally screened in an environment of 1.5-3.0% of sodium chloride and 12-18 DEG C, and rolling and kneading for 20-120 minutes; fermenting for 4-8 hours at the temperature of 12-18 DEG C, and stopping when the pH is reduced to 5.0-5.5 and the consumption of soluble sugar reaches 45-65%; curing the meat raw materials until the central temperature is 75-85 DEG C; pasteurization is carried out at 62-70 DEG C for 10-20 min or ultrahigh pressure treatment is carried out at 300-450 MPa for 5-12 min, so that the lactic acid bacteria are inactivated and converted into metabiotics; and performing vacuum packaging and after-ripening at 0-4 DEG C for 24- Through directional screening, in-situ conversion and mild inactivation, in-situ generation of the fresh-keeping substances in the matrix is realized, and a postbiotic fresh-keeping system is constructed. The shelf life of the product is obviously prolonged, the microbial safety is improved, the quality is excellent, chemical preservatives are not needed, and the label cleaning concept is met.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of food processing and biological preservation, and specifically relates to a postbiotic cooked food preservation process based on in-situ conversion of lactic acid bacteria. BACKGROUND

[0002] Cooked food products refer to instant or semi-instant foods that are heated to a cooked state, including marinated meat products, sauce-marinated products, roasted products, steamed and boiled products, and various types of salad vegetables, and are an important part of China's traditional food industry. However, cooked food products are prone to microbial contamination and spoilage during processing and distribution due to their high nutritional value, high water activity, and moderate pH, and their shelf life is usually only 3-7 days, which severely restricts the market circulation radius and commercial value of the products. How to effectively extend the shelf life of cooked food products while ensuring food safety has been an important technical challenge faced by the food industry.

[0003] Currently, cooked food preservation techniques mainly include chemical preservation and physical preservation. Chemical preservatives such as potassium sorbate and sodium benzoate have significant antibacterial effects, but with the increasing demand for "clean labels" and natural foods among consumers, the use of chemical additives is increasingly restricted. Physical preservation techniques such as high-temperature sterilization, irradiation, and ultra-high pressure can effectively kill microorganisms, but often result in flavor deterioration, texture damage, or loss of nutritional components. Traditional high-temperature and high-pressure sterilization (121℃, 15-30 minutes) can completely kill pathogenic and spoilage bacteria, but can cause cooked meat products to have a noticeable cooked flavor, hard texture, and juice loss, which affects consumer sensory acceptance. Therefore, developing natural preservation techniques that can effectively extend the shelf life while maintaining the original quality of the products has important practical significance.

[0004] In recent years, biological preservation using lactic acid bacteria fermentation has gradually become a research hotspot. Lactic acid bacteria can produce organic acids such as lactic acid and acetic acid to lower the pH value, and produce bacteriocins and hydrogen peroxide to inhibit the growth of spoilage bacteria and pathogenic bacteria during metabolism. Some lactic acid bacteria can also produce extracellular polysaccharides (EPS), which not only improve the texture and water-holding capacity of foods, but also have certain antioxidant and antibacterial effects. However, existing lactic acid bacteria fermentation preservation techniques still have many limitations in practical application.

[0005] On the one hand, in the traditional lactic acid bacteria fermentation preservation method, strains are often screened in conventional culture medium without fully considering the particularity of the cooked food processing environment. Cooked food processing usually involves curing fermentation in a high-salt environment containing 1.5-3% sodium chloride and a low-temperature condition of 12-18°C, while the traditional screening condition is MRS medium and a culture temperature of 30-37°C, which is significantly different from the actual application environment. This leads to a significant decrease in the production of exopolysaccharide and bacteriocin activity of strains that perform well under standard conditions when applied to high-salt and low-temperature cooked food systems, making it difficult to achieve the expected preservation effect. On the other hand, some technologies use the method of adding exogenous composite biological preservatives, i.e., extracting lactic acid bacteria metabolites after in-vitro culture and adding them to food. This method has a certain preservation effect, but it fails to achieve the in-situ generation of preservatives, increases production costs and process complexity, and makes it difficult to ensure uniform distribution of metabolites in the food matrix.

[0006] In addition, the existing lactic acid bacteria fermentation preservation technology also has the following shortcomings: First, during the subsequent maturation and sterilization process of fermented cooked food products, active lactic acid bacteria are partially or completely killed, and functional ingredients such as exopolysaccharides and bacteriocins may also be degraded and inactivated due to high-temperature treatment, resulting in weakened preservation effect. Second, lactic acid bacteria fermentation often serves as an independent pretreatment process, which needs to be carried out in a special fermentation tank or fermentation room, disconnected from the main process flow of cooked food processing, increasing equipment investment and production cycle.

[0007] Postbiotics refers to the collective term for inactivated probiotic cells and their metabolites, including bacteriocins, organic acids, exopolysaccharides, short-chain fatty acids, and other bioactive substances. Compared with active probiotics, postbiotics has better stability and safety, is not limited by the number and survival conditions of live bacteria, and shows good application prospects in food preservation. However, the existing postbiotics preparation method mainly involves in-vitro fermentation of lactic acid bacteria, inactivation of the bacterial cells by heating, freeze-drying, etc., extraction and purification of their metabolites, and then application as an additive in food. This "fermentation-inactivation-extraction-addition" mode has problems such as complex process, high cost, loss of functional ingredients, and difficulty in achieving uniform distribution of metabolites in the food matrix. More importantly, there are significant differences between in-vitro culture conditions and food matrix environment, and the metabolites produced by lactic acid bacteria in in-vitro fermentation broth differ significantly in terms of type, content, and biological activity from those produced by in-situ fermentation in food matrix.

[0008] In summary, the prior art has the following main problems in the preservation of cooked food: first, there is a lack of high-yield exopolysaccharide and bacteriocin-producing lactic acid bacteria strains that are specifically screened for cooked food processing environment (high salt, low temperature); second, there is a lack of technical solutions that combine lactic acid bacteria fermentation with cooked food processing technology to achieve in-situ generation of preservation substances; third, there is a lack of methods for mild inactivation of lactic acid bacteria while maintaining the activity of functional metabolites, forming an efficient bio-preservative system. Therefore, there is an urgent need to develop a new preservation technology that can fully utilize the preservation function of lactic acid bacteria metabolites, seamlessly integrate with existing cooked food processing technology, and ensure product safety and sensory quality. SUMMARY

[0009] Therefore, the purpose of the present application is to provide a bio-preservative cooked food preservation process based on in-situ transformation of lactic acid bacteria, which integrates fermentation process with curing process by screening lactic acid bacteria with high yield of exopolysaccharide and bacteriocin in a simulated cooked food processing environment, and maintains the activity of metabolites by using mild inactivation technology, realizing the transformation of lactic acid bacteria into bio-preservative system in-situ in food matrix, thereby effectively extending the shelf life of cooked food while maintaining the sensory quality and nutritional value of the product.

[0010] A bio-preservative cooked food preservation process based on in-situ transformation of lactic acid bacteria, comprising the following steps: S1, after cutting the raw meat or vegetable raw materials, soak them in a 0.5-1.5% sodium chloride aqueous solution for 40-90 min, and then drain and pre-cool at 4-10℃ for 1-3 h. The purpose of this step is to initially reduce the microbial load on the surface of the raw materials, and to improve the water holding capacity and structure of the raw materials through the osmotic effect of sodium chloride. Preferably, the sodium chloride aqueous solution also contains 0.5-1.5% oligosaccharides, which are at least one of fructooligosaccharides, galactooligosaccharides or isomaltooligosaccharides, as a carbon source for lactic acid bacteria fermentation, to promote the generation of exopolysaccharides in the subsequent fermentation process.

[0011] S2, add curing liquid to the raw materials and inoculate lactic acid bacteria at the same time, the lactic acid bacteria are screened in a simulated curing matrix containing 1.5-3.0% sodium chloride, and the salt-tolerant lactic acid bacteria capable of producing exopolysaccharides and bacteriocins are obtained. The inoculation amount of lactic acid bacteria is CFU / g, roll or stir for 20-120 min at 4-10 rpm.

[0012] The pickling liquid contains 2-5% of sodium chloride, 1-3% of soluble sugar and 0.1-0.5% of spice extract by mass fraction. Among them, sodium chloride not only provides the required salinity for pickling, but also creates a suitable high-salt fermentation environment for lactic acid bacteria; the soluble sugar is at least one of glucose, sucrose or maltose, which is the main carbon source for lactic acid bacteria metabolism; the spice extract is at least one of star anise extract, cassia bark extract, Sichuan pepper extract, ginger extract, garlic extract or chili extract, which not only gives the product a characteristic flavor, but also has a synergistic antibacterial effect.

[0013] Further, the pickling liquid also contains 0.08-0.25% of calcium or magnesium salt by mass fraction. The calcium salt is calcium lactate, calcium chloride or calcium citrate, and the magnesium salt is magnesium lactate, magnesium chloride or magnesium citrate. Calcium ions and magnesium ions can form a cross-linked network structure with the exopolysaccharide produced by lactic acid bacteria, enhancing the stability and water retention capacity of the polysaccharide, and at the same time improving the texture properties of the meat product.

[0014] The lactic acid bacteria are Lactococcus lactis subsp. cremoris or Lactiplantibacillus plantarum obtained by directional screening. These two strains can maintain good metabolic activity in a cooked food processing environment containing 1.5-3.0% sodium chloride at 12-18℃, and efficiently produce exopolysaccharide and bacteriocin. Preferably, the Lactococcus lactis subsp. cremoris and Lactiplantibacillus plantarum are inoculated at a colony forming unit ratio of (2-3):(1-2), which can produce both Nisin and Plantaricin, two types of bacteriocins, and form a synergistic antibacterial effect, having a broad-spectrum inhibitory effect on both Gram-positive and Gram-negative bacteria.

[0015] The screening method of the lactic acid bacteria is as follows: in a simulated pickling medium containing 1.5-3.0% sodium chloride, 0.3-0.8% phosphate and 0.5-1.5% soluble sugar, at 12-18℃ for 24-48h, screening strains that form sticky colonies (indicating high exopolysaccharide production) and have obvious inhibitory effect on indicator spoilage bacteria such as Escherichia coli or Staphylococcus aureus (indicating the production of effective bacteriocins). The phosphate includes at least one of sodium phosphate dibasic and sodium phosphate monobasic commonly used in food processing; this directional screening in a simulated actual application environment ensures the excellent performance of the selected strains under cooked food processing conditions.

[0016] The step S2 and the subsequent step S3 can be continuously completed in the same tumbling or marinating equipment, and the lactic acid bacteria are uniformly dispersed in the raw material matrix and fermentation is started by using tumbling or stirring, so that the marinating and fermentation are integrated, the process flow is simplified, and the equipment investment is reduced.

[0017] S3, fermenting for 4-8h at 12-18℃ to make the lactic acid bacteria metabolize to produce exopolysaccharides, organic acids and bacteriocins. The fermentation is terminated when the pH drops to 5.0-5.5 and the soluble sugar consumption reaches 45-65% of the initial amount; wherein the "initial amount" of the soluble sugar refers to the content of the soluble sugar in the raw material system at the beginning of the fermentation (i.e. before inoculating the lactic acid bacteria and starting the fermentation).

[0018] This step is the core part of the present application, and the in-situ metabolic conversion of the lactic acid bacteria in the food matrix is realized by controlling the fermentation temperature, time and end point indicators. Unlike the traditional in-vitro fermentation-extraction-addition mode, the fermentation process of the present application is directly carried out in the food raw materials, so that the metabolic products (exopolysaccharides, bacteriocins, organic acids, etc.) are uniformly distributed in the entire food matrix, forming a three-dimensional preservation barrier.

[0019] The low-temperature fermentation at 12-18℃ can not only ensure the normal metabolism of the lactic acid bacteria, but also effectively inhibit the growth of miscellaneous bacteria, ensuring the safety of the fermentation process. Preferably, the fermentation temperature is 14-16℃ and the time is 5-7h, under which the exopolysaccharide yield is the highest and the bacteriocin activity is the strongest.

[0020] The use of the double indicators of pH and soluble sugar consumption to control the fermentation end point is an innovation of the present application. Relying solely on pH or time control is easy to lead to insufficient or excessive fermentation: insufficient fermentation results in low yield of preservation substances, and excessive fermentation produces too much lactic acid, leading to excessive sour taste and affecting product flavor. When the pH drops to 5.1-5.4 and the soluble sugar consumption reaches 50-60% of the initial amount, sufficient metabolic product accumulation can be ensured, and excessive acidification can be avoided, so that the product achieves the best balance between preservation effect and sensory quality.

[0021] S4, marinating, steaming or roasting the fermented meat raw material to make the center temperature reach 75-85℃ and maintain for 10-30min to make the raw material cooked. The step is skipped for the vegetable raw material.

[0022] The purpose of this step is to make the meat raw material reach the cooked state, and further reduce the microbial load. The center temperature of 75-85℃ can effectively kill most of the vegetative cell type microorganisms, but the temperature is not too high to cause excessive denaturation of proteins and deterioration of flavor. Different cooking methods (marinating, steaming, roasting) are suitable for different types of cooked food products, meeting the diversified product demand.

[0023] S5, subjecting the meat raw material after the maturation of step S4 or the vegetable raw material after the treatment of step S3 to low-temperature pasteurization at 62-70℃ for 10-20min or high-pressure treatment at 300-450MPa for 5-12min, so that the lactic acid bacteria are inactivated while the structural stability of the exopolysaccharide and the bacteriocin is maintained and the postbiotic is formed.

[0024] Although the traditional high-temperature sterilization (121℃) can completely kill microorganisms, it will lead to degradation of exopolysaccharide, inactivation of bacteriocin, and deterioration of product texture and flavor. The mild inactivation technology of low-temperature pasteurization or high-pressure treatment is adopted in the present application, which can maximize the structural and activity of functional metabolites while ensuring complete inactivation of lactic acid bacteria and microbial safety of the product.

[0025] Low-temperature pasteurization at 62-70℃ can inactivate lactic acid bacteria, but has less impact on exopolysaccharide and bacteriocin which are more heat-resistant. Studies have shown that the retention rate of exopolysaccharide and bacteriocin can reach more than 85% in this temperature range. High-pressure treatment can better maintain the color, flavor and nutritional ingredients of the product by destroying the cell membrane and cell wall of microorganisms through high pressure, while having less impact on the structure of macromolecular polysaccharides and peptide substances.

[0026] After this step, the active lactic acid bacteria are converted into inactivated bacterial cells and their stable metabolites, forming a postbiotic preservation system. Compared with active probiotics, postbiotics have better stability and are not limited by storage conditions, and there is no problem of reduced preservation effect caused by the decrease in the number of live bacteria. At the same time, the inactivated bacterial cells and their metabolites can still exert biological functions such as antibacterial and antioxidant effects.

[0027] S6, vacuum packaging at 0-4℃ and post-ripening for 24-48h.

[0028] Vacuum packaging can isolate the invasion of external oxygen and microorganisms, providing good protection for the product. The cold storage condition of 0-4℃ further inhibits the growth of residual microorganisms and the progress of biochemical reactions. The post-ripening process allows the flavor substances inside the product to further balance and blend, resulting in a more tender and juicy texture. Meanwhile, the functional ingredients in the postbiotic further penetrate and stabilize in the food matrix.

[0029] For different types of cooked food products, the present application also provides preferred process parameter combinations: (1) Salad vegetable product: Step S1: soaking in 0.5-1.0% sodium chloride solution for 40-60min; step S3: fermentation temperature 12-15℃, time 4-6h, end point pH 5.0-5.3; skipping step S4 (vegetables do not need to be matured); step S5: high-pressure treatment at 350-450MPa for 6-10min.

[0030] The chilled vegetable has high water content and crisp and tender organization, the lower concentration of sodium chloride is used to avoid excessive dehydration, the lower fermentation temperature and shorter time are used to prevent the organization from softening, and the ultra-high pressure treatment can realize sterilization and conversion of the post-biont while keeping the crisp and tender taste of the vegetable.

[0031] (2) marinated meat products: step S1 is soaked in 1.0-1.5% sodium chloride solution for 60-90min; step S3 is fermented at 14-16℃ for 5-8h, and the end point pH is 5.2-5.4; step S4 is to make the center temperature reach 75-85℃ by marinating; and step S5 is to carry out low-temperature pasteurization at 62-70℃ for 12-18min.

[0032] The marinated meat products need a long marinating time to be flavored, the end point pH of fermentation is slightly high to keep the unique flavor of the marinated products, the spice components of the marinade penetrate into the meat during the marinating process, and the low-temperature pasteurization can ensure safety and avoid texture deterioration caused by secondary heating.

[0033] (3) cured meat products: step S1 is soaked in 1.0-1.5% sodium chloride solution for 60-90min; step S3 is fermented at 15-18℃ for 4-7h, and the end point pH is 5.3-5.5; step S4 is to make the center temperature reach 75-85℃ by steaming or roasting; and step S5 is to carry out low-temperature pasteurization at 62-68℃ for 15-20min.

[0034] The cured meat products (such as ham and bacon) require high salinity and moderate fermentation acidity, and slightly high fermentation temperature can speed up the fermentation process, and the end point pH is controlled at 5.3-5.5 to ensure preservation effect and not to be excessively acidified to affect the typical flavor.

[0035] The beneficial effects of the present application are as follows: 1. The present application selects lactic acid bacteria in a simulated food processing environment containing 1.5-3.0% sodium chloride and at 12-18℃, the selection conditions are highly consistent with the actual application environment, and the selected strains can still maintain the ability of high exopolysaccharide and bacteriocin production under the conditions of high salt and low temperature in food processing, solving the problem of unstable performance of traditional strains in special environment.

[0036] 2. The present application directly carries out lactic acid bacteria fermentation in food raw materials, realizes in-situ generation and uniform distribution of preservation substances, avoids the complex process and loss of functional components of the traditional "fermentation-extraction-addition" mode. At the same time, through the mild inactivation technology of low-temperature pasteurization or ultra-high pressure treatment, the structural stability and biological activity of exopolysaccharide and bacteriocin are maximized, and a stable and efficient post-biont preservation system is innovatively constructed.

[0037] 3. The present application integrates lactic acid bacteria fermentation and pickling process, continuously completes inoculation, tumbling and fermentation process in the same equipment, does not need independent fermentation equipment, greatly reduces equipment investment and production cost, and is highly compatible with existing cooked food processing production line in process flow, and has good industrial application prospect.

[0038] 4. The cooked food product processed by the process of the present application has a significantly prolonged shelf life under refrigeration conditions and significantly improved microbial safety. The product has natural color, soft and juicy texture, and pure flavor, and has better quality than traditional high-temperature sterilized products. The lactic acid bacteria and its metabolites used in the present application are of natural origin, and no chemical preservatives need to be added, which meets the development trend of "clean label" and natural food. DETAILED DESCRIPTION

[0039] The present application will be further described below in conjunction with specific embodiments, but the present application is not limited to these embodiments. Those skilled in the art should recognize that the present application encompasses all possible alternatives, improvements and equivalents within the scope of the claims.

[0040] Screening and preparation of lactic acid bacteria In a simulated pickling medium (MRS base medium added with 2.0% sodium chloride, 0.5% phosphate and 1.0% glucose), the strain forming a viscous colony was isolated and screened from traditional fermented food after 36h of culture at 15℃. The bacteriostatic activity against Escherichia coli ATCC 25922 and Staphylococcus aureus ATCC 25923 was determined, and the strain with a bacteriostatic ring diameter greater than 15mm was screened. It was identified as Lactococcus lactis subsp. cremoris and Lactiplantibacillus plantarum.

[0041] The screened strain was cultured in MRS medium at 30℃ for 18-24h to the logarithmic growth phase, the bacterial cells were collected by centrifugation, washed twice with sterile normal saline, resuspended in a protective agent containing 10% skim milk, and the bacterial liquid concentration was adjusted to 1.0 x 10 CFU / mL. After aliquotting, it was stored at -80℃ for standby use. When used, the working bacterial liquid was prepared by proportioning. Example 1

[0042] Preparation of marinated pork products S1: Take fresh pork hind leg meat 5kg, trim and cut into meat blocks of about 50g. Prepare a 1.0% sodium chloride aqueous solution, and add 1.0% fructooligosaccharides to the solution. Soak the meat blocks in the solution for 65min, with a meat material ratio of 1:2 (w / v). After soaking, drain and precool in a 6℃ refrigerator for 2h. ​

[0043] S2: Prepare the pickling solution with the following composition: sodium chloride 3.5%, glucose 2.0%, star anise extract 0.2%, cassia extract 0.1%, calcium lactate 0.15%, and water. The amount of pickling solution is 20% of the weight of the meat.

[0044] LC-01 and LP-01 strains are mixed at a colony forming unit ratio of 2.5:1.5, and the inoculation amount is CFU / g of meat. The pickling solution and bacterial solution are added to the meat pieces at the same time, and the meat pieces are placed in a vacuum tumbling machine and tumbled at a speed of 6 rpm for 70 min (tumble for 10 min, stop for 5 min, and alternate).

[0045] S3: After tumbling, the meat pieces are transferred to a pickling container together with the pickling solution and fermented in a constant temperature incubator at 15°C. The pH value and soluble sugar content are measured every 1 h. When the fermentation is 6 h, the pH value decreases to 5.25, and the soluble sugar consumption reaches 55% of the initial amount, and the fermentation is terminated.

[0046] S4: The fermented meat pieces are taken out and drained, and placed in a preheated marinade (marinade formula: water, soy sauce, cooking wine, granulated sugar, star anise, cassia, Sichuan pepper, and ginger, etc. Traditional formula). After boiling at high heat, the medium-low heat is used for marinating, and the central temperature meter is used for monitoring. When the central temperature of the meat pieces reaches 80°C, it is maintained for 20 min.

[0047] S5: The marinated meat pieces are taken out, drained, and immediately subjected to low-temperature pasteurization treatment. The meat pieces are placed in a steamer and set to a temperature of 66°C for 15 min. After treatment, it is quickly cooled to room temperature.

[0048] S6: The cooled meat pieces are vacuum packaged and post-ripened in a 2°C refrigerator for 36 h to obtain the finished product. Example 2

[0049] Preparation of marinated pork products S1: Take fresh pork hind leg 5 kg, trim and cut into meat pieces of about 50 g. Prepare a 0.5% sodium chloride aqueous solution, and add 0.5% fructooligosaccharides. Soak the meat pieces in the solution for 40 min, with a meat-to-water ratio of 1:2 (w / v). After soaking, drain and pre-cool in a 4°C refrigerator for 1 h.

[0050] S2: Prepare the pickling solution with the following composition: sodium chloride 2.5%, glucose 1.5%, star anise extract 0.15%, cassia extract 0.1%, calcium lactate 0.10%, and water. The amount of pickling solution is 20% of the weight of the meat.

[0051] LC-01 and LP-01 strains are mixed at a colony forming unit ratio of 2:1, and the inoculation amount is CFU / g meat. The marinating solution and the bacterial solution were added to the meat pieces simultaneously and tumbling was carried out for 30 min at 4 rpm.

[0052] S3: After tumbling, the meat pieces were transferred to a marinating container together with the marinating solution and fermentation was carried out at 12°C. When the pH value dropped to 5.05 and the soluble sugar consumption reached 48% of the initial amount after 4 h of fermentation, the fermentation was terminated.

[0053] S4-6: Same as Example 1 The marinating, mild inactivation and post-packaging ripening steps were the same as in Example 1. Example 3

[0054] Preparation of marinated pork products S1: Fresh pork hind leg meat was taken, 5 kg, trimmed and cut into pieces of about 50 g. A 1.5% sodium chloride aqueous solution was prepared, to which 1.5% of fructooligosaccharides was added. The meat pieces were soaked in the solution for 90 min, with a meat-to-solution ratio of 1:2 (w / v). After soaking, the meat pieces were drained and pre-cooled in a refrigerator at 10°C for 3 h.

[0055] S2: A marinating solution was prepared, having the following composition: sodium chloride 5.0%, glucose 3.0%, anise extract 0.3%, cassia extract 0.15%, calcium lactate 0.20%, and water. The marinating solution was used in an amount of 20% of the weight of the meat.

[0056] The LC-01 and LP-01 strains were mixed in a ratio of 3:2 of colony forming units, and the inoculation amount was 1.5 x 10 CFU / g meat. The marinating solution and the bacterial solution were added to the meat pieces simultaneously and tumbling was carried out for 120 min at 10 rpm.

[0057] S3: After tumbling, the meat pieces were transferred to a marinating container together with the marinating solution and fermentation was carried out at 18°C. When the pH value dropped to 5.48 and the soluble sugar consumption reached 62% of the initial amount after 8 h of fermentation, the fermentation was terminated.

[0058] S4-6: Same as Example 1 The marinating, mild inactivation and post-packaging ripening steps were the same as in Example 1. Example 4

[0059] Preparation of a cold dish vegetable product S1: Fresh cucumbers were taken, 2 kg, washed and cut into strips. A 0.5% sodium chloride aqueous solution was prepared, to which 0.5% of galactooligosaccharides was added. The cucumber strips were soaked in the solution for 40 min, with a vegetable-to-solution ratio of 1:1.5 (w / v). After soaking, the cucumber strips were drained and pre-cooled at 4°C for 1 h.

[0060] S2: Prepare the pickling solution with the following composition: sodium chloride 2.5%, sucrose 1.5%, garlic extract 0.3%, pepper extract 0.2%, calcium chloride 0.12%, and water. The amount of pickling solution is 15% of the weight of the cucumber.

[0061] LC-01 and LP-01 strains are mixed at a colony forming unit ratio of 2:1, and the inoculation amount is CFU / g of vegetable material. The pickling solution and bacterial solution are added to the cucumber strips, and the mixture is gently stirred by hand for 30 min, with stirring every 5 min.

[0062] S3: After stirring, the cucumber strips are transferred to the pickling container together with the pickling solution and fermented at 12°C. When the fermentation time reaches 5 h, the pH value decreases to 5.10, and the soluble sugar consumption reaches 50% of the initial amount, and the fermentation is terminated.

[0063] S4: The cold dish vegetable product does not need to be cooked, so this step is skipped.

[0064] S5: The fermented cucumber strips are drained and placed in a flexible packaging bag, which is then placed in an ultra-high pressure device. The pressure is set to 400 MPa, and the pressure is maintained for 8 min, with the processing temperature controlled below 20°C.

[0065] S6: The product after ultra-high pressure treatment is immediately vacuum packaged and stored in a cold storage at 2°C for 24 h of post-ripening to obtain the finished product. Example 5

[0066] Preparation of pickled chicken breast products S1: Fresh chicken breast meat 3 kg is cut into slices. A 1.5% sodium chloride aqueous solution is prepared, with the addition of 1.5% of isomaltooligosaccharides. The chicken slices are soaked in the solution for 90 min, with a meat-to-solution ratio of 1:2 (w / v). After soaking, the meat is drained and pre-cooled at 10°C for 3 h.

[0067] S2: A pickling solution is prepared with the following composition: sodium chloride 5.0%, maltose 3.0%, ginger extract 0.3%, pepper extract 0.2%, and magnesium citrate 0.20%, and water is added to make up the volume. The amount of pickling solution is 25% of the weight of the meat.

[0068] LC-01 and LP-01 strains are mixed at a colony forming unit ratio of 3:2, and the inoculation amount is CFU / g of meat. The pickling solution and bacterial solution are added to the chicken slices, and the mixture is rolled and kneaded at a speed of 8 rpm for 100 min.

[0069] S3: After rolling and kneading, the meat slices are transferred to the pickling container together with the pickling solution and fermented at 17°C. When the fermentation time reaches 5.5 h, the pH value decreases to 5.40, and the soluble sugar consumption reaches 60% of the initial amount, and the fermentation is terminated.

[0070] S4: The fermented pork slices were taken out and laid flat in a steaming tray, and placed in a steaming oven. The temperature was set to 100℃, and the pork slices were steamed until the center temperature reached 82℃ and maintained for 25min.

[0071] S5: The steamed pork slices were taken out and slightly cooled to about 60℃, and then subjected to low-temperature pasteurization treatment. The temperature was set to 68℃, and the treatment time was 18min.

[0072] S6: The treated pork slices were cooled to room temperature, vacuum-packed, and then ripened in a 3℃ refrigerator for 48h to obtain the finished product. Comparative Example 1

[0073] Pickled pork product without inoculation of lactic acid bacteria A pickled pork product was prepared according to the method of Example 1, but in step 2, lactic acid bacteria were not inoculated, and in step 3, the fermentation step was skipped, and the pickling was directly followed by the pickling in step 4, and the remaining steps were the same. Comparative Example 2

[0074] Traditional high-temperature sterilized pickled pork product A pickled pork product was prepared according to the method of Example 1, but after step 4, the low-temperature pasteurization in step 5 was replaced by traditional high-temperature high-pressure sterilization: the pickled pork pieces were placed in a high-temperature cooking bag and sterilized at 121℃, 0.1MPa for 20min, and the remaining steps were the same. Comparative Example 3

[0075] Pickled pork product using non-directionally screened lactic acid bacteria A pickled pork product was prepared according to the method of Example 1, but in step 2, the lactic acid bacteria used were Lactococcus lactis and Lactobacillus plantarum (commercially available strains) screened under conventional conditions in MRS medium at 37℃, without directional screening in high-salt low-temperature environment, and the remaining steps were the same. Comparative Example 4

[0076] Cold vegetable product without inoculation of lactic acid bacteria A cold cucumber product was prepared according to the method of Example 4, but in step S2, lactic acid bacteria were not inoculated, and in step S3, the fermentation step was skipped, and the pickling was directly followed by the ultra-high pressure treatment in step S5, and the remaining steps were the same. Performance test

[0077] The products of the above examples and comparative examples were tested for the following indicators: (1) Microbial indicators Total bacterial count: determined according to the method of GB 4789.2-2022 "National Food Safety Standard Food Microbiological Examination Total Bacterial Count Determination".

[0078] (2) Physicochemical indicators pH value: determined according to GB 5009.237-2016 "National Food Safety Standard-Determination of pH value of food".

[0079] Exopolysaccharide content: determined by the phenol-sulfuric acid method, using glucose as the standard to draw a standard curve, and the result was expressed in mg / 100g.

[0080] Bacteriocin activity: determined by the agar diffusion method, using E. coli ATCC 25922 as the indicator bacteria, measuring the diameter of the inhibition zone, and the activity unit AU / mL = inhibition zone area x dilution factor.

[0081] (III) Sensory evaluation Ten trained evaluators were organized, and the color, aroma, taste, texture, and organization state were scored according to the relevant standards, with a full score of 100.

[0082] (IV) Shelf life The samples were stored at 4°C, and the total number of colonies was detected every 3 days. When the total number of colonies exceeded CFU / g, it was determined as the end of shelf life. Test results

[0083] Table 1 Comparison of test results of each example and comparative example: .

[0084] Note: "-" means not detected or very low content.

[0085] Result analysis Example analysis: Example 1 used the optimal parameters (15°C, 6h), and the contents of exopolysaccharide and bacteriocin were the highest (185 mg / 100g, 1280 AU / mL), the shelf life was 22 days, the sensory score was 91, and the comprehensive performance was the best. Example 2 used low-end parameters (12°C, 4h), and the functional ingredient yield was reduced to 160 mg / 100g and 1050 AU / mL due to low fermentation temperature and short time, and the shelf life was 19 days. Example 3 used high-end parameters (18°C, 8h), although the fermentation time was long, but the high temperature led to an increased risk of contamination (bacterial number 4.8×10² was the highest in the examples), the functional ingredient yield was 165 mg / 100g and 1020 AU / mL, the shelf life was 18 days, and the comprehensive effect was not as good as Example 1. Examples 4-5 verified the application effect of cold vegetables and pickled chicken respectively, and the shelf life was 18 days and 20 days respectively, proving that the process had good versatility.

[0086] The comparative example analysis: Comparative example 1 is not inoculated with lactic acid bacteria, no functional ingredients are produced, the initial total number of colonies reaches 8.5x10³ CFU / g, and the shelf life is only 6 days, proving the necessity of in-situ fermentation of lactic acid bacteria. Comparative example 2 uses traditional high-temperature sterilization (121℃), although the shelf life reaches 25 days, but the exopolysaccharide and bacteriocin are largely degraded (retention rate is about 40%), the sensory score is the lowest (76 points), and there are obvious quality problems such as cooking smell and hard texture, which shows that although high-temperature sterilization can prolong the shelf life, it seriously affects the quality. Comparative example 3 uses an undirected screening strain, and the yield of functional ingredients (98 mg / 100g, 680 AU / mL) is significantly lower than that of the examples, and the shelf life is only 13 days, which proves the importance of directional screening. Comparative example 4 is a cold vegetable product without inoculation of lactic acid bacteria, relying only on ultra-high pressure treatment for preservation. Since lactic acid bacteria are not inoculated for fermentation, there is no exopolysaccharide and bacteriocin produced in the product, and the pH value of the finished product is maintained at 6.05, lacking the bacteriostatic effect of organic acids.

[0087] The above is only a preferred specific embodiment of the present application, but the protection scope of the present application is not limited thereto, any person skilled in the art can make equivalent replacement or change according to the technical solution and the inventive concept of the present application within the technical range disclosed by the present application, which should be covered within the protection scope of the present application.

Claims

1. A postbiotic meat preservation process based on in situ conversion of lactic acid bacteria, characterized in that Comprising the following steps: S1, after cutting fresh meat or vegetable raw materials, soaking in a sodium chloride aqueous solution with a mass fraction of 0.5-1.5% for 40-90min, and then draining and precooling at 4-10℃ for 1-3h; S2, adding pickling liquid to the raw material and inoculating lactic acid bacteria at the same time, the lactic acid bacteria being screened in a simulated pickling medium containing 1.5-3.0% sodium chloride, the salt-tolerant lactic acid bacteria capable of producing exopolysaccharide and bacteriocin, and the inoculation amount of the lactic acid bacteria being CFU / g, tumbling or stirring at 4-10 rpm for 20-120 min. S3, fermenting at 12-18℃ for 4-8h to make lactic acid bacteria metabolize to produce exopolysaccharide, organic acid and bacteriocin, and terminating fermentation when pH drops to 5.0-5.5 and soluble sugar consumption reaches 45-65% of the initial amount; S4, marinating, steaming or roasting the fermented meat raw materials to make the center temperature reach 75-85℃ and maintain for 10-30min to make the raw materials mature, and skipping this step for vegetable raw materials; S5, low-temperature pasteurization at 62-70℃ for 10-20min or 300-450MPa ultra-high pressure treatment for 5-12min for the meat raw materials matured in step S4 or the vegetable raw materials treated in step S3, to inactivate lactic acid bacteria while maintaining the structural stability of exopolysaccharide and bacteriocin and forming a postbiotic; S6, vacuum packaging at 0-4℃ and post-ripening for 24-48h.

2. The postbiotic cooked food preservation process according to claim 1, characterized in that, The sodium chloride aqueous solution in step S1 also contains oligosaccharides with a mass fraction of 0.5-1.5%, and the oligosaccharides are at least one of fructooligosaccharides, galactooligosaccharides or isomaltooligosaccharides.

3. The postbiotic cooked food preservation process of claim 1, wherein, The pickling liquid in step S2 contains sodium chloride with a mass fraction of 2-5%, soluble sugar with a mass fraction of 1-3% and spice extract with a mass fraction of 0.1-0.5%, the soluble sugar is at least one of glucose, sucrose or maltose, and the spice extract is at least one of star anise extract, cassia extract, Sichuan pepper extract, ginger extract, garlic extract or chili extract.

4. The postbiotic cooked food preservation process of claim 3, wherein, The pickling liquid in step S2 also contains calcium salt or magnesium salt with a mass fraction of 0.08-0.25%, the calcium salt is calcium lactate, calcium chloride or calcium citrate, and the magnesium salt is magnesium lactate, magnesium chloride or magnesium citrate.

5. The postbiotic cooked food preservation process according to claim 1, characterized in that, The lactic acid bacteria in step S2 are Lactococcus lactis subsp. cremoris or Lactiplantibacillus plantarum obtained by screening.

6. The postbiotic cooked food preservation process of claim 5, wherein, The Lactococcus lactis subsp. cremoris and Lactiplantibacillus plantarum are inoculated at a colony forming unit ratio of (2-3):(1-2) to produce two types of bacteriocins, Nisin and Plantaricin, simultaneously during compound fermentation.

7. The postbiotic cooked food preservation process of claim 1, wherein, The lactic acid bacteria in step S2 are obtained by the following screening method: culturing in a simulated pickling medium containing 1.5-3.0% sodium chloride, 0.3-0.8% phosphate and 0.5-1.5% soluble sugar at 12-18℃ for 24-48h, and screening strains that form viscous colonies and have inhibitory effect on indicator spoilage bacteria such as Escherichia coli or Staphylococcus aureus.

8. The process for preserving cooked food by using postbiotic according to claim 1, wherein, Steps S2 and S3 are continuously completed in the same tumbling or marinating equipment, and the lactic acid bacteria are uniformly dispersed in the raw material matrix and fermentation is started by tumbling or stirring.

9. The postbiotic cooked food preservation process of claim 1, wherein, The fermentation temperature in step S3 is 14-16℃, the time is 5-7h, and the fermentation end point is controlled by two indexes of pH dropping to 5.1-5.4 and soluble sugar consumption reaching 50-60% of the initial amount.

10. The postbiotic cooked food preservation process according to any one of claims 1-9, characterized in that, When preparing a cold dish vegetable product, step S1 is soaked in a 0.5-1.0% sodium chloride solution for 40-60min, the fermentation temperature in step S3 is 12-15℃, the time is 4-6h, the end point pH is 5.0-5.3, step S4 is skipped, and step S5 is treated by 350-450MPa ultra-high pressure for 6-10min; When preparing a marinated meat product, step S1 is soaked in a 1.0-1.5% sodium chloride solution for 60-90min, the fermentation temperature in step S3 is 14-16℃, the time is 5-8h, the end point pH is 5.2-5.4, step S4 is treated by marinating to make the center temperature reach 75-85℃, and step S5 is treated by low-temperature pasteurization at 62-70℃ for 12-18min; When preparing a pickled meat product, step S1 is soaked in a 1.0-1.5% sodium chloride solution for 60-90min, the fermentation temperature in step S3 is 15-18℃, the time is 4-7h, the end point pH is 5.3-5.5, step S4 is treated by steaming or roasting to make the center temperature reach 75-85℃, and step S5 is treated by low-temperature pasteurization at 62-68℃ for 15-20min.