A composition for preserving chicken claws, a pickling material and application thereof

Abstract

The application discloses a composition for preserving chicken claws, a pickling material and application of the composition. The composition comprises the following components in parts by weight: 20-50 parts of epsilon-polylysine hydrochloride and 5-15 parts of streptococcal lactate. The application also provides a pickling material comprising the composition. The cooked meat product treated by the composition and the pickling material has a significantly reduced color difference change during storage, and can effectively stabilize the original color. Meanwhile, the composition and the pickling material can effectively inhibit the decomposition of muscle tissue in the cooked meat product by microorganisms, slow down the decrease of product hardness and elasticity, and thus maintain the excellent food quality of crispness, tenderness and juiciness during long-term storage. The application provides a scheme for color protection and preservation for quality maintenance of cooked meat products, and has a good industrial application prospect.

Description

Technical Field

[0001] This invention belongs to the field of food preservation technology, specifically relating to a composition, marinade and its application for preserving chicken feet. Background Technology

[0002] Boneless chicken feet are rich in water, collagen, and crude protein, making them highly susceptible to microbial contamination throughout the entire process of raw material processing, finished product storage, and transportation. Sources of contamination include the inherent microbial flora in fresh chicken feet, cross-contamination from production equipment, and the excessive proliferation of microorganisms due to uncontrolled storage and transportation temperatures. Existing research has conducted microbial testing on commercially available cooked chicken feet such as pickled chicken feet, lemon-spicy boneless chicken feet, and tiger-skin chicken feet, detecting dominant spoilage bacteria such as Escherichia coli, Chlamydia abortus, Lactobacillus brevis, and Lactobacillus plantarum. The main sources of contamination are improperly cleaned frozen chicken feet and marinating ingredients. Various spoilage microorganisms can secrete proteases and lipases to decompose the proteins, fats, and carbohydrates in chicken feet, causing various spoilage problems: Clostridium metabolites produce gas and hydrogen sulfide, causing packaging bloating and a putrid odor; Weissella and Leuconostoc mesenteroides can cause vacuum-packed chicken feet to turn abnormally green; and the proliferation of Pseudomonas fluorescens and Pseudomonas aeruginosa can make the surface of the chicken feet sticky, completely destroying their commercial value. Microbial contamination not only damages the sensory qualities of chicken feet, such as color, flavor, and texture, but its metabolic toxins can also harm human health. Therefore, effectively inhibiting microbial growth is the key to ensuring the storage quality and food safety of boneless chicken feet.

[0003] Currently, meat product preservation is mainly divided into two categories: physical preservation and chemical preservation. Physical preservation technologies include low temperature, modified atmosphere packaging, vacuum packaging, ultra-high pressure, and irradiation sterilization. While these can delay protein oxidation and inhibit microbial growth, the costs of equipment purchase and cold chain distribution are high. High-temperature and high-pressure treatments can also damage the tissue structure of chicken feet, resulting in dry, hard meat and a poor taste. Chemical preservation often uses artificial preservatives such as nitrites, potassium sorbate, and organic acids. These have stable antibacterial effects, but nitrites pose a safety risk of generating nitrosamines, and synthetic preservatives do not meet the requirements of clean label consumer products. Excessive addition can also produce off-odors, limiting their application in chicken feet products. Biological preservation relies on natural active substances derived from animals, plants, and microorganisms, offering significant safety advantages and making it a hot research topic in the industry. Among them, animal-derived preservatives such as chitosan and lysozyme, and plant extracts such as perilla, clove, and yam all possess antibacterial and antioxidant capabilities. However, high doses of plant extracts can easily cause browning of chicken feet, affecting the product's appearance.

[0004] Existing technologies lack a composite biological preservative formula suitable for medium-temperature storage of boneless chicken feet, which simultaneously addresses antioxidant properties and production costs, and does not contain coloring plant extracts. This patent addresses these industry pain points by providing a composite biological preservative suitable for cooked boneless chicken feet and its corresponding processing technology. Summary of the Invention

[0005] In view of the shortcomings of the prior art described above, the purpose of this invention is to provide a composition, marinade and its application for preserving chicken feet, in order to solve the problems existing in the prior art.

[0006] To achieve the above objectives, the present invention specifically adopts the following technical solution.

[0007] A first aspect of the present invention protects a composition for preserving cooked meat products, comprising the following components in parts by weight:

[0008] 20-50 parts of ε-polylysine hydrochloride

[0009] Nisin 5-15 parts.

[0010] Another aspect of the present invention protects a marinade for preserving cooked meat products, comprising the composition described above.

[0011] Another aspect of the present invention protects the use of the composition or marinade described above in at least one of the following:

[0012] A1) Inhibits the proliferation of microorganisms during the storage of cooked meat products;

[0013] A2) Inhibits protein degradation or fat oxidation during the storage of cooked meat products;

[0014] A3) Reduce color changes in cooked meat products during storage;

[0015] A4) Extend the shelf life of cooked meat products.

[0016] Another aspect of the present invention protects a method for preserving cooked meat products, comprising the following steps:

[0017] 1) Marinate cooked meat products with the composition or marinade described above;

[0018] 2) Vacuum seal the marinated cooked meat products with fresh marinade and store them.

[0019] Another aspect of the present invention protects cooked meat products obtained by the preservation method described above.

[0020] Compared with the prior art, the present invention has the following beneficial effects:

[0021] 1) The composition and marinade for preserving cooked meat products of the present invention contain ε-polylysine and nisin. The two preservatives together inhibit the proliferation of various spoilage microorganisms during the storage of cooked meat products, and can extend the shelf life of medium temperature (15°C) storage from 6 days to at least 12 days. At the same time, they significantly inhibit protein degradation and fat oxidation of cooked meat products during storage, reduce the generation of TVB-N and TBARS, and effectively delay the rancidity and deterioration of cooked meat products.

[0022] 2) Compared with clove extract and perilla extract, the composition and marinade of the present invention for the preservation of cooked meat products will not cause browning of cooked meat, and the color difference changes less during storage, and the original color of cooked meat is stably preserved; it can also inhibit the decomposition of muscle tissue by microorganisms, slow down the decrease in hardness and elasticity, and maintain the crisp and juicy taste of cooked meat products (especially chicken feet) for a long time.

[0023] 3) The composition and marinade for preserving cooked meat products of the present invention are natural microbial food additives that meet the requirements of clean labeling and have high safety. Only ε-polylysine and nisin are added in the original marinating process, without the need for additional processing steps. The process is simple and the production cost is controllable. It is suitable for the industrialized medium-temperature circulation production of pickled peppers and braised cooked meat products.

[0024] 4) The present invention is equipped with a microwave secondary sterilization process. The combination of ε-polylysine and nisin with microwave treatment has a significant synergistic preservation effect. Microwaves rapidly reduce the initial bacterial count, and the compound preservation has a long-lasting effect of inhibiting the metabolism of residual spoilage bacteria. The combination of the two can enable cooked meat products to withstand long-term storage at 42°C, greatly expanding the product circulation scenarios. Attached Figure Description

[0025] Figure 1 The graph shows the effect of ε-PL concentration on the TVC value of chicken feet in Example 1 of the present invention.

[0026] Figure 2 The figure shown is a graph illustrating the effect of ε-PL concentration on the pH value of chicken feet in Example 1 of the present invention.

[0027] Figure 3 The figure shown is a graph illustrating the effects of ε-PL combined with clove and perilla extracts on the TVC and pH value of chicken feet in Example 1 of this invention.

[0028] Figure 4 The figure shown is a graph illustrating the effect of ε-PL composite nisin on the TVC value and pH value of chicken feet in Example 1 of the present invention.

[0029] Figure 5 The figure shown is a result of the effect of ε-PL combined with nisin treatment and ε-PL treatment alone on the hardness and elasticity of chicken feet during storage in Example 2 of the present invention.

[0030] Figure 6 The image shows the effects of ε-PL combined with nisin treatment and ε-PL treatment alone on the sensory scores of chicken feet during storage in Example 2 of the present invention.

[0031] Figure 7 The images shown are sensory images of chicken feet treated with ε-PL and nisin alone during storage, as described in Example 2 of this invention.

[0032] Figure 8 The figure shows the effect of ε-PL combined with nisin treatment and ε-PL treatment alone on the TBARS content of chicken feet during storage in Example 2 of the present invention.

[0033] Figure 9 The figure shows the effect of ε-PL combined with nisin treatment and ε-PL treatment alone on the TVB-N content of chicken feet during storage in Example 2 of the present invention. Detailed Implementation

[0034] In this invention, cooked meat products refer to products processed from fresh (frozen) livestock and poultry products as the main raw materials, including braised meat products, smoked meat, roasted meat, grilled meat, fried meat, Western-style ham, meat sausages, fermented meat products, dried cooked meat products, and other cooked meat products. Based on different processing techniques, they can be divided into two main categories: braised products and marinated products.

[0035] A first aspect of the present invention protects a composition for preserving cooked meat products, comprising the following components in parts by weight:

[0036] 20-50 parts of ε-polylysine hydrochloride

[0037] Nisin 5-15 parts.

[0038] This invention uses cooked meat products as the treatment target. It involves treating cooked meat products with ε-polylysine hydrochloride (ε-PL or polylysine) in combination with clove extract, perilla extract, and nisin, respectively, and then studying the changes in total bacterial count (TVC) and pH value during storage. The results showed that, compared with clove extract and perilla extract, the total bacterial count of cooked meat products treated with the combination of polylysine and nisin, after storage at 15℃ for 12 days, was significantly lower than the upper limit of TVC (5 log5) for cooked meat products specified in GB2726-2019 "National Food Safety Standard for Cooked Meat Products". 10 CFU / g or 10 5The TVC values ​​of polylysine combined with clove extract and perilla extract were lower than the upper limit of TVC values ​​in cooked meat products on the 12th day of storage. Furthermore, the pH value showed the lowest variation during the entire storage period and maintained a high pH value on the 12th day of storage.

[0039] Furthermore, this invention investigated the texture, sensory properties, lipid peroxidation, and protein degradation of cooked meat products treated with a combination of polylysine and nisin. The results showed that after 12 days of storage at 15°C, compared to ε-polylysine hydrochloride alone, the combination treatment significantly improved the firmness and elasticity of the cooked meat products, indicating that the combination treatment helps maintain a good texture and mouthfeel. It also significantly reduced TVB-N and TBARS content, demonstrating that the combination treatment effectively inhibits protein degradation and lipid oxidative rancidity. In addition, the total color difference of the cooked meat products treated with the combination of polylysine and nisin during the entire storage period was significantly lower than that of the ε-polylysine hydrochloride group alone, indicating that the combination treatment has superior color retention. In summary, the composition of this invention not only reduces the interaction between microorganisms and their metabolites and muscle proteins, but also inhibits the oxidation process on the muscle surface and maintains the color of cooked meat products.

[0040] In some embodiments, the polylysine is selected from ε-polylysine hydrochloride. The ε-polylysine hydrochloride of this invention is a product obtained by controlled fermentation of *Streptomyces diastatochromogenes*, followed by adsorption of the culture broth using an ion exchange resin, elution with hydrochloric acid, and purification. It has a pale yellow to white appearance and meets the requirements of GB1886.371-2023, "National Food Safety Standard for Food Additives: ε-polylysine hydrochloride".

[0041] In some embodiments, the weight-average molecular weight of the ε-polylysine hydrochloride is 4130-5776 Da.

[0042] In some embodiments, the ε-polylysine hydrochloride is in the form of 20-30 parts by weight, or 25-40 parts, or 35-50 parts, or 20 parts, 25 parts, 30 parts, 35 parts, 40 parts, 45 parts, or 50 parts.

[0043] In some embodiments, the nisin is expressed in parts by weight of 5-10 parts, or 8-15 parts, or 5 parts, 8 parts, 10 parts, 12 parts, or 15 parts. The nisin of this invention is produced by fermenting skim milk solids or other nitrogenous and carbon-containing substances, such as yeast extract, with Lactococcus lactis subsp. lactis as the main raw material, followed by extraction. It has a light brown to milky white appearance and conforms to the provisions of GB 1886.231-2023 "National Food Safety Standard for Food Additives: Nisin".

[0044] In some embodiments, the potency of the lactic acid nisin is ≥900 IU / mg.

[0045] Another aspect of the present invention protects a marinade for preserving cooked meat products, comprising the composition described above.

[0046] In some embodiments, the ε-polylysine hydrochloride in the composition is 0.2-0.5 wt% based on the total mass of the marinade, or it may be 0.2 wt%, 0.3 wt%, 0.4 wt%, or 0.5 wt%. Preferably, it is 0.3 wt%.

[0047] In some embodiments, the mass percentage of nisin in the composition is 0.05-0.15 wt% based on the total mass of the pickling ingredients, or it can be 0.05 wt%, 0.08 wt%, 0.1 wt%, 0.12 wt%, or 0.15 wt%. Preferably, it is 0.05 wt%.

[0048] In some embodiments, the marinade may also include one or more of garlic, chili peppers, chili sauce, salt, white sugar, oyster sauce, monosodium glutamate, lemon slices, and white vinegar.

[0049] In some embodiments, based on the total mass of the marinade ingredients, the chili sauce accounts for 5-15 wt% of the mass, the chili peppers account for 1-4% of the mass, the garlic accounts for 2-6 wt% of the mass, the salt accounts for 0.5-2 wt% of the mass, the white sugar accounts for 5-15 wt% of the mass, the oyster sauce accounts for 2-6 wt% of the mass, the monosodium glutamate accounts for 0.5-2.5% of the mass, the lemon slices account for 1-4% of the mass, and the white vinegar accounts for 5-9 wt% of the mass.

[0050] In one specific embodiment, the marinade comprises a basic marinade and a composition, wherein the basic marinade comprises: 0.600 kg of chili sauce, 0.125 kg of fresh millet chili, 0.25 kg of garlic, 0.075 kg of salt, 0.600 kg of white sugar, 0.250 kg of oyster sauce, 0.100 kg of monosodium glutamate, 0.125 kg of lemon slices, 0.400 kg of 9° white vinegar, and 3.000 kg of purified water.

[0051] Another aspect of the present invention protects the use of the composition or marinade described above in at least one of the following:

[0052] A1) Inhibits the proliferation of microorganisms during the storage of cooked meat products;

[0053] A2) Inhibits protein degradation or fat oxidation during the storage of cooked meat products;

[0054] A3) Reduce color changes in cooked meat products during storage;

[0055] A4) Extend the shelf life of cooked meat products.

[0056] Another aspect of the present invention protects a method for preserving cooked meat products, comprising the following steps:

[0057] 1) Marinate cooked meat products with the marinade or the combination described above;

[0058] 2) Vacuum seal the marinated cooked meat products with fresh marinade and store them.

[0059] In some embodiments, in 1), the temperature of the mixed marinating is 0-4 ℃, or it can be 0 ℃, 1 ℃, 2 ℃, 3 ℃, or 4 ℃. Low-temperature marinating (0-4 ℃) can not only effectively inhibit the growth of microorganisms, but also allow the marinade to slowly and evenly penetrate into the tissue of the cooked meat product through osmotic pressure.

[0060] In some embodiments, in 1), the mixed marinating time is 6-24 hours, or it can be 6 hours, 10 hours, 12 hours, 15 hours, 18 hours, 20 hours, 22 hours, or 24 hours. The mixed marinating time should not be too long or too short. If it is too long, the cooked meat products will become too soft due to excessive absorption of water or acidic substances, and lose their crisp texture.

[0061] In some embodiments, 1) refers to the cooked meat products as braised meat products. Braised meat products refer to a series of braised meat products made by pre-cooking, soaking, braising, and stewing (or marinating) fresh (frozen) livestock and poultry meat and edible by-products in water with added salt, soy sauce (or no added), and spices. Based on different processing techniques, they can be divided into two main categories: braised products and marinated products. The general category refers to cooked meat products made primarily from fresh (frozen) livestock and poultry meat, which are cleaned, trimmed, seasoned with spices, deboned (or not deboned), shaped (or not shaped), and then braised. The marinated product category refers to cooked meat products made primarily from fresh (frozen) livestock and poultry meat, which are cleaned, trimmed, seasoned with spices, deboned (or not deboned), shaped (or not shaped), and then braised.

[0062] In some embodiments, the braised meat products are braised products, and the braised products are chicken feet.

[0063] In some embodiments, in step 1), the mass ratio of the cooked meat product to the marinade is 5:(1-10), or it can be 5:1, 5:2, 5:3, 5:4, 5:5, 5:6, 5:7, 5:8, 5:8, and 5:10. In a specific embodiment, it is 5:5.

[0064] In some embodiments, in step 2), the mass ratio of the marinated cooked meat product to the fresh marinade is 3:(1-3), or it can be 3:1, 3:2, or 3:3. In a specific embodiment, it is 3:2.

[0065] In some embodiments, in 2), the preservation temperature is 0-45℃, or it can be 0℃, 4℃, 10℃, 12℃, 15℃, 18℃, 20℃, 30℃, 40℃, 42℃, or 45℃.

[0066] In some implementations, in 2), the storage time is not less than 12 days, but can also be 15 days, 18 days, 20 days, 21 days, 30 days, 40 days, 50 days, 60 days, 70 days, 80 days and 90 days.

[0067] In some embodiments, step 2) further includes microwave treatment after vacuum sealing. This invention has found that microwave treatment significantly improves muscle water-holding capacity, inhibits residual microbial metabolic activity, reduces the generation of alkaline degradation products and acidic metabolites, effectively stabilizes the system pH, and enables cooked meat products to withstand accelerated storage conditions at 42°C with a storage period of no less than 21 days. When only ε-PL and nisin were used for combined treatment, the TVC value of cooked meat products increased from an initial 867 CFU / g to 5667 CFU / g under accelerated storage testing (high temperature simulation, 42°C, 21 days). Based on this, after combined microwave treatment with ε-PL and nisin, the TVC value increased from an initial 33 CFU / g to 1000-2667 CFU / g under the same accelerated storage testing (high temperature simulation, 42°C, 21 days). This indicates that microwave treatment not only significantly reduced the initial bacterial load of cooked meat products (by approximately 96.2%), but also continuously inhibited the proliferation of microorganisms in sealed packaging throughout the entire storage period. Compared with simple compound treatment, the TVC value decreased by 53% to 82% after 21 days, demonstrating a significant synergistic effect.

[0068] In some embodiments, the microwave treatment temperature is 60-80°C, or it can be 60°C, 65°C, 70°C, 75°C, or 80°C. Preferably, it is 80°C.

[0069] In some embodiments, the microwave treatment time is 1-5 minutes, or it can be 1 minute, 2 minutes, 3 minutes, 4 minutes, or 5 minutes. Preferably, it is 5 minutes.

[0070] Another aspect of the present invention protects cooked meat products obtained by the preservation method described above.

[0071] In some embodiments, after ε-PL and nisin are combined for preservation treatment, the resulting cooked meat products, when stored at 15°C for 15 days, have a TVC value of less than 5 log. 10 CFU / g; TVC value after 21 days of storage under accelerated storage test (high temperature simulation, 42℃) was less than 5667 CFU / g; TVC value after 21 days of microwave treatment with ε-PL and nisin combined under accelerated storage test (high temperature simulation, 42℃) was less than 2667 CFU / g.

[0072] In some embodiments, the cooked meat products obtained by the preservation method have a hardness value of not less than 440 gf when stored at 15°C for 15 days.

[0073] In some embodiments, the cooked meat products obtained by the preservation method have an elasticity of not less than 0.75 when stored at 15°C for 15 days.

[0074] In some embodiments, when cooked meat products obtained by the preservation method are stored at 15°C for 15 days, the TBARS content is not higher than 0.6 mg / kg.

[0075] In some embodiments, when cooked meat products obtained by the preservation method are stored at 15°C for 15 days, the TVB-N content is not higher than 1.5 mg / 100 g.

[0076] The following specific embodiments illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification.

[0077] Before further describing specific embodiments of the present invention, it should be understood that the scope of protection of the present invention is not limited to the specific embodiments described below; it should also be understood that the terminology used in the embodiments of the present invention is for describing specific embodiments and not for limiting the scope of protection of the present invention. Test methods in the following embodiments that do not specify specific conditions are generally performed under conventional conditions or as recommended by the respective manufacturers.

[0078] When numerical ranges are given in the embodiments, it should be understood that, unless otherwise stated in the present invention, both endpoints of each numerical range and any value between the two endpoints may be selected. Unless otherwise defined, all technical and scientific terms used in this invention have the same meaning as commonly understood by one of ordinary skill in the art. In addition to the specific methods, apparatus, and materials used in the embodiments, based on the knowledge of the prior art possessed by one of ordinary skill in the art and the description of this invention, any prior art methods, apparatus, and materials similar to or equivalent to those described, apparatus, and materials in the embodiments of this invention may be used to implement the present invention.

[0079] The compositions and marinades of this invention are applicable to, but are not limited to, chicken feet. For ease of explanation, chicken feet are used as a representative raw material for cooked meat products in the following examples to verify their application after cooking. The preparation method of cooked chicken feet is as follows:

[0080] Thaw and clean fresh boneless chicken feet, steam in boiling water for 6 minutes, rinse with clean water, soak in 4℃ ice water for 1 hour, drain the surface water, and you will get cooked chicken feet.

[0081] The fresh, boneless chicken feet are supplied by Sunner Group (Jiangxi, China).

[0082] ε-polylysine hydrochloride (abbreviated as ε-PL or ε-polylysine), clove extract, perilla extract, and nisin were all purchased from Zhongchen Biotechnology Co., Ltd. The weight-average molecular weight of ε-polylysine hydrochloride was 5176 Da. The potency of nisin was 950 IU / mg.

[0083] Example 1: Screening of ε-polylysine addition concentration and its combination with other preservatives

[0084] In Example 1, the optimal concentration of ε-polylysine (ε-PL) was screened using TVC and pH as indicators, and then combined with other preservatives to screen for suitable compositions for preserving boneless chicken feet. These included the following:

[0085] 1.1 Screening of ε-polylysine concentration

[0086] A total of 5 groups were designed, with 3 repetitions in each group, and 3 chicken feet in each repetition group, as detailed below:

[0087] CK Group: Basic Marinade

[0088] 0.2% ε-PL group: ε-polylysine is added to the base marinade at a final concentration of 0.2 wt%.

[0089] 0.3% ε-PL group: ε-polylysine is added to the base marinade at a final concentration of 0.3 wt%.

[0090] 0.4% ε-PL group: ε-polylysine is added to the base marinade at a final concentration of 0.4 wt%.

[0091] 0.5% ε-PL group: ε-polylysine is added to the base marinade at a final concentration of 0.5 wt%.

[0092] The basic marinade consists of: 0.600 kg chopped chili sauce, 0.25 kg fresh garlic, 0.125 kg fresh millet chili, 0.075 kg salt, 0.600 kg white sugar, 0.250 kg oyster sauce, 0.100 kg MSG, 0.125 kg lemon slices, 0.400 kg 9° white vinegar, and 3.000 kg purified water, totaling 5.525 kg. The final concentrations are 0.2%ε-PL, 0.3%ε-PL, 0.4%ε-PL, and 0.5%ε-PL, respectively, meaning that 11.05 g, 16.58 g, 22.10 g, and 27.63 g of ε-polylysine are added to the 5.525 kg of basic marinade, respectively.

[0093] According to the above group design, 5,000 kg of cooked boneless chicken feet were mixed with the corresponding marinade and then marinated at 4 ℃ for 16 h.

[0094] Then, remove the marinated chicken feet, vacuum pack them with the corresponding marinade in a 3:2 mass ratio, and store them at 15 ℃.

[0095] TVC and pH were measured for each group on days 0, 2, 4, 6 and 8 of storage.

[0096] pH values ​​were measured using a pH meter (PH-100, Shanghai Lichen Instrument Technology Co., Ltd.). 5 g of chicken feet sample was weighed and added to 50 mL of distilled water, then homogenized using a homogenizer. The pH values ​​of each sample group were then measured at 25 ℃ ± 1 ℃ using a pH meter (calibrated with buffer solutions of pH values ​​4, 7, and 10).

[0097] The Total Viable Count (TVC) determination method is as follows: After weighing the chicken feet sample, add 9 times the amount of sterile physiological saline (0.85%), and homogenize using a homogenizer to prepare a 1:10 sample homogenate. Take 1 mL of the sample homogenate and add 9 mL of sterile physiological saline for serial dilution. Select an appropriate dilution, take 1 mL of the homogenate, and add 15-20 mL of LB agar medium. After mixing and solidification, invert the plate and incubate at 37 ℃ for 48 h before calculating the TVC.

[0098] Microbial contamination is a major cause of spoilage in meat products, and TVC (Total Volume Contamination) reflects the overall level of microbial contamination in meat products. A higher TVC indicates a higher risk of spoilage due to microorganisms. TVC is a core indicator for evaluating the hygienic safety and shelf life of cooked meat products. According to GB2726-2019, the national food safety standard for cooked meat products, the upper limit of TVC in cooked meat products is 5 log [value missing]. 10 CFU / g or 10 5 CFU / g).

[0099] pH value is one of the main indicators of meat products. During storage, the increase and decrease of pH value are usually closely related to microbial activity, and the change of pH value directly affects the flavor of the product.

[0100] See results Figure 1 .

[0101] from Figure 1 It can be seen that the TVC values ​​of chicken feet treated with different concentrations of ε-PL all showed an increasing trend with prolonged storage time. However, the addition of ε-PL generally inhibited the microbial growth of chicken feet during storage. Among them, the 0.30% ε-PL group had the most significant antibacterial effect, with a TVC value of 5.03 log on the 8th day of storage. 10 The CFU / g values ​​were significantly lower than those in the 0.40% ε-PL group (p<0.05) and the 0.50% ε-PL group (p<0.05). Meanwhile, the TVC values ​​in the CK group and the 0.20% ε-PL group were already higher than 7 log on day 6 of storage. 10 The CFU / g value exceeded the acceptable limit, and subsequent counts were not performed due to excessive colony proliferation.

[0102] from Figure 2 It can be seen that the addition of ε-PL generally delayed the change in pH value during the storage period of chicken feet. By day 8 of storage, compared with day 0, the pH decrease rates of the CK group, the 0.20% ε-PL group, the 0.30% ε-PL group, the 0.40% ε-PL group, and the 0.50% ε-PL group were 6.02%, 4.76%, 1.88%, 2.93%, and 3.15%, respectively. Among them, the 0.30% ε-PL group showed the smallest pH fluctuation and the best effect in inhibiting acidification.

[0103] Considering both TVC and pH, 0.30% ε-PL was selected for subsequent compounding with other preservatives.

[0104] 1.2 Screening of ε-polylysine in combination with other preservatives

[0105] Furthermore, ε-PL was compounded with other preservatives, and the optimal combination was screened using TVC and pH values ​​as indicators.

[0106] A total of 10 groups were designed, with 3 repetitions in each group and 3 chicken feet in each repetition, as detailed below:

[0107] CK Group: Basic Marinade

[0108] ε-PL + 0.05% clove extract treatment group: ε-polylysine and clove extract with a final concentration of 0.3 wt% were added to the base marinade.

[0109] ε-PL + 0.10% clove extract treatment group: ε-polylysine and clove extract with a final concentration of 0.3 wt% were added to the base marinade.

[0110] ε-PL + 0.15% clove extract treatment group: ε-polylysine and clove extract with a final concentration of 0.3 wt% were added to the base marinade.

[0111] ε-PL + 0.05% perilla extract treatment group: ε-polylysine with a final concentration of 0.3wt% and perilla extract with a final concentration of 0.05wt% were added to the base marinade.

[0112] ε-PL + 0.10% perilla extract treatment group: ε-polylysine and perilla extract with a final concentration of 0.3wt% were added to the base marinade.

[0113] ε-PL + 0.15% perilla extract treatment group: ε-polylysine with a final concentration of 0.3wt% and perilla extract with a final concentration of 0.15wt% were added to the base marinade.

[0114] ε-PL + 0.05% nisin treatment group: ε-polylysine and nisin were added to the base marinade at a final concentration of 0.3 wt%.

[0115] ε-PL + 0.10% nisin treatment group: ε-polylysine and nisin were added to the base marinade at a final concentration of 0.3 wt%.

[0116] ε-PL + 0.15% nisin treatment group: ε-polylysine and nisin were added to the base marinade at a final concentration of 0.3 wt%.

[0117] The composition of the basic marinade is the same as in step 1.1. The same steps as in step 1.1 are used for mixing, marinating, vacuum sealing, and storage. Then, the TVC and pH of each group are measured on days 0, 3, 6, 9, and 12.

[0118] See results Figure 3 and Figure 4 .

[0119] from Figure 3 and 4 It can be seen that the TVC value of group CK starts from 3 log on day 0. 10 CFU / g rose to 8.2 log on day 6. 10 CFU / g, but later the count became impossible due to the rapid proliferation of microorganisms.

[0120] from Figure 3 It was found that on day 12, the chicken feet treated with ε-PL + 0.15% clove extract had the lowest TVC value, at 5.28 log 10 The CFU / g was lower than that of other treatment groups (ε-PL + 0.05% clove extract, ε-PL + 0.10% clove extract) (p > 0.05); the chicken feet in the ε-PL + 0.15% clove extract treatment group had the highest pH value, which was 4.54.

[0121] from Figure 3 It was found that on day 12, the TVC value of chicken feet in the ε-PL + 0.15% perilla extract treatment group was 6.35 log 10 The CFU / g was significantly lower than that of other treatment groups (ε-PL + 0.05% perilla extract, ε-PL + 0.10% perilla extract) (p<0.05); the chicken feet in the ε-PL + 0.15% perilla extract treatment group had the highest pH value, which was 4.38.

[0122] from Figure 4It can be seen that on day 12, the TVC value of chicken feet in the ε-PL + 0.15% nisin treatment group was 4.01 log 10 CFU / g, compared with the ε-PL + 0.10% nisin treatment group (4.23 log... 10 The CFU / g ratio did not differ significantly, but was significantly lower than the ε-PL + 0.05% nisin treatment group (4.62 log). 10 The chicken feet treated with ε-PL+0.15% nisin had the highest pH value at 4.78, which was not significantly different from that of the ε-PL+0.10% nisin treatment group (4.73), but significantly lower than that of the ε-PL+0.05% nisin treatment group (4.66).

[0123] By comparing the effects of different concentrations of clove extract, perilla extract, and nisin combined with ε-PL on the TVC and pH value of chicken feet, it was found that the combination of ε-PL and 0.15% nisin was the most effective in delaying the increase in TVC and pH value changes during the storage period of chicken feet. Therefore, considering both preservation effect and economic cost factors, a combination of 0.05% nisin and 0.3% ε-PL was selected for further research on the storage quality of chicken feet.

[0124] Example 2: Study on the effects of the composition on the texture, sensory properties, color, lipid peroxidation, and protein degradation of chicken feet.

[0125] 2.1 Group Design

[0126] There are 3 groups in total, with 3 repetitions in each group, and 3 chicken feet in each repetition:

[0127] CK Group: Basic marinade with no added preservatives.

[0128] ε-PL treatment group: ε-polylysine was added to the base marinade at a final concentration of 0.3 wt%.

[0129] ε-PL+ nisin treatment group: ε-polylysine and nisin were added to the base marinade at a final concentration of 0.3 wt% and 0.05 wt% respectively.

[0130] The basic pickling ingredients were the same as in step 1.1. After mixing, pickling, and sealing in the same manner as in step 1.1, each group was stored at 15 ℃ for 15 days. Texture, color, TBARS, TVB-N, and sensory properties were measured on days 0, 3, 6, 9, 12, and 15 of storage. Each treatment was set up in triplicate, and each parallel treatment was repeated three times. The specific measurement methods are as follows:

[0131] Texture determination: Texture analysis was performed using a texture analyzer (Rapid TA+, Shanghai Tengba Instrument Technology Co., Ltd.). Chicken foot samples were cut into approximately 2 cm × 2 cm pieces and placed in the center of the base. The test mode was TPA deformation, the test speed was 2 mm / s, and the test time was 5 s. The sample was compressed to 50% using the cylindrical probe (P / 36R) of the texture analyzer for measurement, yielding hardness and elasticity values.

[0132] Color Measurement: A colorimeter (YS3060, Shenzhen 3nh Technology Co., Ltd.) was used to evaluate the changes in color parameters of the chicken feet samples according to CIELAB coordinates (L*, a*, and b*). L* represents the brightness of the sample, ranging from 0 (pure black) to 100 (pure white); a* positive values ​​represent red, and a* negative values ​​represent green; b* positive values ​​represent yellow, and b* negative values ​​represent blue. Finally, the total color difference (ΔE) was calculated according to the following formula.

[0133]

[0134] In the formula, L0*, a0*, and b0* are the initial color values ​​of the chicken feet samples on day 0 after treatment, and L*, a*, and b* are the color parameters of the chicken feet samples at different storage times.

[0135] Thiobarbituric acid reactive substances (TBARS) determination: 5.00 g of the minced chicken feet sample was placed in a centrifuge tube, along with 10 mL of distilled water and 12.5 mL of 20% TCA solution. The mixture was homogenized at high speed and centrifuged (6000 r / min, 15 min, 4°C). 2.00 mL of the supernatant was collected in a colorimetric tube, and 2 mL of 0.02 mol / L TBA solution was added. The mixture was incubated in boiling water for 20 min, cooled to room temperature, and the absorbance was measured at 532 nm and 600 nm using a spectrophotometer. A blank was prepared using 2 mL of TCA / H₂O (1:1, v / v) + 2 mL of TBA solution. TBARS is a core indicator for evaluating the degree of lipid oxidation.

[0136] Determination of Total Volatile Basic Nitrogen (TVB-N): First, weigh 10 g of evenly minced chicken feet sample and place it in an Erlenmeyer flask. Then, add 100 mL of water, shake for 30 min, and filter. Add 1 g of magnesium oxide to the filtrate and distill for 5 min using a Kjeldahl nitrogen analyzer (SKD-800, Shanghai Peiou Analytical Instruments Co., Ltd.). Add 30 mL of boric acid solution (20 g / L) and 5-6 drops of indicator to the absorption solution. Finally, titrate with hydrochloric acid standard solution (0.1 mol / L). The titration endpoint is reddish-purple. The result is expressed as mg / 100g sample. A reagent blank test is also performed. TVB-N reflects the total amount of alkaline nitrogenous substances such as ammonia and amines produced by the decomposition of proteins in animal foods under the combined action of enzymes and bacteria. These substances are volatile; the higher the content, the more severe the protein degradation, the lower the nutritional value, and the worse the freshness of the product. According to the National Food Safety Standard for Fresh (Frozen) Livestock and Poultry Products (GB 2707-2016), the limit for volatile basic nitrogen (TVB-N) in fresh (frozen) livestock and poultry products is indeed ≤ 15 mg / 100g. The following formula is used to calculate TVB-N:

[0137]

[0138] X represents the TVB-N (mg / 100 g) of the chicken feet sample.

[0139] V1 is the volume (mL) of hydrochloric acid consumed by the chicken feet sample.

[0140] V2 is the volume (mL) of hydrochloric acid consumed by the blank sample;

[0141] V is the volume of filtrate accurately drawn (mL).

[0142] V0 is the total sample volume (mL).

[0143] c represents the concentration of hydrochloric acid;

[0144] m is the sample weight (g).

[0145] Sensory evaluation: A trained panel of 15 people (8 men and 7 women, aged 20 to 35) evaluated the samples using a sensory rating scale, including color and shape, odor and taste, texture and overall acceptability.

[0146] Table 1 Sensory Rating Table

[0147]

[0148] 2.2 Effects on the texture of chicken feet

[0149] The hardness of food reflects its internal binding force that helps it maintain its shape, and is related to its water content, protein content, etc. Elasticity reflects a food's resistance to pressure, and is mainly related to the type of meat product and the physicochemical properties of its proteins. Results are shown below. Figure 5 .

[0150] from Figure 5 It can be seen that the texture properties (hardness, elasticity) of chicken feet in the CK group, ε-PL treatment group, and ε-PL+ nisin treatment group decreased over time during storage (15℃).

[0151] from Figure 5 As shown in Figure a, compared with the control group, the hardness of chicken feet in the ε-PL treatment group and the ε-PL+nisin treatment group showed an increasing trend within 3 days of storage, increasing to 595.30 gf and 666.08 gf, respectively. After 15 days of storage, the hardness of chicken feet in the ε-PL+nisin treatment group was 503.00 gf, which was 1.12 times that of the ε-PL treatment group. This indicates that ε-PL+nisin treatment can more effectively slow down the decline in the hardness of chicken feet.

[0152] from Figure 5 As shown in Figure b, on day 6 of storage, the elasticity of the chicken feet in the CK group (0.84) decreased by 7.70% and 9.68% compared to the ε-PL treatment group and the ε-PL+nisin treatment group, respectively. On day 15 of storage, the elasticity of the chicken feet in the ε-PL+nisin treatment group was 0.82, which was 10.81% higher than that in the ε-PL treatment group (0.74) (p < 0.05). This indicates that the combined treatment of ε-PL and nisin effectively maintained the elasticity of the chicken feet.

[0153] 2.3 Effect on chicken feet color

[0154] Color is one of the most important sensory attributes of food, influencing consumers' purchasing decisions. L* represents the brightness of the sample; a* positive values ​​represent red, a* negative values ​​represent green; b* positive values ​​represent yellow, b* negative values ​​represent blue. ∆E represents the total color difference between two samples; the larger the ∆E value, the more significant the color difference between the samples.

[0155] Table 2. Effects of combined preservation treatment on the color of chicken feet during storage.

[0156]

[0157] As shown in Table 2, the L* values ​​of each group of samples gradually increased with prolonged storage time. The L* value of the control sample increased to 59.00 on day 6. On day 15, the L* values ​​of the chicken feet samples in the preservation treatment group were 60.18 and 58.86, respectively. The L* value of the ε-PL+nisin group was still lower than that of the CK group on day 6. The variability of L* value is mainly explained by the pigment content of oxymyoglobin and metmyoglobin. Myoglobin oxidation leads to a higher L* value, which may be related to deterioration. Other processes such as protein denaturation or moisture loss can also lead to an increase in L* value.

[0158] During storage, the a* value of chicken feet samples showed a trend of first decreasing and then increasing. The a* value of the control sample decreased to 4.53 on day 3 and increased to 4.70 on day 6, significantly higher than that of the preservation treatment group (p < 0.05). The a* value of chicken feet samples in the ε-PL group increased to 4.82 on day 15, while the a* value of the ε-PL+nisin group was 4.37, significantly lower than that of the ε-PL group (p < 0.05). The gradual decrease in a* value was caused by the oxidation of unstable aerobic myosin and deoxyhemoglobin into brown methemoglobin. The subsequent increase in a* value may be related to bacterial growth and reproduction, with bacteria consuming oxygen leading to a decrease in methemoglobin.

[0159] The b* value of the chicken feet samples showed an increasing trend with storage time. On day 6 of storage, the b* value of the CK group was the highest (25.33), which may be due to the formation of a yellow complex by hydrogen sulfide formed by microorganisms and active enzymes that degrade proteins, which binds to hemoglobin. At the end of storage, the b* value of the ε-PL+nisin group (25.50) was lower than that of the ε-PL group (26.17).

[0160] As shown in Table 2, the ∆E values ​​of chicken feet samples in all groups increased significantly during the entire storage period (p < 0.05), especially in the CK group, where the ∆E value was 6.00 after 6 days of storage, indicating a significant color change. On day 15, the ∆E value of chicken feet in the ε-PL+nisin treatment group was 5.64, which was 23.47% lower than that in the ε-PL treatment group (7.37), indicating that the combination of ε-PL and nisin significantly reduced the change in ∆E value of chicken feet during the 15-day storage period (p < 0.05).

[0161] 2.4 Effects on the sensory characteristics of chicken feet

[0162] Figure 6 , Figure 7 This study shows the changes in the sensory attributes of chicken feet during storage, including color and shape, odor and taste, texture, and overall acceptability. In this sensory evaluation, a score of 5 was considered the lower limit of acceptable performance. Plots based on the scores were created using Origin 2022 software. (See attached image.) Figure 6 See actual photos of chicken feet. Figure 7 .

[0163] from Figure 6 It can be seen that on day 0, the scores of all four sensory characteristics of the chicken feet samples in each group were greater than 8.00, indicating that all chicken feet were fresh and qualified. The CK group developed a sour and putrid odor on day 6, and the broth became cloudy; all sensory characteristics of the chicken feet were unqualified, with an overall acceptable score of 2.00. Therefore, the CK group lost its edibility on day 6. The overall acceptability score of the ε-PL treatment group on day 12 was 4.80, with appearance, color, odor, and texture generally unacceptable to the sensory evaluation group. The overall acceptability score of the ε-PL+nisin treatment group on day 12 was 5.90.

[0164] In summary, ε-PL+nisin treatment can minimize changes in the sensory characteristics of chicken feet samples and extend the shelf life from 6 days to more than 12 days.

[0165] 2.5 Effect on TBARS content in chicken feet

[0166] TBARS has been widely used as an indicator of lipid peroxidation in meat. A higher TBARS value indicates a greater degree of lipid oxidation in the product. Free radicals, metal ions, lipoxygenases, peroxidases, and microbial enzymes can induce lipid oxidation in meat. Results are shown below. Figure 8 .

[0167] from Figure 8 It can be seen that the TBARS values ​​of chicken feet samples in all groups showed an increasing trend throughout the storage process. The TBARS value of the CK group increased significantly from 0.23 mg / kg on day 0 to 0.50 mg / kg on day 6, indicating a certain degree of oxidation and the development of a putrid odor. The TBARS value of chicken feet in the ε-PL+nisin treatment group was 0.47 mg / kg on day 12 and 0.59 mg / kg on day 15. The TBARS value of chicken feet in the ε-PL treatment group was 0.6 mg / kg on day 12 and 0.66 mg / kg on day 15. Furthermore, the TBARS values ​​of the ε-PL+nisin treatment group were significantly lower than those of the ε-PL treatment group on days 12 and 15.

[0168] 2.6 Effect on TVB-N content in chicken feet

[0169] TVB-N is frequently used as an important indicator for assessing the freshness of meat products, and its content reflects the degree of protein degradation. During storage, due to the metabolic activities of spoilage microorganisms and the degradation of proteins and non-protein nitrogenous compounds (free amino acids, nucleotide breakdown products, etc.) by endogenous enzymes (such as proteases and deaminases), higher TVB-N content indicates more amino acid degradation, leading to a decrease in the nutritional value of the food. (See results below.) Figure 9 .

[0170] from Figure 9 It can be seen that during the storage process, the TVB-N values ​​of all chicken feet samples showed a continuous upward trend.

[0171] On day 6 of storage, the TVB-N value of chicken feet in the ε-PL+nisin group was only 1.05 mg / 100 g, a decrease of 31.82% and 14.63% compared to the CK group (1.54 mg / 100 g) and the ε-PL group (1.23 mg / 100 g), respectively (p<0.05). By the end of storage (day 15), the TVB-N content in the ε-PL+nisin group was 1.47 mg / 100 g, still lower than the level in the CK group on day 6, indicating that the synergistic effect of ε-PL and nisin can effectively delay the formation of alkaline nitrogenous substances. This may be because the antibacterial activity of ε-PL and nisin reduces the ability of microorganisms to oxidize and dehydrogenate, produce non-protein nitrogen compounds, and degrade proteins, thereby inhibiting the TVB-N formation pathway.

[0172] The results of TBARS oxidation and protein degradation suggest that the combined treatment with ε-PL and nisin effectively delayed changes in chicken feet color parameters and improved sensory properties. This may be because the combined treatment with ε-PL and nisin reduced the interaction between microorganisms and their metabolites and proteins, as well as the oxidation reaction on the muscle surface.

[0173] Example 3: Effects of the combined secondary microwave sterilization composition on the TVC value, pH value, and moisture content of chicken feet.

[0174] Example 3 further explores the preservation effect of microwave secondary sterilization combined with ε-PL+nisin on cooked boneless chicken feet. The experiment investigated the changes in moisture, pH, and TVC values ​​of chicken feet after different microwave treatments under accelerated storage (high temperature simulation) to screen the optimal microwave treatment process.

[0175] 3.1 Experimental Instruments and Equipment

[0176] Vertical pressure steam sterilizer (LDZX-75KBS, Shanghai Shenan Medical Instrument Factory); Clean bench (SW-CJ-2FD, Suzhou Purification Equipment Co., Ltd.); Homogenizer (Scientz-11L, Ningbo Xinzhi Biotechnology Co., Ltd.); Ultraviolet spectrophotometer (UV-1800, Shanghai Shimazu Instrument Co., Ltd.); pH meter (PH-100, Shanghai Lichen Instrument Technology Co., Ltd.); Electronic balance (ME3002, Shanghai Mettler Toledo Instrument Co., Ltd.); Refrigerator (BCD-312WDPV, Shanghai Haier Group Co., Ltd.); Electric thermostatic incubator (ZXDP-A2160, Shanghai Zhicheng Analytical Instrument Manufacturing Co., Ltd.).

[0177] 3.2 Experimental Design

[0178] Set up 8 groups, with 3 repetitions in each group, and 3 chicken feet in each repetition:

[0179] Group CK: Marinated with only basic marinade (without ε-PL and nisin), and not microwaved after vacuum sealing;

[0180] Group Bx: The basic marinade was marinated with 0.30% ε-PL and 0.05% nisin, but was not microwaved after vacuum sealing;

[0181] Group W1: Marinated with only basic marinade (without ε-PL and nisin), vacuum sealed and microwaved at 60°C for 2.5 min;

[0182] Group W2: Marinated with only basic marinade (without ε-PL and nisin), vacuum sealed and microwaved at 60°C for 5 min;

[0183] Group W3: Marinated with only basic marinade (without ε-PL and nisin), vacuum sealed and microwaved at 80°C for 5 min;

[0184] Group Bx+WB1: Add 0.30% ε-PL and 0.05% nisin to the basic marinade, marinate, vacuum seal, and microwave at 60℃ for 2.5 min;

[0185] Group Bx+WB2: Add 0.30% ε-PL and 0.05% nisin to the basic marinade, marinate, vacuum seal, and microwave at 60℃ for 5 min;

[0186] Group Bx+WB3: Add 0.30% ε-PL and 0.05% nisin to the basic marinade, marinate, vacuum seal, and microwave at 80 ℃ for 5 min.

[0187] The composition of the basic marinade was the same as in step 1.1. The same steps as in step 1.1 were followed for mixing and marinating, vacuum sealing, and then storage at 42 ℃. Samples were randomly taken on days 0, 3, 7, 14, and 21 for testing TVC, pH, and moisture content. The methods for testing TVC and pH were the same as in step 1.1. The results are shown in Table 3.

[0188] Moisture content determination method:

[0189] Place the weighing bottle in a drying oven at 101–105℃ with the cap tilted against the side. Heat for 1 hour, then remove, cap, and cool to room temperature in a desiccator. Weigh the bottle and repeat the drying process until constant weight is achieved. Weigh 3–5 g of the finely chopped and mixed deboned chicken feet sample into a pre-weighed weighing bottle. Place the weighing bottle in a drying oven at 101–105℃ with the cap tilted. Dry for 2–4 hours, then remove, cap, and cool in a desiccator for 0.5 hours. Weigh the bottle. Repeat the drying process for 1 hour until constant weight is achieved.

[0190] The moisture content of the sample is as follows:

[0191] In the formula:

[0192]

[0193] X—Moisture content in the sample, g / 100 g;

[0194] m0—constant weight mass of the weighing bottle, in g;

[0195] m1—mass of the sample and weighing bottle before drying, in g;

[0196] m2 — the mass of the dried sample and weighing bottle, in grams.

[0197] 3.3 Effects of the combination of the composition and microwave sterilization on the moisture content, pH and total TVC of chicken feet

[0198] Table 3. Moisture content, pH, and TVC of different treatment groups

[0199]

[0200] As shown in Table 3, the CK group, which did not add ε-PL and nisin and was not microwave-treated, had an initial TVC value as high as 41667 CFU / g. After 3 days of storage, the TVC value rose to 56667 CFU / g, which was close to the national standard limit. After 7 days of storage, the microbial content was seriously exceeded and could not be tested further. Endogenous putrefactive bacteria multiplied rapidly under high temperature conditions, and the product deteriorated in a short period of time.

[0201] Although microwave treatment alone reduced the initial TVC value of groups W1, W2, and W3, the long-term antibacterial ability was insufficient: the initial TVC value of group W1 (microwave at 60℃ for 2.5 min) was 2500 CFU / g, and after 7 days of storage, the TVC value exceeded 25000 CFU / g; groups W2 (microwave at 60℃ for 5 min) and W3 (microwave at 80℃ for 5 min) showed better antibacterial effect than group W1 in the early stage, but the TVC value continued to rise after 14 days of storage, indicating that microwave treatment can only kill existing microorganisms in sealed packaging and cannot inhibit the proliferation of residual microorganisms during storage.

[0202] The initial TVC value of the Bx group, which only added ε-PL and 0.05% nisin, was 867 CFU / g. The colony growth was slow in the first 7 days, but the antibacterial effect decreased with the extension of storage time. After 21 days of storage, the TVC value reached 5667 CFU / g, indicating that treatment with ε-PL and 0.05% nisin alone could not continuously inhibit the proliferation of the bacterial community at 42 ℃.

[0203] The combined microwave treatment groups of ε-PL and nisin (BxW1, BxW2, and BxW3) showed significantly better antibacterial effects than the single treatment groups. Among them, group BxW3 (0.30% ε-PL + 0.05% nisin + microwave treatment at 80 ℃ for 5 min) exhibited the best antibacterial effect, with an initial TVC value of only 33 CFU / g; after 21 days of storage, the TVC value was only 1000 CFU / g. Group BxW2 was second best, with a TVC value of only 2667 CFU / g after 21 days of storage. The antibacterial effect of group BxW1 was weaker than the other two. Comparison of microwave parameters shows that increasing the microwave temperature and extending the appropriate treatment time can enhance the bactericidal effect. High-temperature microwave combined with ε-PL and nisin provides stronger long-term bacterial control. The principle may be that microwaves rapidly kill most of the initial microorganisms, significantly reducing the initial bacterial population; the combination of ε-PL and nisin continuously inhibits the proliferation of residual Gram-positive and Gram-negative putrefactive bacteria, delaying colony growth.

[0204] As shown in Table 3, the pH value of the CK group, which did not contain ε-PL and nisin and was not microwave-treated, fluctuated the most. The initial pH value was 4.80. After 3 days of storage, the pH value rose to 4.99, indicating that the microorganisms decomposed a large amount of myoprotein to produce alkaline substances such as TVB-N, and the system became alkalized. In the later stage, the microbial community produced acid, and the pH value continued to drop to 4.48 at 21 days. The acid-base imbalance indicated that the degree of spoilage was severe.

[0205] Microwave treatment alone in groups W1, W2, and W3 only slightly buffered the drastic pH changes in chicken feet caused by prolonged storage. The pH continued to decline throughout the storage period, indicating that the accumulation of organic acids by spoilage microorganisms made it difficult to maintain acid-base balance. During storage, the pH value of all groups of chicken feet showed a decreasing trend, with group W1 showing the largest decrease, significantly higher than groups W2 and W3. Table 3 shows that the TVC in group W1 was relatively high initially due to weaker microwave treatment intensity and incomplete sterilization, but it rapidly increased to 2.50 × 10⁻⁶ by day 7 of storage. 4 CFU / g, a large amount of acid produced by microbial metabolism leads to a rapid decrease in pH. However, the intensity of treatments W2 and W3 is sufficient to kill most of the initial bacterial population, and TVC remains at a low level throughout the process, with less acid production by microorganisms, resulting in a more gradual pH change.

[0206] Only the Bx group containing ε-PL and 0.05% nisin was able to mitigate the dramatic pH changes to some extent, but there was still a significant downward trend. The pH value dropped to 4.67 after 21 days, indicating that protein degradation continued to occur under long-term high temperature.

[0207] The combined microwave treatment of ε-PL and nisin on the three groups (BxW1, BxW2, and BxW3) significantly reduced the overall pH fluctuation. Group BxW3 exhibited the best pH stability, maintaining a range of 4.73–4.80 throughout the treatment with minimal fluctuation. The underlying principle is likely that microwaves kill alkaline and acid-producing putrefactive microorganisms, while the combination of ε-PL and nisin inhibits the metabolic activity of any remaining microorganisms, reducing the formation of alkaline degradation products and acidic metabolites, effectively stabilizing the system's pH and delaying the spoilage of the chicken feet.

[0208] As shown in Table 3, the moisture content of the CK group, which did not contain ε-PL and nisin and was not microwave-treated, decreased by 14.02% compared to the initial moisture content.

[0209] The three microwave-treated groups (W1, W2, and W3) showed slower moisture loss in the first 7 days. However, after 7 days of storage, microorganisms continued to damage the meat structure, and the moisture content decreased over time. At 21 days, the moisture content decreased by 13.77%, 13.57%, and 5.18% respectively compared to the initial moisture content. W3's initial moisture content was only 68.19%, lower than W1 and W2. This may be because W3 was microwave-treated at 80℃ for 5 minutes, which is the highest temperature and longest time, resulting in slightly more free water loss in the initial stage, thus leading to a smaller decrease in moisture content at 21 days. Furthermore, W3 consistently maintained a low total TVC (TVC). Proteases and lipases secreted during microbial proliferation decompose myofibrils and collagen, damaging the muscle microstructure, leading to decreased water-holding capacity and continuous release of free water. W3 had a smaller microbial population, resulting in less damage to the meat structure than W1 and W2, and a weaker driving force for moisture loss.

[0210] The Bx group, which was supplemented with ε-PL and 0.05% nisin alone, had better water retention than the CK, W1, W2 and W3 treatment groups. However, significant water loss still occurred during long-term storage at high temperature. The water content decreased by 4.71% after 21 days compared with the initial water content.

[0211] The microwave treatment groups (BxW1, BxW2, and BxW3) using ε-PL and nisin significantly maintained muscle water-holding capacity, with water content decreasing by 6.02%, 4.49%, and 3.96% respectively after 21 days compared to the initial levels. Comparing microwave parameters, treatment at 60 ℃ for 5 min (BxW2) showed the best protective effect on water-holding capacity in chicken feet. High-temperature microwave treatment at 80 ℃ slightly damaged muscle structure, resulting in slightly lower water-holding capacity than BxW2. This indicates that proteases and lipases secreted during microbial proliferation decompose myofibrils and collagen, disrupting the muscle microstructure and leading to decreased water-holding capacity and continuous release of free water. ε-PL and nisin synergistically inhibit the activity of endogenous and microbial proteases, maintaining the integrity of muscle tissue structure, reducing the release of bound water, and maximizing the preservation of the juicy and tender quality of chicken feet.

[0212] The above embodiments are merely illustrative of the principles and effects of the present invention and are not intended to limit the invention. Any person skilled in the art can modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or alterations made by those skilled in the art without departing from the spirit and technical concept disclosed in the present invention should still be covered by the claims of the present invention.

Claims

1. A composition for preserving cooked meat products, characterized in that, It contains the following components in parts by weight: 20-50 parts of ε-polylysine hydrochloride Nisin 5-15 parts.

2. The composition according to claim 1, characterized in that, The weight-average molecular weight of the ε-polylysine hydrochloride is 4130-5776 Da; And / or, the ε-polylysine hydrochloride is in the form of 20-30 parts by weight; And / or, the amount of the lactic acid nisin is 5-10 parts by weight; And / or, the potency of the lactic acid nisin is ≥900 IU / mg.

3. A marinade for preserving cooked meat products, characterized in that, It comprises the composition as described in claim 1 or 2.

4. The marinade as described in claim 3, characterized in that, Based on the total mass of the pickling ingredients, the mass percentage of ε-polylysine hydrochloride in the composition is 0.2-0.5 wt%. And / or, based on the total mass of the pickling ingredients, the mass percentage of nisin in the composition is 0.05-0.15 wt%.

5. The marinade as described in claim 4, characterized in that, The marinade also includes one or more of the following: garlic, chili, salt, white sugar, oyster sauce, MSG, lemon slices, and white vinegar.

6. Use of the composition of claim 1 or 2 or the marinade of any one of claims 3-5 in at least one of the following: A1) Inhibits the proliferation of microorganisms during the storage of cooked meat products; A2) Inhibits protein degradation or fat oxidation during the storage of cooked meat products; A3) Reduce color changes in cooked meat products during storage; A4) Extend the shelf life of cooked meat products.

7. A method for preserving cooked meat products, characterized in that, Includes the following steps: 1) The cooked meat product is mixed and marinated with the marinade as described in any one of claims 3-5 or the composition as described in claim 1 or 2; 2) Vacuum seal the marinated cooked meat products with fresh marinade and store them.

8. The preservation method as described in claim 7, characterized in that, In 1), the cooked meat product is a braised meat product; preferably, it is a braised product; more preferably, it is chicken feet; And / or, in 1), the mass ratio of the cooked meat product to the marinade is 3:(1-3); In and / or, 2), the mass ratio of the marinated cooked meat product to the fresh marinade is 3:(1-3); And / or, in 2), the vacuum sealing process also includes microwave treatment; Preferably, the temperature of the microwave treatment is 60-80°C; Preferably, the microwave treatment time is 1-5 minutes.

9. The preservation method as described in claim 7, characterized in that, In step 1), the temperature for the mixed pickling is 0-4℃; And / or, in 1), the mixed marinating time is 6-24 h; And / or, in 2), the preservation temperature is 10-45℃; In and / or, 2), the preservation time is not less than 12 days.

10. Cooked meat products obtained by the preservation method according to any one of claims 7-9.

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