Hydrogel film for preserving chilled fresh meat and preparation method of hydrogel film

Abstract

The invention discloses a hydrogel film for chilled meat preservation and a preparation method of the hydrogel film, and belongs to the technical field of beef preservation, the preparation method of the hydrogel film for chilled meat preservation comprises the following steps: taking carboxymethyl chitosan, dialdehyde glucan and oxidized tannic acid as raw materials, and mixing uniformly; in-situ rapid crosslinking is realized through alternate dipping deposition, and the hydrogel film is prepared. The invention discloses an in-situ rapid cross-linking hydrogel film with good biocompatibility, synergistic antibacterial and antioxidant properties and high barrier property and a preparation method thereof, and fundamentally solves the problem of quality deterioration in the storage process of chilled fresh beef.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of beef preservation, and particularly relates to a hydrogel film for fresh chilled beef preservation and a preparation method thereof. BACKGROUND

[0002] Fresh chilled beef is rich in protein and fat, and during storage, problems such as meat spoilage, color darkening and flavor deterioration may occur due to microbial reproduction, enzymatic reaction and oxidation of protein and lipid. The shelf life of fresh chilled beef under conventional refrigeration (0-4 DEG C) is only 5-7 days, which not only causes economic losses but also may cause safety risks. Therefore, developing a new type of preservation material with high barrier property, antibacterial and antioxidant property and biocompatibility has become a core requirement in the field of fresh chilled beef preservation. In the face of the challenge of microbial spoilage and oxidative rancidity of high-value fresh chilled beef, and the environmental pressure brought by traditional petroleum-based packaging, developing a new type of packaging material with efficient preservation function and biodegradable property has become an urgent requirement in the field of food preservation. The existing fresh chilled beef mainly has three preservation technologies of physics, chemistry and biology. Specifically,

[0003] Physical preservation such as low-temperature refrigeration and modified atmosphere packaging can delay spoilage, but has the bottleneck of limited preservation effect and inability to actively inhibit microorganisms. Chemical preservation relies on synthetic preservatives and antioxidants, which has a certain effect but faces potential safety and does not meet the clean label requirement. The biopreservation material represented by polysaccharide-based degradable packaging has the environmental friendly property, but the single crosslinking or simple blending modification strategy in the existing technology is difficult to realize the synergistic improvement of mechanical strength, barrier property and antibacterial and antioxidant activity, which restricts the practical application of the preservation material in the field of fresh chilled meat preservation.

[0004] Therefore, it is urgent to provide an in-situ rapid crosslinking hydrogel film with good biocompatibility, synergistic antibacterial and antioxidant property and high barrier property and a preparation method thereof, so as to fundamentally solve the quality deterioration problem of fresh chilled beef during storage. SUMMARY

[0005] In view of the above technical problems, the application provides a hydrogel film for fresh chilled meat preservation and a preparation method thereof.

[0006] To achieve the above purpose, the application provides the following technical scheme.

[0007] A preparation method of a hydrogel film for fresh chilled meat preservation, comprising the following steps:

[0008] The hydrogel film is prepared by in-situ rapid crosslinking through alternate immersion deposition of carboxymethyl chitosan, dialdehyde dextran and oxidized tannic acid as raw materials.

[0009] Optionally, the preparation process of the dialdehyde dextran is:

[0010] adding sodium periodate into the dextran aqueous solution to perform a dark stirring reaction to obtain oxidized dextran; adding ethylene glycol into the system to continue stirring to terminate the oxidation reaction, and then performing dialysis and freeze-drying in sequence to obtain dialdehyde dextran powder.

[0011] Further, the concentration of the dextran aqueous solution is 20 g / L.

[0012] The dark stirring reaction is performed for 6 h.

[0013] Optionally, the preparation process of the oxidized tannic acid is as follows:

[0014] adding sodium periodate solution into the tannic acid solution to perform dark stirring, and then performing dialysis, centrifugation and freeze-drying in sequence to obtain oxidized tannic acid.

[0015] Further, the volume ratio of the tannic acid solution to the sodium periodate solution is 1:4.

[0016] Further, the mass concentration of the tannic acid solution is 1.27%.

[0017] The mass concentration of the sodium periodate solution is 1.2%.

[0018] Further, the dark stirring is performed for 2 h; and / or,

[0019] The centrifugation is performed at a speed of 7000 rpm for 10 min.

[0020] Optionally, the specific operation of the alternate immersion deposition is as follows:

[0021] immersing the mold into the carboxymethyl chitosan solution; then, transferring the mold to a mixed solution of dialdehyde dextran and oxidized tannic acid, taking out after 15 seconds of standing, and absorbing the excess liquid on the surface with filter paper; taking this as a deposition cycle, repeating the cycle for 5 times, and finally drying the mold to obtain the hydrogel film.

[0022] Further, the concentration of the carboxymethyl chitosan solution is 0.04 g / mL.

[0023] Further, the concentration of dialdehyde dextran and oxidized tannic acid in the mixed solution is both 1% (w / v) (i.e. 0.01 g / mL).

[0024] A hydrogel film for fresh-keeping of chilled meat, which is prepared by the above preparation method.

[0025] The application constructs a double dynamic crosslinking active packaging film based on carboxymethyl chitosan; the core of the film system is to skillfully use the double crosslinking mechanism: first, using dialdehyde dextran as the main crosslinking agent, high-density aldehyde groups on the dialdehyde dextran react with the amino groups on the carboxymethyl chitosan molecular chain to form a main three-dimensional network with mechanical strength; second, introducing oxidized tannic acid, using the high-reactivity o-quinone group to form a more firm and dense auxiliary covalent crosslinking network with the amino group of carboxymethyl chitosan. The layered crosslinking strategy realizes synergistic enhancement, the structure of dialdehyde dextran guarantees the mechanical integrity and stability of the film, and the introduction of oxidized tannic acid not only further strengthens the polymer network, but also greatly improves the barrier property of the film, and importantly, the oxidized tannic acid itself as a natural polyphenol brings the film sustained and broad-spectrum antibacterial and antioxidant activity.

[0026] Further, the performance characterization of the in-situ rapid crosslinking hydrogel film provided by the application proves that the mechanical strength and water vapor barrier property of the double crosslinking film are significantly improved. In the application experiment of chilled beef, the hydrogel film can effectively inhibit microbial growth and delay lipid oxidation, and significantly prolong the shelf life of chilled beef. Therefore, the application provides an efficient preservation scheme for solving the technical problems of beef preservation and green packaging.

[0027] The application of the above hydrogel film in the preservation of chilled beef is specifically to form the hydrogel film on the surface of the chilled beef by in-situ coating, for prolonging the shelf life.

[0028] Compared with the prior art, the application has the following advantages and technical effects:

[0029] The application uses carboxymethyl chitosan, dialdehyde dextran and oxidized tannic acid to construct a double dynamic crosslinking system, forms a main crosslinking network by the aldehyde groups of dialdehyde dextran and the amino groups of carboxymethyl chitosan to provide mechanical support, and forms an auxiliary crosslinking network by the o-quinone groups of oxidized tannic acid and the amino groups of carboxymethyl chitosan to form an enhanced Schiff base reaction, achieving the effect of synergistically improving the mechanical strength, water vapor barrier property and biological activity of the hydrogel film, and solving the problem that the existing single modified carboxymethyl chitosan film cannot balance the structural performance and functional characteristics.

[0030] In the application, the use of dialdehyde dextran as the main crosslinking agent is crucial, and the high-density aldehyde groups can form a stable three-dimensional network skeleton with the carboxymethyl chitosan molecular chain, significantly improving the mechanical properties and water vapor barrier property of the film. The introduction of oxidized tannic acid is also crucial, and the o-quinone groups have a significantly higher reactivity with the amino groups of carboxymethyl chitosan than ordinary tannic acid, achieving a more dense crosslinking network, and through the polyphenol structure, the o-quinone groups endow the film with persistent antibacterial and antioxidant functions.

[0031] The alternating deposition process and the parameter control of 5 cycles in the preparation process of the application have a decisive influence on the film quality, which ensures the sufficient formation and uniform distribution of the double crosslinking network, so that the film can effectively inhibit the growth of microorganisms and lipid oxidation under refrigerated conditions, and the shelf life of chilled beef is extended to 10-12 days. BRIEF DESCRIPTION OF DRAWINGS

[0032] The accompanying drawings, which form a part of the present application, are used to provide further understanding of the application and are incorporated in and constitute a part of the specification. The illustrative embodiments of the present application and their description serve to explain the present application. In the drawings:

[0033] Figure 1 Thickness of the hydrogel film prepared for Example 1 and Comparative Examples 1-4 of the present application;

[0034] Figure 2 Infrared spectrum of the hydrogel film prepared for Example 1 and Comparative Examples 1-4 of the present application;

[0035] Figure 3 Water vapor permeability of the hydrogel film prepared for Example 1 and Comparative Examples 1-4 of the present application;

[0036] Figure 4 Plate culture results chart of total number of colonies measured for Example 2 and Comparative Examples 5-9 at 1-7d;

[0037] Figure 5 Line chart of total number of colonies of chilled beef during storage at 0, 1, 3, 5, 7 days after embedding the beef with the hydrogel film of Comparative Examples 5-9 and Example 2;

[0038] Figure 6 Line chart of lipid oxidation of chilled beef at 0, 1, 3, 5, 7 days after embedding the beef with the hydrogel film of Comparative Examples 5-9 and Example 2;

[0039] Figure 7 Line chart of total volatile basic nitrogen (TVB-N) value of chilled beef at 0, 1, 3, 5, 7 days after embedding the beef with the hydrogel film of Comparative Examples 5-9 and Example 2. DETAILED DESCRIPTION

[0040] Various illustrative embodiments of the present application will now be described in detail below. The detailed description is not intended to be limiting of the present application, but rather is to provide a more detailed description of certain aspects, features and embodiments of the present application.

[0041] It is to be understood that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the present application. Additionally, for a range of values of, for example, concentrations, amounts, and other parameters, each intervening value of the category is also specifically included within the scope of the present application. The intervening values are each expressly incorporated herein. These are only examples of what is specifically allowed under the terms of the disclosure. Other interventions, including those not specifically enumerated herein, are considered within the scope of various embodiments of the disclosure.

[0042] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. Although methods and materials similar or equivalent to those described herein can be used in the practice or testing of the present application, the preferred methods and materials are described. All documents mentioned herein are incorporated by reference to disclose and describe the methods and / or materials in connection with which the documents are cited. In case of conflict, the present specification will control.

[0043] Various modifications and changes can be made to the specific embodiments of the present application described herein without departing from the scope or spirit of the application. Other embodiments of the application will be apparent to those of ordinary skill in the art from the description and examples presented herein. The description and examples are illustrative of the application and are not intended to limit the scope of the application.

[0044] With respect to the terms "comprising", "including", "containing", "having" and the like, these terms are used inclusively and open- ended. These terms indicate the presence of what is recited, but do not exclude or deny the presence of anything else.

[0045] The embodiment of the present application discloses a kind of in-situ quick crosslinking hydrogel film for fresh-keeping of chilled beef, comprising the following raw materials: carboxymethyl chitosan, dialdehyde dextran and oxidized tannic acid;

[0046] Wherein, carboxymethyl chitosan is used as film-forming substrate, dialdehyde dextran is used as main crosslinking agent, and oxidized tannic acid is used as auxiliary crosslinking agent and functional agent.

[0047] The embodiment of the present application further discloses a preparation method of the in-situ quick crosslinking hydrogel film for fresh-keeping of chilled beef, comprising the following steps:

[0048] The mold is immersed in 4% carboxymethyl chitosan solution to ensure uniform adsorption on the surface, then the mold is immersed in 2% oxidized tannic acid and 2% dialdehyde dextran mixed solution (20 mL) for 15 seconds, and the excess unbound liquid is absorbed with filter paper after taking out; the mold is immersed in carboxymethyl chitosan solution again, then immersed in the mixed solution of oxidized tannic acid and dialdehyde dextran again, and the above steps are repeated for 5 times, and the hydrogel film is obtained after drying at room temperature.

[0049] The specific ratio of the raw material components defined in the present application, the process parameters of the alternate immersion, and the construction of the double crosslinking system are the key conditions for realizing the present application. Among them, the synergistic use of oxidized tannic acid and dialdehyde dextran is a means that is significantly different from the prior art. And the dynamic network structure formed by in-situ crosslinking in the present application makes the hydrogel preservative film have excellent mechanical properties, barrier properties, antibacterial and antioxidant activities, which can effectively prolong the shelf life of chilled beef.

[0050] The "room temperature" described in the present application refers to 20-30℃ unless otherwise specified.

[0051] The raw materials used in the present application are all obtained by purchase on the market.

[0052] The technical solutions of the present application are further illustrated by the following examples.

[0053] Example 1

[0054] A preparation method of a hydrogel film for preserving chilled meat, comprising the following steps:

[0055] 4 g of carboxymethyl chitosan was accurately weighed and dissolved in 100 mL of deionized water, continuously stirred at room temperature for 30 minutes to make it fully dissolved, to obtain a 4% (w / v) carboxymethyl chitosan solution.

[0056] 2 g of dextran was weighed and dissolved in 100 mL of distilled water, and 2 g of sodium periodate was added to oxidize the dextran. After stirring in the dark for 6 hours, 1 mL of ethylene glycol was added to terminate the oxidation reaction, and the system was dialyzed with deionized water for 3 days, changing the water 2-3 times a day. Finally, the dialdehyde dextran powder was obtained by freeze-drying.

[0057] Take 1.2% sodium periodate 25 mL, mix with 100 mL of 1.27% tannic acid solution, and stir for 2 hours under the condition of avoiding light throughout. Then, the reaction solution is transferred into a dialysis bag with a molecular weight cutoff of 3500 Da, and dialyzed in a dark environment for 3 days. After dialysis, centrifuge at 7000 rpm for 10 minutes, collect the supernatant and freeze-dry to obtain the oxidized tannic acid solid.

[0058] Dialdehyde dextran and oxidized tannic acid were dissolved in deionized water, and the volume was adjusted to 100 mL to obtain a mixed solution of dialdehyde dextran and oxidized tannic acid, wherein the final concentration of oxidized tannic acid and dialdehyde dextran was 1% (w / v).

[0059] The mold was immersed in 4% (w / v) carboxymethyl chitosan solution to ensure that its surface was uniformly covered. Subsequently, the mold was transferred to a mixed solution of dialdehyde dextran and oxidized tannic acid (both final concentrations were 1% (w / v)), taken out after 15 seconds, and the excess liquid on the surface was absorbed with filter paper. The above steps constitute a complete deposition cycle. Subsequently, the mold was immersed again in the carboxymethyl chitosan solution, then immersed again in the above-mentioned mixed solution of dialdehyde dextran / oxidized tannic acid, and this cycle was repeated a total of 5 times. Finally, the treated mold was dried at room temperature to obtain a hydrogel film (CDO).

[0060] Comparative Example 1 (without the addition of oxidized tannic acid)

[0061] A method for preparing a hydrogel film, comprising the following steps:

[0062] 4 g of carboxymethyl chitosan was accurately weighed and dissolved in 100 mL of deionized water, and continuously stirred at room temperature for 30 minutes to ensure complete dissolution, to obtain a 4% (w / v) carboxymethyl chitosan solution.

[0063] 2 g of dextran was weighed and dissolved in 100 mL of distilled water, and 2 g of sodium periodate was added to oxidize the dextran. The reaction was carried out in the dark for 6 hours with stirring. After the reaction was completed, 1 mL of ethylene glycol was added to the system to terminate the oxidation reaction, and the system was continuously stirred for 30 minutes. The system was dialyzed against deionized water for 3 days, with water being changed 2-3 times per day, and finally freeze-dried to obtain dialdehyde dextran powder. 2 g of dialdehyde dextran was dissolved in deionized water to make up to 100 mL to obtain a 2% (w / v) dialdehyde dextran solution.

[0064] The mold was immersed in 4% (w / v) carboxymethyl chitosan solution to ensure that its surface was uniformly covered. Subsequently, the mold was transferred to a mixed solution of dialdehyde dextran and oxidized tannic acid (both final concentrations were 1% (w / v)), taken out after 15 seconds, and the excess liquid on the surface was absorbed with filter paper. The above steps constitute a complete deposition cycle. Subsequently, the mold was immersed again in the carboxymethyl chitosan solution, then immersed again in the above-mentioned mixed solution of dialdehyde dextran / oxidized tannic acid, and this cycle was repeated a total of 5 times. Finally, the treated mold was dried at room temperature to obtain a hydrogel film (CDO).

[0065] Comparative Example 2 (without the addition of dialdehyde dextran powder, and the tannic acid was not oxidized)

[0066] A method for preparing a hydrogel film, comprising the following steps:

[0067] 4 g of carboxymethyl chitosan was accurately weighed and dissolved in 100 mL of deionized water, and continuously stirred at room temperature for 30 minutes to ensure complete dissolution, to obtain a 4% (w / v) carboxymethyl chitosan solution.

[0068] Dissolve 2 g tannic acid in deionized water, and dilute to 100 mL to obtain a 2% (w / v) tannic acid solution.

[0069] Subsequently, the mold was transferred to the 2% (w / v) tannic acid solution, removed after 15 seconds, and the excess liquid on the surface was absorbed with filter paper. The above steps constitute a complete deposition cycle. Subsequently, the mold was immersed in the carboxymethyl chitosan solution again, and then immersed in the above-mentioned tannic acid solution again, and this cycle was repeated a total of 5 times. Finally, the treated mold was dried at room temperature to obtain a hydrogel film (CT).

[0070] Comparative Example 3 (no dialdehyde dextran powder was added)

[0071] A method for preparing a hydrogel film, comprising the following steps:

[0072] Accurately weigh 4 g of carboxymethyl chitosan, dissolve it in 100 mL of deionized water, and continuously stir at room temperature for 30 minutes to ensure complete dissolution, to obtain a 4% (w / v) carboxymethyl chitosan solution.

[0073] Take 25 mL of 1.2% sodium periodate and mix it with 100 mL of 1.27% tannic acid solution, and stir under light-free conditions for 2 hours. Subsequently, the reaction solution was transferred to a dialysis bag with a molecular weight cutoff of 3500 Da, and dialyzed in the dark for 3 days. After dialysis, centrifuge at 7000 rpm for 10 minutes, collect the supernatant and freeze-dry, and finally obtain the oxidized tannic acid solid. Dissolve 2 g of oxidized tannic acid in deionized water, and dilute to 100 mL to obtain a 2% (w / v) oxidized tannic acid solution.

[0074] Subsequently, the mold was transferred to the 2% (w / v) tannic acid solution, removed after 15 seconds, and the excess liquid on the surface was absorbed with filter paper. The above steps constitute a complete deposition cycle. Subsequently, the mold was immersed in the carboxymethyl chitosan solution again, and then immersed in the above-mentioned tannic acid solution again, and this cycle was repeated a total of 5 times. Finally, the treated mold was dried at room temperature to obtain a hydrogel film (CT).

[0075] Comparative Example 4 (tannic acid was not oxidized)

[0076] A method for preparing a hydrogel film, comprising the following steps:

[0077] Accurately weigh 4 g of carboxymethyl chitosan and dissolve it in 100 mL of deionized water. Stir continuously at room temperature for 30 minutes to ensure complete dissolution, obtaining a 4% (w / v) carboxymethyl chitosan solution.

[0078] Dissolve 2 g of dextran in 100 mL of distilled water. Add 2 g of sodium periodate and stir in the dark for 6 hours to oxidize the dextran. After the reaction is complete, add 1 mL of ethylene glycol and continue stirring for 30 minutes to terminate the oxidation reaction. Dialyze the system with deionized water for 3 days, changing the water 2-3 times a day, and finally freeze-dry to obtain dialdehyde dextran powder.

[0079] Dissolve dialdehyde dextran and tannic acid in deionized water and dilute to 100 mL, obtaining a mixed solution of dialdehyde dextran and tannic acid, with a final concentration of 1% (w / v) for both.

[0080] Immerse the mold in the 4% (w / v) carboxymethyl chitosan solution, ensuring that the surface is evenly covered. Then, transfer the mold to the mixed solution of dialdehyde dextran and tannic acid (both with a final concentration of 1% (w / v)), leave it for 15 seconds, remove it, and use filter paper to absorb the excess liquid on the surface. This constitutes a complete deposition cycle. Then, immerse the mold again in the carboxymethyl chitosan solution, followed by immersion in the above-mentioned mixed solution of dialdehyde dextran / tannic acid, repeating this cycle a total of 5 times. Finally, dry the treated mold at room temperature to obtain the hydrogel film (CDT).

[0081] Effect verification:

[0082] 1. Measurement of hydrogel film thickness

[0083] The thickness of the hydrogel films prepared in Example 1 and Comparative Examples 1-4 was measured using a micrometer with an accuracy of 0.01 mm. Five points were randomly selected around the periphery and in the middle of the film, and the average of the measured values was taken as the thickness of the film. Three films were tested for each sample. The obtained thickness values were used to calculate the mechanical properties and water vapor transmission rate of the films.

[0084] Figure 1 The thickness of the hydrogel films prepared in Example 1 and Comparative Examples 1-4 is shown in the figure. It can be seen that the thickness of the hydrogel films of Example 1 and Comparative Examples 1-4 was measured and statistically analyzed. The thickness of the film of Comparative Example 1 was significantly lower than that of the other four groups (P < 0.01), while there was no significant difference in thickness between the film samples of Example 1, Comparative Example 2, Comparative Example 3 and Comparative Example 4. This indicates that when dialdehyde dextran is introduced into the carboxymethyl chitosan system for crosslinking alone, the thinnest film is formed. When tannic acid or its oxidized form is introduced, whether alone or in combination with dialdehyde dextran, a thicker hydrogel film is formed, and the thickness of the films is similar to each other.

[0085] 2. Determination of Fourier Transform Infrared Spectroscopy

[0086] Different hydrogel films were analyzed by Fourier Transform Infrared Spectroscopy, resolution 4 cm -1 , scanning range 400-4000 cm -1 , each film sample was scanned 32 times to analyze the changes of chemical bonds and functional groups.

[0087] Figure 2 The infrared spectra of the hydrogel films prepared in Example 1, Comparative Examples 1-4; from the figure, it can be seen that the structure of the hydrogel film samples of Example 1, Comparative Examples 1-4 was characterized by Fourier Transform Infrared Spectroscopy, and the characteristic absorption peak of C=N bond (imine bond) formed by Schiff base reaction at ~1640 cm -1 was mainly investigated.

[0088] Comparative Example 1: A new absorption peak appeared at about 1640 cm -1 , which belonged to C=N stretching vibration, confirming that Schiff base reaction occurred between the amino group of carboxymethyl chitosan and the aldehyde group of dialdehyde dextran.

[0089] Comparative Example 2: A weak C=N absorption peak appeared near 1640 cm -1 , indicating that Schiff base reaction also occurred between carboxymethyl chitosan and tannic acid, but the intensity was lower, which may be related to the lower content of aldehyde group or lower reactivity in tannic acid.

[0090] Comparative Example 3: The C=N absorption peak at 1640 cm -1 was significantly enhanced, indicating that oxidized tannic acid provided more aldehyde groups, promoting more complete Schiff base crosslinking.

[0091] Comparative Example 4: The absorption peak at 1640 cm -1 was further enhanced, indicating that dialdehyde dextran and tannic acid participated in crosslinking together, forming a more dense C=N network structure.

[0092] Example 1: The C=N absorption peak at 1640 cm -1 was the most significant, indicating that dialdehyde dextran and oxidized tannic acid cooperated to achieve the highest degree of Schiff base crosslinking.

[0093] In summary, the C=N characteristic peak (~1640 cm -1 ) in the Fourier Transform Infrared Spectroscopy appeared in all hydrogel film samples, and was more significant in the hydrogel film sample of Example 1, fully proving that Schiff base reaction successfully occurred in all crosslinking systems, and effectively formed a three-dimensional network structure of the hydrogel film.

[0094] 3. Water vapor permeability (WVP) of the film

[0095] Determined by the gravimetric method described in ASTM E96 / E96M (2016) standard. The test cup is a glass petri dish with a diameter of 5.7 cm, the film sample is attached to the rim of the cup with 10 g of anhydrous calcium chloride using Vaseline, and then the film edge is fixed around the petri dish using a rubber band. The sealed device is placed in a desiccator, the bottom of which is filled with a saturated sodium chloride solution to maintain a relative humidity of about 75% therein. The weight of the petri dish is measured every 2 h for the first 10 h and once at 24 h. A plot of weight versus time is prepared from Origin 8, and the slope (Slope) is obtained using linear regression analysis, with 3 replicates for each film. The water vapor permeability can be calculated from the following equation:

[0096] ;

[0097] where A is the area of the cup rim; is the pressure difference across the film (1752.75 Pa, 20 °C).

[0098] Figure 3 The water vapor permeability of the hydrogel films prepared in Example 1, Comparative Examples 1-4 is shown in the figure. It can be seen from the figure that the water vapor permeability of the hydrogel films of Example 1, Comparative Examples 1-4 was measured and statistically analyzed to evaluate the barrier performance of the films as a fresh-keeping material for chilled beef. The water vapor permeability of the hydrogel film in Comparative Example 1 group was the highest (0.1199±0.0091), which was significantly higher than that of the other groups (P<0.05), indicating that it had the weakest barrier performance. The hydrogel film in Comparative Example 2 group showed the lowest water vapor permeability (0.0859±0.0036), followed by the hydrogel film in Comparative Example 3 group, indicating that tannic acid or oxidized tannic acid had enhanced water vapor barrier performance and could effectively block the transmission of water vapor. Compared with the hydrogel film in Comparative Example 1 group, the water vapor permeability of the hydrogel films in Comparative Example 4 and Example 1 groups was 0.0966±0.0058 and 0.1035±0.0098, respectively, which was significantly lower than that of the hydrogel film in Comparative Example 1 group, indicating that the introduction of tannic acid and oxidized tannic acid improved the compactness of the hydrogel network formed by carboxymethyl chitosan and dialdehyde dextran to some extent, thereby enhancing the water vapor barrier effect. Compared with Comparative Example 2, the water vapor barrier performance of the hydrogel film in Comparative Example 3 group was slightly weaker, indicating that the oxidation treatment of tannic acid did not significantly enhance its ability to block the transmission of water vapor. Similarly, the same trend was observed in Comparative Example 4 and Example 1 groups.

[0099] 4. Antimicrobial and antioxidant performance determination

[0100] Example 2

[0101] Chilled beef was purchased from Beijing Hualian Supermarket. The beef was cut into small pieces of 5 x 5 x 5 cm under sterile conditions. The beef pieces were coated with the hydrogel film formulation of Example 1 (the beef pieces were directly immersed, wherein the carboxymethyl chitosan, tannic acid, dextran, etc. are all food grade, and the film can be quickly formed by immersion according to the shape of the sample). That is, the chilled beef pieces were immersed in a 4% carboxymethyl chitosan solution to ensure uniform surface adsorption, then the beef pieces were immersed in a mixed solution of dialdehyde dextran and oxidized tannic acid for 15 s, and then the excess liquid not combined on the surface was absorbed with filter paper. The beef pieces were again immersed in a carboxymethyl chitosan solution, then again immersed in a dialdehyde dextran oxidized tannic acid mixed solution, and repeated 5 times. The coated chilled beef pieces were stored in a refrigerator at 4°C. On days 0, 3, 5, and 7, random samples were taken to test the total number of colonies and the thiobarbituric acid value (TBA) to evaluate the antibacterial and antioxidant properties of the film.

[0102] Comparative Example 5 (blank)

[0103] The chilled beef pieces were cut into small pieces of 5 x 5 x 5 cm under sterile conditions without any film coating treatment, and were directly placed in a refrigerator at 4°C for storage. On days 0, 3, 5, and 7, random samples were taken to test the total number of colonies and the TBA value to evaluate the spoilage of beef without film protection.

[0104] Comparative Example 6 (beef pieces coated with the hydrogel film formulation of Comparative Example 1)

[0105] 4 g of carboxymethyl chitosan was accurately weighed and dissolved in 100 mL of deionized water. The solution was continuously stirred at room temperature for 30 minutes to ensure complete dissolution, resulting in a 4% (w / v) carboxymethyl chitosan solution. 2 g of dextran was dissolved in 100 mL of distilled water, and 2 g of sodium periodate was added. The solution was stirred in the dark for 6 hours to oxidize the dextran. After the reaction was completed, 1 mL of ethylene glycol was added to the system to terminate the oxidation reaction. The solution was dialyzed against deionized water for 3 days, with 2-3 water changes per day. Finally, the dialdehyde dextran powder was obtained by freeze-drying. 2 g of dialdehyde dextran was dissolved in deionized water to make up 100 mL, resulting in a 2% (w / v) dialdehyde dextran solution.

[0106] The chilled beef pieces were immersed in a 4% (w / v) carboxymethyl chitosan solution to ensure uniform surface adsorption, then the beef pieces were immersed in a 2% (w / v) dialdehyde dextran solution for 15 s, and then the excess liquid not combined on the surface was absorbed with filter paper. The above steps constitute a complete deposition cycle. This cycle was repeated a total of 5 times. The coated chilled beef pieces were stored in a refrigerator at 4°C. On days 0, 3, 5, and 7, random samples were taken to test the total number of colonies and the TBA value.

[0107] Comparative Example 7 (beef pieces coated with the hydrogel film formulation of Comparative Example 2)

[0108] Accurately weigh 4 g of carboxymethyl chitosan and dissolve in 100 mL of deionized water. Stir continuously for 30 minutes at room temperature to ensure complete dissolution. This results in a 4% (w / v) carboxymethyl chitosan solution. Dissolve 2 g of tannic acid in deionized water and make up to 100 mL to obtain a 2% (w / v) tannic acid solution.

[0109] Submerge the chilled beef chunks in the 4% (w / v) carboxymethyl chitosan solution to ensure uniform surface adsorption. Then submerge the beef chunks in the 2% (w / v) tannic acid solution for 15 seconds. After removal, use filter paper to absorb the excess liquid that is not bound. The above steps constitute a complete deposition cycle. Repeat this cycle a total of 5 times. Place the wrapped chilled beef chunks in a refrigerator at 4°C for storage. Randomly sample and test for total plate count and TBA values on days 0, 3, 5, and 7.

[0110] Comparative Example 8 (beef chunks wrapped with the hydrogel film formulation of Comparative Example 3)

[0111] Accurately weigh 4 g of carboxymethyl chitosan and dissolve in 100 mL of deionized water. Stir continuously for 30 minutes at room temperature to ensure complete dissolution. This results in a 4% (w / v) carboxymethyl chitosan solution. Take 25 mL of 1.2% sodium periodate and mix with 100 mL of 1.27% tannic acid solution. Stir the reaction under complete light avoidance conditions for 2 hours. Then, transfer the reaction solution to a dialysis bag with a molecular weight cut-off of 3500 Da and dialyze in a dark environment for 3 days. After dialysis, centrifuge at 7000 rpm for 10 minutes. Collect the supernatant and freeze-dry to obtain the oxidized tannic acid solid. Dissolve 2 g of oxidized tannic acid in deionized water and make up to 100 mL to obtain a 2% (w / v) oxidized tannic acid solution.

[0112] Submerge the chilled beef chunks in the 4% (w / v) carboxymethyl chitosan solution to ensure uniform surface adsorption. Then submerge the beef chunks in the 2% (w / v) oxidized tannic acid solution for 15 seconds. After removal, use filter paper to absorb the excess liquid that is not bound. The above steps constitute a complete deposition cycle. Repeat this cycle a total of 5 times. Place the wrapped chilled beef chunks in a refrigerator at 4°C for storage. Randomly sample and test for total plate count and TBA values on days 0, 3, 5, and 7.

[0113] Comparative Example 9 (beef chunks wrapped with the hydrogel film formulation of Comparative Example 4)

[0114] Precisely weigh 4 g of carboxymethyl chitosan and dissolve in 100 mL of deionized water, continuously stirring at room temperature for 30 minutes to make it fully dissolved, to obtain a 4% (w / v) carboxymethyl chitosan solution. Weigh 2 g of dextran and dissolve in 100 mL of distilled water, then add 2 g of sodium periodate and stir in the dark for 6 hours to oxidize the dextran. After the reaction is completed, add 1 mL of ethylene glycol to the system and continue stirring for 30 minutes to terminate the oxidation reaction. Dialyze with deionized water for 3 days, changing the water 2-3 times a day, and finally freeze-dry to obtain dialdehyde dextran powder. Dissolve the dialdehyde dextran and tannic acid in deionized water and dilute to 100 mL to obtain a mixed solution of dialdehyde dextran and tannic acid, both with a final concentration of 1% (w / v).

[0115] Immerse the chilled fresh beef chunks in a 4% (w / v) carboxymethyl chitosan solution to ensure uniform surface adsorption, then immerse the beef chunks in a mixed solution of dialdehyde dextran and tannic acid (both with a final concentration of 1% (w / v)) for 15 seconds, and then remove the excess unbound liquid with filter paper. The above steps constitute a complete deposition cycle. Repeat this cycle a total of 5 times. Place the wrapped chilled fresh beef chunks in a refrigerator at 4°C for storage, and randomly sample for total bacterial count on days 0, 3, 5, and 7.

[0116] Total bacterial count determination: At the time points designed in the experiment, remove the meat samples, remove the packaging film, and then place the meat samples in sterile bags and mix with 90 mL of physiological saline. Dilute the sample 10 times with sterile physiological saline, transfer 1 mL of the appropriate concentration of sample solution to a culture dish, and then pour 20-30 mL of MHA medium into the culture dish and shake on a horizontal shaker for 3 minutes to evenly distribute the bacterial solution in the medium. After the medium solidifies, invert the culture dish and incubate in a 37±1°C incubator for 48±2 hours. Record the number of colonies and multiply by the corresponding dilution, and express the total bacterial count as a logarithmic value.

[0117] Figure 4 Plate culture results for total bacterial count determination of Example 2 and Comparative Examples 5-9 on days 1-7.

[0118] Figure 5The total number of colonies of the cold fresh beef during the storage period of 0, 1, 3, 5 and 7 days after the beef was embedded with the hydrogel film of Examples 2 and Comparative Examples 5-9. As can be seen from the graph, from the colony count results, the hydrogel films of Examples 2 and Comparative Examples 6-9 all showed an inhibitory effect on the growth of bacteria on the surface of the cold fresh beef, but the degree of inhibition varied depending on the type of film and the length of storage time. Comparative Example 5 was cold fresh beef without hydrogel film preservation, and the number of colonies was low at 1 day, but the number of colonies increased rapidly over time, reaching a maximum value (about 370,000 CFU / g) at 7 days, indicating that the bacteria of the cold fresh beef without hydrogel preservation film packaging grew vigorously. Compared with Comparative Example 5, the number of colonies of the beef preserved by the hydrogel film of Comparative Example 6 was reduced, but was still high (about 270,000 CFU / g) at 7 days, indicating that the carboxymethyl chitosan and dialdehyde dextran cross-linked hydrogel had a certain antibacterial effect, but the effect was not significant enough. The number of colonies of the cold fresh beef of Comparative Example 7 was lower than that of Comparative Example 6, about 240,000 CFU / g at 7 days, indicating that tannic acid cross-linking could enhance the antibacterial performance of the film. The number of colonies of the cold fresh beef of Comparative Example 8 was further reduced, about 240,000 CFU / g at 7 days, indicating that oxidized tannic acid cross-linking was more effective than tannic acid. The number of colonies of the cold fresh beef of Comparative Example 9 was further reduced, about 190,000 CFU / g at 7 days, indicating that the mixed cross-linking of dialdehyde dextran and tannic acid had a synergistic antibacterial effect. The number of colonies of the cold fresh beef of Example 2 was the lowest, only about 100,000 CFU / g at 7 days, indicating that the mixed cross-linking of dialdehyde dextran and oxidized tannic acid could significantly inhibit bacterial growth and had the best preservation effect.

[0119] In summary, the hydrogel film treatment disclosed in the present application can effectively delay the reproduction of bacteria in cold fresh beef, and the antibacterial performance of the hydrogel film of Example 2 is the strongest. These results indicate that the hydrogel cross-linked by carboxymethyl chitosan, dialdehyde dextran and oxidized tannic acid has potential application value in beef preservation.

[0120] Figure 6 The lipid oxidation of the cold fresh beef at 0, 1, 3, 5 and 7 days after the beef was embedded with the hydrogel film of Examples 2 and Comparative Examples 5-9. The higher the TBARS value (thiobarbituric acid), the more serious the lipid peroxidation, and the worse the preservation effect of the beef. As shown in the graph, the TBARS value of the beef of Comparative Example 5 was the highest, indicating that the beef without hydrogel preservation film packaging had the worst preservation effect. The TBARS value of the beef of Comparative Example 6 was lower than that of Comparative Example 5, indicating that the carboxymethyl chitosan and dialdehyde dextran cross-linked hydrogel had a certain preservation effect, but the effect was not significant enough. The TBARS value of the beef of Comparative Example 7 was lower than that of Comparative Example 6, indicating that tannic acid cross-linking could enhance the preservation effect of the film. The TBARS value of the beef of Comparative Example 8 was further reduced, indicating that oxidized tannic acid cross-linking was more effective than tannic acid. The TBARS value of the beef of Comparative Example 9 was further reduced, indicating that the mixed cross-linking of dialdehyde dextran and tannic acid had a synergistic preservation effect. The TBARS value of the beef of Example 2 was the lowest, indicating that the mixed cross-linking of dialdehyde dextran and oxidized tannic acid could significantly inhibit bacterial growth and had the best preservation effect. Figure 6As shown, the TBARS values of each group showed an upward trend as the fresh-keeping time was prolonged, but the upward range was different, reflecting the inhibitory effect of different hydrogels on lipid oxidation. The TBARS value of Comparative Example 5 group continuously increased significantly within 7 days, from 0.1077 mg / kg to 0.4046 mg / kg, indicating that the lipid oxidation of beef was serious without fresh-keeping treatment. The TBARS value of Comparative Example 6 group increased less than that of Comparative Example 5 group, but was still high, 0.2246 mg / kg at 7 days, showing a certain antioxidant effect, but not as good as other treatment groups. The TBARS value of Comparative Example 7 group was 0.1908 mg / kg at 7 days, and the antioxidant effect was better than that of Comparative Example 6 group, indicating that tannic acid crosslinking could better inhibit oxidation. The TBARS value of Comparative Example 8 group was 0.1585 mg / kg at 7 days, and the antioxidant effect was significant, indicating that oxidized tannic acid crosslinking had better antioxidant performance than tannic acid crosslinking. The composite crosslinking enhanced the lipid antioxidant capacity through synergistic effect. The TBARS value of Comparative Example 9 group was 0.1592 mg / kg at 7 days, which was similar to that of Comparative Example 8 group, showing that mixed crosslinking could effectively inhibit oxidation. The TBARS value of Example 2 group was 0.1431 mg / kg at 7 days, which was the lowest among all chilled beef groups, indicating that the group had the best antioxidant effect and could most effectively delay beef lipid oxidation.

[0121] In summary, all hydrogel film treatments could inhibit the lipid oxidation of beef to varying degrees, among which the fresh-keeping effect of Example 2 group was the best, the TBARS value was the lowest within 7 days, followed by Comparative Example 8 group and Comparative Example 9 group.

[0122] Figure 7The TVB-N value of chilled beef treated with the carboxymethyl chitosan hydrogel films of Examples 2 and Comparative Examples 5-9 was measured at 0, 1, 3, 5, and 7 days. The TVB-N value is a key indicator of the degree of protein spoilage in meat. The lower the TVB-N value, the better the preservation effect. The TVB-N values of all groups increased with storage time, but the growth rate and final value of the TVB-N values of Examples 2 and Comparative Examples 6-9 were significantly lower than those of Comparative Example 5. This indicates that the carboxymethyl chitosan-based hydrogels can effectively delay the spoilage of beef, but the preservation performance of the crosslinking agents varies significantly. Comparative Example 6 showed better inhibition effect in the early stage (1-5 days), and the TVB-N value was always lower than that of Comparative Example 7. This indicates that the crosslinking network formed by dialdehyde dextran can more effectively block external pollution in the early stage. The TVB-N value of Comparative Example 7 increased slowly in the later stage (5-7 days), and the final value was close to that of Comparative Example 6, which reflects the continuous effect of the inherent antibacterial and antioxidant properties of tannic acid. The preservation effect of Comparative Example 8 was significantly better than that of Comparative Examples 6 and 7. The 7-day TVB-N value (5.790 mg / 100 g) was about 13% lower than that of Comparative Examples 6 and 7. This indicates that the oxidation modification of tannic acid can significantly improve the preservation performance of the hydrogel, and the reason may be that the quinone structure formed after oxidation enhances the crosslinking ability with proteins, forming a more compact film. In addition, the composite crosslinking agent group may enhance the preservation effect through synergistic effect. The preservation effect of Example 2 was significantly better than that of all other groups, and the 7-day TVB-N value was only 5.010 mg / 100 g, which was 41.0% lower than that of the control group. This reflects a significant synergistic effect. Dialdehyde dextran provides a strong physical crosslinking network, while oxidized tannic acid enhances the crosslinking density while contributing strong antibacterial and antioxidant functions, forming a multifunctional high-barrier hydrogel. However, the preservation effect of Comparative Example 9 was not better than that of its individual components, and was even between Comparative Examples 6 and 7. This may be due to the competition or steric hindrance between unoxidized tannic acid and dialdehyde dextran during crosslinking, which fails to form an ideal synergistic network.

[0123] In summary, all hydrogel films can effectively inhibit the increase of the TVB-N value of chilled beef and prolong the shelf life. Among them, Example 2 is the best formula, and its preservation effect is significantly better than that of other groups, indicating that dialdehyde dextran and oxidized tannic acid have strong synergistic preservation effect. At the same time, oxidation modification is the key to improving the performance of tannic acid, and Comparative Example 8 alone has shown superior performance.

[0124] The above merely describes the preferred embodiments of the present application, but the protection scope of the present application is not limited thereto, and any person skilled in the art can easily think of changes or replacements within the technical scope disclosed by the present application, which should be covered within the protection scope of the present application.

Claims

1. A method for preparing a hydrogel film for preserving chilled meat, characterized in that, Includes the following steps: Hydrogel films were prepared by using carboxymethyl chitosan, dialdehyde dextran, and oxidized tannic acid as raw materials to achieve rapid in-situ crosslinking through alternating impregnation deposition.

2. The method for preparing a hydrogel film for preserving chilled meat according to claim 1, characterized in that, The preparation process of the dialdehyde dextran is as follows: Sodium periodate was added to the dextran aqueous solution and stirred in the dark to obtain oxidized dextran. Ethylene glycol was then added to the system and stirring was continued to terminate the oxidation reaction. Subsequently, the mixture was dialyzed and lyophilized to obtain dialdehyde dextran powder.

3. The method for preparing a hydrogel film for preserving chilled meat according to claim 2, characterized in that, The concentration of the dextran aqueous solution is 20 g / L; The reaction time, involving stirring in the dark, was 6 hours.

4. The method for preparing a hydrogel film for preserving chilled meat according to claim 1, characterized in that, The preparation process of the oxidized tannic acid is as follows: Add sodium periodate solution to tannic acid solution, stir in the dark, and then perform dialysis, centrifugation and freeze drying in sequence to obtain oxidized tannic acid.

5. The method for preparing a hydrogel film for preserving chilled meat according to claim 4, characterized in that, The volume ratio of the tannic acid solution to the sodium periodate solution is 1:4; and / or, The tannic acid solution has a mass concentration of 1.27%; and / or, The sodium periodate solution has a mass concentration of 1.2%.

6. The method for preparing a hydrogel film for preserving chilled meat according to claim 4, characterized in that, The stirring time in the dark is 2 hours; and / or, The centrifugation conditions were: centrifugation at 7000 rpm for 10 minutes.

7. The method for preparing a hydrogel film for preserving chilled meat according to claim 1, characterized in that, The specific operation of the alternating impregnation deposition is as follows: Immerse the mold in a carboxymethyl chitosan solution; then transfer the mold to a mixed solution of dialdehyde dextran and oxidized tannic acid, let it stand for 15 seconds, remove it, and use filter paper to absorb excess liquid from the surface. This is used as one deposition cycle, and the cycle is repeated 5 times. Finally, the mold is dried to obtain the hydrogel film.

8. The method for preparing a hydrogel film for preserving chilled meat according to claim 7, characterized in that, The concentration of the carboxymethyl chitosan solution is 0.04 g / mL.

9. The method for preparing a hydrogel film for preserving chilled meat according to claim 7, characterized in that, The concentrations of both dialdehyde dextran and oxidized tannic acid in the mixed solution were 0.01 g / mL.

10. A hydrogel film for preserving chilled meat, characterized in that, It is prepared by the preparation method according to any one of claims 1-9.

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