CN115572397B

CN115572397B - Epsilon-polylysine modified chitosan membrane and application thereof

Info

Publication number: CN115572397B
Application number: CN202211078700.3A
Authority: CN
Inventors: 康大成; 倪来学; 姚现琦
Original assignee: Linyi University; Linyi Jinluo Wenrui Food Co Ltd
Current assignee: Linyi University; Linyi Jinluo Wenrui Food Co Ltd
Priority date: 2022-09-05
Filing date: 2022-09-05
Publication date: 2023-09-05
Anticipated expiration: 2042-09-05
Also published as: CN115572397A

Abstract

The invention discloses an epsilon-polylysine modified chitosan membrane and application thereof, and a preparation method of the chitosan membrane comprises the following steps: (1) Preparing TEMPO oxidized chitosan TO-CH by adopting a TEMPO/NaClO/KBr oxidation system; (2) EDC/NHS mediated reaction is adopted TO graft epsilon-polylysine onto chitosan TO prepare epsilon-polylysine modified chitosan TO-CH-PL; (3) preparation of TO-CH-PL film. Research shows that the TO-CH-PL film has relatively high preservation effect on the quality of pork samples due TO the obvious delay of the increase of colony count, TVB and TBARS and the change of pH value and color of packaged pork. Therefore, the PL modified chitosan film can be used as an alternative method for maintaining pork quality index and prolonging the shelf life of pork in the process of refrigerating and preserving the pork.

Description

Epsilon-polylysine modified chitosan membrane and application thereof

Technical Field

The invention belongs to the technical field of food packaging materials, and particularly relates to an epsilon-polylysine modified chitosan film and application thereof.

Background

The rapid growth in the food industry has made consumers aware that the widespread use of chemical preservatives in foods can cause health problems. Accordingly, many attempts have been made to provide natural preservatives and advanced packaging methods during food processing and storage. The addition of active ingredients such as natural antimicrobial and/or antioxidant substances to food packaging materials can control adverse changes in food quality, and is a promising packaging technology. These active ingredients are absorbed or released from the packaging material and the environment surrounding the food product to ensure the quality and safety benefits of the food product.

In recent years, edible, biodegradable, antibacterial food packaging materials such as chitosan have been used as a base material for active packaging. The linear structure of the chitosan is formed by D-glucosamine and N-acetyl-D-glucosamine through beta- (1, 4) glycosidic bonds, and the chitosan with no toxicity and biocompatibility can be obtained through deacetylation of the chitin. The antibacterial mechanism of chitosan can be attributed to the interaction of the positive charge of chitosan with the negatively charged macromolecules on the cell surface causing the cell membrane to rupture. However, the low water resistance and poor mechanical properties of chitosan limit its application in functional films due to its hydrophilicity. To overcome these drawbacks, the addition of other natural substances such as tea polyphenols, plant extracts and protein isolates to chitosan-based packaging materials has become a current research hotspot. epsilon-Polylysine (PL) is an odorless water-soluble substance, a promising antibacterial substance, which can be added to chitosan substrates to improve the shelf life of foods.

epsilon-Polylysine (PL) is a natural polypeptide produced by Streptomyces albus. The molecular weight of the polymer is generally 2000-5000Da, which is obtained from lysine by polymerization of epsilon-amino groups and alpha-carboxyl groups. Because of its excellent thermal stability and antibacterial activity, PL will find good application prospects in the food industry. At present, PL has been approved for fresh-keeping of fruits and vegetables, and has been studied and applied in fresh-keeping of fruits and vegetables such as apples, spinach, cabbages, lotus roots and the like. The antibacterial mechanism of PL is the cationic surface activity of the free α -amino group on the PL molecular structure in an acidic environment. Positively charged polymers can enhance the permeability of cell membranes and microbial walls, exude the cell contents,

in recent years, many studies have succeeded in preparing a biofilm composed of chitosan and PL and applying it to preservation of meat, fruits and vegetables. For meat and meat products, the contents of moisture and nutrient components are high, so that the meat and meat products are easy to be polluted by microorganisms, the quality of the meat and meat products is poor, and the flavor and the color of the meat and meat products are lost. Lin et al (2018) prove that the biological film formed by compounding chitosan and PL has good antibacterial and fresh-keeping effects on chicken. Alirezalu et al (2021) reported that the PL-chitosan composite membrane had good preservative effect on beef. However, in the prior art, the binding mode of PL and chitosan in a biological membrane is physical binding. Because of the water solubility of PL, PL can be dissolved in films, which when applied to high moisture content foods such as meats and meat products, can dissolve in the food surroundings, reducing the bacteriostatic and preservative properties of the films. Therefore, there is a need to provide a novel PL-modified chitosan film in which PL is chemically grafted onto chitosan to further expand its application range and food preservation effect.

Disclosure of Invention

The invention aims to provide an epsilon-polylysine modified chitosan membrane and application thereof.

The aim of the invention can be achieved by the following technical scheme:

an epsilon-polylysine modified chitosan membrane, the preparation method of which comprises the following steps:

(1) Preparing TEMPO oxidized chitosan TO-CH by adopting a TEMPO/NaClO/KBr oxidation system;

(2) EDC/NHS mediated reaction is adopted TO graft epsilon-polylysine on chitosan TO prepare epsilon-polylysine modified chitosan TO-CH-PL: activating carboxyl of the TO-CH TO obtain an activated TO-CH suspension, adding epsilon-polylysine into the activated TO-CH suspension for grafting reaction, washing after the reaction is finished, and collecting epsilon-polylysine modified chitosan TO-CH-PL freeze-dried powder;

(3) Preparation of TO-CH-PL film: and dissolving the TO-CH-PL powder in an acetic acid solution, adding glycerol, stirring uniformly TO prepare a TO-CH-PL solution, forming a film from the TO-CH-PL solution, neutralizing and drying TO obtain the epsilon-polylysine modified chitosan film.

As a preferable technical scheme, the process for preparing the TEMPO oxidized chitosan TO-CH by adopting a TEMPO/NaClO/KBr oxidation system in the step (1) comprises the following steps: uniformly dissolving KBr and TEMPO in deionized water TO prepare a solution, uniformly mixing dried chitosan and the solution TO prepare a suspension, regulating the pH value TO be 10.5-11 TO obtain a mixed solution, and stirring the mixed solution at room temperature TO react TO obtain TEMPO oxidized chitosan (TO-CH).

Further preferably, the concentration content of each component in the above mixed solution is: KBr of 0.25-0.35 g/100mL, TEMPO of 0.05-0.06 g/100mL, chitosan of 1.9-2.1 g/100mL. Still more preferably: KBr of 0.3g/100mL, TEMPO of 0.06g/100mL, chitosan of 2g/100mL.

Further preferably, after stirring the mixed solution at room temperature for reaction for 6-6.5 hours, adding ethanol TO stop the reaction TO obtain TEMPO oxidized chitosan TO-CH, and centrifugally washing the obtained TEMPO oxidized chitosan TO-CH with pure water TO prepare freeze-dried powder.

Further preferably, when adjusting the pH, firstly, 10% -14% NaClO solution is dripped into the suspension, and then 0.5MHCl is adopted to adjust the pH within the range of 10.5-11.

As a preferred technical scheme, the process of activating the carboxyl group of the TO-CH in the step (2) is as follows: uniformly stirring TO-CH freeze-dried powder in deionized water, adding EDC and NHS, reacting at 24-25 ℃ for 10-15 min TO activate carboxyl of TO-CH TO obtain suspension, and centrifuging the suspension TO remove unreacted EDC and NHS TO obtain activated TO-CH suspension;

the TO-CH freeze-dried powder, EDC and NHS have the following mass ratio: (4.9-5.1): (1.7-1.74): (1.03-1.05);

the TO-CH concentration in the activated TO-CH suspension is: 0.82-0.85% (w/v, g/100 ml).

It is further preferred that the mass ratio of TO-CH TO epsilon-polylysine in step (2) is: (4.9-5.1): 4.5-5.0);

the grafting reaction is carried out for 24-25 h at 25-26 ℃.

As a preferable technical scheme, the process for preparing the TO-CH-PL film in the step (3) comprises the following steps: dissolving the TO-CH-PL powder in acetic acid solution with the volume percentage concentration of 3% -3.2%, stirring at 25-26 ℃ for 12-13 hours until the powder is completely dissolved, adding glycerol and stirring uniformly TO prepare TO-CH-PL solution, forming a film from the TO-CH-PL solution, neutralizing and drying TO obtain the epsilon-polylysine modified chitosan film.

It is further preferable that the amount of the TO-CH-PL powder added in the step (3) in the acetic acid solution is 1.5 TO 1.6g/100mL, and the amount of the glycerol added is 0.1 TO 0.3% of the volume of the TO-CH-PL solution.

The epsilon-polylysine modified chitosan film is applied to food preservation.

The room temperature of the invention is 25+/-5 ℃.

A novel PL modified chitosan film (TO-CH-PL) was synthesized by TEMPO/EDC/NHS oxidation system. First, the physicochemical properties of TO-CH-PL were characterized by Fourier transform infrared spectroscopy, scanning electron microscopy and energy spectroscopy. The results demonstrate that PL was successfully grafted onto chitosan molecules. Based on the permeability of water vapor and oxygen, as well as mechanical analysis, TO-CH-PL films exhibited higher physical properties than other selected films. Secondly, the preservation effect of the TO-CH-PL film on pork slices is examined. As the TO-CH-PL film obviously delays the increase of the total colony count, TVB and TBARS and the change of the pH value and the color of the packaged pork, the method has a good preservation effect on the quality of pork samples. Therefore, the PL modified chitosan film can be used as an alternative method for maintaining pork quality index and prolonging the shelf life of pork in the process of refrigerating and preserving the pork.

The key points of the technical scheme of the invention are as follows:

(1) Firstly preparing oxidized chitosan TO-CH by adopting a TEMPO/NaClO/KBr oxidation system, wherein the TEMPO concentration is a key point of the step, the aim is TO oxidize chitosan into TO-CH, the final concentration is added TO be 0.05-0.06 g/100mL,

(2) EDC/NHS mediated reaction is adopted TO graft epsilon-polylysine on chitosan TO prepare epsilon-polylysine modified chitosan TO-CH-PL on the basis of (1), and the key point is that EDC/NHS is added TO activate carboxyl of TO-CH, and epsilon-polylysine is added TO activated TO-CH suspension TO carry out grafting reaction, so that modified chitosan TO-CH-PL is obtained.

The invention has the beneficial effects that:

a novel PL modified chitosan film is synthesized by adopting a chemical oxidation method, and the defect that the original chitosan film prepared by only physically mixing is easy to cause loss of active ingredients is overcome. Compared with other similar products in the market, the prepared PL modified chitosan film has better physical properties, has better preservation effect on the quality of pork samples, and can prolong the shelf life of the products.

Drawings

FTIR spectroscopic analysis of TO-CH-PL, TO-CH and CH of FIG. 1.

Fig. 2 SEM electron microscopy of two films.

Detailed Description

The following examples further illustrate the invention. In the following detailed description, certain exemplary embodiments of the present invention are described by way of illustration only. It is needless to say that the person skilled in the art realizes that the described embodiments may be modified in various different ways without departing from the spirit and scope of the invention. Accordingly, the description is illustrative in nature and is not intended to limit the scope of the claims.

In this study, first, PL was covalently bound TO chitosan by TEMPO oxidation TO form a novel chitosan film (TO-CH-PL). Secondly, the physical and mechanical properties of the material are studied. Finally, the effect of the film prepared at 4 ℃ and 12d on the microbiological and physicochemical properties of pork was studied.

1. Preparation of epsilon-polylysine modified chitosan film

1 materials and methods

1.1 materials

PL (epsilon-polylysine, average molecular weight: 5000 Da) was purchased from Solarbio Inc. (Beijing, china). Chitosan (average viscosity molecular weight: 10 ten thousand Da), 2, 6-tetramethylpiperidine 1-oxyl (TEMPO), N-hydroxysuccinimide (NHS), and 1- (3-dimethylaminopropyl) -3-ethylcarbodiimide hydrochloride (EDC-HCl) were purchased from Shanghai Relong Co., ltd. Potassium bromide (KBr), sodium hypochlorite (NaClO), LB broth and LB agar medium were all from Shanghai, inc. Other chemicals were selected as analytical grade.

1.2 Preparation of PL-Chitosan film

1.2.1 TEMPO oxidized chitosan (TO-CH)

And preparing the carbonyl chitosan by adopting a TEMPO/NaClO/KBr oxidation system. 1.5g KBr and 0.3g TEMPO were initially dissolved uniformly in 460mL deionized water. 10g of dry chitosan was mixed with the dissolution solution and 30mL of NaClO solution (10% -14%) was added dropwise to the suspension. The pH was adjusted to a range of 10.5 to 11 using 0.5M HCl. The final volume of the mixed solution was set to 500mL, and after stirring at room temperature for 6 hours, 200mL of ethanol was added to stop the reaction (the addition amount of ethanol was 40% of the volume of the mixed solution). TEMPO oxidized chitosan (TO-CH) was centrifugally washed with pure water 4 times (4000 rpm,5 min) TO prepare a lyophilized powder. The carboxylate content of the lyophilized TO-CH was determined TO be 0.39mmol/g according TO the conductivity titration method.

1.2.2 Chitosan grafted PL (TO-CH-PL)

TO-CH-PL was prepared by EDC/NHS mediated reaction. First, 5g of lyophilized TO-CH was stirred uniformly in 600mL of deionized water, 1.72g of EDC and 1.04g of NHS were added, and reacted at 25℃for 10min TO activate the carboxyl group of the TO-CH. The suspension was centrifuged 3 times (4000 rpm,5 min) to remove unreacted EDC and NHS. Then, 4.5g of PL was added TO the activated TO-CH suspension and reacted at 25℃for 24 hours. Finally, the TO-CH-PL suspension was washed 4 times with 250mL deionized water. The lyophilized TO-CH-PL was collected and prepared into a film.

1.2.3 Preparation of TO-CH-PL film

TO obtain a completely dissolved TO-CH-PL solution, 6g of TO-CH-PL powder was dissolved in 400mL of 3% (v/v) acetic acid solution and stirred at 25℃for 12 hours. Subsequently, 0.5mL of glycerol was added TO the chitosan solution and stirred for 30min TO prepare a TO-CH-PL solution. 50mL of the TO-CH-PL solution was poured into a 14cm diameter petri dish and dried at 24℃for 48 hours TO prepare a chitosan-active membrane. Finally, the mixture was neutralized with 5% (w/v) NaOH solution and then washed with pure water. And carrying out balance treatment on the film after neutralization and drying for 48 hours at the temperature of 25+/-1 ℃ and the relative humidity of 60+/-1%, thus obtaining the PL modified chitosan film.

2. Characterization of epsilon-polylysine modified chitosan films

1. Performance analysis

TABLE 1 Properties of PL Chitosan films

¹ Each row of letters a-b represents a difference differentlyHeterosignificantly (p)<0.05)

² The water vapor permeability and the oxygen permeability of the polyethylene film were 6.23.+ -. 0.37g mm/m, respectively ² 24h and 5.20.+ -. 0.16cm ³ mm/m ² ·24h·0.1MPa。

Film thickness can be used to further determine the mechanical properties and water barrier capability of the film, which is a key factor affecting film quality. As shown in Table 1, covalent bonding of PL to chitosan increased the thickness of the chitosan film significantly from 60.45 μm to 73.81. Mu.m. This result demonstrates that amine groups in PL react with hydroxyl groups of chitosan to form a more complex membrane structure.

As shown in Table 1, the TO-CH-PL film had a lower water vapor permeability (5.19 g mm/m.multidot.24 h) than the CH film, indicating that the crosslinking of PL with chitosan imparted a highly dense structure TO the active film. The PE film in this study had a water vapor transmission rate of 6.23.+ -. 0.37g mm/m.multidot.24 h, similar TO TO-CH-PL. Further, the CH film has a high water vapor permeability value, which means that the film has low water resistance, and the minimum water vapor permeability is about 7 gmm/m.multidot.24 h for the composite film produced by Yu et al (2019). Therefore, the PL-chitosan biological film constructed by the TEMPO/EDC/NHS oxidation system has better water resistance.

The nature of the oxygen permeability of the film is an important factor affecting the organoleptic properties of the packaged food product, particularly the degradation of the food ingredients during oxidation. As is evident from Table 1, the oxygen permeability is significantly reduced after covalent attachment of chitosan to PL. The compact and complex structure of TO-CH-PL film is the main reason for its antioxidant properties. Since no study has been reported on the oxygen permeability of PL-chitosan films at present, the oxygen permeability of active chitosan films (Gan et al, 2022) can be compared with the related study of Levan/pullulan/chitosan edible films, the oxygen permeability value of the prepared films is 44.5-487.5 cm mm/m.24h.0.1 MPa, and the oxygen permeability value of the study is 4.06-335.98 cm mm/m.24h.0.1 MPa. Therefore, the PL-chitosan biomembrane constructed by the TEMPO/EDC/NHS oxidation system has better oxygen barrier capability.

Mechanical properties are often important indicators of the water resistance of films, especially in food packaging. The Tensile Strength (TS) and elongation at break (EB) of the film exhibit resistance to tensile stress and shape change, respectively, prior to breaking. After covalent bonding, the TS of the chitosan film is improved from 23.96MPa to 50.94MPa, and the EB is improved from 26.02 to 36.45%. Covalent binding of chitosan TO PL can form complex branched structures, leading TO increased TS and EB for TO-CH-PL membranes. Therefore, the chitosan membrane with the covalent bonding PL modification in the study has good mechanical properties.

Ftir spectroscopic analysis

TO determine covalent bond formation between PL and chitosan under TEMPO/EDC/NHS oxidation system, the secondary structure of CH, TO-CH and TO-CH-PL was detected using FTIR techniques (FIG. 1). FTIR spectra of chitosan with characteristic vibration band of CH, 897 and 1157cm ^-1 The peak at the position belongs to-C-O-C-antisymmetric stretching vibration and is the characteristic absorption peak of chitosan. 1090 cm ^-1 The strong absorption peak at this point is the stretching vibration of the-OH group. 1048cm ^-1 The peak at this point is related to the stretching vibration of the beta-1, 4-glycosidic bond in the chitosan backbone. Other typical bands for chitosan are 1320cm ^-1 (-bending vibration of CH and deformation vibration of CH), 2870cm ^-1 (-stretching vibration of CH); 3411cm ^-1 (hydrogen bonding of OH and-NH groups in chitosan).

In the TO-CH spectrum at 1735cm ^-1 A distinct peak appears at the wavenumber representing the carboxyl vibration. The results indicate that the C-OH at position 6 on the pyran ring has been successfully oxidized to the carboxyl group. Interestingly, 1604cm after TO-CH was further crosslinked with PL ^-1 A newly added peak at this point can be identified as the vibration of N-H in TO-CH-PL. Furthermore, 1260cm in FTIR spectrum of TO-CH-PL ^-1 The peak at which is C-N vibration. In combination with the c=o group determined previously (1640 cm ^-1 ) And N-H groups (3411 cm ^-1 ) Vibration confirmed the formation of covalent bonds between PL and chitosan. Thus, PL was successfully grafted onto chitosan molecules under a TEMPO/EDC/NHS oxidation system to form a network structure.

3. Electron microscope observation

Interactions between components can directly affect the physical, mechanical, and barrier properties of the film and can be reflected in the morphology of the active film. As can be seen from FIG. 2, the TO-CH-PL membrane exhibited a uniform, clear, smooth structure, indicating that the PL in the membrane was covalently bound TO chitosan TO form a complete structure. However, the CH film had a scale shape and had pores, and solid particles were observed on the film surface. These facts can explain the high water vapor transmission rate and oxygen transmission rate values of CH films. In addition, glycerol is added to facilitate the formation of a uniform structure in order to avoid cracking and irregularities on the surface of the film.

3. Application of epsilon-polylysine modified chitosan membrane

1. Analysis of pH during pork storage

As can be seen from Table 2, the pH of the TO-CH-PL, CH and PE film wrapped pork chops increased continuously during storage. The pork with different packaging films had no significant difference in pH (p < 0.05) 4 days before storage. After 6d of storage, the pH value increased from the lowest 5.88 to the highest 7.19, indicating the presence of microbial growth and spoilage in pork. Samples wrapped with PE film had the highest pH at the end of refrigeration. Pork packaged with TO-CH-PL and CH reached pH 6.86 and 7.09, respectively, after 12d storage, and pH was lower than PE film. For TO-CH-PL film with lowest water vapor permeability and oxygen permeability, chitosan and PL can show good antibacterial activity through covalent bonding.

2. Pork color analysis

The color of the various preservative film packaged pork during storage is shown in table 2. From the values of L, the L increases in each group for 4 days prior to storage, mainly due to increased refractive index at the meat surface caused by water loss. However, L tends to decrease after 6 days of storage due to myoglobin oxidation and microbial growth. Samples wrapped with PE films had a faster downward trend. At the end of storage (12 d), the TO-CH-PL film packed pork had the highest L value (47.86). From the above pH analysis, it was found that the lower water vapor transmission rate and oxygen transmission rate values, and the TO-CH-PL bacteriostatic activity all help TO retard the rate of decline of pork L.

From a, the value of a of pork tended to rise in the first 4 days of storage due to the higher value of oxygen permeability of CH. Nevertheless, all treatment groups had a reduced a-value for pork. At the end of storage, the a-value of the TO-CH-PL group was highest, which was related TO the antibacterial and antioxidant properties of the TO-CH-PL film.

TABLE 2 pH and color analysis of different Chitosan film packaged pork during refrigeration

¹ The difference between the letters of the indices a-e in the same column is statistically significant (p<0.05)

² The difference between the different letters of the indices x-z in the same row is statistically significant (p<0.05)

3. Analysis of total number of colonies, TVB and TBARS during pork storage

As can be seen from Table 3, the total colony count of each treatment group gradually increased during storage. The total colony count content of the pork wrapped by the PE film is increased more rapidly. At the end of storage, TO-CH-PL packaged pork had the lowest total number of colonies (6.15 lg CFU/g) and PE film packaged pork had the highest total number of colonies (7.97 lg CFU/g).

The freshness of meats and meat products can be characterized by a TVBN index. As is clear from Table 3, the changes in TBN were similar to the changes in the total number of colonies and pH. The TVCN of PE group pork is 6.33-27.29 mg/100g when stored for 12 days. Meanwhile, TVCNs of CH and TO-CH-PL were 23.26 and 19.84mg/100g, respectively. Therefore, the TO-CH-PL film has a certain protection effect on the deterioration process of pork in the later storage period.

TBARS is an index for evaluating lipid oxidation. As can be seen from Table 3, the TBARS value of the pork ridge increased with the storage time. The TBARS was significantly increased for each treatment group from day 6 TO the end of storage, while the TO-CH-PL film coated pork was significantly lower at each storage time than for the other groups. And the TBARS of the PE group is higher in the whole refrigerating process. PL acts as a natural antioxidant, covalently binding chitosan enhances the antioxidant activity of chitosan membranes. Thus, the inhibition of microbial growth by TO-CH-PL membranes also helps reduce lipid oxidation during refrigeration.

TABLE 3 analysis of colony count, TVB and TBARS of different chitosan film packaged pork during refrigeration

4. Conclusion(s)

A novel PL modified chitosan membrane is successfully prepared by a TEMPO/EDC/NHS oxidation system. Successful grafting of PL onto chitosan was confirmed by FTIR and SEM characterization. Covalent bonding of PL to chitosan increases the water vapor transmission rate, oxygen transmission rate and mechanical properties of the modified membrane. The results show that the PL modified chitosan film has better preservation effect on pork ridge quality performance by delaying pH value and color change, microorganism growth, TVBN and lipid oxidation compared with the chitosan film and PE film which are independently used. Covalent binding of chitosan to PL showed synergistic antioxidant and antibacterial effects. In summary, PL modified chitosan film (TO-CH-PL) is expected TO be a natural film for meat preservation due TO the biodegradability and non-toxicity of PL and chitosan.

Claims

1. The preparation method of the epsilon-polylysine modified chitosan membrane is characterized by comprising the following steps of:

(2) EDC/NHS mediated reaction is adopted TO graft epsilon-polylysine on chitosan TO prepare epsilon-polylysine modified chitosan TO-CH-PL: activating carboxyl of the TO-CH TO obtain an activated TO-CH suspension, adding epsilon-polylysine into the activated TO-CH suspension for grafting reaction, washing after the reaction is finished, and collecting epsilon-polylysine modified chitosan TO-CH-PL freeze-dried powder; the mass ratio of TO-CH TO epsilon-polylysine is as follows: (4.9-5.1): (4.5-5.0);

2. The epsilon-polylysine modified chitosan film of claim 1 wherein the process of preparing TEMPO oxidized chitosan TO-CH in step (1) using TEMPO/NaClO/KBr oxidation system is: uniformly dissolving KBr and TEMPO in deionized water TO prepare a solution, uniformly mixing dried chitosan and the solution TO prepare a suspension, regulating the pH value TO be 10.5-11 TO obtain a mixed solution, and stirring the mixed solution at room temperature TO react TO obtain TEMPO oxidized chitosan (TO-CH).

3. The epsilon-polylysine modified chitosan film of claim 2 wherein the concentration of each component in the mixture is as follows: KBr of 0.25-0.35 g/100mL, TEMPO of 0.05-0.06 g/100mL, and chitosan of 1.9-2.1 g/100mL.

4. The epsilon-polylysine modified chitosan membrane of claim 2, wherein the mixed solution is stirred at room temperature for reaction for 6-6.5 hours, ethanol is added TO stop the reaction TO obtain TEMPO oxidized chitosan TO-CH, and the obtained TEMPO oxidized chitosan TO-CH is centrifugally washed by pure water TO prepare freeze-dried powder.

5. The epsilon-polylysine modified chitosan film of claim 1, wherein the process of activating the carboxyl groups of the TO-CH in step (2) is: uniformly stirring TO-CH freeze-dried powder in deionized water, adding EDC and NHS, reacting at 24-25 ℃ for 10-15 min TO activate carboxyl of TO-CH TO obtain suspension, and centrifuging the suspension TO remove unreacted EDC and NHS TO obtain activated TO-CH suspension;

the TO-CH concentration in the activated TO-CH suspension is: 0.82 to 0.85%.

6. The epsilon-polylysine modified chitosan film of claim 1, wherein the grafting reaction conditions in step (2) are reaction at 25-26 ℃ for 24-25 hours.

7. The epsilon-polylysine modified chitosan film of claim 1, wherein the process of preparing TO-CH-PL film in step (3) is: and dissolving the TO-CH-PL powder in an acetic acid solution with the volume percentage concentration of 3% -3.2%, stirring at 25-26 ℃ for 12-13 hours until the TO-CH-PL powder is completely dissolved, adding glycerol and stirring uniformly TO prepare a TO-CH-PL solution, forming a film from the TO-CH-PL solution, neutralizing and drying TO obtain the epsilon-polylysine modified chitosan film.

8. The epsilon-polylysine modified chitosan film of claim 1 or 7, wherein the TO-CH-PL powder in step (3) is added TO the acetic acid solution in an amount of 1.5-1.6 g/100mL, and the glycerol is added in an amount of 0.1% -0.3% of the TO-CH-PL solution volume.

9. Use of the epsilon-polylysine modified chitosan film of any one of claims 1-8 in food preservation.