CN115572397A

CN115572397A - Epsilon-polylysine modified chitosan membrane and application thereof

Info

Publication number: CN115572397A
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: 2023-01-06
Anticipated expiration: 2042-09-05
Also published as: CN115572397B

Abstract

The invention discloses an epsilon-polylysine modified chitosan film and application thereof, and the preparation method of the chitosan film comprises the following steps: (1) Preparing TEMPO oxidized chitosan TO-CH by using a TEMPO/NaClO/KBr oxidation system; (2) Preparing epsilon-polylysine modified chitosan TO-CH-PL by grafting epsilon-polylysine TO chitosan by adopting EDC/NHS mediated reaction; (3) preparing the TO-CH-PL film. Researches show that the TO-CH-PL film obviously delays the increase of the total number of bacterial colonies, TVBN and TBARS and the change of the pH value and the color of the packaged pork, so that the pork sample has a better preservation effect on the quality of the pork sample. Therefore, the PL modified chitosan film can be used as a substitute method for keeping the pork quality index and prolonging the shelf life of pork in the pork refrigeration and preservation process.

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 development of the food industry has led consumers to realize that the widespread use of chemical preservatives in food products may cause health problems. Therefore, many attempts have been made to use natural preservatives and advanced packaging methods during food processing and storage. The addition of natural antimicrobial and/or antioxidant substances and other active ingredients to food packaging materials can control the undesirable 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 to ensure the quality and safety benefits of the food.

In recent years, edible, biodegradable, antibacterial food packaging materials such as chitosan have been used as base materials for active packaging. The linear structure of the chitosan is formed by D-glucosamine and N-acetyl-D-glucosamine through beta- (1, 4) glycosidic bond, and the chitosan with non-toxicity and biocompatibility can be obtained through deacetylation of chitin. The antibacterial mechanism of chitosan can be attributed to the rupture of cell membranes by the interaction of the positive charge of chitosan with the negatively charged macromolecules on the cell surface. However, due to the hydrophilic property of chitosan, its low water resistance and poor mechanical properties limit its application in functional films. 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 focus. epsilon-Polylysine (PL) is an odorless water-soluble substance, is a promising antibacterial substance, and can be added with chitosan matrix to improve the shelf life of food.

epsilon-Polylysine (PL) is a native polypeptide produced by S.albus. The molecular weight of the polymer is generally 2000-5000Da and it is obtained by polymerizing lysine through epsilon-amino and alpha-carboxyl groups. Due to its excellent thermal stability and antibacterial activity, PL will have good application prospects in the food industry. At present, PL is approved for fruit and vegetable fresh-keeping, and is researched and applied in the aspect of fruit and vegetable fresh-keeping of apples, spinach, chinese cabbages, lotus roots and the like. The antibacterial mechanism of PL consists in the cationic surface activity of the free alpha-amino group on the PL molecular structure in an acidic environment. The positively charged polymer can enhance the permeability of cell membranes and microbial walls, allow the exudation of cellular contents,

in recent years, many studies have succeeded in preparing biofilms composed of chitosan and PL and applying them to the preservation of meat, fruits and vegetables. For meat and meat products, the meat and meat products are easily polluted by microorganisms due to high moisture and nutrient content, so that the meat and meat products have poor quality, lost flavor and discolored. Lin et al (2018) prove that a biological film formed by compounding chitosan and PL has good antibacterial and fresh-keeping effects on chicken. Alirezalu et al (2021) reported that PL-chitosan composite films have good preservative effects on beef. However, in previous studies, the binding mode of PL and chitosan in a biofilm was physical binding. Due to its water solubility, PL can dissolve in films and, when applied to high moisture content food products, such as meats and meat products, can dissolve in the environment surrounding the food product, reducing the bacteriostatic and preservative properties of the film. Therefore, it is required to provide a novel PL modified chitosan film, which is chemically grafted onto chitosan to further expand the application range and food preservation effect thereof.

Disclosure of Invention

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

The purpose of the invention can be realized by the following technical scheme:

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

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

(2) Preparing epsilon-polylysine modified chitosan TO-CH-PL by grafting epsilon-polylysine TO chitosan through EDC/NHS mediated reaction: 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 freeze-dried powder of the epsilon-polylysine modified chitosan TO-CH-PL;

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

As a preferred 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: the preparation method comprises the steps of uniformly dissolving KBr and TEMPO in deionized water TO prepare a dissolved solution, uniformly mixing dried chitosan and the dissolved solution TO prepare a suspension, adjusting the pH value TO be within a range of 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).

More preferably, the concentration contents of the components in the mixed solution are as follows: KBr is 0.25-0.35 g/100mL, TEMPO is 0.05-0.06 g/100mL, chitosan is 1.9-2.1 g/100mL. More preferably: KBr was 0.3g/100mL, TEMPO was 0.06g/100mL, and chitosan was 2g/100mL.

Preferably, the mixed solution is stirred at room temperature for reaction for 6-6.5 h, then 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.

More preferably, when adjusting the pH, 10% -14% NaClO solution is firstly dripped into the suspension, and then the pH is adjusted to be within the range of 10.5-11 by adopting 0.5 MHCl.

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

the TO-CH freeze-dried powder, the EDC and the NHS are in mass ratio as follows: (4.9-5.1): (1.7-1.74): (1.03-1.05);

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

Further preferably, the mass ratio of TO-CH TO epsilon-polylysine in the step (2) is as follows: (4.9-5.1) and (4.5-5.0);

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

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

More preferably, the TO-CH-PL powder in the step (3) is added into 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 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 membrane (TO-CH-PL) is synthesized by a TEMPO/EDC/NHS oxidation system in the research. Firstly, the physical and chemical properties of the TO-CH-PL are represented by a Fourier transform infrared spectrum, a scanning electron microscope and an energy spectrometer. The results demonstrate that PL was successfully grafted onto chitosan molecules. Based on water vapor and oxygen permeability, as well as mechanical analysis, the TO-CH-PL films showed higher physical properties than the other selected films. Secondly, the fresh-keeping effect of the TO-CH-PL film on the pork slices is examined. The TO-CH-PL film obviously delays the increase of the total number of bacterial colonies, TVBN and TBARS and the change of the pH value and the color of the packaged pork, so that the quality of the pork sample is better preserved. Therefore, the PL modified chitosan film can be used as a substitute method for keeping the pork quality index and prolonging the shelf life of pork in the pork refrigeration and preservation process.

The key point of the technical scheme of the invention is as follows:

(1) Firstly, preparing oxidized chitosan TO-CH by using a TEMPO/NaClO/KBr oxidation system, wherein TEMPO concentration is the key point of the step, aiming at oxidizing chitosan into TO-CH with the final addition concentration of 0.05-0.06 g/100mL,

(2) And (2) grafting epsilon-polylysine onto chitosan by adopting EDC/NHS mediated reaction on the basis of (1) TO prepare epsilon-polylysine modified chitosan TO-CH-PL, wherein the key point is that EDC/NHS is added TO activate carboxyl of TO-CH, and then epsilon-polylysine is added into activated TO-CH suspension TO carry out grafting reaction, so as TO obtain the modified chitosan TO-CH-PL.

The invention has the beneficial effects that:

a novel PL modified chitosan membrane is synthesized by adopting a chemical oxidation method, and the defect that the original chitosan membrane prepared by only mixing in a physical mode easily causes loss of active ingredients is overcome. Compared with other similar products on the market, the prepared PL modified chitosan film has better physical properties, better preservation effect on the quality of pork samples, and capability of prolonging the shelf life of the products.

Drawings

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

FIG. 2 SEM electron micrographs of two films.

Detailed Description

The invention is further illustrated by the following examples. In the following detailed description, certain exemplary embodiments of the present invention are described by way of illustration only. Needless to say, a 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 present 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 membrane (TO-CH-PL). Secondly, the physical and mechanical properties thereof were studied. Finally, the influence of the membrane prepared at 4 ℃ for 12 days on the microorganisms and the physicochemical properties of the pork was studied.

1. Preparation of epsilon-polylysine modified Chitosan Membrane

1 materials and methods

1.1 materials

PL (ε -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-ethylcarboxydiimine hydrochloride (EDC-HCl) were purchased from Leilongji, shanghai. Potassium bromide (KBr), sodium hypochlorite (NaClO), LB broth and LB agar media were all from the national drug company, inc. (Shanghai). Other chemicals were selected for analytical grade.

1.2 Preparation of PL-Chitosan Membrane

1.2.1 TEMPO oxidized chitosan (TO-CH)

The carbonyl chitosan is prepared by a TEMPO/NaClO/KBr oxidation system. 1.5g of KBr and 0.3g of TEMPO were first dissolved homogeneously in 460mL of deionized water. 10g of dried 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 is determined to be 500mL, and after stirring for 6h at room temperature, 200mL of ethanol is added to stop the reaction (the addition amount of the ethanol is 40% of the volume of the mixed solution). TEMPO oxidized chitosan (TO-CH) was washed 4 times (4000rpm, 5min) with pure water by centrifugation TO prepare a lyophilized powder. The carboxylate content of the lyophilized TO-CH was determined TO be 0.39mmol/g according TO conductometric titration.

1.2.2 Chitosan graft PL (TO-CH-PL)

Preparing TO-CH-PL by EDC/NHS mediated reaction. First, 5g of lyophilized TO-CH was stirred well 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 TO-CH. The suspension was centrifuged 3 times (4000 rpm,5 min) to remove unreacted EDC and NHS. Then, 4.5g PL was added TO the activated TO-CH suspension and reacted at 25 ℃ for 24h. The TO-CH-PL suspension was finally washed 4 times with 250mL of deionized water. Lyophilized TO-CH-PL was collected TO prepare a thin film.

1.2.3 Preparation of TO-CH-PL thin film

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

2. Characterization of epsilon-polylysine modified Chitosan membranes

1. Performance analysis

TABLE 1 Performance of PL-chitosan films

¹ The letters a to b in each row are different and represent remarkable difference (p)<0.05)

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

The film thickness can be used to further determine the mechanical properties and water barrier capability of the film, which are key factors affecting the film quality. As shown in table 1, covalent binding of PL to chitosan significantly increased the thickness of the chitosan film from 60.45 μm to 73.81 μm. This result confirms that the amine group in PL reacts with the hydroxyl group of chitosan to form a more complex film structure.

As shown in Table 1, the TO-CH-PL membranes had lower water vapor transmission rates (5.19 g mm/m.24 h) compared TO CH membranes, indicating that cross-linking of PL with chitosan imparts a highly dense structure TO the active membrane. The water vapor transmission rate of the PE film in this study was 6.23. + -. 0.37g mm/m.multidot.24 h, similar TO TO-CH-PL. In addition, the CH film has a high water vapor transmission value, indicating that the water resistance of the film is low, and the minimum water vapor transmission rate for the composite film produced by Yu et al (2019) is about 7 gmm/m.multidot.24 h. Therefore, the PL-chitosan biomembrane constructed by the TEMPO/EDC/NHS oxidation system in the research 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 food ingredients during oxidation. As is apparent from Table 1, the oxygen permeability is significantly reduced after chitosan is covalently bound to PL. The compact and complex structure of the TO-CH-PL thin film is the main reason of the oxygen resistance. Since no study reports the oxygen permeability of PL-chitosan films, reference can be made to Levan/pullulan/chitosan edible films to compare the oxygen permeability of active chitosan films (Gan et al, 2022), the oxygen permeability value of the prepared films is 44.5-487.5 cm mm/m.24 h.0.1 MPa, while the oxygen permeability value of the present study is 4.06-335.98 cm mm/m.24 h.0.1 MPa. Therefore, the PL-chitosan biomembrane constructed by the TEMPO/EDC/NHS oxidation system in the research has better oxygen blocking capability.

Mechanical properties are often an important indicator of the water resistance of a film, especially in food packaging. The Tensile Strength (TS) and elongation at break (EB) of the film exhibit resistance to tensile stress before break and shape change, respectively. After covalent bonding, TS of the chitosan film is increased from 23.96MPa to 50.94MPa, and EB is increased from 26.02 to 36.45%. Chitosan covalently binds TO PL, resulting in a complex branched structure, leading TO increased TS and EB in TO-CH-PL films. Therefore, the chitosan membrane modified by covalent bonding with PL in the study has good mechanical properties.

FTIR Spectroscopy

TO determine the formation of covalent bonds between PL and chitosan under TEMPO/EDC/NHS oxidation system, secondary structures of CH, TO-CH and TO-CH-PL were examined using FTIR techniques (FIG. 1). FTIR spectra of chitosan with characteristic vibration bands of CH, 897 and 1157cm ^-1 The peak belongs to-C-O-C-antisymmetric stretching vibration and is a characteristic absorption peak of chitosan. 1090 cm ^-1 The strong absorption peak is the tensile vibration of-OH group. 1048cm ^-1 The peak at (a) is related to the stretching vibration of the beta-1, 4-glycosidic bond in the chitosan backbone. Other typical bands of chitosan are 1320cm ^-1 (-CH bending vibration and-CH deforming vibration), 2870cm ^-1 Stretching vibration of (-CH); 3411cm of ^-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 of (c), representing the carboxyl group vibration. The results showed that the C-OH at position 6 on the pyran ring had been formedThe work oxidation is to carboxyl. Interestingly, 1604cm after further TO-CH cross-linking with PL ^-1 A newly added peak at (a) can be identified as a vibration of the N-H in the TO-CH-PL. Furthermore, 1260cm in the FTIR spectrum of TO-CH-PL ^-1 The peak at (A) is the C-N vibration. Combined with the previously identified C = O group (1640 cm) ^-1 ) And N-H groups (3411 cm) ^-1 ) Upon shaking, it was confirmed that a covalent bond was formed between PL and chitosan. Thus, PL was successfully grafted onto chitosan molecules under the TEMPO/EDC/NHS oxidation system to form a network structure.

3. Observation by electron microscope

The interaction between the 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 in FIG. 2, the TO-CH-PL film exhibited a uniform, clear, smooth structure, indicating that PL covalently bonded TO chitosan in the film formed a complete structure. However, the CH membrane was flaky and had pores, and solid particles were observed on the membrane surface. These facts may explain the high water vapor and oxygen permeability values of CH membranes. In addition, the addition of glycerol also facilitates the formation of a homogeneous structure in order to avoid cracks and irregularities on the surface of the film.

3. Application of epsilon-polylysine modified chitosan membrane

1. pH analysis of pork during storage

As can be seen from Table 2, the pH of the TO-CH-PL, CH and PE film-packaged steaks increased during storage. Pork from different packaging films showed no significant difference in pH value 4 days before storage (p < 0.05). After 6 days of storage, the pH increased from a minimum of 5.88 to a maximum of 7.19, indicating microbial growth and spoilage in the pork. The pH of the PE film-wrapped samples was highest at the end of the refrigeration. The pH of the pork packaged with TO-CH-PL and CH was 6.86 and 7.09 respectively after 12 days of storage, and was lower than that of the PE film. For the TO-CH-PL membrane with the lowest water vapor transmission rate and oxygen transmission rate, chitosan and PL can show good bacteriostatic activity through covalent bonding.

2. Pork color analysis

The color of the different preservative film packaged pork during storage is shown in table 2. From the L values, there was an increase in L for each group 4 days prior to storage, mainly due to the increase in refraction at the meat surface caused by water loss. But L is on a downward trend after 6 days of storage due to myoglobin oxidation and microbial growth. The PE film wrapped sample had a faster tendency to decline. At the end of storage (12 d), the TO-CH-PL film packaged pork had the highest L value (47.86). From the pH value analysis, the water vapor transmission rate and the oxygen transmission rate are low, and the bacteriostatic activity of the TO-CH-PL is helpful TO delay the reduction rate of the L & ltx & gt of the pork.

From a, the a value of the pork is in an increasing trend in the first 4 days of storage due to the high oxygen permeability value of CH. Nevertheless, all the treated pork had a-value decreased. The highest a value of the TO-CH-PL group at the end of storage is associated with the antibacterial and antioxidant properties of the TO-CH-PL films.

TABLE 2 analysis of pH and color of different chitosan films packed pork during refrigeration

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

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

3. Analysis of colony count, TVBN and TBARS during pork storage

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

The freshness of meat and meat products can be characterized by a TVBN index. As can be seen from Table 3, the change in TVBN was similar to the change in the total number of colonies and the change in pH. The TVBN of the PE pork group changes in the range of 6.33-27.29 mg/100g when the storage time is 12 days. Meanwhile, TVBN of CH and TO-CH-PL was 23.26 and 19.84mg/100g, respectively. Therefore, the TO-CH-PL film has certain protection effect on the deterioration process of the 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 pork loins increases with the storage time. The TBARS of each treatment group was significantly increased from day 6 TO the end of storage, while the TBARS of TO-CH-PL film-coated pork was significantly lower than that of the other groups at each storage time. While the TBARS was higher in the PE group throughout the cold storage. PL, as a natural antioxidant, covalently binds to chitosan enhancing the antioxidant activity of chitosan films. Thus, the inhibition of microbial growth by the TO-CH-PL membrane also contributes TO the reduction of lipid oxidation during cold storage.

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

¹ The different letters of the indices a-e in the same row represent the difference with statistical significance (p)<0.05)

4. Conclusion

A novel PL modified chitosan membrane is successfully prepared through a TEMPO/EDC/NHS oxidation system. Successful grafting of PL onto chitosan was confirmed by FTIR and SEM characterization. The covalent bonding of PL and chitosan improves the water vapor transmission rate, oxygen transmission rate and mechanical properties of the modified membrane. The results show that the PL modified chitosan membrane has a better preservation effect on pork back quality performance by retarding pH and color change, microbial growth, TVBN and lipid oxidation compared to chitosan membrane and PE membrane used alone. The covalent binding of chitosan to PL shows 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 epsilon-polylysine modified chitosan membrane is characterized in that the preparation method of the chitosan membrane comprises the following steps:

(3) Preparing a TO-CH-PL film: and dissolving the TO-CH-PL powder in an acetic acid solution, adding glycerol, uniformly stirring 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.

2. The epsilon-polylysine-modified chitosan film of claim 1, wherein the TEMPO oxidized chitosan TO-CH preparation process using TEMPO/NaClO/KBr oxidation system in step (1) is: the preparation method comprises the steps of uniformly dissolving KBr and TEMPO in deionized water TO prepare a dissolved solution, uniformly mixing dried chitosan and the dissolved solution TO prepare a suspension, adjusting the pH value TO be within a range of 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 membrane of claim 2, wherein the concentration content of each component in the mixed solution is: KBr is 0.25-0.35 g/100mL, TEMPO is 0.05-0.06 g/100mL, chitosan is 1.9-2.1 g/100mL.

4. The epsilon-polylysine modified chitosan membrane of claim 2, wherein the mixture is stirred at room temperature for 6-6.5 h, 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 the TO-CH freeze-dried powder in deionized water, adding EDC and NHS, reacting at 24-25 ℃ for 10-15 min TO activate the carboxyl of the TO-CH TO obtain a suspension, and centrifuging the suspension TO remove unreacted EDC and NHS TO obtain an activated TO-CH suspension;

the TO-CH freeze-dried powder, the EDC and the NHS are in mass ratio as follows: (4.9-5.1), (1.7-1.74), (1.03-1.05);

the concentration of the TO-CH in the activated TO-CH suspension is as follows: 0.82 to 0.85 percent.

6. The epsilon-polylysine modified chitosan film according TO claim 1, wherein the mass ratio of TO-CH TO epsilon-polylysine in step (2) is: (4.9-5.1) and (4.5-5.0);

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

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

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

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