Rosin modified food packaging material and method for preparing the same

Abstract

The application discloses a preparation method of rosin quaternary ammonium salt and zwitterionic sulfosuccinimidyl rosin modified chitosan, a food packaging film prepared from the same and application. The preparation of the rosin quaternary ammonium salt and zwitterionic sulfosuccinimidyl rosin modified chitosan comprises the following steps: first, preparing acyl chloride from the rosin quaternary ammonium salt and zwitterionic sulfosuccinimidyl rosin; then, reacting the acyl chloride with chitosan under the catalysis of N,N-dimethylformamide; and finally, purifying the chitosan to obtain the rosin quaternary ammonium salt and zwitterionic sulfosuccinimidyl rosin modified chitosan. The raw material components of the food packaging film comprise 5-50 parts of the rosin quaternary ammonium salt and zwitterionic sulfosuccinimidyl rosin modified chitosan, 50-100 parts of gelatin, 20-40 parts of glycerol and 800-1500 parts of water. The rosin quaternary ammonium salt and zwitterionic sulfosuccinimidyl rosin are grafted into the chitosan by using the grafting method, the water solubility of the chitosan is improved, and the antibacterial effect of the chitosan is enhanced. Meanwhile, the prepared packaging film has good mechanical properties, strong antibacterial property and high biological safety, has the dual effects of shielding ultraviolet rays and high visible light transmittance, and can significantly prolong the shelf life of food.

Description

Technical Field

[0001] This invention relates to a rosin quaternary ammonium salt and zwitterionic sulfonyl rosin-modified chitosan, a modified chitosan / gelatin food packaging film prepared therefrom, and their preparation methods, belonging to the field of food packaging technology. Background Technology

[0002] Rosin is a type of natural antibacterial material. People first discovered that the resin flowing from pine trees could reduce the damage caused by insect pests. As a result, it was extracted from pine trees and sprayed on fruit trees with solvents to protect them from pests and ensure fruit yield.

[0003] Chitosan was discovered from abundant marine resources; this type of polymer can be extracted in large quantities from crustaceans. Chitosan is a readily film-forming material; its molecular chains break down easily when dissolved in acidic solutions, making it suitable for preparing bio-based packaging films. Furthermore, chitosan chains contain abundant amino groups (-NH2), which can be protonated in weakly acidic aqueous solutions to form polycationic structures. Therefore, chitosan possesses natural antibacterial properties and is often used as an antibacterial additive. However, chitosan's insolubility in neutral and alkaline water limits its applications.

[0004] Gelatin is also a type of bio-based material that is easy to form films, but it is difficult to play a role in thin film applications due to its softness and brittleness.

[0005] To address the issues of poor film-forming properties of biodegradable gelatin, poor water solubility of chitosan, and limited application in the food packaging field, the inventors proposed a rosin quaternary ammonium salt and zwitterionic sulfonyl rosin-modified chitosan and a modified chitosan / gelatin food packaging film prepared from it. In the preparation of the packaging film, modified chitosan and gelatin are used as the main raw materials, and glycerin is used as a plasticizer, which can produce a food packaging film with good mechanical properties, strong antibacterial properties, and high biosafety. Summary of the Invention

[0006] This invention provides a rosin quaternary ammonium salt and zwitterionic sulfonyl rosin-modified chitosan, a modified chitosan / gelatin food packaging film prepared therefrom, and their preparation methods, in order to solve the problems of poor film-forming properties of biodegradable gelatin, poor water solubility of chitosan, and limited application in the food packaging field, and to enhance antibacterial effects and extend the shelf life of packaged foods.

[0007] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows:

[0008] A method for preparing rosin quaternary ammonium salt and zwitterionic sulfonyl rosin-modified chitosan includes the following steps:

[0009] 1) Rosin quaternary ammonium salt and zwitterionic sulfonyl rosin are acyl chlorided separately to prepare rosin quaternary ammonium salt acyl chloride and zwitterionic sulfonyl rosin acyl chloride;

[0010] 2) Rosin quaternary ammonium salt acyl chloride and zwitterionic sulforosin acyl chloride react with chitosan under the catalysis of N,N-dimethylformamide (DMF), and then purified to obtain rosin quaternary ammonium salt and zwitterionic sulforosin modified chitosan.

[0011] Step 2) above is carried out in a 1% acetic acid solution in dichloromethane. A 1% acetic acid solution in dichloromethane means that the dichloromethane contains 1% acetic acid. The percentages mentioned above are by volume.

[0012] The aforementioned rosin quaternary ammonium salt and zwitterionic sulfonyl rosin-modified chitosan can be used to prepare food packaging films.

[0013] Compared to rosin quaternary ammonium salt grafted only, modified chitosan grafted with zwitterionic sulfonyl rosin has better detergency, further enhances antibacterial effect, reduces bacterial adhesion and accumulation, and allows the film to better exert its antibacterial effect.

[0014] To ensure the synergistic effect on the packaging film, the preparation method of zwitterionic sulfonyl rosin in step 1) above is as follows: tertiary ammonium maleic acridinium compound is dissolved in tetrahydrofuran, heated to 50-60°C, and after the solution becomes clear, 1,3-propane sulfonyl lactone is added to react and precipitate a white crude zwitterionic sulfonyl rosin product. The crude zwitterionic sulfonyl rosin product is washed with tetrahydrofuran and then vacuum dried at 40-50°C for 18-24 hours to obtain pure zwitterionic sulfonyl rosin MPA-BN+SO3-.

[0015] To improve reaction efficiency, the mass ratio of the above-mentioned tertiary ammonium maleic acridinium compound, 1,3-propanesulfonyl lactone, and tetrahydrofuran is 1–1.2:0.3–0.5:20–30; the reaction time is 24–48 hours, and the reaction temperature is 50–70°C.

[0016] As one specific implementation scheme, in step 1) above, the acyl chloride method for rosin quaternary ammonium salt and zwitterionic sulfonyl rosin is as follows: at 0-5℃, oxalyl chloride and N,N-dimethylformamide are added dropwise to the mixture of rosin quaternary ammonium salt or zwitterionic sulfonyl rosin and dichloromethane, respectively, and stirred until completely dissolved. The mixture is then reacted in an oil bath at 40-50℃ for 2-3 hours. During the reaction, the solution gradually changes from transparent and clear to yellow. The solvent is removed by rotary evaporation to obtain a yellow solid, which is rosin quaternary ammonium salt acyl chloride or zwitterionic sulfonyl rosin acyl chloride.

[0017] In step (1) above, oxalyl chloride and N,N-dimethylformamide are added slowly, with a preferred addition rate of 2 to 4 mL / min; stirring in this step requires slow stirring, with a preferred stirring speed of 100 to 200 rpm.

[0018] To improve the modification effect, in step (1) above, the mass ratio of rosin quaternary ammonium salt or zwitterionic sulfonyl rosin to oxaloyl chloride is (0.5-1.5):(1-2); the mass-volume ratio of rosin quaternary ammonium salt or zwitterionic sulfonyl rosin to N,N-dimethylformamide is (0.5-1.5g):(0.5-1.5mL).

[0019] To fully utilize the effects of each component, in step 2), the mass ratio of rosin quaternary ammonium chloride, zwitterionic sulforosin chloride, chitosan, and N,N-dimethylformamide is 0.5–1.5:0.5–1.5:1.0–2:1.0–3.0; the reaction time is 18–24 hours, and the reaction temperature is 30–60°C.

[0020] To enhance the performance of the food film, step 2) is as follows: Rosin quaternary ammonium chloride and zwitterionic sulforosin chloride obtained in step 1) are dissolved in dichloromethane at room temperature to obtain a dichloromethane solution of rosin quaternary ammonium chloride and zwitterionic sulforosin chloride. Simultaneously, chitosan (CS) is dissolved in dichloromethane containing 1% acetic acid to obtain a chitosan solution. The dichloromethane solution of rosin quaternary ammonium chloride and zwitterionic sulforosin chloride is then added dropwise to the chitosan solution. After mixing thoroughly, DMF (N,N-dimethylformamide) is added, and the mixture is stirred under a nitrogen atmosphere until the reaction is complete. After purification, rosin quaternary ammonium salt and zwitterionic sulforosin-modified chitosan are obtained.

[0021] In step (2) above, the dichloromethane solution of rosin quaternary ammonium salt acyl chloride and zwitterionic sulforosin acyl chloride is slowly added dropwise to the 1% dichloromethane acetate solution of chitosan, preferably at a dropwise rate of 3 to 6 mL / min.

[0022] To improve product purity, in step 2) above, the purification process is as follows: the obtained reaction material is poured into petroleum ether and the precipitate is collected. The precipitate is dissolved in deionized water and centrifuged to remove unreacted chitosan. The supernatant is placed in a dialysis bag and dialyzed in deionized water for 24-48 hours, with the water changed every 8-12 hours. Finally, it is freeze-dried to obtain pure rosin quaternary ammonium salt and zwitterionic sulfonyl rosin modified chitosan (referred to as modified chitosan).

[0023] In order to improve product purity, the dialysis bag specifications in step (3) above are MW: 1000~2000.

[0024] A rosin quaternary ammonium salt and zwitterionic sulfonyl rosin-modified chitosan / gelatin food packaging film with antibacterial properties (a rosin-modified food packaging material) comprises the following raw material components: 5-50 parts of rosin quaternary ammonium salt and zwitterionic sulfonyl rosin-modified chitosan, 50-100 parts of gelatin, 20-40 parts of glycerol, and 800-1500 parts of water, wherein the parts are by weight; wherein the rosin quaternary ammonium salt and zwitterionic sulfonyl rosin-modified chitosan are prepared by the preparation method according to any one of claims 1-8.

[0025] The gelatin and chitosan used in this application are bio-based raw materials that are inexpensive and readily available, and the resulting packaging film has good antibacterial effect and excellent mechanical properties.

[0026] The preparation method of the above-mentioned antibacterial rosin quaternary ammonium salt and zwitterionic sulfonyl rosin modified chitosan / gelatin food packaging film is as follows: rosin quaternary ammonium salt, zwitterionic sulfonyl rosin modified chitosan, gelatin, glycerin and water are mixed evenly, stirred at 60-80℃ for 1-2 hours, and then allowed to stand at 60-80℃ for 30-40 minutes to eliminate bubbles, thus preparing a film liquid. Then, it is coated at room temperature and allowed to stand to obtain the antibacterial rosin quaternary ammonium salt and zwitterionic sulfonyl rosin modified chitosan / gelatin food packaging film.

[0027] The above-mentioned food packaging film, which uses modified chitosan and gelatin as the main raw materials and adds glycerin as a plasticizer, can be prepared with good mechanical properties, strong antibacterial properties, and high biosafety.

[0028] The film thickness of the above-mentioned film-coating machine is 100-1000μm. Film thickness refers to the gap height between the film-coating blade and the glass plate, which is also the initial thickness of the film (thickness before drying).

[0029] The above-mentioned reaction of tertiary ammonium maleic acridinium compound and 1,3-propane sulfonyl lactone yields zwitterionic sulfonyl rosin. After oxychlorination of the rosin quaternary ammonium salt and zwitterionic sulfonyl rosin, it is grafted onto chitosan via a reaction of acyl chloride and amino groups to obtain modified chitosan. Using modified chitosan and gelatin as the main raw materials, with glycerol as a plasticizer and water as a solvent, a film solution is prepared by uniform mixing under high temperature conditions. The film solution is then evenly coated using a film scraper and naturally air-dried to obtain an antibacterial food packaging film.

[0030] Unless otherwise specified, all work in this application was performed at room temperature, which includes a temperature range of 20–40°C.

[0031] Any techniques not mentioned in this invention are based on existing technologies.

[0032] The present invention has the following beneficial effects:

[0033] 1) In this invention, a novel zwitterionic sulfonyl rosin, rosin quaternary ammonium salt, and zwitterionic sulfonyl rosin-modified chitosan were synthesized. The zwitterionic ions provide a detergency effect, give chitosan a stronger antibacterial effect, reduce bacterial adhesion and accumulation, and increase the multifunctionality of chitosan.

[0034] 2) This invention alters the water solubility of chitosan, enabling it to be better combined with water-soluble bio-based materials such as gelatin to prepare films without the need for the addition of acidic substances, thus solving the application problems of chitosan and expanding its application directions.

[0035] 3) This invention solves the problem of poor film-forming properties of biodegradable gelatin, significantly enhancing the mechanical properties of food packaging films, with an elongation at break of up to 88.3%.

[0036] 4) The packaging film prepared by this invention does not require heating to dry the film; it can be formed by natural air drying.

[0037] 5) The food packaging film prepared by this invention has high transparency, not only with extremely high transmittance in the visible light region, but also with obvious shielding effect against ultraviolet rays, which is beneficial to the preservation of the food inside; at the same time, it has a cleaning effect, which can reduce bacterial adhesion after killing bacteria, so that the film can play a continuous sterilization effect.

[0038] 6) The raw materials used in this invention are environmentally friendly, safe, and renewable. The prepared film has high biosafety and good biodegradability. Attached Figure Description

[0039] Figure 1 The tensile strength diagrams of the membranes obtained in each example are shown.

[0040] Figure 2 The graphs show the UV transmittance of the membranes obtained in each example.

[0041] Figure 3 The following figures illustrate the preservation effects of the films obtained in each example on strawberries (in the figures, (a) is a photograph of the actual strawberries, 0 / 1 / 3 / 5 / 7 represent photographs of the actual strawberries on day 0 / day 1 / day 3 / day 5 / day 7 respectively; (b), (c), (d), and (e) are the pH, hardness, soluble solids content, and colony count of the strawberries preserved by the films obtained in each example on day 7 respectively, Fresh represents fresh strawberries, Blank represents the blank group, PE represents the PE preservation film group, K-1 is the film obtained in Example 3; K-2 is the film obtained in Example 4; and K-3 is the film obtained in Example 5). Detailed Implementation

[0042] To better understand the present invention, the following embodiments further illustrate the content of the present invention, but the content of the present invention is not limited to the following embodiments.

[0043] In each example, "room temperature" is 20–30°C; the rate of addition, whether dropwise or slow, is 4 mL / min unless otherwise specified; the stirring speed is 200 r / min unless otherwise specified; "MPA-BN+" is "rosin quaternary ammonium salt"; "MPA-BN+SO3-" is "zwitterionic sulfonyl rosin"; "CS" is chitosan; "CS-BS" is modified chitosan; "K-0" is the membrane obtained in Comparative Example 1; "K-1" is the membrane obtained in Example 3; "K-2" is the membrane obtained in Example 4; and "K-3" is the membrane obtained in Example 5. The refined rosin was sourced from Guangdong Weisida New Materials Co., Ltd.

[0044] Example 1

[0045] Preparation of zwitterionic sulfonyl rosin:

[0046] Weigh 100g of refined rosin and place it in a 500mL three-necked flask. Heat the rosin to 180℃ in a constant-temperature oil bath with stirring until it melts into a liquid state. Then cool the flask to 140℃ and add 35g of maleic anhydride and 40mL of acetic acid (at 140℃). Continue the reaction for 4 hours. After cooling to room temperature, add 100mL of acetic acid to precipitate crystals. Filter the crystals to obtain crude maleic acridinium. Recrystallize twice with acetic acid to obtain purified maleic acridinium.

[0047] 10 g of purified maleic acrid acid was added to a 500 mL three-necked flask, followed by 250 mL of anhydrous ethanol and stirring until completely dissolved. While stirring, 3 mL of 3-dimethylaminopropylamine was slowly added dropwise (3 mL / min) to the flask. The flask was then placed in a constant temperature oil bath and heated to 85 °C. After reacting for 3 h, the mixture was cooled to room temperature, and crude crystals of tertiary ammonium-modified maleic acrid acid (MPA-BN) precipitated. After recrystallization with ethanol, high-purity tertiary ammonium-modified maleic acrid acid compound MPA-BN was obtained.

[0048] 1 g of the tertiary ammonium maleic acridinium compound from the previous step was dissolved in 20 mL of tetrahydrofuran. The solution was heated to 60 °C and, after it became clear, 0.3 g of 1,3-propanesulfonyl lactone (10 mL) was added and the reaction was carried out for 30 h. During the reaction, a white amphoteric sulfonyl rosin (MPA-BN+SO3-) crude product gradually precipitated. After the reaction was completed, the product was washed three times with tetrahydrofuran and dried under vacuum at 50 °C for 24 h to obtain pure amphoteric sulfonyl rosin MPA-BN+SO3- (yield 95%).

[0049] Example 2

[0050] Methods for modifying chitosan with rosin quaternary ammonium salt and zwitterionic sulfonyl rosin:

[0051] First, the two rosin-based raw materials were acyl-chlorinated. The specific procedure was as follows: 0.52 g of purified MPA-BN+ (prepared according to the preparation of rosin quaternary ammonium salt in patent application No. 202311065768.2) was added to a 250 mL three-necked flask containing 100 mL of dichloromethane. 1.2 g of oxalyl chloride and 0.7 mL of DMF were slowly added dropwise at 0 °C, with slow stirring until completely dissolved. After the mixture returned to room temperature, the flask was placed in an oil bath at 50 °C for 3 hours. During the reaction, the solution gradually changed from transparent and clear to yellow. Excess solvent was removed by rotary evaporation to obtain a yellow solid, which is the acyl-chlorinated rosin quaternary ammonium salt MPACl-BN+. Simultaneously, 0.61g of MPA-BN+SO3- was subjected to the same operation as above (except that 0.52g of purified MPA-BN+ was replaced with 0.61g of MPA-BN+SO3-, and everything else was the same) to obtain acyl chloride zwitterionic sulfonyl rosin MPACl-BN+SO3-.

[0052] Secondly, the acyl chloride product was grafted onto the chitosan structure through the substitution reaction of -Cl and -NH2. The specific experimental steps are as follows: 0.5g MPACl-BN+ and 0.6g MPACl-BN+SO3- were dissolved in 40mL dichloromethane at room temperature, and 1g chitosan (CS) was dissolved in dichloromethane containing 1% acetic acid. The two were then mixed evenly. Then, a dichloromethane solution of MPACl-BN+ and MPACl-BN+SO3- was slowly added dropwise to the chitosan solution. After mixing evenly, 3 mL of N,N-dimethylformamide was added dropwise. The solution was observed to gradually become turbid and turn white. The reaction was completed by stirring at 50°C for 12 h under a nitrogen atmosphere. The mixed solution was poured into petroleum ether and the precipitate was collected. The precipitate was dissolved in deionized water and centrifuged to remove unreacted chitosan. The supernatant was placed in a dialysis bag (MW: 2000) and dialyzed in deionized water for 24 h, with the water changed every 8 h. Finally, the modified chitosan was freeze-dried to obtain pure product.

[0053] Infrared spectroscopy was performed on the above-mentioned zwitterionic sulfonyl rosin and modified chitosan: the samples were mixed with dry KBr powder and analyzed using an FTIR spectrometer at 400-4000 cm⁻¹. -1 Within the range, 32 scans were performed, with a resolution of 4cm. -1 The analysis is as follows:

[0054] Infrared images of rosin quaternary ammonium salt (MPA-BN+) and zwitterionic sulfonyl rosin (MPA-BN+SO3-) were compared from 1200 cm⁻¹ to 3000 cm⁻¹. -1 The characteristic peaks of the rosin structure are well preserved, such as 1692 cm⁻¹. -1 The peak is the stretching vibration peak of the carbonyl group (-C═O) in (-CO-N-OC-), at 1761 cm⁻¹. -1The stretching vibration peak of CN is 1716 cm⁻¹. -1 The absorption peaks at the corresponding carboxyl groups are basically consistent, while MPA-BN+SO3- also has an additional peak at 1038 cm⁻¹. -1 and 608cm -1 Based on the peaks corresponding to the S═O groups and the information above, it can be concluded that zwitterionic sulfonyl rosin (MPA-BN+SO3-) has been successfully synthesized.

[0055] Further comparison of the infrared images of chitosan (CS), rosin quaternary ammonium salt (MPA-BN+), zwitterionic sulfonyl rosin (MPA-BN+SO3-), and modified chitosan (CS-BS) revealed that chitosan has a 1602 cm⁻¹... -1 The corresponding -NH2 peak changes to 1560 cm⁻¹ in the product (CS-BS). -1 The peak here corresponds to the -NH-secondary amine; simultaneously, the carboxyl peaks on MPA-BN+ and MPA-BN+SO3- disappear. This indicates that the -COOH group on the rosin structure reacted with the -NH2 group on the chitosan, while the product CS-BS retained the characteristic peak of rosin (1692 cm⁻¹). -1 The stretching vibration peak of -C═O in -CO-N-OC- and 1761 cm⁻¹ -1 The results show that MPA-BN+ and MPA-BN+SO3- were grafted onto chitosan, yielding modified chitosan (CS-BS).

[0056] Comparative Example 1

[0057] The preparation of a food packaging film includes the following steps:

[0058] (1) Dissolve 1g gelatin, 0g modified chitosan and 0.3g glycerol in 10mL of water, stir at 80℃ for 1 hour, sonicate for 10 minutes and then let stand at 80℃ for 1 hour to eliminate bubbles, and obtain high temperature membrane liquid.

[0059] (2) Quickly pour the high-temperature film solution prepared in step (1) onto the glass plate of the automatic film scraper. Form a thin film (film thickness of 1000 μm) at a scraping speed of 10 mm / s.

[0060] (3) Place the glass plate with the film scraped in step (2) at room temperature for 6 hours to allow the film to form. Then peel off the film with a spatula.

[0061] Example 3

[0062] A method for preparing a chitosan / gelatin food packaging film modified with rosin quaternary ammonium salt and zwitterionic sulfonyl rosin includes the following steps:

[0063] (1) Dissolve 0.9g gelatin, 0.1g modified chitosan (prepared in Example 2) and 0.3g glycerol in 10mL of water, stir at 80°C for 1 hour, sonicate for 10 minutes, and then let stand at 80°C for 1 hour to eliminate bubbles, thus obtaining a high-temperature membrane solution.

[0064] (2) Quickly pour the high-temperature film solution prepared in step (1) onto the glass plate of the automatic film scraper. Form a thin film (film thickness of 1000 μm) at a scraping speed of 10 mm / s.

[0065] (3) Place the glass plate with the film scraped in step (2) at room temperature for 6 hours. After the film is formed, peel it off with a spatula and name it K-1 film.

[0066] Example 4

[0067] A method for preparing a chitosan / gelatin food packaging film modified with rosin quaternary ammonium salt and zwitterionic sulfonyl rosin includes the following steps:

[0068] (1) Dissolve 0.8g gelatin, 0.2g modified chitosan (prepared in Example 2) and 0.3g glycerol in 10mL of water, stir at 80°C for 1 hour, sonicate for 10 minutes, and then let stand at 80°C for 1 hour to eliminate bubbles, thus obtaining a high-temperature membrane solution.

[0069] (2) Quickly pour the high-temperature film solution prepared in step (1) onto the glass plate of the automatic film scraper. Form a thin film (film thickness of 1000 μm) at a scraping speed of 10 mm / s.

[0070] (3) Place the glass plate with the film scraped in step (2) at room temperature for 6 hours to allow the film to form. Peel off the film with a spatula and name it K-2 film.

[0071] Comparative Example 2

[0072] The only difference between this example and Example 4 is the type of modified chitosan used; all other aspects are the same as in Example 4.

[0073] The only difference between the preparation of modified chitosan in this example and that in Example 4 is that when the acyl chloride product reacts with chitosan, only the acyl chloride rosin quaternary ammonium salt MPACl-BN+ is added, and the zwitterionic sulfonyl rosin MPACl-BN+SO3- is not added. All other steps are the same as in Example 4.

[0074] Example 5

[0075] A method for preparing a chitosan / gelatin food packaging film modified with rosin quaternary ammonium salt and zwitterionic sulfonyl rosin includes the following steps:

[0076] (1) Dissolve 0.7g gelatin, 0.3g modified chitosan (prepared in Example 2) and 0.3g glycerol in 10mL of water, stir at 80°C for 1 hour, sonicate for 10 minutes, and then let stand at 80°C for 1 hour to eliminate bubbles, thus obtaining a high-temperature membrane solution.

[0077] (2) Quickly pour the high-temperature film solution prepared in step (1) onto the glass plate of the automatic film scraper. Form a thin film (film thickness of 1000 μm) at a scraping speed of 10 mm / s.

[0078] (3) Place the glass plate with the film scraped in step (2) at room temperature for 6 hours to allow the film to form. Peel off the film with a spatula and name it K-3 film.

[0079] The membranes obtained from the above embodiments were subjected to performance tests.

[0080] 1. Mechanical property testing: The test was conducted according to the national standard (GB / T1040) on a WDW-50E universal testing machine. The test temperature was room temperature, the distance between the clamps was 30 mm, the specimen width was 15 mm, the tensile rate was 10 mm / min, and the pressure measuring element was 100 N. The obtained stress-strain curves are shown below. Figure 1 .

[0081] By conducting tensile comparison tests on films prepared with different proportions, the basic mechanical properties of the different films can be obtained. From the stress-strain curves ( Figure 1 From the perspective of the modified chitosan content, the overall elongation at break and tensile strength both improved with increasing additions, indicating that the introduction of the rosin tricyclic diterpenoid structure enhances the mechanical properties of the film, exhibiting higher strength and toughness compared to pure gelatin films. Among them, the K-2 film showed the best mechanical properties, with the highest elongation at break reaching 88.3% and the highest tensile strength reaching 10.2 MPa. This suggests that a modified chitosan to gelatin ratio of 2:8 is more suitable, resulting in optimal film mechanical properties. The reason for this might be that a higher proportion of modified chitosan affects the internal structure of the film, leading to uneven distribution and agglomeration, thus reducing the film's density and preventing further improvement in mechanical properties.

[0082] 2. Transparency Test of the Film: The UV-Vis transmittance of the film samples in the range of 200–800 nm was recorded using a UV-2550 (Shimadzu, Japan) UV-Vis spectrophotometer. For food packaging, high transparency allows for easy observation of the contents; common commercially available food preservation films all have high UV transmittance. The chitosan / gelatin food packaging film prepared in this application also exhibits high transparency. Figure 2The paper demonstrates the state of the packaging film (K-3 film) when packaging strawberries. While tightly wrapping the strawberries, the surface color, texture, and freshness of the strawberries are clearly visible. This is further confirmed by testing the film's UV transmittance. The film prepared in this application exhibits good visible light transmittance, reaching over 95% (K-1-3 film) in the 400–800 nm visible light region, indicating high transparency and minimal impact on details such as the color of the packaged contents. In the 200–400 nm ultraviolet light region, the ultraviolet transmittance of the packaging film containing modified chitosan (K-1-3 film) drops to 0 at 300 nm, and the ultraviolet transmittance in the 200–300 nm range is also low. This range includes the absorption peak at 282 nm from the double bond in the rosin structure, and the absorption peak at around 270 nm from chitosan and gelatin. Overall, the modified chitosan / gelatin packaging film not only slightly affects the transmittance in the visible light region, but also has a certain ultraviolet shielding effect, which is beneficial to the preservation of the food inside.

[0083] 3. Biodegradability Test: The film was discarded in natural soil, and changes were observed over three months. Gelatin and chitosan are both bio-based raw materials with excellent biodegradability. Observing the decomposition of K-2 film in natural soil shows that over time, the film is gradually decomposed and decayed by microorganisms, eventually mixing into the soil (no residue is visible to the naked eye). K-1 and K-3 films showed the same degradation effect. This proves that the prepared packaging material is biodegradable and has low environmental pollution.

[0084] 4. Antibacterial performance test of the membrane: modified from GB / T 4789.2, prepare the bacterial solution in advance and dilute it to a concentration of (5.0~10.0)×10. 7 A bacterial suspension with a concentration of CFU / mL was used as the test bacterial suspension. 0.2 mL of the suspension with a concentration of (5.0–10.0) × 10⁻⁶ CFU / mL was pipetted onto the suspension. 7 CFU / mL of bacterial suspension was spread evenly on sterile culture medium. Wells with a diameter of 6 mm and a height of 6 mm were made on the medium. After shaking the antibacterial agent to be tested evenly, 100 μL was added dropwise into the wells. The wells were then sealed and incubated at 37°C and 90% RH for 24 h.

[0085] The diameter of the inhibition zone can be calculated using formula (1).

[0086]

[0087] D1, D2, and D3 are the diameters of the same inhibition zone measured at three different angles, and the diameter of the inhibition zone is the average of the three measurements.

[0088] The antibacterial ability of membrane solutions containing different proportions of modified chitosan was compared by observing their inhibition zones. The pure gelatin membrane solution showed no inhibition zone, indicating it had no antibacterial effect. In contrast, the membrane solution containing modified chitosan exhibited a significant inhibition zone, and the inhibition zone gradually increased with increasing modified chitosan content, demonstrating that the addition of modified chitosan greatly enhanced the antibacterial ability of the membrane solution. Compared to *Escherichia coli* (Gram-positive bacteria), the antibacterial membrane solution with the same proportion showed a more significant antibacterial effect against *Staphylococcus aureus* (Gram-negative bacteria), with the inhibition zone reaching a maximum of 19 mm, indicating a clear antibacterial effect.

[0089]

[0090] 5. The fruit preservation performance test method is as follows: Fresh, ripe strawberries were selected as food models for packaging and preservation experiments. The films prepared in each example were cut into 10cm*10cm pieces and wrapped with uniformly sized strawberries (from the same batch and of the same variety). The strawberries were stored at 37℃ and 70% RH for 7 days. Photos of the strawberries were taken daily, and samples were taken from the surface of the strawberries on the 7th day to test the surface bacterial count, pH, color difference, firmness, and soluble solids content. (See attached figures). Figure 3 .like Figure 3 As shown, fresh strawberries showed signs of mold and blackening on the third day. The strawberries wrapped in plastic wrap at room temperature had the highest degree of spoilage. This is because the plastic wrap is airtight, preventing the strawberries from breathing and exchanging gases with the outside world. The moisture accumulated inside the plastic wrap makes it easier for bacteria and mold to grow. In contrast, the control group exposed to air only showed slight signs of mold and blackening. The film prepared with modified chitosan showed the lowest degree of blackening on the surface and no mold growth. Furthermore, as the content of modified chitosan increased, the degree of decay first decreased and then increased. Among them, the K-2 film showed the best effect. On the seventh day, the strawberries were cut in half to observe the internal decay. The results showed that the strawberries wrapped in PE plastic wrap were 100% moldy on the outside, and the unwrapped strawberries in the control group were also 100% moldy on the outside. However, the strawberries wrapped with the film prepared with the modified chitosan of this application had no mold on the outside (0%). The strawberries wrapped in PE plastic wrap were completely rotten inside, and the unwrapped strawberries in the control group also had a certain degree of internal decay (50% to 70%). The strawberries wrapped with the film prepared with the modified chitosan of this application had no internal decay, and the color was lighter, indicating a higher degree of freshness.

[0091] like Figure 3 As shown, in order to more thoroughly evaluate the freshness of different strawberries, the pH, firmness, soluble solids content, and bacterial count on the surface of strawberries preserved in different embodiments were tested after 7 days. The conclusions obtained are consistent with those mentioned above. Figure 3Similar to (a)), the strawberries wrapped in the film with the highest modified chitosan content exhibited the highest freshness, with all values ​​more closely resembling those of fresh strawberries, while the strawberries wrapped in plastic wrap showed the highest degree of spoilage. In summary, the rosin-modified chitosan / gelatin film prepared in this study has a significant effect on extending the shelf life of food.

[0092] The K-2 film was tested to have a decontamination effect. After the K-2 film was contaminated with bacteria (E. coli, covering the entire surface) for 24 hours, the surface remained clean as before, proving that the film prepared with the modified chitosan of this application has excellent decontamination and antibacterial effects.

[0093] The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of the present invention shall be considered equivalent substitutions and shall be included within the protection scope of the present invention.

Claims

1. A rosin-modified food packaging material, characterized in that: Its raw material components include: 5-50 parts of rosin quaternary ammonium salt and zwitterionic sulfonyl rosin modified chitosan, 50-100 parts of gelatin, 20-40 parts of glycerin, and 800-1500 parts of water, wherein the parts are by weight. The preparation method of rosin quaternary ammonium salt and zwitterionic sulfonyl rosin modified chitosan includes the following steps: 1) Rosin quaternary ammonium salt and zwitterionic sulfonyl rosin are acyl chlorided separately to prepare rosin quaternary ammonium salt acyl chloride and zwitterionic sulfonyl rosin acyl chloride; 2) Rosin quaternary ammonium salt acyl chloride and zwitterionic sulforosin acyl chloride react with chitosan under the catalysis of N,N-dimethylformamide, and then purified to obtain rosin quaternary ammonium salt and zwitterionic sulforosin modified chitosan. In step 1), the preparation method of zwitterionic sulfonyl rosin is as follows: A. Add 10 g of purified maleic acrid acid to a 500 mL three-necked flask, pour in 250 mL of anhydrous ethanol and stir until completely dissolved. While stirring, add 3 mL of 3-dimethylaminopropylamine dropwise to the flask at a rate of 3 mL / min. Place the flask in a constant temperature oil bath and heat to 85 °C. After reacting for 3 h, cool to room temperature to precipitate crude crystals of tertiary ammonium maleic acrid acid compound. After recrystallization with ethanol, high-purity tertiary ammonium maleic acrid acid compound is obtained. B. Dissolve the tertiary ammonium maleic acridinium compound in tetrahydrofuran, heat to 50-60 °C, and after the solution becomes clear, add 1,3-propane sulfonyl lactone to react and precipitate a white zwitterionic sulfonyl rosin crude product. Wash the zwitterionic sulfonyl rosin crude product with tetrahydrofuran and then vacuum dry at 40-50 °C for 18-24 hours to obtain pure zwitterionic sulfonyl rosin. In step 1), the preparation method of rosin quaternary ammonium salt is as follows: A. Weigh 100g of refined rosin and place it in a 500ml three-necked flask. Heat the rosin to 180℃ in a constant temperature oil bath and stir until it melts into a liquid state. Then cool it down to 140℃, add 35g of maleic anhydride and 40mL of acetic acid to the flask and continue the reaction for 4h. Cool to room temperature, add 100ml of acetic acid to precipitate crystals, and obtain crude maleic acrid acid by filtration. Then, obtain purified maleic acrid acid by recrystallization twice with acetic acid. B. Add 10g of purified maleic acrid acid to a 500ml three-necked flask, pour in 250mL of anhydrous ethanol and stir until completely dissolved. While stirring, add 3mL of 3-dimethylaminopropylamine dropwise to the flask at a rate of 3mL / min. Place the flask in a constant temperature oil bath and heat to 85℃. After reacting for 3h, cool to room temperature to precipitate crude crystals of tertiary ammonium maleic acrid acid. After recrystallization with ethanol, high-purity tertiary ammonium maleic acrid acid is obtained. C. Dissolve 1g of high-purity tertiary ammonium maleic acid in THF, heat to 60℃, and after the solution becomes clear, add 3.1ml of bromoethane dropwise. React for 24h. The crude product of maleic acid quaternary ammonium salt gradually precipitates in the reaction system. Then wash three times with tetrahydrofuran to obtain purified rosin quaternary ammonium salt.

2. The rosin-modified food packaging material as described in claim 1, characterized in that: The mass ratio of tertiary ammonium maleic acridinium compound, 1,3-propanesulfonyl lactone, and tetrahydrofuran is 1~1.2 : 0.3~0.5 : 20~30; the reaction time is 24~48 hours, and the reaction temperature is 50~70℃.

3. The rosin-modified food packaging material as described in claim 1 or 2, characterized in that: In step 1), the acyl chloride method for rosin quaternary ammonium salt and zwitterionic sulfonyl rosin is as follows: at 0~5℃, oxalyl chloride and N,N-dimethylformamide are added dropwise to the mixture of rosin quaternary ammonium salt or zwitterionic sulfonyl rosin and dichloromethane, respectively, and stirred until completely dissolved. The mixture is reacted in an oil bath at 40~50℃ for 2~3 hours, and the solvent is removed by rotary evaporation to obtain a yellow solid, which is rosin quaternary ammonium salt acyl chloride or zwitterionic sulfonyl rosin acyl chloride.

4. The rosin-modified food packaging material as described in claim 3, characterized in that: The mass ratio of rosin quaternary ammonium salt or zwitterionic sulfonyl rosin to oxaloyl chloride is (0.5~1.5):(1~2); the mass-volume ratio of rosin quaternary ammonium salt or zwitterionic sulfonyl rosin to N,N-dimethylformamide is (0.5~1.5 g):(0.5~1.5 mL).

5. The rosin-modified food packaging material as described in claim 1 or 2, characterized in that: In step 2), the mass ratio of rosin quaternary ammonium salt acyl chloride, zwitterionic sulforosin acyl chloride, chitosan, and N,N-dimethylformamide is 0.5~1.5 : 0.5~1.5 : 1.0~2 : 1.0~3.0; the reaction time is 18~24 hours, and the reaction temperature is 30~60℃.

6. The rosin-modified food packaging material as described in claim 1 or 2, characterized in that: Step 2) is as follows: At room temperature, the rosin quaternary ammonium salt acyl chloride and zwitterionic sulforosin acyl chloride obtained in step 1) are dissolved in dichloromethane to obtain a dichloromethane solution of rosin quaternary ammonium salt acyl chloride and zwitterionic sulforosin acyl chloride. At the same time, chitosan is dissolved in dichloromethane containing 1% acetic acid to obtain a chitosan solution. The dichloromethane solution of rosin quaternary ammonium salt acyl chloride and zwitterionic sulforosin acyl chloride is then added dropwise to the chitosan solution. After mixing evenly, DMF is added, and the mixture is stirred under a nitrogen atmosphere until the reaction is complete. After purification, rosin quaternary ammonium salt and zwitterionic sulforosin modified chitosan are obtained.

7. The rosin-modified food packaging material as described in claim 6, characterized in that: In step 2), the purification process is as follows: the obtained reaction material is poured into petroleum ether and the precipitate is collected. The precipitate is dissolved in deionized water and centrifuged to remove unreacted chitosan. The supernatant is placed in a dialysis bag and dialyzed in deionized water for 24-48 hours, with the water changed every 8-12 hours. Finally, it is freeze-dried to obtain pure rosin quaternary ammonium salt and zwitterionic sulfonyl rosin modified chitosan.

8. A method for preparing a rosin-modified food packaging material according to any one of claims 1-7, characterized in that: Rosin quaternary ammonium salt, zwitterionic sulfonated rosin-modified chitosan, gelatin, glycerin, and water are mixed and stirred at 60-80°C for 1-2 hours. After standing at 60-80°C for 30-40 minutes to eliminate air bubbles, a film liquid is prepared. Then, it is coated at room temperature and allowed to stand to obtain a food packaging film with antibacterial properties made from rosin quaternary ammonium salt and zwitterionic sulfonated rosin-modified chitosan / gelatin.

9. The use of the rosin-modified food packaging material according to any one of claims 1-7, characterized in that: Used for food preservation, and / or allows visible light to pass through while blocking ultraviolet rays.

Images