Preparation method and application of chitosan-gelatin-tea polyphenol composite preservative film

Abstract

The invention belongs to the technical field of food packaging materials, and particularly relates to a preparation method and application of a chitosan-gelatin-tea polyphenol composite preservative film. The invention discloses a chitosan / gelatin / tea polyphenol composite membrane which is prepared by taking chitosan and gelatin as matrixes and tea polyphenol as an active additive through a film casting method. When the addition amount of the tea polyphenol is 1.5%, the comprehensive performance of the composite film is optimal, the ultraviolet light transmittance is as low as 0.113%, and the antibacterial rates on escherichia coli and staphylococcus aureus respectively reach 73.34% and 99.78%. When the strawberry preservative is applied to strawberry preservation, the mass loss rate is only 15.27% after 11 days, the sensory quality is well kept, and the shelf life is prolonged by 4 days. The composite film has excellent antibacterial and fresh-keeping performance, the raw materials are natural and degradable, and the composite film has wide application prospects in the field of fruit and vegetable fresh-keeping.

Description

Technical Field

[0001] The invention belongs to the technical field of food packaging materials, and particularly relates to a preparation method and application of a chitosan-gelatin-tea polyphenol composite fresh-keeping film. Background Art

[0002] During food distribution and storage, food packaging plays a crucial role in ensuring food quality. External bacteria and fungi can cause food to spoil. During this spoilage, many foodborne spoilage bacteria can multiply and produce toxins within the food. These toxins can enter the body along with the food, causing foodborne illnesses and potentially impacting human health. Antimicrobial food packaging materials can effectively protect food from bacterial infection, significantly impacting food safety and human health.

[0003] Existing food packaging materials have the following problems in keeping fruits and vegetables fresh:

[0004] 1. Single-component chitosan or gelatin films have defects in mechanical properties, barrier properties, and antibacterial properties, such as being brittle, fragile, and easily hydrolyzed in water;

[0005] 2. Traditional plastic packaging materials (such as PE film) lack antibacterial properties and have limited preservation effects;

[0006] 3. The existing plastic wrap has insufficient UV blocking ability and cannot effectively delay the photooxidation and deterioration of fruits and vegetables.

[0007] Tea polyphenols, as a natural antibacterial antioxidant, have potential application value in the field of food preservation, but how to effectively integrate them into packaging materials and maintain stable performance remains a technical difficulty. Summary of the Invention

[0008] In order to solve the above technical problems, the present invention provides the following technical solutions:

[0009] A composite film containing chitosan-gelatin-tea polyphenols, comprising chitosan, gelatin, tea polyphenols, glycerol and glacial acetic acid; the mass percentage of the chitosan is 1.0-2.0%, the mass percentage of the gelatin is 0.5-1.5%, the mass percentage of the tea polyphenols is 0.5-2.5%, the mass percentage of the glycerol is 1-3%, the mass percentage of the glacial acetic acid is 0.5-2%, and the balance is water.

[0010] Preferably, the mass percentage of the tea polyphenols is 1.5%.

[0011] A method for preparing a composite film containing chitosan, gelatin and tea polyphenols comprises the steps of preparing a chitosan solution, preparing a gelatin solution, preparing a composite solution and casting the film.

[0012] Preferably, the preparation method is:

[0013] (1) Preparation of chitosan solution: Disperse chitosan powder in deionized water, add glacial acetic acid solution, and stir until completely dissolved;

[0014] (2) Prepare gelatin solution: Disperse gelatin powder in deionized water and stir at 40°C until completely dissolved;

[0015] (3) Preparation of composite solution: chitosan solution and gelatin solution were mixed in a volume ratio of 3:2, glycerol was added, stirred evenly, and then divided into several portions, and tea polyphenols in different proportions were added to each portion, and stirred at 40°C until completely dissolved to obtain a composite solution;

[0016] (4) Film casting: The composite solution was poured into a flat plate mold, allowed to stand for defoaming, dried at 60° C. for 24 hours, and the film was peeled off to obtain a composite film.

[0017] Preferably, the composite solution contains 1.0-2.0% chitosan, 0.5-1.5% gelatin, 0.5-2.5% tea polyphenols, 1-3% glycerol, 0.5-2% glacial acetic acid, and the remainder is water.

[0018] Preferably, the mass percentage of the tea polyphenols is 1.5%.

[0019] The invention discloses an application of a composite film containing chitosan, gelatin and tea polyphenols in food preservation.

[0020] A composite film containing chitosan, gelatin and tea polyphenols is used in food antibacterial treatment.

[0021] Beneficial effects of the present invention:

[0022] The composite film containing chitosan-gelatin-tea polyphenols of the present invention has the following advantages:

[0023] 1. Antibacterial properties: When the addition amount of tea polyphenols is 1.5%, the antibacterial rates of the composite film against Escherichia coli and Staphylococcus aureus reach 73.34% and 99.78% respectively;

[0024] 2. Physical properties: UV transmittance is as low as 0.113%, with excellent UV blocking ability;

[0025] Moderate water solubility, reduced water content and smaller swelling rate;

[0026] 3. Freshness preservation effect: After 11 days, the mass loss rate of strawberries was only 15.27%, significantly lower than that of the blank group (24.64%) and the PE film group (18.47%). Sensory evaluation showed that it can effectively delay the decay of strawberries and extend the shelf life by 4 days.

[0027] 4. Environmental protection: All components are natural degradable materials and are environmentally friendly. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 is the test result of composite film thickness;

[0029] Figure 2 Water content of composite films with different tea polyphenols addition amounts;

[0030] Figure 3 Water solubility of composite films with different tea polyphenols addition amounts;

[0031] Figure 4 Swelling degree of composite films with different tea polyphenols addition amounts;

[0032] Figure 5 Light transmittance of composite films with different tea polyphenols addition amounts;

[0033] Figure 6 The antibacterial rate test results of the composite film;

[0034] Figure 7 This is the test result of strawberry mass loss rate;

[0035] Figure 8 Effects of different types of plastic wrap on sensory evaluation of strawberries;

[0036] Figure 9 Morphological changes of strawberries during storage. DETAILED DESCRIPTION

[0037] To make the objectives, technical solutions, and advantages of the present invention more clear, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making any creative efforts shall fall within the scope of protection of the present invention.

[0038] The present invention is further described in detail below through examples, but the protection scope of the present invention is not limited thereto.

[0039] Example 1

[0040] 1 Materials and Methods

[0041] 1.1 Materials and Reagents

[0042] The main reagents of the present invention are shown in Table 1.

[0043] Table 1 Experimental materials

[0044]

[0045] 1.2 Instruments and Equipment

[0046] The main instruments of this study are shown in Table 2.

[0047] Table 2 Main instruments

[0048]

[0049] 1.3 Methods

[0050] 1.3.1 Preparation of chitosan / gelatin / tea polyphenols composite film

[0051] (1) Preparation of chitosan stock solution: 3.00 g chitosan powder was accurately weighed using an analytical balance and dispersed in 200 mL of deionized water. 1% glacial acetic acid solution was added and stirred with a magnetic constant temperature stirrer until completely dissolved. The solution was then set aside.

[0052] (2) Preparation of gelatin stock solution: 1.875 g of gelatin powder was accurately weighed using an analytical balance and dispersed in 150 mL of deionized water. The solution was stirred at 40°C using a magnetic constant temperature stirrer until completely dissolved and set aside.

[0053] (3) Preparation of chitosan / gelatin / tea polyphenols complex stock solution: chitosan solution and gelatin solution were mixed in a ratio of 3:2, and 2% glycerol solution was added. The mixture was stirred with a magnetic constant temperature stirrer until fully mixed. The mixture was divided into 6 equal parts, and 0%, 0.5%, 1%, 1.5%, 2%, and 2.5% tea polyphenols were added respectively. The mixture was stirred with a magnetic constant temperature stirrer at 40°C until completely dissolved and set aside.

[0054] (4) Preparation of chitosan / gelatin / tea polyphenol composite film: Pour 20 ml of chitosan / gelatin / tea polyphenol composite solution into a flat plate, let it stand for defoaming, and then place it in a 60°C oven to dry for 24 hours. After peeling off the film, the composite film is ready for use.

[0055] 1.3.2 Determination of composite membrane properties

[0056] (1) Thickness: Measure the thickness of the film using an electronic digital micrometer (accuracy 0.001 mm). Randomly measure at three different locations and take the average value. The average value of the measurement results of five parallel samples is used as the final thickness of the film.

[0057] (2) Water content, water solubility, and swelling: Referring to the method of Li Shuangjian et al., the film was cut into equal sizes and weighed (m1). The film was then dried at 105°C for 12 h to a constant weight (m2). The film was placed in 30 mL of deionized water and allowed to stand for 24 h. After removal, the surface moisture of the film was wiped off and the film was weighed (m3). The film was then dried again at 105°C to a constant weight and weighed (m4).

[0058] Calculate the water content using the following formula:

[0059] Water content (%) = (m1-m2) / m1×100%

[0060] Where m1 represents the initial mass of the sample, g; m2 represents the mass after the first constant weight, g.

[0061] Calculate water solubility using the following formula:

[0062] Water solubility (%) = (m2-m4) / m2×100%

[0063] Where m2 is the mass after the first constant weight, g; m4 is the mass after the second constant weight, g.

[0064] The swelling ratio was calculated using the following formula:

[0065] Swelling rate (%) = (m3-m2) / m2×100%

[0066] Where m2 is the mass after the first constant weight, g; m3 is the weight of the sample after wiping off the surface water, g.

[0067] (3) Optical properties: The UV-visible absorption spectrum of the film was measured using a multifunctional enzyme marker; the transmittance of the film was measured using a UV-visible spectrophotometer.

[0068] (4) Antibacterial rate: The antibacterial activity of different films against Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus) was evaluated using the standard colony counting method according to GB 4789.2-2022. The films were immersed in a bacterial suspension (1 mL, 10 4 CFU / mL) for 2 hours. The bacterial solution was then exposed to light or kept in the dark. Next, 100 μL of the dilution was plated onto a Luria-Bertanl (LB) agar plate. A control group of bacterial solutions without a film was used. After 12 hours of incubation, the visible colony units (CFU) were counted and calculated. The inhibition rate of the film was determined using the following method:

[0069] Antibacterial rate (%) = (N0-N1) / N0×100

[0070] Where: N0 is the number of colonies in the control group; N1 is the number of colonies in the experimental group.

[0071] 1.3.3 Strawberry fruit freshness preservation performance test

[0072] Fresh strawberries were used to test the effectiveness of the CS / GEL / TP composite film in inhibiting decay. Strawberries of similar size and maturity were randomly divided into four groups, each containing an equal number of strawberries: a blank group, a commercially available PE film group, a CS / GEL composite film group, and a CS / GEL / TP composite film group. The strawberries were placed in a food-grade fresh-keeping container and covered with each film group to prevent direct contact with the outside environment. The four groups of samples were stored at room temperature (25±2°C) and taken out daily for photographing and weighing during storage.

[0073] (1) Mass loss rate: The weight change of strawberries treated in different groups during storage was measured. The difference between the initial mass of the strawberries (m0, g) and the mass measured at each time (m, g) was defined as the mass loss rate of the strawberries, which was calculated as the percentage of the initial mass loss. The mass loss rate was calculated as follows:

[0074] Mass loss rate (%) = (m0-m0) / m0×100%

[0075] Where m0 represents the initial mass of the strawberry, g; m is the subsequently measured mass of the strawberry, g.

[0076] (2) Sensory quality evaluation: Samples were collected daily during storage for sensory evaluation, using the sensory scoring standards of Feng Wenjie et al. Ten professionally trained personnel evaluated the sensory quality. The sensory evaluation of strawberries during storage was conducted based on four indicators: color, odor, degree of decay, and morphology. The total sensory score was 10 points. The score and evaluation criteria for each indicator are shown in Table 3.

[0077] Table 3 Sensory evaluation standards for strawberries

[0078]

[0079] 2 Data processing

[0080] The data are expressed as "mean ± standard deviation". The obtained results were subjected to one-way analysis of variance (ANOVA). Duncan's new multiple range test was performed using Origin software to determine the significant differences between samples with a 95% confidence interval.

[0081] Example 1: Preparation of composite membrane

[0082] 1. Weigh 3.00g chitosan powder and disperse it in 200mL deionized water. Add 2mL of glacial acetic acid solution and stir until completely dissolved.

[0083] 2. Weigh 1.875g of gelatin powder and disperse it in 150mL of deionized water. Stir at 40℃ until completely dissolved.

[0084] 3. Mix chitosan solution and gelatin solution in a volume ratio of 3:2, add 7 mL of glycerol, stir evenly and divide into 6 parts, add 0%, 0.5%, 1%, 1.5%, 2%, and 2.5% tea polyphenols respectively, and stir at 40°C until completely dissolved;

[0085] 4. Pour 20mL of the composite solution into a flat plate mold, let it stand to defoam, dry it at 60℃ for 24 hours, and remove the film for later use.

[0086] The composite film contains 1.0-2.0% chitosan, 0.5-1.5% gelatin, 0.5-2.5% tea polyphenols, 1-3% glycerol, 0.5-2% glacial acetic acid and the remainder water.

[0087] Example 2: Composite membrane performance test

[0088] Composite film thickness test

[0089] from Figure 1 It can be seen that the thickness of the composite film increased with the addition of TP, which is consistent with the research results of Lu Junyu et al. This is because TP, as a solid-phase additive, directly increases the solid content of the film-forming system. Furthermore, incomplete dissolution or uneven dispersion of TP particles can cause localized uneven thickness in the composite film.

[0090] Composite membrane moisture content, water solubility and swelling test

[0091] from Figure 2 It can be seen that the moisture content of the composite film gradually decreases with increasing TP addition. This is because the addition of TP makes the composite film structure denser by enhancing cross-linking, changing the hydrophilicity and hydrophobicity, and restructuring the hydrogen bond network, thereby reducing the adsorption and retention of water molecules, ultimately leading to a decrease in moisture content. A film with a high moisture content can lead to problems such as microbial growth and loss of functional components, while too low a moisture content can affect the film's texture, making it too hard and brittle. The results show that CS / GEL composite films with an appropriate amount of TP have a moderate texture and reduced moisture content, making them suitable for strawberry preservation.

[0092] from Figure 3 The composite film with a 1.5% TP addition exhibits the highest water solubility. This is likely due to TP altering the composite film's microstructure, introducing hydrophilic groups, reducing crystallinity, and regulating the local chemical environment, synergistically promoting the interaction between water molecules and the membrane material, ultimately resulting in increased water solubility. Highly water-soluble composite films are suitable for soluble packaging, short-term storage, and environmentally sensitive applications, making them ideal for preserving strawberries.

[0093] from Figure 4It can be seen that the swelling degree of the composite film added with TP is generally decreased. This may be due to the hydrophobic benzene ring group contained in TP, which enhances the hydrophobicity of the film, and the hydroxyl, amino and other groups on the CS macromolecular chain combine with the large amount of phenolic hydroxyl groups contained in TP to form hydrogen bonds during the mixing process, thereby increasing the intermolecular force and increasing the compactness of the composite film, and reducing the swelling rate. Swelling rate is one of the indicators for evaluating the water resistance of film materials. The lower the swelling rate, the higher the water resistance of the film, and the better the protection effect in food packaging.

[0094] From Figure 5 It can be seen that the light transmittance of the film decreases with the increase of the amount of TP added. When the amount of TP added is 1%, the composite film has completely shielded the middle wave ultraviolet light. It can be seen from the results that TP has strong ultraviolet blocking effect. The reason is that the aromatic ring structure contained in polyphenols has good ultraviolet absorption capacity. With the increase of the amount of TP added, the ability of the composite film to shield ultraviolet light is also enhanced.

[0095] Bacteriostatic rate test: standard colony counting method was used to determine the number of bacteria from Figure 6 It can be seen that the composite film has antibacterial activity against E. coli and S. aureus. Among them, the composite film with 2.5% TP has the highest bacteriostatic rate, with a bacteriostatic rate of 85.52% against E. coli and a bacteriostatic rate of 99.81% against S. aureus. The results show that the antibacterial performance of the composite film is enhanced with the increase of the content of TP.

[0096] Example 3: strawberry preservation experiment

[0097] 1. Fresh strawberries were divided into four groups: blank group, commercially available PE film group, CS / GEL composite film group and CS / GEL / 1.5% TP composite film group;

[0098] 2. The strawberries were placed in food-grade preservation boxes and covered with the films of each group, and stored at 25±2℃;

[0099] 3. The mass loss rate was determined and sensory evaluation was performed regularly;

[0100] 4. The results show that after 11 days, the mass loss rate of the CS / GEL / 1.5% TP composite film group is 15.27%, and the sensory score is the best, and the preservation effect is significant.

[0101] From Figure 7It can be seen that the mass loss rate of strawberries in each group increased with storage time. During storage, strawberry mass loss is a natural phenomenon, caused by aerobic respiration, and water volatilization also causes a decrease in strawberry mass. After 11 days of storage, the mass loss rate of the blank group reached 24.64%, the mass loss rate of the commercial PE film group reached 18.47%, the mass loss rate of the CS / GEL composite film group reached 16.27%, and the mass loss rate of the CS / GEL / 1.5% TP composite film group reached 15.27%. Therefore, the composite film with a 1.5% TP addition reduced strawberry mass loss compared to the blank group, the commercial PE film group, and the CS / GEL composite film group. This means that the CS / GEL / 1.5% TP composite film has a certain preservation effect, effectively reducing water evaporation from the strawberry surface, inhibiting respiration, and reducing water loss.

[0102] Figure 8 The sensory scoring test results for strawberries. Figure 9 It was found that the strawberries in the blank control group began to show rot spots on the 2nd day, began to rot and the calyx withered on the 4th day, began to grow mold, release water, and have an odor on the 8th day, and grew a large amount of mold and had a distinct rotten odor on the 10th day; the strawberries in the commercially available PE film group began to turn dark red locally on the 4th day, began to rot, a small amount of mold grew on the calyx, and had an odor on the 8th day, and grew a large amount of mold and had an obvious rotten odor on the 10th day; the CS / GEL composite film group showed 2-3 rot spots on the 4th day, the rot spots became larger, a small amount of mold grew on the calyx on the 8th day, and local mold and an odor appeared on the 10th day; the CS / GEL / 1.5% TP composite group had obvious effects in the preservation experiment, with 2-3 rot spots starting to appear on the 6th day, the calyx shrank, and the rot spots enlarged on the 10th day. Compared with other groups, the preservation effect was obvious, and the storage period of strawberries could be effectively extended by 4 days.

[0103] This study prepared chitosan / gelatin composite films with varying tea polyphenol addition levels and investigated their properties. The results showed that TP, CS, and GEL exhibited excellent film-forming properties, resulting in smooth, dense composite films. The addition of TP improved the composite film's water solubility and reduced its water content, swelling rate, and UV and visible light transmittance. Experiments revealed that a 1.5% TP addition resulted in the best overall performance, significantly enhancing UV shielding and reducing UV transmittance to 0.113%. The CS / GEL / 1.5% TP composite film exhibited excellent antibacterial properties, with antibacterial rates against E. coli and S. aureus reaching 73.34% and 99.78%, respectively. In a fresh-keeping experiment, the composite film coated with the CS / GEL / 1.5% TP composite film achieved the best sensory evaluation results and the lowest strawberry mass loss, effectively extending the storage life of strawberries by 4 days. Experiments show that the CS / GEL / TP composite film has a good application effect on the preservation of strawberries, which can extend the shelf life of strawberries and improve the sensory quality during storage.

Claims

1. A composite film containing chitosan-gelatin-tea polyphenols, characterized in that: The composite film comprises chitosan, gelatin, tea polyphenols, glycerol and glacial acetic acid; the mass percentage of the chitosan is 1.0-2.0%, the mass percentage of the gelatin is 0.5-1.5%, the mass percentage of the tea polyphenols is 0.5-2.5%, the mass percentage of the glycerol is 1-3%, the mass percentage of the glacial acetic acid is 0.5-2%, and the balance is water.

2. The composite membrane according to claim 1, characterized in that The mass percentage of the tea polyphenols is 1.5%.

3. A method for preparing the composite membrane according to claim 1 or 2, characterized in that: The method includes chitosan solution preparation, gelatin solution preparation, composite solution preparation and film casting.

4. The preparation method according to claim 3, characterized in that The preparation method is: (1) Preparation of chitosan solution: Disperse chitosan powder in deionized water, add glacial acetic acid solution, and stir until completely dissolved; (2) Prepare gelatin solution: Disperse gelatin powder in deionized water and stir at 40°C until completely dissolved; (3) Preparation of composite solution: chitosan solution and gelatin solution were mixed in a volume ratio of 3:2, glycerol was added, stirred evenly, and then divided into several portions, and tea polyphenols in different proportions were added to each portion, and stirred at 40°C until completely dissolved to obtain a composite solution; (4) Film casting: The composite solution was poured into a flat plate mold, allowed to stand for defoaming, dried at 60° C. for 24 hours, and the film was peeled off to obtain a composite film.

5. The preparation method according to claim 4, characterized in that The composite solution contains 1.0-2.0% chitosan, 0.5-1.5% gelatin, 0.5-2.5% tea polyphenols, 1-3% glycerol, 0.5-2% glacial acetic acid and the remainder is water.

6. The preparation method according to claim 4, characterized in that The mass percentage of the tea polyphenols is 1.5%.

7. Use of the composite film according to claim 1 or 2 or the composite film obtained by the preparation method according to any one of claims 3 to 5 in food preservation.

8. Use of the composite film according to claim 1 or 2 or the composite film obtained by the preparation method according to any one of claims 3 to 5 in food antibacterial treatment.

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