Composite preservative film as well as preparation method and application thereof

Abstract

The invention relates to the technical field of food packaging, and discloses a composite preservative film as well as a preparation method and application thereof. The composite preservative film comprises a pectin film layer and a chitosan film layer which are arranged up and down, the pectin film layer contains an additive, the chitosan film layer contains lignin, and the additive is anthocyanin and / or an anthocyanin silver ion compound. The method comprises the following steps that S1, under the condition that a solvent exists, pectin and an additive are mixed I, then a pectin film layer is prepared through a tape casting method, and the additive is anthocyanin and / or an anthocyanin silver ion compound; in the presence of a solvent, chitosan and lignin are mixed II, and a chitosan film layer is prepared through a tape casting method; and S2, compounding the pectin film layer and the chitosan film layer to prepare the composite preservative film. The composite preservative film has antibacterial activity on various food spoilage bacteria and is high in oxidation resistance.

Description

Technical Field

[0001] The present invention relates to the technical field of food packaging, and particularly relates to a composite fresh-keeping film and a preparation method and application thereof. Background Art

[0002] Fresh fruits maintain a high physiological activity after being picked. Especially for fruits with a large water content, they are more likely to rot and deteriorate, bringing great difficulties to storage and transportation.

[0003] Some existing fruit and vegetable fresh-keeping methods mostly use chemical substances for treatment to achieve fruit fresh-keeping. Therefore, chemical substances are likely to remain on the fruit surface, thus affecting the hygienic safety of the fruit. Most of the current fruit fresh-keeping films use perforations on the fresh-keeping film to achieve the respiration of fruits and vegetables. Due to the too large pores, the water of the fruits volatilizes too fast and loses water seriously, and the fresh-keeping and storage quality guarantee time is extremely short. The fruit fresh-keeping method by opening holes in the fresh-keeping film allows the fruits to directly contact the air, resulting in the fruits being easily affected by the oxygen in the air and accelerating ripening and rotting. How to reduce the loss during the storage of fresh fruits and extend the storage period is particularly important. Therefore, studying the fresh-keeping method of fresh fruits has important practical significance.

[0004] Currently, the basic film-forming raw materials studied at home and abroad are polysaccharides, proteins, and lipids. In recent years, biomass food fresh-keeping materials have attracted much attention due to their potential in the fresh-keeping application of fruits and vegetables. One promising biomass packaging material is polysaccharide polyelectrolyte packaging. These packaging materials can be used as carriers of natural active substances, such as antioxidants, antibacterial agents, etc. In polysaccharide polyelectrolyte packaging, chitosan and pectin are widely used in the fresh-keeping application of fruits and vegetables due to their good biocompatibility and physicochemical properties. However, the single packaging based on chitosan or pectin has a weak inhibitory effect on bacteria and cannot meet the requirements of fruit fresh-keeping. Moreover, the existing composite fresh-keeping films have poor antibacterial properties, resulting in the generation of antibacterial properties after the reproduction of bacteria and accelerating food spoilage. Summary of the Invention

[0005] The purpose of the present invention is to overcome the problem that the existing fresh-keeping film has a weak inhibitory effect on bacteria, and provide a composite fresh-keeping film and a preparation method and application thereof. The composite fresh-keeping film has good antibacterial properties and antioxidant properties.

[0006] To achieve the above purpose, in the first aspect of the present invention, a composite fresh-keeping film is provided. The composite fresh-keeping film includes a pectin film layer and a chitosan film layer arranged up and down. The pectin film layer contains additives, and the chitosan film layer contains lignin. The additives are anthocyanin and / or anthocyanin silver ion compound.

[0007] Preferably, in the chitosan film layer, the content of the lignin is 1-15 wt%, preferably 10-15 wt%.

[0008] More preferably, in the pectin film layer, the content of the additive is 10-15 wt%.

[0009] More preferably, the thickness ratio of the chitosan film layer to the pectin film layer is 1:1-3.

[0010] Preferably, in the anthocyanin silver ion compound, the mass ratio of the silver ion to the anthocyanin is 1:2-4.

[0011] More preferably, the silver ion is a nano silver ion.

[0012] More preferably, the preparation method of the anthocyanin silver ion compound includes: under alkaline conditions, bringing the anthocyanin solution into contact reaction with the silver ion solution.

[0013] Preferably, the pectin film layer and / or the chitosan film layer further contain a plasticizer and a stabilizer.

[0014] More preferably, the plasticizer is selected from at least one of glycerol, tributyl citrate, and acetyl tributyl citrate.

[0015] More preferably, the stabilizer is calcium carbonate and / or sorbitol.

[0016] The second aspect of the present invention provides a preparation method of a composite fresh-keeping film, and the method includes the following steps:

[0017] S1. In the presence of a solvent, mixing pectin and an additive in a first mixing and then obtaining a pectin film layer by a casting method, wherein the additive is anthocyanin and / or an anthocyanin silver ion compound;

[0018] In the presence of a solvent, mixing chitosan and lignin in a second mixing and then obtaining a chitosan film layer by a casting method;

[0019] S2. Composite the pectin film layer and the chitosan film layer to form a composite fresh-keeping film.

[0020] Preferably, in the chitosan film layer, the content of the lignin is 1-15 wt%, preferably 10-15 wt%.

[0021] More preferably, in the pectin film layer, the content of the additive is 10-15 wt%.

[0022] More preferably, the thickness ratio of the chitosan film layer to the pectin film layer is 1:1-3.

[0023] Preferably, the conditions for the first mixing at least include: pH of 13 - 14, temperature of 25 - 35°C, and time of 12 - 14 h;

[0024] The conditions for the second mixing at least include: pH of 2 - 3, temperature of 25 - 35°C, and time of 12 - 14 h.

[0025] Preferably, the method further includes adding a plasticizer and a stabilizer during the first mixing process and / or the second mixing process.

[0026] More preferably, the plasticizer is selected from at least one of glycerol, tributyl citrate, and triacetyl citrate.

[0027] More preferably, the stabilizer is calcium carbonate and / or sorbitol.

[0028] Preferably, the mass ratio of silver ions to anthocyanins in the silver ion anthocyanin compound is 1:2 - 4.

[0029] More preferably, the silver ions are nano - silver ions.

[0030] More preferably, the method for preparing the silver ion anthocyanin compound includes: carrying out a contact reaction between the anthocyanin solution and the silver ion solution under alkaline conditions.

[0031] The third aspect of the present invention provides the application of the composite fresh - keeping film described in the first aspect above or the composite fresh - keeping film prepared by the method described in the second aspect above in fruit fresh - keeping.

[0032] Through the above technical solutions, the present invention has the following beneficial effects:

[0033] (1) The composite fresh - keeping film provided by the present invention includes a pectin film layer and a chitosan film layer arranged up and down. The pectin film layer contains additives, and the chitosan film layer contains lignin. The additives are anthocyanins and / or silver ion anthocyanin compounds. Through the synergistic effect between the double - layer films, the composite fresh - keeping film has antibacterial activity against a variety of food spoilage bacteria, and has strong antioxidant performance, which can significantly improve the storage period. Further, it is found that the composite fresh - keeping film has good anti - ultraviolet shielding performance, gas - barrier and moisture - barrier properties, and is transparent and shiny.

[0034] (2) The preparation process of the composite fresh - keeping film of the present invention is simple in operation, convenient to use, has sufficient raw material supply, is easy to promote and apply, has a very broad application prospect, and is easy to be compounded with other fresh - keeping methods to achieve better effects. Description of the Drawings

[0035] Figure 1 It is a comparative diagram of the tensile strength and elongation at break of the pectin / chitosan double - layer films prepared in Preparation Examples 2 and 3 of the present invention;

[0036] Figure 2 This is the comparative Fourier transform infrared spectroscopy (FT-IR) diagram of the composite fresh-keeping film prepared in Example 1 of the present invention;

[0037] Figure 3 This is the comparative ultraviolet spectrum diagram of the composite fresh-keeping film prepared in Example 1 of the present invention;

[0038] Figure 4 This is the application diagram of the composite fresh-keeping film prepared in Example 1 of the present invention on cherries. Detailed implementation manners

[0039] In the ranges disclosed herein, the endpoints and any values are not limited to the exact ranges or values. These ranges or values should be understood to include values close to these ranges or values. For numerical ranges, between the endpoint values of each range, between the endpoint values of each range and individual point values, and between individual point values, they can be combined with each other to obtain one or more new numerical ranges, and these numerical ranges should be regarded as specifically disclosed herein.

[0040] The first aspect of the present invention provides a composite fresh-keeping film, which includes a pectin film layer and a chitosan film layer arranged up and down. The pectin film layer contains additives, and the chitosan film layer contains lignin. The additives are anthocyanins and / or anthocyanin silver ion compounds.

[0041] During the research on composite fresh-keeping films, the inventors of the present invention unexpectedly found that by using a pectin film layer and a chitosan film layer arranged up and down, the pectin film layer contains additives, the chitosan film layer contains lignin, and the additives are anthocyanins or anthocyanin silver ion compounds. Through the synergistic effect between the double layers of the film, the composite fresh-keeping film has good gas and moisture barrier properties, is transparent and shiny, has antibacterial activity against a variety of food spoilage bacteria, and has strong antioxidant properties, which can significantly improve the storage period.

[0042] According to the present invention, preferably, in the chitosan film layer, the content of lignin is 1-15 wt%, specifically it can be 1 wt%, 5 wt%, 10 wt%, 15 wt%, or any value between the above two values. More preferably, it is 10-15 wt%, specifically it can be 10 wt%, 12 wt%, 15 wt%, or any value between the above two values. The inventors found that when the above preferred implementation manner is adopted, the antibacterial activity of the composite fresh-keeping film against a variety of food spoilage bacteria can be further improved, and the antioxidant property of the composite fresh-keeping film can be further improved.

[0043] According to the present invention, further preferably, in the pectin film layer, the content of the additive is 10-15 wt%, specifically it can be 10 wt%, 13 wt%, 15 wt%, or any value between the above two values. The inventors found that when the above preferred embodiment is adopted, the antibacterial activity of the composite fresh-keeping film against various food spoilage bacteria can be further improved, and the antioxidant performance of the composite fresh-keeping film can be further improved.

[0044] According to the present invention, preferably, the mass ratio of silver ions to the anthocyanin in the silver ion anthocyanin compound is 1:2-4, specifically it can be 1:2, 1:3, 1:4, or any value between the above two ratios. The inventors found that when the above preferred embodiment is adopted, the antibacterial activity of the composite fresh-keeping film against various food spoilage bacteria can be further improved, and the antioxidant performance of the composite fresh-keeping film can be further improved.

[0045] According to the present invention, further preferably, the thickness ratio of the chitosan film layer to the pectin film layer is 1:1-3, specifically it can be 1:1, 1:2, 1:3, or any value between the above two values. The inventors found that when the above preferred embodiment is adopted, the antibacterial activity of the composite fresh-keeping film against various food spoilage bacteria can be further improved, and the antioxidant performance of the composite fresh-keeping film can be further improved.

[0046] According to the present invention, further preferably, the silver ions are nano silver ions. The inventors found that when the above preferred embodiment is adopted, the antibacterial activity of the composite fresh-keeping film against various food spoilage bacteria can be further improved, and the antioxidant performance of the composite fresh-keeping film can be further improved.

[0047] According to the present invention, further preferably, the preparation method of the silver ion anthocyanin compound includes: under alkaline conditions, bringing the anthocyanin solution into contact reaction with the silver ion solution. The alkaline conditions can use a commonly used alkali solution in the art as a solvent to construct an alkaline environment. The alkali solution is selected from at least one of sodium hydroxide solution, potassium hydroxide solution, and ammonia water solution. The anthocyanin and silver ions are dissolved in the same alkaline solution, or the anthocyanin and silver ions can be dissolved in different alkaline solutions. Further preferably, the anthocyanin is dissolved in sodium hydroxide solution to form an anthocyanin solution, and the mass concentration of sodium hydroxide in the solution is 5-6% (W / V), and the mass concentration of anthocyanin is 4-7% (W / V). Exemplarily, 0.25-0.35 g of anthocyanin can be dissolved in 5-6 mL of NaOH solution (5-6% W / V), and ultrasonic treatment is performed to obtain solution A. The silver ions are dissolved in ammonia water to form a silver ion solution, and the concentration of silver ions in the solution is 8-10 mg / mL. Exemplarily, under magnetic stirring, in 10-12 mL of AgNO3 solution (80-85 mM Ag +Slowly add 5 - 6 mL (0.175 - 0.18 g / mL) of NH₃·H₂O to obtain Solution B.

[0048] As a relatively preferred embodiment of the present invention, the following method can be used to prepare the anthocyanin silver ion compound:

[0049] Dissolve 0.25 - 0.35 g of anthocyanin in 5 - 6 mL of NaOH solution (5 - 6% W / V), and perform ultrasonic treatment to obtain Solution A; subsequently, slowly add 5 - 6 mL (0.175 - 0.18 g / mL) of NH₃·H₂O to 10 - 12 mL of AgNO₃ solution (80 - 85 mM Ag + ) to obtain Solution B; then slowly add Solution A to Solution B, and stir magnetically for 1 - 2 h. Finally, dialyze the product in deionized water for 72 - 80 h and make up the volume to 100 mL with ionized water.

[0050] Auxiliaries can also be added to the composite fresh - keeping film of the present invention. The present invention has no strict restrictions on the auxiliaries, and plasticizers, stabilizers, antioxidants, etc. can be added according to the conventional methods in the art; preferably, the pectin film layer and / or the chitosan film layer also contain plasticizers and stabilizers. The inventors found that when the above - mentioned preferred embodiment is adopted, the antibacterial activity of the composite fresh - keeping film against various food spoilage bacteria can be further improved, and the antioxidant performance of the composite fresh - keeping film can be further improved.

[0051] According to the present invention, further preferably, the plasticizer is selected from at least one of glycerol, tributyl citrate, and acetyl tributyl citrate. More preferably, the glycerol is a glycerol solution with a mass concentration of 20 - 25 wt%, specifically 20 wt%, 21 wt%, 22 wt%, 23 wt%, 24 wt%, 25 wt%, or any value between the above two values. The inventors found that when the above - mentioned preferred embodiment is adopted, the antibacterial activity of the composite fresh - keeping film against various food spoilage bacteria can be further improved, and the antioxidant performance of the composite fresh - keeping film can be further improved.

[0052] According to the present invention, further preferably, the stabilizer is calcium carbonate and / or sorbitol. More preferably, the calcium carbonate is a calcium carbonate solution with a mass concentration of 1 - 2 wt%, specifically 1 wt%, 1.5 wt%, 2 wt%, or any value between the above two values. The inventors found that when the above - mentioned preferred embodiment is adopted, the antibacterial activity of the composite fresh - keeping film against various food spoilage bacteria can be further improved, and the antioxidant performance of the composite fresh - keeping film can be further improved.

[0053] The second aspect of the present invention provides a method for preparing a composite fresh - keeping film, and the method includes the following steps:

[0054] S1. In the presence of a solvent, pectin and an additive are mixed I and then a pectin film layer is prepared by a casting method. The additive is anthocyanin and / or an anthocyanin silver ion compound;

[0055] In the presence of a solvent, chitosan and lignin are mixed II and then a chitosan film layer is prepared by a casting method;

[0056] S2. The pectin film layer and the chitosan film layer are compounded to form a composite fresh-keeping film.

[0057] The inventors found that for the pectin film layer and the chitosan film layer arranged up and down prepared by the above method, the pectin film layer contains an additive, the chitosan film layer contains lignin, and the additive is anthocyanin and / or an anthocyanin silver ion compound. Through the synergistic effect between the double layers of films, the composite fresh-keeping film has antibacterial activity against a variety of food spoilage bacteria, and has strong antioxidant performance, which can significantly improve the storage period.

[0058] The present invention does not strictly limit the specific process of the casting method, and it can be carried out according to the methods commonly used in the art. Exemplarily, a multi-layer casting method can be adopted. Before preparing the composite fresh-keeping film by the multi-layer casting method, the prepared film solution can be ultrasonically treated to remove the gas in the film solution. The composite fresh-keeping film can be stored in a dryer with a relative humidity of 50 - 55% and a temperature of 25 - 30°C for at least 48 hours and then used.

[0059] The present invention does not strictly limit the solvent used in the preparation method, and solvents commonly used in the art can be adopted. For example, the solvent can be an acetic acid solution and / or water. Preferably, the volume ratio of acetic acid in the acetic acid solution is 2 - 3% (V / V).

[0060] The present invention also does not strictly limit the mixing order. Chitosan can be dissolved in the solvent and then mixed with lignin; or pectin can be dissolved in the solvent and then mixed with the additive. In order to make the solution mixing more uniform, heating, shaking, and stirring can be used to accelerate dissolution.

[0061] In the present invention, both chitosan and pectin are biological macromolecules, and light may trigger photochemical reactions in them. Taking chitosan as an example, some chemical bonds in its molecular structure may break under the action of light, resulting in the degradation of chitosan, and thus changing its molecular weight and chemical properties. This will not only affect the film-forming performance of chitosan, such as the strength and flexibility of the film, but may also affect the subsequent experimental or application effects. For pectin, light may also cause oxidation, decomposition and other reactions, destroying the molecular structure of pectin and affecting the stability of the pectin solution and the film-forming characteristics. Preferably, the above preparation process is carried out and reacted under light-proof conditions. The inventors have found that when the above preferred implementation mode is adopted, the antibacterial activity of the composite fresh-keeping film against a variety of food spoilage bacteria can be further improved, and the antioxidant performance of the composite fresh-keeping film can be further improved.

[0062] According to the present invention, preferably, in the chitosan film layer, the content of lignin is 1-15 wt%, specifically it can be 1 wt%, 5 wt%, 10 wt%, 15 wt%, or any value between the above two values. More preferably, it is 10-15 wt%, specifically it can be 10 wt%, 12 wt%, 15 wt%, or any value between the above two values. The inventors have found that when the above preferred implementation mode is adopted, the antibacterial activity of the composite fresh-keeping film against a variety of food spoilage bacteria can be further improved, and the antioxidant performance of the composite fresh-keeping film can be further improved.

[0063] According to the present invention, further preferably, in the pectin film layer, the content of the additive is 10-15 wt%, specifically it can be 10 wt%, 13 wt%, 15 wt%, or any value between the above two values. The inventors have found that when the above preferred implementation mode is adopted, the antibacterial activity of the composite fresh-keeping film against a variety of food spoilage bacteria can be further improved, and the antioxidant performance of the composite fresh-keeping film can be further improved.

[0064] According to the present invention, preferably, the conditions for the first mixing at least include: the pH is 13 - 14, and the specific pH value can be 13, 13.5, 14, or any value between the above two values; the temperature is 25 - 35 °C, and the specific temperature can be 25 °C, 30 °C, 35 °C, or any value between the above two values; the time is 12 - 14 h, and the specific time can be 12 h, 13 h, 14 h, or any value between the above two values; the conditions for the second mixing at least include: the pH is 2 - 3, and the specific pH value can be 2, 2.5, 3, or any value between the above two values; the temperature is 25 - 35 °C, and the specific temperature can be 25 °C, 30 °C, 35 °C, or any value between the above two values; the time is 12 - 14 h, and the specific time can be 12 h, 13 h, 14 h, or any value between the above two values. The alkaline environment can be obtained by dissolving the raw materials in an alkaline solution; the acidic environment can be obtained by dissolving the raw materials in an acidic solution; for example, chitosan can be dissolved in an acetic acid solution with a volume concentration of 2 - 3% (V / V). The inventors found that when the above preferred embodiments are adopted, the antibacterial activity of the composite fresh-keeping film against various food spoilage bacteria can be further improved, and the antioxidant performance of the composite fresh-keeping film can be further improved.

[0065] According to the present invention, preferably, the method further includes adding a plasticizer and a stabilizer during the first mixing process and / or the second mixing process. Specifically, a plasticizer and a stabilizer can be added during both the first mixing and the second mixing processes; or only a plasticizer and a stabilizer are added during the first mixing process; or only a plasticizer and a stabilizer are added during the second mixing process. The inventors found that when the above preferred embodiments are adopted, the antibacterial activity of the composite fresh-keeping film against various food spoilage bacteria can be further improved, and the antioxidant performance of the composite fresh-keeping film can be further improved.

[0066] According to the present invention, more preferably, the plasticizer is selected from at least one of glycerol, tributyl citrate, and acetyl tributyl citrate. The inventors found that when the above preferred embodiments are adopted, the antibacterial activity of the composite fresh-keeping film against various food spoilage bacteria can be further improved, and the antioxidant performance of the composite fresh-keeping film can be further improved.

[0067] According to the present invention, more preferably, the stabilizer is calcium carbonate and / or sorbitol. Specifically, only calcium carbonate can be added, or only sorbitol can be added, or both calcium carbonate and sorbitol can be added. The inventors found that when the above preferred embodiments are adopted, the antibacterial activity of the composite fresh-keeping film against various food spoilage bacteria can be further improved, and the antioxidant performance of the composite fresh-keeping film can be further improved.

[0068] According to the present invention, preferably, the mass ratio of silver ions to anthocyanins in the silver ion anthocyanin compound is 1:2 - 4, specifically it can be 1:2, 1:3, 1:4, or any value between the above two ratios. The inventors found that when the above preferred implementation mode is adopted, the antibacterial activity of the composite fresh-keeping film against various food spoilage bacteria can be further improved, and the antioxidant performance of the composite fresh-keeping film can be further improved.

[0069] According to the present invention, further preferably, the thickness ratio of the chitosan film layer to the pectin film layer is 1:1 - 3, specifically it can be 1:1, 1:2, 1:3, or any value between the above two values. The inventors found that when the above preferred implementation mode is adopted, the antibacterial activity of the composite fresh-keeping film against various food spoilage bacteria can be further improved, and the antioxidant performance of the composite fresh-keeping film can be further improved.

[0070] According to the present invention, further preferably, the silver ions are nano silver ions. The inventors found that when the above preferred implementation mode is adopted, the antibacterial activity of the composite fresh-keeping film against various food spoilage bacteria can be further improved, and the antioxidant performance of the composite fresh-keeping film can be further improved.

[0071] According to the present invention, further preferably, the preparation method of the silver ion anthocyanin compound includes: under alkaline conditions, bringing the anthocyanin solution and the silver ion solution into contact reaction. The alkaline conditions can use a commonly used alkali solution in the art as a solvent to construct an alkaline environment. The alkali solution is selected from at least one of sodium hydroxide solution, potassium hydroxide solution, and ammonia water solution. Anthocyanins and silver ions are dissolved in the same alkaline solution, or anthocyanins and silver ions can be dissolved in different alkaline solutions. Further preferably, the anthocyanins are dissolved in sodium hydroxide solution to form an anthocyanin solution, and the mass concentration of sodium hydroxide in the solution is 5 - 6% (W / V), and the mass concentration of anthocyanins is 4 - 7% (W / V). Exemplarily, 0.25 - 0.35 g of anthocyanins can be dissolved in 5 - 6 mL of NaOH solution (5 - 6% W / V), and ultrasonic treatment is performed to obtain solution A. The silver ions are dissolved in ammonia water to form a silver ion solution, and the concentration of silver ions in the solution is 8 - 10 mg / mL. Exemplarily, 5 - 6 mL (0.175 - 0.18 g / mL) of NH3·H2O is slowly added to 10 - 12 mL of AgNO3 solution (80 - 85 mM Ag + ) under magnetic stirring to obtain solution B.

[0072] As a relatively preferred implementation mode of the present invention, the following method can be used to prepare the silver ion anthocyanin compound:

[0073] Dissolve 0.25 - 0.35 g of anthocyanin in 5 - 6 mL of NaOH solution (5 - 6% W / V), and obtain solution A by ultrasonic treatment. Subsequently, slowly add 5 - 6 mL (0.175 - 0.18 g / mL) of NH3·H2O to 10 - 20 mL of AgNO3 solution (80 - 85 mM Ag + ), and obtain solution B. Then slowly add solution A to solution B, and stir magnetically for 1 h. Finally, dialyze the product in deionized water for 72 - 80 h and make up the volume to 100 mL with ionized water.

[0074] The third aspect of the present invention provides the application of the composite fresh-keeping film described in the first aspect above or the composite fresh-keeping film prepared by the method described in the second aspect above in fruit fresh-keeping.

[0075] In addition to the above applications, the composite fresh-keeping film provided by the present invention can also be applied to the packaging of disinfection utensils, vegetables and seafood, inhibit the growth of bacteria, and extend the fresh-keeping period. Immerse fresh fruits in the composite film solution, take them out and air-dry quickly, or spray the composite film solution onto the surface of fresh fruits and air-dry quickly to form a composite film.

[0076] The present invention will be described in detail below through examples.

[0077] In the following examples, chitosan, lignin, anthocyanin, glycerol, acetic acid, calcium carbonate are all provided by Sinopharm Chemical Reagent Co., Ltd. (Shanghai); pectin is purchased from Yantai Andeli Pectin Co., Ltd.; Staphylococcus aureus and Escherichia coli are purchased from Ningbo Mingzhou Biotechnology Co., Ltd. The experimental methods used are all conventional methods unless otherwise specified, and the materials, reagents, etc. used can be obtained from commercial channels unless otherwise specified.

[0078] The composition of the culture medium (solid culture medium) used in the following test examples is as follows:

[0079] Staphylococcus aureus growth medium: 3 g / L of beef extract, 10 g / L of peptone, 5 g / L of sodium chloride and 1000 mL of distilled water;

[0080] Escherichia coli growth medium LB: 5 g / L of yeast extract, 10 g / L of peptone, 10 g / L of sodium chloride and 1000 mL of distilled water.

[0081] Test on the addition amount of plasticizer

[0082] S1. Under the condition of water bath heating at 50 °C, dissolve 2 g of pectin in 100 mL of distilled water, and then stir in the dark for 12 h at 25 °C to obtain a pectin solution, abbreviated as P; divide 100 mL of the pectin solution into 4 equal parts, and add glycerol with mass fractions of 0%, 10%, 20% and 40% (W / V) as plasticizers respectively. After adding the plasticizer, ultrasonically treat for 30 min to remove the bubbles in the solution for standby;

[0083] Under the condition of water bath heating at 50 °C, dissolve 2 g of chitosan in 100 mL of acetic acid aqueous solution with a volume concentration of 2% (V / V), and then stir in the dark for 12 h at 25 °C to obtain a chitosan solution, abbreviated as C; divide 100 mL of the chitosan solution into 4 equal parts, and divide 100 mL of the pectin solution into 4 equal parts, and add glycerol with mass fractions of 0%, 10%, 20% and 40% (W / V) as plasticizers respectively. After adding the plasticizer, ultrasonically treat for 30 min to remove the bubbles in the solution for standby;

[0084] S2. Pour 4 portions of the chitosan solution into the corresponding molds, transfer the molds to an incubator at 45 °C for drying to make chitosan films; then pour 4 portions of the pectin solution onto the corresponding chitosan films with mass fractions of 0%, 10%, 20% and 40% glycerol (W / V) respectively, and put them into the incubator at 45 °C again for drying for 14 h to demold, and obtain pectin / chitosan bilayer films, abbreviated as P / C films.

[0085] Store the prepared pectin / chitosan bilayer films in a dryer with a relative humidity of 50% and a temperature of 25 °C for 48 h, and then conduct mechanical property tests and optical property detections. The test methods are conventional detection methods in this field. The test results are shown in Table 1 and Figure 1 as follows.

[0086] Table 1

[0087]

[0088]

[0089] As can be seen from Table 1, adding glycerol will change the tensile strength (TS) and elongation at break (EAB) of the pectin / chitosan bilayer films. When 20% of glycerol is added, the mechanical properties of the pectin / chitosan bilayer films are the best.

[0090] Test on the addition amount of stabilizer

[0091] S1. Under the condition of water bath heating at 50 °C, dissolve 2 g of pectin in 100 mL of distilled water, and then stir in the dark for 12 h at 25 °C to obtain a pectin solution, abbreviated as P; divide 100 mL of the pectin solution into 5 equal parts, add glycerol with a mass concentration of 20% as a plasticizer respectively, and then add calcium carbonate with mass fractions of 0%, 1%, 1.5%, 2%, and 5% (W / V) as a stabilizer respectively to increase the mechanical strength of the film. After adding calcium carbonate, ultrasonically treat for 30 min to remove the bubbles in the solution for standby;

[0092] Under the condition of water bath heating at 50 °C, dissolve 2 g of chitosan in 100 mL of acetic acid aqueous solution with a volume concentration of 2% (V / V), and then stir in the dark for 12 h at 25 °C to obtain a chitosan solution, abbreviated as C; divide 100 mL of the chitosan solution into 5 equal parts, add glycerol with a mass concentration of 20% as a plasticizer respectively, and then add calcium carbonate with mass fractions of 0%, 1%, 1.5%, 2%, and 5% (W / V) as a stabilizer respectively to increase the mechanical strength of the film. After adding calcium carbonate, ultrasonically treat for 30 min to remove the bubbles in the solution for standby;

[0093] S2. Pour 5 portions of the chitosan solution into the corresponding molds, transfer the molds to an incubator at 45 °C to dry to form chitosan films; then pour 5 portions of the pectin solution onto the corresponding chitosan films with mass fractions of 0%, 1%, 1.5%, 2%, and 5% calcium carbonate respectively, and add calcium carbonate with mass fractions of 0%, 1%, 1.5%, 2%, and 5% (W / V) as a stabilizer respectively. Put them into the incubator at 45 °C again to dry for 14 h and then demold to obtain pectin / chitosan bilayer films, abbreviated as P / C films.

[0094] Store the prepared pectin / chitosan bilayer films in a dryer with a relative humidity of 50% and a temperature of 25 °C for 48 hours, and then conduct mechanical property tests and optical property detections. The test methods are conventional detection methods in this field. The test results are shown in Table 2 and Figure 1 as follows.

[0095] Table 2

[0096] Calcium carbonate content Light transmittance Tensile strength Elongation at break 0％ 87.23 60.15 6.64％ 1％ 87.47 63.77 6.86％ 1.5％ 87.92 74.92 7.20％ 2％ 87.60 70.18 7.17％ 5％ 87.50 68.89 6.41％

[0097] As can be seen from Table 2, adding calcium carbonate will change the tensile strength (TS) and elongation at break (EAB) of the pectin / chitosan bilayer films. For different calcium carbonate addition amounts, the mechanical properties of the pectin / chitosan bilayer film with 1.5% calcium carbonate added are the best.

[0098] Preparation Example 1

[0099] Preparation of anthocyanin-silver nanoion compound solution

[0100] Dissolve 0.25 g of anthocyanin in 5 mL of NaOH solution (5% W / V), and obtain solution A by ultrasonic treatment. Subsequently, slowly add 5 mL (0.175 g / mL) of NH₃·H₂O to 10 mL of AgNO₃ solution (80 mM Ag + ) to obtain solution B. Then slowly add solution A to solution B and stir magnetically for 1 h. Finally, put the product into a dialysis bag with a molecular weight cut-off of 3000 D and dialyze it in deionized water for 72 h, changing the water every 4 h. Transfer the product in the dialysis bag to a 100 mL volumetric flask, make up the volume with ionic water, and use atomic absorption spectrometry (AAS) combined with HPLC to determine that the concentration of the anthocyanin-silver ion compound in the made-up solution is about 0.45 g / mL, and the mass ratio of silver ions to the anthocyanin is 1:2.

[0101] Preparation Example 2

[0102] Preparation of anthocyanin-silver ion compound solution

[0103] Dissolve 0.5 g of anthocyanin in 10 mL of NaOH solution (5% W / V), and obtain solution A by ultrasonic treatment. Subsequently, slowly add 5 mL (0.175 g / mL) of NH₃·H₂O to 10 mL of AgNO₃ solution (80 mM Ag + ) to obtain solution B. Then slowly add solution A to solution B and stir magnetically for 1 h. Finally, put the product into a dialysis bag with a molecular weight cut-off of 3000 D and dialyze it in deionized water for 72 h, changing the water every 4 h. Transfer the product in the dialysis bag to a 100 mL volumetric flask, make up the volume with ionic water, and use atomic absorption spectrometry (AAS) combined with HPLC to determine that the concentration of the anthocyanin-silver ion compound in the made-up solution is about 0.53 g / mL, and the mass ratio of silver ions to the anthocyanin is 1:3.

[0104] Preparation Example 3

[0105] Preparation of anthocyanin-silver ion compound solution

[0106] Dissolve 1 g of anthocyanin in 15 mL of NaOH solution (5% W / V), and obtain solution A by ultrasonic treatment. Subsequently, slowly add 5 mL (0.175 g / mL) of NH₃·H₂O to 10 mL of AgNO₃ solution (80 mM Ag +5 mL (0.175 g / mL) of NH3·H2O was slowly added to [the solution] to obtain Solution B. Then Solution A was slowly added to Solution B, and magnetic stirring was carried out for 1 h. Finally, the product was placed in a dialysis bag with a molecular weight cut-off of 3000 D and dialyzed in deionized water for 72 h, with the water changed every 4 h. The product in the dialysis bag was transferred to a 100 mL volumetric flask, made up to the mark with ionic water, and the concentration of the anthocyanin-silver ion compound in the made-up solution was determined to be approximately 0.59 g / mL by atomic absorption spectrometry (AAS) combined with HPLC. The mass ratio of silver ions to the anthocyanin was 1:4.

[0107] Preparation Example 4

[0108] The anthocyanin-silver ion compound solution was prepared according to the method of Preparation Example 1, except that the silver nitrate providing the nano silver ions was replaced with silver ion powder providing ordinary silver ions, and the silver ion powder was purchased from Shanghai Macklin Biochemical Co., Ltd.

[0109] Example 1

[0110] S1. Under the condition of water bath heating at 50 °C, 2 g of pectin was dissolved in 100 mL of distilled water and then mixed with 5 mL of the anthocyanin-nano silver ion compound solution prepared in Preparation Example 1, and dark stirring was carried out at 25 °C for 12 h to obtain a pectin anthocyanin-nano silver ion solution (2%, W / V), abbreviated as PG; 20% by mass of glycerol was added as a plasticizer and 1.5% by mass of calcium carbonate was added as a stabilizer (W / V). After adding calcium carbonate, ultrasonic treatment was carried out for 30 min to remove the bubbles in the solution for standby;

[0111] Under the condition of water bath heating at 50 °C, 2 g of chitosan was dissolved in 100 mL of acetic acid solution with a volume concentration of 2% (V / V). 100 mL of the chitosan solution was added with 15% by mass of lignin (W / V). Dark stirring was carried out at 25 °C for 12 h to obtain a chitosan lignin solution, abbreviated as CL; 20% by mass of glycerol was added as a plasticizer and 1.5% by mass of calcium carbonate was added as a stabilizer (W / V) to the chitosan lignin solution. After adding calcium carbonate, ultrasonic treatment was carried out for 30 min to remove the bubbles in the solution for standby;

[0112] S2. 20 mL of the chitosan solution was poured into a mold with a specification of 10×10 cm, and the mold was transferred to an incubator at 45 °C for drying to form a chitosan film; then 20 mL of the pectin solution was poured onto the chitosan film, and it was placed in an incubator at 45 °C again for drying for 14 h and then demolded to obtain a composite fresh-keeping film, abbreviated as PG / CL film. The thickness ratio of the chitosan film layer to the pectin film layer was 1:1.

[0113] The prepared composite fresh-keeping film was stored in a desiccator with a relative humidity of 50% and a temperature of 25 °C for 48 hours, and then its performance was tested.

[0114] Example 2

[0115] The composite fresh-keeping film was prepared according to the method of Example 1, except that the mass fraction of lignin added to the chitosan solution in step S1 was 10%.

[0116] Example 3

[0117] The composite fresh-keeping film was prepared according to the method of Example 1, except that the mass fraction of lignin added to the chitosan solution in step S1 was 5%.

[0118] Example 4

[0119] The composite fresh-keeping film was prepared according to the method of Example 1, except that the mass fraction of lignin in the chitosan solution in step S1 was 1%.

[0120] Example 5

[0121] S1. Under the condition of water bath heating at 50 °C, 2 g of pectin was dissolved in 100 mL of distilled water and then mixed with 5 mL of the anthocyanin-nanosilver ion compound solution prepared in Preparation Example 2, and stirred in the dark for 13 h at 30 °C to obtain a pectin anthocyanin-nanosilver ion solution (2%, W / V), abbreviated as PG; 20% by mass of tributyl citrate was added as a plasticizer and 1.5% by mass of calcium carbonate was added as a stabilizer (W / V). After adding calcium carbonate, ultrasonic treatment was carried out for 30 min to remove the bubbles in the solution for standby;

[0122] Under the condition of water bath heating at 50 °C, 2 g of chitosan was dissolved in 100 mL of acetic acid solution with a volume concentration of 2% (V / V). 100 mL of the chitosan solution was added with lignin with a mass fraction of 15% lignin, and stirred in the dark for 13 hours at 25 °C to obtain a chitosan lignin solution, abbreviated as CL; 20% by mass of tributyl citrate was added as a plasticizer and 1.5% by mass of calcium carbonate was added as a stabilizer (W / V) to the chitosan lignin solution. After adding calcium carbonate, ultrasonic treatment was carried out for 30 min to remove the bubbles in the solution for standby;

[0123] S2. 20 mL of the chitosan solution was poured into a mold with a specification of 10×10, and the mold was transferred to an incubator at 40 °C for drying to form a chitosan film; then 40 mL of the pectin solution was poured onto the chitosan film, and it was put into an incubator at 45 °C again for drying for 14 h and demolded to obtain a composite fresh-keeping film, abbreviated as PG / CL film. The thickness ratio of the chitosan film layer to the pectin film layer is 1:2.

[0124] The prepared composite fresh-keeping film was stored in a desiccator with a relative humidity of 50% and a temperature of 30 °C for 48 hours, and then its performance was tested.

[0125] Example 6

[0126] S1. Under the condition of water bath heating at 50 °C, 2 g of pectin was dissolved in 100 mL of distilled water, and then mixed with 5 mL of the anthocyanin-nanosilver ion compound solution prepared in Preparation Example 3. The mixture was stirred in the dark at 35 °C for 14 h to obtain a pectin anthocyanin-nanosilver ion solution (2%, W / V), abbreviated as PG. Glycerol with a mass fraction of 20% was added as a plasticizer and sorbitol with a mass fraction of 1.5% was added as a stabilizer (W / V). After adding sorbitol, the solution was ultrasonically treated for 30 min to remove the bubbles in the solution for standby;

[0127] Under the condition of water bath heating at 50 °C, 2 g of chitosan was dissolved in 100 mL of acetic acid solution with a volume concentration of 2% (V / V). 100 mL of the chitosan solution was added with lignin with a mass fraction of 15%. The mixture was stirred in the dark at 25 °C for 14 hours to obtain a chitosan lignin solution, abbreviated as CL. Glycerol with a mass fraction of 20% was added as a plasticizer and sorbitol with a mass fraction of 1.5% was added as a stabilizer (W / V) to the chitosan lignin solution. After adding sorbitol, the solution was ultrasonically treated for 30 min to remove the bubbles in the solution for standby;

[0128] S2. 20 mL of the chitosan solution was poured into a mold with a specification of 10×10, and the mold was transferred to an incubator at 45 °C for drying to form a chitosan film; then 60 mL of the pectin solution was poured onto the chitosan film, and it was put into the incubator at 45 °C again for drying for 14 h and then demolded to obtain a composite fresh-keeping film, abbreviated as PG / CL film. The thickness ratio of the chitosan film layer to the pectin film layer is 1:3.

[0129] The prepared composite fresh-keeping film was stored in a desiccator with a relative humidity of 50% and a temperature of 25 °C for 48 hours, and then its performance was tested.

[0130] Example 7

[0131] The composite fresh-keeping film was prepared according to the method of Example 1, except that the anthocyanin-nanosilver ion compound solution prepared in Preparation Example 1 was replaced with anthocyanin.

[0132] Example 8

[0133] The composite fresh-keeping film was prepared according to the method of Example 1, except that the anthocyanin-nanosilver ion compound solution prepared in Preparation Example 1 was replaced with the anthocyanin-silver ion compound solution prepared in Preparation Example 4.

[0134] Example 9

[0135] Prepare a composite fresh-keeping film according to the method of Example 1, except that the thickness ratio of the chitosan film layer to the pectin film layer is 1:0.5.

[0136] Comparative Example 1

[0137] Prepare a double-layer film according to the method of Example 1, except that anthocyanin is not added to the pectin solution, abbreviated as P / CL.

[0138] Comparative Example 2

[0139] Prepare a double-layer film according to the method of Example 1, except that lignin is not added to the chitosan solution, abbreviated as PG / C.

[0140] Comparative Example 3

[0141] S1. Under the condition of water bath heating at 50 °C, dissolve 2 g of pectin in 100 mL of distilled water, then stir darkly at 25 °C for 12 h to obtain a pectin solution; add glycerol with a mass fraction of 20% as a plasticizer (W / V) to 100 mL of the pectin solution, and then add an aqueous solution of calcium carbonate with a mass fraction of 1.5% as a stabilizer (W / V) to increase the mechanical strength of the film. After adding calcium carbonate, ultrasonically treat for 30 min to remove the bubbles in the solution for standby;

[0142] Under the condition of water bath heating at 50 °C, dissolve 2 g of chitosan in 100 mL of acetic acid aqueous solution with a volume concentration of 2% (V / V), then stir darkly at 25 °C for 12 h to obtain a chitosan solution; add glycerol with a mass fraction of 20% as a plasticizer (W / V) to 100 mL of the chitosan solution, and then add an aqueous solution of calcium carbonate with a mass fraction of 1.5% as a stabilizer (W / V) to increase the mechanical strength of the film. After adding calcium carbonate, ultrasonically treat for 30 min to remove the bubbles in the solution for standby;

[0143] S2. Pour 20 mL of the chitosan solution into the corresponding mold, transfer the mold to an incubator at 45 °C to dry to form a chitosan film; then pour 20 mL of the pectin solution onto the chitosan film, and put it into the incubator at 45 °C again to dry for 14 h and demold to obtain a pectin / chitosan double-layer film, abbreviated as P / C film.

[0144] Comparative Example 4

[0145] Prepare a double-layer film according to the method of Example 1, except that lignin is added to the pectin film layer and an anthocyanin silver ion compound is added to the chitosan film layer.

[0146] Test Example 1

[0147] The composite fresh-keeping films and double-layer films prepared in the examples and comparative examples were put into a Fourier transform infrared detector for detection to obtain the corresponding Fourier transform infrared detection spectrograms, as specifically shown in Figure 2 . Through Figure 2 It can be seen that compared with the double-layer film of the comparative example, the absorption peak related to hydrogen bond in the composite fresh-keeping film containing anthocyanin-nano silver ions did not show an obvious shift, indicating that the addition of anthocyanin-nano silver ions had no effect on the degree of association of hydroxyl groups in the composite fresh-keeping film. With the increase of the lignin content, the positions of the absorption peaks of the composite fresh-keeping film were different between the spectral bands, but no new peaks appeared in the spectral bands, indicating that the addition of lignin did not change the structure of the film matrix. Therefore, the spectral band changes in the Fourier transform infrared (FT-IR) spectrum indicate that anthocyanin-nano silver ions and lignin are embedded in the pectin / chitosan matrix through intermolecular hydrogen bond interactions.

[0148] Test Example 2

[0149] The antioxidant rates of the composite fresh-keeping films and double-layer films prepared in the examples and comparative examples were tested. The test method was determined according to the method in the reference document "Development of a chitosan / pectin-based multi-active food packaging with both UV and microbial defense functions for effectively preserving of strawberry". The test results are shown in Table 3. The antioxidant activities of the composite fresh-keeping films and double-layer films were evaluated by measuring the DPPH radical scavenging rate and the ABTS radical scavenging rate. When the lignin mass concentration was 1%, 5%, 10%, and 15%, the antioxidant activity of the composite fresh-keeping film increased with the increase of the lignin addition amount, and the radical scavenging rate increased with the increase of the proportion of the CL film thickness. Therefore, the composite fresh-keeping film containing lignin and anthocyanin is expected to be applied to delay the oxidative deterioration of fruits.

[0150] Table 3

[0151] Number DPPH(%) ABTS(%) Example 1 71.17 71.44 Example 2 70.98 70.12 Example 3 52.45 54.45 Example 4 40.90 51.51 Example 5 67.22 69.69 Example 6 65.19 66.23 Example 7 50.73 55.49 Example 8 40.66 50.73 Example 9 40.12 48.77 Comparative example 1 10.90 13.87 Comparative example 2 10.66 11.45 Comparative example 3 10.12 13.11 Comparative example 4 11.37 10.33

[0152] Test Example 3

[0153] The ultraviolet spectra of the composite fresh-keeping film prepared in the example and the double-layer film prepared in the comparative example were tested, and the test results are as Figure 3 shown. From Figure 3It can be seen that compared with the double-layer film of the comparative example, the composite fresh-keeping film loaded with anthocyanin and lignin exhibits stronger UV shielding ability. After adding anthocyanin to the P / C film, the blocking efficiency of the fresh-keeping film (PG / C) for ultraviolet light and visible light is improved. After adding lignin, the UV transmittance of the composite fresh-keeping film (PG / CL) is significantly reduced, especially in the range of 200-350 nm. When the lignin concentration > 5%, the UV transmittance of the composite fresh-keeping film is very low, indicating that the composite fresh-keeping film loaded with lignin and anthocyanin can effectively block ultraviolet rays. Therefore, adding lignin to chitosan and compounding it with pectin containing anthocyanin-nano silver ion compound, the chitosan film, as a biological defense substance, absorbs ultraviolet-visible light. The photodegradation process of anthocyanin is expected to be controlled by lignin. Based on the spectral superposition theory, protected by lignin, anthocyanin will maintain continuous antioxidant activity and be applied to the fresh-keeping packaging of fruits.

[0154] Test Example 4

[0155] The composite fresh-keeping film prepared in the example and the double-layer film prepared in the comparative example were subjected to antibacterial tests. The specific test method: The bacterial strain was cultured in nutrient broth for 24 hours, and then 0.1 ml of the inoculum containing pathogens was evenly distributed on the nutrient broth (LB) medium. The prepared membrane discs (diameter 10 mm) were placed in a petri dish filled with LB medium and incubated at 37 °C for 24 hours. The inhibition diameter was measured using a micrometer. The P / C film of Comparative Example 3, the PG / CL 1% film of Example 4, and the PG / CL 15% film of Example 1 were selected as membrane samples, and no film was used as a control. The film samples were irradiated with ultraviolet light and placed on the same horizontal line to be parallel to the ultraviolet lamp (253.7 nm, 15 W), and the linear distance was 30 cm. The film samples were tested after being exposed to ultraviolet light for different time periods (0, 1, 2, 3 hours). The test results are shown in Table 4. The results show that the composite fresh-keeping film prepared in the example has obvious changes in the antibacterial zones against Staphylococcus aureus and Escherichia coli. After adding lignin to the pectin / chitosan double-layer film, the P / CL film shows obvious inhibitory effects on Staphylococcus aureus and Escherichia coli, and obvious antibacterial zones are formed around the film. As the lignin concentration increases, the diameter of the antibacterial zone gradually increases. The antibacterial zones of the PG / CL 15% composite fresh-keeping film prepared in Example 1 against Staphylococcus aureus and Escherichia coli are significantly larger than those of the P / C double-layer film prepared in Comparative Example 3 (p < 0.05). After adding lignin and anthocyanin to the pectin / chitosan double-layer film, it exhibits strong antibacterial activity. This indicates that the composite fresh-keeping film containing lignin and anthocyanin has good antibacterial effects and can have good application prospects as a new type of antibacterial packaging material in fruit preservation.

[0156] Table 4

[0157]

[0158] Test Example 5

[0159] Cherry freshness preservation tests will be conducted on the P / C film of Comparative Example 3, the PG / CL 1% film of Example 4, and the PG / CL 15% film of Example 1. The control group is cherries without film coating treatment. The cherries are sourced from Nanjing Baiguoyuan Company. The specific test method is as follows: The selection of cherries is based on the absence of visible mechanical damage or deteriorated areas on the surface, consistent maturity, and medium size. The harvested cherries are randomly divided into four treatment groups: no packaging treatment (CK); P / C film coating; PG / CL 1% film coating; PG / CL 15% film coating. The cherries are successively immersed in a 2% (W / V) pectin solution for 30 seconds, then placed in a 2% chitosan solution for 30 seconds, and then fished out; the cherries are dried until a double-layer film is formed on the fruit surface; the coated cherries are taken out and dried in a fume hood at 25°C for 15 minutes to form film-coated cherries, and then stored at room temperature of 25°C for 8 days. See specifically Figure 4 . During the test process, it was found that with the extension of the storage time, the cherries showed a certain degree of decay and dehydration. After 4 days of storage at room temperature, the double-layer film prepared in Comparative Example 1 and the cherries without film coating treatment showed decay and dehydration, while the composite fresh-keeping films of Example 1 and Example 4 remained fresh after 8 days of storage, and no bacterial infection occurred during the entire storage period (generally about 7-8 days) of the cherries. This indicates that the composite fresh-keeping film prepared by the present invention can be used as a new type of fresh-keeping packaging material and has good application prospects in fruit freshness preservation.

[0160] It can be seen from the results in Tables 1 - 4 that the composite fresh-keeping film containing lignin and anthocyanin of the present invention has significantly better antibacterial and freshness preservation effects than the pectin / chitosan double-layer film without lignin and without lignin and anthocyanin.

[0161] In summary, the raw materials of the composite fresh-keeping film of the present invention are safe, non-toxic, and widely sourced, and have certain film-forming properties by themselves. While having a certain freshness preservation effect, it can play an antibacterial and antioxidant role. The raw materials used are all widely sourced, inexpensive, and easily available, and are safe and non-toxic to the human body, ensuring a certain degree of popularization.

[0162] The composite fresh-keeping film provided by the present invention comprises a pectin film layer and a chitosan film layer which are arranged up and down. The pectin film layer contains anthocyanin and / or anthocyanin silver ion compound, and the chitosan film layer contains lignin. Through the synergistic effect between the double-layer films, the composite fresh-keeping film has antibacterial activity against a variety of food spoilage bacteria, strong antioxidant performance, and can significantly improve the storage period. It is further found that the composite fresh-keeping film has good ultraviolet shielding performance, gas barrier and moisture barrier properties, and is transparent and shiny. The preparation process of the composite fresh-keeping film is simple in operation, convenient to use, sufficient in raw material supply, easy to popularize and apply, has a very broad application prospect, and is easy to be compounded with other fresh-keeping methods to achieve better effects.

[0163] The preferred embodiments of the present invention have been described in detail above. However, the present invention is not limited thereto. Within the scope of the technical concept of the present invention, various simple modifications can be made to the technical solutions of the present invention, including any other suitable combination of each technical feature. These simple modifications and combinations should also be regarded as the content disclosed by the present invention and fall within the protection scope of the present invention.

Claims

1. A composite cling film, characterized in that: The composite fresh-keeping film comprises a pectin film layer and a chitosan film layer arranged up and down, the pectin film layer contains an additive, the chitosan film layer contains lignin, and the additive is anthocyanin and / or anthocyanin silver ion compound.

2. The composite cling film according to claim 1, characterized in that: In the chitosan film layer, the content of lignin is 1-15wt%, preferably 10-15wt%; Preferably, in the pectin film layer, the content of the additive is 10-15wt%; Preferably, the thickness ratio of the chitosan film layer to the pectin film layer is 1:1-3.

3. The composite fresh-keeping film according to claim 1 or 2, characterized in that: The mass ratio of silver ions to anthocyanins in the anthocyanin silver ion compound is 1:2-4; Preferably, the silver ions are nano silver ions; Preferably, the method for preparing the anthocyanin silver ion compound comprises: contacting the anthocyanin solution and the silver ion solution under alkaline conditions.

4. The composite fresh-keeping film according to claim 1 or 2, characterized in that: The pectin film layer and / or the chitosan film layer also contain a plasticizer and a stabilizer; Preferably, the plasticizer is selected from at least one of glycerol, tributyl citrate and acetyl tributyl citrate; Preferably, the stabilizer is calcium carbonate and / or sorbitol.

5. A method for preparing a composite cling film, characterized in that: The method comprises the following steps: S1. In the presence of a solvent, pectin and an additive are mixed and then a pectin film layer is prepared by a casting method, wherein the additive is anthocyanidin and / or anthocyanidin silver ion compound; In the presence of a solvent, chitosan and lignin are mixed II and then a chitosan film layer is prepared by a casting method; S2, compounding the pectin film layer and the chitosan film layer to form a composite fresh-keeping film.

6. The method according to claim 5, characterized in that In the chitosan film layer, the content of lignin is 1-15wt%, preferably 10-15wt%; Preferably, in the pectin film layer, the content of the additive is 10-15wt%; Preferably, the thickness ratio of the chitosan film layer to the pectin film layer is 1:1-3.

7. The method according to claim 5, characterized in that The mixing conditions of the mixing I include at least: pH 13-14, temperature 25-35°C, and time 12-14h; The conditions of the mixing II at least include: pH 2-3, temperature 25-35° C., and time 12-14 h.

8. The method according to claim 5, characterized in that The method further comprises adding a plasticizer and a stabilizer during the mixing I process and / or the mixing II process; Preferably, the plasticizer is selected from at least one of glycerol, tributyl citrate and acetyl tributyl citrate; Preferably, the stabilizer is calcium carbonate and / or sorbitol.

9. The method according to any one of claims 5 to 8, characterized in that: The mass ratio of silver ions to anthocyanins in the anthocyanin silver ion compound is 1:2-4; Preferably, the silver ions are nano silver ions; Preferably, the method for preparing the anthocyanin silver ion compound comprises: contacting the anthocyanin solution and the silver ion solution under alkaline conditions.

10. Use of the composite preservative film according to any one of claims 1 to 4 or the composite preservative film prepared by the method according to any one of claims 5 to 9 in preserving fruits.

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