Food packaging film as well as preparation method and application thereof

Abstract

The invention relates to the technical field of food packaging films, and particularly discloses a food packaging film as well as a preparation method and application thereof. According to the invention, guar gum, acidified chitosan and polyvinylpyrrolidone are used as substrates, so that the hydrogel has excellent biocompatibility and good food safety, and a simple and efficient synthesis method is adopted. The purple sweet potato extract is used as an indicator, and the change of freshness is displayed by the change of film color, so that the use value of the purple sweet potatoes is improved. The food packaging film prepared by the invention is biodegradable, can reduce environmental pollution caused by petroleum-based plastic, is energy-saving and environment-friendly, and solves the technical problem of environmental pollution of the existing petroleum-based packaging material.

Description

Technical Field

[0001] The invention relates to the technical field of food packaging materials, and in particular to a food packaging film and a preparation method and application thereof. Background Art

[0002] Smart packaging is a new type of food packaging material that has sensing, communication and monitoring functions, and can record and provide instant feedback on the quality changes and safety status of packaged food during storage, transportation and sales. pH indicator is a widely used method in smart packaging. It can provide consumers with reliable information about food quality through simple, fast and accurate color changes, and assist consumers and regulators in judging the quality of food during storage and transportation. Meat and protein-rich foods are excellent places for the development of spoilage bacteria. Meat and other foods spoil very quickly. Macromolecular proteins undergo oxidative degradation during the spoilage process, producing a large amount of volatile biogenic amines such as inorganic ammonia, trimethylamine, and cadaverine. These volatile amines will gradually accumulate inside the package as the food spoils. As the degree of food spoilage increases, the volatile gases inside the package will gradually be adsorbed by the smart membrane, hydrolyzed in the membrane to generate H+ or OH-, thereby changing the pH of the response membrane.

[0003] Most of the existing smart packaging materials are petroleum-based. The development and application of petroleum-based packaging materials bring convenience to consumers while causing serious damage to the environment. The emission of harmful gases in the production process and the lack of necessary recycling measures will cause serious environmental pollution. Summary of the invention

[0004] The purpose of the present invention is to overcome the deficiencies of the prior art, provide a food packaging film and a preparation method and application thereof, and solve the technical problem of environmental pollution caused by existing petroleum-based packaging materials.

[0005] In order to achieve the above object, the present invention adopts the following technical solutions: The present invention provides a food packaging film, which uses guar gum, acidified chitosan and polyvinyl pyrrolidone as a matrix, and loads purple sweet potato extract as a freshness indicator and an antioxidant to obtain a food packaging film that can display the freshness of packaged food. The food packaging film comprises the following components by weight: 12 to 18 parts of guar gum, 1 to 14 parts of acidified chitosan, 1 to 10 parts of polyvinyl pyrrolidone, and 2 to 10 parts of purple sweet potato extract.

[0006] The present invention provides a method for preparing the above-mentioned food packaging film, and the specific steps are as follows: Guar gum is refined by water-soluble alcohol precipitation method to obtain refined guar gum; fresh purple sweet potato is subjected to heat treatment by steaming, peeled, freeze-dried and ground to obtain purple sweet potato powder; the purple sweet potato powder is subjected to ultrasonic extraction treatment in a solvent system to obtain purple sweet potato extract; refined guar gum, acidified chitosan, polyvinyl pyrrolidone, plasticizer, purple sweet potato extract and solvent are uniformly mixed, and after defoaming treatment, a mixed solution is obtained; the mixed solution is used to prepare a food packaging film by a solution casting method.

[0007] Optionally, the mass proportion of the guar gum in the mixed solution is 1.2wt% to 1.8wt%, the mass proportion of the acidified chitosan in the mixed solution is 0.1wt% to 1.4wt%, the mass proportion of the polyvinyl pyrrolidone in the mixed solution is 0.1wt% to 1.0wt%, the mass proportion of the plasticizer in the mixed solution is 0.5wt% to 1.5wt%, and the mass proportion of the purple sweet potato extract in the mixed solution is 0.2wt% to 1.0wt%.

[0008] Optionally, the plasticizer is a glycerol aqueous solution, and the mass concentration of the glycerol aqueous solution is 45% to 55%.

[0009] Optionally, the defoaming treatment is a centrifugal treatment, the centrifugal speed of the centrifugal treatment is 3000r / min to 4000r / min, and the time of the centrifugal treatment is 10min to 20min.

[0010] Optionally, the guar gum is purified by water-alcohol precipitation method, which comprises the following steps: dissolving guar gum powder in water, subjecting it to precipitation treatment, washing the precipitate with ketones and ethers, freeze-drying, and grinding it into powder to obtain purified guar gum.

[0011] Optionally, the ultrasonic extraction process comprises the following steps: ultrasonically extracting the aqueous solution of purple sweet potato powder, then centrifugally separating it, taking the supernatant and subjecting it to reduced pressure distillation, concentration and cold drying to obtain the purple sweet potato extract.

[0012] Optionally, the preparation of the acidified chitosan comprises the following steps: mixing and dissolving chitosan powder, water and glacial acetic acid to obtain a chitosan solution, and subjecting the solution to alcohol precipitation, filtration, washing the precipitate, and freeze-drying and grinding to obtain the acidified chitosan.

[0013] The present invention provides an application of the above-mentioned food packaging film in preparing intelligent packaging materials.

[0014] Compared with the prior art, the present invention has the following advantages: The present invention uses guar gum, acidified chitosan and polyvinyl pyrrolidone as a matrix, has excellent biocompatibility, good food safety, and adopts a simple and efficient synthesis method. By using purple sweet potato extract as an indicator, the film color changes to show the change of freshness, thereby improving the use value of purple sweet potato. And the food packaging film prepared by the present invention can be biodegraded, can reduce the environmental pollution caused by petroleum-based plastics, is energy-saving and environmentally friendly, and solves the technical problem of environmental pollution in existing petroleum-based packaging materials.

[0015] In addition, the food packaging film prepared by the present invention can display the freshness of the packaged food in real time, conveniently and quickly. The food packaging film prepared by the present invention has high transparency and high ultraviolet barrier properties, which can enable consumers to better observe the packaged goods while reducing food oxidation degradation. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 The stress-strain curves and mechanical property diagrams of the food packaging films prepared in Examples 1 to 6 of the present invention are shown in Figures 1 to 6. (a) is a stress-strain curve diagram, and (b) is a mechanical property diagram.

[0017] Figure 2 The transparency comparison diagrams of the food packaging films prepared in Examples 1 to 6 of the present invention and Comparative Examples 1 to 3 are shown in FIG. (a) is a comparison diagram of the actual test results, and (b) is a comparison diagram of the transparency performance test.

[0018] Figure 3 The UV barrier properties of the food packaging films prepared in Examples 1 to 6 of the present invention and Comparative Examples 1 to 3 are shown in Figure 1. (a) is a comparison diagram of the actual test results, and (b) is a comparison diagram of the UV barrier properties test.

[0019] Figure 4 The DPPH antioxidant activity diagram of the food packaging films prepared in Examples 1 to 6 of the present invention and Comparative Examples 1 to 3.

[0020] Figure 5 This is a graph showing the ammonia sensitivity of the food packaging films prepared in Examples 1 to 5 of the present invention.

[0021] Figure 6 This is a diagram showing the freshness and color of the food packaging film prepared in Example 5 of the present invention.

[0022] Figure 7The diagrams are for the reusability of the food packaging film prepared in Example 5 of the present invention in an acidic and alkaline environment. (a) L value change diagram of the color reaction of the food packaging film in five acid-base cycles, (b) a value change diagram of the color reaction of the food packaging film in five acid-base cycles, (c) b value change diagram of the color reaction of the food packaging film in five acid-base cycles, (d) △E value change diagram of the color reaction of the food packaging film in five acid-base cycles, (e) actual change diagram of the color reaction of the food packaging film in five acid-base cycles.

[0023] Figure 8 The biodegradability diagrams of the food packaging film prepared in Example 5 of the present invention are shown in Figure 1. (a) is a physical diagram of the degradation of the food packaging film by soil microorganisms when the food packaging film is buried in moist compost soil, and (b) is a physical diagram of the degradation of the food packaging film by soil microorganisms when the food packaging film is placed on the surface of moist compost soil. DETAILED DESCRIPTION

[0024] In order to solve the above technical problems, the present invention provides a food packaging film and a preparation method and application thereof. The technical scheme and embodiments of the present invention are now described in detail in conjunction with the accompanying drawings.

[0025] A method for preparing a guar gum-based smart film and its freshness monitoring application, comprising the following steps: (1) Refining guar gum by water-alcohol precipitation method: dissolving guar gum powder in water to prepare a viscous gum solution, adding ethanol for precipitation, stirring with a glass rod to fully precipitate, filtering to remove the filtrate, washing the precipitate twice with acetone and ether respectively, freeze-drying and grinding into powder to obtain refined guar gum.

[0026] (2) Preparation of purple sweet potato extract: Wash fresh purple sweet potatoes, steam them, peel them and freeze them in a refrigerator for 48 hours. After freezing, freeze-dry the purple sweet potatoes and grind them into fine powder. Place the purple sweet potato powder in pure water, stir it magnetically at room temperature for 2 hours, perform ultrasonic extraction, and then centrifuge. Place the supernatant in a rotary evaporator, perform vacuum distillation, concentrate, and freeze them in a refrigerator for 48 hours. After freeze-drying, grind the sample into powder to obtain the purple sweet potato extract.

[0027] (3) Preparation of acidified chitosan: Place chitosan powder in pure water, stir magnetically, add glacial acetic acid to dissolve it, and after complete dissolution, add ten times the volume of ethanol, then filter and wash the precipitate. The precipitate is freeze-dried and ground into powder to obtain water-soluble acidified chitosan.

[0028] (4) Preparation of film: 1.4wt% of refined guar gum, 0.4wt% of acidified chitosan, 0.2wt% of polyvinyl pyrrolidone and 1.4wt% of purple sweet potato extract were dissolved in pure water and stirred magnetically to fully dissolve. 0.1wt% of glycerol aqueous solution was further added to the above solution as a plasticizer, and the mixture was stirred for 2h to mix evenly, and then centrifuged to remove bubbles. The mixed solution was poured into a polyethylene petri dish (10 cm×10 cm) and dried to obtain a food packaging film.

[0029] Specifically, in step (1), the volume ratio of the glue solution to ethanol is 1:1.

[0030] Specifically, in step (2), the ultrasonic time is 120 min and the ultrasonic power is 320 W.

[0031] Specifically, the reduced pressure distillation temperature in step (2) is 60°C.

[0032] Specifically, the centrifugation time in step (2) is 30 minutes and the rotation speed is 3500 rpm.

[0033] Specifically, in step (4), the drying temperature is 30° C. and the drying time is 48 h.

[0034] Specifically, the mass concentration of the glycerol aqueous solution in step (4) is 50%.

[0035] The food packaging film prepared by the invention can be used for monitoring the freshness of protein foods.

[0036] According to subsequent experimental results, the film prepared by the present invention is smooth, uniform, tough, highly transparent and can achieve a UV blocking rate of 99.99%. EB% can reach 38.26%, and TS is 35.42 MPa. In an ammonia atmosphere, the film turns green and then turns yellow, indicating that it is highly sensitive to pH. When the shrimp is slightly deteriorated (TVB-N is 18.24 mg / 100g), the film changes from flesh pink to brownish yellow, indicating that it is intelligent in monitoring the freshness of the shrimp.

[0037] The present invention is described in detail below through specific examples. The examples are exemplary and intended to be used to explain the present invention, but should not be understood as limiting the present invention.

[0038] Example 1 A method for preparing a food packaging film comprises the following steps: (1) Refined guar gum: Take guar gum powder and add water to dissolve it into a viscous gum solution, add ethanol to precipitate it, use a glass rod to stir it to fully precipitate it, filter it to remove the filtrate, wash the precipitate twice with acetone and ether respectively, freeze-dry it and grind it into powder. The volume ratio of the viscous gum solution to ethanol is 1:1.

[0039] (2) Preparation of purple sweet potato extract: Wash fresh purple sweet potatoes, steam them, peel them and freeze them in a refrigerator for 48 hours. After freezing, freeze-dry the purple sweet potatoes and grind them into fine powder. Place the purple sweet potato powder in pure water, stir it magnetically at room temperature for 2 hours, perform ultrasonic extraction, and then centrifuge. Place the supernatant in a rotary evaporator, perform vacuum distillation, concentrate, and freeze it in a refrigerator for 48 hours. The sample is freeze-dried and then ground into powder. The ultrasonic extraction time is 120 minutes, the ultrasonic power is 320W, the vacuum distillation temperature is 60°C, the centrifugal separation time is 30 minutes, and the centrifugal speed is 3500rpm.

[0040] (3) Preparation of acidified chitosan: Place chitosan powder in pure water, stir magnetically, add glacial acetic acid to dissolve it, and after complete dissolution, add ten times the volume of ethanol, then filter and wash the precipitate. The precipitate is freeze-dried and ground into powder to obtain water-soluble acidified chitosan.

[0041] (4) Preparation of membrane: 1.4wt% of refined guar gum, 0.4wt% of acidified chitosan, 0.2wt% of polyvinyl pyrrolidone and 1.0wt% of purple sweet potato extract were dissolved in pure water and stirred magnetically to fully dissolve. 1.0wt% of glycerol aqueous solution was further added to the above solution as a plasticizer, and the mixture was stirred for 2h to mix evenly, and then centrifuged to remove bubbles. The mixed solution was poured into a polyethylene culture dish (10cm×10cm) and dried to obtain a food packaging film named GCPP. 1.0 The drying temperature is 30°C, the drying time is 48h, and the mass concentration of the glycerol aqueous solution is 50%.

[0042] Example 2 The difference from Example 1 is that 0.2 wt% of purple sweet potato extract is added in step (3), and the remaining steps and parameters are the same. The obtained food packaging film is named GCPP 0.2 .

[0043] Example 3 The difference from Example 1 is that 0.4 wt% of purple sweet potato extract is added in step (3), and the remaining steps and parameters are the same. The obtained food packaging film is named GCPP 0.4 .

[0044] Example 4 The difference from Example 1 is that 0.6 wt% of purple sweet potato extract is added in step (3), and the remaining steps and parameters are the same. The obtained food packaging film is named GCPP 0.6 .

[0045] Example 5 The difference from Example 1 is that 0.8 wt% of purple sweet potato extract is added in step (3), and the remaining steps and parameters are the same. The obtained food packaging film is named GCPP 0.8 .

[0046] Comparative Example 1 The difference from Example 1 is that purple sweet potato extract is not added in step (3), and the remaining steps and parameters are the same. The obtained food packaging film is named GCP.

[0047] Comparative Example 2 The difference from Example 1 is that purple sweet potato extract and chitosan are not added in step (3), and the remaining steps and parameters are the same. The obtained food packaging film is named GP.

[0048] Comparative Example 3 The difference from Example 1 is that purple sweet potato extract and polyvinyl pyrrolidone are not added in step (3), and the remaining steps and parameters are the same. The obtained food packaging film is named GC.

[0049] Comparative Example 4 The difference from Example 1 is that purple sweet potato extract and guar gum are not added in step (3), and the remaining steps and parameters are the same. The obtained food packaging film is named CP.

[0050] The food packaging films prepared in Examples 1 to 5 and Comparative Examples 1 to 3 were subjected to relevant performance tests. The raw materials and instruments used in the tests are as follows:

[0051] Guar gum was sourced from Beijing Guarrun Technology Co., Ltd. Chitosan (BR), glycerol, and glacial acetic acid were sourced from Shanghai Sinopharm Chemical Reagent Co., Ltd. Polyvinylpyrrolidone, calcium chloride, methanol, and sodium hydroxide were sourced from Shanghai MacLean Biochemical Technology Co., Ltd. 2,2-Diphenyl-1-picrylhydrazide (DPPH), hydrochloric acid, magnesium oxide, boric acid, methyl red, and bromocresol green were sourced from Shanghai Aladdin Reagent Co., Ltd. All of the above reagents were AR grade.

[0052] Fresh purple sweet potatoes, sourced from the local market.

[0053] Rotary evaporator: XD-3000A, Shanghai Xiande Experimental Instrument Co., Ltd. Freeze dryer: Lab-1A-50E, Beijing Boyikang Experimental Instrument Co., Ltd. UV spectrophotometer: UV-5500PC, Shanghai Yuanxi Instrument Co., Ltd. Universal testing machine: CMT2103, Shenzhen Sansi Experimental Equipment Co., Ltd. Colorimeter: LS173B, Shenzhen Linshang Technology Co., Ltd. Centrifuge: AURORA550D, Biens (Shanghai) Scientific Instrument Co., Ltd.

[0054] Related tests and characterizations are as follows: (1) Mechanical property test: The film thickness was measured using a micrometer (211-101, Dongguan Sanliang Measuring Tools Co., Ltd.) with an accuracy of 0.001 mm. The measurement results of ten random positions were recorded and the average value was taken as the final result. The tensile strength (TS) and elongation at break (EB) of the food packaging film were tested using a universal testing machine (CMT2103, Shenzhen Sansi Experimental Equipment Co., Ltd.). First, the film was cut into rectangular strips (70 mm × 20 mm). The film was tested in a dry state. The initial clamping separation was set to 50 mm, and the sample was clamped and stretched at room temperature. The test parameters were as follows: displacement control, inlet force of 0.01 N, test speed of 50 mm / min, fixed force attenuation rate of 40%, and return speed of 500 mm / min. Each sample was measured at least three times. The tensile strength TS and elongation at break EB of the prepared film were calculated according to formulas (1) and (2).

[0055] (1); (2); Where F represents the force; S represents the cross-sectional area of ​​the membrane; L represents the length of the membrane after stretching; L 0 represents the initial length of the membrane.

[0056] (2) Appearance: The appearance of the film is obtained by photography.

[0057] (3) Opacity: Cut the sample film into a rectangle (10 mm × 40 mm) and use a UV-5500PC spectrophotometer (Shanghai Yuanxi Instrument Co., Ltd.) to perform a full wavelength scan at 200 to 800 nm to measure the light blocking performance of the film to determine its light blocking ability. Use a cuvette without film as a blank reference. The opacity value of the film is calculated using formula (3):

[0058] (3); Where A600 represents the absorbance at 600nm; d represents the thickness of the film in millimeters.

[0059] (4) Antioxidant activity assay: To measure the antioxidant activity, 200 mg of food packaging film was reacted with 4 mL of 187.5 μM 2,2-diphenyl-1-picrylhydrazyl (DPPH) methanol solution for 6 hours, and the UV absorbance of the solution after the reaction was measured at 517 nm. The percentage of DPPH scavenging activity was calculated using formula (4).

[0060] (4); Among them A DPPH and A sampleThe absorbance values ​​of DPPH methanol solution and sample extract at 517nm are respectively. Pure methanol solution without DPPH is used as blank. Each sample is tested three times.

[0061] (5) Ammonia sensitivity test: Place the food packaging film (2 cm × 2 cm) 1 cm above a bottle containing ammonia solution (1 M, 5 mL) and record the film ammonia sensitivity (color change) at 25°C. Use a camera to record the color of the film at 0, 0.5, 1, 1.5, 2, 3, 6, 9, and 12 h and calculate the response sensitivity S.

[0062] (6) Reusability: The food packaging film samples were exposed to an ammonia solution (20 mL, 2 M) for 10 minutes and then exposed to acetic acid (20 mL, 2 M) for 10 minutes. The actual images and UV-visible spectral characteristics of the food packaging film samples before and after exposure to ammonia were recorded.

[0063] (7) Monitoring of freshness by food packaging film: Food packaging film samples (1 cm × 2 cm) were pasted on the inner top of a polypropylene container (7 cm in diameter, 4 cm in height). Fresh shrimp were then placed at the bottom of the container and kept at 25°C for 32 hours. The color of the film samples was recorded every day.

[0064] (8) Biodegradation experiment: Cut the food packaging film into 30mm×50mm rectangular pieces and store them vertically in 50g of 30-mesh compost soil in a 250mL beaker. Water the soil with 5mL of water every day to keep it moist, then take out the buried film from the compost and take photos. Place 50g of 30-mesh compost soil in a petri dish, take a part of the cut food packaging film and place it on the soil surface, and take photos every day.

[0065] The results of relevant tests and characterizations are as follows: The mechanical properties of food packaging films reflect their ability to maintain good integrity and sustainability in the food supply chain. TS reflects the toughness of the film and the maximum external stress it can withstand, and EB reflects the ductility of the film.

[0066] See also Figure 1 , the tensile strength of the food packaging film is higher than 35Mpa, indicating that it has good mechanical properties and can withstand large forces. The addition of purple sweet potato extract has little effect on the tensile strength of the food packaging film. A small amount of purple sweet potato extract can increase the tensile strength of the film, which is related to the formation of a more stable and dense film network through hydrogen bond interactions. With the continuous increase of the content of purple sweet potato extract, the tensile strength of the film decreases slightly, but the properties remain good.

[0067] like Figure 2 As shown, the food packaging film has good transparency. Figure 2The appearance and opacity of the film are shown. It can be seen that as the content of purple sweet potato extract increases, the color of the film gradually deepens and becomes dark yellow. However, the pattern below can still be clearly seen through the film.

[0068] Ultraviolet and visible light can cause oxidation and degradation of food, leading to quality problems for packaged food. Figure 3 It can be seen that after ultraviolet light irradiation, the anti-counterfeiting marks covered by GC, GP, and GCP films are clearly presented. After the food packaging film is covered, the anti-counterfeiting mark gradually dims with the increase of the content of purple sweet potato extract in the film. When the content of purple sweet potato extract reaches 0.6wt%, the food packaging film has completely blocked ultraviolet light, and the anti-counterfeiting mark is no longer visible, indicating that the food packaging film has a good ultraviolet blocking rate. The addition of purple sweet potato extract significantly enhances the barrier ability of food packaging film to ultraviolet light (200nm~400nm), because the polyphenol compounds in purple sweet potato extract can absorb ultraviolet-visible light radiation. At 280nm, the ultraviolet light transmittance of the food packaging film can be reduced to a minimum of 0.01% (GCPP 1.0 ). The addition of purple sweet potato extract can effectively improve the UV barrier performance of food packaging film.

[0069] Packaging films with strong antioxidant capacity can protect food from oxidation and extend the shelf life of food. The antioxidant activity (free radical scavenging activity) of the film was tested using DPPH ethanol solution. Figure 5 The DPPH antioxidant activity of food packaging film was shown. Purple sweet potato extract contains a large number of polyphenol compounds, and a large number of hydroxyl groups in polyphenol compounds can eliminate free radicals. The antioxidant activity of food packaging film after adding purple sweet potato extract was significantly improved, and it increased with the increase of purple sweet potato extract addition, from 37.11% (GCPP 0.2 ) increased to 78.55% (GCPP 1.0 ).

[0070] Using GCPP 0.8 The shrimps were packaged with a film to demonstrate the monitoring of freshness. The results are as follows Figure 6As shown. When the TVB-N value exceeds 15 mg / 100g, the shrimp meat becomes stale and unfit for consumption; when the TVB-N value exceeds 35 mg / 100g, the shrimp meat begins to deteriorate; when the TVB-N value exceeds 50 mg / 100g, the shrimp meat completely deteriorates. When the TVB-N value of shrimp meat increases from 6.02 mg / 100g to 22.34 mg / 100g, the color of the food packaging film changes from flesh pink to brown, and the ΔE is 12.89, which is greater than 5 and can be easily identified by the naked eye. When TVB-N reaches 37.34 mg / 100g, which is higher than 35 mg / 100g, the shrimp meat deteriorates and cannot be eaten anymore. At this time, the color of the food packaging film also changes from brown to yellow-green. This shows that the film can be used to visually monitor the freshness changes of protein-rich foods.

[0071] like Figure 7 As shown, GCPP 0.8 The film appears light pink in an acidic environment and yellow-green in an alkaline environment, with a very obvious color difference. It can be seen that the film can still have good color response ability after five acid-base cycles and has good reusability.

[0072] GCPP 0.8 The film was buried in moist compost soil and its degradation by soil microorganisms was observed. Figure 8 As shown in (a), GCPP 0.8 The film showed cracks on the third day and was completely degraded on the fifth day, indicating that GCPP 0.8 The membrane is degradable. Guar gum, acidified chitosan, purple sweet potato extract and polyvinyl pyrrolidone are all hydrophilic, which makes them swell and dissolve in water medium to promote degradation.

[0073] GCPP 0.8 The film was placed on the surface of moist compost soil to observe the degradation of soil microorganisms. Figure 8 As shown in (b). GCPP 0.8 White spots appeared on the membrane on the 3rd day and a large number of hyphae appeared on the 15th day, indicating that the microorganisms were involved in GCPP 0.8 Membrane decomposition. On the 25th day GCPP 0.8 Cracks appeared on the membrane, GCPP on the 45th day 0.8 The film becomes thinner and the cracks become larger, indicating that GCPP 0.8 The above results show that the prepared GCPP can be used in soil or on the soil surface. 0.8 The film has good biodegradability, which indicates that the food packaging film provided by the present invention has good biodegradability.

[0074] The above description is only a preferred embodiment of the present invention, and the above specific embodiment is not intended to limit the present invention. Various deformations and modifications may occur within the scope of the technical concept of the present invention, and any modification, modification or equivalent replacement made by a person of ordinary skill in the art based on the above description shall fall within the scope of protection of the present invention.

Claims

1. A food packaging film, characterized in that: Guar gum, acidified chitosan and polyvinyl pyrrolidone were used as the matrix, purple sweet potato extract was loaded as the freshness indicator and antioxidant, and a food packaging film that can show the freshness of packaged food was obtained; Wherein, the food packaging film comprises the following components in parts by weight: 12-18 parts of guar gum, 1-14 parts of acidified chitosan, 1-10 parts of polyvinyl pyrrolidone, and 2-10 parts of purple sweet potato extract.

2. A method for preparing a food packaging film as claimed in claim 1, characterized in that: The specific steps are as follows: The guar gum is refined by a water-soluble alcohol precipitation method to obtain refined guar gum; The fresh purple sweet potato is subjected to a heat treatment of steaming, and then peeled, freeze-dried and ground to obtain purple sweet potato powder; the purple sweet potato powder is subjected to an ultrasonic extraction treatment in a solvent system to obtain a purple sweet potato extract; The refined guar gum, acidified chitosan, polyvinyl pyrrolidone, plasticizer, purple sweet potato extract and solvent are uniformly mixed and subjected to defoaming treatment to obtain a mixed solution; The mixed solution is casted into a food packaging film.

3. The method for preparing the food packaging film according to claim 2, characterized in that: The mass proportion of the refined guar gum in the mixed solution is 1.2wt% to 1.8wt%, the mass proportion of the acidified chitosan in the mixed solution is 0.1wt% to 1.4wt%, the mass proportion of the polyvinyl pyrrolidone in the mixed solution is 0.1wt% to 1.0wt%, the mass proportion of the plasticizer in the mixed solution is 0.5wt% to 1.5wt%, and the mass proportion of the purple sweet potato extract in the mixed solution is 0.2wt% to 1.0wt%.

4. The method for preparing a food packaging film according to claim 3, characterized in that: The plasticizer is a glycerol aqueous solution, and the mass concentration of glycerol in the glycerol aqueous solution is 45% to 55%.

5. The method for preparing a food packaging film according to claim 3, characterized in that: The defoaming treatment is a centrifugal treatment, the centrifugal speed of the centrifugal treatment is 3000r / min to 4000r / min, and the time of the centrifugal treatment is 10min to 20min.

6. The method for preparing a food packaging film according to claim 2, characterized in that: The guar gum is refined by water-soluble alcohol precipitation method, which comprises the following steps: The guar gum powder is dissolved in water, precipitated, washed with ketones and ethers, freeze-dried, and ground into powder to obtain refined guar gum.

7. The method for preparing a food packaging film according to claim 2, characterized in that: The ultrasonic extraction process comprises the following steps: The purple sweet potato powder aqueous solution is subjected to ultrasonic extraction and then centrifugal separation, and the supernatant is subjected to reduced pressure distillation, concentration and cold drying to obtain the purple sweet potato extract.

8. The method for preparing a food packaging film according to claim 2, characterized in that: The preparation of the acidified chitosan comprises the following steps: Chitosan powder, water and glacial acetic acid are mixed and dissolved to obtain a chitosan solution, which is then precipitated with alcohol, filtered, washed and precipitated, and then freeze-dried and ground to obtain acidified chitosan.

9. Use of the food packaging film according to claim 1 in preparing smart packaging materials.

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