4D printing film for fruit preservation and preparation method and application thereof

Abstract

The application discloses a 4D printing film for fruit preservation and a preparation method and application thereof. A soapnut gum is added into distilled water and stirred at room temperature to obtain a soapnut gum solution; the soapnut gum solution is irradiated by a ray; the irradiated object is freeze-dried to obtain modified soapnut gum; a soybean protein isolate and a high-methoxyl pectin solution are respectively prepared and mixed to obtain a soybean protein isolate-high-methoxyl pectin mixed solution; garlic essential oil is added into the soybean protein isolate-high-methoxyl pectin mixed solution, and the precipitate is collected by centrifugal dehydration to obtain a garlic essential oil high internal phase emulsion; the soapnut gum is mixed with water to obtain a soapnut gum solution; the garlic essential oil high internal phase emulsion is added into the obtained soapnut gum solution to obtain printing ink for a lower layer structure of a film; a soapnut gum solution without radiation treatment is used as printing ink for an upper layer structure of the film; the printing ink is filled into a syringe of a printer for room-temperature printing to obtain a 4D printing deformation preservation film.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of food antibacterial preservation, and particularly relates to a 4D-printed film for fruit preservation and a preparation method and application thereof. BACKGROUND

[0002] According to the data of the Food and Agriculture Organization of the United Nations, some fruits, such as mangosteen, litchi and kiwi, have thick skins that cover the freshness of their internal pulp, making the internal deterioration invisible, resulting in about 50 million US dollars of fresh fruits being wasted every year. Essential oil slow-release film can continuously release plant essential oil during fruit storage to inhibit the growth of microorganisms and prolong the shelf life of fruits, which is a simple, effective, economical and environmentally friendly preservation method. At present, there are patents reporting the preparation method and application scene of slow-release essential oil preservation film. For example, Zhang Wangan et al. (Application No. CN201811505278.9) added oregano essential oil to a homogeneous solution of carboxymethyl cellulose and Tween, and adjusted the number of micropores of the film by changing the amount of Tween added, so as to control the release of essential oil; Li Li et al. (Application No. CN201510300611.2) added lemon aldehyde-cyclodextrin microcapsules to ethylene-vinyl alcohol copolymer, and realized the slow-release effect by using the binding effect of microcapsules on essential oil; Li Xinxin et al. (Application No. CN201910652320.8) ultrasonically mixed cinnamomum essential oil-corn oil-sinapyl succinate starch sodium Pickering emulsion with a paste of denatured starch solution, and the essential oil was hindered from volatilizing by the starch matrix to obtain an essential oil slow-release film; Liu Yang et al. (Application No. 202010325689.0) prepared a double-layer film using ginger essential oil and sodium alginate, and the sodium alginate was cross-linked into a dense outer layer film and a porous inner layer film under the action of Ca + These essential oil slow-release films have a certain preservation effect on fresh foods such as meat, fruits and vegetables. SUMMARY

[0003] The technical problem solved by the present application is to provide a 4D-printed film for fruit preservation and a preparation method and application thereof, which aims to use 4D printing technology to prepare a deformation preservation film based on essential oil slow-release to prolong the shelf life of climacteric fruits, while not affecting the existing good quality of fruits such as flavor, color and nutritional value.

[0004] Technical solution: A preparation method of a 4D-printed film for fruit preservation, comprising the following steps: (1) 60 Co gamma ray irradiation modification of soap gourd bean gum: add soap gourd bean gum into distilled water and stir at room temperature to obtain a soap gourd bean gum solution; irradiate the soap gourd bean gum solution with Co gamma rays to obtain a modified soap gourd bean gum solution; add the modified soap gourd bean gum solution into a 4D printer and print to obtain a 4D-printed film for fruit preservation. 60(1) modified soap Gleditsia sinensis L. gum: irradiating the soap Gleditsia sinensis L. gum with Co γ rays; freeze-drying the irradiated material to obtain the modified soap Gleditsia sinensis L. gum; (2) preparing garlic essential oil high internal phase emulsion: preparing soybean protein isolate and high methoxyl pectin solutions respectively, mixing the two solutions in a volume ratio of 1:(1-3), and homogenizing to obtain a soybean protein isolate-high methoxyl pectin mixed solution; adding garlic essential oil to the soybean protein isolate-high methoxyl pectin mixed solution, high-pressure homogenizing, and centrifuging to collect the precipitate to obtain the garlic essential oil high internal phase emulsion; (3) printing essential oil slow-release preservative film: mixing the soap Gleditsia sinensis L. gum with water to obtain a soap Gleditsia sinensis L. gum solution; adding the garlic essential oil high internal phase emulsion obtained in step (2) to the obtained soap Gleditsia sinensis L. gum solution, and homogenizing to obtain printing ink for the lower layer structure of the film; the soap Gleditsia sinensis L. gum solution not subjected to radiation treatment is used as printing ink for the upper layer structure of the film; the printing ink is filled into a syringe of a printer for room temperature printing, and a 4D printed shape-changing preservative film is obtained after standing.

[0005] The soap Gleditsia sinensis L. gum has a purity of 87%, a molecular weight of 669 KDa, a galactose to mannose ratio of 1:3-1:4, and a mass concentration of the soap Gleditsia sinensis L. gum solution of 1%-3%.

[0006] 60 Before being irradiated with Co γ rays, the soap Gleditsia sinensis L. gum solution is coated into a coating layer with a thickness of 1-3 mm, the radiation intensity is 1-4 KGy / cm 2 , and the radiation time is 1-5 h; the final water content of the soap Gleditsia sinensis L. gum is 3wt.%-3.5wt.%.

[0007] The concentrations of the soybean protein isolate and high methoxyl pectin solutions are 3%-5% (m / v, g / mL) respectively, the garlic essential oil is added in an amount of 10%-15% (m / v, g / mL), the pressure of the high-pressure homogenizer is 40-60 MPa, the number of processing times is 5-8, the temperature of the centrifuge is 4-10°C, and the rotation speed is 4000-5000 r / min.

[0008] The concentration of the soap Gleditsia sinensis L. gum solution is 2%-6% (w / v, g / mL), the addition amount of the garlic essential oil high internal phase emulsion is not more than 15wt.%, the rotation speed of the homogenizer is 12000-15000 r / min, and the homogenization time is 10-15 min.

[0009] The storage modulus of the printing ink is 50-80 kPa, the loss modulus is 7-15 kPa, the yield stress is 200-400 Pa, and the flow stress is 300-400 Pa.

[0010] The printer is an extrusion type printer, the extrusion pressure is 60 kPa, the nozzle diameter is 0.4-0.8 mm, the extrusion speed is 20-25 mm / s, and the filling rate is 30%-100%.

[0011] The film is a double-layer structure, the printing filling patterns of the upper and lower layers are straight lines, the included angle of the upper and lower layer lines is 60°, the printing precision is ≥95%, the length, width and height of the printed film are 6 cm, 1.5 cm and 0.8-1.6 mm respectively, and the water content of the film is 10 wt.%-15 wt.%.

[0012] The film is recombined according to a specific structure by using food printing technology, the soapberry gum (upper layer structure) with high hydrophilic ability and the radiated soapberry gum (lower layer structure) with high hydrophobic ability, when exposed to a high humidity environment generated by fruit respiration, the soapberry gum of the upper layer structure absorbs water and expands, and at the same time, the soapberry gum of the lower layer structure acts as a water diffusion barrier due to low water absorption and generates mechanical constraints. The mechanical shear stress generated by the upper and lower structures of the film causes the plane film to bend in a shape perpendicular to the angle of the upper filling line.

[0013] The fruit fresh-keeping 4D printed film prepared by the method.

[0014] The application of the prepared fruit fresh-keeping 4D printed film in the antibacterial fresh-keeping packaging of climacteric fruits, the fruit packaging is a plastic box in the shape of a rectangular parallelepiped, the center of the plastic box cover is adhered with a box with four walls and a bottom filled with holes to load the prepared fruit fresh-keeping film; before the climacteric fruit enters the respiratory peak, the essential oil in the film is released slowly, and the release rate is in the range of 0.1-0.2 g / d; when the fruit enters the respiratory peak and the late respiratory peak, at this time, due to the high humidity environment generated by respiration and transpiration, the fresh-keeping film changes in shape, and the pulling force generated by the film in the shape change process causes the microstructure to be damaged, and the essential oil contained in the film is accelerated to be released, and the release rate is 0.3-0.45 g / d to inhibit the rapid reproduction of microorganisms of the fruit in the ripening stage, thereby more effectively prolonging the shelf life of the fruit.

[0015] Beneficial effects: the modified soapberry gum loaded with garlic essential oil emulsion is used as printing ink, a printing fresh-keeping film with a double-layer film structure is designed by using food printing technology, the printing fresh-keeping film is deformed to different degrees after accumulating the water generated by the fruit, and the release amount of the essential oil can be changed according to the change of the external environment. Compared with the traditional method (flow casting method), the essential oil slow-release film prepared by the 4D printing technology can prolong the shelf life of the fruit by 2-6 days. BRIEF DESCRIPTION OF DRAWINGS

[0016] Figure 1 Comparison of the application of the essential oil slow-release films prepared by flow casting and 4D printing in the control of total bacterial count of kiwifruit during storage;

[0017] Figure 2Comparison of essential oil sustained-release film prepared by casting method and 4D printing for controlling total bacterial count during persimmon storage

[0018] Figure 3 Comparison of essential oil sustained-release film prepared by casting method and 4D printing for controlling total bacterial count during mango storage. DETAILED DESCRIPTION

[0019] In order to make the objects, technical solutions and advantages of the present application clearer, the present application will be further described in detail below in combination with embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and should not be used to limit the present application.

[0020] Example 1: Comparison of essential oil sustained-release film prepared by casting method and 4D printing for controlling total bacterial count during kiwifruit storage

[0021] (1) 10 g of Gleditsia sinensis Lam. gum was added to 1000 mL of distilled water, and after magnetic stirring at room temperature at 200 r / min for 12 h, a Gleditsia sinensis Lam. gum solution was obtained. The solution was applied to a glass plate with an application thickness of 1.5 mm. 60 The Co γ-ray treatment radiation intensity was 2 KGy / cm 2 , and the radiation time was 3.5 h. Subsequently, the irradiated material was freeze-dried for 24 h to obtain modified Gleditsia sinensis Lam. gum.

[0022] (2) Soybean protein isolate and high-methoxyl pectin solutions with a volume ratio of 1:3 were mixed, and a mixed solution A was obtained by homogenization treatment at a rotation speed of 15000 r / min for 20 min. 10 g of garlic essential oil was added to 100 mL of the mixed solution A, and after 5 times of high-pressure homogenization treatment at 60 MPa, centrifugation was performed at 4°C and 4000 r / min, and the precipitate was collected to obtain a garlic essential oil high internal phase emulsion;

[0023] (3) Add 5 g of garlic essential oil high internal phase emulsion obtained in step (2) to 100 mL of 2% (w / v, g / mL) of soapberry gum solution obtained in step (1) and homogenize at 15000 r / min for 10 min to obtain a mixed solution B. Casting method: Pour the mixed solution B into a 6 x 1.5 cm (length x width) glass plate mold to form a film with a thickness of 0.8 mm, and then place the glass plate in a fume hood for 24 h. On this basis, an equal amount of unmodified soapberry gum solution is poured into the above glass plate and left in the fume hood for 24 h to obtain an essential oil slow-release film prepared by the casting method. 4D printing method: Add 9 g of garlic essential oil high internal phase emulsion obtained in step (2) to 100 mL of 2% (w / v, g / mL) of soapberry gum solution obtained in step (1) and homogenize at 15000 r / min for 10 min to obtain a mixed solution C. 2% (w / v, g / mL) of unmodified soapberry gum solution is the printing ink for the upper structure of the film, and the mixed solution C is the printing ink for the lower structure. The printing parameters are set as follows: nozzle diameter 0.4 mm, extrusion speed 20 mm / s, upper and lower structure filling rate 30% and 100% respectively, and the included angle of the upper and lower filling lines 60°, and the printing model is a 6 cm x 1.5 cm x 0.8 mm (length x width x height) cuboid. Then, the printed film is left in the fume hood for 24 h to obtain an essential oil slow-release film prepared by 4D printing. The films prepared by the casting method and 4D printing contain the same amount of essential oil.

[0024] (4) Add 500 g of kiwifruit and the film prepared in step (3) into a sealed plastic box and store at 25°C, and observe the change of the total number of colonies of the kiwifruit during storage.

[0025] Figure 1 For comparison of the essential oil slow-release films prepared by the casting method and 4D printing in the control of the total number of colonies of kiwifruit during storage, the results show that when the total number of colonies exceeds 6 lg CFU / g, the fruit appears to be rotten. Compared with the film prepared in the control group, the films prepared by the casting method and 4D printing delay the time for the total number of colonies of kiwifruit to reach the upper limit by 3 days and 9 days, respectively. The film prepared by 4D printing has a better preservation effect than the film prepared by the casting method because the former can change its shape according to the accumulated moisture generated by the fruit, and the change in shape is accompanied by a change in microstructure, resulting in different amounts of essential oil release rather than uniform release, which further better inhibits the growth of microorganisms, especially in the later stage of storage. Compared with the casting method, the 4D printing film can extend the shelf life of kiwifruit by 6 days.

[0026] Example 2: Comparison of essential oil slow-release films prepared by casting method and 4D printing in the control of total number of colonies of persimmon during storage

[0027] (1) 20 g of Gleditsia sinensis L. gum was added to 1000 mL of distilled water, and after stirring at 200 r / min for 12 h at room temperature, a Gleditsia sinensis L. gum solution was obtained. The solution was spread on a glass plate and the spreading thickness was 1 mm. 60 The Co gamma ray treatment radiation intensity was 2 KGy / cm 2 and the radiation time was 4 h. Subsequently, the irradiated material was freeze-dried for 24 h to obtain modified Gleditsia sinensis L. gum.

[0028] (2) Soybean protein isolate and high-methoxyl pectin solution with a volume ratio of 1:3 were mixed, and a mixed solution A was obtained by homogenization treatment at a rotation speed of 15000 r / min for 20 min. 10 g of garlic essential oil was added to 100 mL of the mixed solution A, and after high-pressure homogenization treatment at 60 MPa for 5 times, centrifugation was performed at 4°C and 4000 r / min, and the precipitate was collected to obtain a garlic essential oil high internal phase emulsion.

[0029] (3) 6 g of the garlic essential oil high internal phase emulsion obtained in step (2) was added to 100 mL of 2% (w / v, g / mL) Gleditsia sinensis L. gum solution obtained in step (1), and homogenization treatment was performed at 15000 r / min for 10 min to obtain a mixed solution B. Casting method: the mixed solution B was poured into a 6x1.5 cm (lengthxwidth) glass plate mold to form a thin film with a thickness of 1.2 mm, and then the glass plate was placed in a fume hood for 24 h. On this basis, an equal amount of unmodified Gleditsia sinensis L. gum solution was poured into the above glass plate and placed in a fume hood for 24 h to obtain an essential oil slow-release film prepared by the casting method. 4D printing method: 10 g of the garlic essential oil high internal phase emulsion obtained in step (2) was added to 100 mL of 2% (w / v, g / mL) Gleditsia sinensis L. gum solution obtained in step (1), and homogenization treatment was performed at 15000 r / min for 10 min to obtain a mixed solution C. 2% (w / v, g / mL) unmodified Gleditsia sinensis L. gum solution was used as the printing ink of the upper structure of the thin film, and the mixed solution C was used as the printing ink of the lower structure. The printing parameters were set as follows: nozzle diameter 0.6 mm, extrusion speed 20 mm / s, upper and lower structure filling rate 50% and 100%, respectively, and the included angle of the upper and lower filling lines was 60°, and the printing model was a 6 cmx1.5 cmx1.2 mm (lengthxwidthxheight) cuboid. Subsequently, the printed film was placed in a fume hood for 24 h to obtain an essential oil slow-release film prepared by 4D printing. The films prepared by the casting method and 4D printing contained the same amount of essential oil.

[0030] (4) 800 g of persimmons and the film prepared in step (3) were added to a sealed plastic box and stored at 25°C, and the change in the total number of colonies of the persimmons was observed.

[0031] Figure 2The comparison of the application of the essential oil sustained-release films prepared by the casting method and 4D printing to the total number of colonies control of persimmons during storage showed that when the total number of colonies exceeded 6 lg CFU / g, the fruits appeared to be rotten. Compared with the films prepared by the control group, the films prepared by the casting method and 4D printing delayed the time when the total number of colonies of persimmons reached the upper limit for 1 day and 4 days, respectively. The film prepared by printing had better preservation effect than the film prepared by the casting method because the former could change the shape according to the accumulated moisture generated by the fruits, and the change of the shape was accompanied by the change of the microstructure, which led to different essential oil release amounts instead of uniform release, and thus better inhibited the growth of microorganisms, especially in the later stage of storage. Compared with the casting method, the 4D printing film could make the shelf life of persimmons be extended for 3 days.

[0032] Example 3: Comparison of the application of the essential oil sustained-release films prepared by the casting method and 4D printing to the total number of colonies control of mangoes during storage

[0033] (1) 30 g of Gleditsia sinensis L. gum was added to 1000 mL of distilled water, and after magnetic stirring at room temperature at 200 r / min for 12 h, a Gleditsia sinensis L. gum solution was obtained. The solution was applied to a glass plate and the application thickness was 1.2 mm. 60 The radiation intensity of Co γ rays was 4 KGy / cm 2 , and the radiation time was 2 h. Subsequently, the irradiated material was freeze-dried for 24 h to obtain modified Gleditsia sinensis L. gum.

[0034] (2) Soybean protein isolate and high-methoxyl pectin solutions with a volume ratio of 1:2 were mixed, and a mixed solution A was obtained by homogenization treatment at a speed of 10000 r / min for 15 min. 10 g of garlic essential oil was added to 100 mL of the mixed solution A, and after 5 times of high-pressure homogenization treatment at 60 MPa, centrifugation was performed at 4°C and 4000 r / min, and the precipitate was collected to obtain a garlic essential oil high internal phase emulsion;

[0035] (3) 8 g of garlic essential oil high internal phase emulsion obtained in step (1) was added to 100 mL of 2% (w / v, g / mL) Gellan Gum solution obtained in step (1) and homogenized at 15000 r / min for 10 min to obtain a mixed solution B. Casting method: the mixed solution B was poured into a glass plate to form a film with a thickness of 1.6 mm, and then the glass plate was placed in a fume hood for 24 h. On this basis, an equal amount of unmodified Gellan Gum solution was poured into the above glass plate and placed in a fume hood for 24 h to obtain an essential oil slow-release film prepared by the casting method. 4D printing method: 9.6 g of garlic essential oil high internal phase emulsion obtained in step (2) was added to 100 mL of 2% (w / v, g / mL) Gellan Gum solution obtained in step (1) and homogenized at 15000 r / min for 10 min to obtain a mixed solution C. 2% (w / v, g / mL) unmodified Gellan Gum solution was the printing ink of the upper structure of the film, and the mixed solution C was the printing ink of the lower structure. The printing parameters were set as follows: nozzle diameter 0.8 mm, extrusion speed 20 mm / s, upper and lower structure filling rate 40% and 100% respectively, and the included angle of the upper and lower filling lines 60°, and the printing model was a rectangular prism with a size of 6 cm x 1.5 cm x 1.6 mm (length x width x height). Then, the printed film was placed in a fume hood for 24 h to obtain an essential oil slow-release film prepared by 4D printing. The films prepared by the casting method and 4D printing contained the same amount of essential oil.

[0036] (4) 600 g of mangoes and the film prepared in step (2) were added to a sealed plastic box and stored at 25°C, and the change in the total number of colonies of the mangoes was observed.

[0037] Figure 3 For comparison of the application of the essential oil slow-release films prepared by the casting method and 4D printing in the control of the total number of colonies of mangoes during storage, the results showed that when the total number of colonies exceeded 11 lg CFU / g, the fruits showed signs of decay, and compared with the film prepared in the control group, the films prepared by the casting method and 4D printing delayed the time when the total number of colonies of mangoes reached the upper limit by 3 days and 5 days, respectively. The reason why the film prepared by 4D printing had a better preservation effect than the film prepared by the casting method was that the former could change its shape according to the accumulated moisture produced by the fruits, and the change in shape was accompanied by a change in microstructure, resulting in different amounts of essential oil release rather than uniform release, which in turn better inhibited the growth of microorganisms, especially in the later stage of storage. Compared with the casting method, the 4D printing film could extend the shelf life of mangoes by 2 days.

[0038] The above has been described schematically for the present invention and its embodiments, which are not limited, so if a person skilled in the art is inspired by it, without departing from the purpose of the present invention, similar structural ways and embodiments of the technical solutions are not designed creatively and should belong to the protection scope of the present invention.

Claims

1. A method for preparing a 4D-printed film for fruit preservation, characterized in that, The steps are as follows: (1) 60 Co-γ ray irradiation modified soybean gum: Soybean gum was added to distilled water and stirred at room temperature to obtain a soybean gum solution; the soybean gum solution was then... 60 (1) Irradiate with Coγ rays; freeze-dry the irradiated material to obtain modified soapberry gum; (2) Prepare garlic essential oil high internal phase emulsion: prepare soy protein isolate and high methoxy pectin solution respectively, mix the two solutions at a volume ratio of 1: (1~3), and homogenize to obtain soy protein isolate-high methoxy pectin mixed solution; add garlic essential oil to soy protein isolate-high methoxy pectin mixed solution, homogenize under high pressure, centrifuge to dehydrate and collect precipitate to obtain garlic essential oil high internal phase emulsion; (3) Print essential oil slow-release preservation film: mix modified soapberry gum with water and dissolve fully to obtain modified soapberry gum solution; add garlic essential oil high internal phase emulsion obtained in step (2) to the obtained modified soapberry gum solution, homogenize to obtain printing ink for the lower layer structure of the film; The film has a double-layer structure; the untreated soapberry gum solution is used as the printing ink for the upper layer of the film. Printing ink is filled into the printer's syringe for room temperature printing, then left to stand to obtain a 4D printed deformable food preservation film.

2. The method for preparing a 4D-printed film for fruit preservation according to claim 1, characterized in that, The purity of the soapberry gum is 87%, the molecular weight is 669 kDa, the ratio of galactose to mannose in the soapberry gum is 1:3 to 1:4, and the mass concentration of the soapberry gum solution is 1% to 3%.

3. The method for preparing a 4D-printed film for fruit preservation according to claim 1, characterized in that, 60 Before irradiation with Co-γ rays, a coating of soapberry gum solution with a thickness of 1-3 mm is applied, with a radiation intensity of 1-4 KGy / cm. 2 The irradiation time is 1-5 h; the final moisture content of the soapberry gum is 3wt.%-3.5wt.%.

4. The method for preparing a 4D-printed film for fruit preservation according to claim 1, characterized in that, The concentration of the soy protein isolate solution is 3%~5%, the concentration of the high methoxyl pectin solution is 3%~5%, the amount of garlic essential oil added is 10%~15%, the pressure of the high pressure homogenizer is 40~60 MPa, the number of high pressure homogenization treatments is 5~8, the temperature of the centrifuge is 4~10 ℃, and the speed is 4000~5000 r / min.

5. The method for preparing a 4D-printed film for fruit preservation according to claim 1, characterized in that, The concentration of the modified soapberry gum solution is 2%~6%, the amount of garlic essential oil high internal phase emulsion added does not exceed 15wt.%, the homogenizer speed is 12000~15000 r / min, and the homogenization time is 10~15 min.

6. The method for preparing a 4D-printed film for fruit preservation according to claim 1, characterized in that, The printing ink has a storage modulus of 50~80 kPa, a loss modulus of 7~15 kPa, a yield stress of 200~400 Pa, and a flow stress of 300~400 Pa.

7. The method for preparing a 4D-printed film for fruit preservation according to claim 1, characterized in that, The printer is an extrusion printer with an extrusion pressure of 60 kPa, a nozzle diameter of 0.4~0.8 mm, an extrusion speed of 20~25 mm / s, and a filling rate of 30%~100%.

8. The method for preparing a 4D-printed film for fruit preservation according to claim 1, characterized in that, The upper and lower layer printing patterns are straight lines with an included angle of 60°. The printing accuracy is ≥95%. The length, width and height of the printed film are 6cm, 1.5cm and 0.8~1.6mm respectively. The moisture content of the film is 10wt.%~15wt.%.

9. A 4D-printed film for fruit preservation prepared by any one of claims 1-8.

10. The application of the 4D-printed film for fruit preservation as described in claim 9 in respiratory catalytic antibacterial preservation packaging for fruits, characterized in that, The fruit packaging is a rectangular plastic box, with a perforated box on all four sides and bottom glued to the center of the lid to hold the prepared fruit preservation film.

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