Tropical fruit preservative film and preparation method thereof

Abstract

The invention provides a tropical fruit preservative film which is of a double-layer structure, the outer layer is a moisture-resistant antibacterial layer, and the inner layer is a water-absorbing antifogging antibacterial layer; and the water-absorbing anti-fog antibacterial layer also comprises a pH sensitive microcapsule. The outer layer is prepared from polyhydroxyalkanoate, a humidity sensitive type block copolymer and CuO / SiO2 antibacterial nano-enzyme; and the water-absorbing anti-fog antibacterial layer comprises polyhydroxyalkanoate, a humidity-sensitive block copolymer, hygroscopic zeolite, thymol, gallic acid and a pH-sensitive microcapsule. The preservative film has a certain hydrophobic effect, the humidity of a packaging microenvironment can be adjusted, breeding of putrefying bacteria can be inhibited, meanwhile, thymol and gallic acid form a slow-release antibacterial system, and tropical fruits keep good quality in the storage and transportation links through cooperation of all the components; besides, the pH sensitive microcapsules can respond to acidic substances generated by corruption in real time, help merchants to quickly sort deteriorated fruits, and provide a visual judgment basis for consumers at the same time.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of food packaging, and particularly relates to a tropical fruit preservative film and a preparation method thereof. BACKGROUND

[0002] Tropical fruits, such as litchi, mango, longan, etc., are favored for their unique flavor and rich nutrition. Hainan, with its unique natural conditions, has become an important production area of tropical fruits in China. Its fruits not only sell well in the domestic market, but also are exported overseas. However, the unique physiological characteristics of tropical fruits and the stringent storage conditions pose great challenges to preservation. Tropical fruits have a high metabolic rate, with a respiratory intensity 2-3 times that of temperate fruits, and a high sensitivity to ethylene. A trace amount of ethylene can trigger the ripening reaction. After picking, the respiration continues, which quickly consumes the internal nutrients, leading to fruit aging and quality degradation. At the same time, the high humidity of tropical environment is conducive to the breeding and reproduction of microorganisms such as mold and yeast, accelerating the decay and deterioration of fruits. The average humidity in Hainan during summer is above 80%, creating favorable conditions for the breeding of microorganisms. In addition, most tropical fruits are sensitive to low temperature and are prone to cold damage, making ordinary cold storage preservation unsuitable.

[0003] Currently, there are various preservation film technologies on the market. Traditional plastic preservation films, such as polyethylene (PE) and polyvinyl chloride (PVC), can block oxygen and microorganisms to some extent, but their gas permeability and moisture permeability are difficult to accurately control, which can easily cause fruit "wetness" or water loss. PVC preservation films also have the risk of plasticizer migration, threatening food safety. Edible preservation films, such as polysaccharide and protein-based films, have the advantages of biodegradability, safety, and non-toxicity. However, polysaccharide films have high hydrophilicity and are prone to moisture absorption and stickiness in high humidity, and protein films have poor water resistance, limiting their application in tropical fruit preservation. Multi-layer co-extrusion films are environmentally friendly and low-cost, but their barrier properties are limited by the number of layers, which cannot meet the high barrier requirements of tropical fruits.

[0004] To solve the above technical problems, the present application provides a tropical fruit preservative film with a double-layer structure and quality change indication function. The outer layer is added with CuO / SiO2 antibacterial nanozyme to block environmental humidity and inhibit bacterial growth. The inner layer is loaded with hygroscopic zeolite, thymol, and gallic acid, which have water absorption, anti-fog, and antibacterial functions. In addition, the inner layer also introduces pH-sensitive microcapsules mainly composed of chitosan and anthocyanins, which can change color according to the acidic substances produced by fruit deterioration, directly indicating the preservation state of the fruit. The present application fundamentally solves the problem of tropical fruit preservation and provides a better solution for its storage and transportation, with a broad application prospect. SUMMARY

[0005] The application provides a tropical fruit preservative film and a preparation method thereof. The preservative film of the application is divided into two layers, and the outer layer mainly functions as bacteriostasis and hydrophobicity to prevent the breeding of external microorganisms. The inner layer has the functions of water absorption, anti-fogging and antibiosis, and also has the function of indicating the quality change of fruits, so that the quality of fruits can be dynamically monitored, and the preservative film has a wide application prospect in the storage and transportation of tropical fruits.

[0006] The application adopts the technical scheme of a tropical fruit preservative film with a double-layer structure, wherein the outer layer is a moisture-resistant and antibacterial layer, and the inner layer is a water-absorbing, anti-fogging and antibacterial layer; and the water-absorbing, anti-fogging and antibacterial layer further comprises pH-sensitive microcapsules.

[0007] Preferably, the total thickness of the tropical fruit preservative film is 50-80 μm, the thickness of the inner layer is 30-40 μm, and the thickness of the outer layer is 20-40 μm.

[0008] Preferably, the composition of the outer layer comprises polyhydroxyalkanoate, humidity-sensitive block copolymer and CuO / SiO2 antibacterial nanometer enzyme; and the composition of the water-absorbing, anti-fogging and antibacterial layer comprises polyhydroxyalkanoate, humidity-sensitive block copolymer, hygroscopic zeolite, thymol, gallic acid and pH-sensitive microcapsules.

[0009] The application provides a preparation method of the above-mentioned tropical fruit preservative film, comprising the following steps: S1: polyhydroxyalkanoate is added into an ethyl acetate / ethanol mixed solvent, and then subjected to magnetic stirring at 300-400 r / min under 50-60 ℃ for 1-1.5 h to obtain a polyhydroxyalkanoate solution; humidity-sensitive block copolymer is added and continuously stirred until dissolved; finally, CuO / SiO2 antibacterial nanometer enzyme, food-grade Span-80, PEG-400 and plasticizer tributyl citrate are added, and ultrasonic dispersion is performed at 300-400 W for 40-45 min; and vacuum defoaming treatment is performed for 20-30 min to obtain an outer layer spinning solution; S2: polyhydroxyalkanoate is added into an ethyl acetate / ethanol mixed solvent, and then subjected to magnetic stirring at 300-400 r / min under 50-60 ℃ for 1-1.5 h to obtain a polyhydroxyalkanoate solution; humidity-sensitive block copolymer is added and continuously stirred until dissolved; hygroscopic zeolite, thymol and gallic acid are sequentially added and stirred for 1-1.5 h; finally, pH-sensitive microcapsules, L-ascorbic acid, food-grade Span-80 and plasticizer tributyl citrate are added, and ultrasonic dispersion is performed at 200-250 W for 30-35 min; and vacuum defoaming treatment is performed for 20-30 min to obtain an inner layer spinning solution; S3: using solution airflow spinning technology to spin the outer layer spinning solution and the inner layer spinning solution in turn, after spinning, the double-layer film is taken off from the roller, the vacuum degree is maintained at-0.09 MPa, and vacuum drying is performed at 40°C for 6 h, to obtain the tropical fruit preservative film.

[0010] Preferably, the volume ratio of ethyl acetate and ethanol in the ethyl acetate / ethanol mixed solvent in S1 and S2 is 7:3.

[0011] Preferably, the ratio of polyhydroxyalkanoate, ethyl acetate / ethanol mixed solvent, humidity-sensitive block copolymer, CuO / SiO2 antibacterial nanozyme, food-grade Span-80, PEG-400 and plasticizer tributyl citrate in S1 is 100 parts: (500-600) parts: (15-25) parts: (1-3) parts: (0.2-0.6) parts: (2-5) parts: (3-8) parts by weight.

[0012] Preferably, the preparation method of CuO / SiO2 antibacterial nanozyme in S1 is as follows: Into the container, add ethanol 90 mL, deionized water 10 mL, and ammonia water 2.5 mL in turn, and stir at 600 rpm in a 25°C constant temperature water bath; slowly add tetraethyl orthosilicate 4.0 g, continue to stir for 30 min, and get a milky white SiO2 sol; mix 20 mL of 0.2 M Cu(NO3)2 solution with 10 mL of 0.05 M cetyltrimethylammonium bromide solution, and then add them uniformly to the SiO2 sol, and maintain 40 kHz, 200 W ice bath ultrasonic during the adding process; continue to ultrasonic for 20 min after the adding is completed, to obtain a sol; Add 0.25 g of dodecyl triethoxysilane to the sol, heat to 50°C and stir for 2 h, and form a wet gel after standing at room temperature for 12 h; then vacuum dry at 60°C for 6 h to obtain a light yellow dry gel block; In a muffle furnace, heat to 550°C at a rate of 3°C / min, and keep the temperature for 3 h in air atmosphere to remove cetyltrimethylammonium bromide and form CuO nanocrystals; after natural cooling, a black powder is obtained, which is dispersed in 0.1 M NaOH for 30 min, and then washed with ethanol and deionized water for 2 times respectively; finally, vacuum dry at 80°C for 4 h to obtain CuO / SiO2 antibacterial nanozyme.

[0013] Preferably, the ratio of polyhydroxyalkanoate, ethyl acetate / ethanol mixed solvent, humidity-sensitive block copolymer, hygroscopic zeolite, thymol, gallic acid, pH-sensitive microcapsule, L-ascorbic acid, food-grade Span-80 and plasticizer tributyl citrate in S2 is 100 parts: (500-600) parts: (15-25) parts: (5-10) parts: (0.5-2) parts: (0.5-2) parts: (1-3) parts: (0.1-0.2) parts: (0.3-0.8) parts: (4-9) parts by weight.

[0014] Preferably, the preparation method of the pH-sensitive microcapsule in S2 is as follows: Dissolve chitosan in a 1% acetic acid solution, stir at room temperature until completely dissolved, to obtain a 2% chitosan acetic acid solution; dissolve anthocyanin in deionized water, ultrasonic for 10 min to obtain a 1% anthocyanin solution; under constant temperature water bath at 50 ℃, slowly drop the anthocyanin solution into the chitosan acetic acid solution according to the volume ratio of 1:5, and stir at 400 r / min, continue to stir for 2 h after the drop is completed, to form a chitosan-anthocyanin complex solution; Dissolve sodium alginate in deionized water, stir at room temperature until completely dissolved, to obtain a 2% sodium alginate solution; dissolve CaCl2 in deionized water to prepare a 5% calcium chloride solution; add the sodium alginate solution drop by drop into the calcium chloride solution with a syringe, filter after solidification for 30 min, and wash with deionized water for 3 times, to obtain calcium alginate microspheres with a diameter of 1 mm; Soak the calcium alginate microspheres in the chitosan-anthocyanin complex solution, oscillate at room temperature for 2 h, so that the chitosan-anthocyanin complex is adsorbed on the surface of the microspheres, then soak the microspheres in a 1% sodium tripolyphosphate solution for crosslinking for 30 min, repeat the above steps to make the microspheres alternately adsorb chitosan-anthocyanin complex and crosslink in the sodium tripolyphosphate solution, and after 3-5 cycles, obtain a microcapsule suspension; Adjust the solid content in the microcapsule suspension to 5%, and adjust the parameters of the spray dryer: inlet air temperature 170 ℃, outlet air temperature 75 ℃, peristaltic pump flow rate 10 mL / min, atomization pressure 0.2 MPa, collect the dried powder through an 80 mesh sieve, to obtain the pH-sensitive microcapsule.

[0015] Preferably, the specific operation of the solution air-jet spinning technology in S3 is as follows: the air humidity is 35-50%, the temperature is 25-30 ° C, the outer layer spinning solution and the inner layer spinning solution are respectively placed in the injection unit of the micro-injection pump, the inner layer spinning solution is delivered separately, the flow rate is 0.8-1.0 mL / h, the pressure is 0.15 MPa, and the base layer is pre-spun on the drum for 10 min to form the base layer. The spinning is paused, and 50 μL of a 6:4 volume ratio of ethyl acetate / ethanol mixed solvent is sprayed on the surface of the base layer to make the surface swell slightly for 15-30 s; the inner layer pump and the outer layer pump are started, the flow rate of the inner layer pump is 0.8-1.0 mL / h, the pressure is 0.15 MPa, the flow rate of the outer layer pump is 1.0-1.2 mL / h, the pressure is 0.17 MPa, the drum speed is 30-40 r / min, the receiving distance is 20-25 cm, and the spinning time is 60-90 min.

[0016] The present invention also provides the tropical fruit fresh-keeping film and the use of the tropical fruit fresh-keeping film obtained by the preparation method in the storage and transportation of tropical fruits.

[0017] Compared with the prior art, the present invention has the following beneficial effects: The outer spinning solution of the present invention contains CuO / SiO2 antibacterial nanoenzymes that can inhibit the growth of spoilage bacteria such as Penicillium and Escherichia coli, and also has a certain hydrophobic effect. The hygroscopic zeolite in the inner spinning solution can also regulate the humidity of the packaging microenvironment (to prevent condensed water from breeding mold). At the same time, thymol and gallic acid form a slow-release antibacterial system. The three synergistically maintain the good quality of tropical fruits during storage and transportation. The inner spinning solution of the present invention contains pH-sensitive microcapsules (containing anthocyanins) that respond in real time to acidic substances produced by fruit spoilage through color changes: when the fruit begins to spoil, the membrane material begins to change color (ΔE>5), providing an earlier warning than traditional sensory judgment (such as odor and softening). This feature helps merchants quickly sort spoiled fruit, reducing losses caused by delayed processing, while providing consumers with an intuitive basis for judging freshness. The optimized ratio of polyhydroxyalkanoate and moisture-sensitive block copolymer in the present invention provides the cling film with excellent mechanical properties, allowing it to withstand extrusion and friction during transportation. Furthermore, the film material has an oxygen permeability as low as 20 cm³ / (m²·d·atm) and a water vapor permeability as low as 150 g / (m²·d), which can inhibit excessive respiration of fruit and prevent shriveling due to water loss, maintaining stable performance even in high-temperature and high-humidity tropical transportation environments. All ingredients used in the present invention do not release toxic or harmful substances, the functional ingredients are evenly dispersed, the addition of pH-sensitive microcapsules does not affect the mechanical properties of the membrane material, and the synergistic effect of the antibacterial ingredients and the hygroscopic ingredients enhances the storage quality of the fruit rather than simply superimposing them. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 This is a scanning electron microscope image of the tropical fruit preservative film prepared in Example 7. DETAILED DESCRIPTION

[0019] The embodiments of the present application are described in detail below with reference to the accompanying drawings.

[0020] The following describes the embodiments of the present application through specific examples, and those skilled in the art can easily understand other advantages and effects of the present application from the contents disclosed in this specification. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. The present application can also be implemented or applied through other different specific embodiments, and the details in this specification can also be modified or changed in various ways based on different viewpoints and applications without departing from the spirit of the present application. It should be noted that, in the absence of conflict, the features in the following embodiments and embodiments can be combined with each other. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without making creative work are within the scope of protection of this application.

[0021] It should be understood that the following limitations on the proportions of each substance added during the preparation of the outer spinning solution, inner spinning solution, CuO / SiO2 antibacterial nanoenzyme, and pH-sensitive microcapsules in the present invention, as well as the process parameters of the solution air-spinning technology, are preferred embodiments and should not be construed as limitations on the scope of protection of the independent claims. The embodiments are only used to explain the present invention and are not intended to limit the scope of the invention. Unless otherwise specified, the test methods used in the following examples are conventional methods; the materials, reagents, etc. used, unless otherwise specified, are reagents and materials that can be obtained from commercial channels. Example 1

[0022] Preparation of CuO / SiO2 antibacterial nanozymes: 90 mL of ethanol, 10 mL of deionized water, and 2.5 mL of ammonia water were added to the container in sequence, and stirred at 600 rpm in a constant temperature water bath at 25 °C. 4.0 g of tetraethyl orthosilicate was slowly added dropwise and stirred for 30 min to obtain a milky white SiO2 sol. 20 mL of 0.2 M Cu(NO3)2 solution and 10 mL of 0.05 M hexadecyltrimethylammonium bromide solution were mixed evenly and then added dropwise to the SiO2 sol at a uniform rate. During the addition process, ultrasonic waves were maintained at 40 kHz and 200 W in an ice bath. After the addition was completed, ultrasonic waves were continued for 20 min to obtain a sol. To the sol, 0.25 g of dodecyltriethoxysilane was added, heated to 50 ℃ and stirred for 2 h, and a wet gel was formed after standing at room temperature for 12 h; then vacuum dried at 60 ℃ for 6 h to obtain a light yellow dry gel block; In a muffle furnace, the temperature was raised to 550 ℃ at a rate of 3 ℃ / min, and the temperature was kept for 3 h under air atmosphere to remove hexadecyltrimethylammonium bromide and form CuO nanocrystals; after natural cooling, the black powder was dispersed in 0.1 M NaOH for 30 min, and then washed with ethanol and deionized water for 2 times each; finally, vacuum drying at 80 ℃ for 4 h, CuO / SiO2 antibacterial nanoscale enzyme was obtained. Example 2

[0023] Preparation of pH-sensitive microcapsules: 2 g of chitosan was dissolved in 100 mL of 1% acetic acid solution, stirred at room temperature until completely dissolved, to obtain a chitosan acetic acid solution with a mass concentration of 2%; 1 g of anthocyanin was dissolved in 100 mL of deionized water, and after ultrasonic treatment for 10 min, a 1% anthocyanin solution was obtained; under a constant temperature water bath at 50 ℃, the anthocyanin solution was slowly added into the chitosan acetic acid solution at a volume ratio of 1:5, while stirring at 400 r / min, and after the addition was completed, the stirring was continued for 2 h to form a chitosan-anthocyanin complex solution; 2 g of sodium alginate was dissolved in 100 mL of deionized water, stirred at room temperature until completely dissolved, to obtain a sodium alginate solution with a mass concentration of 2%; 5 g of CaCl2 was dissolved in 100 mL of deionized water to prepare a 5% calcium chloride solution; the sodium alginate solution was added dropwise into the calcium chloride solution using a syringe, and after solidification for 30 min, it was filtered and washed with deionized water for 3 times to obtain calcium alginate microspheres with a diameter of 1 mm; The calcium alginate microspheres were soaked in the chitosan-anthocyanin complex solution and oscillated at room temperature for 2 h, so that the chitosan-anthocyanin complex was adsorbed on the surface of the microspheres; after filtration, the microspheres were soaked in a 1% sodium tripolyphosphate solution for crosslinking for 30 min, and the above steps were repeated to alternately adsorb the chitosan-anthocyanin complex on the microspheres and crosslink them in the sodium tripolyphosphate solution; after 3-5 cycles, a microcapsule suspension was obtained; The solid content in the microcapsule suspension was adjusted to 5%, and the parameters of the spray dryer were adjusted: the inlet air temperature was 170 ℃, the outlet air temperature was 75 ℃, the peristaltic pump flow rate was 10 mL / min, the atomization pressure was 0.2 MPa, and the dried powder was collected through an 80-mesh sieve to obtain pH-sensitive microcapsules. Example 3

[0024] A tropical fruit preservative film was prepared by the following steps: S1: 100 parts of polyhydroxyalkanoate were added to 500 parts of a mixed solvent of ethyl acetate / ethanol with a volume ratio of 7:3, and stirred at 300 r / min under magnetic stirring at 50 ℃ for 1 h to obtain a polyhydroxyalkanoate solution, 15 parts of a humidity-sensitive block copolymer was added, and stirring was continued until dissolution, and finally 1 part of CuO / SiO2 antibacterial nanozyme, 0.2 part of food-grade Span-80, 2 parts of PEG-400 and 3 parts of plasticizer tributyl citrate were added, and 300 W ultrasonic dispersion was carried out for 40 min, and vacuum degassing treatment was carried out for 20 min to obtain an outer layer spinning solution; S2: 100 parts of polyhydroxyalkanoate were added to 500 parts of a mixed solvent of ethyl acetate / ethanol with a volume ratio of 7:3, and stirred at 300 r / min under magnetic stirring at 50 ℃ for 1 h to obtain a polyhydroxyalkanoate solution, 15 parts of a humidity-sensitive block copolymer was added, and stirring was continued until dissolution, and 5 parts of 4A type hygroscopic zeolite, 0.5 parts of thymol, 0.5 parts of gallic acid were added in turn and stirred for 1 h, and finally 1 part of pH-sensitive microcapsule, 0.1 part of L-ascorbic acid, 0.3 part of food-grade Span-80 and 4 parts of plasticizer tributyl citrate were added, and 200 W ultrasonic dispersion was carried out for 30 min, and vacuum degassing treatment was carried out for 20 min to obtain an inner layer spinning solution; S3: The outer layer spinning solution and the inner layer spinning solution were spun using solution airflow spinning technology, the air humidity was 35%, and the temperature was 25 ℃, the outer layer spinning solution and the inner layer spinning solution were respectively placed in the injection unit of a micro-injection pump, the inner layer spinning solution was separately conveyed, the flow rate was 0.8 mL / h, the pressure was 0.15 MPa, and the substrate layer was formed on the drum after pre-spinning for 10 min, the spinning was paused, 50 μL of a mixed solvent of ethyl acetate / ethanol with a volume ratio of 6:4 was sprayed on the surface of the substrate layer to make the surface slightly swell for 15 s, the inner layer pump and the outer layer pump were started, the flow rate of the inner layer pump was 0.8 mL / h, the pressure was 0.15 MPa, the flow rate of the outer layer pump was 1.0 mL / h, the pressure was 0.17 MPa, the rotating speed of the drum was 30 r / min, the receiving distance was 20 cm, and the spinning time was 60 min. After the spinning was completed, the double-layer film was taken off from the drum, the vacuum degree was maintained at-0.09 MPa, and vacuum drying was carried out at 40 ℃ for 6 h to obtain a tropical fruit preservative film with a total thickness of 50 μm, an inner layer thickness of 30 μm and an outer layer thickness of 20 μm. Example 4

[0025] A tropical fruit preservative film was prepared by the following steps: S1: 100 parts of polyhydroxyalkanoate were added to 550 parts of a mixed solvent of ethyl acetate / ethanol with a volume ratio of 7:3, and stirred at 350 r / min under magnetic stirring at 55 ℃ for 1.2 h to obtain a polyhydroxyalkanoate solution, 20 parts of a humidity-sensitive block copolymer was added, and stirring was continued until dissolution, and finally 2 parts of CuO / SiO2 antibacterial nanozyme, 0.3 parts of food-grade Span-80, 3 parts of PEG-400 and 4 parts of plasticizer tributyl citrate were added, and 350 W ultrasonic dispersion was carried out for 40-45 min, and vacuum degassing treatment was carried out for 20 min to obtain an outer layer spinning solution; S2: 100 parts of polyhydroxyalkanoate were added to 550 parts of a mixed solvent of ethyl acetate / ethanol with a volume ratio of 7:3, and stirred at 350 r / min under magnetic stirring at 55 ℃ for 1.2 h to obtain a polyhydroxyalkanoate solution, 20 parts of a humidity-sensitive block copolymer was added, and stirring was continued until dissolution, and 7 parts of 4A type hygroscopic zeolite, 1 part of thymol, 1 part of gallic acid were added in turn and stirred for 1.2 h, and finally 2 parts of pH-sensitive microcapsules, 0.2 parts of L-ascorbic acid, 0.5 parts of food-grade Span-80 and 6 parts of plasticizer tributyl citrate were added, and 220 W ultrasonic dispersion was carried out for 32 min, and vacuum degassing treatment was carried out for 25 min to obtain an inner layer spinning solution; S3: The outer layer spinning solution and the inner layer spinning solution were spun using solution airflow spinning technology, the air humidity was 40%, and the temperature was 28 ℃, the outer layer spinning solution and the inner layer spinning solution were placed in the injection unit of a micro-injection pump respectively, the inner layer spinning solution was separately conveyed, the flow rate was 0.9 mL / h, the pressure was 0.15 MPa, and the substrate layer was formed on the drum after pre-spinning for 10 min, the spinning was paused, 50 μL of a mixed solvent of ethyl acetate / ethanol with a volume ratio of 6:4 was sprayed on the surface of the substrate layer to make the surface slightly swell for 20 s, the inner layer pump and the outer layer pump were started, the flow rate of the inner layer pump was 0.9 mL / h, the pressure was 0.15 MPa, the flow rate of the outer layer pump was 1.1 mL / h, the pressure was 0.17 MPa, the rotating speed of the drum was 35 r / min, the receiving distance was 23 cm, and the spinning time was 70 min. After the spinning was completed, the double-layer film was taken off from the drum, the vacuum degree was maintained at-0.09 MPa, and vacuum drying was carried out at 40 ℃ for 6 h to obtain a tropical fruit preservative film with a total thickness of 60 μm, an inner layer thickness of 30 μm and an outer layer thickness of 30 μm. Example 5

[0026] A tropical fruit preservative film was prepared by the following steps: S1: 100 parts of polyhydroxyalkanoate were added to 550 parts of a mixed solvent of ethyl acetate / ethanol with a volume ratio of 7:3, and 400 r / min magnetic stirring was carried out at 60 ℃ for 1 h to obtain a polyhydroxyalkanoate solution, 23 parts of a humidity-sensitive block copolymer was added, and stirring was continued until dissolution, and finally 3 parts of CuO / SiO2 antibacterial nanozyme, 0.5 parts of food-grade Span-80, 4 parts of PEG-400 and 6 parts of plasticizer tributyl citrate were added, and 360 W ultrasonic dispersion was carried out for 40 min, and vacuum degassing treatment was carried out for 30 min to obtain an outer layer spinning solution; S2: 100 parts of polyhydroxyalkanoate were added to 550 parts of a mixed solvent of ethyl acetate / ethanol with a volume ratio of 7:3, and 400 r / min magnetic stirring was carried out at 55 ℃ for 1 h to obtain a polyhydroxyalkanoate solution, 23 parts of a humidity-sensitive block copolymer was added, and stirring was continued until dissolution, and 8 parts of 4A type hygroscopic zeolite, 1 part of thymol and 1 part of gallic acid were added in sequence and stirred for 1.5 h, and finally 1.5 parts of pH-sensitive microcapsules, 0.2 parts of L-ascorbic acid, 0.6 parts of food-grade Span-80 and 6 parts of plasticizer tributyl citrate were added, and 230 W ultrasonic dispersion was carried out for 33 min, and vacuum degassing treatment was carried out for 25 min to obtain an inner layer spinning solution; S3: The outer layer spinning solution and the inner layer spinning solution were spun using a solution airflow spinning technology, the air humidity was 45%, and the temperature was 28 ℃, the outer layer spinning solution and the inner layer spinning solution were respectively placed in the injection unit of a micro-injection pump, the inner layer spinning solution was separately conveyed, the flow rate was 1.0 mL / h, the pressure was 0.15 MPa, a base layer was formed on a roller after pre-spinning for 10 min, the spinning was paused, 50 μL of a mixed solvent of ethyl acetate / ethanol with a volume ratio of 6:4 was sprayed on the surface of the base layer to slightly swell the surface for 25 s, the inner layer pump and the outer layer pump were started, the flow rate of the inner layer pump was 1.0 mL / h, the pressure was 0.15 MPa, the flow rate of the outer layer pump was 1.0 mL / h, the pressure was 0.17 MPa, the roller rotation speed was 35 r / min, the receiving distance was 25 cm, and the spinning time was 75 min. After the spinning was completed, the double-layer film was taken off from the roller, the vacuum degree was maintained at -0.09 MPa, and vacuum drying was carried out at 40 ℃ for 6 h to obtain a tropical fruit preservative film with a total thickness of 65 μm, an inner layer thickness of 30 μm and an outer layer thickness of 35 μm. Example 6

[0027] A tropical fruit preservative film was prepared by the following steps: S1: 100 parts of polyhydroxyalkanoate were added to 580 parts of a mixed solvent of ethyl acetate / ethanol with a volume ratio of 7:3, and stirred at 370 r / min under magnetic stirring at 57 ℃ for 1.4 h to obtain a polyhydroxyalkanoate solution, 23 parts of a humidity-sensitive block copolymer was added, and stirring was continued until dissolution, and finally 2.5 parts of CuO / SiO2 antibacterial nanoreactor, 0.5 parts of food-grade Span-80, 3.5 parts of PEG-400 and 7 parts of plasticizer tributyl citrate were added, and dispersed under ultrasonic wave at 380 W for 42 min, and then vacuum degassing treatment was carried out for 28 min to obtain the outer layer spinning solution; S2: 100 parts of polyhydroxyalkanoate were added to 580 parts of a mixed solvent of ethyl acetate / ethanol with a volume ratio of 7:3, and stirred at 370 r / min under magnetic stirring at 57 ℃ for 1.4 h to obtain a polyhydroxyalkanoate solution, 23 parts of a humidity-sensitive block copolymer was added, and stirring was continued until dissolution, and then 7 parts of 4A type hygroscopic zeolite, 1.8 parts of thymol, 1.8 parts of gallic acid were added and stirred for 1.5 h, and finally 2.5 parts of pH-sensitive microcapsules, 0.15 parts of L-ascorbic acid, 0.75 parts of food-grade Span-80 and 7 parts of plasticizer tributyl citrate were added, and dispersed under ultrasonic wave at 240 W for 34 min, and then vacuum degassing treatment was carried out for 27 min to obtain the inner layer spinning solution; S3: The outer layer spinning solution and the inner layer spinning solution were spun using solution airflow spinning technology, the air humidity was 40%, and the temperature was 30 ℃, the outer layer spinning solution and the inner layer spinning solution were respectively placed in the injection unit of a micro-injection pump, the inner layer spinning solution was separately conveyed, the flow rate was 1.0 mL / h, the pressure was 0.15 MPa, and the substrate layer was formed on the drum after pre-spinning for 10 min, the spinning was paused, 50 μL of a mixed solvent of ethyl acetate / ethanol with a volume ratio of 6:4 was sprayed on the surface of the substrate layer to make the surface slightly swell for 20 s, the inner layer pump and the outer layer pump were started, the flow rate of the inner layer pump was 1.0 mL / h, the pressure was 0.15 MPa, the flow rate of the outer layer pump was 1.1 mL / h, the pressure was 0.17 MPa, the rotating speed of the drum was 40 r / min, the receiving distance was 24 cm, and the spinning time was 80 min. After the spinning was completed, the double-layer film was taken off from the drum, the vacuum degree was maintained at -0.09 MPa, and vacuum drying was carried out at 40 ℃ for 6 h to obtain a tropical fruit preservative film with a total thickness of 70 μm, an inner layer thickness of 35 μm and an outer layer thickness of 35 μm. Example 7

[0028] A tropical fruit preservative film was prepared by the following steps: S1: 100 parts of polyhydroxyalkanoate were added to 600 parts of a mixed solvent of ethyl acetate / ethanol with a volume ratio of 7:3, and stirred at 57 °C and 300 r / min for 1.5 h by magnetic stirring to obtain a polyhydroxyalkanoate solution. Then, 20 parts of a humidity-sensitive block copolymer was added and stirred until dissolved. Finally, 1.5 parts of CuO / SiO2 antibacterial nanoreactor, 0.5 parts of food-grade Span-80, 5 parts of PEG-400 and 6 parts of plasticizer tributyl citrate were added, and ultrasonic dispersion was performed at 350 W for 40 min. After vacuum degassing treatment for 25 min, an outer layer spinning solution was obtained; S2: 100 parts of polyhydroxyalkanoate were added to 600 parts of a mixed solvent of ethyl acetate / ethanol with a volume ratio of 7:3, and stirred at 57 °C and 300 r / min for 1.5 h by magnetic stirring to obtain a polyhydroxyalkanoate solution. Then, 22 parts of a humidity-sensitive block copolymer was added and stirred until dissolved. Then, 8 parts of 4A type hygroscopic zeolite, 2 parts of thymol, 1.5 parts of gallic acid were added and stirred for 1.5 h. Finally, 2.5 parts of pH-sensitive microcapsules, 0.2 parts of L-ascorbic acid, 0.6 parts of food-grade Span-80 and 8 parts of plasticizer tributyl citrate were added, and ultrasonic dispersion was performed at 250 W for 32 min. After vacuum degassing treatment for 30 min, an inner layer spinning solution was obtained; S3: The outer layer spinning solution and the inner layer spinning solution were spun using a solution airflow spinning technology. The air humidity was 35%, and the temperature was 30 °C. The outer layer spinning solution and the inner layer spinning solution were placed in the injection units of micro-injection pumps, respectively. The inner layer spinning solution was separately conveyed at a flow rate of 1.0 mL / h and a pressure of 0.15 MPa. A base layer was formed on a drum after pre-spinning for 10 min. The spinning was paused, and 50 μL of a mixed solvent of ethyl acetate / ethanol with a volume ratio of 6:4 was sprayed on the surface of the base layer to slightly swell the surface for 30 s. The inner layer pump and the outer layer pump were started. The flow rate of the inner layer pump was 1.0 mL / h, and the pressure was 0.15 MPa. The flow rate of the outer layer pump was 1.0 mL / h, and the pressure was 0.17 MPa. The drum rotation speed was 30 r / min, the receiving distance was 20 cm, and the spinning time was 85 min. After the spinning was completed, the double-layer film was taken off from the drum. The vacuum degree was maintained at -0.09 MPa, and the double-layer film was vacuum dried at 40 °C for 6 h to obtain a tropical fruit preservative film with a total thickness of 75 μm, an inner layer thickness of 40 μm and an outer layer thickness of 35 μm. Figure 1 A scanning electron microscope image of the tropical fruit preservative film prepared in this example Example 8

[0029] A tropical fruit preservative film was prepared by the following steps: S1: 100 parts of polyhydroxyalkanoate were added to 580 parts of a mixed solvent of ethyl acetate / ethanol with a volume ratio of 7:3, and 400 r / min magnetic stirring was carried out at 60 ℃ for 1.5 h to obtain a polyhydroxyalkanoate solution. Then, 25 parts of a humidity-sensitive block copolymer was added and stirring was continued until dissolution. Finally, 3 parts of CuO / SiO2 antibacterial nanoreactor, 0.6 parts of food-grade Span-80, 4 parts of PEG-400 and 8 parts of plasticizer tributyl citrate were added, and 400 W ultrasonic dispersion was carried out for 45 min. After vacuum degassing treatment for 30 min, the outer layer spinning solution was obtained; S2: 100 parts of polyhydroxyalkanoate were added to 580 parts of a mixed solvent of ethyl acetate / ethanol with a volume ratio of 7:3, and 400 r / min magnetic stirring was carried out at 60 ℃ for 1.5 h to obtain a polyhydroxyalkanoate solution. Then, 25 parts of a humidity-sensitive block copolymer was added and stirring was continued until dissolution. Then, 10 parts of 4A type hygroscopic zeolite, 2 parts of thymol and 2 parts of gallic acid were added and stirred for 1.5 h. Finally, 3 parts of pH-sensitive microcapsules, 0.2 parts of L-ascorbic acid, 0.8 parts of food-grade Span-80 and 9 parts of plasticizer tributyl citrate were added, and 250 W ultrasonic dispersion was carried out for 35 min. After vacuum degassing treatment for 30 min, the inner layer spinning solution was obtained; S3: The outer layer spinning solution and the inner layer spinning solution were spun using solution airflow spinning technology. The air humidity was 50% and the temperature was 30 ℃. The outer layer spinning solution and the inner layer spinning solution were placed in the injection units of the micro-injection pump respectively, and the inner layer spinning solution was conveyed alone at a flow rate of 1.0 mL / h and a pressure of 0.15 MPa. The base layer was formed on the drum after pre-spinning for 10 min. The spinning was paused, and 50 μL of a mixed solvent of ethyl acetate / ethanol with a volume ratio of 6:4 was sprayed on the surface of the base layer to make the surface slightly swell for 30 s. The inner layer pump and the outer layer pump were started, and the inner layer pump was operated at a flow rate of 1.0 mL / h and a pressure of 0.15 MPa, while the outer layer pump was operated at a flow rate of 1.2 mL / h and a pressure of 0.17 MPa. The drum rotated at a speed of 40 r / min, the receiving distance was 25 cm, and the spinning time was 90 min. After spinning, the double-layer film was taken off from the drum, and vacuum drying was carried out at 40 ℃ for 6 h under a vacuum degree of-0.09 MPa. Thus, a tropical fruit preservative film with a total thickness of 80 μm, an inner layer thickness of 40 μm and an outer layer thickness of 40 μm was obtained. Comparative Example 1

[0030] The difference between this comparative example and Example 7 is that the outer layer spinning solution does not contain CuO / SiO2 antibacterial nanoreactor, and the rest of the conditions are the same as those in Example 7. Comparative Example 2

[0031] The difference between this comparative example and Example 7 is that the inner layer spinning solution does not contain hygroscopic zeolite, thymol and gallic acid, and the rest of the conditions are the same as those in Example 7. Comparative Example 3

[0032] The difference between this comparative example and Example 7 is that the outer layer spinning solution does not contain CuO / SiO2antibacterial nanoreactor, and the inner layer spinning solution does not contain hygroscopic zeolite, thymol and gallic acid, and the rest of the conditions are consistent with Example 7. Comparative Example 4

[0033] The difference between this comparative example and Example 7 is that the base layer is not pre-spun on the roller for 10 min, and the rest of the conditions are consistent with Example 7. Comparative Example 5

[0034] The difference between this comparative example and Example 7 is that the inner layer spinning solution does not contain pH-sensitive microcapsules, and the rest of the conditions are consistent with Example 7.

[0035] The physical performance indicators of the preservative films prepared in Examples 3-8 and Comparative Examples 1-5 were measured, the tensile strength and elongation at break were determined according to GB / T 1040.3-2022, the oxygen transmission rate was determined according to GB / T 19789-2022, and the water vapor transmission rate was determined according to GB / T 1037-2021. The results are shown in Table 1.

[0036] The tensile strength and elongation at break of Example 7 are the highest, indicating that its mechanical properties are the best, which is related to the synergistic effect of the ratio of inner / outer layer spinning solution and spinning process parameters, and the structure is more compact and flexible; the examples are better than the comparative examples. The comparative examples are the worst in mechanical properties because of the absence of antibacterial nanoreactor and hygroscopic antibacterial ingredients, and the pre-spinning of the inner layer film, the compatibility of the film material decreases. The oxygen transmission rate and water vapor transmission rate of Example 7 are the lowest, indicating that its barrier properties are the best, which can inhibit excessive respiration of fruits (reduce O2entry) and water loss (control water vapor transmission); the barrier property of the comparative examples is significantly reduced due to the double absence of antibacterial and hygroscopic ingredients, and the loose structure of the film material.

[0037] The typical spoilage microorganism antibacterial performance of the preservative films prepared in Examples 3-8 and Comparative Examples 1-5 was determined according to GB / T 21510-2023, and the results are shown in Table 2.

[0038]

[0039] As can be seen from Table 2, the bacteriostatic rate of Example 7 is the highest, because the CuO / SiO2antibacterial nanoreactor in the outer layer and the thymol and gallic acid in the inner layer form a synergistic antibacterial system, which can inhibit a wide range of molds and bacteria; the bacteriostatic rate of Comparative Example 1 (lacking antibacterial nanoreactor) decreases, indicating the importance of antibacterial ingredients in the outer layer; the bacteriostatic rate of Comparative Example 2 (lacking thymol and gallic acid) is lower than that of the examples, indicating the role of antibacterial ingredients in the inner layer; the antibacterial system of Comparative Example 3 is completely ineffective due to the double absence, and the bacteriostatic rate is the lowest.

[0040] With the tropical fruit mango as the object, 100 mangoes with uniform quality, consistent maturity, and no mold, rot, browning, and damage on the surface were prepared, and stored for 7 days under the conditions of an external environment of 25 ℃ and a humidity of 50% RH. The preservative effect of the preservative films prepared in Examples 3-8 and Comparative Examples 1-4 was verified, including the determination of the weight loss rate, browning index, rot rate, and PH sensitive microcapsule response time. Among them, the weight loss rate was determined by GB / T 10658-2021; the browning grading standard was as follows: 0 level: no browning on the peel; 1 level: browning area ≤10%; 2 level: browning area 11%-30%; 3 level: browning area 31%-50%; 4 level: browning area >50%. The browning index = ∑(fruit number of each level × corresponding level number) / (total fruit number × highest level number) × 100%; the rot rate (%) = rot fruit number / total fruit number × 100%; the pH sensitive microcapsule response time refers to the time length from the release of acidic substances by the fruit to the color change (ΔE>5) of the preservative film, which gradually turns purple red when the pH is 5.0-6.0, turns pink when the pH further decreases to 4.0-5.0 (in the middle and later stages of corruption), and turns bright red if the corruption is severe (pH<4.0). The results are shown in Table 3.

[0041]

[0042] It can be seen that the weight loss rate, browning index, and rot rate are all lowest in Example 7, because its barrier property and antibacterial property are optimal, and the moisture-absorbing zeolite in the inner layer can adjust the microenvironment humidity and reduce condensate water; the comparative examples have no antibacterial and moisture-absorbing ingredients, so the fruit loses water quickly (high weight loss rate), microorganisms multiply rapidly (high rot rate), and browning is the most serious; Example 7 has the shortest response time, indicating that its pH sensitive microcapsules are more evenly distributed and more sensitive to acidic substances; Comparative Examples 1-3 (containing pH sensitive microcapsules but lacking outer and inner antibacterial ingredients) respond more slowly, because the fruit rots faster, and the accumulation rate of acidic substances is not matched with the microcapsules; Comparative Example 5 has no pH sensitive microcapsules and has no response at all.

[0043] The above examples are only for the purpose of illustrating the technical concept and characteristics of the present application, and the purpose is to enable those skilled in the art to understand the content of the present application and to implement it, and cannot limit the protection scope of the present application. Any equivalent changes or modifications made in accordance with the essence of the present application should be covered within the protection scope of the present application.

Claims

1. A tropical fruit preservative film, characterized in that: The fresh-keeping film has a double-layer structure, the outer layer is a moisture-blocking and antibacterial layer, and the inner layer is a water-absorbing and anti-fog-proof and antibacterial layer; the water-absorbing and anti-fog-proof and antibacterial layer also includes pH-sensitive microcapsules.

2. The tropical fruit preservative film according to claim 1, wherein The outer layer is composed of polyhydroxyalkanoate, humidity-sensitive block copolymer, and CuO / SiO2 antibacterial nanozyme; the water-absorbing anti-fog antibacterial layer is composed of polyhydroxyalkanoate, humidity-sensitive block copolymer, hygroscopic zeolite, thymol, gallic acid and pH-sensitive microcapsules.

3. The method for preparing the tropical fruit preservative film according to any one of claims 1 to 2, comprising the steps of: S1: Add polyhydroxyalkanoate to ethyl acetate / ethanol mixed solvent, and stir magnetically at 300-400 r / min at 50-60 °C for 1-1.5 h to obtain a polyhydroxyalkanoate solution. Add the moisture-sensitive block copolymer and continue stirring until dissolved. Finally, add CuO / SiO2 antibacterial nanozyme, food-grade Span-80, PEG-400, and plasticizer tributyl citrate. Ultrasonic dispersion is performed at 300-400 W for 40-45 min, and vacuum degassing is performed for 20-30 min to obtain the outer layer spinning solution. S2: Add polyhydroxyalkanoate to an ethyl acetate / ethanol mixed solvent, and stir magnetically at 300-400 r / min at 50-60°C for 1-1.5 h to obtain a polyhydroxyalkanoate solution. Add the moisture-sensitive block copolymer and continue stirring until dissolved. Then, add hygroscopic zeolite, thymol, and gallic acid in sequence and stir for 1-1.5 h. Finally, add pH-sensitive microcapsules, L-ascorbic acid, food-grade Span-80, and plasticizer tributyl citrate. Ultrasonic dispersion is performed at 200-250 W for 30-35 min. After vacuum degassing for 20-30 min, the inner layer spinning solution is obtained. S3: The outer layer spinning solution and the inner layer spinning solution are spun sequentially using solution air-jet spinning technology. After the spinning is completed, the double-layer film is removed from the drum, the vacuum degree is maintained at -0.09 MPa, and vacuum drying is performed at 40°C for 6 hours to obtain the tropical fruit cling film.

4. The preparation method according to claim 3, wherein The volume ratio of ethyl acetate to ethanol in the ethyl acetate / ethanol mixed solvent in S1 and S2 is both 7:

3.

5. The preparation method according to claim 3, wherein In parts by weight, the ratio of polyhydroxyalkanoate, ethyl acetate / ethanol mixed solvent, moisture-sensitive block copolymer, CuO / SiO2 antibacterial nanozyme, food-grade Span-80, PEG-400 and plasticizer tributyl citrate in S1 is 100 parts: (500-600) parts: (15-25) parts: (1-3) parts: (0.2-0.6) parts: (2-5) parts: (3-8) parts.

6. The preparation method according to claim 3, wherein The preparation method of the CuO / SiO2 antibacterial nanozyme in S1 is as follows: 90 mL of ethanol, 10 mL of deionized water, and 2.5 mL of ammonia water were added to the container in sequence, and stirred at 600 rpm in a constant temperature water bath at 25 °C. 4.0 g of tetraethyl orthosilicate was slowly added dropwise and stirred for 30 min to obtain a milky white SiO2 sol. 20 mL of 0.2 M Cu(NO3)2 solution and 10 mL of 0.05 M hexadecyltrimethylammonium bromide solution were mixed evenly and then added dropwise to the SiO2 sol at a uniform rate. During the addition process, ice-bath ultrasonication was maintained at 40 kHz and 200 W. After the addition was completed, ultrasonication was continued for 20 min to obtain a sol. 0.25 g of dodecyltriethoxysilane was added to the sol, and the mixture was heated to 50 °C and stirred for 2 h. The mixture was allowed to stand at room temperature for 12 h to form a wet gel. The mixture was then vacuum dried at 60 °C for 6 h to obtain a light yellow dry gel block. The temperature was raised to 550°C at 3°C / min in a muffle furnace and kept in air atmosphere for 3 h to remove hexadecyltrimethylammonium bromide and form CuO nanocrystals; after natural cooling, black powder was obtained, which was dispersed in 0.1 M NaOH for 30 min, and then washed twice with ethanol and deionized water; finally, it was vacuum dried at 80°C for 4 h to obtain CuO / SiO2 antibacterial nanozyme.

7. The preparation method according to claim 3, wherein In parts by weight, the ratio of polyhydroxyalkanoate, ethyl acetate / ethanol mixed solvent, humidity-sensitive block copolymer, hygroscopic zeolite, thymol, gallic acid, pH-sensitive microcapsules, L-ascorbic acid, food-grade Span-80 and plasticizer tributyl citrate in S2 is 100 parts: (500-600) parts: (15-25) parts: (5-10) parts: (0.5-2) parts: (0.5-2) parts: (1-3) parts: (0.1-0.2) parts: (0.3-0.8) parts: (4-9) parts.

8. The preparation method according to claim 3, wherein The preparation method of the pH sensitive microcapsules in S2 is as follows: Chitosan was dissolved in 1% acetic acid solution and stirred at room temperature until completely dissolved to obtain a 2% chitosan acetic acid solution. Anthocyanin was dissolved in deionized water and sonicated for 10 minutes to obtain a 1% anthocyanin solution. In a 50°C constant temperature water bath, the anthocyanin solution was slowly added dropwise to the chitosan acetic acid solution at a volume ratio of 1:5 while stirring at 400 rpm. After the addition was complete, stirring was continued for 2 hours to form a chitosan-anthocyanin complex solution. Sodium alginate was dissolved in deionized water and stirred at room temperature until completely dissolved to obtain a 2% sodium alginate solution. CaCl2 was dissolved in deionized water to prepare a 5% calcium chloride solution. The sodium alginate solution was added dropwise to the calcium chloride solution using a syringe. After solidification for 30 minutes, the solution was filtered and washed three times with deionized water to obtain calcium alginate microspheres with a diameter of 1 mm. Calcium alginate microspheres were immersed in a chitosan-anthocyanidin complex solution and shaken at room temperature for 2 h to allow the chitosan-anthocyanidin complex to adsorb on the surface of the microspheres. After filtration, the microspheres were immersed in a 1% sodium tripolyphosphate solution for cross-linking for 30 min. The above steps were repeated to allow the microspheres to alternately adsorb the chitosan-anthocyanidin complex and cross-link in the sodium tripolyphosphate solution. After 3-5 cycles, a microcapsule suspension was obtained. The solid content of the microcapsule suspension was adjusted to 5%, and the spray dryer parameters were adjusted as follows: inlet air temperature 170 °C, outlet air temperature 75 °C, peristaltic pump flow rate 10 mL / min, atomization pressure 0.2 MPa. The dried powder was collected and passed through an 80-mesh sieve to obtain pH-sensitive microcapsules.

9. The preparation method according to claim 3, wherein The specific operation of the solution air-jet spinning technology in S3 is as follows: the air humidity is 35-50% and the temperature is 25-30°C, the outer layer spinning solution and the inner layer spinning solution are respectively placed in the injection unit of the micro-injection pump, the inner layer spinning solution is separately delivered at a flow rate of 0.8-1.0 mL / h and a pressure of 0.15 MPa, and the base layer is pre-spun on the drum for 10 minutes to form the base layer, the spinning is paused, and 50 μL of a mixed solvent of ethyl acetate / ethanol with a volume ratio of 6:4 is sprayed on the surface of the base layer to make the surface slightly swell for 15-30 seconds; the inner layer pump and the outer layer pump are started, the flow rate of the inner layer pump is 0.8-1.0 mL / h and the pressure is 0.15 MPa, the flow rate of the outer layer pump is 1.0-1.2 mL / h and the pressure is 0.17 MPa, the drum speed is 30-40 r / min, the receiving distance is 20-25 cm, and the spinning time is 60-90 min.

10. Use of the tropical fruit preservative film according to any one of claims 1 to 2 and the tropical fruit preservative film obtained by the preparation method according to any one of claims 3 to 9 in the storage and transportation of tropical fruits.

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