Polysaccharide-based preservative film liquid as well as preparation method and application thereof

Abstract

The invention belongs to the technical field of food packaging films, and particularly relates to polysaccharide-based preservative film liquid as well as a preparation method and application thereof. The polysaccharide-based preservative film liquid is prepared from high-viscosity sodium carboxymethyl cellulose, HKUST-1, cinnamon essential oil, liquid paraffin, tween-80 and water. The selected hydrophobic functional component loading agent is a copper-based metal organic framework HKUST-1 with excellent characteristics of chemical stability, environmental sustainability, low cost and the like; finally, an emulsion carrying system is formed by the cinnamon essential oil, high-viscosity sodium carboxymethyl cellulose and tween-80 to quickly prepare a plant essential oil humidity response release coating, so that the cinnamon essential oil and the liquid paraffin can be slowly released along with humidity change and act on the surfaces of the mangoes for a long time. The method is simple to operate, green and environment-friendly, and can effectively improve the mango quality.

Description

Technical Field

[0001] The present application belongs to the technical field of food packaging films, and specifically relates to a polysaccharide-based cling film liquid and a preparation method and application thereof. Background Art

[0002] Mango (Mangifera indica Linn) belongs to the genus Mangifera of the Anacardiaceae family. It has delicate flesh, unique flavor and high nutritional value. It is a famous fruit in tropical regions and is deeply loved by consumers. Mango is a typical respiratory climacteric fruit. It is generally harvested when the fruit is not fully ripe. Its respiration rises in the early stage of storage until it reaches its peak respiration. After reaching the maturity period, its respiration begins to decrease as the storage time increases. Mangoes will undergo a series of changes during the post-harvest storage process. The peel gradually changes from green when picked to yellow or golden yellow, and the fruit gradually softens. At the same time, the harvested mango is also susceptible to infection by pathogenic microorganisms, which makes the fruit intolerant to storage and transportation, and prone to diseases such as anthrax, stem rot and aspergillus.

[0003] In recent years, due to the good biodegradability of coating preservation technology, it has been increasingly used in fruits and vegetables. The coating changes the micro-gas environment on the surface of fruits and vegetables, effectively preventing the loss of water and microbial infection of fruits and vegetables, thereby achieving the purpose of preservation. Carboxymethyl cellulose is an anionic polysaccharide produced by introducing -CH2COOH groups into the cellulose molecular chain. Although a single carboxymethyl cellulose coating has the advantages of excellent film-forming ability, water solubility, easy cleaning, safety and low cost, it has high water vapor permeability, poor mechanical strength, and unobvious preservation effect. By adding a hydrophobic preservative to the carboxymethyl cellulose coating, its barrier, antibacterial and antioxidant properties can be improved in a targeted manner. Plant essential oils and liquid paraffin, as safe food additives and spices, have been proven to have good barrier, antioxidant and antibacterial functions. However, the poor water solubility, volatility and strong aroma of essential oils and liquid paraffin greatly limit their application in food. Therefore, it is necessary to prepare a carrier system that can load a large amount of essential oils. Summary of the invention

[0004] The purpose of the embodiments of the present application is to provide a polysaccharide-based cling film liquid, which can at least solve the problems of the current coating having high water vapor permeability, poor mechanical strength, and unclear fresh-keeping effect, and the essential oils and liquid paraffin having poor water solubility, high volatility, and strong aroma.

[0005] In order to solve the above technical problems, this application is implemented as follows: In a first aspect, an embodiment of the present application provides a polysaccharide-based cling film liquid, the polysaccharide-based cling film liquid comprising high-viscosity sodium carboxymethyl cellulose, HKUST-1, cinnamon essential oil, liquid paraffin, Tween-80 and water; The weight ratio of the high-viscosity sodium carboxymethyl cellulose, the HKUST-1, the cinnamon essential oil, the liquid paraffin, the Tween-80 and the water is 2-3: 0.2-0.4: 0.4-0.6: 0.2-0.3: 0.3-0.5: 100.

[0006] The present invention adopts water-resistant HKUST-1 to load cinnamon essential oil and liquid paraffin, constructs an emulsion carrier system through Tween-80, and embeds HKUST-1 in combination with high-viscosity sodium carboxymethyl cellulose through a one-pot method to prepare a coating liquid, so that the cinnamon essential oil and liquid paraffin can respond to humidity changes and slowly act on the surface of fruits and vegetables, thereby prolonging the preservation effect.

[0007] In a second aspect, the present application provides a method for preparing a polysaccharide-based cling film liquid, comprising the following steps: High-viscosity sodium carboxymethyl cellulose, Tween-80, cinnamon essential oil, liquid paraffin and HKUST-1 in a preset weight ratio are dissolved in water, and stirred for reaction at 25° C.-45° C. for 1 h-2 h to obtain the polysaccharide-based cling film liquid.

[0008] The preset weight ratio of the high-viscosity sodium carboxymethyl cellulose, Tween-80, cinnamon essential oil, liquid paraffin, HKUST-1 and water is 2-3: 0.3-0.5: 0.4-0.6: 0.2-0.3: 0.2-0.4: 100.

[0009] Optionally, the above HKUST-1 is obtained by the following steps: Copper nitrate trihydrate, 1,3,5-benzoic acid and polyvinyl pyrrolidone are dissolved in N,N-dimethylformamide, stirred, centrifuged and freeze-dried to obtain the HKUST-1.

[0010] Optionally, the usage ratio of the copper nitrate trihydrate, the 1,3,5-benzoic acid, the polyvinyl pyrrolidone and the N,N-dimethylformamide is 15 mmol-20 mmol: 8 mmol-10 mmol: 0.15 mmol-0.25 mmol: 100 mL.

[0011] Optionally, the stirring operation is performed at a temperature of 85°C-95°C and for a time of 24 h-48 h.

[0012] Optionally, the viscosity of the high-viscosity sodium carboxymethyl cellulose is 800-1200 mPa·s.

[0013] In a third aspect, the embodiments of the present application provide a polysaccharide-based cling film liquid or the use of the polysaccharide-based cling film liquid prepared by the above-mentioned preparation method in food preservation.

[0014] Optionally, the above food is mango In a third aspect, the present application provides a method for preserving mangoes, comprising the following steps: The pretreated mango is immersed in the above-mentioned polysaccharide-based preservative film liquid or the polysaccharide-based preservative film liquid prepared by the above-mentioned preparation method, taken out after 1 min to 3 min, and naturally air-dried.

[0015] Optionally, the freshly picked mangoes are washed and then soaked in a sodium hypochlorite disinfectant, and then taken out and dried naturally after the soaking.

[0016] The volume concentration of the sodium hypochlorite disinfectant is 0.1%-0.5%.

[0017] The beneficial effects of the present invention are: The preparation method for preserving mango after harvest proposed by the present invention selects a water-resistant HKUST-1 porous material to load a large amount of active ingredient cinnamon essential oil and hydrophobic component liquid paraffin, combines a high-viscosity sodium carboxymethyl cellulose film-forming matrix and a Tween-80-induced emulsion carrier system, and quickly synthesizes a humidity-responsive multifunctional coating through a simple one-pot method, while solving the problems of cumbersome synthesis steps, self-structural disintegration, and limited functions of the embedded metal organic framework membrane. The plant essential oil humidity-responsive release coating is a preservative material with environmental self-regulation and powerful preservation function. Compared with traditional emulsion coatings, it has a good functional component loading rate, antibacterial and antioxidant, barrier properties, etc., and can respond to the increase of the humidity on the surface of fruits and vegetables to increase the release of functional components. At the same time, the hydrophobic functional component loading agent selected by the present invention is a copper-based metal organic framework HKUST-1 with excellent characteristics such as chemical stability, environmental sustainability, and low cost; finally, an emulsion carrier system is formed with high-viscosity sodium carboxymethyl cellulose and Tween-80 to quickly prepare a plant essential oil humidity-responsive release coating, so that cinnamon essential oil and liquid paraffin can be slowly released with humidity changes and act on the mango surface for a long time. The method is simple to operate, green and environmentally friendly, and can effectively improve the quality of mangoes. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0019] Figure 1 are the data results related to the functional properties of the film samples provided in some embodiments of the present application, (a) active ingredient loading rate, (b) inhibition zone area, (c) water vapor permeability coefficient (WVP); Figure 2The humidity response release behavior of cinnamon essential oil in film samples provided by some embodiments of the present application (10%, 30%, 40% simulated humidity); Figure 3 The appearance changes of mangoes during storage provided by some embodiments of the present application; Figure 4 The color parameter changes of mangoes during storage provided by some embodiments of the present application ( L , a* , b* ); Figure 5 These are scanning electron microscope (SEM) images of Cu-BTC and 1% PVP@Cu-BTC provided in some embodiments of the present application after being immersed in water for 0, 1, 8 and 24 hours; a (Cu-BTC, 10,000 times); b (1% PVP@Cu-BTC, 30,000 times); Figure 6 These are scanning electron microscope (SEM) images of the surface morphology of each film provided by some embodiments of the present application: comparative example 1 film (A, 1000 times; a, 5000 times), comparative example 2 film (B, 5000 times; b, 10000 times), comparative example 3 film (C, 5000 times; c, 10000 times), comparative example 4 film (D, 2000 times; d, 10000 times), example 4 film (E, 5000 times; e, 30000 times), and example 1 film (F, 5000 times; f, 30000 times). DETAILED DESCRIPTION

[0020] The following will be combined with the drawings in the embodiments of the present application to clearly and completely describe the technical solutions in the embodiments of the present application. Obviously, the described embodiments are part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0021] In the following, in conjunction with the accompanying drawings, the polysaccharide-based cling film liquid, preparation method and application provided in the embodiments of the present application are described in detail through specific embodiments and their application scenarios.

[0022] In a first aspect, the present application provides a polysaccharide-based cling film liquid, which comprises high-viscosity sodium carboxymethyl cellulose, HKUST-1, cinnamon essential oil, liquid paraffin, Tween-80 and water; The weight ratio of high-viscosity sodium carboxymethyl cellulose, HKUST-1, cinnamon essential oil, liquid paraffin, Tween-80 and water is 2-3: 0.2-0.4: 0.4-0.6: 0.2-0.3: 0.3-0.5: 100.

[0023] Beneficial effects: The hydrophobic functional component loading agent selected by the present invention is the copper-based metal organic framework HKUST-1 with excellent characteristics such as chemical stability, environmental sustainability, and low cost; finally, by forming an emulsion carrier system with high-viscosity sodium carboxymethyl cellulose and Tween-80, a plant essential oil humidity-responsive release coating is quickly prepared, so that cinnamon essential oil and liquid paraffin can be slowly released with humidity changes and act on the mango surface for a long time. The method is simple to operate, green and environmentally friendly, and can effectively improve the quality of mangoes.

[0024] In a second aspect, the present application provides a method for preparing a polysaccharide-based cling film liquid, comprising the following steps: High-viscosity sodium carboxymethyl cellulose, Tween-80, cinnamon essential oil, liquid paraffin and HKUST-1 are dissolved in water, and stirred to react at 25° C.-45° C. for 1 h-2 h to obtain the polysaccharide-based fresh-keeping film liquid.

[0025] Beneficial effects: The present invention selects water-resistant HKUST-1 porous material to load a large amount of active ingredient cinnamon essential oil and hydrophobic component liquid paraffin, combines a high-viscosity sodium carboxymethyl cellulose film-forming matrix and a Tween-80-induced emulsion delivery system, and quickly synthesizes a humidity-responsive multifunctional coating through a simple one-pot method, while solving the problems of cumbersome synthesis steps, self-structural disintegration, and limited functions of the embedded metal organic framework membrane.

[0026] In some embodiments, HKUST-1 is obtained by the following steps: Copper nitrate trihydrate, 1,3,5-benzoic acid and polyvinyl pyrrolidone are dissolved in N,N-dimethylformamide, stirred, centrifuged and freeze-dried to obtain the HKUST-1. Compared with conventional HKUST-1, the HKUST-1 prepared by the method of the present invention has reduced moisture sensitivity to a certain extent and improved its tolerance in water.

[0027] In some embodiments, the amount ratio of copper nitrate trihydrate, 1,3,5-benzoic acid, polyvinyl pyrrolidone and N,N-dimethylformamide is 15 mmol-20 mmol: 8 mmol-10 mmol: 0.15 mmol-0.25 mmol: 100 mL. In the method of the present invention, excessive or insufficient amounts of these raw materials will lead to problems such as easy collapse of HKUST-1 structure, low purity, uneven size distribution, and poor dispersibility.

[0028] In some embodiments, the temperature during the stirring operation is 85°C-95°C, and the time is 24 h-48 h. The preparation method of the present invention has the advantages of low energy consumption, controllable reaction, and few by-products in this temperature range. In addition, too high a temperature may increase the crystal particle size, morphological distortion, thermal decomposition, etc., and too high a temperature may cause slow crystal growth, irregular morphology, incomplete reaction, etc.

[0029] In some embodiments, the viscosity of high viscosity sodium carboxymethyl cellulose is 800-1200 mPa·s.

[0030] In a third aspect, the present application provides an application of a polysaccharide-based cling film liquid in food preservation.

[0031] In some embodiments, the food is mango.

[0032] In a fourth aspect, the present application provides a method for preserving mangoes, comprising the following steps: Soak the pretreated mango in the above-mentioned polysaccharide-based plastic wrap solution, take it out after 1 min-3 min, and air-dry it naturally.

[0033] In some embodiments, the pre-processing steps are as follows: Wash the freshly picked mangoes and soak them in sodium hypochlorite disinfectant. After soaking, take them out and dry them naturally.

[0034] The volume concentration of the sodium hypochlorite disinfectant is 0.1%-0.5%.

[0035] Beneficial effects: The polysaccharide-based cling film liquid of the present invention is used for the preservation of mangoes after harvest. Compared with traditional emulsion coatings, it has a good functional component loading rate, antibacterial and antioxidant properties, barrier properties, etc., and can increase the release of functional components in response to the increase in humidity on the surface of fruits and vegetables.

[0036] Example 1 A polysaccharide-based cling film liquid, the preparation process of which comprises the following steps: (1) Synthesis of water-resistant HKUST-1 porous support material: 15 mmol copper nitrate trihydrate, 8 mmol 1,3,5-benzoic acid and 0.15 mmol polyvinyl pyrrolidone were weighed and fully dissolved in 100 mL N,N-dimethylformamide. After continuous high-speed stirring at 90°C for 24 h, the precipitate was centrifuged at 6000 g and finally freeze-dried to obtain water-resistant HKUST-1. This was recorded as 1% PVP@Cu-BTC.

[0037] (2) Preparation of polysaccharide-based cling film liquid: Weigh 2 g of high-viscosity sodium carboxymethyl cellulose, 0.3 g of Tween-80, 0.4 g of cinnamon essential oil, 0.2 g of liquid paraffin and 0.2 g of HKUST-1 prepared in step (1), dissolve them in 100 mL of distilled water, stir rapidly at 25°C for 1 h, and prepare a uniform coating liquid by a one-pot method. Pour the solution (coating liquid) evenly into a plastic dish and air-dry at 25°C for 24 h to form a film; record it as CMC / 1%PVP@Cu-BTC / CEO / LP.

[0038] The polysaccharide-based preservative film liquid prepared by the above method is used for mango preservation, and the process is as follows: S1. Pre-treat mangoes: select fresh mangoes with no obvious mechanical damage, no pests and diseases, uniform size, and commercial maturity (about 70%), rinse them twice with distilled water, and then soak them in a sodium hypochlorite disinfectant with a volume concentration of 0.2% for disinfection and sterilization, remove them, and let them air-dry naturally.

[0039] S2. Fresh-keeping treatment: soak the mangoes pretreated in S1 in the polysaccharide-based fresh-keeping film solution prepared above for 1 minute, then take them out, air-dry them naturally, and store them at room temperature.

[0040] Example 2 A polysaccharide-based cling film liquid, the preparation process of which comprises the following steps: (1) Synthesis of water-resistant HKUST-1 porous support material: 15 mmol copper nitrate trihydrate, 10 mmol 1,3,5-benzoic acid and 0.25 mmol polyvinyl pyrrolidone were weighed and fully dissolved in 100 mL N,N-dimethylformamide. After continuous high-speed stirring at 95°C for 24 h, the precipitate was centrifuged at 10,000 g and finally freeze-dried to obtain water-resistant HKUST-1. This was recorded as 1% PVP@Cu-BTC.

[0041] (2) Preparation of polysaccharide-based cling film liquid: 3 g of high-viscosity sodium carboxymethyl cellulose, 0.5 g of Tween-80, 0.6 g of cinnamon essential oil, 0.3 g of liquid paraffin and 0.4 g of HKUST-1 prepared in step (1) were weighed and dissolved in 100 mL of distilled water. The mixture was rapidly stirred at 45 °C for 2 h to obtain a uniform coating liquid by a one-pot method.

[0042] The polysaccharide-based preservative film liquid prepared by the above method is used for mango preservation, and the process is as follows: S1. Pre-treat mangoes: select fresh mangoes with no obvious mechanical damage, no pests and diseases, uniform size, and commercial maturity (about 70%), rinse them twice with distilled water, and then soak them in a sodium hypochlorite disinfectant with a volume concentration of 0.5% for disinfection and sterilization, remove them, and let them air-dry naturally.

[0043] S2. Fresh-keeping treatment: soak the mangoes pretreated in step S1 in the polysaccharide-based fresh-keeping film solution prepared above for 3 minutes, then take them out, air-dry them naturally, and store them at room temperature.

[0044] Example 3 A polysaccharide-based cling film liquid, the preparation process of which comprises the following steps: (1) Synthesis of water-resistant HKUST-1 porous support material: 18 mmol copper nitrate trihydrate, 9 mmol 1,3,5-benzoic acid and 0.2 mmol polyvinyl pyrrolidone were weighed and fully dissolved in 100 mL N,N-dimethylformamide. After continuous high-speed stirring at 85°C for 36 h, the precipitate was centrifuged at 8000 g and finally freeze-dried to obtain water-resistant HKUST-1. This was recorded as 1% PVP@Cu-BTC.

[0045] (2) Preparation of polysaccharide-based cling film liquid: 2.5 g of high-viscosity sodium carboxymethyl cellulose, 0.4 g of Tween-80, 0.5 g of cinnamon essential oil, 0.25 g of liquid paraffin and 0.3 g of HKUST-1 prepared in step (2) were weighed and dissolved in 100 mL of distilled water. The mixture was rapidly stirred at 30 °C for 0.5 h to prepare a uniform coating liquid by a one-pot method.

[0046] The polysaccharide-based preservative film liquid prepared by the above method is used for mango preservation, and the process is as follows: S1. Pre-treat mangoes: select fresh mangoes with no obvious mechanical damage, no pests and diseases, uniform size, and commercial maturity (about 70%), rinse them twice with distilled water, and then soak them in a sodium hypochlorite disinfectant with a volume concentration of 0.1% for disinfection and sterilization, remove them, and let them air-dry naturally.

[0047] S2. Fresh-keeping treatment: soak the mango pretreated in step S1 in the polysaccharide-based fresh-keeping film solution prepared above for 2 minutes, then take it out, air-dry it naturally, and store it at room temperature.

[0048] Example 4 A polysaccharide-based cling film liquid, the preparation process of which comprises the following steps: (1) Synthesis of water-resistant HKUST-1 porous support material: 15 mmol copper nitrate trihydrate, 8 mmol 1,3,5-benzoic acid and 0.15 mmol polyvinyl pyrrolidone were weighed and fully dissolved in 100 mL N,N-dimethylformamide. After continuous high-speed stirring at 90°C for 24 h, the precipitate was centrifuged at 6000 g and finally freeze-dried to obtain water-resistant HKUST-1. This was recorded as 1% PVP@Cu-BTC.

[0049] (2) Preparation of polysaccharide-based essential oil preservative film liquid: Weigh 2 g of high-viscosity sodium carboxymethyl cellulose, 0.2 g of Tween-80, 0.4 g of cinnamon essential oil and 0.2 g of HKUST-1 prepared in step (1), dissolve them in 100 mL of distilled water, stir rapidly at 25°C for 1 h, and prepare a uniform coating liquid by a one-pot method. Pour the solution evenly into a plastic dish and air-dry at 25°C for 24 h to form a film. Recorded as CMC / 1%PVP@Cu-BTC / CEO.

[0050] Comparative Example 1 A pure polysaccharide-based cling film liquid, the preparation method of which specifically comprises the following steps: Weigh 2 g of high-viscosity sodium carboxymethyl cellulose, dissolve it in 100 mL of distilled water, and stir rapidly at 25°C for 1 h to prepare a uniform coating solution. Pour the solution evenly into a plastic dish and air-dry it at 25°C for 24 h to form a film. Recorded as CMC.

[0051] Comparative Example 2 A polysaccharide-based conventional emulsion coating liquid, the preparation method of which specifically comprises the following steps: Weigh 2 g of high-viscosity sodium carboxymethyl cellulose, 0.2 g of Tween-80, and 0.4 g of cinnamon essential oil, dissolve them in 100 mL of distilled water, and stir rapidly at 35°C for 1.5 h to prepare a uniform coating solution. Pour the solution evenly into a plastic dish and air-dry at 25°C for 24 h to form a film, which is recorded as CMC / CEO.

[0052] The conventional emulsion coating liquid prepared by the above method is used for mango preservation, and the process is as follows: (1) Pretreatment of mangoes: Select fresh mangoes with no obvious mechanical damage, no pests and diseases, uniform size, and commercial maturity (about 70%). Rinse them twice with distilled water, then soak them in a 0.2% volume concentration of sodium hypochlorite disinfectant for disinfection and sterilization. Remove them and let them air dry naturally.

[0053] (2) Soak the mangoes pretreated in step (1) in a conventional polysaccharide-based emulsion for 1 min, then take them out, air-dry them naturally, and store them at room temperature.

[0054] Comparative Example 3 A composite coating liquid, the preparation process of which specifically comprises the following steps: (1) Synthesis of water-resistant HKUST-1 porous support material: 15 mmol copper nitrate trihydrate, 8 mmol 1,3,5-benzoic acid and 0.15 mmol polyvinyl pyrrolidone were weighed and fully dissolved in 100 mL N,N-dimethylformamide. After continuous high-speed stirring at 90°C for 24 h, the precipitate was centrifuged at 6000 g and finally freeze-dried to obtain water-resistant HKUST-1. This was recorded as 1% PVP@Cu-BTC.

[0055] (2) Preparation of polysaccharide-based HKUST-1 preservative film solution: Weigh 2 g of high-viscosity sodium carboxymethyl cellulose and 0.2 g of HKUST-1 prepared in step (1), dissolve them in 100 mL of distilled water, and stir rapidly at 25°C for 1 h to prepare a uniform coating solution. Pour the solution evenly into a plastic dish and air-dry at 25°C for 24 h to form a film. Recorded as CMC / 1%PVP@Cu-BTC.

[0056] Comparative Example 4 A composite coating liquid, the preparation process of which specifically comprises the following steps: (1) Synthesis of conventional HKUST-1 porous support material: Weigh 15 mmol copper nitrate trihydrate and 8 mmol 1,3,5-benzoic acid, fully dissolve them in 100 mL N,N-dimethylformamide, stir them at 90°C for 24 h, centrifuge at 6000 g to obtain the precipitate, and finally freeze-dry to obtain conventional HKUST-1, which is denoted as Cu-BTC.

[0057] (2) Preparation of polysaccharide-based essential oil preservative film liquid: Weigh 2 g of high-viscosity sodium carboxymethyl cellulose, 0.4 g of cinnamon essential oil and 0.2 g of HKUST-1 prepared in step (1), dissolve them in 100 mL of distilled water, and stir rapidly at 25°C for 1 h to prepare a uniform coating liquid. Pour the solution evenly into a plastic dish and air-dry at 25°C for 24 h to form a film, which is recorded as CMC / Cu-BTC / CEO.

[0058] The functional properties of the membrane samples of Examples 1 and 4 and Comparative Examples 1-4 were measured, and the specific process is as follows: Figure 1 (a) in the figure is a graph showing the determination of cinnamon essential oil content in the film by UV-visible spectrophotometry. The process is as follows: First, the film sample (2 cm × 2 cm) was weighed and added with distilled water (50 mL) and stirred rapidly for 8 min. After no obvious suspended particles were visible in the solution, ethanol (50 mL) was added to the solution and stirred for 5 min. The absorbance of the final extract was measured at 286 nm using an ultraviolet-visible (UV-vis) spectrophotometer (UV-1600PC, Mapada, China). Before the test, the maximum absorption peak of cinnamon essential oil was determined as the measurement wavelength using a full-band scan, and a standard curve was made to determine the concentration of cinnamon essential oil in the sample. The cinnamon essential oil content loaded on the film was calculated using the following formula: in, w , V , m 1 and m0 are the cinnamon essential oil content in the extract (μg / mL), the volume of the extract, the weight of the film used for measurement (2 cm × 2 cm), and the weight of the entire film (diameter: 12 cm).

[0059] in, C 1 and C 0 are the loading capacities of the sample film and CMC / 1%PVP@Cu-BTC / CEO film, respectively.

[0060] Figure 1 (b) is the disk diffusion method used to evaluate the prepared composite film against Staphylococcus aureus ( S. aureus , CMCC 26001) and Escherichia coli ( E. coli , CMCC 43888), the process is: The two bacteria were used as representatives of Gram-positive and Gram-negative bacteria, respectively. 6 CFU / mL) was evenly coated on the surface of the solid culture medium and dried naturally. Then a film disc with a diameter of 1 cm was placed on the solid culture medium and inverted in a 37°C incubator for 24 h. The area of ​​the inhibition zone was determined using ImageJ software to represent the antibacterial activity of each sample.

[0061] Figure 1 (c) is the water vapor transmission rate (WVTR) of the film, and the process is: According to the international standard ASTM E398, the evaluation was performed by measuring the dynamic RH, which was performed using a PERMATRAN-W150 water vapor transmission rate tester (Mocon, USA). The instrument was calibrated at 37.8°C using a NIST-certified polyester film with known water vapor transmission properties. The measurement was performed at 37.8°C with a relative humidity gradient of 10% / 40% for all samples. The water vapor permeability coefficient (WVP) was calculated by the following formula: in L , P sat and △RH (%) represent film thickness, saturated water vapor pressure at 37.8℃ and relative humidity gradient percentage respectively.

[0062] Figure 2 It is the humidity response behavior diagram, and the process is: The film samples (2 cm × 2 cm) were immersed in ethanol solutions (50 mL) (90%, 70%, 60%), and the release of cinnamon essential oil in different simulated humidity concentrations (10%, 30%, 40%) was evaluated at 25 °C and stored in the dark. Samples were taken regularly for measurement, and after each measurement, an equal amount of simulated solution was added to the immersion solution.

[0063] The results are as follows Figure 1-Figure 2 shown by Figure 1 The results of the analysis show that: Figure 1 As shown in (a), due to the large droplet size and thermodynamic instability of the traditional emulsion, the relative loading rate of comparative example 2 is only 22%; compared with comparative example 2, the relative loading rate of example 4 is increased by 3.55 times, indicating that the uniform micropores of the water-resistant HKUST-1 efficiently capture cinnamon essential oil; compared with example 4, the relative loading rate of example 1 is increased by 0.24 times, indicating that the liquid paraffin with lower solubility slows down the Ostwald ripening of the emulsion film and improves the stability of cinnamon essential oil; because Figure 1 As shown in (b), Comparative Examples 1 and 2 do not have bactericidal effects; while Comparative Example 3 and Examples 1 and 4 show good antibacterial activity against Gram-positive and Gram-negative bacteria, indicating that the Cu released by HKUST-1 2+ The oxidant effect and the cell adsorption of metal active sites can easily lead to bacterial inactivation; compared with comparative example 3, examples 1 and 4 have stronger antibacterial activity against Gram-positive bacteria, which is due to the different resistance of the cell wall structures of the two bacteria to lipophilic substances. Therefore, adding HKUST-1 and cinnamon essential oil to the coating can effectively improve the problem that CMC membrane is susceptible to bacterial infection.

[0064] Depend on Figure 1 As shown in (c), the water vapor permeability of Comparative Example 1 is 3.4×10 -10 gm -1 s -1 Pa -1 Compared with Comparative Example 1, the water vapor permeability of Comparative Example 2 is reduced by about 27.0%; Compared with Comparative Example 1, the water vapor permeability of Example 4 is reduced by about 42.3%, because the HKUST-1 adsorbed with cinnamon essential oil occupies the gaps in the CMC matrix as a hydrophobic layer, extending the path for water molecules to penetrate the film; due to the strong hydrophobicity of liquid paraffin, compared with Example 4, the water vapor permeability of Example 1 is further reduced, which is 55% lower than that of Comparative Example 1, indicating that the polysaccharide-based multifunctional composite fresh-keeping coating designed in the present invention has strong water-blocking properties.

[0065] like Figure 2are the release behaviors of cinnamon essential oil of the films under 10%, 30% and 40% simulated humidity (ethanol-water solution) respectively (where a represents 10% simulated humidity, b represents 30% simulated humidity and c represents 40% simulated humidity). With the increase of moisture content, the instantaneous release and release rate of cinnamon essential oil of all films increase. Compared with comparative examples 2 and 4, the release rates of Examples 1 and 4 under 10%-40% humidity are slower, indicating better sustained release effect. Cinnamon essential oil is released quickly under low humidity conditions in Comparative Examples 2 and 4, indicating that the conventional emulsion and conventional HKUST-1 membrane structure are destroyed under low humidity conditions and do not have humidity response characteristics; while Examples 1 and 4, due to certain hydrophobicity and structural density, show a trend of gradually releasing cinnamon essential oil with increasing humidity, and have the potential to release cinnamon essential oil in response to environmental humidity.

[0066] Mangoes were preserved using the coating solutions of Examples 1-4 and Comparative Example 2, and fresh mangoes treated in the same manner with distilled water were used as blank controls. 100 mangoes of uniform size and shape were selected from each group of Examples 1-4 and Comparative Example 2 for treatment. The quality of mangoes after 12 days of storage was measured, and the test results are shown in Figure 3 , Figure 4 and Table 1.

[0067] Depend on Figure 3 and Figure 4It can be seen that at the beginning of storage, all mangoes showed a bright yellow appearance, with a smooth and shiny surface, without any visible signs of discoloration or decay. The mangoes in the blank control group showed obvious black spots and shrinkage after 12 days, which was due to the rapid ripening and decay of mangoes due to the surge in respiration and ethylene production after harvest. However, the mangoes treated with the coating in Example 1 remained bright in color within 12 days and only showed slight shrinkage. In contrast, all color parameters of mangoes in the blank control group changed significantly, while the color parameters of mangoes treated with the coating in Example 1 changed little during the 12-day storage period. Other coating treatments, especially the treatment in Comparative Example 2, easily cause the mango skin to turn black. In addition, when the mango skin turns black over a large area, the quality of the pulp will also be affected. Compared with aerobic respiration, anaerobic respiration leads to the metabolism of many nutrients and produces incompletely oxidized toxic products, thereby accelerating the aging of fruits and vegetables; in Example 1, due to the addition of natural wax, the oxygen barrier is reduced, the anaerobic respiration is weakened, and the problem of mango turning black is improved. Therefore, the negative symptoms of mango skin color in Comparative Example 2 and Example 4 may be due to the fact that the coating destroys the microenvironment of the mango epidermis, disrupts its physiological metabolic balance, affects the respiration rate, ethylene production, fungal invasion, etc., which is also consistent with the poor preservation effect of Comparative Example 2 and Example 4. On the other hand, improper essential oil concentration may cause browning of fragile peels such as leafy vegetables and fresh-cut products. Uneven coating on the surface of mango peel may cause excessive concentration of cinnamon essential oil in local areas, thereby causing peel damage. These results intuitively show that the coating of Example 1 can effectively delay the discoloration and decay of mangoes due to its rich essential oil content, good barrier properties, antibacterial activity, etc. Therefore, the mangoes treated with the coating of Example 1 have the best appearance quality.

[0068] Table 1 Effects of different treatments on the quality of fresh mangoes after 12 days of storage From the results of the above table, it can be seen that compared with the blank control group, both the examples and the comparative examples have a better preservation effect on mangoes. Compared with comparative example 2, example 4 has a better preservation effect on mangoes, while examples 1, 2 and 3 have a better preservation effect on mangoes, which not only delays the softening and weight loss rate of fresh mangoes, but also maintains the pH and soluble solid content. This shows that HKUST-1 has a good preservation effect by loading a large amount of plant essential oil, delays the release of essential oil, and improves its effect time. At the same time, it synergizes with the hydrophobic liquid paraffin and the functional properties of HKUST-1 itself (such as Figure 1 , Figure 2 The results show that the quality of mangoes decreased significantly during storage.

[0069] Figure 5Shown are scanning electron microscopy (SEM) images of Cu-BTC and 1% PVP@Cu-BTC after immersion in water for 0, 1, 8, and 24 h (a, 10,000 times) (b, 30,000 times).

[0070] Figure 6 Shown are scanning electron microscope (SEM) images of the surface morphology of each film: Comparative Example 1 film (A, 1000 times; a, 5000 times), Comparative Example 2 film (B, 5000 times; b, 10000 times), Comparative Example 3 film (C, 5000 times; c, 10000 times), Comparative Example 4 film (D, 2000 times; d, 10000 times), Example 4 film (E, 5000 times; e, 30000 times), and Example 1 film (F, 5000 times; f, 30000 times).

[0071] Depend on Figure 6 It can be seen that the surface of the film of Comparative Example 1 is smooth and uniform, without cracks, holes and bubbles ( Figure 6 A and 6a). Slight protrusions and oil spots were observed on the surface of the emulsion film of Comparative Example 2 ( Figure 6 B and Figure 6 b), which may be due to the encapsulation of cinnamon essential oil in the film, indicating that due to the hydrophobicity of cinnamon essential oil, it is still incompatible with the hydrophilic sodium carboxymethylcellulose molecules in the conventional emulsion film. Although the 1% PVP@Cu-BTC particles are evenly distributed in the sodium carboxymethylcellulose matrix when they are directly added to the sodium carboxymethylcellulose solution, they are easily aggregated during the film preparation process, and the octahedral structure is severely damaged by water, forming irregular aggregates ( Figure 6 C and Figure 6 c). In the film of Comparative Example 4, the HKUST-1 structure without polyvinyl pyrrolidone has been partially destroyed ( Figure 6 D and Figure 6 d). Importantly, 1% PVP@Cu-BTC is uniformly embedded in the film of Example 4 and retains a complete octahedral morphology ( Figure 6 E and Figure 6 e). Further observation revealed that the surface of the 1% PVP@Cu-BTC film in Example 1 was covered with a layer of obvious liquid paraffin ( Figure 6 F and Figure 6 f), which may improve the overall properties of the film such as water barrier properties. Overall, based on the unique synthetic strategy, i.e., polysaccharide matrix (sodium carboxymethyl cellulose), water-resistant HKUST-1, and emulsion delivery system, a multifunctional active film based on HKUST-1 can be produced.

[0072] The embodiments of the present application are described above in conjunction with the accompanying drawings. Specific examples are used herein to illustrate the principles and implementation methods of the present application. The description of the above embodiments is only used to help understand the core idea of ​​the present application, but the present application is not limited to the above-mentioned specific implementation methods. The above-mentioned specific implementation methods are merely illustrative and not restrictive. Under the inspiration of the present application, ordinary technicians in this field can also make many forms without departing from the scope of protection of the purpose of the present application and the claims, all of which are within the protection of the present application.

Claims

1. A polysaccharide-based preservative film liquid, characterized in that: The polysaccharide-based preservative film liquid comprises high-viscosity sodium carboxymethyl cellulose, HKUST-1, cinnamon essential oil, liquid paraffin, Tween-80 and water; The weight ratio of the high-viscosity sodium carboxymethyl cellulose, the HKUST-1, the cinnamon essential oil, the liquid paraffin, the Tween-80 and the water is 2-3: 0.2-0.4: 0.4-0.6: 0.2-0.3: 0.3-0.5:

100.

2. A method for preparing the polysaccharide-based cling film liquid according to claim 1, characterized in that: The following steps are involved: High-viscosity sodium carboxymethyl cellulose, Tween-80, cinnamon essential oil, liquid paraffin and HKUST-1 in a preset weight ratio are dissolved in water, and stirred for reaction at 25° C.-45° C. for 1 h-2 h to obtain the polysaccharide-based cling film liquid.

3. The preparation method according to claim 2, characterized in that: The HKUST-1 is obtained by the following steps: Copper nitrate trihydrate, 1,3,5-benzoic acid and polyvinyl pyrrolidone are dissolved in N,N-dimethylformamide, stirred, centrifuged and freeze-dried to obtain the HKUST-1.

4. The preparation method according to claim 3, characterized in that: The usage ratio of the copper nitrate trihydrate, the 1,3,5-benzoic acid, the polyvinyl pyrrolidone and the N,N-dimethylformamide is 15 mmol-20 mmol: 8 mmol-10 mmol: 0.15 mmol-0.25 mmol: 100 mL.

5. The preparation method according to claim 3, characterized in that: The stirring operation is performed at a temperature of 85°C-95°C and for a time of 24 h-48 h.

6. The preparation method according to claim 2, characterized in that: The viscosity of the high-viscosity sodium carboxymethyl cellulose is 800-1200 mPa·s.

7. Use of the polysaccharide-based cling film liquid according to claim 1 or the polysaccharide-based cling film liquid prepared by the preparation method according to any one of claims 2 to 6 in food preservation.

8. The use according to claim 7, characterized in that: The food is mango.

9. A method for preserving mangoes, characterized in that: The following steps are involved: The pretreated mango is immersed in the polysaccharide-based cling film liquid according to claim 1 or the polysaccharide-based cling film liquid prepared by the preparation method according to any one of claims 2 to 6, taken out after 1 min to 3 min, and naturally air-dried.

10. The method according to claim 9, characterized in that The steps of the pre-processing are as follows: Wash the freshly picked mangoes and soak them in sodium hypochlorite disinfectant. After soaking, take them out and dry them naturally. The volume concentration of the sodium hypochlorite disinfectant is 0.1%-0.5%.

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