Fruit active fresh-keeping material, preparation method and application thereof

Abstract

The application discloses a fruit active fresh-keeping material and a preparation method and application thereof. Modified amphiphilic nano carbon particles are selected as a self-assembly coating, and an amphiphilic multi-walled carbon nanotube coating with high bacteriostatic effect is loaded on a self-developed substrate by using a self-assembly coating technology, so that a multilayer molecular film is formed on the surface of the substrate, metabolic gas and moisture permeability are effectively adjusted, the high oxygen resistance, low moisture permeability and excellent bacteriostatic function of the fruit active fresh-keeping material are realized. The fruit active fresh-keeping material prepared by the application contains a plurality of substances with natural bacteriostatic function in raw materials, adopts a substrate and a multilayer molecular film structure, guarantees mechanical properties, has high oxygen resistance, low moisture permeability and high bacteriostatic performance, better blocks microorganisms and environmental pollution, can adjust a fruit storage sealed micro-gas environment, reduces a physiological metabolic rate of the fruit, realizes the functions of prolonging fruit storage time and shelf life, and improves quality safety of the fruit.

Description

Technical Field

[0001] This invention relates to the field of new material organic chemical preparation technology, specifically to an active fruit preservation material, its preparation method, and its application. Background Technology

[0002] With the improvement of socio-economic levels, fruit preservation and processing technologies and equipment are constantly being updated and emerging. After harvesting, fruits are prone to spoilage due to continued metabolism, accelerated water loss, and high respiration rates. Fruits are rich in vitamins and carbohydrates, essential nutrients for humans. Post-harvest spoilage reduces the nutritional quality of fruits. Furthermore, improper storage, transportation, and processing can lead to a 10%-15% loss rate in fresh fruits during this period. Therefore, developing new fruit preservation technologies to reduce spoilage and extend shelf life is essential.

[0003] Currently available plastic wrap is not suitable for packaging fruits and vegetables because its gas barrier properties are too good. This causes carbon dioxide and water vapor produced by the respiration and metabolism of fruits and vegetables to adhere to the inside of the packaging, making the environment inside the packaging ideal for the growth and reproduction of microorganisms, thus accelerating the spoilage of fruits and vegetables.

[0004] Existing research on food preservation films either focuses on a single function, making them unsuitable for fruit packaging (e.g., CN105001459A discloses a water- and oil-resistant fully degradable plastic film for food packaging and its preparation method). This method involves adding appropriate amounts of polyvinyl alcohol (PVA) and starch-based materials, followed by the addition of trioctyl citrate and butyl lactate, which lowers the melting point of PVA, facilitating industrial production and improving strength and flexibility, resulting in a durable film. Alternatively, some films offer multiple functions but have highly complex compositions and processes, hindering industrial production (e.g., CN 106674835). A2 discloses a high-transmittance polyvinyl alcohol (PVA) fruit and vegetable preservation film and its preparation method. Camellia seed oil is prepared using raw materials such as camellia seeds, chamomile, evening primrose, and clove flowers. This oil not only inhibits bacterial and microbial growth but also has a highly efficient and broad-spectrum sterilization effect. The prepared camellia seed oil is adsorbed onto nano-calcium carbonate and modified with titanate. Chitosan is used to coat the calcium carbonate particles, and quaternary ammonium salts are grafted onto their surface to further enhance the antibacterial ability of the preservation film. The PVA-prepared film has good transparency and gloss, high tensile and tear strength, excellent gas barrier properties, good heat sealing and adhesion, and its water solubility and biodegradability can effectively solve the problem of poor environmental friendliness in many packaging films. Furthermore, heating and melting chitosan film particles with PVA increases the crosslinking and polymerization degree of PVA, further enhancing the flexibility and transmittance of the preservation film. The addition of inorganic nano-calcium carbonate increases the weight of the film, improving its transparency while further enhancing its strength and flexibility, resulting in better preservation effects.

[0005] Therefore, it is essential to develop a fruit active preservation material with a simple formula and process, which is easy to industrialize and has high oxygen barrier, low moisture permeability and excellent antibacterial function, in order to effectively solve the problem of fruit preservation during storage and transportation. Summary of the Invention

[0006] To address the aforementioned technical problems, this invention proposes an active preservative material for fruits, its preparation method, and its application.

[0007] To achieve the above objectives, the technical solution of the present invention is as follows:

[0008] In the first aspect, the fruit active preservation material proposed in this invention is first prepared by mixing liquid A, liquid B and liquid C in a volume ratio of 2:5:3 to form a matrix, and then using liquid D as a load coating, which is coated on the surface of the matrix using a layer-by-layer self-assembly technology.

[0009] Solution A is composed of the following raw materials by weight percentage: 6% high amylose corn starch, 2% glycerol, 2% urea, 1% chitosan, and 89% deionized water;

[0010] Solution B is composed of the following raw materials by weight percentage: 4% polyvinyl alcohol and 96% deionized water;

[0011] Solution C is composed of the following raw materials by weight percentage: sodium alginate 1% and deionized water 99%;

[0012] Solution D is composed of the following raw materials by weight percentage: 0.2% amphiphilic multi-walled carbon nanotubes and 99.8% deionized water.

[0013] Furthermore, the preparation process of the amphiphilic multi-walled carbon nanotubes is as follows: multi-walled carbon nanotubes with natural antibacterial properties are selected and their structure is modified by acidification and oxidation; the modified multi-walled carbon nanotubes are grafted with the highly substituted polymer hydroxypropyl methylcellulose in an aqueous solution using layer-by-layer self-assembly technology to obtain amphiphilic multi-walled carbon nanotubes.

[0014] Furthermore, the preparation process of the amphiphilic multi-walled carbon nanotubes specifically includes the following steps:

[0015] A mixed acid solution (H₂SO₄:HNO₃ volume ratio = 1:1) was added to multi-walled carbon nanotube powder at a solid-liquid ratio of 10:1. The mixture was ultrasonically dispersed in a water bath for 20 min, then stirred in a magnetic stirrer at 50℃ for 3 h, and repeatedly washed with deionized water until neutral. The mixture was then dried in a vacuum oven to obtain modified multi-walled carbon nanotubes. Highly substituted hydroxypropyl methylcellulose was mixed with the modified multi-walled carbon nanotubes at a volume ratio of 1:4, and an ethanol solution (C₂H₅OH:H₂O volume ratio = 2:1) was added. The mixture was magnetically stirred at a constant temperature for 24 h, then centrifuged at 3500 r / min to separate the bottom precipitate. Deionized water was added to the bottom precipitate again, and centrifugation was repeated under the same conditions. This process was repeated several times until no bubbles appeared in the upper layer of the centrifuge tube after stirring. The bottom precipitate was then freeze-dried under vacuum to obtain amphiphilic multi-walled carbon nanotubes.

[0016] Secondly, the present invention also proposes a method for preparing the above-mentioned active preservative material for fruits, comprising the following steps:

[0017] Step 1: According to weight percentage, mix 6% high amylose corn starch, 2% glycerol, 2% urea, 1% chitosan, and 89% deionized water, and heat and stir at 85°C to obtain solution A; according to weight percentage, mix 4% polyvinyl alcohol and 96% deionized water, and heat and stir at 80°C to obtain solution B; according to weight percentage, mix 1% sodium alginate and 99% deionized water, and heat and stir at 80°C to obtain solution C; according to weight percentage, mix 0.2% amphiphilic multi-walled carbon nanotubes and 99.8% deionized water, and stir until homogeneous to obtain solution D.

[0018] Step 2: Mix the A, B and C solutions obtained in Step 1 in a volume ratio of 2:5:3, stir well, pour the mixed solution into an acrylic mold, and dry it in an oven at 80°C for 3 hours to obtain the matrix.

[0019] Step 3: Immerse the matrix obtained in Step 2 in the D solution obtained in Step 1 for 30 minutes, then wash the material with pure water and dry it in an oven at 80°C. After the surface of the material is completely dry, take it out and repeat the above immersion and drying operation 1-5 times to obtain the fruit active preservation material.

[0020] Furthermore, in step four, the soaking and drying processes are repeated three times.

[0021] Thirdly, the present invention also proposes the application of the above-mentioned active fruit preservation material as a fruit packaging material.

[0022] Furthermore, the fruit is blueberry or cherry tomato.

[0023] Compared with the prior art, the technical effects of the present invention are as follows:

[0024] 1. The method for preparing fruit active preservation material proposed in this invention selects modified amphiphilic carbon nanoparticles as a self-assembled coating. Using coating self-assembly technology, an amphiphilic multi-walled carbon nanotube coating with high antibacterial effect is loaded onto a self-developed substrate, so that a multilayer molecular film is formed on the substrate surface, which effectively regulates the permeability of metabolic gases and water, and realizes the characteristics of high oxygen barrier, low moisture permeability and excellent antibacterial function of fruit active preservation material.

[0025] 2. The fruit active preservative material prepared by this invention contains various substances with natural antibacterial functions (such as highly substituted hydroxypropyl methylcellulose and multi-walled carbon nanotubes). Utilizing a matrix and multilayer molecular membrane structure, it ensures mechanical properties while exhibiting high oxygen barrier, low moisture permeability, and high antibacterial performance, effectively blocking microbial and environmental contamination. Placing fruit within this active preservative material can regulate the sealed micro-gas environment during fruit storage, reduce the physiological metabolic rate of the fruit, extend its storage time and shelf life, and improve its quality and safety. Attached Figure Description

[0026] Figure 1 This is a schematic diagram illustrating the structural changes of each raw material during the self-assembly process;

[0027] Figure 2 The effect of the volume ratio of liquids A, B, and C on the mechanical properties and water solubility of the matrix;

[0028] Figure 3Infrared spectral curves of MWCNTs and HPMC / AO-MWCNTs;

[0029] Figure 4 XRD patterns of MWCNTs and HPMC / AO-MWCNTs nanoparticles;

[0030] Figure 5 TEM images of MWCNTs(a) and HPMC / AO-MWCNTs(b) nanoparticles;

[0031] Figure 6 Effects of HM-CSA-AP on blueberry fruit firmness and weight loss;

[0032] Figure 7 The effect of HM-CSA-AP on the physiological metabolic rate of blueberry fruit;

[0033] Figure 8 Actual photos showing the shelf life of blueberries for different packaging materials and storage times.

[0034] Figure 9 The effect of different packaging materials on antibacterial properties. Detailed Implementation

[0035] To enable those skilled in the art to better understand the technical solutions of the present invention, the present invention will be further described in detail below with reference to embodiments and accompanying drawings. Obviously, the described embodiments are merely some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0036] Unless otherwise specified, the experimental methods described in the following examples are conventional methods.

[0037] Unless otherwise specified, the experimental materials used in the following examples were purchased from conventional biochemical reagent stores or prepared by known synthetic methods.

[0038] The fruit active preservative material prepared in this invention consists of two parts: a matrix (DTT) and a self-assembled layer. The number of self-assembled layers plays a major role in preservation. Discussions regarding the matrix focus on its excellent mechanical properties, while also possessing transparency and water resistance, ensuring its suitability for packaging materials. Component A of the matrix includes high-amylose corn starch, glycerol, urea, chitosan, and deionized water. High-amylose corn starch (HACS) is the main component of the matrix, glycerol acts as a plasticizer, urea acts as a hydrophobic agent, and chitosan increases viscosity and antibacterial properties. Polyvinyl alcohol (PVA) in component B and sodium alginate (SAA) in component C, along with high-amylose corn starch in component A, are the three factors that most significantly affect the material's performance. For the matrix component, the most critical performance is mechanical properties, followed by transparency and water solubility. The analysis of mechanical properties is mainly determined by the composition and ratio of the matrix; the self-assembled layer is very thin and has little impact on mechanical properties. The main components of the matrix, namely high-amylose corn starch, sodium alginate, and polyvinyl alcohol, cannot be substituted. This is mainly because the groups contained in these three components have molecular bond interactions with the self-assembled amphiphilic multi-walled carbon nanotubes (HPMC / AO-MWCNTs), with hydrogen bonds being the primary component.

[0039] This invention relates to modified amphiphilic multi-walled carbon nanotubes (self-assembled coatings). As an amphiphilic nanoparticle, its surface contains numerous hydrophilic groups such as (-COOH), which can interact with the (-OH) hydrophilic groups in the raw material molecules of the matrix (sodium alginate, polyvinyl alcohol, and high-amylose corn starch) through intermolecular hydrogen bonding. This allows the modified multi-walled carbon nanotubes to self-assemble and be loaded onto the matrix surface. Simultaneously, the surface of the modified multi-walled carbon nanotubes also contains hydrophobic groups, whose double bonds can be converted into hydroxyl groups, which can chemically adsorb onto the second self-assembled film layer. This process is repeated multiple times to achieve multi-layer self-assembly of the modified multi-walled carbon nanotube film. This process is monitored using a UV-Vis spectrophotometer to ensure uniformity of the self-assembly process for each layer until the target number of layers is reached. The structural changes of each raw material during the self-assembly process are as follows: Figure 1 As shown.

[0040] Experimental Example 1: Study on the effect of the volume ratio of liquids A, B, and C on the mechanical properties and water solubility of the matrix.

[0041] Under the conditions of ensuring that the mass fraction of each individual solution is the same, and that the stirring temperature and time, and drying temperature and time of the mixed solution are the same, the content of solution B (containing polyvinyl alcohol) is kept constant at 50%. The volume ratios of solution A (containing high-amylose corn starch) and solution C (containing sodium alginate) in the mixed solution are varied to obtain samples with different component contents (A:B:C = 1:5:4, A:B:C = 2:5:3, A:B:C = 3:5:2, A:B:C = 4:5:1). The transparency (%), water solubility (%), and mechanical properties (MPa) are tested respectively, and the results are as follows: Figure 2 As shown.

[0042] The results showed that the mechanical properties, water solubility, and transparency of the matrix changed accordingly with the changes in the main components. Taking into account the test data, this invention, while ensuring good mechanical properties, also achieved good water insolubility and transparency. Ultimately, a volume ratio of 2:5:3 for liquid A: liquid B: liquid C was selected as the blank matrix formulation.

[0043] Example 1

[0044] The fruit active preservative material provided by this invention is prepared by mixing liquid A, liquid B, and liquid C in a volume ratio of 2:5:3 to form a matrix, using liquid D as the loading material, and performing self-assembly of the coating on the matrix to prepare a self-assembled active preservative material. Liquid A includes high-amylose corn starch, glycerol, urea, chitosan, and deionized water, with the following weight percentages: high-amylose corn starch 6%, glycerol 2%, urea 2%, chitosan 1%, and deionized water 89%; Liquid B includes polyvinyl alcohol and deionized water, with the following weight percentages: polyvinyl alcohol 4% and deionized water 96%; Liquid C includes sodium alginate and deionized water, with the following weight percentages: sodium alginate 1% and deionized water 99%; Liquid D includes amphiphilic multi-walled carbon nanotubes and deionized water, with the following weight percentages: amphiphilic multi-walled carbon nanotubes 0.2% and deionized water 99.8%; the self-assembled coating consists of one layer.

[0045] The preparation process of the above-mentioned amphiphilic multi-walled carbon nanotubes is as follows: 30 mL of mixed acid solution was added to 300 mg of multi-walled carbon nanotube (MWCNTs) powder. The mixed acid solution was a solution with a volume ratio of H2SO4:HNO3 of 1:1. The mixture was ultrasonically dispersed in a water bath for 20 min, stirred in a magnetic stirrer at 50 °C for 3 h, and then repeatedly washed with deionized water until it became neutral. Then it was placed in a vacuum oven at 60 °C and dried to obtain acid-oxidative modified multi-walled carbon nanotubes (AO-MWCNTs). Highly substituted hydroxypropyl methylcellulose (HPMC) and the modified multi-walled carbon nanotubes (AO-MWCNTs) were then mixed. Ts) were mixed at a volume ratio of 1:4, and then ethanol solution was added to prepare a solution with a volume concentration of 1 g / 100 ml. The ethanol solution was prepared by a volume ratio of C2H5OH:H2O of 2:1. The mixture was magnetically stirred at a constant temperature for 24 h, and then centrifuged at 3500 r / min to separate the bottom precipitate. Deionized water was added to the bottom precipitate again, and centrifugation was repeated under the same conditions. This process was repeated several times until no bubbles were observed after stirring the upper layer of the centrifuge tube. The bottom precipitate was then removed and freeze-dried under vacuum to obtain amphiphilic multi-walled carbon nanotubes (HPMC / AO-MWCNTs). Infrared characterization and XRD and TEM analyses are as follows. Figure 3-5 As shown.

[0046] Infrared characterization such as Figure 3 The figures shown are the infrared spectra of MWCNTs and HPMC / AO-MWCNTs, respectively. At 3427 cm⁻¹... -1 A strong absorption peak appears, which is the (OH) stretching vibration peak in the hydroxyl group; at 2583 cm⁻¹ -1 and 2923cm -1 The position is generated by the antisymmetric / symmetric stretching vibration of CH on the methyl group in HPMC; furthermore, at 1629 cm⁻¹ -1 and 1737cm -1 The absorption at 1030 cm⁻¹ represents the absorption of the (C=O) bond in the carboxyl group; -1 1083cm -1 The absorption peak at 1629 cm⁻¹ is related to the stretching vibration of (COC), and the presence and variation of these oxygen-containing groups should be related to the acidification and oxidation treatment of multi-walled carbon nanotubes. Compared with the infrared spectrum of MWCNTs, HPMC / AO-MWCNTs show a higher absorption peak at 1629 cm⁻¹. -1 3427cm -1 1030cm -1A stronger absorption peak appears at 3100-3600 cm⁻¹, indicating the introduction of hydrophilic groups such as (-OH). Simultaneously, the overall absorption peak intensity of HPMC / AO-MWCNTs shows a significant decrease. This is attributed to the esterification reaction between the polar oxygen-containing groups (-COOH) on the surface of MWCNTs and the (-OH) groups in HPMC under covalent bonding after acidification and oxidation, promoting the grafting of HPMC onto the surface of AO-MWCNTs and thus reducing the polarity of the oxygen-containing groups. Furthermore, the infrared spectrum of HPMC / AO-MWCNTs shows a stronger absorption peak in the 3100-3600 cm⁻¹ range. -1 The presence of a broad absorption peak at this point is due to the (-OH) stretching vibration in HPMC, which proves the grafting process of HPMC onto AO-MWCNTs and demonstrates the successful modification of HPMC / AO-MWCNTs.

[0047] XRD analysis, such as Figure 4 The figures show the infrared spectra of MWCNTs and HPMC / AO-MWCNTs, respectively. MWCNTs exhibited the strongest diffraction peak at 2θ = 25.62°, and the interlayer distance of MWCNTs, calculated using the Bragg formula (2dsinθ = nλ), is approximately 0.16 nm. However, HPMC / AO-MWCNTs showed a cellulose diffraction peak at 2θ = 20.2°, with the strongest diffraction peak at 2θ = 25.32°. Calculations indicate that the interlayer distance of HPMC / AO-MWCNTs is approximately 0.18 nm, which is larger than that of MWCNTs, while the intensity of the characteristic absorption peaks is also reduced. This is because most of the HPMC is grafted onto the surface of AO-MWCNTs via covalent bonds, while a small amount of HPMC is coated onto the surface of AO-MWCNTs through physical adsorption, resulting in a larger interlayer distance for HPMC / AO-MWCNTs.

[0048] TEM analysis such as Figure 5 As shown, comparison Figure 5 In (a) and (b), it can be clearly observed that the structure of multi-walled carbon nanotubes undergoes significant changes after combined modification by acid solution oxidation and HPMC grafting. Figure 5 As shown in (a), MWCNTs have long tubes with almost no breaks. Due to their SP2 carbon atom structure and small molecular size, MWCNTs tend to entangle and aggregate. However, in modified amphiphilic multi-walled carbon nanotubes (HPMC / AO-MWCNTs), impurities such as carbon atoms attached to the surface are removed during acidification and oxidation. Simultaneously, the ends of the metastable carbon nanotubes break, thus improving the aggregation phenomenon. Figure 5As shown in (b). Simultaneously, the HPMC / AO-MWCNTs tube bundles acquire amphiphilic properties through the grafting modification process. Under the mutual repulsion of water absorption and hydrophobicity, the arrangement of the tube bundles gradually disperses and tends towards regularity. Figure 5 As shown in (b). This is beneficial for further use as a coating. The TEM results are consistent with the FT-IR, X-RD, and SEM results, indicating that HPMC / AO-MWCNTs are stable and amphiphilic.

[0049] The preparation method of the above-mentioned active preservative material for fruits is as follows:

[0050] Step 1: According to weight percentage, mix 6% high amylose corn starch, 2% glycerol, 2% urea, 1% chitosan, and 89% deionized water, and heat and stir at 85°C to obtain solution A; according to weight percentage, mix 4% polyvinyl alcohol and 96% deionized water, and heat and stir at 80°C to obtain solution B; according to weight percentage, mix 1% sodium alginate and 99% deionized water, and heat and stir at 80°C to obtain solution C; according to weight percentage, mix 0.2% amphiphilic multi-walled carbon nanotubes and 99.8% deionized water, and stir until homogeneous to obtain solution D.

[0051] Step 2: Mix the A, B and C solutions obtained in Step 1 in a volume ratio of 2:5:3, stir well, pour the mixed solution into an acrylic mold, and dry it in an oven at 80°C for 3 hours to obtain the matrix (DTT).

[0052] Step 3: Immerse the matrix obtained in Step 2 in the D solution obtained in Step 1 for 30 minutes (obtained by monitoring that the concentration of D solution does not change). After sufficient self-assembly, thoroughly wash the material with pure water, remove the unassembled components, and place it in an oven to dry at 80°C. After the surface of the material is completely dry, take it out to obtain the fruit active preservation material.

[0053] Example 2

[0054] The fruit active preservative material provided by this invention is prepared by mixing liquid A, liquid B, and liquid C in a volume ratio of 2:5:3 to form a matrix, using liquid D as a loading material, and performing coating self-assembly on the matrix to prepare a self-assembled active preservative material; wherein the formulations of liquids A, B, C, and D are the same as in Example 1; the number of self-assembled coating layers is two. The preparation process of the amphiphilic multi-walled carbon nanotubes is the same as in Example 1. The preparation method of the fruit active preservative material is the same as in Example 1, repeating step three of soaking and drying once, and the number of self-assembled coating layers is two, thus obtaining the fruit active preservative material.

[0055] Example 3

[0056] The fruit active preservative material provided by this invention is prepared by mixing liquids A, B, and C in a volume ratio of 2:5:3 to form a matrix, using liquid D as a loading material, and performing coating self-assembly on the matrix to obtain a self-assembled active preservative material. The formulations of liquids A, B, C, and D are the same as in Example 1; the number of self-assembled coating layers is three. The preparation process of the amphiphilic multi-walled carbon nanotubes is the same as in Example 1. The preparation method of the fruit active preservative material is the same as in Example 1, repeating step three (soaking and drying) twice, resulting in a three-layer self-assembled coating, thus obtaining the fruit active preservative material.

[0057] Example 4

[0058] The fruit active preservative material provided by this invention is prepared by mixing liquid A, liquid B, and liquid C in a volume ratio of 2:5:3 to form a matrix, using liquid D as a loading material, and performing coating self-assembly on the matrix to prepare a self-assembled active preservative material; wherein the formulations of liquids A, B, C, and D are the same as in Example 1; the number of self-assembled coating layers is four. The preparation process of the amphiphilic multi-walled carbon nanotubes is the same as in Example 1. The preparation method of the fruit active preservative material is the same as in Example 1, repeating step three of soaking and drying operations three times, and the number of self-assembled coating layers is two, thus obtaining the fruit active preservative material.

[0059] Example 5

[0060] The fruit active preservative material provided by this invention is prepared by mixing liquids A, B, and C in a volume ratio of 2:5:3 to form a matrix, using liquid D as a loading material, and performing coating self-assembly on the matrix to prepare a self-assembled active preservative material; wherein the formulations of liquids A, B, C, and D are the same as in Example 1; the number of self-assembled coating layers is five. The preparation process of the amphiphilic multi-walled carbon nanotubes is the same as in Example 1. The preparation method of the fruit active preservative material is the same as in Example 1, repeating step three of soaking and drying operations four times, and the number of self-assembled coating layers is two, thus obtaining the fruit active preservative material.

[0061] Example 6

[0062] The fruit active preservative material provided by this invention is prepared by mixing liquids A, B, and C in a volume ratio of 2:5:3 to form a matrix, using liquid D as a loading material, and performing coating self-assembly on the matrix to prepare a self-assembled active preservative material; wherein the formulations of liquids A, B, C, and D are the same as in Example 1; the number of self-assembled coating layers is six. The preparation process of the amphiphilic multi-walled carbon nanotubes is the same as in Example 1. The preparation method of the fruit active preservative material is the same as in Example 1, repeating step three of soaking and drying operations five times, and the number of self-assembled coating layers is two, thus obtaining the fruit active preservative material.

[0063] Experimental Example 2: Study on the Mechanical Properties of Active Preservatives for Fruits

[0064] As shown in Table 1, the tensile strength and elongation at break of fruit active preservatives with different self-assembled layers show a trend of first increasing and then decreasing with the increase of the number of self-assembled layers. Among them, the tensile strength and elongation at break of the active preservative sheets with lower self-assembled layers are slightly higher than those of the DTT matrix. When the number of self-assembled layers is 3, the tensile strength and elongation at break of the active preservative material reach the maximum, which are 68.44 MPa and 25.36%, respectively.

[0065] Table 1. Tensile strength and elongation at break of the fruit active preservative materials prepared in Examples 1-6

[0066] Materials (number of self-assembled layers) Tensile strength (MPa) Elongation at break (%) Matrix (DTT) (0 layers) 53.53+0.53 19.05+0.33 Example 1 (1 layer) 55.69+0.56 21.89+0.32 Example 2 (2 layers) 57.86+0.53 22.11+0.41 Example 3 (3 layers) 68.44+0.51 25.36+0.49 Example 4 (4 layers) 63.03+0.55 24.33+0.55 Example 5 (5 layers) 60.86+0.49 23.25+0.45 Example 6 (6 layers) 58.12+0.52 21.26+0.54

[0067] Experimental Example 3: Study on the oxygen barrier properties and water vapor permeability of active preservative materials for fruits

[0068] As shown in Table 2, with the gradual increase in the number of self-assembled layers, the oxygen barrier properties and water vapor permeability of fruit active preservatives with different numbers of self-assembled layers show a trend of first decreasing and then leveling off. Considering the production process cost and mechanical properties, a total of 3 self-assembled layers was ultimately selected.

[0069] Table 2 Results of oxygen barrier properties and water vapor permeability of the fruit active preservative materials prepared in Examples 1-6

[0070]

[0071]

[0072] Experimental Example 4: Study on the antibacterial properties of active fruit preservatives

[0073] As shown in Table 3, the antibacterial properties of the active preservative materials prepared in Examples 1-5 were tested. The results showed that as the number of self-assembled layers gradually increased, the antibacterial properties gradually decreased. Considering the mechanical properties, the self-assembled active preservative material prepared with a three-layer coating (hereinafter referred to as HM-CSA-AP) had the best overall performance, which laid the foundation for its practical application on blueberries.

[0074] Table 3. Results of antibacterial performance of fruit active preservative materials prepared in Examples 1-5

[0075] Materials (number of self-assembled layers) Antibacterial properties Example 1 (1 layer) <![CDATA[1.78×10 6 cfu / ml]]> Example 2 (2 layers) <![CDATA[1.45×10 6 cfu / ml]]> Example 3 (3 layers) <![CDATA[1.17×10 6 cfu / ml]]> Example 4 (4 layers) <![CDATA[1.03×10 6 cfu / ml]]> Example 5 (5 layers) <![CDATA[0.97×10 6 cfu / ml]]>

[0076] Experimental Example 5: Effect of HM-CSA-AP on Blueberry Fruit Firmness

[0077] The effects of HM-CSA-AP coating on blueberry firmness under different temperature conditions (4℃, 14℃, 24℃, 34℃, 44℃) were investigated. The results showed that during the entire 7-day accelerated shelf-life period, the weight loss rate of blueberries in both the control group and the HM-CSA-AP group decreased under different temperature conditions. Specific experimental results are as follows: Figure 6 As shown in (b), the hardness of blueberries varied significantly with increasing temperature throughout the storage period. In the control group, the hardness of blueberries stored at 4℃, 14℃, 14℃, 24℃, 34℃, and 44℃ were 2.0541 kg / cm², respectively. 2 1.9543 kg / cm 2 1.4052 kg / cm 2 20.7325 kg / cm 2 0.7126 kg / cm 2 The hardness of blueberries in the HM-CSA-AP sheet group was 2.1069 kg / cm². 2 2.0321 kg / cm 2 1.8623 kg / cm 2 1.7102 kg / cm 2 1.5676 kg / cm 2 It is about twice that of the control group, and is still in the edible stage, such as Figure 6 As shown in (a), the active preservation sheet of the present invention can effectively slow down the decrease in the firmness of blueberries and delay the ripening and softening of blueberries. In the blank control group, the blueberries became unmeasurable in firmness starting from the 6th day of storage due to excessive weight loss.

[0078] Experimental Example 6: Study on the physiological metabolic rate of blueberry fruit using HM-CSA-AP

[0079] Blueberries were coated with HM-CSA-AP (the invention's result), commercially available plastic wrap, commercially available PE film, and a blank substrate, respectively, with a blank control group included. Results showed that the substrate metabolic rate began to decrease as blueberries transitioned from full maturity to the senescence stage. Specifically, the respiration rate of blueberries in the HM-CSA-AP group remained at a consistently low level, with the respiratory climacteric peak occurring two days later than in the blank control group, plastic wrap group, and PE film group. Figure 7 As shown. Because HM-CSA-AP can regulate the "sealed" micro-gas environment and has good antibacterial properties to reduce microbial invasion, it reduces the nutrients consumed by blueberries due to microbial metabolism and slows down the respiration rate of blueberries.

[0080] Experiment 7: Effects of different packaging materials and storage times on the shelf life of blueberries

[0081] like Figure 8 As shown, a is the control group, b is the commercially available plastic wrap group, c is the PE film group, d is the base film group, and e is the active preservative material group (HM-CSA-AP). The results showed that blueberries preserved with HM-CSA-AP maintained their freshness for longer than those in the control group. The control group shrank on day 3, while the active preservative material group remained fresh. On day 6, the blueberries in other groups shrank significantly, while those in the active preservative material group remained fresh.

[0082] Experimental Example 8: Effect of Different Packaging Materials on Antibacterial Properties

[0083] Four types of bacteria (Escherichia coli, Staphylococcus aureus, yeast, and mold) were treated with HM-CSA-AP sheet group, multi-walled carbon nanotube group, and highly substituted hydroxypropyl cellulose group, respectively. Figure 9 As shown. Among them, the HM-CSA-AP group (the result of this invention) showed OD values ​​for four bacteria. 260 and OD 280 The values ​​were all higher than those of the other three groups (multi-walled carbon nanotube group, hydroxypropyl cellulose group and blank control group), indicating that HM-CSA-AP has a strong destructive effect on the cell membranes of four bacteria: Escherichia coli, Staphylococcus aureus, yeast and mold. Therefore, it can cause the cytoplasm inside the bacterial membrane to flow out, which verifies that it has a certain destructive effect on microorganisms.

[0084] The foregoing has only described certain exemplary embodiments of the present invention by way of illustration. Undoubtedly, those skilled in the art can modify the described embodiments in various ways without departing from the spirit and scope of the present invention. Therefore, the foregoing drawings and descriptions are illustrative in nature and should not be construed as limiting the scope of protection of the claims of the present invention.

Claims

1. A fruit active fresh-keeping material, characterized in that, The fruit active preservative material is first prepared by mixing liquid A, liquid B and liquid C in a volume ratio of 2:5:3 to form a matrix, and then using liquid D as a load coating, which is coated on the surface of the matrix using a layer-by-layer self-assembly technology. Solution A is composed of the following raw materials by weight percentage: 6% high amylose corn starch, 2% glycerol, 2% urea, 1% chitosan, and 89% deionized water. Solution B is composed of the following raw materials by weight percentage: 4% polyvinyl alcohol and 96% deionized water; Solution C is composed of the following raw materials by weight percentage: sodium alginate 1%, deionized water 99%; Solution D is composed of the following raw materials by weight percentage: 0.2% amphiphilic multi-walled carbon nanotubes and 99.8% deionized water; The preparation process of the amphiphilic multi-walled carbon nanotubes is as follows: multi-walled carbon nanotubes with natural antibacterial properties are selected and their structure is modified by acidification and oxidation; the modified multi-walled carbon nanotubes are grafted with the highly substituted polymer hydroxypropyl methylcellulose in an aqueous solution using layer-by-layer self-assembly technology to obtain amphiphilic multi-walled carbon nanotubes.

2. The fruit active fresh-keeping material according to claim 1, characterized in that, The preparation process of the amphiphilic multi-walled carbon nanotubes specifically includes the following steps: A mixed acid solution (H₂SO₄:HNO₃ volume ratio = 1:1) was added to multi-walled carbon nanotube powder at a solid-liquid ratio of 10:

1. The mixture was ultrasonically dispersed in a water bath for 20 min, then stirred in a magnetic stirrer at 50℃ for 3 h, and repeatedly washed with deionized water until neutral. The mixture was then dried in a vacuum oven to obtain modified multi-walled carbon nanotubes. Highly substituted hydroxypropyl methylcellulose was mixed with the modified multi-walled carbon nanotubes at a volume ratio of 1:4, and an ethanol solution (C₂H₅OH:H₂O volume ratio = 2:1) was added. The mixture was magnetically stirred at a constant temperature for 24 h, then centrifuged at 3500 r / min to separate the bottom precipitate. Deionized water was added to the bottom precipitate again, and centrifugation was repeated under the same conditions. This process was repeated several times until no bubbles were observed in the upper layer of the centrifuge tube after stirring. The bottom precipitate was then freeze-dried under vacuum to obtain amphiphilic multi-walled carbon nanotubes.

3. The method for preparing the fruit active preservative material according to claim 1, characterized in that, Includes the following steps: Step 1: According to weight percentage, mix 6% high amylose corn starch, 2% glycerol, 2% urea, 1% chitosan, and 89% deionized water, and heat and stir at 85°C to obtain solution A; according to weight percentage, mix 4% polyvinyl alcohol and 96% deionized water, and heat and stir at 80°C to obtain solution B; according to weight percentage, mix 1% sodium alginate and 99% deionized water, and heat and stir at 80°C to obtain solution C; according to weight percentage, mix 0.2% amphiphilic multi-walled carbon nanotubes and 99.8% deionized water, and stir until homogeneous to obtain solution D. Step 2: Mix the A, B and C solutions obtained in Step 1 in a volume ratio of 2:5:3, stir well, pour the mixed solution into an acrylic mold, and dry it in an oven at 80°C for 3 hours to obtain the matrix. Step 3: Immerse the matrix obtained in Step 2 in the D solution obtained in Step 1 for 30 minutes, then wash the material with pure water and dry it in an oven at 80°C. After the surface of the material is completely dry, take it out and repeat the above immersion and drying operation 1-5 times to obtain the fruit active preservation material.

4. The method for preparing the fruit active preservative material according to claim 3, characterized in that, In step one, the preparation process of the amphiphilic multi-walled carbon nanotubes is as follows: a mixed acid solution is added to the multi-walled carbon nanotube powder at a solid-liquid ratio of 10:1, wherein the mixed acid solution is a solution with a volume ratio of H2SO4:HNO3 of 1:1; the mixture is ultrasonically dispersed in a water bath for 20 min, stirred in a magnetic stirrer at 50℃ for 3 h, and then repeatedly washed with deionized water until neutral; then it is dried in a vacuum oven to obtain the modified multi-walled carbon nanotubes; highly substituted hydroxypropyl methylcellulose is mixed with the modified multi-walled carbon nanotubes at a volume ratio of 1:4, and an ethanol solution is added, wherein the ethanol solution is prepared with a volume ratio of C2H5OH:H2O of 2:1; the mixture is magnetically stirred at a constant temperature for 24 h, and then centrifuged at 3500 r / min to separate the bottom precipitate; deionized water is added to the bottom precipitate again and centrifuged under the same centrifugation conditions; Repeat this process several times until there are no more bubbles in the upper layer of the centrifuge tube after stirring. The bottom precipitate was removed and subjected to vacuum freeze-drying to obtain amphiphilic multi-walled carbon nanotubes.

5. The method for preparing the fruit active preservative material according to claim 3, characterized in that, In step four, repeat the soaking and drying process three times.

6. The application of the fruit active preservative material according to claim 1 as a fruit packaging material.

7. The application according to claim 6, characterized in that, The fruit in question is either blueberry or cherry tomato.

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