An antibacterial fresh-keeping coating solution and a preparation method thereof, an antibacterial fresh-keeping composite film and a fruit and vegetable fresh-keeping method

Abstract

The application provides an antibacterial fresh-keeping coating liquid and a preparation method thereof, an antibacterial fresh-keeping composite film and a fruit and vegetable fresh-keeping method, and belongs to the technical field of fruits and vegetables. The antibacterial fresh-keeping coating liquid comprises the following components: epsilon-polylysine, silica aerogel, water-based polyurethane and water; and the epsilon-polylysine is loaded on the surface and pores of the silica aerogel. The antibacterial fresh-keeping coating liquid provided by the application takes silica aerogel as a carrier, loads epsilon-polylysine natural antibacterial agent, and takes water-based polyurethane as a film-forming material, so that the antibacterial fresh-keeping coating liquid has broad-spectrum antibacterial effect and better slow-release effect, the formed antibacterial fresh-keeping composite film has high plasticity and uniform film formation, and the three have a synergistic effect, thereby significantly prolonging the shelf life of fruits and vegetables.

Description

Technical Field

[0001] This invention belongs to the field of fruit and vegetable agricultural technology, specifically relating to an antibacterial preservation coating liquid and its preparation method, an antibacterial preservation composite film, and a method for preserving fruits and vegetables. Background Technology

[0002] Fruits and vegetables are important agricultural products, and with the development of global agro-food systems and cold chain logistics, the demand for post-harvest preservation of fruits and vegetables continues to increase. China is a major producer of fruits and vegetables; data from the National Bureau of Statistics shows that in 2023, the national vegetable output reached 830 million tons, and the output of orchard fruits reached 240 million tons. Due to their high water content and fragile texture after harvest, fruits and vegetables are prone to dehydration, softening, and pathogen infection during storage and transportation, with post-harvest losses typically reaching 20-50%. Preservation technology has become a key bottleneck restricting the industry's development. Existing technologies include methods for preparing preservation films by mixing antibacterial agents with film-forming materials, but their antibacterial and preservation effects still need further improvement. Summary of the Invention

[0003] The purpose of this invention is to provide an antibacterial preservative coating liquid and its preparation method, an antibacterial preservative composite film, and a method for preserving fruits and vegetables. The antibacterial preservative coating liquid provided by this invention has a better antibacterial and preservative effect.

[0004] To achieve the above-mentioned objectives, the present invention provides the following technical solution: The present invention provides an antibacterial and preservative coating liquid, comprising the following components: ε-polylysine, silica aerogel, aqueous polyurethane and water; wherein the ε-polylysine is loaded on the surface and in the pores of the silica aerogel.

[0005] Preferably, the silica aerogel has a pore size of 20-70 nm, a porosity of 95-98%, and a specific surface area of ​​150-250 m². 2 / g.

[0006] Preferably, the solid content of the waterborne polyurethane in the antibacterial and preservative coating liquid is 8-12 wt%.

[0007] This invention also provides a method for preparing the antibacterial and preservative coating liquid described in the above technical solution, comprising the following steps: (1) Mix silica aerogel, ε-polylysine and water to obtain ε-polylysine / silica aerogel dispersion; (2) The ε-polylysine / silica aerogel dispersion obtained in step (1) is mixed with aqueous polyurethane to obtain an antibacterial and fresh-keeping coating liquid.

[0008] Preferably, in step (1), the mass ratio of silica aerogel to water is (0.5~0.75):100.

[0009] Preferably, in step (1), the mass ratio of ε-polylysine to water is (10~50) mg: 1 mL.

[0010] Preferably, the mixing time in step (1) is 2 to 60 minutes.

[0011] Preferably, the pH value of the ε-polylysine / silica aerogel dispersion in step (1) is 8~9.

[0012] The present invention also provides an antibacterial preservation composite film, which is prepared from the antibacterial preservation coating liquid described in the above technical solution or the antibacterial preservation coating liquid prepared by the preparation method described in the above technical solution.

[0013] The present invention also provides a method for preserving fruits and vegetables, comprising: The antibacterial preservative coating liquid described in the above technical solution or the antibacterial preservative coating prepared by the preparation method described in the above technical solution is applied to the surface of fruits and vegetables to be preserved and then dried.

[0014] This invention provides an antibacterial and preservative coating liquid, comprising the following components: ε-polylysine, silica aerogel, aqueous polyurethane, and water; wherein the ε-polylysine is loaded onto the surface and pores of the silica aerogel. The antibacterial and preservative coating liquid provided by this invention uses silica aerogel as a carrier, loads ε-polylysine as a natural antibacterial agent, and uses aqueous polyurethane as a film-forming substance, resulting in a broad-spectrum antibacterial coating liquid with better sustained-release effects. The formed antibacterial and preservative composite film has high plasticity and uniform film formation. The three components have a synergistic effect, significantly extending the shelf life of fruits and vegetables. Attached Figure Description

[0015] Figure 1 This refers to the process of coating and peeling off the mango in Example 1. Figure 2 The disease incidence of mango after inoculation with anthrax bacteria is shown in Example 2. Figure 3 This is a graph showing the diameter of lesions on mangoes after inoculation with anthracnose, as shown in Example 2. Figure 4 This is a graph showing the changes in mangoes during room temperature storage, as illustrated in Example 3. Figure 5 This is a graph showing the changes in mangoes on day 18 of low-temperature storage, as used in Example 3. Figure 6 This is a graph showing the color change of mangoes during room temperature storage in Example 3. Figure 7 This is a graph showing the change in hardness of mangoes during room temperature storage in Example 3. Figure 8 The graph shows the ethylene release rate of mangoes during room temperature storage in Example 3. Figure 9 The graph shows the weight loss and decay rate of mangoes during room temperature storage in Example 3. Figure 10 The area and inhibition rate of the in vitro anthrax-inhibiting film after drying of the coating solutions in Examples 1-16 and Comparative Examples 1-4 are used in Example 4. Figure 11 The results of in vitro anthrax inhibition tests on films obtained after drying the coating solutions of Examples 1-16 and Comparative Examples 1-4 in Application Example 4; Figure 12 The area and inhibition rate of the in vitro inhibitory region for Fusarium spp. after drying of the coating solutions in Examples 1-16 and Comparative Examples 1-4 in Application Example 5 are shown. Figure 13 The results of in vitro tests on the inhibition of Fusarium by the films after drying of the coating solutions in Examples 1-16 and Comparative Examples 1-4 in Application Example 5; Figure 14 The diagram shows the elongation at break, tensile strength, and stress-strain curves of the films after drying the coating liquid of Example 1 and Comparative Examples 1-5 in Application Example 6. Figure 15 SEM images of the films after drying of the coating solutions from Example 1, Comparative Example 1, and Comparative Example 5 in Application Example 7; Figure 16 Thermogravimetric curves of the films after drying of the coating solutions of Examples 1, 1, and 5 in Application Example 10; Figure 17 The disease incidence of cherry tomatoes on the sixth day after inoculation with gray mold in Example 11; Figure 18 This is a graph showing the diameter of lesions on cherry tomatoes after inoculation with Botrytis cinerea at room temperature, as shown in Example 11. Figure 19 The disease incidence on the fourth day after tomatoes were inoculated with gray mold in Example 12; Figure 20 This is a graph showing the diameter of lesions on tomatoes after inoculation with Botrytis cinerea at room temperature, as shown in Example 12. Figure 21 This is an image of the durian stored at room temperature on the fourth day in Application Example 13. Detailed Implementation

[0016] The present invention provides an antibacterial and preservative coating liquid, comprising the following components: ε-polylysine, silica aerogel, aqueous polyurethane and water; wherein the ε-polylysine is loaded on the surface and in the pores of the silica aerogel.

[0017] The antibacterial and preservative coating liquid provided by this invention includes ε-polylysine. ε-polylysine possesses broad-spectrum antibacterial properties, exhibiting highly effective inhibition against common pathogens (such as anthracnose fungus and stem rot fungus). It is strong in antibacterial activity, non-toxic, and can be used in the field of fruit and vegetable preservation. In synergy with silica aerogel and waterborne polyurethane, it enhances the antibacterial and preservative effect.

[0018] The antibacterial and preservative coating liquid provided by the present invention also includes silica aerogel; the ε-polylysine is loaded on the surface and in the pores of the silica aerogel.

[0019] In one embodiment, the silica aerogel is a hydrophilic silica aerogel; the pore size of the silica aerogel can be 20~70 nm; the porosity of the silica aerogel can be 95~98%, and more specifically 96%; the specific surface area of ​​the silica aerogel can be 150~250 m². 2 / g; the particle size of the silica aerogel can be 5~30μm. This invention uses silica aerogel as a carrier and controls its parameters, enabling it to synergistically interact with ε-polylysine, effectively encapsulating ε-polylysine, improving sustained-release performance, and possessing unidirectional thermal conductivity. After being coated onto the surface of fruits and vegetables to form a preservative film, it can dissipate the heat within the film, further improving the preservation effect of fruits and vegetables.

[0020] This invention does not specifically limit the source of the silica aerogel; any commercially available product well-known to those skilled in the art can be used, ensuring that the parameters of the silica aerogel are within the required range. As one embodiment, the silica aerogel can be purchased from Ruixiu Fireproof Materials Factory in Dacheng County, Hebei Province. The product is "Laboratory Sample Aerogel Powder (Thermal Insulation Nano-Hydrophilic Silica Aerogel Powder)," with a specification of 500g / pack.

[0021] The antibacterial and preservative coating liquid provided by this invention also includes water-based polyurethane.

[0022] In one embodiment, the solid content of the aqueous polyurethane in the antibacterial and preservative coating liquid can be 8-12 wt%, specifically 8 wt%, 9 wt%, 10 wt%, 11 wt%, or 12 wt%; the aqueous polyurethane is anionic aliphatic polyurethane. This invention uses the above-mentioned aqueous polyurethane and controls its solid content to ensure the uniformity and flexibility of the film. The formed film regulates gas exchange in food, slows down respiratory metabolism, and works synergistically with ε-polylysine and silica aerogel to significantly extend the shelf life of fruits and vegetables.

[0023] The antibacterial and preservative coating liquid provided by this invention also includes water.

[0024] The antibacterial and preservative coating liquid provided by this invention uses silica aerogel as a carrier, loads ε-polylysine antibacterial active material, and uses water-based polyurethane as the film-forming material. It can be coated onto the surface of fruits and vegetables by dipping, spraying, brushing, etc. After drying, it can be stored. After the storage period, the formed preservation film can be peeled off by hand or washed off. It has good antibacterial and preservative properties and can effectively inhibit the growth of anthracnose and Fusarium, which are common pathogenic fungi in tropical fruits, as well as inhibit the growth of tomato gray mold. This inhibits postharvest diseases of fruits and vegetables, reduces water loss, reduces ethylene peak, delays fruit ripening and softening, and thus extends the shelf life of fruits and vegetables.

[0025] The beneficial effects of this invention are as follows: Synergistic preservation mechanism: The porous structure of silica aerogel enables the slow release of ε-polylysine, which continuously inhibits the growth of pathogens; the protective film formed by water-based polyurethane regulates gas exchange in fruits and slows down respiratory metabolism. The synergistic effect of the three significantly extends the shelf life of fruits and vegetables.

[0026] Broad-spectrum antibacterial properties: ε-polylysine has a highly effective inhibitory effect on common postharvest pathogens of mango (such as anthracnose and stem rot), and has strong antibacterial properties.

[0027] Excellent film-forming properties: The composite film formed by the coating liquid on the surface of fruits and vegetables has good flexibility and adhesion, which can effectively reduce the weight loss and decay of fruits and vegetables. The shelf life can be extended to 18-24 days at room temperature and to 30-36 days at low temperature (10-13℃).

[0028] Safe and environmentally friendly: The antibacterial raw materials used are food-grade and meet food safety standards, and there is no risk of chemical residues in other ingredients.

[0029] Performance characteristics: The coated fruits and vegetables can be peeled off and washed off before consumption.

[0030] This invention also provides a method for preparing the antibacterial and preservative coating liquid described in the above technical solution, comprising the following steps: (1) Mix silica aerogel, ε-polylysine and water to obtain ε-polylysine / silica aerogel dispersion; (2) The ε-polylysine / silica aerogel dispersion obtained in step (1) is mixed with aqueous polyurethane to obtain an antibacterial and fresh-keeping coating liquid.

[0031] This invention involves mixing silica aerogel, ε-polylysine, and water to obtain an ε-polylysine / silica aerogel dispersion.

[0032] As one implementation method, the water can be distilled water.

[0033] In one embodiment, the mass ratio of silica aerogel to water can be (0.5~0.75):100, or specifically 0.5:100, 0.55:100, 0.6:100, 0.65, 0.7:100, or 0.75:100. By controlling the mass ratio of silica aerogel to water within the above range, this invention enables the silica aerogel to be fully dispersed.

[0034] In one embodiment, the mass-to-volume ratio of ε-polylysine to water can be (10~50) mg:1 mL, or specifically 10 mg:1 mL, 15 mg:1 mL, 20 mg:1 mL, 25 mg:1 mL, 30 mg:1 mL, 35 mg:1 mL, 40 mg:1 mL, 45 mg:1 mL, or 50 mg:1 mL. By controlling the mass-to-volume ratio of ε-polylysine to water within the above range, this invention ensures that ε-polylysine is fully dissolved and uniformly dispersed on the surface and in the pores of the silica aerogel.

[0035] As one implementation, the mixing time of the silica aerogel, ε-polylysine, and water can be 2 to 60 minutes.

[0036] In one embodiment, the mixing of silica aerogel, ε-polylysine, and water can be performed as follows: silica aerogel and water are sequentially mixed and sonicated to obtain a silica aerogel dispersion; the silica aerogel dispersion and ε-polylysine are sequentially mixed and sonicated to obtain an ε-polylysine / silica aerogel dispersion.

[0037] In one embodiment, the temperature of the first mixing can be room temperature; the mixing time can be 10-15 min; the first mixing can be carried out under stirring conditions; the stirring rate can be 200-300 rpm; the frequency of the first ultrasound can be 40-60 kHz; the duration of the first ultrasound can be 60-180 s; the temperature of the second mixing can be room temperature; the mixing time can be 15-20 min; the second mixing can be carried out under stirring conditions; the stirring rate can be 300-400 rpm; the frequency of the second ultrasound can be 40-60 kHz; the duration of the second ultrasound can be 1-3 min. This invention controls the mixing method and parameters within the above ranges, enabling the silica aerogel to be fully dispersed, and ε-polylysine to be completely dissolved and uniformly dispersed on the surface and in the pores of the silica aerogel.

[0038] As one embodiment, the pH value of the ε-polylysine / silica aerogel dispersion can be 8-9. When the pH value of the ε-polylysine / silica aerogel dispersion is not within the above range, the present invention can add an alkaline solution to the mixed system to adjust the pH value of the system; the alkaline solution can be an aqueous sodium hydroxide solution; the concentration of the aqueous sodium hydroxide solution can be 0.5-1 mol / L. The present invention does not have a special limitation on the amount of the alkaline solution used, as long as the pH value of the system is within the required range. Controlling the pH value of the ε-polylysine / silica aerogel dispersion within the above range can improve the deprotonation degree of the silanol groups on the surface of silica aerogel, enhance the dispersion stability of silica aerogel in aqueous phase; maintain ε-polylysine rich in cations in a neutral to alkaline environment, resulting in higher stability; and facilitate the entry and loading of ε-polylysine into the pores of silica aerogel through electrostatic interactions and hydrogen bonding, thereby improving the uniformity and sustained-release stability of the subsequent coating solution.

[0039] After obtaining the ε-polylysine / silica aerogel dispersion, the present invention mixes the ε-polylysine / silica aerogel dispersion with aqueous polyurethane to obtain an antibacterial and preservative coating liquid.

[0040] As one embodiment, the solid content of the waterborne polyurethane can be 27-37%; the pH value of the waterborne polyurethane at 25°C can be 5-6; the waterborne polyurethane can be purchased from Shenzhen Yoshida Chemical Co., Ltd., product number F0401.

[0041] The present invention does not impose any special limitation on the amount of waterborne polyurethane used, as long as the solid content of waterborne polyurethane in the antibacterial and preservative coating liquid is within the required range.

[0042] As one embodiment, the mixing of the ε-polylysine / silica aerogel dispersion and the aqueous polyurethane can be performed as follows: aqueous polyurethane is added to the ε-polylysine / silica aerogel dispersion, followed by sequential shaking, stirring, and ultrasonication to obtain an antibacterial and preservative coating solution; the stirring rate can be 500-600 rpm; the stirring time can be 1-5 min; the ultrasonic frequency can be 60-80 kHz; and the ultrasonic time can be 1-5 min. This invention does not impose any special limitations on the shaking operation; any technical solution well-known to those skilled in the art can be used. Using the above mixing method, a uniform and stable antibacterial and preservative coating solution can be obtained.

[0043] The present invention also provides an antibacterial preservation composite film, which is prepared from the antibacterial preservation coating liquid described in the above technical solution or the antibacterial preservation coating liquid prepared by the preparation method described in the above technical solution.

[0044] In one embodiment, the antibacterial and food-preserving composite film prepared by this invention is transparent to off-white, with a thickness of up to 0.282 mm ± 0.15 mm and an average tensile strength of 3.75 N / mm². 2 The average elastic modulus is 31.26 MPa, the elongation at break can reach 299.25%, and the water contact angle is 53.37°±0.46°.

[0045] The present invention also provides a method for preserving fruits and vegetables, comprising: The antibacterial preservative coating liquid described in the above technical solution or the antibacterial preservative coating prepared by the preparation method described in the above technical solution is applied to the surface of fruits and vegetables to be preserved and then dried.

[0046] This invention does not specifically limit the types of fruits and vegetables to be preserved; they can be selected according to actual needs. As one embodiment, the fruits and vegetables to be preserved can be climacteric fruits or fruits, and more specifically, mangoes or tomatoes.

[0047] This invention does not impose any particular limitation on the coating method; any coating method well known to those skilled in the art can be used. As one embodiment, the coating may specifically be dip coating, spray coating, or brush coating.

[0048] In one embodiment, the present invention involves completely immersing the fruits and vegetables to be preserved in the antibacterial preservative coating liquid for 1-3 minutes, then removing them and allowing them to air dry naturally at room temperature and a relative humidity of 30-40%. In this invention, the antibacterial preservative coating liquid forms a removable composite film on the surface of the fruits and vegetables after natural drying, tightly covering the outer surface of the fruits and vegetables. The film can be peeled off by hand or washed before consumption.

[0049] The technical solutions of this invention will be clearly and completely described below with reference to the embodiments thereof. Obviously, the described embodiments are only a part of the embodiments of this invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0050] In the various embodiments and comparative examples, the silica aerogels had pore sizes of 20-70 nm, porosity of 96%, and specific surface areas of 200-220 m². 2 / g, with a particle size of 5~30μm, purchased from Ruixiu Fireproof Materials Factory of Dacheng County; the initial solid content of waterborne polyurethane is 35%, purchased from Shenzhen Yoshida Chemical Co., Ltd., item number F0401.

[0051] Example 1 An antibacterial and preservative coating liquid is composed of the following components: ε-polylysine, silica aerogel, aqueous polyurethane and water, wherein the ε-polylysine is loaded on the surface and pores of the silica aerogel. The preparation method of the antibacterial and freshness-preserving coating liquid is as follows: (1) Take 32 mL of distilled water into a beaker, add silica aerogel (the mass ratio of silica aerogel to distilled water is 0.5:100), stir at 250 rpm for 10 min, and then sonicate at 50 kHz for 60 s. Then add ε-polylysine (the mass ratio of ε-polylysine to the volume ratio of distilled water is 50 mg:1 mL), stir at 350 rpm for 15 min, and then sonicate at 50 kHz for 2 min. Under stirring conditions, adjust the pH value to 8 with 1 mol / L sodium hydroxide aqueous solution to obtain ε-polylysine / silica aerogel dispersion. (2) Take 20 mL of the ε-polylysine / silica aerogel dispersion obtained in step (1), add waterborne polyurethane to it, shake and stir at 550 rpm for 3 min, and then sonicate at 70 kHz for 3 min to obtain antibacterial and freshness-preserving coating liquid. The solid content of waterborne polyurethane in the antibacterial and freshness-preserving coating liquid is 10%.

[0052] Examples 2-16, Comparative Examples 1-4 The difference from Example 1 is that the mass ratio of silica aerogel to distilled water and the mass ratio of ε-polylysine to distilled water are different, while all other aspects are the same as in Example 1.

[0053] The mass ratios of silica aerogel and distilled water, the mass of ε-polylysine, and the volume of distilled water in Examples 1-16 and Comparative Examples 1-4 are shown in Table 1.

[0054] Table 1 shows the mass ratio of silica aerogel to distilled water, and the mass ratio of ε-polylysine to distilled water in Examples 1-16 and Comparative Examples 1-4.

[0055] Comparative Example 5 Waterborne polyurethane and distilled water are mixed to obtain a polyurethane coating liquid (WPU) with a polyurethane solid content of 10%.

[0056] Application Example 1 Mangoes were disinfected by soaking in a 0.2% (v / v) NaClO aqueous solution for 8 minutes, then washed in deionized water and air-dried at 20°C. The treated mangoes were then completely immersed in the antibacterial preservative coating solution from Example 1 for 1 minute, removed, and air-dried at room temperature. After 24 hours, the coating could be peeled off by hand. Figure 1 As shown.

[0057] Application Example 2 Select Taiwanese mangoes that are similar in size, intact in appearance, healthy and free from pests and diseases, and in the green ripening stage, and randomly group them. Soak the mangoes in 0.2% (v / v) NaClO aqueous solution for 8 minutes to disinfect them, then wash them in deionized water and air dry them naturally at 20°C. Immerse the treated mangoes completely in the antibacterial preservation coating liquid of Example 1 for 1 minute, and then air dry them at room temperature. Four small holes, 1.5 cm deep, were evenly punched on one side of the mango using a 3 mm diameter punch. 20 μL of anthracnose spore suspension was added to each hole (10 mL of sterile water was added to a petri dish inoculated with anthracnose; the spores were gently scraped onto the surface of the bacteria with a spreader, and then filtered through four layers of sterile gauze to obtain the anthracnose spore suspension). The suspension was then air-dried at room temperature and stored in a preservation basket at room temperature. The disease incidence of the mangoes was observed daily. Once all mangoes showed signs of disease, photographs were taken and the size of the lesions was measured using the cross-hatching method (the control group was not immersed in the antibacterial preservation coating). The results are as follows: Figure 2 and Figure 3 As shown.

[0058] from Figure 2 and Figure 3 As can be seen, the lesions impregnated with the antibacterial preservative coating showed almost no development or developed very slowly, indicating that the antibacterial preservative composite film had a good antibacterial effect. The observation that the fruit did not turn yellow suggests that the delayed ripening may have resulted in lower fruit maturity, making it less susceptible to anthracnose infection and thus improving the fruit's disease resistance. The significant difference in lesion diameter between the antibacterial preservative coating group and the control group further demonstrates the antibacterial efficacy of the antibacterial preservative composite film.

[0059] Application Example 3 Mangoes were disinfected by soaking in 0.2% (v / v) NaClO aqueous solution for 8 min, then washed in deionized water and air-dried at 20℃. The treated mangoes were then completely immersed in the antibacterial preservative coating solution of Example 1 for 1 min, and then air-dried at room temperature. They were randomly divided into 4 groups: (1) room temperature control group; (2) room temperature coating group (ε-PL-SiO2-WPU); (3) low temperature control group; (4) low temperature coating group. Storage experiments were then conducted. The room temperature storage conditions were 23±2℃ and the relative humidity was 30±5%; the low temperature storage conditions were 10±2℃ and the relative humidity was 60±5%. The results are as follows. Figures 4-9 As shown. Figure 4 This describes the changes in mangoes during storage at room temperature. Figure 5 The changes in mangoes after 18 days of low-temperature storage; Figure 6 Changes in mango color during room temperature storage ( Figure 6 A is L Value (brightness), B is a Value (red-green tint, the larger the value, the more reddish; the smaller the value, the more greenish), C is b Value (yellowish-blue tint; the larger the value, the more yellowish; the smaller the value, the more blue). Figure 7 The change in mango firmness during room temperature storage; Figure 8 The ethylene release rate of mangoes during room temperature storage; Figure 9 The weight loss rate (A) and rot rate (B) of mangoes during normal temperature storage.

[0060] from Figure 4 and Figure 5 As can be seen, under normal temperature conditions, due to the low initial maturity of the fruit, it can be stored for up to 18 days, but its edibility and marketability are greatly reduced after 18 days. Coating the surface of the mango with an ε-PL-SiO2-WPU film can effectively reduce the yellowing rate and slow down its ripening speed. Under low temperature conditions, the fruit ripening process is still slow, and its yellowing is even slower compared to the control group.

[0061] from Figure 6 As can be seen from this, under normal temperature conditions, L The trends of the control group and the ε-PL-SiO2-WPU coating group were roughly the same, with the same inflection point, but the composite coating led to a decrease in fruit brightness. A similar situation occurred under low-temperature conditions, and both groups showed similar trends at a... The changes in values ​​were more pronounced during the process. Compared with the control group, the b value of the ε-PL-SiO2-WPU coating group was significantly higher. The ε-PL-SiO2-WPU coating showed low levels under both ambient and low temperature conditions, indicating a slow rate of fruit yellowing and relatively low ripening progress. This suggests that the ε-PL-SiO2-WPU coating significantly delays fruit ripening and senescence, thus extending its storage life and preserving its freshness.

[0062] from Figure 7 As can be seen, under both room temperature and low temperature conditions, compared with the control group, the hardness of the ε-PL-SiO2-WPU coating group decreased more slowly, but the SSC steadily increased.

[0063] from Figure 8 It can be seen that under normal temperature conditions, the peak ethylene release in the fruit occurs at approximately 12 days, while the ethylene release rate in the control group can reach 1.89 μL / kg. -1 h -1 The ε-PL-SiO2-WPU coating group showed a slow increase in ethylene levels at 16 days, indicating slow ripening and a delayed ethylene peak. Under low-temperature conditions, the fruit's ethylene peak also occurred around 12 days, while the control group's ethylene release rate reached 0.64 μL / kg. -1 h -1 The ε-PL-SiO2-WPU coating group showed a lower level, only 0.31 μL kg.-1 h -1 .

[0064] from Figure 9 The results show that the ε-PL-SiO2-WPU coating significantly reduced fruit weight loss and decay rates. Compared with the control group, the weight loss rate decreased by 32.18% at room temperature and by 7.71% at low temperature; the decay rate decreased by 40.69% at room temperature and by 2.78% at low temperature. At room temperature for 18 days, the color change rate of the ε-PL-SiO2-WPU coating group reached 83.33% at room temperature for 24 days and 61.11% at low temperature for 30 days. The experiment demonstrates that the ε-PL-SiO2-WPU film, through coating, not only enhances fruit disease resistance and inhibits bacterial growth, but also potentially better preserves fruit quality, showcasing its advantages and potential as a new antibacterial and preservative material for fruits and vegetables.

[0065] Application Example 4 Take 3 mL of the coating solution from Examples 1-16 and Comparative Examples 1-4 respectively into a drying mold (a circular plastic mold with a diameter of 45±2 mm), and dry it in a forced-air drying oven at 65℃ for 3 hours. Spread 100 μL of anthrax spore suspension onto sterilized PDA medium. After spreading until slightly dry, place a composite film with a diameter of 45±2 mm in the center of a petri dish and incubate it in a constant temperature incubator at 28℃. On day 5, photograph and record the growth of the colonies. Use a mixed medium of PDA and sterile water as a blank control group. Perform 3 replicates. Calculate the inhibition rate of ε-polylysine on mycelial growth using the following formula. The results are as follows: Figure 10 and Figure 11 As shown: .

[0066] from Figure 10 and Figure 11 As can be seen, when the ε-PL content reaches 10 mg / mL, a relatively obvious inhibition zone begins to appear on the PDA culture plate; when the content reaches 50 mg / mL, the antibacterial effect is most significant.

[0067] Application Example 5 The only difference from Application Example 4 is that the anthrax spore suspension was replaced with a Fusarium spore suspension; everything else is the same as in Application Example 4, and the results are as follows. Figure 12 and Figure 13 As shown.

[0068] from Figure 12 and Figure 13 It can be seen that when the ε-PL content reaches 10 mg / mL, a relatively obvious inhibition zone begins to appear on the PDA culture plate; when the content reaches 50 mg / mL, the antibacterial effect is the most significant.

[0069] Application Example 6 3 mL of the coating solution from Example 1 and Comparative Examples 1-5 were respectively placed in a drying mold (a circular plastic mold with a diameter of 45±2 mm) and dried in a forced-air drying oven at 65°C for 3 hours. The elongation at break and tensile strength of the film were determined using an electronic universal testing machine. During the test, the film was cut into rectangular pieces with a length of 1.0 cm and a width of 4.0 cm, vertically clamped in a fixture, with a target value of 20.0 cm, a trigger point load of 0.02 N, and a test speed of 0.50 mm / s. -1 The elongation at break and tensile strength of the film are calculated according to the following formulas, and the results are as follows: Figure 14 As shown ( Figure 14 (In the diagram, A represents elongation at break, B represents tensile strength, and C represents the stress-strain curve.) , Where: ΔL - the increase in length of the film when it breaks during stretching, mm; L - the initial length of the film, mm; , Where: F - the load the film bears when it breaks during stretching, N; t - film thickness, mm; w - film width, mm.

[0070] like Figure 14 As shown in (A), among the WPU films and WPU films with different proportions of SiO2 (WPU+0.25%SiO2, WPU+0.5%SiO2, WPU+0.75%SiO2, WPU+1%SiO2), except for WPU+1%SiO2, the elongation at break is at a relatively high level and the differences between them are not significant, indicating that adding SiO2 within a certain range has little effect on the elongation at break. However, the elongation at break of WPU+1%SiO2 is significantly reduced, indicating that adding too high a proportion of SiO2 will significantly weaken the film's ductility. The elongation at break of WPU+0.5%SiO2+ε-PL is also low, showing a significant difference from most other samples; Figure 14 As shown in (B), the WPU film has a certain tensile strength, which significantly decreases after adding 0.25% SiO2. The tensile strengths of WPU + 0.5% SiO2 and WPU + 0.75% SiO2 are relatively high and show no significant difference between them, indicating that adding an appropriate amount of SiO2 can improve the tensile strength. The tensile strengths of WPU + 1% SiO2 and WPU + 0.5% SiO2 + ε-PL are significantly reduced; excessive SiO2 addition or the addition of ε-PL may damage the film structure and reduce the tensile strength. Figure 14As shown in (C), in the initial segment of the curves, the stress of each film increases with increasing strain, and the slope reflects the initial modulus of the material. The curve for WPU+0.75%SiO2 has a larger slope, indicating a relatively high initial modulus; the curve for WPU+0.5%SiO2+ε-PL has a smaller slope, indicating a lower initial modulus. As strain increases, the curves show different trends, reflecting the differences in the mechanical response of the material at different strain stages. For example, WPU+0.75%SiO2 can withstand higher stress and strain, while the stress increase of WPU+0.5%SiO2+ε-PL is relatively slower and the stress change inflection point appears earlier, reflecting its mechanical property characteristics.

[0071] Application Example 7 3 mL of the coating solution from Example 1, Comparative Example 1, and Comparative Example 5 were respectively placed in a drying mold (a circular plastic mold with a diameter of 45 ± 2 mm) and dried in a forced-air drying oven at 65°C for 3 hours. The dried films were then adhered to conductive adhesive, sputtered with gold, and their surface and cross-sectional morphology characteristics were tested (measurement voltage 5 kV). The obtained SEM images are shown below. Figure 15 As shown. From Figure 15 As can be seen, the surfaces and cross-sections of the three thin films are different.

[0072] Application Example 8 Take 3 mL of the coating solution from Example 1, Comparative Example 1, and Comparative Example 5 respectively and place it in a drying mold (a circular plastic mold with a diameter of 45±2 mm). Dry it in a forced-air drying oven at 65°C for 3 hours. Cut each dried film into a square sheet of 1.0 cm × 1.0 cm and place it flat on the experimental table. Then, take 10.0 μL of distilled water and add it to the surface of the film. At the moment the droplet contacts the film, immediately use image analysis software to measure the water contact angle of the film. The results are shown in Table 2.

[0073] Table 2. Water contact angles of the films after drying of the coating solutions in Examples 1, 1 (Comparative Example 1), and 5 (Comparative Example 5).

[0074] As shown in Table 2, the addition of SiO2 aerogel can partially eliminate the hydrophilicity caused by the addition of high concentrations of ε-PL, thereby improving the hydrophobicity of the composite film surface and making the composite film less prone to complete wetting. Maintaining a relatively humid environment is conducive to the effective release of ε-PL. The addition of SiO2 aerogel gives the film a slightly grainy texture, while the composite film exhibits a relatively uniform, whitish, frosted texture.

[0075] Application Example 9 3 mL of the coating solution from Example 1, Comparative Example 1, and Comparative Example 5 were respectively placed in a drying mold (a circular plastic mold with a diameter of 45±2 mm) and dried in a forced-air drying oven at 65°C for 3 h. The XRD patterns of each dried film were measured using a Cu target, a conventional wide-angle (5~90°), and a scanning speed of 2° / min. The results are shown in Table 3.

[0076] Table 3. Elemental distribution data of the films after drying of the coating solutions in Examples 1, 1, and 5.

[0077] As can be seen from Table 3, the amount of nitrogen increases significantly when ε-PL is added to the film, indicating the widespread presence of ε-PL in the composite film.

[0078] Application Example 10 3 mL of the coating solutions from Example 1, Comparative Example 1, and Comparative Example 5 were respectively placed in drying molds (circular plastic molds with a diameter of 45 ± 2 mm) and dried in a 65°C forced-air drying oven for 3 hours. The thermal stability of each dried film was determined using a HITACHI STA200 differential thermal-thermogravimetric analyzer. Zeroing was performed using a blank alumina crucible. After the baseline stabilized, 10–13 mg of sample was evenly added to the right crucible and placed on the sample tray. The initial temperature was set to 30°C, the final temperature to 800°C, and the heating rate to 10°C / min. The next sample was measured after the instrument baseline stabilized again. The results are as follows: Figure 16 As shown, Figure 16 In the figures, A is Comparative Example 5, B is Comparative Example 1, and C is Example 1.

[0079] from Figure 16 As can be seen, at 800℃, the mass residue rates of WPU film, WPU+SiO2 aerogel film and ε-PL / SiO2 aerogel composite film are 1.75%, 10.81% and 12.63%, respectively. This indicates that the addition of SiO2 aerogel and ε-PL improves the mass residue rate of the film after thermal degradation to a certain extent, and SiO2 aerogel has a greater impact on improving the mass residue rate, which may be the more important factor.

[0080] Application Example 11 10 mL of sterile water was poured into a petri dish containing *Botrytis cinerea*. The mixture was then gently scraped from the surface of the fungus using a spreading stick and filtered through four layers of sterile gauze to obtain a *Botrytis cinerea* spore suspension. Cherry tomatoes were first disinfected by soaking in a 0.2% (v / v) NaClO aqueous solution for 8 minutes, then washed in deionized water and air-dried at 20°C. Next, cherry tomatoes of similar size, with intact appearance, healthy, and free from pests and diseases were selected and randomly grouped. Each group of fruits was soaked in the antibacterial preservative coating solution from Example 1 for 1 minute, then removed and air-dried. Using a 1 mL disposable sterile syringe, 20 μL of the *Botrytis cinerea* spore suspension was injected into the center of each of the four sides of the cherry tomatoes, with a hole depth of approximately 2 mm subcutaneously. The fruits were then air-dried at room temperature and placed in a preservation basket. They were stored at room temperature, and the disease condition of the cherry tomatoes was observed daily, with regular photographic records taken. The size of the lesions was measured using the cross-hatching method. The results are shown below. Figure 17 and Figure 18 As shown. Figure 17 Disease incidence on the sixth day after inoculating cherry tomatoes with gray mold; Figure 18 Diameter of lesions after inoculating cherry tomatoes with gray mold.

[0081] from Figure 17 and Figure 18 It can be seen that in the control group, the inoculation site of *Botrytis cinerea* quickly developed depressions, and the mycelium grew rapidly in the later stages. The lesions in the composite coating group developed slowly, indicating that the composite film had a good antibacterial effect. Compared with the control group, the diameter of the lesions in the composite coating group was significantly different, demonstrating the antibacterial efficacy of the composite film.

[0082] Application Example 12 The difference from Application Example 11 is that cherry tomatoes were replaced with regular tomatoes, and the result is as follows: Figure 19 and Figure 20 As shown. Figure 19 Disease incidence on tomatoes on the fourth day after inoculation with gray mold; Figure 20 The diameter of lesions on tomatoes after inoculation with gray mold. Figure 19 and Figure 20 It can be seen that in the control group, the inoculation site of *Botrytis cinerea* quickly developed depressions, and the mycelium grew rapidly in the later stages. The lesions in the composite coating group developed slowly, indicating that the composite film had a good antibacterial effect. Compared with the control group, the diameter of the lesions in the composite coating group was significantly different, demonstrating the antibacterial efficacy of the composite film.

[0083] Application Example 13 The durians were first disinfected by soaking in a 0.2% (v / v) NaClO aqueous solution for 8 minutes, then washed in deionized water and air-dried at 20°C. After drying, the durians were soaked in the antibacterial preservative coating solution of Example 1 for 1 minute, then removed and air-dried again, and subsequently stored at room temperature. The results on the fourth day of storage were as follows: Figure 21 As shown. From Figure 21 The results show that, at room temperature, the durians in the coated group turned yellow more slowly, indicating that the coating effectively delayed the ripening of the fruit; the mold growth on the durians in the coated group was also slower, indicating that the coating effectively inhibited mold infection and spoilage.

[0084] In summary, the antibacterial and preservative coating liquid provided by this invention has excellent antibacterial and preservative properties. It can effectively inhibit the growth of common pathogens in fruits and vegetables, suppress postharvest diseases, reduce water loss, lower ethylene peak, delay fruit ripening and softening, and extend the shelf life of fruits and vegetables.

[0085] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. An antibacterial and preservative coating liquid, characterized in that, It comprises the following components: ε-polylysine, silica aerogel, aqueous polyurethane, and water; wherein the ε-polylysine is loaded on the surface and in the pores of the silica aerogel.

2. The antibacterial and preservative coating liquid according to claim 1, characterized in that, The silica aerogel has a pore size of 20-70 nm, a porosity of 95-98%, and a specific surface area of ​​150-250 m². 2 / g.

3. The antibacterial and preservative coating liquid according to claim 1, characterized in that, The solid content of the waterborne polyurethane in the antibacterial and preservative coating liquid is 8-12 wt%.

4. The method for preparing the antibacterial and preservative coating liquid according to any one of claims 1 to 3, characterized in that, Includes the following steps: (1) Mix silica aerogel, ε-polylysine and water to obtain ε-polylysine / silica aerogel dispersion; (2) The ε-polylysine / silica aerogel dispersion obtained in step (1) is mixed with aqueous polyurethane to obtain an antibacterial and fresh-keeping coating liquid.

5. The preparation method according to claim 4, characterized in that, In step (1), the mass ratio of silica aerogel to water is (0.5~0.75):

100.

6. The preparation method according to claim 4, characterized in that, In step (1), the mass ratio of ε-polylysine to water is (10~50) mg: 1 mL.

7. The preparation method according to claim 4, characterized in that, The mixing time in step (1) is 2 to 60 minutes.

8. The preparation method according to claim 4, characterized in that, The pH value of the ε-polylysine / silica aerogel dispersion in step (1) is 8~9.

9. An antibacterial preservation composite film, prepared from the antibacterial preservation coating liquid according to any one of claims 1 to 3 or the antibacterial preservation coating liquid prepared by the preparation method according to any one of claims 4 to 8.

10. A method for preserving fruits and vegetables, comprising: The antibacterial preservative coating liquid according to any one of claims 1 to 3 or the antibacterial preservative coating prepared by the preparation method according to any one of claims 4 to 8 is applied to the surface of the fruits and vegetables to be preserved and then dried.

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