Film-forming solutions for fruit and vegetable packaging coatings, and methods of making and using the same

Abstract

The application discloses a fruit and vegetable packaging coating film-forming solution and a preparation method and application thereof. The film-forming solution comprises natamycin, potassium sorbate, vitamin C, tea polyphenol and a film-forming base material. The preparation method comprises the following steps: heating and dissolving the film-forming base material to obtain a base coating film solution; adding natamycin, potassium sorbate, vitamin C and tea polyphenol into the base coating film solution and stirring and dissolving to obtain a film solution; and depositing the film solution on the surface of a polyethylene film in the form of microdroplets through a spray gun, and the release of active substances can be controlled by humidity change. The fruit and vegetable packaging coating film-forming solution provided by the application is an active packaging film with antibacterial and antioxidant effects, low cost and high activity, has a significant fresh-keeping effect, can effectively guarantee the quality of fruits and vegetables, and can be applied to fruit and vegetable preservation, has the advantages of low cost and high adaptability, and is suitable for industrial production and large-scale commercial application.

Description

Technical Field

[0001] This invention belongs to the field of active packaging technology for fruit and vegetable preservation, and particularly relates to a film-forming solution for fruit and vegetable packaging coating, its preparation method and application. Background Technology

[0002] Fresh fruits and vegetables have a high water content and vigorous respiration and metabolism, making them susceptible to infection by microorganisms and pests. During post-harvest processing, transportation, and storage, they are easily damaged, leading to softening, browning, and spoilage, resulting in severe quality deterioration and significant economic losses. With the improvement of living standards in my country, the market demand for effective fruit and vegetable preservation is increasing. Finding methods to create high-quality, high-value products that meet the needs of new business models is crucial. Therefore, researching and developing new, pollution-free fruit and vegetable preservation and antibacterial technologies to promote high-value processing and quality upgrades, and driving the high-quality and sustainable development of the fruit and vegetable industry, is an important trend for future development.

[0003] Applying packaging materials with preservation properties is one of the simplest and most practical methods to reduce fruit and vegetable spoilage and ensure product quality. With the development of new technologies and materials, active packaging has shown unique advantages in the field of food preservation due to its antibacterial and antioxidant activities, attracting widespread attention and research. Active packaging achieves food preservation by releasing active ingredients that interact with the packaged food or the surrounding environment. In traditional food packaging, active substances are usually added directly to the food, resulting in problems such as high drug residues, impaired food quality, and insignificant preservation effects. Furthermore, current active packaging technology suffers from high costs, complex preparation processes, and insufficient large-scale processing methods, making large-scale production and industrial application difficult, and it remains largely confined to the laboratory stage. Summary of the Invention

[0004] The technical problem this invention aims to solve is to overcome the shortcomings of existing technologies, providing a film-forming solution for fruit and vegetable packaging coatings, its preparation method, and its application. This constructs an active packaging film with antibacterial and antioxidant properties, low cost, and high activity, exhibiting significant preservation effects, effectively ensuring the quality of fruits and vegetables. It is also low-cost, highly adaptable, and suitable for industrial production and large-scale commercial applications. This invention not only demonstrates in-depth exploration and technological innovation in the field of food preservation science but also reflects a comprehensive consideration for improving food quality, protecting consumer health, and promoting environmental sustainability.

[0005] To address the aforementioned technical problems, the present invention provides a film-forming solution for fruit and vegetable packaging coatings, the film-forming solution comprising natamycin, potassium sorbate, vitamin C, tea polyphenols, and a film-forming substrate.

[0006] In the aforementioned film-forming solution for fruit and vegetable packaging coatings, the concentration of natamycin is further specified as 0.01 wt% to 0.1 wt%, the concentration of potassium sorbate is 0.05 wt% to 0.15 wt%, the concentration of vitamin C is 0.1 wt% to 1 wt%, and the concentration of tea polyphenols is 0.01 wt% to 0.1 wt%. Alternatively, the concentration of natamycin may be 0.03 wt%, the concentration of potassium sorbate is 0.09 wt%, the concentration of vitamin C is 0.3 wt%, and the concentration of tea polyphenols is 0.01 wt%.

[0007] The film-forming solution for the above-mentioned fruit and vegetable packaging coating further comprises pullulan as the film-forming substrate.

[0008] In the aforementioned film-forming solution for fruit and vegetable packaging coatings, the concentration of the film-forming substrate is further described as 1 wt% to 2 wt%.

[0009] Based on a general technical concept, the present invention also provides a method for preparing the film-forming solution of the fruit and vegetable packaging coating, the preparation method comprising the following steps:

[0010] S1. The film-forming substrate is heated and dissolved to obtain a base coating liquid;

[0011] S2. Add natamycin, potassium sorbate, vitamin C and tea polyphenols to the base coating solution and stir to dissolve to obtain the coating solution.

[0012] In the above preparation method, the heating and dissolving process in S1 specifically involves heating in a water bath at 30°C to 60°C for 10 to 30 minutes.

[0013] In the above preparation method, the stirring and dissolving in step S2 specifically involves: continuously stirring with a magnetic stirrer at a speed of 600–1000 r / min for 1–4 h.

[0014] Based on a general technical concept, the present invention also provides an application of the film-forming solution of the fruit and vegetable packaging coating in the preservation of fruits and vegetables.

[0015] Further, the method of the above application includes: adding the film-forming solution of the fruit and vegetable packaging coating into a 0.5mm diameter spray gun, spraying it evenly on the inside of the polyethylene packaging film, drying it at 50°C to obtain a film sheet, placing the fruit and vegetables into a packaging box, and wrapping and sealing them with the film sheet.

[0016] Further, the application method described above includes: uniformly applying the film-forming solution of the fruit and vegetable packaging coating onto fruit and vegetable absorbent paper, drying it at 50°C to obtain padding paper, placing the padding paper into a packaging box, placing the fruits and vegetables to be preserved inside, and sealing it.

[0017] The above application, further, the method of the application includes:

[0018] (1) Add the film-forming solution of the fruit and vegetable packaging coating to a 0.5 mm diameter spray gun, spray it evenly on the inside of the polyethylene packaging film, and dry it at 50°C to obtain a film sheet; evenly apply the film-forming solution of the fruit and vegetable packaging coating to the fruit and vegetable absorbent paper, and dry it at 50°C to obtain a pad paper.

[0019] (2) Place the liner paper into the packaging box, put in the fruits and vegetables that need to be preserved, and wrap and seal it with a film.

[0020] Compared with the prior art, the advantages of the present invention are as follows:

[0021] (1) The present invention provides a film-forming solution for fruit and vegetable packaging coating, which is composed of edible materials and the active substances are selected from four low-cost, high-activity food additives that comply with the "GB 2760-2014 Standard for the Use of Food Additives".

[0022] Natamycin is a natural antibacterial agent produced by Streptomyces fermentation. It specifically inhibits the growth of filamentous fungi such as yeasts and molds, possessing numerous advantages including natural broad-spectrum activity, high efficiency, and safety. It also exhibits low toxicity to mammalian cells, demonstrating extremely high safety. Sorbic acid and its potassium salts are internationally recognized as highly effective, safe, and inexpensive food preservatives. They are easily absorbed and metabolized by the human body, ultimately converting into carbon dioxide and water. Potassium sorbate inhibits the growth of spoilage bacteria and molds by binding to the sulfhydryl groups of microbial enzyme systems, thereby disrupting many enzyme systems and achieving the purpose of preserving fruits and vegetables. Compared to traditional chemical preservatives, the combined use of natamycin and potassium sorbate provides a safer and more natural antibacterial pathway. The combined use of these two antibacterial agents has a synergistic antibacterial effect, effectively broadening the antibacterial spectrum, enhancing the inhibitory effect, and forming a multi-target attack on microorganisms. Simultaneously, it reduces the dosage of single antibacterial agents, thereby lowering the cost of food preservation and storage, and improving food safety.

[0023] Vitamin C and tea polyphenols, as antioxidants, primarily function by effectively scavenging free radicals and inhibiting oxidation reactions in fruit and vegetable cells. Vitamin C (ascorbic acid), an important nutrient in plants and a safe and potent antioxidant, acts as an electron donor in the antioxidant defense system, participating in the catalysis of hydroxyl radical (OH) removal from cells. - O 2-It helps to combat reactive oxygen species such as H2O2, resisting free radical damage to cells while protecting other antioxidant components in fruits. Tea polyphenols, especially catechins, are natural phenolic antioxidants and antibacterial agents with strong antioxidant capacity and highly effective broad-spectrum antibacterial effects, showing significant antibacterial effects against both Gram-positive and Gram-negative bacteria, and can slow down the aging process of fruits and vegetables. Vitamin C and tea polyphenols, as naturally sourced antioxidants, better meet current consumer demand for healthy and natural foods.

[0024] Its working principle lies in utilizing the abundant moisture generated by the respiration of fruits and vegetables to dissolve the active substances located on the inner side. These active substances are then released into the food packaging via gas diffusion, creating a contactless preservation and antibacterial effect. This effectively delays the physiological aging and spoilage of fruits and vegetables, maximizing the protection of their sensory quality and nutritional value. This invention uses natural ingredients as active packaging components, reducing reliance on synthetic chemicals and contributing to a more environmentally friendly and sustainable development of the food packaging industry. The compounding of active substances reduces drug consumption while enhancing efficacy, ensuring food safety while minimizing environmental pollution and resource consumption.

[0025] (2) The present invention provides a film-forming solution for fruit and vegetable packaging coating, using Lulan polysaccharide as the film-forming substrate, which is biodegradable and has good biocompatibility, making food preservation and storage more effective, safer and healthier.

[0026] (3) This invention provides an application of a film-forming solution for fruit and vegetable packaging coatings in fruit and vegetable preservation. Employing active packaging technology, it can improve the gaseous environment within the fruit and vegetable packaging, regulate the interactions between various components within the packaging environment, and effectively inhibit the loss of volatile flavor and aromatic substances, thereby slowing down the physiological decay of fruits and vegetables due to contact with the external environment. It can also exert antibacterial and antioxidant effects through the release of active substances, effectively inhibiting the growth and reproduction of microorganisms while maintaining the nutritional value of fruits and vegetables, thus extending their post-harvest life and shelf life. Simultaneously, active packaging is environmentally friendly, safe, and sustainable, representing an important development direction for future fruit and vegetable preservation packaging technology.

[0027] (4) This invention provides an application of a film-forming solution for fruit and vegetable packaging coatings in fruit and vegetable preservation. Using modern spraying technology, active compounds such as antibacterial agents and antioxidants are sprayed onto the inside of the packaging material, rather than being directly added to the food surface. This method ensures uniform coverage of the active substances and effective release, enhancing the overall preservation effect and avoiding potential safety issues such as large residues caused by direct contact between active substances and food. The packaging material used in this invention is polyethylene film. As a major type of plastic packaging material on the market, polyethylene film has advantages such as high mechanical strength, low cost, and safety (non-toxic). It has been mass-produced and applied in various fields such as food, medicine, and daily necessities.

[0028] (5) This invention provides an application of a film-forming solution for fruit and vegetable packaging coatings in fruit and vegetable preservation. The film-forming principle utilizes the surface tension of the liquid to form a dense "film" on the polyethylene film. Using natural polysaccharide polymer food raw materials as the film-forming matrix, the edible film formed through intermolecular interactions possesses excellent barrier properties, mechanical properties, and optical properties, among other physical characteristics. Furthermore, the edible film serves as a carrier for the active ingredients, giving the film antibacterial and antioxidant effects. Attached Figure Description

[0029] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings.

[0030] Figure 1 The static shear rheological curves are those of the film-forming solutions in Examples 1 and 2 of Experiment 1 of this invention.

[0031] Figure 2 The results show the antioxidant activity of the coating film-forming solution and active ingredients in Experiment 2 of this invention.

[0032] Figure 3 The figures show the tensile strength (TS) and elongation at break (EB) of different membranes in Experiment 3 of this invention. In the figure, A represents the tensile strength of different membranes; and B represents the elongation at break.

[0033] Figure 4 The thickness measurement results are for composite preservation films prepared with film-forming substrates of different concentrations in Experiment 4 of this invention.

[0034] Figure 5 The results of the preservation effect, sensory evaluation and degree of decay of oyster mushrooms by different treatment groups during storage in Experiment 5 of this invention are shown.

[0035] Figure 6 The results of the preservation effect, sensory evaluation and degree of decay of Cordyceps flowers by different treatment groups during storage in Experiment 5 of this invention are as follows.

[0036] Figure 7 The results of the preservation effect, sensory evaluation and degree of decay of chili peppers by different treatment groups during storage in Experiment 5 of this invention are as follows.

[0037] Figure 8 The results of the preservation effect, sensory evaluation and degree of decay of strawberries by different treatment groups during storage in Experiment 5 of this invention are as follows.

[0038] Figure 9 The results of the preservation effect, sensory evaluation and degree of decay of winter jujubes by different treatment groups during storage in Experiment 5 of this invention are as follows.

[0039] Figure 10 The results of the preservation effect, sensory evaluation and degree of decay of longan by different treatment groups during storage in Experiment 5 of this invention are as follows.

[0040] Figure 11 This is the result of the weight loss rate changes of different fruits and vegetables during storage in Experiment Six of this invention.

[0041] Figure 12 This is the result of the change in hardness of different fruits and vegetables during storage in Experiment 7 of this invention.

[0042] Figure 13 This is the result of changes in soluble solids in different fruits and vegetables during storage in Experiment Nine of this invention.

[0043] Figure 14 This is the result of the total acidity change of different fruits and vegetables during storage in Experiment Nine of this invention. Detailed Implementation

[0044] The present invention will be further described below with reference to specific preferred embodiments, but this does not limit the scope of protection of the present invention.

[0045] The materials, reagents, and instruments used in the following examples are all commercially available. Unless otherwise specified, the experimental methods used in the following examples are conventional methods in the art.

[0046] Among them, the biopolymers are: locust bean gum, sodium alginate, and sodium methyl cellulose (food grade), from Xinzhiwei Food Ingredients Mall; guar gum and xanthan gum (food grade); konjac flour extract (food grade), from Hubei Qiangsen Konjac Technology Co., Ltd.; gelatin and carrageenan (food grade), from Guangdong Jubaiwei Food Ingredients; chitosan oligosaccharide and chitosan (food grade), from Qingdao Honghai Biotechnology Co., Ltd.; sodium carboxymethyl cellulose (food grade), from Changshu Weiyi Technology Co., Ltd.; and pullulan (food grade), from Shandong Kangnaxin Biotechnology Co., Ltd.

[0047] Active compounds: Polylysine, ε-polylysine hydrochloride (food grade), Zhejiang Xinyinxiang Bioengineering Co., Ltd.; Tea polyphenols (food grade), Anhui Hongxing Pharmaceutical Co., Ltd.; Nisin (food grade), Zhengzhou Chaofan Chemical Co., Ltd.; Vitamin C (food grade), CSPC Vitamin C Pharmaceutical (Shijiazhuang) Co., Ltd.; Natamycin (food grade), Lvkang Biochemical Co., Ltd.; Potassium sorbate (food grade), Ningbo Wanglong Biotechnology Co., Ltd.

[0048] Test reagents: Ethanol (99% purity), Zhengzhou Pani Chemical Reagent Factory; Methanol, potassium persulfate, ABTS, and DPPH were all purchased from Sinopharm Chemical Reagent Co., Ltd.

[0049] Test subjects: oyster mushrooms, strawberries, jujubes, chili peppers, cordyceps flowers, and longans were all purchased from local supermarkets.

[0050] Example 1

[0051] A film-forming solution for an edible fruit and vegetable packaging coating of the present invention comprises 2% pullulan, 0.03% natamycin, 0.09% potassium sorbate, 0.3% vitamin C and 0.01% tea polyphenols.

[0052] Its preparation method includes the following steps:

[0053] (1) Preparation of base solution: Weigh 2% pullulan polysaccharide, add the remaining deionized water or distilled water to dissolve it, and then heat it in a 50℃ water bath for 20 minutes until it is mixed evenly to obtain 2% (w / v) polysaccharide base coating solution.

[0054] (2) Weighing raw materials: Weigh 0.03% natamycin, 0.09% potassium sorbate, 0.3% vitamin C and 0.01% tea polyphenols according to the mass percentage of the components.

[0055] (3) Preparation of film solution: Add the raw materials weighed in step (2) to the coating solution prepared in step (1), and then use a magnetic stirrer to stir continuously for 2 hours at 600-1000 r / min to fully dissolve the raw materials and remove the air bubbles in the solution to obtain the film-forming solution.

[0056] Example 2

[0057] A film-forming solution for an edible fruit and vegetable packaging coating of the present invention comprises 1% pullulan, 0.03% natamycin, 0.09% potassium sorbate, 0.3% vitamin C and 0.01% tea polyphenols.

[0058] Its preparation method is the same as that in Example 1.

[0059] Experiment 1: Investigating the flowability of the film-forming solutions from Examples 1 and 2:

[0060] Rheological analysis of film-forming solutions can reflect their spreadability, uniformity, mechanical properties, and application characteristics, which are crucial for the preparation and use of coating solutions. These properties affect the coating uniformity, adaptability to fruits and vegetables of different shapes, and resilience under stress. Controlling these rheological properties ensures the high efficiency and reliability of the coating in protecting fruits and vegetables, thereby improving the overall performance of the packaging. Furthermore, the apparent viscosity of the film solution is critical to the preservation effect of fruits and vegetables. Excessive viscosity can clog the spray gun or cause uneven droplet distribution, severely impacting the preservation effect.

[0061] Therefore, this experiment investigated the rheological properties of different film-forming substrates, including: chitosan, gelatin, pullulan, chitosan oligosaccharide, sodium methyl cellulose, locust bean gum, sodium alginate, guar gum, konjac starch extract, carrageenan, sodium carboxymethyl cellulose, xanthan gum, and film-forming solution (NPVT). Static rheological measurements were performed on these film-forming substrates using a rotational rheometer with a flat plate (40 mm diameter, 1 mm gap). Samples were homogenized and air bubbles removed before analysis. The measurements were conducted at 25 °C for 0.1–100 s. -1 Static shearing tests were conducted at a shear rate of [value missing].

[0062] Figure 1 The figures show the static shear rheological curves of the film-forming solutions from Examples 1 and 2. In the figures, A and B represent the film-forming solution of Example 1, and C and D represent the film-forming solution of Example 2; B and D are detail views of the blue areas in A and C, respectively. It can be seen from the figures that the apparent viscosity of each curve decreases with increasing shear rate, indicating that each film-forming solution exhibits typical pseudoplastic characteristics. At concentrations of 1% and 2%, pullulan has relatively low apparent viscosity, and after the addition of bioactive substances, the apparent viscosity of the NPVT group did not increase but instead decreased to some extent, possibly due to the reduction of intermolecular forces in the film solution after the addition of bioactive substances. This study demonstrates that pullulan is suitable as a substrate for spray coating solutions.

[0063] Experiment 2: Investigating the antioxidant activity of the film-forming solution.

[0064] The antioxidant activity of the film-forming solution in fruit and vegetable packaging coatings is extremely important because it helps protect fruits and vegetables from oxidative damage, slows down the aging process, and thus extends their shelf life. By preventing the oxidation of vitamins and other nutrients in fruits and vegetables, coatings with antioxidant activity can maintain their nutritional value and freshness, while reducing waste caused by premature spoilage. The antioxidant effect of the sprayed film solution can scavenge free radicals and inhibit oxidation chain reactions, thereby extending the storage time of fruits and vegetables. This is of great significance in maintaining food quality, improving transportation efficiency, and reducing economic losses.

[0065] Antioxidant capacity is assessed by assessing DPPH free radical scavenging ability.

[0066] NPVT group: Film-forming solution from Example 2 (comprising: 1% pullulan, 0.03% natamycin, 0.09% potassium sorbate, 0.3% vitamin C, and 0.01% tea polyphenols). NATA group: Contains 1% natamycin. Rs group: Contains 1% solid lysozyme. Ri group: Contains 1% liquid lysozyme. Ps group: Contains 1% potassium sorbate. PLH group: Contains 1% ε-polylysine hydrochloride. Ninsin group: Contains 1% nisin.

[0067] Experimental Procedure: Dissolve the films from each group in deionized water, mix with DPPH (0.1 mM) methanol solution at a 1:1 ratio, and then place the mixture in a water bath at 37°C in the dark. Centrifuge the mixture at 10,000 rpm for 5 min at room temperature. Detect the samples at 517 nm using a microplate reader. Formula for calculating DPPH free radical scavenging activity:

[0068] DPPH removal rate (%) = (A0-A1) / A0×100. Where A0 and A1 are the DPPH absorbance of the control and the film, respectively.

[0069] The antioxidant activity of the membrane was evaluated by determining its ABTS radical scavenging ability. Experimental procedure: A 1:1 mixture of 7 mM ABTS and 2.45 mM potassium persulfate solution was prepared and mixed for 12 h. The solution was then diluted with ethanol until the absorbance at 734 nm reached 0.70 ± 0.02. The membrane was dissolved in deionized water and then mixed with the ABTS solution. The mixture was then incubated in the dark for 30 min and centrifuged at 10,000 rpm for 5 min at room temperature. The samples were detected at 734 nm using a microplate reader. The ABTS radical scavenging activity was calculated using the formula: ABTS scavenging rate (%) = (A0 - A1) / A0 × 100, where A0 and A1 are the ABTS absorbance of the control and the membrane, respectively.

[0070] Figure 2The results show the antioxidant activity of the coating film-forming solution and active ingredients. As can be seen from the figure, the NPVT group, due to the appropriate addition of vitamin C and tea polyphenols, exhibits extremely strong free radical scavenging ability, significantly higher than other groups. The ABTS free radical scavenging rate reaches 84.69%, and the DPPH free radical scavenging rate reaches 94.44%. Vitamin C can act as an excellent electron donor during the storage of fruits and vegetables, participating in free radical reactions, thereby effectively helping to scavenge free radicals and delaying oxidative deterioration. Furthermore, tea polyphenols are potent natural antioxidants that can effectively resist oxidative stress by scavenging free radicals, chelating metal ions, inhibiting oxidases, and exhibiting strong reducing power, thus helping to prevent various chronic diseases and promote health. Therefore, the prepared NPVT possesses excellent antioxidant properties.

[0071] Example 3

[0072] A composite preservation film prepared using the film-forming solution of the fruit and vegetable packaging coating of Example 1 or Example 2 is prepared by means of: adding the dissolved film solution into a 0.5 mm diameter spray gun and spraying it evenly on the inner side of the polyethylene packaging film, so that it covers a unit area of ​​5.12 L / m². 3 (5.12×10 3 mL / cm 3 The film is dried at 50°C to obtain a composite preservation film.

[0073] Example 4

[0074] A fruit and vegetable packaging paper prepared using a film-forming solution of the fruit and vegetable packaging coating of Example 1 or Example 2, the preparation method of which includes: uniformly applying the dissolved film solution onto the fruit and vegetable absorbent paper, so that it covers a unit area of ​​18.07 L / m². 3 (18.07×10 3 mL / cm 3 The fruit and vegetable pads are dried at 50°C to obtain fruit and vegetable padding paper.

[0075] Experiment 3: Measuring the mechanical properties of the active coating film.

[0076] Mechanical properties are crucial parameters for evaluating the stress resistance of food packaging materials during handling, transportation, and storage. This includes the strength and durability of the packaging material to withstand pressure and prevent breakage; flexibility and adaptability to accommodate products of different shapes; puncture and tear resistance to protect against damage from sharp objects; and good sealing and airtightness to prevent external contamination and maintain product freshness. Mechanical properties not only protect products but also have a vital impact on improving customer satisfaction and maintaining product quality. A texture analyzer was used to analyze the tensile strength (TS) and elongation at break (EAB) of the test film. The film was first cut into strips with a width of 10 × 100 mm. Each strip was tested five times, and the average value was taken.

[0077] Figure 3 The tensile strength (TS) and elongation at break (EB) of different membranes were determined. Figure A represents the tensile strength of different membranes; Figure B represents the elongation at break. The figures show that the effects of the matrices, such as sodium alginate, chitosan, and pullulan, are particularly outstanding. The mechanical strength of pullulan is directly proportional to its concentration; the TS of 2% pullulan is higher than that of 1% concentration (increasing from 21.80 MPa to 39.73 MPa); the EB of 2% pullulan is also higher than that of 1% concentration (increasing from 3.27% to 5.65%).

[0078] Experiment 4: Determine the thickness of each polymer base film.

[0079] The film thickness was measured using a handheld digital thickness gauge with an accuracy of 0.001 mm. Each sample was tested from 5 different locations, and the average of the measured values ​​was taken as the thickness of each film.

[0080] Figure 4 The thickness measurements of composite preservation films prepared with film-forming substrates of different concentrations are shown in the figure. It can be seen from the figure that the thickness is lower with 1% pullulan, while the thickness is moderate with 2% concentration. Based on these results, 2% pullulan was selected as the film-forming matrix for subsequent studies.

[0081] Example 5

[0082] The application of the composite preservation film of Example 2 in food preservation includes the following method: Six kinds of fruits and vegetables—strawberries, jujubes, longans, oyster mushrooms, cordyceps flowers, and chili peppers—are selected as test subjects. These fruits and vegetables must be free from pests, diseases, and mechanical damage, have roughly the same degree of maturity, and be uniform in color and size. Appropriate amounts of strawberries (30-40g), jujubes (40-50g), longans (40-50g), oyster mushrooms (60-65g), cordyceps flowers (15-20g), and chili peppers (35-40g) are weighed and placed in a packaging box, then covered with the composite preservation film of Example 2 for sealing. Three parallel groups are set up for each type of fruit and vegetable, and the samples are stored in a constant temperature and humidity chamber for 1, 3, 5, and 7 days, and named Group P.

[0083] Comparative Example 1

[0084] Six fruits and vegetables were selected as test subjects: strawberries, jujubes, longans, oyster mushrooms, cordyceps flowers, and chili peppers. These were required to be free from pests, diseases, and mechanical damage, with roughly uniform ripeness, color, and size. Appropriate amounts of strawberries (30–40g), jujubes (40–50g), longans (40–50g), oyster mushrooms (60–65g), cordyceps flowers (15–20g), and chili peppers (35–40g) were weighed and placed in packaging boxes without any treatment. Three parallel groups were set up for each type of fruit and vegetable, and the samples were stored in a constant temperature and humidity chamber for 1, 3, 5, and 7 days, and named the UT group.

[0085] Example 6

[0086] The application of the composite preservation film of Example 2 and the fruit and vegetable liner of Example 3 in food preservation includes the following method: Six kinds of fruits and vegetables—strawberries, jujubes, longans, oyster mushrooms, cordyceps flowers, and peppers—are selected as test subjects. These fruits and vegetables must be free from pests, diseases, and mechanical damage, have roughly the same maturity, and be uniform in color and size. The fruit and vegetable liner of Example 3 is placed in a packaging box, followed by weighed strawberries (30-40g), jujubes (40-50g), longans (40-50g), oyster mushrooms (60-65g), cordyceps flowers (15-20g), and peppers (35-40g). The box is then covered with the composite preservation film of Example 2 for sealing. Three parallel groups are set up for each type of fruit and vegetable, and the boxes are stored in a constant temperature and humidity chamber for 1, 3, 5, and 7 days, and named as group PZ.

[0087] Comparative Example 2

[0088] Six fruits and vegetables—strawberries, jujubes, longans, oyster mushrooms, cordyceps flowers, and chili peppers—were selected as test subjects. These vegetables were required to be free from pests, diseases, and mechanical damage, have roughly the same degree of ripeness, and be uniform in color and size. Appropriate amounts of strawberries (30–40g), jujubes (40–50g), longans (40–50g), oyster mushrooms (60–65g), cordyceps flowers (15–20g), and chili peppers (35–40g) were weighed and placed in packaging boxes, which were then sealed with commercially available pure PE film. Three parallel groups were set up for each type of fruit and vegetable, and the samples were stored in a constant temperature and humidity chamber for 1, 3, 5, and 7 days, designated as the CK group.

[0089] Example 7

[0090] The application of the composite preservation film of Example 2 and the fruit and vegetable liner of Example 3 in food preservation includes the following method: Six kinds of fruits and vegetables—strawberries, jujubes, longans, oyster mushrooms, cordyceps flowers, and peppers—are selected as test subjects. These fruits and vegetables must be free from pests, diseases, and mechanical damage, have roughly the same maturity, and be uniform in color and size. The fruit and vegetable liner of Example 3 is placed in a packaging box, followed by weighed strawberries (30-40g), jujubes (40-50g), longans (40-50g), oyster mushrooms (60-65g), cordyceps flowers (15-20g), and peppers (35-40g). Small holes are evenly punched into the composite preservation film of Example 2, and the treated film is then used for sealing. Three parallel groups are set up for each type of fruit and vegetable, and the products are stored in a constant temperature and humidity chamber for 1, 3, 5, and 7 days, and named the PZK group.

[0091] Comparative Example 3

[0092] Six fruits and vegetables—strawberries, jujubes, longans, oyster mushrooms, cordyceps flowers, and chili peppers—were selected as test subjects. These vegetables were required to be free from pests, diseases, and mechanical damage, have roughly the same level of ripeness, and be uniform in color and size. Appropriate amounts of strawberries (30–40g), jujubes (40–50g), longans (40–50g), oyster mushrooms (60–65g), cordyceps flowers (15–20g), and chili peppers (35–40g) were weighed and placed in packaging boxes, which were then sealed with commercial preservative film. Three parallel groups were set up for each type of fruit and vegetable, and the samples were stored in a constant temperature and humidity chamber for 1, 3, 5, and 7 days, designated as the SD group.

[0093] Experiment 5: Sensory evaluation and decay rate of fruits and vegetables in Examples 5 to 7.

[0094] The effectiveness of the membrane solution in preserving fruits and vegetables was visually assessed using sensory evaluation methods. The sensory evaluation consisted of four indicators: visual evaluation, olfactory evaluation, tactile evaluation, and decay assessment. Specific evaluation criteria were as follows: Visual evaluation (3 points), including: Color (1 point): Assessing whether the color of fruits and vegetables meets the maturity standards of a specific variety, examining the uniformity and vibrancy of the color; Shape and size (1 point): Checking whether the shape and size of fruits and vegetables meet the standards according to variety characteristics; Appearance defects (1 point): Checking for cracks, spots, scars, or other physical damage on the surface. Olfactory evaluation (2 points), including: Freshness of odor (1 point): Identifying the natural odor of fruits and vegetables, assessing their freshness, and checking for any abnormal odors; Maturity-related odor (1 point): Detecting the characteristic odor of specific fruit and vegetable maturity. Tactile evaluation (3 points), including: Firmness / texture (1.5 points): Assessing whether the firmness of fruits and vegetables meets their maturity requirements through touch and slight pressure; Moisture content (1.5 points): Sensing the moisture level of the surface and cut surfaces of fruits and vegetables, assessing whether the moisture content is appropriate. Evaluation of the degree of decay (2 points): The degree of microbial infection on the surface of fruits and vegetables is evaluated through visual observation. The total score is 10 points, and the average score is taken after evaluation by multiple groups.

[0095] The degree of decay in fruits and vegetables is determined using a grading system. The decay levels are as follows: Level 0: No decay; Level 1: 0 ≤ decayed area < 10%; Level 2: 10% ≤ decayed area < 30%; Level 3: 30% ≤ decayed area < 50%; Level 4: 50% ≤ decayed area < 100%. The calculation formula is as follows:

[0096]

[0097] Figure 5 The results show the preservation effect, sensory evaluation, and degree of decay of oyster mushrooms under different treatment groups during storage.

[0098] Figure 6 The results show the preservation effect, sensory evaluation, and degree of decay of Cordyceps flowers under different treatment groups during storage.

[0099] Figure 7 The results show the preservation effect, sensory evaluation, and degree of decay of chili peppers under different treatment groups during storage.

[0100] Figure 8 The results show the preservation effect, sensory evaluation, and degree of decay of strawberries under different treatment groups during storage.

[0101] Figure 9 The results show the preservation effect, sensory evaluation, and degree of decay of winter jujubes under different treatment groups during storage.

[0102] Figure 10 The results show the preservation effect, sensory evaluation, and degree of decay of longan under different treatment groups during storage.

[0103] Depend on Figures 5-10 It can be seen that the P, PZ, and PZK experimental groups showed significant preservation effects, especially in maintaining a low probability of rotting fruit during longer storage periods for some fruits and vegetables, with significantly lower rot rates than other groups. Differences in oyster mushroom and cordyceps flower preservation began to appear on day 1 of storage, with particularly pronounced results on day 5; the sensory evaluation value of the oyster mushroom PZ group was 7.33, with a rot rate of only 0.23, while the sensory evaluation value of the cordyceps flower PZ group was 6, with a rot rate of only 0.1. Due to being freshly cut, peppers showed severe rot on day 3, with the CK group exhibiting an off-odor, while the freshly cut peppers in the PZ group remained in good condition. Significant preservation effects were observed in both the P and PZ groups during the 1-7 day storage period for strawberries; on day 7, the strawberries were full-colored and glossy, with no obvious off-odor, a sensory evaluation value of 7.17, and a rot rate of less than 0.2%. There was no significant difference between winter jujubes and longans. Winter jujubes were mainly distinguished by the reddening and mold on the peel, while longans could only be identified by the degree of mold on the peel without being peeled. The longan pulp in the CK group had a distinct odor on day 7 after being peeled, which could be identified by smell.

[0104] Experiment 6: Investigate the weight loss rate of fruits and vegetables in Examples 5 to 7.

[0105] Weight loss rate (%) = (A0 - A1) / A0 × 100

[0106] A0 and A1 represent the initial and post-storage fruit weights, respectively.

[0107] Figure 11This presents the results of weight loss rate changes of different fruits and vegetables during storage in Experiment Six of this invention. Among the six types of fruits and vegetables stored, the UT group showed extremely high weight loss rates, reaching 89.17% and 82.04% respectively by day 7 of storage for oyster mushrooms and cordyceps flowers. The PZK group also had a relatively high weight loss rate compared to other groups due to the presence of pores in its membrane; by day 7 of storage for cordyceps flowers, the PZK group had a weight loss rate of 80.71%. The weight loss rates of the CK, P, PZ, and standard groups were not significantly different, all ranging from 2% to 20%.

[0108] Experiment 7: To examine the firmness of the fruits and vegetables in Examples 5 to 7.

[0109] The firmness of six fruits and vegetables—strawberries, jujubes, longans, oyster mushrooms, cordyceps flowers, and chili peppers—was measured using a texture analyzer. Puncture tests were performed on the central area of ​​all fruits and vegetables. A TA 39 probe was used, with a probe testing speed of 1 mm / s, a clamp distance of 70 mm, a trigger point load of 0.1 N, and a target value distance of 5 mm for strawberries, jujubes, longans, oyster mushrooms, and chili peppers, and 1 mm for cordyceps flowers.

[0110] Figure 12 This figure shows the results of the hardness changes of different fruits and vegetables during storage in Experiment 7 of this invention. As can be seen from the figure: During the storage of oyster mushrooms, due to moisture loss, the hardness of the UT group and the PZK group increased from 1.36 on day 0 to 11.1 and 1.87 on day 7, respectively. The CK and SD groups softened due to the metabolic activity of the oyster mushrooms themselves and the decomposition by microorganisms during storage, decreasing from 1.36 on day 0 to 0.57 on day 7, a decrease of 58.09%. The PZ group, which showed the best preservation effect, maintained a hardness of 1.34 from day 0 to day 5, decreasing to 1.02 on day 7, a decrease of only 25%, demonstrating good preservation. During the storage and preservation of strawberries, the strawberry hardness was 1.62 on day 0. On day 7, compared to 0.61 in the CK group, the strawberries in the PZ group still had a hardness of 1.09, a decrease of 30% less than the CK group. We can draw similar conclusions in the storage and preservation of other fruits and vegetables. Therefore, groups P and PZ have a good effect on preserving the freshness of fruits and vegetables during storage and preservation.

[0111] Experiment 8: Investigate the color difference of fruits and vegetables in Examples 5 to 7.

[0112] The L, a, and b color indices of fruits and vegetables are determined using a colorimeter. The total color difference (ΔE) and whiteness index (WI) of the fruits and vegetables are calculated using the following formulas:

[0113]

[0114] Tables 1 to 6 show the color difference changes of fruits and vegetables in different treatment groups during storage.

[0115] Table 1: Color difference changes of oyster mushrooms after different treatment groups during storage

[0116]

[0117]

[0118] Table 2: Color difference changes of Cordyceps flowers after different treatment groups during storage

[0119]

[0120] Table 3: Color difference changes of chili peppers after different treatment groups during storage

[0121]

[0122]

[0123] Table 4: Color difference changes of strawberries in different treatment groups during storage

[0124]

[0125] Table 5: Color difference changes of winter jujubes after different treatment groups during storage

[0126]

[0127]

[0128] Table 6: Color difference changes of longan after different treatment groups during storage

[0129]

[0130] The results in Tables 1 to 6 show that during storage, fruits and vegetables generally exhibited an increasing L value and a decreasing ΔE value. This is due to oxidative browning, which leads to darkening of color and reduction in brightness. The a and b values ​​varied depending on the characteristics of the different fruits and vegetables. For example, the a value of peppers and jujubes gradually increased as their color changed from green to red during storage, while the b value of longan gradually decreased. Overall, groups P and PZ showed the best results compared to other groups, maintaining the best color difference data during storage. This indicates that the composite spray coating has a significant impact on the color of fruits and vegetables. This is related to the good barrier properties and antibacterial and antioxidant properties of the active coating, which blocks the contact area between fruits and vegetables and external oxygen, inhibiting microbial infection and thus slowing down color changes during storage. Furthermore, adding padding paper coated with the film can better maintain the brightness and color of fruits and vegetables. This may be because the antioxidant active substances in the film have an ultraviolet shielding effect, effectively preventing photodegradation of fruits and vegetables.

[0131] Experiment 9: Investigate the soluble solids and total acid of the fruits and vegetables in Examples 5 to 7.

[0132] Soluble solids (TSS) and total acid (TA) were determined using a handheld refractometer. Fruits and vegetables from different treatment groups were juiced in batches, transferred to 10 mL centrifuge tubes, and centrifuged at 6076 × g and 4 °C for 15 min. 20 μL of the supernatant was accurately taken for measurement. Soluble solids content was expressed in Brix, and total acid content was expressed as a percentage (%).

[0133] Figure 13 This figure shows the changes in soluble solids (TSS) of different fruits and vegetables during storage in Experiment Nine of this invention. As can be seen from the figure, with the extension of storage time, all treatment groups showed a trend of first increasing and then decreasing TSS. This is because in the early stage of storage, nutrients (such as starch and cellulose) in fruits and vegetables are degraded into monosaccharides and disaccharides during physiological metabolism. In the later stage of storage, TSS begins to decrease, which means that the quality of fruits and vegetables deteriorates. This is accompanied by the action of microorganisms; bacteria and fungi utilize the sugars in fruits and vegetables for growth, development, and reproduction, promoting spoilage. The CK group showed a significant decrease in TSS from day 1 to day 7 of storage, which was particularly evident in the strawberry storage experiment, where TSS decreased from 8.9 to 6.2, a loss rate of 30.34%. In contrast, the P and PZ groups, which underwent pesticide spraying, did not show a significant decrease compared to the CK and "standard" groups, and their TSS remained relatively stable. During strawberry storage, the TSS (Total Solids) of group P decreased from 9 on day 1 to 7.8, with a TSS loss rate of 13.33%, while that of group PZ decreased from 9.1 on day 1 to 8.5, with a TSS loss rate of only 6.59%, demonstrating a significant protective effect on the soluble solids of strawberry fruit. This is likely because the antioxidants and antibacterial agents in the membrane solution inhibited the growth of microorganisms and the oxidation of nutrients in fruits and vegetables, thus preventing drastic changes in TSS. Furthermore, on day 7 of storage, the TSS of group PZ in various fruits and vegetables was at its highest level except for group PZK. Due to the presence of pores, the water content in fruits and vegetables decreased, and the proportion of TSS increased accordingly. Therefore, group PZK showed a higher TSS level in jujubes, peppers, and longans.

[0134] Figure 14This figure shows the total acid (TA) changes of different fruits and vegetables during storage in Experiment Nine of this invention. As can be seen from the figure, respiration and microbial activity are the main reasons for the changes in TA values ​​of fruits and vegetables. Fruits and vegetables participate in energy metabolism by consuming organic acids, while microorganisms, through infecting fruit and vegetable tissues, utilize their nutrients for growth, development, and reproduction, producing organic acids in their metabolism. This leads to the fruits and vegetables becoming acidic, reducing their edible value, and posing safety and health risks. During the storage of various fruits and vegetables, the TA values ​​of the CK group and the standard group generally showed significant changes. When strawberries, longans, cordyceps, and oyster mushrooms were stored for 7 days, and peppers were stored for 3 days, the TA values ​​of the CK group and the standard group were significantly higher than those of the P and PZ groups. However, the TA values ​​of the P and PZ group samples remained relatively stable during storage. Especially during the storage of longan, the TA value of the CK and standard groups increased from 0.91 g / 100 mL on day 0 to 1.42 g / 100 mL and 1.72 g / 100 mL on day 7, respectively, representing increases of 56.04% and 89.01%. The PZ group showed the most stable TA value, increasing from 0.91 g / 100 mL to 1.05 g / 100 mL, an increase of only 15.38%, achieving the desired preservation effect on fruit and vegetable quality. The differences in TA value after different treatments may be due to the self-defense mechanism of fruit and vegetable samples in response to post-harvest environmental stress. The CK and standard groups produced a large amount of organic acids due to this stress, and microbial contamination also increased the TA content in the environment. In contrast, the P and PZ groups, protected by the coating material, did not exhibit drastic changes in TA value.

[0135] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make many possible variations and modifications to the technical solutions of the present invention using the methods and techniques disclosed above, or modify them into equivalent embodiments with equivalent changes, without departing from the spirit and technical essence of the present invention. Therefore, any simple modifications, equivalent substitutions, equivalent changes, and modifications made to the above embodiments based on the technical essence of the present invention without departing from the content of the technical solutions of the present invention shall still fall within the protection scope of the technical solutions of the present invention.

Claims

1. The application of a film-forming solution for fruit and vegetable packaging coating in fruit and vegetable preservation, characterized in that, The film-forming solution comprises natamycin, potassium sorbate, vitamin C, tea polyphenols, and a film-forming substrate; the concentration of natamycin is 0.01wt%–0.1wt%, the concentration of potassium sorbate is 0.05wt%–0.15wt%, the concentration of vitamin C is 0.1wt%–1wt%, and the concentration of tea polyphenols is 0.01wt%–0.1wt%. The film-forming substrate is pullulan; The concentration of the film-forming substrate is 1 wt% to 2 wt%. The application method includes: (1) Add the film-forming solution to a spray gun with a nozzle diameter of 0.1 to 1 mm, spray it evenly on the inside of the polyethylene packaging film, and dry it at 30 to 60°C to obtain a composite preservation film; apply the film-forming solution evenly to fruit and vegetable absorbent paper, and dry it at 30 to 60°C to obtain fruit and vegetable pad paper. (2) Place the fruit and vegetable padding paper into the packaging box, put in the fruits and vegetables that need to be preserved, and wrap and seal them with the composite preservation film; The preparation method of the film-forming solution includes the following steps: S1. The film-forming substrate is heated and dissolved to obtain a base coating liquid; S2. Add natamycin, potassium sorbate, vitamin C and tea polyphenols to the substrate coating solution and stir to dissolve to obtain a film-forming solution; The heating and dissolution process in S1 is as follows: heating in a water bath at 30℃~60℃ for 10min~30min; The stirring and dissolving process in S2 involves continuously stirring with a magnetic stirrer at a speed of 600–1000 r / min for 1–4 hours.

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