Film-forming solution of fruit and vegetable packaging coating as well as preparation method and application of film-forming solution

Abstract

The invention discloses a film-forming solution of a fruit and vegetable packaging coating as well as a preparation method and application of the film-forming solution. 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 a film-forming base material to obtain a substrate film coating solution; and adding natamycin, potassium sorbate, vitamin C and tea polyphenol into the base film coating liquid, stirring and dissolving to obtain film liquid, forming tiny liquid drops through a spray gun, depositing the tiny liquid drops on the surface of a polyethylene film, and regulating and controlling the release of active matters by utilizing humidity change. The film-forming solution of the fruit and vegetable packaging coating is an active packaging film which has antibacterial and antioxidant effects and is low in cost and high in activity, has a remarkable fresh-keeping effect, can effectively guarantee the quality of fruits and vegetables, can be applied to fresh keeping of the fruits and vegetables, has the advantages of being low in cost, high in adaptability and the like, and is suitable for industrial production and large-scale commercial application.

Description

Technical Field

[0001] The invention belongs to the technical field of fruit and vegetable fresh-keeping active packaging, and in particular relates to a film-forming solution of a fruit and vegetable packaging coating, a preparation method and application thereof. Background Art

[0002] Fresh fruits and vegetables have high water content, vigorous respiration and metabolism, and are susceptible to infection by microorganisms, pests and diseases. They are easily damaged and induced during post-harvest processing, transportation, and storage, resulting in softening, browning, corruption and other adverse phenomena, which lead to serious deterioration of fruit and vegetable quality and large economic losses of products. With the improvement of the quality of life of Chinese residents, the market demand for effective preservation of fruits and vegetables is increasing. It is crucial to find ways to create high-quality and high-value series products that meet the conditions of new business formats. Therefore, it is an important trend for future development to research and develop new pollution-free fruit and vegetable preservation and antibacterial technologies, promote high-value processing and quality upgrades, and promote high-quality and sustainable development of the fruit and vegetable industry.

[0003] The use of packaging materials with preservation properties is one of the simplest and most practical ways to reduce fruit and vegetable losses and ensure product quality. With the development of new technologies and new materials, active packaging has shown unique advantages in the field of food preservation due to its antibacterial and antioxidant activities, and has received widespread attention and research. Active packaging achieves the purpose of food preservation by releasing active ingredients and interacting with packaged food or the surrounding environment. In traditional food packaging, active substances are usually added directly to food, which leads to problems such as large drug residues, impaired food quality, and unclear preservation effects. At the same time, the current active packaging technology has the disadvantages of high cost, complex preparation process, and insufficient large-scale processing and molding methods, which makes it difficult to mass produce and industrialize, and basically remains in the laboratory stage. Summary of the invention

[0004] The technical problem to be solved by the present invention is to overcome the deficiencies in the prior art, provide a film-forming solution for fruit and vegetable packaging coating, a preparation method and application thereof, and construct an active packaging film with antibacterial and antioxidant properties, low cost and high activity, which has a significant preservation effect, can effectively ensure the quality of fruits and vegetables, and is low in cost and highly adaptable, suitable for industrial production and large-scale commercial applications. The present invention not only demonstrates in-depth exploration and technological innovation in the field of food preservation science, but also reflects a comprehensive consideration of improving food quality, protecting consumer health and promoting environmental sustainability.

[0005] In order to solve the above technical problems, the present invention provides a film-forming solution for fruit and vegetable packaging coating, wherein the film-forming solution comprises natamycin, potassium sorbate, vitamin C, tea polyphenols and a film-forming substrate.

[0006] The above-mentioned film-forming solution for fruit and vegetable packaging coating, further, the concentration of natamycin is 0.01wt% to 0.1wt%, the concentration of potassium sorbate is 0.05wt% to 0.15wt%, the concentration of vitamin C is 0.1wt% to 1wt%, and the concentration of tea polyphenols is 0.01wt% to 0.1wt%. Further, the concentration of natamycin is 0.03wt%, the concentration of potassium sorbate is 0.09wt%, the concentration of vitamin C is 0.3wt%, and the concentration of tea polyphenols is 0.01wt%.

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

[0008] The above-mentioned film-forming solution for the fruit and vegetable packaging coating, further, the concentration of the film-forming base material is 1wt% to 2wt%.

[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, heating and dissolving the film-forming substrate to obtain a base coating liquid;

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

[0012] In the above preparation method, further, the heating and dissolving in S1 is specifically: heating in a water bath at 30° C. to 60° C. for 10 min to 30 min.

[0013] In the above preparation method, further, the stirring and dissolving in S2 is specifically: using a magnetic stirrer to continuously stir at a speed of 600 to 1000 r / min for 1 to 4 hours.

[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] The above application, further, the application method includes: adding the film-forming solution of the fruit and vegetable packaging coating into a 0.5 mm caliber spray gun, spraying it evenly on the inner side of the polyethylene packaging film and drying it at 50° C. to obtain a film sheet, placing the fruits and vegetables in a packaging box, and wrapping and encapsulating them with the film sheet.

[0016] The above application, further, the application method includes: evenly applying the film-forming solution of the fruit and vegetable packaging coating on fruit and vegetable absorbent paper, drying at 50°C to obtain padding paper, putting the padding paper into a packaging box, putting fruits and vegetables to be kept fresh, and packaging.

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

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

[0019] (2) Place the paper pad in the packaging box, put the fruits and vegetables to be kept fresh, and wrap them with film.

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

[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 natamycin, potassium sorbate, vitamin C and tea polyphenols, four low-cost and high-activity food additives that comply with the "GB 2760-2014 Food Additives Usage Standard".

[0022] Natamycin is a natural antimicrobial produced by the fermentation of Streptomyces. It can specifically inhibit the growth of filamentous fungi such as yeast and mold. It has many advantages such as natural broad spectrum, high efficiency and safety, and is low toxic to mammalian cells, with extremely high safety. Sorbic acid and its potassium salts are currently internationally recognized efficient, safe and low-cost food preservatives. They are easily absorbed and metabolized by the human body and eventually converted into carbon dioxide and water. Potassium sorbate can inhibit the growth of spoilage bacteria and molds, and destroy many enzyme systems by combining with the sulfhydryl groups of microbial enzyme systems, thereby achieving the purpose of fruit and vegetable preservation. Compared with traditional chemical preservatives, the combined use of natamycin and potassium sorbate provides a safer and more natural antibacterial approach. The combined use of these two antimicrobial agents has a synergistic antibacterial effect, which can effectively expand the antibacterial spectrum, enhance the inhibitory effect, and form a multi-target attack on microorganisms; at the same time, it reduces the dosage of a single antimicrobial agent, thereby reducing the cost of food preservation and storage, and improving food safety.

[0023] As antioxidants, the mechanism of action of vitamin C and tea polyphenols is mainly reflected in their ability to effectively remove free radicals and inhibit oxidation reactions in fruit and vegetable cells. Vitamin C (ascorbic acid) is an important nutrient in plants and a green, safe and strong antioxidant. It acts as an electron donor in the antioxidant defense system and participates in catalyzing the removal of OH by cells. - , O 2- , H 2 O 2Tea polyphenols, especially catechin compounds, as a natural phenolic antioxidant and antibacterial agent, have strong antioxidant capacity and high-efficiency broad-spectrum antibacterial effect. They have significant antibacterial effect on both Gram-positive and Gram-negative bacteria and can delay the aging process of fruits and vegetables. Vitamin C and tea polyphenols, as antioxidants from natural sources, are more in line with the current consumer demand for healthy and natural foods.

[0024] Its working principle is: a large amount of water vapor generated by the respiration of fruits and vegetables is used to dissolve the active substances located on the inside, and the active substances are released into the food packaging in the form of gas diffusion, forming a contactless preservation and antibacterial effect, which can more effectively delay the physiological aging and spoilage of fruits and vegetables, and maximize the protection of the sensory quality and nutritional value of food. The present invention uses natural ingredients as active packaging ingredients, which not only reduces the dependence on synthetic chemicals, but also helps to promote the development of the food packaging industry in a more environmentally friendly and sustainable direction. The compounding of active substances reduces the consumption of drugs but improves their effects, which can reduce environmental pollution and resource consumption while ensuring food safety.

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

[0026] (3)) The present invention provides an application of a film-forming solution of a fruit and vegetable packaging coating in the preservation of fruits and vegetables. The active packaging technology can improve the gas environment in the fruit and vegetable packaging, regulate the interaction between various components in the packaging environment, effectively inhibit the loss of volatile flavors 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 inhibit the growth and reproduction of microorganisms while maintaining the nutritional value of fruits and vegetables, so as to extend the post-harvest life and shelf life of fruits and vegetables. At the same time, active packaging has the characteristics of environmental protection, safety, sustainability, etc., and is an important development direction of fruit and vegetable preservation packaging technology in the future.

[0027] (4) The present invention provides an application of a film-forming solution of a fruit and vegetable packaging coating in the preservation of fruits and vegetables. Modern spraying technology is used to spray active compounds such as antibacterial agents and antioxidants on the inside of the packaging material instead of directly adding them to the surface of the food. This method allows the active substances to cover an even area and be effectively released, enhancing the overall preservation effect and avoiding potential safety issues such as large residues caused by direct contact between the active substances and the food. The packaging material used in the present invention is polyethylene film. As a product that accounts for a large proportion of plastic packaging materials on the market, polyethylene film has the advantages of high mechanical strength, low cost, safety and non-toxicity, etc. It has been mass-produced and applied to many fields such as food, medicine, and daily necessities.

[0028] (5) The present invention provides an application of a film-forming solution for fruit and vegetable packaging coating in the preservation of fruits and vegetables. The film-forming principle is to use the surface tension of the liquid to form a tight "film" of active substances on the polyethylene film. The edible film formed by the interaction between molecules using natural polysaccharide polymer food raw materials as the film-forming matrix has excellent barrier properties, mechanical properties, optical properties and other physical properties. In addition, the edible film acts as a carrier of active ingredients, so that the film has antibacterial and antioxidant properties. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] In order to make the purpose, technical solution and advantages of the embodiments of the present invention more clear, the technical solution in the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings in the embodiments of the present invention.

[0030] Figure 1 This is the static shear rheology curve of the film-forming solutions of Example 1 and Example 2 in Experiment 1 of the present invention.

[0031] Figure 2 These are the antioxidant activity results of the coating film-forming solution and active substances in Experiment 2 of the present invention.

[0032] Figure 3 The tensile strength (TS) and elongation at break (EB) of different films in Experiment 3 of the present invention, A in the figure is the tensile strength of different films; B in the figure is the elongation at break.

[0033] Figure 4 These are the thickness measurement results of the composite cling film prepared with film-forming substrates of different concentrations in Experiment 4 of the present invention.

[0034] Figure 5 These are the results of the preservation effect, sensory evaluation and decay degree of Pleurotus ostreatus in different treatment groups during storage in Experiment 5 of the present invention.

[0035] Figure 6 The present invention is the experiment five of the present invention, the different treatment groups during the storage period of the cordyceps flower preservation effect, sensory evaluation and decay degree results.

[0036] Figure 7 These are the results of the preservation effect, sensory evaluation and decay degree of peppers in different treatment groups during storage in Experiment 5 of the present invention.

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

[0038] Fig. 9 These are the results of the preservation effect, sensory evaluation and decay degree of the winter jujube in different treatment groups during storage in Experiment 5 of the present invention.

[0039] Fig.10 These are the results of the preservation effect, sensory evaluation and decay degree of longan in different treatment groups during storage in Experiment 5 of the present invention.

[0040] Fig.11 This is the result of the weight loss rate change of different fruits and vegetables during storage in Experiment 6 of the present invention.

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

[0042] Fig.13 This is the result of the change of soluble solids of different fruits and vegetables during storage in Experiment 9 of the present invention.

[0043] Fig.14 This is the result of the total acid changes of different fruits and vegetables during storage in Experiment 9 of the present invention. DETAILED DESCRIPTION

[0044] The present invention is further described below in conjunction with specific preferred embodiments, but the protection scope of the present invention is not limited thereby.

[0045] The materials, reagents and instruments used in the following examples can all be purchased from commercial channels. The experimental methods in the following examples are all conventional methods in the art unless otherwise specified.

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

[0047] Active compounds: polylysine, ε-polylysine hydrochloride (food grade), Zhejiang Xinyinxiang Bioengineering Co., Ltd.; tea polyphenols (food grade), Anhui Red Star Pharmaceutical Co., Ltd.; nisin (food grade), Zhengzhou Chaofan Chemical Co., Ltd.; vitamin C (food grade), Shijiazhuang Pharmaceutical Co., Ltd.; natamycin (food grade), Lukang Biochemical Co., Ltd.; potassium sorbate (food grade), Ningbo Wanglong Biotechnology Co., Ltd.

[0048] Test reagents: ethanol (purity 99%), Zhengzhou Paini Chemical Reagent Factory; methanol, potassium persulfate, ABTS, DPPH were purchased from Sinopharm Chemical Reagent Co., Ltd.

[0049] Test objects: Oyster mushroom, strawberry, winter jujube, pepper, cordyceps flower and longan were purchased from local supermarkets.

[0050] Example 1

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

[0052] The preparation method comprises the following steps:

[0053] (1) Preparation of base liquid: Weigh 2% pullulan by mass, add the remaining amount of deionized water or distilled water to dissolve, and then heat in a 50° C. water bath for 20 min until mixed evenly to obtain a 2% (w / v) polysaccharide base coating liquid.

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

[0055] (3) Preparation of membrane 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 them and remove bubbles in the solution to obtain a membrane-forming solution.

[0056] Example 2

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

[0058] The preparation method is consistent with that in Example 1.

[0059] Experiment 1: Investigating the fluidity of the film-forming solutions of Example 1 and Example 2:

[0060] Rheological analysis of the film-forming liquid can reflect the spreadability, uniformity, mechanical properties and application of the film-forming liquid, which is crucial for the preparation and use of the coating film solution. These characteristics affect the coating's coating uniformity, its ability to adapt to fruits and vegetables of different shapes, and its recovery after being subjected to force. Regulating these rheological properties can ensure the efficiency and reliability of the coating in protecting fruits and vegetables, thereby improving the overall performance of the packaging. In addition, the apparent viscosity of the film liquid is crucial to the storage and preservation of fruits and vegetables. If the viscosity of the film liquid is too high, it will cause clogging of the spray gun or cause uneven spray droplets, seriously affecting the preservation effect of the film liquid.

[0061] To this end, this experiment investigated the rheological properties of different film-forming substrates, including: chitosan, gelatin, pullulan, chitosan oligosaccharides, sodium methylcellulose, locust bean gum, sodium alginate, guar gum, konjac flour, carrageenan, sodium carboxymethylcellulose, xanthan gum, and film-forming solution (NPVT). The above-mentioned film-forming substrates were subjected to static rheological measurements in a rotational rheometer with a flat plate (diameter 40 mm, gap 1 mm). The samples were mixed and bubbles were removed before analysis. At a temperature of 25°C, 0.1-100s -1 Static shear tests were performed at a shear rate of .

[0062] Figure 1 It is the static shear rheological curve of the film-forming solution of Example 1 and Example 2. A and B in the figure are the film-forming solutions of Example 1, and C and D are the film-forming solutions of Example 2; B and D are detailed pictures of the blue areas of A and C, respectively. It can be seen from the figure that the apparent viscosity of each curve decreases with the increase of shear rate, indicating that each film-forming solution exhibits typical pseudoplastic properties. The apparent viscosity of pullulan is relatively low at concentrations of 1% and 2%, and after the addition of bioactive substances, the apparent viscosity of the NPVT group did not increase, but decreased to a certain extent, which may be because after the addition of bioactive substances, the intermolecular forces of the membrane solution are reduced. Studies have shown that pullulan is suitable as a substrate for spraying membrane liquid.

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

[0064] The antioxidant activity of the film-forming solution of fruit and vegetable packaging coatings is extremely important because it helps protect fruits and vegetables from oxidative damage and delays the aging process of fruits and vegetables, thereby extending their shelf life. By preventing the oxidation of vitamins and other nutrients in fruits and vegetables, coatings with antioxidant activity can maintain the nutritional value and freshness of fruits and vegetables while reducing waste caused by premature decay. The antioxidant effect of the spray film solution can scavenge free radicals and hinder the oxidation chain reaction, 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] The antioxidant capacity was evaluated by scavenging DPPH free radicals.

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

[0067] Experimental steps: Dissolve the film of each group in deionized water, mix with DPPH (0.1mM) methanol solution in a ratio of 1:1, and then place the mixture in a water bath and react at 37°C in the dark. Centrifuge the mixture at 10000rpm for 5min at room temperature. The sample is detected using an ELISA reader at 517nm. The calculation formula of DPPH free radical scavenging activity is:

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

[0069] The antioxidant activity of the film was evaluated by measuring the ABTS free radical scavenging ability. Experimental steps: 7mM ABTS and 2.45mM potassium persulfate solution were prepared and mixed in a 1:1 ratio for 12h, and then the solution was diluted with ethanol until the absorbance at 734nm reached 0.70±0.02. The film was dissolved in deionized water and then mixed with the ABTS solution. Then, the mixture was incubated in the dark for 30 minutes, and the mixture was centrifuged at 10000rpm for 5min at room temperature. The sample was detected using an enzyme reader at 734nm. The calculation formula for ABTS free radical scavenging activity: ABTS scavenging rate (%) = (A0-A1) / A0×100. Where A0 and A1 are the ABTS absorbance of the control and the film, respectively.

[0070] Figure 2The results of the antioxidant activity of the coating film-forming solution and the active ingredients. As can be seen from the figure: Due to the reasonable addition of vitamin C and tea polyphenols, the NPVT group has a very strong free radical scavenging ability, which is 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 participate in free radical reactions as an excellent electron donor during the storage of fruits and vegetables, thereby effectively helping to scavenge free radicals and delay the oxidation and deterioration of fruits and vegetables. In addition, tea polyphenols are powerful natural antioxidants that can effectively resist oxidative stress by scavenging free radicals, chelating metal ions, inhibiting oxidases, and showing strong reducing ability, which helps prevent a variety of chronic diseases and promote health. Therefore, the prepared NPVT has excellent antioxidant properties.

[0071] Example 3

[0072] A composite fresh-keeping film prepared by using the film-forming solution of the fruit and vegetable packaging coating of Example 1 or Example 2, wherein the preparation method comprises: adding the dissolved film solution into a 0.5 mm caliber spray gun, and spraying it evenly on the inner side of the polyethylene packaging film so that the coverage unit area is 5.12 L / m 3 (5.12×10 3 mL / cm 3 ) and drying at 50°C to obtain a composite fresh-keeping film.

[0073] Example 4

[0074] A fruit and vegetable padding paper prepared by using the film-forming solution of the fruit and vegetable packaging coating of Example 1 or Example 2, wherein the preparation method comprises: applying the dissolved film solution evenly on the fruit and vegetable absorbent paper so that the coverage unit area is 18.07 L / m 3 (18.07×10 3 mL / cm 3 ) and dried at 50°C to obtain fruit and vegetable padding paper.

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

[0076] Mechanical properties are important 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 rupture; flexibility and adaptability to adapt to products of different shapes; puncture and tear resistance to resist damage from sharp objects; and good closure and sealing to prevent external contamination and keep the product fresh. Mechanical properties not only protect the product, 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 10×100mm. Each film was tested 5 times and the average value was finally taken.

[0077] Figure 3 The tensile strength (TS) and elongation at break (EB) of different films were measured. A in the figure is the tensile strength of different films; B in the figure is the elongation at break. It can be seen from the figure that the effects of matrices such as sodium alginate, chitosan, and pullulan are particularly prominent. The mechanical strength of pullulan is proportional to its concentration. The TS of 2% pullulan is higher than that of 1% (increased from 21.80MPa to 39.73MPa); the EB of 2% pullulan is higher than that of 1% (increased from 3.27% to 5.65%).

[0078] Experiment 4: Determine the thickness of each polymer substrate 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 positions, and the average of the measured values ​​was taken as the thickness of each film.

[0080] Figure 4 The thickness measurement results of composite cling film prepared with different concentrations of film-forming substrates. It can be seen from the figure that the thickness of 1% pullulan is relatively low, and the thickness is moderate at 2% concentration. Based on the above results, 2% pullulan was selected as the film-forming substrate in subsequent studies.

[0081] Example 5

[0082] An application of the composite preservative film of Example 2 in food preservation, the application method of which includes: selecting six kinds of fruits and vegetables, namely strawberry, winter jujube, longan, oyster mushroom, cordyceps flower and pepper, as test objects, requiring no pests and mechanical damage, generally consistent maturity, and uniform color and size. Appropriate amounts of strawberry (30-40g), winter jujube (40-50g), longan (40-50g), oyster mushroom (60-65g), cordyceps flower (15-20g) and pepper (35-40g) are weighed and put into a packaging box, and covered with the composite preservative film of Example 2 for sealed packaging. Three groups of each kind of fruit and vegetable are set in parallel, placed in a constant temperature and humidity chamber for storage for 1, 3, 5, and 7 days, and named as Group P.

[0083] Comparative Example 1

[0084] Six kinds of fruits and vegetables, including strawberry, winter jujube, longan, oyster mushroom, cordyceps flower and pepper, were selected as test objects. They were required to be free of pests and diseases and mechanical damage, with roughly the same maturity and uniform color and size. Appropriate amounts of strawberry (30-40g), winter jujube (40-50g), longan (40-50g), oyster mushroom (60-65g), cordyceps flower (15-20g) and pepper (35-40g) were weighed and put into the packaging box without any treatment. Three groups of each kind of fruit and vegetable were set up in parallel and placed in a constant temperature and humidity chamber for 1, 3, 5, and 7 days, and named as UT group.

[0085] Example 6

[0086] The composite preservative film of Example 2 and the fruit and vegetable padding paper of Example 3 are used in food preservation, and the application method includes: selecting six kinds of fruits and vegetables, including strawberry, winter jujube, longan, oyster mushroom, cordyceps flower and pepper, as test objects, requiring no pests and mechanical damage, substantially the same maturity, and uniform color and size. The fruit and vegetable padding paper of Example 3 is placed in a packaging box, and then weighed strawberries (30-40g), winter jujube (40-50g), longan (40-50g), oyster mushroom (60-65g), cordyceps flower (15-20g) and pepper (35-40g) are placed, and the composite preservative film of Example 2 is covered for sealing and packaging, and three groups of each kind of fruit and vegetable are set in parallel, placed in a constant temperature and humidity box for storage for 1, 3, 5, and 7 days, and named as PZ group.

[0087] Comparative Example 2

[0088] Six kinds of fruits and vegetables, including strawberry, winter jujube, longan, oyster mushroom, cordyceps flower and pepper, were selected as test objects. They were required to be free of pests and diseases and mechanical damage, with roughly the same maturity and uniform color and size. Appropriate amounts of strawberry (30-40g), winter jujube (40-50g), longan (40-50g), oyster mushroom (60-65g), cordyceps flower (15-20g) and pepper (35-40g) were weighed and placed in a packaging box, and covered with pure PE film sold on the market for sealed packaging. Three groups of each kind of fruit and vegetable were set up in parallel and placed in a constant temperature and humidity chamber for 1, 3, 5, and 7 days, and named CK group.

[0089] Example 7

[0090] The composite preservative film of Example 2 and the fruit and vegetable padding paper of Example 3 are used in food preservation, and the application method includes: selecting six kinds of fruits and vegetables, strawberry, winter jujube, longan, oyster mushroom, cordyceps flower and pepper, as test objects, requiring no pests and mechanical damage, roughly the same maturity, and uniform color and size. The fruit and vegetable padding paper of Example 3 is placed in a packaging box, and then weighed strawberries (30-40g), winter jujube (40-50g), longan (40-50g), oyster mushroom (60-65g), cordyceps flower (15-20g) and pepper (35-40g) are placed. The composite preservative film of Example 2 is evenly perforated, and the treated film is covered for sealing and packaging. Three groups of each kind of fruit and vegetable are set in parallel, placed in a constant temperature and humidity box for storage for 1, 3, 5, and 7 days, and named PZK group.

[0091] Comparative Example 3

[0092] Six kinds of fruits and vegetables, including strawberry, winter jujube, longan, oyster mushroom, cordyceps flower and pepper, were selected as test objects. They were required to be free of pests and diseases and mechanical damage, with roughly the same maturity and uniform color and size. Appropriate amounts of strawberry (30-40g), winter jujube (40-50g), longan (40-50g), oyster mushroom (60-65g), cordyceps flower (15-20g) and pepper (35-40g) were weighed and placed in packaging boxes, and covered with commercial preservative coating for sealed packaging. Three groups of each kind of fruit and vegetable were set up in parallel and stored in a constant temperature and humidity chamber for 1, 3, 5, and 7 days, and named 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 liquid in preserving fruits and vegetables is visually tested by sensory evaluation, which is divided into four indicators: visual evaluation, olfactory evaluation, tactile evaluation and decay degree evaluation. The specific evaluation criteria are: visual evaluation (3 points), including color (1 point): evaluate whether the color of fruits and vegetables meets the maturity standards of specific varieties, and examine the uniformity and brightness of the color. Shape and size (1 point): check whether the shape and size of fruits and vegetables are standard according to the characteristics of the variety. Appearance defects (1 point): check whether there are cracks, spots, scars or other physical damage on the surface. Olfactory evaluation (2 points), including odor freshness (1 point): identify the natural odor of fruits and vegetables, evaluate their freshness and whether there are any abnormal odors. Maturity-related odor (1 point): detect the characteristic odor of the maturity of specific fruits and vegetables. Tactile evaluation (3 points), including hardness / texture (1.5 points): evaluate whether the hardness of fruits and vegetables meets their maturity requirements by touching and slightly pressing. Moisture content (1.5 points): feel the wetness of the surface and cut surface of fruits and vegetables, and evaluate whether the moisture content is appropriate. Evaluation of the degree of decay (2 points): The microbial infection on the surface of fruits and vegetables is evaluated by visual observation. The total score is 10 points, and the average value is taken after evaluation by multiple groups.

[0095] The rot degree of fruits and vegetables is measured using a grading method. The rot levels are as follows: Level 0: no rot; Level 1: 0 ≤ rotten area of ​​fruits and vegetables < 10%; Level 2: 10% ≤ rotten area of ​​fruits and vegetables < 30%; Level 3: 30% ≤ rotten area of ​​fruits and vegetables < 50%; Level 4: 50% ≤ rotten area of ​​fruits and vegetables < 100%. The calculation formula is as follows:

[0096]

[0097] Figure 5 These are the results of the preservation effect, sensory evaluation and decay degree of Pleurotus ostreatus in different treatment groups during storage.

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

[0099] Figure 7 It is the result of the preservation effect, sensory evaluation and decay degree of peppers in different treatment groups during storage.

[0100] Figure 8 It is the result of preservation effect, sensory evaluation and decay degree of strawberries in different treatment groups during storage.

[0101] Fig. 9 These are the results of the preservation effect, sensory evaluation and decay degree of winter jujube in different treatment groups during storage.

[0102] Fig.10 These are the results of the preservation effect, sensory evaluation and decay degree of longan in different treatment groups during storage.

[0103] Depend on Figures 5 to 10 It can be seen that the preservation effect of the P, PZ, and PZK test groups is more obvious, especially in the long storage period of some fruits and vegetables, the probability of rotten fruit can still be maintained at a low level, and the degree of decay is significantly lower than that of other groups. The differences between the oyster mushroom and the cordyceps flower began to appear on the first day of storage, and the test results on the fifth day were particularly prominent; the sensory evaluation value of the oyster mushroom PZ group was 7.33, and the degree of decay was only 0.23, and the sensory evaluation value of the cordyceps flower PZ group was 6, and the degree of decay was only 0.1. The peppers were severely rotten on the third day because they were freshly cut. The CK group had a peculiar smell, while the fresh-cut peppers in the PZ group remained in good condition. The P and PZ groups can both observe significant preservation effects during the 1-7d storage period of strawberries. On the 7th day, the color was full and shiny, with no obvious corruption odor, the sensory evaluation values ​​were both 7.17, and the decay rate was less than 0.2. There was no obvious difference between winter jujube and longan. The main difference between winter jujube and longan was red peel and moldy, while longan could only be judged by the degree of moldy peel without peeling. The peeled longan pulp of CK group had obvious odor on the 7th day, 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] Where A0 and A1 are the initial and after storage fruit weights, respectively.

[0107] Fig.11This is the result of the weight loss rate change of different fruits and vegetables during storage in Experiment 6 of the present invention. During the storage of the six kinds of fruits and vegetables, the weight loss rate of the UT group was extremely high. When the oyster mushroom and cordyceps flower were stored for 7 days, the water loss rate reached 89.17% and 82.04% respectively. The water loss rate of the PZK group was also higher than that of other groups due to the presence of holes on the membrane. During the storage of cordyceps flower, the weight loss rate of the PZK group reached 80.71% on the 7th day. There was no significant difference in the weight loss rate of the CK, P, PZ and standard groups, all between 2% and 20%.

[0108] Experiment 7: Investigate the hardness of fruits and vegetables in Examples 5 to 7.

[0109] The hardness of six kinds of fruits and vegetables, strawberry, winter jujube, longan, oyster mushroom, cordyceps flower and pepper, was measured using a texture analyzer. The central area of ​​the fruits and vegetables was uniformly selected for the puncture test, and the probe was TA 39, the probe test speed was 1mm / s, the fixture distance was 70mm, the trigger point load was 0.1N, and the target value distance was 5mm for strawberry, winter jujube, longan, oyster mushroom and pepper, and 1mm for cordyceps flower.

[0110] Fig.12 It is the result of the hardness change of different fruits and vegetables during storage in Experiment 7 of the present invention. It can be seen from the figure that during the storage of Pleurotus ostreatus, due to the loss of water, the hardness of the UT group and the PZK group increased from 1.36 on the 0th day to 11.1 and 1.87 on the 7th day. The CK and SD groups softened due to the metabolic activity of the Pleurotus ostreatus itself and the decomposition of microorganisms during storage, and the hardness decreased from 1.36 on the 0th day to 0.57 on the 7th day, with a decrease of 58.09%. The PZ group with the best preservation effect maintained the hardness at 1.34 from 1.36 on the 0th day to the 5th day, and decreased to 1.02 on the 7th day, with a decrease of only 25%, which played a good preservation effect. During the storage and preservation of strawberries, the hardness of strawberries on the 0th day was 1.62, and on the 7th day, compared with 0.61 of the CK group, the PZ group strawberries still had a hardness of 1.09, and the decrease was 30% lower than that of the CK group. We can also draw similar conclusions during the storage and preservation of other fruits and vegetables. Therefore, the P and PZ groups have a good preservation effect on the freshness of fruits and vegetables during the storage and preservation process.

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

[0112] The three color indices of L, a, and b of fruits and vegetables are determined by a colorimeter. The total color difference (ΔE) and whiteness index (WI) of fruits and vegetables are calculated according to the formula:

[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 Pleurotus ostreatus after different treatments 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 peppers after different treatment groups during storage

[0121]

[0122]

[0123] Table 4: Color difference changes of strawberries after different treatments during storage

[0124]

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

[0126]

[0127]

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

[0129]

[0130] From the results in Tables 1 to 6, it can be seen that during the storage process, fruits and vegetables basically showed an increasing L value and a decreasing △E trend. This is because the fruits and vegetables underwent oxidative browning, which led to darkening of color and reduced brightness. The a and b values ​​changed according to the characteristics of different fruits and vegetables. Among them, the a value of peppers and winter dates gradually increased because the color changed from green to red during storage; the b value of longan gradually decreased. On the whole, the P and PZ groups had the best effect compared with other groups, and the various color difference data measured during the storage of fruits and vegetables could basically be maintained in the best state. It shows that the composite spray film liquid has a significant effect on the color of fruits and vegetables, which is related to the good barrier and antibacterial and antioxidant properties of the active coating, blocking the contact area between fruits and vegetables and external oxygen, inhibiting the infection of microorganisms, and thus slowing down the color state change of fruits and vegetables during the storage period. And adding pad paper sprayed with film liquid can better maintain the brightness and color of fruits and vegetables. This may be because the antioxidant active substances in the film liquid play a UV shielding role, effectively avoiding the 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 measured using a handheld refractometer. Fruits and vegetables from different treatment groups were squeezed in batches and transferred into 10 mL centrifuge tubes. The juice was centrifuged at a speed of 6076 × g and a temperature of 4°C for 15 min, and 20 uL of the supernatant was accurately aspirated for measurement. The soluble solids content was expressed in Brix, and the total acid content was expressed in percentage (%).

[0133] Fig.13 It is the result of the change of soluble solids of different fruits and vegetables during storage in Experiment 9 of the present invention. It can be seen from the figure that with the extension of storage time, each treatment group showed a trend of soluble solids rising first and then falling. This is because in the early stage of storage, the nutrients (such as starch and cellulose) in fruits and vegetables are degraded into monosaccharides and disaccharides in physiological metabolic activities. In the later stage of storage, TSS began to decline, which means that the quality of fruits and vegetables deteriorated. During this period, it was also accompanied by the action of microorganisms. Bacteria and fungi promoted the deterioration of fruits and vegetables by using the sugars in fruits and vegetables to grow, develop and reproduce. The TSS of the CK group decreased significantly from the 1st to the 7th day of storage, which was particularly obvious in the storage experiment of strawberries. TSS dropped from 8.9 to 6.2, and the loss rate reached 30.34%. Compared with the CK and "standard" groups, the P and PZ groups treated with spraying did not show a significant downward trend, and TSS was relatively stable. During the storage of strawberries, the TSS loss rate of the P group decreased from 9 on the first day to 7.8, and the TSS loss rate was 13.33%. The TSS loss rate of the PZ group decreased from 9.1 on the first day to 8.5, and the TSS loss rate was only 6.59%, which had a significant protective effect on the soluble solids of strawberry fruits. This may be because the antioxidants and antibacterial agents in the membrane liquid inhibited the growth of microorganisms and the oxidation of nutrients in fruits and vegetables, thereby preventing drastic changes in TSS. And on the seventh day of storage, the TSS of the PZ group in various fruits and vegetables was at the highest level except for the PZK group. Due to the presence of pores, the moisture content in fruits and vegetables decreases, and the proportion of TSS will increase accordingly, so the TSS of the PZK group in winter jujube, pepper and longan is at a higher level.

[0134] Fig.14It is the result of the total acid change of different fruits and vegetables during storage in Experiment 9 of the present invention. It can be seen from the figure that respiration and microbial action are the main reasons for the change in TA value of fruits and vegetables. Fruits and vegetables participate in energy metabolism activities by consuming organic acids, while microorganisms metabolize and produce organic acids by infecting fruit and vegetable tissues and using their nutrients to grow, develop and reproduce, causing fruits and vegetables to become sour, reducing their edible value and bringing safety and health risks. During the storage of various fruits and vegetables, the TA values ​​of the CK group and the standard group generally changed significantly. When strawberries, longans, cordyceps and oyster mushrooms were stored for the 7th day, and peppers were stored for the 3rd day, the TA values ​​of the CK group and the standard group samples were significantly higher than those of the P and PZ groups. For the samples of the P and PZ groups, the TA value was relatively stable during the storage process. Especially during the storage of longan, the TA value of CK and standard groups increased from 0.91g / 100mL on the 0th day to 1.42g / 100mL and 1.72g / 100mL on the 7th day, respectively, with an increase of 56.04% and 89.01%, while the TA value of PZ group was the most stable, increasing from 0.91g / 100mL to 1.05g / 100mL, with an increase of only 15.38%, achieving the preservation effect on the quality of fruits and vegetables. The difference in TA value after different treatments may be due to the self-defense mechanism of fruit and vegetable samples in response to post-harvest in vitro environmental stress. The CK group and the standard group produced a large amount of organic acid due to the stress, and the infection of microorganisms also increased the TA content in the environment, while the P and PZ groups did not produce drastic changes in TA value due to the protection of the coating material.

[0135] The above is only a preferred embodiment of the present invention and does not limit the present invention in any form. Although the present invention has been disclosed as above in the preferred embodiment, it is not used to limit the present invention. Any technician familiar with the art can make many possible changes and modifications to the technical solution of the present invention by using the methods and technical contents disclosed above without departing from the spirit and technical solution of the present invention, or modify it into an equivalent embodiment of equivalent changes. Therefore, any simple modification, equivalent replacement, equivalent change and modification made to the above embodiments according to the technical essence of the present invention without departing from the content of the technical solution of the present invention, still fall within the scope of protection of the technical solution of the present invention.

Claims

1. A film-forming solution for fruit and vegetable packaging coating, characterized in that: The film-forming solution comprises natamycin, potassium sorbate, vitamin C, tea polyphenols and a film-forming substrate.

2. The film-forming solution for fruit and vegetable packaging coating according to claim 1, characterized in that: The concentration of natamycin is 0.01wt% to 0.1wt%, the concentration of potassium sorbate is 0.05wt% to 0.15wt%, the concentration of vitamin C is 0.1wt% to 1wt%, and the concentration of tea polyphenols is 0.01wt% to 0.1wt%.

3. The film-forming solution for fruit and vegetable packaging coating according to claim 1 or 2, characterized in that: The film-forming substrate is pullulan; And / or, the concentration of the film-forming substrate is 1 wt % to 2 wt %.

4. A method for preparing a membrane-forming solution according to any one of claims 1 to 3, characterized in that: The preparation method comprises the following steps: S1, heating and dissolving the film-forming substrate to obtain a base coating liquid; S2. Add natamycin, potassium sorbate, vitamin C and tea polyphenols to the base coating solution, stir and dissolve, and obtain a film-forming solution.

5. The preparation method according to claim 4, characterized in that: The heating and dissolving in S1 specifically comprises: heating in a water bath at 30°C to 60°C for 10min to 30min; The stirring and dissolving in S2 specifically includes: using a magnetic stirrer to continuously stir at a rotation speed of 600 to 1000 r / min for 1 to 4 hours.

6. Use of the film-forming solution according to any one of claims 1 to 3 in preserving fruits and vegetables.

7. The use according to claim 6, characterized in that: The application method comprises: adding the film-forming solution into a 0.5 mm caliber spray gun, spraying it evenly on the inner side of a polyethylene packaging film, drying at 50° C. to obtain a composite preservative film, placing fruits and vegetables in a packaging box, and wrapping and sealing them with the composite preservative film.

8. The use according to claim 6, characterized in that: The application method comprises: evenly applying the film-forming solution on fruit and vegetable absorbent paper, drying at 50° C. to obtain fruit and vegetable padding paper, placing the fruit and vegetable padding paper into a packaging box, placing fruits and vegetables to be kept fresh, and packaging.

9. The use according to claim 6, characterized in that: The method of application includes: (1) adding the film-forming solution to a 0.1-1 mm diameter spray gun, spraying it evenly on the inner side of a polyethylene packaging film, and drying it at 30-60° C. to obtain a composite fresh-keeping film; applying the film-forming solution evenly on fruit and vegetable absorbent paper, and drying it at 30-60° C. to obtain fruit and vegetable padding paper; (2) Put the fruit and vegetable padding paper into the packaging box, put the fruits and vegetables to be kept fresh, and wrap and seal them with the composite preservative film.

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