Preparation method and application of multi-effect compound preservative for fruits and vegetables

Abstract

The invention belongs to the technical field of fruit and vegetable fresh-keeping, and particularly relates to a preparation method and application of a multi-effect compound fresh-keeping agent for fruits and vegetables. According to the invention, sodium alginate and low-acyl gellan gum are used as film forming substrates, and nano SiO2, nano TiO2, anti-nano ZnO, 1-MCP and DSE are added to obtain a multi-effect composite fresh-keeping solution; the ratio and dosage of the reagents are optimized to obtain a preservative formula with optimal antibacterial and fresh-keeping effects; a thin-layer coating can be formed on the outer surface of the fruit and vegetable by adopting a simple and convenient process; meanwhile, the prepared multi-effect composite fresh-keeping solution has excellent fresh-keeping properties such as antibacterial property, oxidation resistance, ultraviolet light resistance and water resistance, and can well maintain the hardness and color of the fruits and maintain good flavor and taste, so that the shelf life of the fruits is prolonged, the edible and economic values of the fruits are ensured, and the economic loss is reduced. Moreover, the method is simple to operate, safe, environment-friendly, easy for industrial production and wide in application prospect.

Description

Technical Field

[0001] The present invention belongs to the technical field of fruit and vegetable preservation, and particularly relates to a preparation method and application of a multi-effect composite preservative for fruits and vegetables. Background Art

[0002] After fresh fruits are harvested, they are very prone to mechanical damage and rot during transportation and storage, or the water quickly evaporates due to environmental factors, thus affecting their sensory quality and economic benefits. Under this market demand background, food preservation films play an important role in fruit preservation.

[0003] Traditional food preservative films are usually wrapped on the surface of fruits, and mainly rely on isolating oxygen and preventing water evaporation to achieve the preservation function. Petroleum-based synthetic polymers, such as polyethylene (PE) and polyvinyl chloride (PVC), are widely used in the preparation of preservative films due to their low cost and good physical properties. However, such synthetic petroleum-based preservative films have significant defects in terms of biodegradability, and harmful gases are released during their incineration process, causing serious environmental impacts. Therefore, it is urgent to explore biodegradable and environmentally friendly alternative materials to reduce the negative impact on the ecological environment and enhance the sustainability of fruit preservation.

[0004] The film coating preservation technology can effectively prevent food oxidation and water loss by forming a film on the surface of food, maintaining the freshness and taste of food. The film can appropriately block the opening parts of the food, inhibit the respiration, reduce nutrient consumption, and at the same time inhibit water evaporation and the invasion of microorganisms, preventing spoilage and deterioration, thereby prolonging the storage period of food. The film coating preservation technology can improve the color and brightness of food, increase the appearance attractiveness of food, and thus improve the commercial value of food. This technology is suitable for large-scale processing with a high degree of mechanization and can meet the requirements of industrial production.

[0005] In recent years, biodegradable natural polymers have gradually attracted attention. These materials not only have good packaging properties but also environmental friendliness. The preparation methods of active films and coatings in food packaging mainly involve directly immersing food in a film-forming solution or spraying the film-forming solution on the surface of food to form a thin film or coating on the food surface. This coating has functions such as antibacterial, antioxidant, and gas scavenging, and is particularly suitable for perishable fruit and vegetable products. The application of this technology not only helps to solve the environmental problems brought by traditional petroleum-based packaging but also improves the safety and sustainability of food packaging, meeting the market demand for natural and safe foods.

[0006] Sodium alginate is a natural polysaccharide compound extracted from kelp, fungi, and algae plants. Its aqueous solution has high viscosity and stability, good film-forming and moisturizing abilities, is non-toxic, odorless, and has a low cost. Sodium alginate can form a uniform film, which can effectively isolate oxygen and moisture, thereby slowing down the oxidation of food and the evaporation of moisture, and extending the shelf life of perishable foods (such as fruits, vegetables, and meats). Chinese Patent CN114403211B discloses a fresh-keeping method of dipping fruit pulp into a calcium salt solution and a thickener solution in sequence to form a thin-layer coating. The thickener solution is made by mixing a certain proportion of sodium alginate, curdlan, and carrageenan. This method isolates the oxygen contact between the pulp and the liquid in the solution, and slows down the loss of sour and sweet components in the pulp. However, although the film formed by sodium alginate and calcium ions usually has good tensile strength, there is a technical problem of poor extensibility, which cannot achieve good fresh-keeping effects in practical applications and is not conducive to practical applications.

[0007] In order to improve the rapid decline in edible quality or short shelf life of fruits and vegetables caused by water loss, microbial infection, oxidative browning, and post-ripening, the present invention uses sodium alginate and low acyl gellan gum as film-forming matrices, supplemented with glycerol as a plasticizer, and at the same time uses nano-SiO2 as a water-retaining agent, nano-TiO2 as a light-shielding agent, nano-ZnO as an antibacterial agent, D-sodium erythorbate (DSE) as an antioxidant, and 1-methylcyclopropene (1-MCP) as an ethylene inhibitor to prepare a multifunctional fresh-keeping agent for the fresh-keeping of fruits and vegetables. Summary of the Invention

[0008] Aiming at the deficiencies of the prior art, the present invention provides a preparation and application method of a composite fresh-keeping agent for fruits and vegetables; the present invention uses sodium alginate (SA) and low acyl gellan gum (LG) as film-forming matrices, and adds a water-retaining agent (nano-SiO2), a light-shielding agent (nano-TiO2), an antibacterial agent (nano-ZnO), an ethylene inhibitor (1-MCP), an antioxidant (DSE), a plasticizer glycerol, and a cross-linking agent calcium chloride to prepare a multi-component composite fresh-keeping agent, and optimizes the ratio and concentration of nano-SiO2, nano-TiO2, nano-ZnO, 1-MCP, and DSE to obtain the fresh-keeping agent formula with the best antibacterial and fresh-keeping effects, so as to achieve effective fresh-keeping of fruits and vegetables.

[0009] In order to achieve the above objectives, the present invention adopts the following technical solutions;

[0010] A preparation method of a multi-effect composite fresh-keeping agent, the steps are as follows:

[0011] Step 1: Weigh sodium alginate powder and add it to deionized water. Let it stand for a period of time to allow the sodium alginate powder to fully absorb water and swell. Subsequently, stir it under water bath conditions. After stirring and dissolving, a sodium alginate solution is obtained.

[0012] Step 2: Weigh low-acyl gellan gum powder and add it to deionized water. After standing for a period of time, stir it under water bath conditions. After stirring and dissolving, a low-acyl gellan gum solution is obtained.

[0013] Step 3: Mix the sodium alginate solution obtained in Step 1 and the low-acyl gellan gum solution in Step 2, and then add glycerol. Stir and mix evenly to prepare a mixed solution.

[0014] Step 4: After the mixed solution obtained in Step 3 is cooled to room temperature, add nano-SiO2 powder, nano-TiO2 powder, nano-ZnO powder, 1-MCP powder and DSE powder to it. After homogenization and ultrasonic degassing treatment, a multi-effect composite fresh-keeping solution is prepared, which is the multi-effect composite fresh-keeping agent.

[0015] Preferably, the standing time in Step 1 is 10 - 12 h, the water bath heating temperature is 65 - 75 °C, the stirring time is 5 - 10 min, and the mass concentration of the sodium alginate solution is 0.5 - 1.0 g / 100 mL.

[0016] Preferably, the standing time in Step 2 is 10 - 12 h, the water bath heating temperature is 85 - 95 °C; the mass concentration of the low-acyl gellan gum solution is 0.5 - 1.0 g / 100 mL.

[0017] Preferably, in the mixed solution of Step 3, the volume ratio of sodium alginate to the low-acyl gellan gum solution is (2 - 7):(3 - 8); the volume ratio of glycerol to the mixed solution is (1 - 1.5):100.

[0018] Preferably, in the multi-effect composite fresh-keeping solution of Step 4, the concentration of nano-SiO2 is 0.05 - 0.1 g / 100 mL, the concentration of nano-TiO2 is 0.02 - 0.08 g / 100 mL, the concentration of nano-ZnO is 0.02 - 0.08 g / 100 mL, the concentration of 1-MCP is 20 - 50 μg / 100 mL, and the concentration of DSE is 0.5 - 1.5 g / 100 mL; among them, the particle size of nano-SiO2 is 100 nm, the particle size of nano-TiO2 is 100 nm, and the particle size of nano-ZnO is 50 nm.

[0019] Homogenization is carried out at a rotation speed of 6000 - 1000 rpm for 2 - 5 min, and ultrasonic degassing treatment is carried out by ultrasonic wave at a frequency of 40 KHZ for 10 - 15 min.

[0020] The use of the multi-effect composite fresh-keeping agent for fruit and vegetable fresh-keeping is as follows:

[0021] S1: Add calcium chloride powder to deionized water, stir and dissolve to obtain a calcium chloride solution;

[0022] S2: After fixing the fruits and vegetables, immerse them in the multi-effect composite fresh-keeping solution. After impregnating for a period of time, lift the fruits and vegetables out of the multi-effect composite fresh-keeping solution and stay in the air for a certain time to complete one impregnation; repeat the impregnation several times like this to obtain fruits and vegetables with a multi-effect composite fresh-keeping solution coated on the surface;

[0023] S3: Immerse the fruits and vegetables with the multi-effect composite fresh-keeping solution coated on the surface in the calcium chloride solution obtained in step S1 again at a certain speed, and after impregnating and staying for a certain time, lift the fruits and vegetables out of the calcium chloride solution at a certain speed, and a hydrogel will be formed on the surface of the fruits and vegetables, that is, fruits and vegetables with a multi-effect composite fresh-keeping hydrogel coated on the surface are obtained;

[0024] S4: Finally, dry the fruits and vegetables with the multi-effect composite fresh-keeping hydrogel coated on the surface in step S3. After drying, the fresh-keeping of the fruits and vegetables can be realized.

[0025] Preferably, the concentration of the calcium chloride solution in step S1 is 1 - 5 g / 100 mL.

[0026] Preferably, the speed at which the fruits and vegetables are immersed in the multi-effect composite fresh-keeping solution in step S2 is 1 - 10 cm / s, the impregnation time is 30 - 60 s, the speed at which the fruits and vegetables are lifted out of the multi-effect composite fresh-keeping solution is 1 - 10 cm / s, and the time of staying in the air is 40 - 90 s; the number of repeated impregnations is 2 - 5 times.

[0027] Preferably, the speed at which the fruits and vegetables are immersed in the calcium chloride solution in step S3 is 2 - 12 cm / s, the impregnation and staying time in the calcium chloride solution is 30 - 60 s, and the speed at which the fruits and vegetables are lifted out of the calcium chloride solution is 1 - 10 cm / s.

[0028] Preferably, the drying temperature in step S4 is 20 - 25 °C.

[0029] Advantages of the present invention

[0030] (1) In the present invention, sodium alginate and low-acyl gellan gum are used as film-forming matrices, nano-SiO2 is used as a water-retaining agent, nano-TiO2 is used as a light-shielding agent, nano-ZnO is used as an antibacterial agent, DSE is used as an antioxidant, 1-MCP is used as an ethylene inhibitor, glycerol is used as a plasticizer, and calcium chloride is used as a cross-linking agent to prepare a multifunctional fresh-keeping agent for the fresh-keeping of fruits and vegetables.

[0031] Among them, low-acyl gellan gum is a multifunctional hydrophilic colloid, which is safe, non-toxic, acid-resistant, heat-resistant, and has good biodegradability and biocompatibility. In the present invention, adding low-acyl gellan gum to the sodium alginate solution can effectively improve the ductility of the film formed by the cross-linking of sodium alginate and calcium ions.

[0032] Nanosilica (SiO2) has the advantages of large specific surface area, low toxicity, good biocompatibility, optical transparency, good chemical / thermal / water stability, etc. At the same time, strong hydrogen bond interactions can be formed between SiO2 and film-forming molecules such as polysaccharides, which can improve the water resistance of hydrophilic colloids such as polysaccharides and ensure the effective extension of the shelf life of food. Combining with titanium dioxide (TiO2) can enhance biocompatibility, photocatalysis and antibacterial properties. At the same time, TiO2 can also act as a cross-linking agent to improve the mechanical and barrier properties of the film. Nanozinc oxide (ZnO), as an inorganic nano-scale antibacterial agent, has good antibacterial properties, ultraviolet resistance, biocompatibility and chemical stability. At the same time, the surface energy of nano-ZnO is relatively high, and it can directly or indirectly inhibit and kill target bacteria by continuously releasing zinc ions into the system, interacting with the bacterial surface, and generating reactive free radicals in the bacteria, further enhancing the antibacterial performance.

[0033] In addition, D-sodium erythorbate (DSE) used in combination in the present invention can inhibit the browning of fruits and vegetables, scavenge excess free radicals in the fruits, and protect the fruit membrane tissue from damage. 1-Methylcyclopropene (1-MCP) can preemptively bind to ethylene receptors, thereby preventing ethylene from binding to its receptors, slowing down the ripening rate of climacteric fruits and vegetables, and extending their shelf life.

[0034] (2) The present invention not only pays creative labor in the material selection level, but also creatively optimizes the use conditions of the materials to effectively exert the synergistic effect of the materials. The present invention utilizes the characteristic that the multi-component composite fresh-keeping film solution and the calcium salt solution can form a thermally irreversible gel. By continuously optimizing the ratios and concentrations of nanosilica, nanometer titanium dioxide, nanozinc oxide, 1-MCP and DSE, a thin-layer coating is formed on the surface of fruits and vegetables by a simple process. At the same time, calcium chloride is used as a cross-linking agent, which is more conducive to the formation of the fresh-keeping film solution and its adhesion to the surface of fruits and vegetables, realizing excellent fresh-keeping properties such as antibacterial, antioxidant, ultraviolet resistance and water resistance, being able to better maintain the hardness and color of the fruits, retain their good flavor and taste, thereby extending the shelf life of the fruits, ensuring their edible and economic value, and reducing economic losses.

[0035] (3) The edible coating provided by the present invention can slow down the respiration of fruits, reduce their respiratory metabolism, so that the respiration rate is slow, thereby delaying spoilage.

[0036] (4) The multi-effect composite preservative provided by the present invention is non-toxic, harmless, safe, environmentally friendly and low in cost, and is suitable for large-scale use in factories; at the same time, the preparation method is simple, the film-forming property is stable, and it has good application prospects and high market value. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 The weight loss rate of bananas treated in the comparative example and each example on the 5th day.

[0038] Figure 2 The fruit firmness of bananas treated in the comparative example and each example on the 5th day.

[0039] Figure 3 The total soluble sugar content of bananas treated in the comparative example and each example on the 5th day.

[0040] Figure 4 The total phenol content of bananas treated in the comparative example and each example on the 5th day.

[0041] Figure 5 The appearance of bananas coated with the comparative example and Example 2 from the 1st to the 5th day after coating.

[0042] Figure 6 The appearance of mangoes coated with Example 2 and Example 7 on the 5th day after coating.

[0043] Figure 7 The appearance of mangoes coated with Example 2 and Example 8 on the 5th day after coating.

[0044] Figure 8 The appearance of mangoes coated with Example 2 and Example 9 on the 6th day after coating.

[0045] Figure 9 The appearance of mangoes coated with Example 2 and Example 10 on the 5th day after coating.

[0046] Figure 10 The appearance of mangoes coated with Example 2 and Example 11 on the 5th day after coating. DETAILED DESCRIPTION OF THE INVENTION

[0047] The various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as a limitation of the present invention, but should be understood as a more detailed description of certain aspects, characteristics and embodiments of the present invention.

[0048] It should be understood that the terms described in the present invention are only for describing specific embodiments and are not intended to limit the present invention. Additionally, for the numerical ranges in the present invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Each intermediate value within any stated value or stated range, as well as each smaller range between any other stated value or intermediate value within the stated range, is also included in the present invention. The upper and lower limits of these smaller ranges can be independently included or excluded from the range.

[0049] Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. Although the present invention only describes preferred methods and materials, any methods and materials similar or equivalent to those described herein can also be used in the practice or testing of the present invention. All documents mentioned in this specification are incorporated by reference to disclose and describe the methods and / or materials related to the documents. In case of conflict with any incorporated document, the content of this specification shall prevail.

[0050] Without departing from the scope or spirit of the present invention, various modifications and variations can be made to the specific embodiments of the present invention specification, which are obvious to those skilled in the art. Other embodiments obtained from the specification of the present invention are obvious to those skilled in the art. The specification and examples of the present invention are merely exemplary.

[0051] Regarding the use of "comprising", "including", "having", "containing", etc. herein, they are all open-ended terms, meaning including but not limited to.

[0052] Material description: In this example, the particle size of the nano-SiO2 used is 100 nm, the particle size of the nano-TiO2 is 100 nm, and the particle size of the nano-ZnO is 50 nm.

[0053] Comparative Example 1:

[0054] Step 1: Add calcium chloride powder to deionized water, stir and dissolve to obtain a calcium chloride solution with a concentration of 5 g / 100 mL.

[0055] Step 2: After fixing the banana with a dip coater, immerse it in 200 mL of deionized water at a speed of 5 cm / s and soak for 30 s; then, lift the banana out of the deionized aqueous solution at a speed of 5 cm / s and stay in the air for 40 s to complete one dip; then repeat the dip operation once according to the same procedure. After the repeated dip, the dipped banana is obtained.

[0056] Step 3: Immerse the impregnated bananas into the calcium chloride solution described in Step 1 at a speed of 2 cm / s, and after staying immersed for 30 s, then pull them out of the calcium chloride solution at a speed of 2 cm / s to obtain bananas with a calcium chloride solution coated on their surfaces.

[0057] Step 4: Place the bananas with a calcium chloride solution coated on their surfaces described in Step 3 in a hair dryer, adjust the temperature of the hair dryer to 23 °C, and after the aqueous solution on the banana surfaces is fully dried, bananas with a calcium chloride solution coated on their surfaces are obtained.

[0058] Example 1:

[0059] Step 1: Weigh sodium alginate powder and add it to deionized water, and let it stand for 12 h to allow the sodium alginate powder to fully absorb water and swell; subsequently, stir it under the condition of water bath heating at 65 °C, and after stirring and dissolving, a sodium alginate solution (denoted as SA) is obtained, with a concentration of 0.5 g / 100 mL;

[0060] Step 2: Weigh low-acyl gellan gum powder and add it to deionized water, and let it stand for 12 h; subsequently, stir it while heating in a water bath at 90 °C, and after dissolving, a low-acyl gellan gum solution (denoted as LA) is obtained, with a concentration of 1 g / 100 mL.

[0061] Step 3: Take 60 mL of the sodium alginate solution described in Step 1 and 140 mL of the low-acyl gellan gum solution described in Step 2, mix them while they are hot, and then add 2 mL of glycerol to prepare a mixed solution.

[0062] Step 4: After the mixed solution described in Step 3 is cooled to room temperature, add nano-SiO₂, nano-TiO₂, nano-ZnO, DSE, and 1-MCP, and homogenize it at a speed of 8000 rpm for 2 min, and then ultrasonicate it at a frequency of 40 KHz for 10 min to prepare a multi-effect composite preservation solution; where the concentration of nano-SiO₂ is 0.1 g / 100 mL, the concentration of nano-TiO₂ is 0.08 g / 100 mL, the concentration of nano-ZnO is 0.08 g / 100 mL, the concentration of 1-MCP is 20 μg / 100 mL, and the concentration of DSE is 0.5 g / 100 mL.

[0063] Based on the use of the multi-effect composite preservative for fruit and vegetable preservation, the steps are as follows:

[0064] S1: Add calcium chloride powder to deionized water, stir and dissolve it to obtain a calcium chloride solution with a concentration of 5 g / 100 mL

[0065] S2: Fix the banana using a dip coater. Immerse the banana into the multi-effect composite fresh-keeping solution prepared in Step 4 at a speed of 5 cm / s and soak for 30 s. Subsequently, lift the banana out of the multi-effect composite fresh-keeping solution at a speed of 5 cm / s, and let it stay in the air for 40 s to complete one dipping; then repeat the dipping operation 2 times according to the same procedure to obtain a banana with a multi-effect composite fresh-keeping solution coated on its surface.

[0066] S3: Immerse the banana with the multi-effect composite fresh-keeping solution coated on its surface as described in Step S2 into the calcium chloride solution as described in Step S1 using a dip coater at a speed of 2 cm / s, soak for 30 s, and then lift it out of the calcium chloride solution at a speed of 2 cm / s to obtain a banana with a multi-effect composite fresh-keeping hydrogel coated on its surface.

[0067] S4: Place the banana with the multi-effect composite fresh-keeping hydrogel coated on its surface as described in Step S3 into a drying machine, adjust the temperature of the drying machine to 23 °C, and after the hydrogel on the banana surface is fully dried, a banana coated with a multi-effect composite fresh-keeping agent on its surface is obtained.

[0068] Example 2:

[0069] Step 1: Weigh sodium alginate powder and add it to deionized water, and let it stand for 12 h to allow the sodium alginate powder to fully absorb water and swell; subsequently, stir it under the condition of water bath heating at 65 °C, and after stirring and dissolving, a sodium alginate solution with a concentration of 1 g / 100 mL is obtained.

[0070] Step 2: Weigh low-acyl gellan gum powder and add it to deionized water, and let it stand for 12 h; subsequently, stir it while heating in a water bath at 90 °C, and after dissolving, a low-acyl gellan gum solution with a concentration of 1 g / 100 mL is obtained.

[0071] Step 3: Take 60 mL of the sodium alginate solution described in Step 1 and 140 mL of the low-acyl gellan gum solution described in Step 2, mix them while they are hot, and then add 2 mL of glycerol to prepare a mixed solution.

[0072] Step 4: After the mixed solution described in Step 3 is cooled to room temperature, add nano-SiO2, nano-TiO2, nano-ZnO, DSE, and 1-MCP, and homogenize it at a speed of 8000 rpm for 2 min, and then ultrasonicate it at a frequency of 40 KHz for 10 min to prepare a multi-effect composite fresh-keeping solution; wherein the concentration of nano-SiO2 is 0.08 g / 100 mL, the concentration of nano-TiO2 is 0.03 g / 100 mL, the concentration of nano-ZnO is 0.05 g / 100 mL, the concentration of DSE is 1 g / 100 mL, and the concentration of 1-MCP is 40 μg / 100 mL.

[0073] Based on the use of the multi-effect composite fresh-keeping agent for fruit and vegetable fresh-keeping, the steps are as follows:

[0074] Step S1: Add CaCl2 powder into deionized water, stir and dissolve to obtain a CaCl2 solution with a concentration of 5 g / 100 mL.

[0075] Step S2: Fix bananas and mangoes using a dip coater, immerse them into the multi-effect composite fresh-keeping solution prepared in Step 4 at a speed of 8 cm / s, and soak for 60 s. Subsequently, lift the bananas and mangoes out of the multi-effect composite fresh-keeping solution at a speed of 8 cm / s, stay in the air for 40 s, and then immerse them into the multi-effect composite fresh-keeping solution again at a speed of 8 cm / s. Repeat the immersion and lifting operations 5 times to obtain bananas and mangoes with a multi-effect composite fresh-keeping solution coated on their surfaces.

[0076] Step S3: Immerse the bananas and mangoes with the multi-effect composite fresh-keeping solution coated on their surfaces as described in Step S2 into the CaCl2 solution described in Step S1 at a speed of 5 cm / s, and soak for 40 s to complete one immersion; then repeat the immersion once according to the same operation to obtain bananas and mangoes with a multi-effect composite fresh-keeping hydrogel coated on their surfaces.

[0077] Step S4: Place the bananas and mangoes with the multi-effect composite fresh-keeping hydrogel coated on their surfaces as described in Step S3 in a hair dryer, adjust the temperature of the hair dryer to 20 °C, and wait until the hydrogel on the surfaces of the bananas and mangoes is fully dried to obtain bananas and mangoes with a multi-effect composite fresh-keeping agent coated on their surfaces.

[0078] Example 3:

[0079] Step 1: Weigh sodium alginate powder and add it into deionized water, let it stand for 12 h to allow the sodium alginate powder to fully absorb water and swell. Subsequently, stir under the condition of water bath heating at 65 °C, and obtain a sodium alginate solution with a concentration of 1 g / 100 mL after stirring and dissolving;

[0080] Step 2: Weigh low acyl gellan gum powder and add it into deionized water, let it stand for 12 h; subsequently, stir while heating in a water bath at 90 °C, and obtain a low acyl gellan gum solution with a concentration of 1 g / 100 mL after dissolving.

[0081] Step 3: Take 60 mL of the sodium alginate solution described in Step 1 and 140 mL of the low acyl gellan gum solution described in Step 2, mix them while they are hot, and then add 2 mL of glycerol to prepare a mixed solution.

[0082] Step 4: After the mixed solution described in Step 3 is cooled to room temperature, nano-SiO2, nano-TiO2, nano-ZnO, DSE, and 1-MCP are added, and homogenized at 8000 rpm for 2 min, and then sonicated at a frequency of 40 KHz for 10 min to prepare a multi-effect composite fresh-keeping solution; wherein the concentration of nano-SiO2 is 0.08 g / 100 mL, the concentration of nano-TiO2 is 0.08 g / 100 mL, the concentration of nano-ZnO is 0.02 g / 100 mL, the concentration of DSE is 0.5 g / 100 mL, and the concentration of 1-MCP is 40 μg / 100 mL.

[0083] Based on the use of the multi-effect composite fresh-keeping agent for fruit and vegetable preservation, the steps are as follows:

[0084] Step S1: Add CaCl2 powder to deionized water, stir and dissolve to obtain a CaCl2 solution with a concentration of 5 g / 100 mL.

[0085] Step S2: After fixing the bananas with a dip coater, immerse them in the multi-effect composite fresh-keeping solution prepared in Step 4 at a speed of 10 cm / s and soak for 60 s. Subsequently, lift the bananas out of the multi-effect composite fresh-keeping solution at a speed of 10 cm / s and stay in the air for 70 s to complete one dipping; then repeat the dipping 5 times according to the same operation to obtain bananas with a multi-effect composite fresh-keeping solution coated on the surface.

[0086] Step S3: Immerse the bananas with the multi-effect composite fresh-keeping solution coated on the surface described in Step S2 into the CaCl2 solution described in Step S1 at a speed of 12 cm / s, soak for 60 s, and then lift them out of the CaCl2 solution at a speed of 10 cm / s to obtain bananas with a multi-effect composite fresh-keeping hydrogel coated on the surface.

[0087] Step S4: Place the bananas with the multi-effect composite fresh-keeping hydrogel coated on the surface described in Step S3 in a hair dryer, adjust the temperature of the hair dryer to 25 °C, and after the hydrogel on the banana surface is fully dried, bananas coated with the multi-effect composite fresh-keeping agent on the surface are obtained.

[0088] Example 4:

[0089] Step 1: Weigh sodium alginate powder and add it to deionized water, and let it stand for 12 h to allow the sodium alginate powder to fully absorb water and swell. Subsequently, stir under the condition of water bath heating at 65 °C, and after stirring and dissolving, obtain a sodium alginate solution with a concentration of 1 g / 100 mL;

[0090] Step 2: Weigh low-acyl gellan gum powder and add it to deionized water, and let it stand for 12 h; subsequently, stir while heating in a water bath at 90 °C, and after dissolving, obtain a low-acyl gellan gum solution with a concentration of 1 g / 100 mL.

[0091] Step 3: Take 60 mL of the sodium alginate solution described in Step 1 and 140 mL of the low-acyl gellan gum solution described in Step 2, mix them while they are hot, and then add 2 mL of glycerol to prepare a mixed solution.

[0092] Step 4: After the mixed solution described in Step 3 is cooled to room temperature, add nano-SiO₂, nano-TiO₂, nano-ZnO, DSE, and 1-MCP, and homogenize at a speed of 8000 rpm for 2 min, and then ultrasonicate at a frequency of 40 KHZ for 10 min to prepare a multi-effect composite fresh-keeping solution; wherein the concentration of nano-SiO₂ is 0.08 g / 100 mL, the concentration of nano-TiO₂ is 0.03 g / 100 mL, the concentration of nano-ZnO is 0.05 g / 100 mL, the concentration of DSE is 1.5 g / 100 mL, and the concentration of 1-MCP is 40 μg / 100 mL.

[0093] Based on the use of the multi-effect composite fresh-keeping agent for fruit and vegetable fresh-keeping, the steps are as follows:

[0094] Step S1: Add CaCl₂ powder to deionized water, stir and dissolve it to obtain a CaCl₂ solution with a concentration of 5 g / 100 mL;

[0095] Step S2: Fix the banana with a dip coater, immerse it in the multi-effect composite fresh-keeping solution prepared in Step 4 at a speed of 5 cm / s, and soak for 45 s; then, pull the banana out of the multi-effect composite fresh-keeping solution at a speed of 5 cm / s and stay in the air for 60 s to complete one dip; then repeat the dip 5 times according to the same operation to obtain a banana with a multi-effect composite fresh-keeping solution coated on its surface.

[0096] Step S3: Immerse the banana with the multi-effect composite fresh-keeping solution coated on its surface described in Step S2 in the CaCl₂ solution described in Step S1 at a speed of 10 cm / s, soak for 45 s, and then pull it out of the CaCl₂ solution at a speed of 5 cm / s to obtain a banana with a multi-effect composite fresh-keeping hydrogel coated on its surface.

[0097] Step S4: Place the banana with the multi-effect composite fresh-keeping hydrogel coated on its surface described in Step S3 in a hair dryer, adjust the temperature of the hair dryer to 20 °C, and wait until the hydrogel on the banana surface is fully dried to obtain a banana with a multi-effect composite fresh-keeping agent coated on its surface.

[0098] Example 5:

[0099] Step 1: Weigh sodium alginate powder and add it to deionized water. Let it stand for 12 h to allow the sodium alginate to fully absorb water and swell. Subsequently, stir it under the condition of water bath heating at 65 °C. After stirring and dissolving, a sodium alginate solution with a concentration of 1 g / 100 mL is obtained.

[0100] Step 2: Weigh low-acyl gellan gum powder and add it to deionized water. Let it stand for 12 h. Subsequently, stir it while heating in a water bath at 90 °C. After dissolution, a low-acyl gellan gum solution with a concentration of 1 g / 100 mL is obtained.

[0101] Step 3: Take 60 mL of the sodium alginate solution described in Step 1 and 140 mL of the low-acyl gellan gum solution described in Step 2, mix them while they are hot, and then add 2 mL of glycerol to prepare a mixed solution.

[0102] Step 4: After the mixed solution described in Step 3 is cooled to room temperature, add nano-SiO2, nano-TiO2, nano-ZnO, DSE, and 1-MCP, and homogenize it at a speed of 8000 rpm for 2 min, and then ultrasonic it at a frequency of 40 KHz for 10 min to prepare a multi-effect composite fresh-keeping solution; where the concentration of nano-SiO2 is 0.05 g / 100 mL, the concentration of nano-TiO2 is 0.03 g / 100 mL, the concentration of nano-ZnO is 0.05 g / 100 mL, the concentration of DSE is 1 g / 100 mL, and the concentration of 1-MCP is 20 μg / 100 mL.

[0103] Based on the use of the multi-effect composite fresh-keeping agent for fruit and vegetable preservation, the steps are as follows:

[0104] Step S1: Add CaCl2 powder to deionized water, stir and dissolve it to obtain a CaCl2 solution with a concentration of 5 g / 100 mL.

[0105] Step S2: Fix the banana with a dipping machine, immerse it in the multi-effect composite fresh-keeping solution prepared in Step 4 at a speed of 5 cm / s, and stay immersed for 45 s. Subsequently, pull the banana out of the multi-effect composite fresh-keeping solution at a speed of 5 cm / s and stay in the air for 60 s to complete one dipping. Then repeat the dipping operation 5 times according to the same operation to obtain a banana with a multi-effect composite fresh-keeping solution coated on its surface.

[0106] Step S3: Use a dipping machine to immerse the banana with the multi-effect composite fresh-keeping solution coated on its surface described in Step S2 into the CaCl2 solution described in Step S1 at a speed of 10 cm / s, stay immersed for 45 s, and then pull it out of the CaCl2 solution at a speed of 5 cm / s to obtain a banana with a multi-effect composite fresh-keeping hydrogel coated on its surface.

[0107] Step S4: Place the bananas with the multi-effect composite fresh-keeping hydrogel coated on the surface in a drying machine, adjust the temperature of the drying machine to 20 °C, and wait until the hydrogel on the surface of the bananas is fully dried, then the bananas with the multi-effect composite fresh-keeping agent coated on the surface are obtained.

[0108] Example 6:

[0109] Step 1: Weigh sodium alginate powder and add it to deionized water, and let it stand for 12 h to allow the sodium alginate powder to fully absorb water and swell. Subsequently, stir it under the condition of water bath heating at 65 °C, and after stirring and dissolving, a sodium alginate solution with a concentration of 1 g / 100 mL is obtained;

[0110] Step 2: Weigh low-acyl gellan gum powder and add it to deionized water, and let it stand for 12 h; subsequently, stir it while heating in a water bath at 90 °C, and after dissolving, a low-acyl gellan gum solution with a concentration of 1 g / 100 mL is obtained.

[0111] Step 3: Take 60 mL of the sodium alginate solution described in Step 1 and 140 mL of the low-acyl gellan gum solution described in Step 2, mix them while they are hot, and then add 2 mL of glycerol to prepare a mixed solution.

[0112] Step 4: After the mixed solution described in Step 3 is cooled to room temperature, add nano-SiO2, nano-TiO2, nano-ZnO, DSE and 1-MCP, and homogenize it at a speed of 8000 rpm for 2 min, and then ultrasonicate it at a frequency of 40 KHz for 10 min to prepare a multi-effect composite fresh-keeping solution; where the concentration of nano-SiO2 is 0.08 g / 100 mL, the concentration of nano-TiO2 is 0.03 g / 100 mL, the concentration of nano-ZnO is 0.08 g / 100 mL, the concentration of DSE is 1 g / 100 mL, and the concentration of 1-MCP is 50 μg / 100 mL.

[0113] Based on the use of the multi-effect composite fresh-keeping agent for fruit and vegetable preservation, the steps are as follows:

[0114] Step S1: Add CaCl2 powder to deionized water, stir and dissolve it to obtain a CaCl2 solution with a concentration of 5 g / 100 mL;

[0115] Step S2: Fix the bananas with a lifting impregnation machine, immerse them in the multi-effect composite fresh-keeping solution prepared in Step 4 at a speed of 5 cm / s, and immerse and stay for 45 s; subsequently, lift the bananas out of the multi-effect composite fresh-keeping solution at a speed of 5 cm / s, and stay in the air for 60 s to complete one impregnation; then repeat the impregnation 5 times according to the same operation to obtain the bananas with the multi-effect composite fresh-keeping solution coated on the surface.

[0116] Step S3: Use a lifting impregnation machine to immerse the bananas with the multi-effect composite fresh-keeping solution on the surface in step S2 into the CaCl₂ solution in step S1 at a speed of 10 cm / s, and after impregnating and staying for 45 s, then lift the bananas out of the CaCl₂ solution at a speed of 5 cm / s to obtain bananas with a multi-effect composite fresh-keeping hydrogel on the surface.

[0117] Step S4: Place the bananas with the multi-effect composite fresh-keeping hydrogel on the surface in step S3 in a hair dryer, adjust the temperature of the hair dryer to 20 °C, and after the hydrogel on the banana surface is fully dried, bananas coated with a multi-effect composite fresh-keeping agent on the surface are obtained.

[0118] Example 7:

[0119] Step 1: Weigh sodium alginate powder and add it to deionized water, and let it stand for 12 h to allow the sodium alginate powder to fully absorb water and swell. Subsequently, stir it under the condition of water bath heating at 65 °C, and after stirring and dissolving, a sodium alginate solution with a concentration of 0.5 g / 100 mL is obtained;

[0120] Step 2: Weigh low-acyl gellan gum powder and add it to deionized water, and let it stand for 12 h; subsequently, stir it while heating in a water bath at 90 °C, and after dissolving, a low-acyl gellan gum solution with a concentration of 1 g / 100 mL is obtained.

[0121] Step 3: Take 60 mL of the sodium alginate solution in step 1 and 140 mL of the low-acyl gellan gum solution in step 2, mix them while they are hot, and then add 2 mL of glycerol to prepare a mixed solution.

[0122] Step 4: After the mixed solution in step 3 is cooled to room temperature, add nano-SiO₂, nano-TiO₂, nano-ZnO, DSE, and 1-MCP, and homogenize it at a rotation speed of 8000 rpm for 2 min, and then ultrasonicate it at a frequency of 40 KHz for 10 min to prepare a multi-effect composite fresh-keeping solution; where the concentration of nano-SiO₂ is 0 g / 100 mL, the concentration of nano-TiO₂ is 0.03 g / 100 mL, the concentration of nano-ZnO is 0.05 g / 100 mL, the concentration of DSE is 0.5 g / 100 mL, and the concentration of 1-MCP is 40 μg / 100 mL.

[0123] Regarding the use of the multi-effect composite fresh-keeping agent for fruit and vegetable preservation, the steps are as follows:

[0124] Step S1: Add CaCl₂ powder to deionized water, stir and dissolve it to obtain a CaCl₂ solution with a concentration of 5 g / 100 mL;

[0125] Step S2: Fix the bananas and mangoes using a dip coater, immerse them in the multi-effect composite preservative solution prepared in Step 4 at a speed of 5 cm / s, and soak for 45 s. Subsequently, lift the bananas and mangoes out of the multi-effect composite preservative solution at a speed of 5 cm / s, and let them stay in the air for 60 s to complete one dipping. Then repeat the dipping operation 5 times according to the same procedure to obtain bananas and mangoes with the multi-effect composite preservative solution coated on their surfaces.

[0126] Step S3: Immerse the bananas and mangoes with the multi-effect composite preservative solution coated on their surfaces as described in Step S2 into the CaCl2 solution as described in Step S1 using a dip coater at a speed of 10 cm / s, soak for 45 s, and then lift them out of the CaCl2 solution at a speed of 5 cm / s to obtain bananas and mangoes with the multi-effect composite preservative hydrogel coated on their surfaces.

[0127] Step S4: Place the bananas and mangoes with the multi-effect composite preservative hydrogel coated on their surfaces as described in Step S3 into a hair dryer, adjust the temperature of the hair dryer to 20 °C, and after the hydrogel on the surfaces of the bananas and mangoes is fully dried, bananas and mangoes coated with the multi-effect composite preservative on their surfaces are obtained.

[0128] Example 8:

[0129] Step 1: Weigh sodium alginate powder and add it to deionized water, and let it stand for 12 h to allow the sodium alginate powder to fully absorb water and swell. Subsequently, stir it under the condition of water bath heating at 65 °C, and after stirring and dissolving, a sodium alginate solution with a concentration of 1 g / 100 mL is obtained.

[0130] Step 2: Weigh low acyl gellan gum powder and add it to deionized water, and let it stand for 12 h. Subsequently, stir it while heating in a water bath at 90 °C, and after dissolving, a low acyl gellan gum solution with a concentration of 1 g / 100 mL is obtained.

[0131] Step 3: Take 60 mL of the sodium alginate solution described in Step 1 and 140 mL of the low acyl gellan gum solution described in Step 2, mix them while they are hot, and then add 2 mL of glycerol to prepare a mixed solution.

[0132] Step 4: After the mixed solution described in Step 3 is cooled to room temperature, add nano-SiO2, nano-TiO2, nano-ZnO, DSE, and 1-MCP, homogenize it at a rotation speed of 8000 rpm for 2 min, and then ultrasonicate it at a frequency of 40 KHz for 10 min to prepare a multi-effect composite preservative solution. The concentration of nano-SiO2 is 0.08 g / 100 mL, the concentration of nano-TiO2 is 0 g / 100 mL, the concentration of nano-ZnO is 0.05 g / 100 mL, the concentration of DSE is 0.5 g / 100 mL, and the concentration of 1-MCP is 40 μg / 100 mL.

[0133] Use of a multi-effect composite preservative for preserving fruits and vegetables, the steps are as follows:

[0134] Step S1: Add CaCl2 powder to deionized water, stir and dissolve to obtain a CaCl2 solution with a concentration of 5 g / 100 mL.

[0135] Step S2: Fix bananas and mangoes using a dip coater, immerse them in the multi-effect composite preservation solution prepared in step 4 at a speed of 5 cm / s, and soak for 45 s; then, pull out the bananas and mangoes from the multi-effect composite preservation

[0136] solution at a speed of 5 cm / s and stay in the air for 60 s to complete one dipping; then repeat the dipping 5 times according to the same operation to obtain bananas and mangoes with a multi-effect composite preservation solution coated on their surfaces.

[0137] Step S3: Use a dip coater to immerse the bananas and mangoes with the multi-effect composite preservation solution coated on their surfaces in the CaCl2 solution described in step S1 at a speed of 10 cm / s, soak for 45 s, and then pull them out of the CaCl2 solution at a speed of 5 cm / s to obtain bananas and mangoes with a multi-effect composite preservation hydrogel coated on their surfaces.

[0138] Step S4: Place the bananas and mangoes with the multi-effect composite preservation hydrogel coated on their surfaces in a hair dryer, adjust the temperature of the hair dryer to 20 °C, and wait until the hydrogel on the surfaces of the bananas and mangoes is fully dried to obtain bananas and mangoes coated with a multi-effect composite preservative on their surfaces.

[0139] Example 9:

[0140] Step 1: Weigh sodium alginate powder and add it to deionized water, let it stand for 12 h to allow the sodium alginate powder to fully absorb water and swell. Then, stir under the condition of water bath heating at 65 °C, and after stirring and dissolving, obtain a sodium alginate solution with a concentration of 1 g / 100 mL.

[0141] Step 2: Weigh low acyl gellan gum powder and add it to deionized water, let it stand for 12 h; then, stir while heating in a water bath at 90 °C, and after dissolving, obtain a low acyl gellan gum solution with a concentration of 1 g / 100 mL.

[0142] Step 3: Take 60 mL of the sodium alginate solution described in step 1 and 140 mL of the low acyl gellan gum solution described in step 2, mix them while they are hot, and then add 2 mL of glycerol to prepare a mixed solution.

[0143] Step 4: After the mixed solution described in Step 3 is cooled to room temperature, nano-SiO2, nano-TiO2, nano-ZnO, DSE and 1-MCP are added, and homogenized at a speed of 8000 rpm for 2 min, and then ultrasonicated at a frequency of 40 KHZ for 10 min to prepare a multi-effect composite fresh-keeping solution; wherein the concentration of nano-SiO2 is 0.08 g / 100 mL, the concentration of nano-TiO2 is 0.03 g / 100 mL, the concentration of nano-ZnO is 0 g / 100 mL, the concentration of DSE is 0.5 g / 100 mL, and the concentration of 1-MCP is 40 μg / 100 mL.

[0144] Based on the use of the multi-effect composite fresh-keeping agent for fruit and vegetable preservation, the steps are as follows:

[0145] Step S1: Add CaCl2 powder to deionized water, stir and dissolve to obtain a CaCl2 solution with a concentration of 5 g / 100 mL;

[0146] Step S2: Use a dip coater to fix bananas and mangoes, immerse them in the multi-effect composite fresh-keeping solution prepared in Step 4 at a speed of 5 cm / s, and soak for 45 s; then, pull out the bananas and mangoes from the multi-effect composite fresh-keeping

[0147] solution and stay in the air for 60 s to complete one dip; then repeat the dip 5 times according to the same operation to obtain bananas and mangoes with a multi-effect composite fresh-keeping solution coated on the surface.

[0148] Step S3: Use a dip coater to immerse the bananas and mangoes with the multi-effect composite fresh-keeping solution coated on the surface in Step S2 into the CaCl2 solution described in Step S1 at a speed of 10 cm / s, and soak for 45 s, and then pull out the CaCl2 solution at a speed of 5 cm / s to obtain bananas and mangoes with a multi-effect composite fresh-keeping hydrogel coated on the surface.

[0149] Step S4: Place the bananas and mangoes with the multi-effect composite fresh-keeping hydrogel coated on the surface in Step S3 in a hair dryer, adjust the temperature of the hair dryer to 20 °C, and wait until the hydrogel on the surface of the bananas and mangoes is fully dried to obtain bananas and mangoes coated with a multi-effect composite fresh-keeping agent on the surface.

[0150] Example 10:

[0151] Step 1: Weigh sodium alginate powder and add it to deionized water, and let it stand for 12 h to fully absorb water and swell. Then, stir under the condition of water bath heating at 65 °C, and after stirring and dissolving, obtain a sodium alginate solution with a concentration of 1 g / 100 mL;

[0152] Step 2: Weigh the low acyl gellan gum powder and add it to deionized water, then let it stand for 12 h. Subsequently, heat it in a water bath at 90 °C with stirring. After dissolution, a low acyl gellan gum solution with a concentration of 1 g / 100 mL is obtained.

[0153] Step 3: Take 60 mL of the sodium alginate solution described in Step 1 and 140 mL of the low acyl gellan gum solution described in Step 2, mix them while they are still hot, and then add 2 mL of glycerol to prepare a mixed solution.

[0154] Step 4: After the mixed solution described in Step 3 is cooled to room temperature, add nano-SiO2, nano-TiO2, nano-ZnO, DSE, and 1-MCP, and homogenize it at a speed of 8000 rpm for 2 min, then ultrasonicate it at a frequency of 40 KHz for 10 min to prepare a multi-effect composite fresh-keeping solution. Among them, the concentration of nano-SiO2 is 0.08 g / 100 mL, the concentration of nano-TiO2 is 0.03 g / 100 mL, the concentration of nano-ZnO is 0.05 g / 100 mL, the concentration of DSE is 0 g / 100 mL, and the concentration of 1-MCP is 40 μg / 100 mL.

[0155] Based on the use of the multi-effect composite fresh-keeping agent for fruit and vegetable preservation, the steps are as follows:

[0156] Step S1: Add CaCl2 powder to deionized water, stir and dissolve it to obtain a CaCl2 solution with a concentration of 5 g / 100 mL.

[0157] Step S2: Use a dip coater to fix the bananas and mangoes, immerse them in the multi-effect composite fresh-keeping solution prepared in Step 4 at a speed of 5 cm / s, and soak for 45 s. Subsequently, pull the bananas and mangoes out of the multi-effect composite fresh-keeping

[0158] solution, and let them stay in the air for 60 s to complete one dip. Then repeat the dipping operation 5 times according to the same procedure to obtain bananas and mangoes with a multi-effect composite fresh-keeping solution coated on their surfaces.

[0159] Step S3: Use a dip coater to immerse the bananas and mangoes with a multi-effect composite fresh-keeping solution coated on their surfaces described in Step S2 into the CaCl2 solution described in Step S1 at a speed of 10 cm / s, soak for 45 s, and then pull them out of the CaCl2 solution at a speed of 5 cm / s to obtain bananas and mangoes with a multi-effect composite fresh-keeping hydrogel coated on their surfaces.

[0160] Step S4: Place the bananas and mangoes with a multi-effect composite fresh-keeping hydrogel coated on their surfaces described in Step S3 in a hair dryer, adjust the temperature of the hair dryer to 20 °C. After the hydrogel on the surfaces of the bananas and mangoes is fully dried, bananas and mangoes coated with a multi-effect composite fresh-keeping agent on their surfaces are obtained.

[0161] Example 11:

[0162] Step 1: Weigh sodium alginate powder and add it to deionized water. Let it stand for 12 h to allow the sodium alginate powder to fully absorb water and swell. Subsequently, stir it under the condition of water bath heating at 65 °C. After stirring and dissolving, a sodium alginate solution with a concentration of 1 g / 100 mL is obtained.

[0163] Step 2: Weigh low-acyl gellan gum powder and add it to deionized water. Let it stand for 12 h. Subsequently, stir it while heating in a water bath at 90 °C. After dissolving, a low-acyl gellan gum solution with a concentration of 1 g / 100 mL is obtained.

[0164] Step 3: Take 60 mL of the sodium alginate solution described in Step 1 and 140 mL of the low-acyl gellan gum solution described in Step 2, mix them while they are hot, and then add 2 mL of glycerol to prepare a mixed solution.

[0165] Step 4: After the mixed solution described in Step 3 is cooled to room temperature, add nano-SiO2, nano-TiO2, nano-ZnO, DSE, and 1-MCP, and homogenize it at a speed of 8000 rpm for 2 min, and then ultrasonicate it at a frequency of 40 KHz for 10 min to prepare a multi-effect composite fresh-keeping solution; where the concentration of nano-SiO2 is 0.08 g / 100 mL, the concentration of nano-TiO2 is 0.03 g / 100 mL, the concentration of nano-ZnO is 0.05 g / 100 mL, the concentration of DSE is 0.5 g / 100 mL, and the concentration of 1-MCP is 0 μg / 100 mL.

[0166] Based on the use of the multi-effect composite fresh-keeping agent for fruit and vegetable fresh-keeping, the steps are as follows:

[0167] Step S1: Add CaCl2 powder to deionized water, stir and dissolve it to obtain a CaCl2 solution with a concentration of 5 g / 100 mL.

[0168] Step S2: Use a dip coater to fix bananas and mangoes, immerse them in the multi-effect composite fresh-keeping solution prepared in Step 4 at a speed of 5 cm / s, and immerse and stay for 45 s. Subsequently, pull the bananas and mangoes out of the multi-effect composite fresh-keeping solution at a speed of 5 cm / s, and stay in the air for 60 s to complete one dip. Then repeat the dipping operation 5 times according to the same operation to obtain bananas and mangoes with a multi-effect composite fresh-keeping solution coated on the surface.

[0169] Step S3: Use a dip coater to immerse the bananas and mangoes with the multi-effect composite fresh-keeping solution coated on the surface described in Step S2 into the CaCl2 solution described in Step S1 at a speed of 10 cm / s, and after immersing and staying for 45 s, then pull them out of the CaCl2 solution at a speed of 5 cm / s to obtain bananas and mangoes with a multi-effect composite fresh-keeping hydrogel coated on the surface.

[0170] Step S4: Place the bananas and mangoes with the multi-functional composite fresh-keeping hydrogel coated on their surfaces in a drying machine, adjust the temperature of the drying machine to 20°C, and after the hydrogel on the surfaces of the bananas and mangoes is fully dried, the bananas and mangoes with the multi-functional composite fresh-keeping agent coated on their surfaces are obtained.

[0171] Table 1 shows the addition amounts of various substances in each example.

[0172] Table 1 Addition amounts of various substances in each example

[0173]

[0174]

[0175] Table 2 shows the test results of the main indicators of the fresh-keeping effect of banana coating in the comparative example and each example.

[0176] Table 2 Test conditions of various main indicators of banana coating in the comparative example and each example after 5 days of fresh-keeping

[0177]

[0178]

[0179] For the fresh-keeping of fruits and vegetables, the weight loss rate, soluble sugar, hardness, and total phenol content are important indicators; as can be seen from Table 2 and Figure 1-4 it can be seen that for the numerical values of the weight loss rate and soluble sugar content of bananas, the examples are all less than those of the comparative example, while for the numerical values of the fruit hardness and total phenol content, the examples are all greater than those of the comparative example, effectively proving that the coatings of the present invention all have good fresh-keeping effects.

[0180] In addition, among all the examples, Example 2 shows the smallest numerical values of the weight loss rate and soluble sugar content of bananas, and the highest fruit hardness and total phenol content, indicating that Example 2 has the best fresh-keeping effect.

[0181] To further verify the fresh-keeping effect of Example 2, a semi-coating experiment was carried out; in the experiment, each banana was coated on one half and not coated on the other half to reduce the experimental error caused by individual differences of bananas. The results are as Figure 5As shown, in the comparative example, as the storage time of the bananas extended, the same degree of browning occurred in the upper half of the bananas without coating and the lower half of the bananas coated only with calcium chloride, proving that calcium chloride could not achieve a fresh-keeping effect; while in Example 2, severe browning occurred on the uncoated upper surface of the bananas, but no obvious browning occurred on the coated lower surface, which verified the fresh-keeping effect of the fresh-keeping coating solution in Example 2. The reasons for this difference illustrate that the coating fresh-keeping of the present invention has the following technical effects: (1) After coating, a protective film will be formed on the surface of the fruits and vegetables, forming a barrier to oxygen and weakening the browning caused by the oxidation on the surface of the bananas; (2) The light-blocking property of the protective film weakens the browning caused by light on the surface of the bananas; (3) The antibacterial property of the protective film weakens the browning caused by the proliferation of microorganisms on the surface of the bananas; (4) The effect of inhibiting ripening of the protective film weakens the phenomenon of the color deepening of the bananas due to ripening.

[0182] Meanwhile, in order to prove the universality of the fresh-keeping of the fresh-keeping coating and the necessity of each component in the fresh-keeping solution, the present invention took mangoes as the objects of fresh-keeping application, and carried out a semi-coating experiment on mangoes with the multi-effect composite fresh-keeping solution of Example 2 as an auxiliary, and the control cases were Examples 7-11 (the preparation components of the fresh-keeping solution were missing); two mangoes were selected for one group of experiments, and after treatment, they were left standing for 5 days and then the appearance was observed. The specific experimental effects are as Figures 6-10 :

[0183] From Figure 6 it can be seen that compared with the coating in Example 2, obvious water loss and shrinkage occurred on the coated part of the mango peel in Example 7. Without complete components, good water retention could not be formed. From Figure 7 it can be seen that the coating in Example 2 could keep the mango itself green, while the coated part of Example 8 with missing components turned yellow, and there was an obvious color difference between the two (the black spots on the surface of the mango in the figure are the markings on the mango epidermis, not browning). From Figure 8 it can be seen that no mildew spots appeared on the coated part of Example 2, while obvious dark brown disease spots appeared on the coated part of Example 9. From Figure 9 it can be seen that no browning occurred on the peel of the coated part of Example 2, while browning occurred on the surface color of the mango coated in Example 10. From Figure 10 it can be seen that the color of the peel coated in Example 11 was more yellow than that of the peel coated in Example 2, and the degree of surface ripening was higher.

[0184] In summary, on the premise of the complete components in this aspect and supplemented by specific dosage conditions, the prepared multi-effect composite preservative can delay the ripening of mangoes, slow down the maturation of mangoes, slow down the evaporation of mango moisture, delay the oxidative browning on the surface of mangoes, and at the same time has antibacterial properties and can inhibit the mildew of mangoes; when used for post-harvest preservation of fruits and vegetables, it can better maintain the hardness and color of fruits, retain their good flavor and taste, thereby extending the shelf life of fruits, ensuring their edible and economic value, reducing economic losses, and achieving very remarkable technical effects.

Claims

1. A method for preparing a multi-effect composite preservative for fruits and vegetables, characterized in that: The following steps are involved: Step 1: Weigh sodium alginate powder and add it to deionized water. Let it stand for a while to allow the sodium alginate powder to fully absorb water and swell. Then, stir it in a water bath to obtain a sodium alginate solution after stirring and dissolving. Step 2: Weigh low acyl gellan gum powder and add it to deionized water. After standing for a period of time, stir it in a water bath to obtain a low acyl gellan gum solution after stirring and dissolving. Step 3: Mix the sodium alginate solution obtained in step 1 and the low acyl gellan gum solution in step 2, add glycerol, stir and mix evenly, and prepare a mixed solution; Step 4: After the mixed solution obtained in step 3 is cooled to room temperature, nano-SiO2, nano-TiO2, nano-ZnO, 1-MCP and DSE are added thereto, and after homogenization and ultrasonic exhaust treatment, a multi-effect composite fresh-keeping solution is prepared, that is, a multi-effect composite fresh-keeping agent.

2. The method for preparing a multi-effect composite preservative for fruits and vegetables according to claim 1, characterized in that: In step 1, the standing time is 10-12 hours, the water bath heating temperature is 65-75° C., the stirring time is 5-10 minutes, and the mass concentration of the sodium alginate solution is 0.5-1.0 g / 100 mL.

3. The method for preparing a multi-effect composite preservative for fruits and vegetables according to claim 1, characterized in that: The standing time in step 2 is 10-12 hours, the water bath heating temperature is 85-95° C., and the mass concentration of the low acyl gellan gum solution is 0.5-1.0 g / 100 mL.

4. The method for preparing a multi-effect composite preservative for fruits and vegetables according to claim 1, characterized in that: In step 3, the volume ratio of sodium alginate to low acyl gellan gum solution in the mixed solution is (2-7):(3-8); the volume ratio of glycerol to the mixed solution is (1-1.5):

100.

5. The method for preparing a multi-effect composite preservative for fruits and vegetables according to claim 1, characterized in that: In the multi-effect composite preservative solution of step 4, the concentration of nano-SiO2 is 0.05-0.1g / 100mL, the concentration of nano-TiO2 is 0.02-0.08g / 100mL, the concentration of nano-ZnO is 0.02-0.08g / 100mL, the concentration of 1-MCP is 20-50μg / 100mL, and the concentration of DSE is 0.5-1.5g / 100mL; wherein, the particle size of nano-SiO2 is 100nm, the particle size of nano-TiO2 is 100nm, and the particle size of nano-ZnO is 50nm.

6. The method for preparing a multi-effect composite preservative for fruits and vegetables according to claim 1, characterized in that: In step 4, the homogenization is carried out at a rotation speed of 6000-1000 rpm for 2-5 minutes, and the ultrasonic exhaust treatment is carried out at a frequency of 40KHZ for 10-15 minutes.

7. A multi-effect composite preservative prepared according to any one of claims 1 to 6.

8. Use of the multi-effect composite preservative according to claim 7 for preserving fruits and vegetables.

9. Use of the multi-effect composite preservative according to claim 8 for preserving fruits and vegetables, characterized in that: Here are the steps: S1: adding calcium chloride powder into deionized water, stirring and dissolving to obtain a calcium chloride solution; S2: After fixing the fruits and vegetables, immerse them in the multi-effect composite fresh-keeping solution. After immersing for a period of time, pull the fruits and vegetables out of the multi-effect composite fresh-keeping solution and leave them in the air for a certain period of time to complete one immersion. After repeating the immersion several times, fruits and vegetables with the multi-effect composite fresh-keeping solution coated on the surface are obtained; S3: immersing the fruits and vegetables coated with the multi-effect composite fresh-keeping solution in step S2 into the calcium chloride solution obtained in step S1 again at a certain speed, and after being immersed for a certain period of time, the fruits and vegetables are pulled out of the calcium chloride solution at a certain speed, and hydrogels are formed on the surfaces of the fruits and vegetables, that is, fruits and vegetables coated with the multi-effect composite fresh-keeping hydrogels are obtained; S4: Finally, the fruits and vegetables coated with the multi-effect composite fresh-keeping hydrogel described in S3 are dried. After drying, the fresh-keeping of the fruits and vegetables can be achieved.

10. The use according to claim 9, characterized in that The concentration of the calcium chloride solution in step S1 is 1-5 g / 100 mL.

11. The use according to claim 9, characterized in that In step S2, the speed of immersing fruits and vegetables into the multi-effect composite fresh-keeping solution is 1-10 cm / s, the immersion period is 30-60 seconds, the speed of pulling fruits and vegetables out of the multi-effect composite fresh-keeping solution is 1-10 cm / s, and the time they stay in the air is 40-90 seconds; the immersion is repeated 2-5 times.

12. The use according to claim 9, characterized in that In step S3, the speed at which the fruits and vegetables are immersed in the calcium chloride solution is 2-12 cm / s, the time for them to stay in the calcium chloride solution is 30-60 s, and the speed at which the fruits and vegetables are pulled out of the calcium chloride solution is 1-10 cm / s.

13. The use according to claim 9, characterized in that The drying temperature in step S4 is 20-25°C.

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