Edible fruit and vegetable coating preservative and preparation method thereof

Abstract

The invention belongs to the technical field of fruit and vegetable preservation, and particularly relates to an edible fruit and vegetable coating preservative and a preparation method thereof. The preparation method comprises the following steps: firstly, preparing a ph-enzyme double-response microcapsule, adopting food-grade sodium alginate and gelatin to compound a wall material, constructing a double-response microcapsule with an interpenetrating network structure by utilizing a synergistic effect of a Ca < 2 + > ionic crosslinking method and a TG enzyme enzymatic crosslinking method, designing an inner and outer double-layer composite coating structure, taking quaternized chitosan as a matrix on the inner layer, and loading the microcapsule; and the outer layer takes konjac glucomannan / hydrophobic nano SiO2 as a matrix, and the konjac glucomannan / hydrophobic nano SiO2 are respectively prepared and then are sequentially coated, so that multifunctional synergy and physical barrier reinforcement are realized. According to the edible fruit and vegetable coating preservative prepared by the preparation method disclosed by the invention, the inner layer provides a dual antibacterial mechanism of instant contact antibacterial and response sterilization, and the outer layer provides excellent moisture and oxygen barrier properties and enhanced surface hydrophobicity. The two layers cooperate to solve the loss problem after fruit and vegetable harvesting, and an efficient, safe and innovative technical scheme is provided.

Description

Technical Field

[0001] This invention belongs to the technical field of fruit and vegetable preservation, specifically relating to an edible fruit and vegetable coating preservative and its preparation method. Background Technology

[0002] Postharvest losses of fruits and vegetables are mainly caused by microbial infection, physiological metabolic disorders (respiration, ethylene release, and enzymatic browning), and moisture loss. Edible coating technology, as a green and safe physical preservation method, can effectively delay the above-mentioned deterioration processes by forming a functional film on the surface of fruits and vegetables, and is currently a research hotspot.

[0003] Traditional edible coatings (such as single-component chitosan films and sodium alginate films) mainly rely on their physical barrier function, offering limited functionality and preservation effects. To improve these effects, researchers have attempted to load natural antibacterial agents, antioxidants, and other active ingredients into the coatings. However, current technologies often directly disperse or simply embed the active ingredients within the membrane matrix. For example, sodium humate solution is directly used as a preservative, or calcium alginate is used to encapsulate cinnamaldehyde. This release behavior primarily relies on passive diffusion or the slow degradation of the wall material, constituting a form of indiscriminate release.

[0004] Furthermore, some studies have introduced synthetic polymer materials (such as thermosensitive PNIPAM) or complex chemical polymerization processes (such as UV-initiated polymerization). These non-food-grade raw materials or processes may pose safety risks and do not meet the stringent requirements for raw material safety in edible coatings. At the same time, fruit and vegetable spoilage is often a complex process involving multiple factors and occurring sequentially, making it difficult for single-function coatings to provide comprehensive and long-lasting protection. Summary of the Invention

[0005] To address the above problems, the present invention aims to provide an edible fruit and vegetable coating preservative and its preparation method.

[0006] The technical content of this invention is as follows: This invention provides a method for preparing an edible fruit and vegetable coating preservative, comprising the following steps: 1) pH-enzyme dual-response microcapsules Sodium alginate and gelatin are dissolved in deionized water at 40-60℃ at a mass ratio of (2~1):1 to prepare a gel solution with a total concentration of 3~6 wt%. The solution is stirred until completely dissolved and then cooled for later use. Sodium alginate (anionic polysaccharide) and gelatin (amphoteric protein) are natural, edible raw materials. The gel network formed by their combination is the core framework of the microcapsule wall material, possessing both hydrophilicity and film-forming properties, providing structural support for the subsequent encapsulation of active ingredients; sodium alginate can react with Ca... 2+Ionic cross-linking occurs, forming a hydrogel. This gel exhibits decreased stability and accelerated dissolution in alkaline environments (high pH), endowing the microcapsules with pH responsiveness. Gelatin, a hydrolysis product of collagen, has peptide chains that serve as substrates for specific proteases (such as proteases secreted by bacteria or fungi), allowing for enzymatic hydrolysis and thus endowing the microcapsules with enzyme responsiveness.

[0007] The active ingredients eugenol, ε-polylysine, resveratrol, and vitamin E are mixed in a mass ratio of 1:(0.2~0.5):(0.1~0.3):(0.1~0.3), and added to a 1%~3% (w / v) Tween-80 aqueous solution in a mass ratio of 1:(5~10). The mixture is stirred at high speed in an ice-water bath to form an O / W type nanoemulsion. Among the active ingredients, eugenol provides broad-spectrum and potent antibacterial activity; ε-polylysine possesses both antibacterial and enzyme-inhibiting capabilities; resveratrol and vitamin E are strong antioxidants that can scavenge free radicals and delay the oxidative aging of fruits and vegetables. The nanoscale emulsion formed by high-speed stirring allows for more uniform dispersion of the active ingredients, improving the encapsulation rate of microcapsules and the uniformity of active ingredient release.

[0008] The nanoemulsion was slowly dripped into the gel solution at a volume ratio of 1:(3~5), and then emulsified at high speed at 8000~12000 rpm for 3~5 min to form an O / W type composite emulsion. Under magnetic stirring, a 10%~20% (v / v) calcium chloride-transglutaminase mixed solution was slowly added dropwise to the composite emulsion. The mixture was stirred continuously at 35~40℃ for 30~60 min. After the reaction was completed, the mixture was cooled, centrifuged and filtered, and washed with deionized water 2~3 times to remove unreacted ions and enzymes. The resulting powdered microcapsules were obtained by spray drying, and the particle size of the obtained microcapsules was 1~5 μm. In the calcium chloride-transglutaminase mixed solution, the CaCl2 concentration is 1.0%~2.0% (w / v), and the TG enzyme activity is 20-50 U / mL (in enzyme activity units). Using Ca 2+ Cross-linking occurs when the gelatin binds to the carboxyl group of sodium alginate. Simultaneously, the carboxyl group of sodium alginate imparts pH responsiveness. When organic acids are produced during the respiration of fruits and vegetables during storage (pH decreases), the carboxyl group is protonated, the cross-linked structure loosens, and active ingredients are released. TG enzyme catalyzes the formation of isopeptide bonds between the amino group of lysine and the carboxyl group of glutamic acid in the gelatin molecule, further enhancing the stability of the wall material. At the same time, the protein structure of gelatin can be degraded by proteases (such as collagenase) released during the storage of fruits and vegetables, achieving enzyme-responsive release. 2) Inner layer preservative Take quaternized chitosan, dissolve it in 1% acetic acid aqueous solution to prepare a 2-4 wt% solution, add 30%-50% glycerol (plasticizer) and 60-90% pH-enzyme dual-response microcapsules according to the dry weight of quaternized chitosan in sequence, stir at high speed of 5000-8000 rpm for 5 min, let stand to degas, and obtain the inner layer preservative. Quaternized chitosan is highly water-soluble and carries a strong positive charge. After forming a film, it acts as a physical barrier, blocking oxygen and some moisture. More importantly, its positive charge can disrupt the negatively charged cell membranes of microorganisms, providing an immediate, contact-based, broad-spectrum antibacterial effect. 3) Outer layer preservative Take konjac glucomannan, dissolve it in deionized water, stir and swell at 50~60℃ to prepare a 1~2 wt% solution, add 10%~30% (w / w) of hydrophobic vapor phase SiO2 nanoparticles accounting for konjac glucomannan dry weight, and stir at high speed to obtain an outer layer preservative. Konjac glucomannan is a natural edible polysaccharide with strong hydrophilicity, which can form a film with a certain degree of air permeability. At 50~60℃, konjac glucomannan can be rapidly swollen and dissolved, avoiding uneven coating caused by incomplete swelling at low temperatures, while not damaging its polysaccharide structure. Hydrophobically modified nano-SiO2 can reduce the hydrophilicity of the outer coating, avoiding excessive water absorption and mold growth, and can improve the wear resistance and stability of the outer coating, avoiding damage to the coating during transportation. Nano-SiO2 is uniformly dispersed in the konjac glucomannan matrix, avoiding agglomeration that could cause pores or defects in the coating, affecting the moisturizing and breathable effect.

[0009] First, spray or dip the inner layer of preservative onto the cleaned and dried surface of fruits and vegetables to form an inner layer of preservative film. After the surface is dry, apply an outer layer of preservative. After both layers are dried together, you will get the preservative film.

[0010] The present invention also provides an edible fruit and vegetable coating preservative obtained by the above preparation method, which includes an inner layer preservative and an outer layer preservative.

[0011] The beneficial effects of this invention are as follows: The method for preparing the edible fruit and vegetable coating preservative of the present invention firstly involves preparing pH-enzyme dual-responsive microcapsules, using a composite wall material of food-grade sodium alginate and gelatin, and utilizing Ca... 2+The synergistic effect of ionic crosslinking and TG enzyme-catalyzed crosslinking constructed a dual-response microcapsule with an interpenetrating network structure. Under normal fruit and vegetable conditions, the microcapsules slowly release nutrients, maintaining basic protection. Upon sensing an alkaline environment and / or protease signal triggered by spoilage, the capsule wall is synergistically deconstructed, accelerating the release of active ingredients and improving their utilization efficiency. A double-layer composite coating structure was designed, with the inner layer using quaternized chitosan as a matrix to load the aforementioned microcapsules; the outer layer using konjac glucomannan / hydrophobic nano-SiO2 as a matrix, prepared separately and coated sequentially, achieving multifunctional synergy and enhanced physical barrier. The entire preparation process used only nationally permitted food additives or natural products (sodium alginate, gelatin, TG enzyme, chitosan, konjac gum, etc.), with water as the dispersion medium and mild conditions including stirring, emulsification, and enzymatic reaction.

[0012] The edible fruit and vegetable coating preservative prepared in this invention can significantly extend the shelf life of fruits and vegetables. Its inner preservative provides a dual antibacterial mechanism of immediate contact antibacterial action and responsive bactericidal action, while the outer preservative provides excellent moisture and oxygen barrier properties and enhanced surface hydrophobicity. The two layers synergistically address the problem of post-harvest loss of fruits and vegetables, providing an efficient, safe, and innovative technical solution with significant industrial application value. Detailed Implementation

[0013] The present invention will be further described in detail below through specific implementation examples. It should be understood that these embodiments are only used to illustrate the present invention and are not intended to limit the scope of protection of the present invention. After reading the present invention, any modifications of the present invention in various equivalent forms by those skilled in the art fall within the scope of the appended claims.

[0014] Unless otherwise specified, all raw materials and reagents used in this invention are from the conventional market.

[0015] Example 1 A method for preparing an edible fruit and vegetable coating preservative 1) pH-enzyme dual-response microcapsules Dissolve 20 g of sodium alginate and 10 g of gelatin in 970 g of deionized water at 40°C to prepare a gel solution with a total concentration of 3 wt%. Stir until completely dissolved and cool for later use. Mix 10g of active ingredients eugenol, 2g of ε-polylysine, 1g of resveratrol and 1g of vitamin E, add them to 50g of 1% (w / v) Tween-80 aqueous solution, and stir at high speed of 8000rpm for 2min in an ice water bath to form an O / W type nanoemulsion. The nanoemulsion was slowly dripped into 150 mL of gel solution, and then emulsified at 8000 rpm for 3 min to form an O / W composite emulsion. 1 g of calcium chloride and TG enzyme (the enzyme activity of the system after dissolving in water is 20 U / mL) were dissolved in 10 mL of water (CaCl2 concentration is about 1.0% w / v) to form a calcium chloride-transglutaminase mixed solution. Under magnetic stirring, the calcium chloride-transglutaminase mixed solution was slowly added dropwise to the composite emulsion. The mixture was stirred continuously at 35℃ for 60 min. After the reaction was completed, the mixture was cooled, centrifuged and filtered, and washed with deionized water 2-3 times to remove unreacted ions and enzymes. The mixture was then spray-dried to obtain powdered microcapsules. 2) Inner layer preservative Take 20 g of quaternized chitosan, dissolve it in 980 g of 1% acetic acid aqueous solution to prepare a 2wt% solution, add 6 g of glycerol and 12 g of pH-enzyme dual-response microcapsules in sequence, stir at 5000 rpm for 5 min, let stand to remove bubbles, and obtain the inner layer preservative. 3) Outer layer preservative Take 10 g of konjac glucomannan, dissolve it in 990 g of deionized water, stir and swell at 50℃ to prepare a 1 wt% solution, add 1 g of hydrophobic vapor phase SiO2 nanoparticles (based on the dry weight of konjac glucomannan), and stir at 6000 rpm for 3 min to obtain the outer preservative.

[0016] Example 2 A method for preparing an edible fruit and vegetable coating preservative 1) pH-enzyme dual-response microcapsules Dissolve 18 g of sodium alginate and 12 g of gelatin in 970 g of deionized water at 50°C to prepare a gel solution with a total concentration of 3 wt%. Stir until completely dissolved and cool for later use. Mix 10g of active ingredients eugenol, 3.5g of ε-polylysine, 2g of resveratrol and 2g of vitamin E, add them to 80g of 3% (w / v) Tween-80 aqueous solution, and stir at 10000rpm for 1min in an ice water bath to form an O / W type nanoemulsion. The nanoemulsion was slowly dropped into 320 mL of gel solution, and then emulsified at 10000 rpm for 1 min to form an O / W composite emulsion. 3 g of calcium chloride and TG enzyme (the enzyme activity of the system after dissolving in water is 35 U / mL) were dissolved in 20 mL of water (CaCl2 concentration is about 1.5% w / v) to form a calcium chloride-transglutaminase mixed solution. Under magnetic stirring, the calcium chloride-transglutaminase mixed solution was slowly added dropwise to the composite emulsion. The mixture was stirred continuously at 37℃ for 40 min. After the reaction was completed, the mixture was cooled, centrifuged and filtered, and washed with deionized water 2-3 times to remove unreacted ions and enzymes. The mixture was then spray-dried to obtain powdered microcapsules. 2) Inner layer preservative Take 30 g of quaternized chitosan, dissolve it in 970 g of 1% acetic acid aqueous solution to prepare a 3 wt% solution, add 12 g of glycerol and 24 g of pH-enzyme dual-response microcapsules in sequence, stir at 6500 rpm for 5 min, let stand to remove bubbles, and obtain the inner layer preservative. 3) Outer layer preservative Take 15 g of konjac glucomannan, dissolve it in 985 g of deionized water, stir and swell at 55℃ to prepare a 1.5 wt% solution, add 3 g of hydrophobic vapor phase SiO2 nanoparticles, and stir at 6000 rpm for 3 min to obtain the outer preservative.

[0017] Example 3 A method for preparing an edible fruit and vegetable coating preservative 1) pH-enzyme dual-response microcapsules Dissolve 24 g of sodium alginate and 20 g of gelatin in 956 g of deionized water at 55°C to prepare a gel solution with a total concentration of 4.4 wt%. Stir until completely dissolved and cool for later use. Mix 10g of active ingredients eugenol, 4g of ε-polylysine, 2.5g of resveratrol, and 2.5g of vitamin E, add them to 90g of 2.5% (w / v) Tween-80 aqueous solution, and stir at 9000rpm for 1.5min in an ice-water bath to form an O / W type nanoemulsion. The nanoemulsion was slowly dropped into 4000 mL of gel solution, and then emulsified at 9000 rpm for 2 min to form an O / W composite emulsion. 4.5 g of calcium chloride and TG enzyme (the enzyme activity of the system after dissolving in water is 40 U / mL) were dissolved in 25 mL of water (CaCl2 concentration is about 1.8% w / v) to form a calcium chloride-transglutaminase mixed solution. Under magnetic stirring, the calcium chloride-transglutaminase mixed solution was slowly added dropwise to the composite emulsion. The mixture was stirred continuously at 38℃ for 50 min. After the reaction was completed, the mixture was cooled, centrifuged and filtered, and washed with deionized water 2-3 times to remove unreacted ions and enzymes. The mixture was then spray-dried to obtain powdered microcapsules. 2) Inner layer preservative Take 35 g of quaternized chitosan, dissolve it in 965 g of 1% acetic acid aqueous solution to prepare a 3.5 wt% solution, add 15.5 g of glycerol and 30 g of pH-enzyme dual-response microcapsules in sequence, stir at 7000 rpm for 2 min, let stand to remove bubbles, and obtain the inner layer preservative. 3) Outer layer preservative Take 18 g of konjac glucomannan, dissolve it in 982 g of deionized water, stir and swell at 58℃ to prepare a 1.8 wt% solution, add 4.5 g of hydrophobic vapor phase SiO2 nanoparticles, and stir at 6000 rpm for 3 min to obtain the outer preservative.

[0018] Example 4 A method for preparing an edible fruit and vegetable coating preservative 1) pH-enzyme dual-response microcapsules Dissolve 30 g of sodium alginate and 30 g of gelatin in 940 g of deionized water at 60℃ to prepare a gel solution with a total concentration of 6wt%. Stir until completely dissolved and cool for later use. Mix 10g of active ingredients eugenol, 5g of ε-polylysine, 3g of resveratrol and 3g of vitamin E, add them to 100g of 3% (w / v) Tween-80 aqueous solution, and stir at high speed of 10000rpm for 1min in an ice water bath to form an O / W type nanoemulsion. The nanoemulsion was slowly dropped into 500 mL of gel solution, and then emulsified at 10,000 rpm for 1 min to form an O / W composite emulsion. 6 g of calcium chloride and TG enzyme (the enzyme activity of the system after dissolving in water is 45 U / mL) were dissolved in 30 mL of water (CaCl2 concentration is about 2% w / v) to form a calcium chloride-transglutaminase mixed solution. Under magnetic stirring, the calcium chloride-transglutaminase mixed solution was slowly added dropwise to the composite emulsion. The mixture was stirred continuously at 40℃ for 60 min. After the reaction was completed, the mixture was cooled, centrifuged and filtered, and washed with deionized water 2-3 times to remove unreacted ions and enzymes. The mixture was then spray-dried to obtain powdered microcapsules. 2) Inner layer preservative Take 40 g of quaternized chitosan, dissolve it in 960 g of 1% acetic acid aqueous solution to prepare a 4 wt% solution, add 20 g of glycerol and 36 g of pH-enzyme dual-response microcapsules in sequence, stir at 7500 rpm for 2 min, let stand to remove bubbles, and obtain the inner layer preservative. 3) Outer layer preservative Take 10 g of konjac glucomannan, dissolve it in 990 g of deionized water, stir and swell at 50℃ to prepare a 1 wt% solution, add 1 g of hydrophobic vapor phase SiO2 nanoparticles accounting for the dry weight of konjac glucomannan, and stir at 6000 rpm for 3 min to obtain the outer preservative. First, spray or dip the inner layer of preservative onto the cleaned and dried surface of fruits and vegetables to form an inner layer of preservative film. After the surface is dry, apply an outer layer of preservative. After both layers are dried together, you will get the preservative film.

[0019] Comparative Example 1 As a control group for Example 2, in the preparation of microcapsules in Comparative Example 1, gelatin was replaced with an equal amount of sodium alginate, and only calcium chloride solution of the same concentration was used. TG enzyme was not added, and other steps remained unchanged.

[0020] Comparative Example 2 As a control group for Example 2, in the preparation of microcapsules in Comparative Example 2, sodium alginate was replaced with an equal amount of gelatin, and no calcium chloride solution was added. Only TG enzyme was used. To form the initial microcapsules, the composite emulsion was first cooled to 4°C after emulsification to allow the gelatin to gel, and then the temperature was raised to 37°C and TG enzyme solution was added for a reaction of 45 minutes. Other steps remained unchanged.

[0021] Comparative Example 3 As a control group for Example 2, in step 1) of Comparative Example 3, only O / W type nanoemulsion was prepared, and the pH-enzyme dual-response microcapsules in step 2) were replaced in equal amounts, while other steps remained unchanged.

[0022] Comparative Example 4 As a control group for Example 2, Comparative Example 4 did not prepare an outer layer preservative, but only an inner layer preservative, with the same steps as in Example 2.

[0023] The prepared preservative and its application were subjected to corresponding performance tests: 1. Basic properties of pH-enzyme dual-response microcapsules Particle size and distribution: The particle size distribution of the microcapsule powders obtained in Examples 1-4 and Comparative Examples 1 and 2 dispersed in water was determined using a laser particle size analyzer, and the volume average particle size (D50) was recorded.

[0024] Encapsulation efficiency: A certain amount (W0) of microcapsule powder was accurately weighed, and the core material eugenol was completely crushed and extracted using an organic solvent (such as anhydrous ethanol). The content of eugenol in the extract (W1) was determined by high performance liquid chromatography. Encapsulation efficiency (%) = (W1 / W0 × theoretical percentage of eugenol in the core material) × 100%.

[0025] Table 1. Particle size and encapsulation efficiency of microcapsules

[0026] As shown in Table 1, the microcapsules obtained in the embodiments of the present invention have a particle size distribution in the range of 1-5 μm, and the distribution is relatively uniform (lower PDI), with good encapsulation efficiency (>75%). Comparative Example 1 (pure sodium alginate wall material) has a smaller particle size and a slightly higher encapsulation efficiency, possibly because its wall material cross-links faster and more densely. Comparative Example 2 (pure gelatin wall material) has a significantly larger particle size and wider distribution, with a low encapsulation efficiency, indicating the absence of sodium alginate / Ca. 2+ Under this system, it is difficult to form a uniform and dense microcapsule structure.

[0027] 2. Release performance of pH-enzyme dual-response microcapsules Release medium: A (acidic enzyme-free): pH 5.5 phosphate buffer (simulating the surface of healthy fruits and vegetables); B (Alkaline Enzyme-Free): pH 8.0 Tris-HCl buffer (simulating a damaging alkaline environment); C (acidic enzyme): pH 5.5 buffer + 1 mg / mL trypsin (simulating the environment of certain fungal proteases); D (alkaline enzyme): pH 8.0 buffer + 1 mg / mL trypsin (simulating a common bacterial infection environment).

[0028] Procedure: Equal amounts (containing equal amounts of eugenol) of the microcapsules from Example 2, Comparative Example 1, and Comparative Example 2 were placed in the four media mentioned above and subjected to constant temperature shaking at 37°C. Samples were taken at predetermined time points, filtered, and the concentration of eugenol in the released solution was measured to calculate the cumulative release rate.

[0029] Table 2 Release rate of eugenol from microcapsules

[0030] As shown in Table 2, the microcapsules of Example 2 released the fastest and most completely in medium D (alkaline and enzyme-containing), exhibiting a significant synergistic effect of both pH and enzyme response. Release was accelerated under a single stimulus (B or C), but not complete, and was controllable. In Comparative Example 1, release was significantly accelerated only under alkaline conditions (B and D), showing no sensitivity to enzymes. The release rate in medium D was lower than that of MC-2, demonstrating that the lack of an enzymatic pathway led to incomplete release. Comparative Example 2 released rapidly under acidic conditions (A and C) (gelatin wall material itself has poor stability at 37°C and is easily enzymatically hydrolyzed), lacking stability in a healthy acidic environment.

[0031] It is evident that the microcapsules of the present invention achieve an ideal mode of sustained release under normal conditions and accelerated release when putrefactive signals (alkalinity and / or enzymes) are present.

[0032] 3. Physical and antibacterial properties of preservative coatings Water vapor transmission rate: Each coating agent was cast into a film and dried to constant weight. The water vapor transmission rate (WVTR) was determined at 38℃ and 90% RH gradient, in accordance with GB / T 1037 standard.

[0033] Contact angle: The static contact angle of deionized water on the coating surface is measured using a contact angle meter to evaluate the surface hydrophobicity.

[0034] Inhibition zone test: The agar diffusion method was used. The coating solution was made into dry film discs, which were placed in the center of a plate inoculated with Staphylococcus aureus (bacteria) or Botrytis cinerea (fungus, the main putrefactive fungus of strawberries). After incubation, the diameter of the inhibition zone was measured.

[0035] Table 3 Physical and antibacterial properties of preservative coatings

[0036] As shown in Table 3, in terms of moisture barrier properties, the double-layer coating of the present invention (Example 2) has the lowest WVTR and the best moisture barrier performance. The single-layer coating (D4) has poor moisture barrier properties. The outer konjac glucomannan / nano-SiO2 layer significantly improves the overall water vapor barrier capability.

[0037] In terms of hydrophobicity, the contact angle results show that the hydrophobic nano-SiO2 added to the outer layer effectively improves the hydrophobicity of the coating surface, which helps to prevent surface free water from wetting and reduces microbial attachment points.

[0038] In terms of antibacterial properties, the coating of this invention has the largest inhibition zone, indicating that its comprehensive antibacterial ability (contact antibacterial effect of quaternized chitosan + microcapsule responsive release antibacterial effect) is the strongest. The physical hybrid type (D3) has good initial antibacterial power but poor persistence due to the easy loss of active ingredients (experiments show that its inhibition zone shrinks the fastest over time).

[0039] 4. Strawberry preservation effect Strawberries of uniform size, maturity, and without damage were selected and randomly divided into 5 groups. Each group was treated with a preservative according to Examples 2, 4, 3, and 4, respectively. The strawberries were washed and dried. The inner layer of each preservative was sprayed onto the strawberry surface and allowed to air dry at room temperature until a non-sticky film formed. Then, the outer layer of the preservative was sprayed on and the strawberries were thoroughly dried at 10°C and 85% relative humidity, forming a composite preservative film on the strawberry surface. A water treatment was used as a blank control (CK). The treated strawberries were stored at 5±1°C and 85-90% RH. Samples were taken every 3 days for analysis. Rot rate: The percentage of fruits with obvious mold spots or soft rot on the surface is counted; Weight loss rate: (initial weight - current weight) / initial weight × 100%; Hardness: The hardness of the strawberry equatorial region was measured using a texture analyzer; Soluble solids and total acid: Soluble solids (TSS) were measured using a handheld refractometer, and titratable acid (TA) was determined by titration. Sensory evaluation: Evaluators rated the color, flavor, and overall acceptability on a 5-point scale.

[0040] The preservation results after 12 days of storage are as follows: Table 4. Preservation effect of strawberries

[0041] As shown in Table 4, the preservative of this invention significantly outperformed all comparative examples and the blank control in all preservation indicators during the strawberry preservation test, demonstrating its comprehensive preservation efficacy. Example 4 (high load) showed slight superiority over Example 2 in some indicators, reflecting the adjustability of the formulation. Comparative Example 4 (single-layer film) demonstrated better preservation than physical mixing (Comparative Example 3), proving the effectiveness of the inner matrix itself in the double-layer structure; however, its higher weight loss rate (due to the lack of an outer moisture barrier) led to accelerated quality decline in the later stages. Comparative Example 3 (physical mixing) showed some initial effectiveness, but later indicators such as rot control and firmness maintenance declined significantly, confirming the disadvantages of non-microencapsulated active ingredients being easily degraded, volatile, and having uncontrollable release.

Claims

1. A method for preparing an edible fruit and vegetable coating preservative, characterized in that, Includes the following steps: 1) pH-enzyme dual-response microcapsules Sodium alginate and gelatin are dissolved in deionized water at 40-60℃ at a mass ratio of (2~1):1 to prepare a gel solution with a total concentration of 3~6wt%. The solution is stirred until completely dissolved and then cooled for later use. The active ingredients eugenol, ε-polylysine, resveratrol and vitamin E are mixed and added to an aqueous solution containing Tween-80 at a mass ratio of 1: (5~10). The mixture is stirred at high speed in an ice-water bath to form an O / W type nanoemulsion. The nanoemulsion was slowly dripped into the gel solution at a volume ratio of 1:(3~5), and then emulsified at high speed of 8000~12000 rpm for 3~5 min to form an O / W type composite emulsion. Under magnetic stirring, a 10%~20% (v / v) calcium chloride-transglutaminase mixed solution was slowly added dropwise to the composite emulsion. The mixture was stirred continuously at 35~40℃ for 30~60 min. After the reaction was completed, the mixture was cooled, centrifuged and filtered, and washed with deionized water 2~3 times to remove unreacted ions and enzymes. The mixture was then spray-dried to obtain powdered microcapsules. 2) Inner layer preservative Take quaternized chitosan, dissolve it in 1% acetic acid aqueous solution to prepare a 2-4 wt% solution, add glycerol and pH-enzyme dual-response microcapsules in sequence, stir at high speed of 5000-8000 rpm for 5 min, let stand to degas, and obtain the inner layer preservative. 3) Outer layer preservative Take konjac glucomannan, dissolve it in deionized water, stir and swell at 50~60℃ to prepare a 1~2 wt% solution, add hydrophobic vapor phase carbon dioxide nano-SiO2, and stir at high speed to obtain an outer layer preservative.

2. The preparation method of the edible fruit and vegetable coating preservative according to claim 1, characterized in that, The concentration of Tween-80 in the aqueous solution is 1% to 3% (w / v).

3. The preparation method of the edible fruit and vegetable coating preservative according to claim 1, characterized in that, The mass ratio of eugenol, ε-polylysine, resveratrol, and vitamin E in the active ingredients is 1:(0.2~0.5):(0.1~0.3):(0.1~0.3).

4. The preparation method of the edible fruit and vegetable coating preservative according to claim 1, characterized in that, The calcium chloride-transglutaminase mixed solution contains 1.0%~2.0% CaCl2 (w / v) and TG enzyme activity of 20-50 U / mL, expressed in enzyme activity units.

5. The preparation method of the edible fruit and vegetable coating preservative according to claim 1, characterized in that, The glycerol accounts for 30% to 50% of the dry weight of the quaternized chitosan, and the pH-enzyme dual-response microcapsules account for 60% to 90% of the dry weight of the quaternized chitosan.

6. The method for preparing the edible fruit and vegetable coating preservative according to claim 1, characterized in that, The hydrophobic vapor phase SiO2 nanoparticles account for 10% to 30% of the dry weight of konjac glucomannan.

7. The method for preparing the edible fruit and vegetable coating preservative according to claim 1, characterized in that, The application of preservatives is as follows: First, spray or dip the inner layer preservative onto the cleaned and dried surface of fruits and vegetables to form an inner layer of preservative film. After the surface is dry, apply an outer layer of preservative. After both layers are dried together, the preservative film is obtained.

8. An edible fruit and vegetable coating preservative obtained by the preparation method according to any one of claims 1-7, characterized in that, The edible fruit and vegetable coating preservative includes an inner layer preservative and an outer layer preservative.

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