Film-forming agent for preventing split fruit of nectarine and preparation method thereof

Abstract

This invention discloses a film-forming agent for preventing cracking in nectarines and its preparation method. The film-forming agent, by weight, comprises the following components: 4.0-7.0 parts film-forming matrix, 0.2-0.5 parts calcium-based nanoparticles, 0.2-0.5 parts calcium source, 0.6-1.0 parts antibacterial agent, 0.4-0.7 parts insect repellent, 0.2-0.4 parts crosslinking agent, 0.9-1.3 parts plasticizer, 0.9-1.3 parts quality-improving and color-enhancing additive, 0.3-0.5 parts process aid, 0.1-0.3 parts pH adjuster, and 86.0-91.0 parts deionized water. The film-forming agent integrates multiple functions such as preventing cracking, sun protection, antibacterial properties, insect repellency, and nutritional color enhancement. It achieves a crack prevention rate ≥96%, a sunburn incidence rate ≤2%, and significantly improves color uniformity. The film formed by the film-forming agent has high air permeability, high transparency, strong water resistance and high tensile strength. It can firmly adhere to the smooth skin of the nectarine and extend as the fruit expands, and is not easy to break.

Description

Technical Field

[0001] This invention belongs to the field of fruit planting technology, and specifically relates to a film-forming agent for preventing cracking of nectarines and its preparation method. Background Technology

[0002] As a smooth-skinned, hairless stone fruit, nectarines are susceptible to various damages during their growth, such as fruit cracking, fungal infection, insect infestation, sunburn, and wind and rain damage, which seriously affect the marketable fruit rate and economic benefits.

[0003] While traditional paper or plastic bagging techniques can provide some protection for nectarines, they suffer from problems such as high labor costs, difficult operation, environmental pollution, hindering gas exchange and photosynthesis in the fruit, uneven coloring, and flavor degradation. Furthermore, due to the smooth skin of nectarines, general-purpose fruit bags have poor adhesion and are prone to falling off, thus offering limited protection.

[0004] Bagging-free film-forming agents are a potential alternative; however, commercially available general-purpose film-forming agents often have the following shortcomings: limited functionality, lacking synergistic protection against multiple stresses such as cracking, disease, insects, scorching, and injury during the nectarine's growth period; difficulty in achieving a balance between key properties such as rain resistance, adequate moisture permeability, strong adhesion to smooth, hydrophobic surfaces, and film elasticity to accommodate rapid fruit expansion, leading to premature film damage, peeling, or excessive sealing; insufficient targeting and safety: formulations not designed specifically for the physiological characteristics of nectarines may unreasonably interfere with the fruit's color-changing process or skin metabolism, and some products use adjuvants that pose food safety or environmental residue risks; and insufficient formulation stability: some products are prone to stratification, precipitation, or microbial mold growth during storage, affecting efficacy and shelf life. Summary of the Invention

[0005] The present invention provides a film-forming agent for preventing cracking of nectarines and a method for preparing the same, so as to at least partially solve the technical defects of the film-forming agents for nectarines mentioned in the background art.

[0006] Therefore, the present invention provides a film-forming agent for preventing cracking of nectarines, comprising the following components by weight: 4.0-7.0 parts film-forming matrix, 0.2-0.5 parts calcium-based nanoparticles, 0.2-0.5 parts calcium source, 0.6-1.0 parts antibacterial agent, 0.4-0.7 parts insect repellent, 0.2-0.4 parts crosslinking agent, 0.9-1.3 parts plasticizer, 0.9-1.3 parts quality-improving and color-enhancing additive, 0.3-0.5 parts process aid, 0.1-0.3 parts pH adjuster, and 86.0-91.0 parts deionized water.

[0007] In some embodiments of the present invention, the film-forming matrix is ​​selected from one or more combinations of polyvinyl alcohol, carboxymethyl chitosan, hydroxypropyl methylcellulose, sodium alginate, pectin, konjac glucomannan, and sodium carboxymethyl cellulose.

[0008] In some embodiments of the present invention, the calcium-based nanoparticles are selected from one or more combinations of hollow mesoporous silica nanoparticles, zeolite nanoparticles, hydroxyapatite nanowires, and layered double hydroxide nanosheets with a particle size of 10-50 nm.

[0009] In some embodiments of the present invention, the calcium source is selected from one or more combinations of calcium chloride, calcium lactate, calcium gluconate, calcium citrate, and amino acid chelated calcium.

[0010] In some embodiments of the present invention, the antibacterial agent is selected from one or more combinations of ε-polylysine, parabens, thymol, eugenol, cinnamaldehyde, citronellol, nano zinc oxide, and food-grade nano titanium dioxide.

[0011] In some embodiments of the present invention, the insect repellent is selected from one or more combinations of azadirachtin, pyrethroids, citral, menthol, allicin, and euphorbia fischeriana.

[0012] In some embodiments of the present invention, the crosslinking agent is genipin; the plasticizer is glycerin.

[0013] In some embodiments of the present invention, the quality-improving and color-enhancing additives are selected from one or more combinations of potassium dihydrogen phosphate, potassium humate, betaine, vitamin C, β-carotene, brassinolide, and S-inducer. In some embodiments of the present invention, the process aid includes one or more combinations of surfactants, suspension stabilizers and hydrophobic agents; the pH adjuster is citric acid and / or sodium bicarbonate.

[0014] The present invention also provides a method for preparing the film-forming agent for preventing cracking of nectarines, the method comprising: S1. Pre-prepared solution: Mix deionized water and pH adjuster to adjust the pH of the system to 4.0-5.0; add chitosan powder and stir until the chitosan is completely dissolved to obtain a chitosan acid solution. Hollow mesoporous silica nanoparticles were added to a calcium solution with a mass concentration of 8%-12% and stirred to obtain a calcium-based slow-release nanoparticle suspension. Nano-titanium dioxide, surfactant and deionized water are mixed to obtain nano-titanium dioxide dispersion; The antibacterial agent, insect repellent and propylene glycol are mixed to obtain an antibacterial and insect repellent premix; S2: Add at least two of the following to the chitosan acid solution in sequence: polyvinyl alcohol, hydroxypropyl methylcellulose, sodium alginate, pectin, konjac glucomannan, and sodium carboxymethyl cellulose. Stir to obtain the base material composite liquid. S3: Add plasticizer and crosslinking agent to the base material composite liquid in sequence to carry out crosslinking reaction; S4: After the cross-linking reaction is completed, add the quality-improving and color-enhancing additive, calcium-based nano-slow-release particle suspension, nano-titanium dioxide dispersion and antibacterial and insect-repellent premix to the reaction system in sequence. S5: Add process aids to the reaction system and stir to obtain an emulsion; adjust the pH of the emulsion to 5.8-6.8, add deionized water and stir, then defoam and obtain a film-forming agent for preventing cracking of nectarines.

[0015] Compared with the prior art, the advantages and positive effects of the present invention are: Comprehensive functions and highly targeted: Addressing the shortcomings of nectarines such as easy cracking, need for coloring, and susceptibility to sunburn, the film-forming agent for preventing cracking of nectarines in this invention integrates multiple functions such as crack prevention, sun protection, antibacterial, insect repellent, and nutritional color promotion. The crack prevention rate is ≥96%, the sunburn incidence rate is ≤2%, and the coloring uniformity is significantly improved.

[0016] Excellent film-forming properties: The film formed by the film-forming agent for preventing cracking of nectarines in this invention has high air permeability (air permeability > 85%), high transparency (light transmittance > 90%), strong water resistance and high tensile strength (elongation at break ≥ 220%). It can firmly adhere to the smooth skin of nectarines and extend as the fruit expands, making it less prone to cracking.

[0017] Safe and environmentally friendly: The film-forming agent of this invention for preventing cracking of nectarines mainly uses natural or food-grade raw materials, with no toxic or harmful residues, and the film layer can be naturally degraded, meeting the requirements of green agriculture.

[0018] Good stability and easy operation: The film-forming agent for preventing cracking of nectarines of the present invention has good storage stability and can remain unchanged for up to 6 months at room temperature; The film-forming agent for preventing cracking of nectarines of the present invention is applied by field spraying, which is highly efficient, labor-intensive, and costs only about 1 / 4 of traditional bagging.

[0019] Significantly improves fruit quality: The application of the film-forming agent of the present invention for preventing cracking of nectarines can effectively increase the marketable fruit rate, single fruit weight and soluble solids content of nectarines, and improve the appearance quality of the fruit.

[0020] Other features and advantages of the present invention will become clearer after reading the detailed embodiments of the invention in conjunction with the accompanying drawings. Attached Figure Description

[0021] Figure 1 This is a storage stability diagram of the film-forming agent used in Example 1 of the present invention for preventing cracking of nectarines; Figure 2 This is a diagram showing the film-forming effect after spraying the film-forming agent used in Example 1 of the present invention for preventing cracking of nectarines; Figure 3 This is a test diagram of the anti-cracking performance of the film-forming agent used in Example 1 of the present invention for preventing cracking of nectarines; Figure 4 This is a test diagram of the antibacterial properties of the film-forming agent used in Example 1 of the present invention for preventing cracking of nectarines; Figure 5 This is a graph showing the test results of the rejection rate of the film-forming agent used in Example 1 of the present invention for preventing cracking of nectarines; Figure 6 This is a graph showing the fruit sunburn incidence rate of the film-forming agent used in Example 1 of the present invention for preventing cracking of nectarines; Figure 7 This is a graph showing the sugar content of the film-forming agent used in Example 1 of the present invention for preventing cracking of nectarines. Detailed Implementation

[0022] The present invention will be further illustrated below with reference to specific embodiments. These embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Furthermore, after reading this invention, those skilled in the art can make various modifications or alterations to the invention, and these equivalent forms also fall within the scope defined by the appended claims.

[0023] This invention provides a film-forming agent for preventing cracking in nectarines, comprising the following components by weight: 4.0-7.0 parts film-forming matrix, 0.2-0.5 parts calcium-based nanoparticles, 0.2-0.5 parts calcium source, 0.6-1.0 parts antibacterial agent, 0.4-0.7 parts insect repellent, 0.2-0.4 parts crosslinking agent, 0.9-1.3 parts plasticizer, 0.9-1.3 parts quality-improving and color-enhancing additive, 0.3-0.5 parts process aid, 0.1-0.3 parts pH adjuster, and 86.0-91.0 parts deionized water.

[0024] Preferably, the film-forming agent for preventing cracking of nectarines according to the present invention comprises, by weight, the following components: 5.0-6.0 parts film-forming matrix, 0.3-0.4 parts calcium-based nanoparticles, 0.3-0.4 parts calcium source, 0.7-0.9 parts antibacterial agent, 0.5-0.6 parts insect repellent, 0.2-0.3 parts crosslinking agent, 1.0-1.2 parts plasticizer, 1.0-1.2 parts quality-improving and color-enhancing additive, 0.3-0.4 parts process aid, 0.1-0.2 parts pH adjuster, and 87-90 parts deionized water.

[0025] In some embodiments of the present invention, the film-forming matrix is ​​selected from one or more combinations of polyvinyl alcohol, carboxymethyl chitosan, hydroxypropyl methylcellulose, sodium alginate, pectin, konjac glucomannan, and sodium carboxymethyl cellulose. The film-forming matrix of the present invention has good water solubility and film-forming properties. The film-forming matrix forms a continuous film on the surface of the nectarine through intermolecular hydrogen bonds, possessing both transparency and air permeability, and will not affect the photosynthesis and sugar accumulation of the nectarine.

[0026] In some embodiments of the present invention, the calcium-based nanoparticles are selected from one or more combinations of hollow mesoporous silica nanoparticles, zeolite nanoparticles, hydroxyapatite nanowires, and layered double hydroxide nanosheets. After being absorbed by the nectarine peel cells, the calcium nanoparticles of the present invention can increase the cell wall toughness of the nectarine, thereby preventing fruit cracking.

[0027] In some embodiments of the present invention, the calcium-based nanoparticles have a particle size of 10-50 nm. The calcium-based nanoparticles of the present invention have a large specific surface area and a high loading rate. The nano-sized calcium-based nanoparticles can efficiently enter the fruit cells through the stomata on the surface of the peel via endocytosis, strengthen the cell wall structure, and combine with the cell wall pectin to form "calcium bridge" calcium pectate, which significantly enhances the stability of the cell wall structure; enhances the intercellular adhesion of the nectarine peel, strengthens the cell wall from the inside, reduces the brittleness of the peel, and fundamentally prevents the nectarine from cracking.

[0028] In some embodiments of the present invention, the calcium source is selected from one or more combinations of calcium chloride, calcium lactate, calcium gluconate, calcium citrate, and amino acid chelated calcium.

[0029] This invention pre-prepares a 5%-15% (w / w) calcium solution to impregnate and load calcium-based nanoparticles. These nanoparticles protect calcium ions from rapid erosion by rainwater and allow for slow release as the fruit grows, continuously strengthening the cell wall. The organic acid calcium or chelated calcium form of this invention helps improve calcium transport and absorption efficiency, specifically preventing physiological fruit cracking in nectarines caused by drastic moisture changes.

[0030] In some embodiments of the present invention, the antibacterial agent is selected from one or more combinations of ε-polylysine, parabens, thymol, eugenol, cinnamaldehyde, citronellol, nano zinc oxide, and food-grade nano titanium dioxide. The antibacterial agent of the present invention is a combination of natural plant-derived antibacterial agents and food-grade antimicrobial peptides, exhibiting broad-spectrum antibacterial effects and being safe and environmentally friendly. Nano titanium dioxide can generate photocatalytic activity under light irradiation, assisting in the degradation of pathogens and possessing a certain self-cleaning effect. The antibacterial agent binds to the charge of the pathogen cell membrane through its electric charge, disrupting the cell membrane's integrity and stability, thus extending its shelf life.

[0031] In some embodiments of the present invention, the insect repellent is selected from one or more combinations of azadirachtin, pyrethroids, citral, menthol, allicin, and euphorbia fischeriana. The insect repellent of the present invention is selected from plant-derived or biological repellents, which reduce the feeding of aphids, fruit borers, and other pests on nectarine fruits by interfering with the olfactory sense of pests or producing a repellent effect, and is safe for the environment and non-target organisms.

[0032] In some embodiments of the present invention, the crosslinking agent is genipin, and the plasticizer is glycerol. The crosslinking agent reacts with chitosan and other polysaccharide molecules in the film-forming matrix to form a three-dimensional network polymer structure, thereby enhancing the cohesion and mechanical strength of the film layer; reducing the water sensitivity of the film layer, and preventing the film layer from swelling and detaching when exposed to water. The plasticizer can weaken the intermolecular forces, reduce the brittleness of the film layer, and enhance the flexibility, extensibility, and resistance to deformation of the film layer, preventing phenomena such as cracking and breakage when the film layer dries or when the fruit expands.

[0033] In some embodiments of the present invention, the quality-improving and color-enhancing additives are selected from one or more combinations of potassium dihydrogen phosphate, potassium humate, betaine, vitamin C, β-carotene, brassinolide, and S-inducer; supplementing potassium and other nutrients and applying plant growth regulators can synergistically regulate the sugar and acid metabolism and pigment (anthocyanin, carotenoid) accumulation in fruits, improve fruit coloring and flavor, and enhance fruit resistance.

[0034] In some embodiments of the present invention, the process aids include one or more combinations of surfactants, suspension stabilizers and hydrophobic agents.

[0035] The surfactant is selected from one or more combinations of Tween 80, alkyl glycosides, imidazoline amphoteric surfactants, dodecyl dimethyl betaine, and isomeric alcohol ethers. The surfactant of this invention can reduce the contact angle between the film-forming agent and the nectarine peel, which is beneficial for the uniform dispersion of the film-forming agent on the surface of the nectarine peel.

[0036] Among them, the suspension stabilizer can be xanthan gum. The suspension stabilizer can improve the viscosity and thixotropy of the film-forming agent system, prevent the particles in the formula from settling, agglomerating and stratifying during storage, improve the atomization performance of the film-forming agent, reduce droplet flow during spraying, and help the film-forming agent spread evenly on the smooth surface of the peach to form a continuous film layer of uniform thickness.

[0037] Among them, the hydrophobic agent can be carnauba wax. The hydrophobic agent can improve the resistance to rain erosion, form a hydrophobic barrier on the surface of the film, greatly reduce the water sensitivity of the film, and prevent the film from being dissolved and destroyed by water during rainfall; reduce the adhesion of the film and keep the fruit surface smooth.

[0038] In some embodiments of the present invention, the pH adjuster is citric acid and / or sodium bicarbonate.

[0039] This invention also provides a method for preparing a film-forming agent for preventing cracking in nectarines, the method comprising the following steps: S1. Pre-prepared solution: ① Preparation of chitosan acid solution: Weigh 10%-20% of the total amount of deionized water into the first reaction vessel according to the formula, add pH adjuster, and stir until completely dissolved. Adjust the pH of the system to 4.0-5.0. While stirring continuously, slowly add chitosan powder, heat to 40-50℃, and continue stirring for 60-120 minutes until the chitosan is completely dissolved, obtaining a clear, viscous chitosan acid solution. Cool to room temperature for later use.

[0040] In the above steps, the chitosan powder has a fineness of 100-120 mesh, which can ensure dissolution efficiency and completeness, ensure that the chitosan powder is completely dissolved, avoid the problem of slow or incomplete dissolution of coarse chitosan particles, and also prevent the chitosan powder from agglomerating and forming difficult-to-dissolve micelles, avoid molecular chain degradation, and ensure film strength.

[0041] In the above steps, the system pH value is 4.0-5.0; if the pH value is below 4.0, it may lead to excessive degradation of chitosan and affect the film strength; if the pH value is above 5.0, it will cause slow dissolution and incomplete dissolution of chitosan.

[0042] In the above steps, it is necessary to control the feeding rate of chitosan powder. The chitosan powder should be added slowly, in batches, at a low and uniform speed. Rapid pouring or adding a large amount of powder in a short period is strictly prohibited. Adding too quickly or insufficient stirring can easily form insoluble clumps. A continuous stirring rate of 300 rpm and a feeding rate of 1-3 g / min are required.

[0043] ② Preparation of calcium-based sustained-release nanoparticle suspension: Weigh hollow mesoporous silica nanoparticles according to the specified ratio and slowly add them to a calcium chloride solution with a mass concentration of 8%-12%. At room temperature, magnetically stir at a rate of 400-600 rpm for 120-180 minutes to ensure that calcium ions are fully loaded into the mesoporous channels of the nanoparticles. After stirring, allow to stand for 30 minutes to mature, obtaining a stable calcium-based sustained-release nanoparticle suspension.

[0044] In the above steps, magnetic stirring at a rate of 400-600 rpm for 120-180 minutes is crucial to ensure loading efficiency; if the stirring rate is too low or the stirring time is too short, calcium ions may not be able to be loaded into the mesoporous channels of the nanoparticles sufficiently and uniformly.

[0045] In the above steps, allowing the mixture to stand and mature for 30 minutes can facilitate the diffusion of calcium ions into the depths of the pores, achieving effective slow release and resulting in a stable calcium-based nano-slow-release particle suspension.

[0046] ③ Preparation of nano-titanium dioxide dispersion: Mix food-grade nano-titanium dioxide with a portion of metered surfactant (such as alkyl glycoside) and deionized water, and perform ultrasonic dispersion treatment (power 300-500W, time 20-30 minutes) to obtain a uniform semi-transparent dispersion, which is the nano-titanium dioxide dispersion.

[0047] ④ Preparation of antibacterial and insect repellent premix: Mix the antibacterial agent and insect repellent with propylene glycol and gently shake until completely miscible to obtain the antibacterial and insect repellent premix.

[0048] S2. Preparation of the base material composite liquid: The chitosan acid solution was transferred to a main reactor equipped with heating and stirring devices. Under gentle stirring, polyvinyl alcohol (PVA), hydroxypropyl methylcellulose (HPMC), and optionally konjac glucomannan (KGM) were added sequentially. The temperature was slowly increased to 85-95°C, and the stirring speed was increased to 300-500 rpm. Stirring was continued at this temperature for 90-180 minutes until all polymer base materials were completely dissolved and the solution was homogeneous, transparent, and free of particles. Heating was then stopped, and the solution was cooled to 40-50°C to obtain the base material composite solution.

[0049] The heating process needs to be gradual and uniform to prevent localized overheating that could lead to polymer chain degradation. Components such as PVA require high temperatures to fully dissolve; insufficient temperature or time can result in uneven solution formation, affecting the continuity of the final film.

[0050] S3. Crosslinking and plasticizing: First, add the plasticizer to the base composite liquid and stir at 200-300 rpm for 10 minutes to ensure uniform mixing. Then, while continuing to stir, slowly add the aqueous solution of the crosslinking agent (pre-dissolved in a small amount of water). After the addition is complete, maintain the system temperature at 35-45℃ and continue stirring at 300-400 rpm for 60-90 minutes to carry out the crosslinking reaction.

[0051] In the above steps, genipin needs to be added slowly to control the crosslinking rate, with a stirring speed of 300-400 rpm, a system temperature of 35-45℃, and a dropping speed controlled at 0.5-1.0 mL / min.

[0052] In the above steps, the crosslinking temperature is 35-45℃, and the crosslinking time is 60-90 minutes. Under these mild and suitable conditions, the crosslinking reaction is stable and uniform, and the film layer balances high tensile strength and toughness. If the crosslinking temperature is too low or the crosslinking time is insufficient, the crosslinking reaction will be incomplete, the degree of crosslinking will be insufficient, the polymer network will be loose, the mechanical strength of the film layer will be insufficient, and it will be prone to tensile cracking. If the crosslinking temperature is too high, local over-crosslinking and gelation of the system will occur, resulting in excessively brittle film layer that is prone to cracking. If the crosslinking time is too long, the reaction will be excessive, the film layer will be too dense, and the film layer will be too brittle and prone to cracking.

[0053] S4. Functional ingredient integration: After the cross-linking reaction is completed, the quality-improving and color-enhancing additive, calcium-based nano-slow-release particle suspension, nano-titanium dioxide dispersion and antibacterial and insect-repellent premix are added in sequence. After each component is added, the mixture is stirred at 200-400 rpm for 10-15 minutes until it is uniformly mixed to obtain a mixture.

[0054] The quality-enhancing and color-promoting additives, calcium-based nano-slow-release particle suspension, nano-titanium dioxide dispersion, and antibacterial and insecticidal premix should be added in sequence and ensured to be evenly dispersed in order to maintain system stability.

[0055] S5. Homogenization, volume setting, and post-processing: Add process aids to the mixture, heat the system to 50-60°C, and stir at 500-700 rpm for 30 minutes to ensure all components are fully incorporated. Then, transfer the mixture to a high-pressure homogenizer and homogenize 2-3 times at 30-50 MPa to obtain a highly homogeneous and stable emulsion. Cool the homogenized emulsion to room temperature and precisely adjust the pH to 5.8-6.8 using a pH adjuster (such as sodium bicarbonate solution). Finally, add deionized water to the specified total mass, stir at a low speed of 100-200 rpm for 20 minutes, and allow to stand for 24 hours to defoam, thus obtaining the film-forming agent of this invention for preventing cracking in nectarines.

[0056] In the above steps, homogenizing and cycling 2-3 times under a pressure of 30-50 MPa is a key step to ensure that the nanoparticles do not agglomerate and that the oil phase components are stably emulsified, thus ensuring that a highly uniform and stable emulsion can be obtained.

[0057] In the above steps, the pH value of the system is 5.8-6.8, which is crucial to the stability of chitosan and the shelf life of the overall formulation.

[0058] In the above steps, allowing the mixture to stand for 24 hours to defoam can eliminate air bubbles introduced during processing and ensure the spraying effect.

[0059] This invention also provides a method for using a film-forming agent to prevent cracking in nectarines, as detailed below, to ensure that its integrated protective function is fully utilized: 1. Spraying timing and cycle The initial spraying should be done after the physiological fruit drop of the nectarine, when the fruit is in the early stage of rapid expansion. To maintain the continuous protective effect of the film layer, periodic supplementary spraying should be carried out throughout the key stages of fruit development. The recommended spraying cycle is: spray once every 10 to 15 days until 15 to 20 days before harvest. In particular, timely supplementary spraying should be carried out after the fruit hardening stage, before the high incidence of fruit cracking, and before and after encountering wind, rain, or forecasting adverse weather.

[0060] 2. Spraying Operation Procedures Use conventional agricultural spraying equipment (such as backpack electric sprayers or motorized sprayers) and select fan-shaped or cone-shaped nozzles with good atomization effect. Key operating parameters are as follows: Working pressure: Controlled at 0.25 ~ 0.4 MPa to obtain fine and uniform droplets.

[0061] Spraying amount: Depending on the size of the tree canopy and the density of the fruit, the recommended amount is 20 to 50 mL per square meter of projected tree canopy area. Spray until the fruit and leaf surfaces are completely wetted and the droplets just begin to drip naturally, avoiding excessive flow.

[0062] Spraying technique: Keep the nozzle 30-50 cm away from the fruit surface and spray evenly from different angles on the inside and outside of the canopy and the sun-shaded side of the fruit. Ensure that the fruit stalk cavity and the lower part of the fruit, which are prone to water accumulation, are also lightly covered by the pesticide solution to ensure the integrity of the film formation.

[0063] 3. Applicable and Incompatible Environmental Conditions Suitable conditions: Choose a sunny, windless or lightly windy day for application. The best time to spray is before 10:00 AM or after 4:00 PM. The ambient temperature should be between 15℃ and 30℃, and the relative humidity should be ≤ 80%.

[0064] Contraindications: Spraying is strictly prohibited within 6 hours before or after midday when temperatures are high (>35℃), under direct sunlight, in strong winds (>3 levels), or before or after rainfall. High temperatures and strong sunlight can cause the moisture in the droplets to evaporate rapidly before adhesion, resulting in uneven film formation and particle agglomeration; excessive humidity or rain after spraying will wash away the uncured film layer, seriously affecting the adhesion and protective effect.

[0065] 4. Precautions for mixing and preparation The film-forming agent for preventing cracking in nectarines of this invention can be used immediately after preparation with most commonly used non-alkaline foliar fertilizers, micronutrient fertilizers, insecticides, and fungicides (small-scale compatibility tests are recommended beforehand). The film-forming agent for preventing cracking in nectarines of this invention must not be mixed with strongly alkaline substances (such as lime sulfur, Bordeaux mixture, etc.) to avoid damaging the stability of the nanoparticles and the polymer film-forming system. When preparing the solution, a two-stage dilution method should be used: first, mix the film-forming agent for preventing cracking in nectarines of this invention with a small amount of water in a container to form a stock solution, then pour it into a sprayer already filled halfway with water, and finally add the remaining water and stir well.

[0066] The raw materials used in the following examples are all commercially available agricultural or food-grade products, and their specific sources are as follows: Chitosan: Deacetylation degree ≥90%, viscosity 100-200 mPa·s, sourced from Shandong Aokang Biotechnology Co., Ltd.

[0067] Hydroxypropyl methylcellulose: viscosity 4000 mPa·s (2%, 20℃), sourced from Hubei Dinghong Biotechnology Co., Ltd.

[0068] Konjac glucomannan: purity ≥90%, viscosity ≥15000 mPa·s, sourced from Hubei Qiangsen Konjac Technology Co., Ltd.

[0069] Polyvinyl alcohol: degree of alcoholysis 99%, degree of polymerization 1750±50, sourced from Sinopharm Chemical Reagent Co., Ltd.

[0070] Genipin: Purity ≥98% (HPLC), sourced from Nanjing Songguan Biotechnology Co., Ltd.

[0071] Glycerin: Food grade, purity ≥99%, sourced from Aladdin Biochemical Technology Co., Ltd.

[0072] ε-Polylysine: Food grade, purity ≥95%, sourced from Zhejiang Xinyinxiang Biotechnology Co., Ltd.

[0073] Eugenol: Naturally extracted, purity ≥99%, sourced from Jiangxi Xinsen Natural Plant Oil Co., Ltd.

[0074] Cinnamaldehyde: Food grade, purity ≥98%, sourced from Shanghai Saen Chemical Technology Co., Ltd.

[0075] Azadirachtin: Plant extract, azadirachtin A (AZA) content ≥2%, sourced from Deqiang Biotechnology Co., Ltd.

[0076] Menthol: Natural L-menthol, purity ≥99%, sourced from Nantong Menthol Factory Co., Ltd.

[0077] Potassium dihydrogen phosphate: Superior grade for agricultural use, purity ≥99%, sourced from Sichuan Lanjian Chemical Co., Ltd.

[0078] Potassium humate: Mineral-derived humic acid content ≥60%, water-soluble, sourced from Xinjiang Shuanglong Humic Acid Co., Ltd.

[0079] Vitamin C: Food-grade L-ascorbic acid, purity ≥99%, sourced from Shijiazhuang Weisheng Pharmaceutical Co., Ltd.

[0080] β-Carotene: 10% water-dispersible microcapsules, sourced from Zhejiang NHU Co., Ltd.

[0081] All other raw materials are commercially available products, and their purity meets agricultural application standards.

[0082] Example 1 The film-forming agent for preventing cracking in nectarines in this embodiment comprises the following components by weight (based on 1000g of film-forming agent): Film-forming matrix: 18g chitosan, 12g hydroxypropyl methylcellulose (HPMC, viscosity 180 mPa·s), 8g konjac glucomannan, 22g polyvinyl alcohol (PVA 1700, degree of alcoholysis 99%). Calcium-based sustained-release nanoparticles: 3.2 g of calcium-loaded hollow mesoporous silica nanoparticles (10-30 nm) (prepared by pretreatment with 10% calcium chloride solution); Antibacterial agents: ε-polylysine 3g, eugenol 2.5g, nano titanium dioxide (30 nm) 2.6g.

[0083] Insect repellent: Azadirachtin (96% purity) 4g, citral 1.5g; Crosslinking agent: Genipin 2.8g; Plasticizer: Glycerin (food grade) 11g; Quality and color enhancement additives: 4g potassium dihydrogen phosphate, 3.5g potassium humate, 3.2g vitamin C, 0.6g β-carotene; Processing aids: Tween 80 1.0g, xanthan gum 0.5g, carnauba wax (3μm) 2.2g; pH adjuster: 1.8g citric acid; Solvent: Deionized water, 889.4g.

[0084] The preparation method of the film-forming agent for preventing cracking of nectarines in this embodiment includes the following steps: S1. Pre-prepared solution Preparation of chitosan acid solution: Weigh 250g of deionized water into a beaker, add 1.8g of citric acid, and stir to dissolve. While stirring at 300rpm, slowly add 18g of chitosan powder, heat to 50℃, and continue stirring for 90 minutes until completely dissolved to obtain a homogeneous and transparent chitosan acid solution. Cool to room temperature for later use.

[0085] Preparation of calcium-based nanoparticle suspension: Weigh 3.2 g of hollow mesoporous silica nanoparticles (particle size 10-30 nm) and slowly add them to 32 g of 10% calcium chloride solution. Stir magnetically at 500 rpm for 120 minutes at 25 °C to fully load calcium ions. Let stand for 30 minutes to mature, and obtain calcium-based nanoparticle suspension.

[0086] Preparation of nano-titanium dioxide dispersion: 2.6g of nano-titanium dioxide was mixed with 0.5g of Tween 80 and 50g of deionized water, and ultrasonically dispersed at 400W power for 25 minutes to obtain nano-titanium dioxide dispersion.

[0087] Preparation of antibacterial and insecticidal premix: Mix 2.5g of eugenol and 1.5g of citral, and gently shake until miscible to obtain the antibacterial and insecticidal premix.

[0088] S2. Preparation of base material composite liquid Transfer the chitosan acid solution to a three-necked flask equipped with a stirrer and heater. Start the stirrer (200 rpm) and add 12 g of hydroxypropyl methylcellulose, 8 g of konjac glucomannan, and 22 g of polyvinyl alcohol sequentially. Gradually increase the temperature to 90°C, increase the stirring speed to 400 rpm, and maintain this temperature for 120 minutes until all the base materials are completely dissolved and the solution is homogeneous, transparent, and viscous. Stop heating and cool the system to 45°C to obtain the base material composite solution.

[0089] S3. Crosslinking and Plasticization To the base composite solution at 45°C, first add 11g of glycerol and stir at 250 rpm for 10 minutes to mix thoroughly. Then, dissolve 2.8g of genipin in 10g of deionized water beforehand and slowly add it dropwise to the system while continuously stirring. After the addition is complete, maintain the reaction temperature at 40°C and continue stirring at 300 rpm for 75 minutes to carry out the crosslinking reaction.

[0090] S4. Functional Ingredient Concentration and Protection Keep stirring (250 rpm) and add the components in the following order, stirring for 10-15 minutes after each addition until well mixed.

[0091] Quality and color-enhancing additives (potassium dihydrogen phosphate 4g, potassium humate 3.5g, vitamin C 3.2g, β-carotene 0.6g), calcium-based nanoparticle suspension, nano titanium dioxide dispersion, ε-polylysine 3g, antibacterial and insecticidal premix, azadirachtin 4g.

[0092] S5. Homogenization, volume determination, and post-processing Add the remaining process aids to the above mixture: the remaining 0.5g Tween 80, 0.5g xanthan gum, and 2.2g carnauba wax. Heat the system to 55°C and stir at 600 rpm for 40 minutes to ensure complete emulsification and dispersion of the wax. Then, transfer the material to a high-pressure homogenizer and homogenize twice at 35 MPa to obtain a fine and uniform emulsion. Cool the emulsion to room temperature and adjust the pH to 6.0 with a small amount of 5% sodium bicarbonate solution. Finally, add deionized water to bring the total mass to 1000g, stir at 150 rpm for 20 minutes, and allow to stand for 24 hours to defoam, thus obtaining the film-forming agent of this invention for preventing cracking in nectarines.

[0093] Blank control group: No film-forming agent was applied; Commercially available product group: Traditional bagging; Product group of this invention: The film-forming agent of this invention for preventing cracking of nectarines is sprayed onto nectarines using a conventional agricultural sprayer.

[0094] I. Core Protection Effectiveness Test Results 1. Fruit crack prevention performance test The cumulative fruit cracking rate during the entire nectarine fruit expansion to harvest period (a total of 42 days) is as follows: Figure 3 As shown, the details are as follows: The blank control group had a fruit cracking rate of 18.7% ± 2.1%.

[0095] Commercially available products: fruit cracking rate was 9.4% ± 1.5%.

[0096] The product group of this invention significantly reduced the fruit cracking rate to 3.2% ± 0.8%.

[0097] Results Analysis: Analysis of variance showed a highly significant difference in fruit cracking rate among the treatment groups (p<0.01). The anti-cracking effect of the product of this invention was significantly better than that of commercially available products and the blank control. The sustained action of calcium-based nano-slow-release particles and the buffering effect of the highly elastic composite film on fruit expansion stress are the main reasons for the outstanding anti-cracking effect.

[0098] 2. Antibacterial performance test Plate inhibition zone method: For the brown rot pathogen of nectarines, the diameter of the inhibition zone formed by the product of this invention is 15.3 ± 0.7 mm, which is significantly larger than the 8.5 ± 0.9 mm of commercially available products.

[0099] In vitro fruit inoculation method: such as Figure 4 As shown, 7 days after inoculation with anthrax bacteria, the incidence rate of fruits treated with the product of this invention was 20%, and the disease index was 15.2; significantly lower than the incidence rate of 65% and the disease index of 48.5 in the commercially available product group, and the incidence rate of 100% and the disease index of 86.7 in the blank group.

[0100] Results Analysis: The data show that the product of this invention possesses a dual antibacterial mechanism of direct inhibition and physical barrier protection. The synergistic effect of ε-polylysine, eugenol, and nano-titanium dioxide, as well as the membrane layer's barrier to spore attachment, contribute to the excellent overall antibacterial effect.

[0101] 3. Insecticidal and insect-resistant feeding tests A 24-hour selective feeding rejection test on the peach fruit borer showed that, Figure 5 As shown, the average rejection rate of the product of this invention was 78.5% ± 5.2%, which was significantly higher than the 35.4% ± 7.1% of the commercially available product group. The average number of eggs laid on the treated fruit was reduced by 85% compared with the blank control.

[0102] Results analysis: The combination of azadirachtin and citral produced a strong olfactory repellency and feeding inhibition effect, proving that the product of this invention can effectively reduce the risk of pest damage.

[0103] 4. Sunburn resistance test After a week of continuous high temperatures (daily maximum temperature >35℃), the incidence of sunburn on fruits on the outer edge of the tree canopy was as follows: Figure 6 As shown: the blank control group had a rate of 32%, the commercially available product group had a rate of 18%, and the product group of this invention had a rate of only 7%.

[0104] Results analysis: The film layer formed by the product of this invention reflects and scatters some of the ultraviolet rays in sunlight. At the same time, the film layer reduces local high temperature on the fruit surface, effectively mitigating sunburn damage.

[0105] II. Test Results of Film-Forming Physicochemical Properties 5. Film adhesion and rainwater erosion resistance test Adhesion (cross-cut test): On a simulated hydrophobic surface of a nectarine, the film adhesion of the product of this invention reaches level 1 (smooth edges, no cross-cutting). In contrast, most commercially available products are level 3 (partial peeling at the edges).

[0106] Rain erosion resistance: After being subjected to simulated rainfall (intensity 30 mm / h, lasting 30 minutes), the film layer retention rate of the product of this invention is over 92%, and the complete and continuous film layer is still visible on the fruit surface; the film layer of commercially available products is basically destroyed, with a retention rate of less than 40%.

[0107] Results analysis: The network structure formed by the cross-linking of chitosan, konjac glucomannan and genipin endows the film with excellent cohesion and adhesion on a smooth hydrophobic surface, and the addition of carnauba wax further enhances the water resistance.

[0108] 6. Membrane permeability test The water vapor transmission rate (WVTR) of the membrane produced in this invention is 220 ± 15 g / m²·24h, which is approximately 65% ​​of that of the blank control without a membrane. A commercially available brand of membrane agent, due to its excessive density, has a WVTR of only 110 ± 20 g / m²·24h.

[0109] Results analysis: The product of this invention maintains suitable air permeability while ensuring protection, which is conducive to normal gas exchange and respiration of the fruit and avoids the formation of an anaerobic environment.

[0110] III. Results of Formulation Storage Stability Tests 7. Storage stability test like Figure 1 As shown, after 90 days of storage under accelerated conditions at 40℃ and 180 days of storage under normal temperature conditions at 25℃, the product of this invention did not exhibit stratification, precipitation, flocculation, or mold growth. The appearance remained uniform, transparent, and colorless, and the pH value remained stable between 5.8 and 6.2.

[0111] Figure 2The film-forming agent of this invention forms a continuous, complete, uniform, and highly transparent ultra-thin protective film layer on the surface of nectarines, without sagging, agglomeration, pinholes, or edge lifting and peeling.

[0112] Results analysis: Scientific component design, the suspension stabilizing effect of xanthan gum, and high-pressure homogenization process ensured the long-term physical and chemical stability of the formulation, especially the nanoparticles.

[0113] IV. Test Results on the Impact on Fruit Quality 8. Fruit appearance and internal quality testing Measurements were taken at the time of harvest.

[0114] Appearance quality: The fruit treated with the product of this invention has uniform coloring, the highest redness of the peel (a value) measured by the colorimeter, and suitable brightness (L value), which is significantly better than the bagged control with uneven coloring and the commercially available product group.

[0115] Intrinsic qualities: Soluble solids content (saccharide content): such as Figure 7 As shown, the percentage of the present invention group was 13.8%, which was significantly higher than the 12.1% of the commercially available product group and the 11.0% of the blank control group.

[0116] Fruit firmness: The fruit firmness of the group of this invention is 8.5 N, which is better than the other two groups.

[0117] Vitamin C content: The content of this invention group is 12.5 mg / 100g, which remains at a high level.

[0118] Sugar-acid ratio (sugar-acid ratio): The ratio of this invention is 28.5, resulting in a better flavor.

[0119] Results analysis: Moderate breathability ensured the accumulation of photosynthetic products, and the synergistic effect of the quality-improving and color-enhancing additives optimized sugar and acid metabolism and pigment synthesis. Ultimately, while ensuring the protective effect, it significantly improved the commercial appearance and edible flavor of nectarines.

[0120] The above test results show that the film-forming agent for preventing cracking of nectarines provided by this invention has significant effects in core protective functions such as crack prevention, antibacterial, insect repellent, and sunburn resistance. Its key physical properties such as film adhesion, rain resistance, and air permeability are excellent, the formulation has high stability, and it can ultimately improve the overall quality of the fruit. It overcomes many defects of existing bagging technology and general film-forming agents described in the background art and has good application prospects.

[0121] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit them. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions claimed by the present invention.

Claims

1. A film-forming agent for preventing cracking in nectarines, characterized in that, By weight, it includes the following components: Film-forming matrix 4.0-7.0 parts, calcium-based nanoparticles 0.2-0.5 parts, calcium source 0.2-0.5 parts, antibacterial agent 0.6-1.0 parts, insect repellent 0.4-0.7 parts, crosslinking agent 0.2-0.4 parts, plasticizer 0.9-1.3 parts, quality-improving and color-enhancing additives 0.9-1.3 parts, process aids 0.3-0.5 parts, pH adjuster 0.1-0.3 parts, deionized water 86.0-91.0 parts.

2. The film-forming agent for preventing cracking of nectarines according to claim 1, characterized in that, The film-forming matrix is ​​selected from one or more combinations of polyvinyl alcohol, carboxymethyl chitosan, hydroxypropyl methylcellulose, sodium alginate, pectin, konjac glucomannan, and sodium carboxymethyl cellulose.

3. The film-forming agent for preventing cracking of nectarines according to claim 1, characterized in that, The calcium-based nanoparticles are selected from one or more combinations of hollow mesoporous silica nanoparticles, zeolite nanoparticles, hydroxyapatite nanowires, and layered double hydroxide nanosheets with a particle size of 10-50 nm.

4. The film-forming agent for preventing cracking of nectarines according to claim 1, characterized in that, The calcium source is selected from one or more combinations of calcium chloride, calcium lactate, calcium gluconate, calcium citrate, and amino acid chelated calcium.

5. The film-forming agent for preventing cracking of nectarines according to claim 1, characterized in that, The antibacterial agent is selected from one or more combinations of ε-polylysine, parabens, thymol, eugenol, cinnamaldehyde, citronellol, nano zinc oxide, and food-grade nano titanium dioxide.

6. The film-forming agent for preventing cracking of nectarines according to claim 1, characterized in that, The insect repellent is selected from one or more combinations of azadirachtin, pyrethrin, citral, menthol, allicin, and euphorbia fischeriana.

7. The film-forming agent for preventing cracking of nectarines according to claim 1, characterized in that, The crosslinking agent is genipin; the plasticizer is glycerin.

8. The film-forming agent for preventing cracking of nectarines according to claim 1, characterized in that, The quality-improving and color-enhancing additives are selected from one or more combinations of potassium dihydrogen phosphate, potassium humate, betaine, vitamin C, β-carotene, brassinolide, and S-inducer.

9. The film-forming agent for preventing cracking of nectarines according to claim 1, characterized in that, The process aids include one or more of surfactants, suspension stabilizers, and hydrophobic agents; the pH adjuster is citric acid and / or sodium bicarbonate.

10. A method for preparing a film-forming agent for preventing cracking of nectarines according to any one of claims 1-9, characterized in that, The method includes: S1. Pre-prepared solution: Mix deionized water and pH adjuster to adjust the pH of the system to 4.0-5.0; add chitosan powder and stir until the chitosan is completely dissolved to obtain a chitosan acid solution. Hollow mesoporous silica nanoparticles were added to a calcium solution with a mass concentration of 8%-12% and stirred to obtain a calcium-based slow-release nanoparticle suspension. Nano-titanium dioxide, surfactant and deionized water are mixed to obtain nano-titanium dioxide dispersion; The antibacterial agent, insect repellent and propylene glycol are mixed to obtain an antibacterial and insect repellent premix; S2: Add at least two of the following to the chitosan acid solution in sequence: polyvinyl alcohol, hydroxypropyl methylcellulose, sodium alginate, pectin, konjac glucomannan, and sodium carboxymethyl cellulose. Stir to obtain the base material composite liquid. S3: Add plasticizer and crosslinking agent to the base material composite liquid in sequence to carry out crosslinking reaction; S4: After the cross-linking reaction is completed, add the quality-improving and color-enhancing additive, calcium-based nano-slow-release particle suspension, nano-titanium dioxide dispersion and antibacterial and insect-repellent premix to the reaction system in sequence. S5: Add process aids to the reaction system and stir to obtain an emulsion; adjust the pH of the emulsion to 5.8-6.8, add deionized water and stir, then defoam and obtain a film-forming agent for preventing cracking of nectarines.

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