Method for prolonging fresh-keeping storage period of garlic

Abstract

The invention relates to a method for prolonging the fresh-keeping storage period of garlic, belongs to the technical field of food fresh keeping, and provides a collaborative fresh-keeping method based on double-layer coating and low-temperature regulation aiming at the problems of short fresh-keeping period, quality reduction and the like caused by improper humidity control, microorganism breeding and germination in traditional garlic storage. The method is characterized by comprising the following steps: selecting damage-free garlic, pre-cooling and drying in the shade, and sequentially immersing the garlic into an inner-layer film coating liquid and an outer-layer film coating liquid, the inner-layer film coating liquid is prepared by compounding 8-12 mmol / L glycine betaine and 400-600 [mu] mol / L melatonin according to a ratio of (0.8-1.2): 1, the outer-layer film coating liquid is prepared from 1.5-2.5 wt% of sodium alginate, 1-1.5 wt% of hydroxypropyl trimethyl ammonium chloride chitosan, 0.2-0.5 wt% of nano zinc oxide and 0.1-0.3 wt% of calcium chloride, and the outer-layer film coating liquid is prepared from 1-1.5 wt% of sodium alginate, 1-1.5 wt% of hydroxypropyl trimethyl ammonium chloride chitosan, 0.2-0.5 wt% of nano zinc oxide and 0.1-0.3 wt% of calcium chloride. And filling the coated garlic into a mesh bag with the aperture of 0.08-0.12 cm, and storing in a refrigeration house with the temperature of 0-1 DEG C and the humidity of 65-75%. According to the method, water loss and microorganism breeding are inhibited through the composite coating, the storage period of garlic can be remarkably prolonged, the plumpness and flavor of garlic cloves are kept, and the method is suitable for large-scale storage and cold-chain transportation scenes.

Description

Technical Field

[0001] The present invention relates to the technical field of food preservation. More specifically, the present invention relates to a method for prolonging the fresh storage period of garlic. Background Art

[0002] As an important food and agricultural product, the storage and preservation of garlic have always been the research focus in the fields of agriculture and food. After garlic is harvested, it usually has a dormancy period of 2 - 3 months. When the natural temperature, humidity and other factors are suitable, after the dormancy ends, the young buds in the thick scales begin to grow, and the scales gradually become loose, soft, and the commercial quality decreases. The loss of fresh garlic after harvesting in China reaches more than 30%, resulting in waste and economic losses. Therefore, how to control the softening, post - ripening and senescence of purple - skinned garlic, maintain its commercial quality and extend the shelf life has long been an urgent problem that people want to solve. Traditional storage methods mostly rely on low - temperature environment (0 - 5°C) combined with ventilation management, but there are still the following problems in practical applications: 1. Insufficient precision in regulating storage humidity leads to quality deterioration; Conventional cold - storage storage mostly controls the environment through a single humidity setting (such as 60% - 70%), but the garlic epidermis has a dense structure, and the internal moisture is difficult to diffuse evenly, resulting in local humidity fluctuations. When the humidity in the warehouse is higher than 75%, the garlic cloves absorb water and swell, activating the endogenous enzymatic reaction and accelerating germination (the germination rate can reach 30% - 40%); when the humidity is lower than 60%, the water loss rate of the epidermis accelerates, and shriveled garlic cloves are easily formed (the weight loss rate > 15%). In the prior art, humidity sensors are mostly arranged at the edge of the warehouse body, making it difficult to reflect the micro - environment inside the garlic stack in real time, resulting in a lag in regulation. In addition, the coupling effect of humidity and temperature has not been fully studied. For example, high humidity at low temperature is likely to form a condensed water film on the surface of the garlic skin, becoming a breeding ground for molds (such as Penicillium and Aspergillus).

[0003] 2. Functional limitations of single coating materials; Existing coating preservation technologies mostly use a single film - forming matrix (such as sodium alginate or chitosan), and their performance has obvious shortcomings. For example, although the sodium alginate film has good moisture - barrier properties, its antibacterial activity is weak (the inhibition rate against Aspergillus niger < 50%); although the chitosan film has antibacterial properties, its film is brittle and easy to crack after film - forming (the tensile strength < 10 MPa), and high - deacetylation - degree chitosan is prone to molecular chain entanglement in an acidic solution, resulting in unstable viscosity of the coating solution (the viscosity fluctuation range is ±20%). In addition, traditional coating solutions do not consider the influence of the garlic epidermal wax layer on the adhesion of the coating. Some coating materials (such as gelatin) are difficult to spread evenly on the wax surface due to insufficient hydrophobicity, forming local defects (the porosity > 5%), weakening the barrier effect.

[0004] 3. Poor compatibility of the coating liquid compounding system; To improve the coating performance, the prior art attempts to compound inorganic nanomaterials (such as nano-titanium dioxide) with organic film-forming matrices. However, due to high surface energy, nanoparticles are prone to agglomeration (particle size > 200 nm), resulting in uneven dispersion in the coating liquid. For example, when nano-zinc oxide is directly added to the sodium alginate solution, due to insufficient electrostatic repulsion force, the particle sedimentation rate can reach 0.5 mm / min, and finally the nanoparticles in the coating are discretely distributed (spacing > 1 μm), unable to form a continuous antibacterial interface. In addition, phase separation is easily triggered during multi-component compounding. For example, due to the too-fast charge neutralization between quaternary ammonium salt of chitosan and sodium alginate, the gelation time of the composite system is shortened (< 10 min), and the applicable period of the coating liquid is insufficient, making it difficult to meet the requirements of continuous production.

[0005] 4. Inefficient pre-cooling and air-drying processes; Traditional pre-cooling mostly uses forced ventilation to cool down. However, when the stacking density of garlic is high (> 300 kg / m³), the cooling rate in the central area is significantly lagged (temperature difference can reach 4 - 6 °C), resulting in the pre-cooling time being extended to more than 72 h and the energy consumption increasing. The air-drying process mostly relies on natural ventilation. The fluctuation of environmental humidity (±15%) is likely to cause differences in the epidermal moisture gradient. When the local moisture content > 25%, the penetration depth of the coating liquid is uneven (coefficient of variation > 30%), affecting the integrity of film formation. In addition, the existing air-drying technology does not distinguish between the rapid dehydration and equilibrium dehydration stages. Direct high-temperature drying (> 30 °C) is likely to cause micro-cracks on the epidermis (length > 50 μm), which become channels for microbial invasion during the storage period.

[0006] 5. Immature surface modification technology of nanomaterials; To improve the dispersibility of nanoparticles, the prior art uses physical grinding or ultrasonic treatment. However, after long-term ultrasonic treatment (> 60 min) of materials such as nano-zinc oxide, the crystal structure may be damaged (lattice distortion rate > 5%), weakening its photocatalytic antibacterial performance. Although the chemical modification method (such as treatment with silane coupling agent) can improve the dispersibility, the residue of the coupling agent (such as the hydrolysis product of KH-550) may reduce the biological safety of the coating, and small deviations (±5%) in the modification process parameters (such as reaction temperature, pH) will cause significant fluctuations in the grafting rate (±40%), affecting the batch stability.

[0007] The root causes of the above problems are as follows: the complexity of the garlic epidermal structure and physiological characteristics (such as the difference in the thickness of the wax layer and porosity), the uncontrollability of the interfacial action in the multi-component coating system, and the lack of a collaborative regulation mechanism for multiple parameters (temperature, humidity, gas composition) in the storage environment. Solving these problems requires breaking through multiple technical bottlenecks such as material compounding design, nano-dispersion stabilization, and refinement of process parameters, and the prior art has not provided a systematic solution. Summary of the Invention

[0008] An object of the present invention is to provide a method for prolonging the fresh-keeping storage period of garlic, which can significantly extend the storage period of garlic.

[0009] To achieve these objects and other advantages of the present invention, according to one aspect of the present invention, the present invention provides a method for extending the fresh-keeping storage period of garlic, comprising the following steps: Step 1: Select garlic without mechanical damage and pests and diseases, and pre-cool and air-dry the epidermis; Step 2: Completely immerse the garlic obtained in Step 1 after pre-cooling and air-drying the epidermis in the inner coating solution for 8 - 12 min, take it out and drain, then immerse the garlic treated with the inner coating in the outer coating solution, soak for 5 - 10 min, and drain; Step 3: Put the drained garlic obtained in Step 2 into a plastic mesh bag with a pore size of 0.08 - 0.12 cm, and store it in a cold storage at a temperature of 0 - 1°C and a humidity of 65% - 75%; Wherein, the inner coating solution is prepared by mixing glycine betaine with a concentration of 8 - 12 mmol / L and melatonin with a concentration of 400 - 600 μmol / L in a volume ratio of 0.8 - 1.2:1; the outer coating solution is prepared by mixing sodium alginate with a concentration of 1.5 - 2.5 wt%, hydroxypropyl trimethyl ammonium chloride chitosan with a concentration of 1 - 1.5 wt%, nano-zinc oxide with a concentration of 0.2 - 0.5 wt% and calcium chloride with a concentration of 0.1 - 0.3 wt%, and the volume ratio of sodium alginate, hydroxypropyl trimethyl ammonium chloride chitosan, nano-zinc oxide, and calcium chloride is (3 - 5.5):(2 - 3.5):1:(0.35 - 0.65) Preferably, the pre-cooling process in Step 1 is as follows: Put the selected garlic into a vacuum pre-cooling machine, control the vacuum degree at 6 - 8 kPa, and cool down in stages. In the first stage, cool down to 10 - 12°C within 0.5 h, in the second stage, cool down at a rate of 1.5 - 2°C / h to 4 - 6°C, in the third stage, maintain the temperature at 2 - 3°C, and keep the relative humidity at 60 - 80% for 23 - 48 h to complete the pre-cooling process.

[0010] Preferably, the air-drying process in Step 1 is as follows: Air-dry the pre-cooled garlic by natural ventilation combined with a dehumidifier. The air-drying process is divided into two stages: rapid dehydration and equilibrium dehydration. Use a near-infrared moisture meter to scan the moisture of the garlic epidermis. When the epidermis moisture drops to 20 - 22%, switch to the equilibrium dehydration stage until the epidermis moisture stabilizes at 15 - 20%, and the air-drying process ends; Wherein, the temperature in the rapid dehydration stage is 20 - 25°C, the relative humidity is controlled at 40 - 50%, and the wind speed is 2 - 3 m / s; the temperature in the equilibrium dehydration stage is 15 - 20°C, the relative humidity is maintained at 50 - 60%, and the wind speed drops to 0.5 - 1 m / s.

[0011] Preferably, the sodium alginate in the outer coating liquid needs to be pretreated before compounding. Specifically, it is as follows: Dissolve sodium alginate in deionized water to make a solution with a mass fraction of 2% - 3%. Under a water bath at 40 - 50 °C, add citric acid accounting for 0.5% - 1% of the mass of sodium alginate, and stir at 200 - 300 r / min for 30 - 45 min to slightly crosslink and carboxylate sodium alginate. Subsequently, remove the solvent by freeze-drying to obtain pretreated sodium alginate.

[0012] Preferably, the hydroxypropyltrimethylammonium chloride chitosan in the outer coating liquid needs to be pretreated before compounding. Specifically, it is as follows: Mix hydroxypropyltrimethylammonium chloride chitosan and nano-montmorillonite in a mass ratio of 1:0.05 - 0.1, add an acetic acid solution with a volume fraction of 1% - 2%, and perform ultrasonic treatment at 300 - 400 W and 40 - 50 kHz for 20 - 30 min to disperse hydroxypropyltrimethylammonium chloride chitosan between the nano-montmorillonite lamellae to form a nano-composite structure, and then perform vacuum drying to obtain pretreated hydroxypropyltrimethylammonium chloride chitosan.

[0013] Preferably, the nano-zinc oxide in the outer coating liquid needs to be pretreated before compounding. Specifically, it is as follows: Disperse nano-zinc oxide in absolute ethanol to make a suspension with a mass fraction of 5% - 8%. Add silane coupling agent KH-550 accounting for 1% - 2% of the mass of nano-zinc oxide, and perform reflux stirring in an oil bath at 60 - 70 °C for 2 - 3 h to graft the silane coupling agent onto the surface of nano-zinc oxide, and then perform vacuum drying to obtain pretreated nano-zinc oxide.

[0014] Preferably, the specific preparation process of the outer coating liquid is as follows: Step a: Prepare a solution with a concentration of 1.5 - 2.5 wt% of pretreated sodium alginate and a solution with a concentration of 1 - 1.5 wt% of pretreated hydroxypropyltrimethylammonium chloride chitosan. Mix the two, and under the condition of 30 - 40 °C, stir at a speed of 400 - 500 r / min for 1 - 1.5 h to form a preliminary composite system through electrostatic interaction and hydrogen bonding between the two; Step b: Prepare a solution with a concentration of 0.2 - 0.5 wt% of pretreated nano-zinc oxide, and slowly drop it into the composite system obtained in step a. The dropping speed is controlled at 1 - 2 mL / min, and at the same time, stir at a high speed of 500 - 600 r / min for 1.5 - 2 h to uniformly disperse nano-zinc oxide in the composite system to form a nano-composite coating liquid; Step c: Prepare a calcium chloride solution with a concentration of 0.1 - 0.3 wt%, and slowly add it to the nano-composite coating solution obtained in Step b. During the addition process, reduce the stirring speed to 200 - 300 r / min, continuously stir for 30 - 45 min, and then let it stand at room temperature for 1 - 2 h to obtain the outer layer coating solution.

[0015] Preferably, the addition amount of calcium chloride is dynamically regulated in Step c, specifically: When the deacetylation degree DA value of the sodium alginate is 70 - 80%, the volume ratio of the sodium alginate solution to the calcium chloride solution is 5 - 5.5:0.5; When the DA value is 80 - 90%, the volume ratio of the sodium alginate solution to the calcium chloride solution is 4 - 5:0.5; When the DA value is 90 - 95%, the volume ratio of the sodium alginate solution to the calcium chloride solution is 3 - 4:0.5.

[0016] Preferably, the relationship between the volumes of the inner layer coating solution and the outer layer coating solution and the mass of the garlic is as follows: ; where V1 is the volume of the inner layer coating solution, in L; V2 is the volume of the outer layer coating solution, in L; m is the mass of the garlic, in kg; a is the reference proportion coefficient of the inner layer coating solution, with a value of 1.5 L / kg; k1 is the proportion coefficient, with a value of 0.5 L / mmol; b is the reference proportion coefficient of the outer layer coating solution, with a value of 1.0 L / kg; k2 is the proportion coefficient, with a value of 0.25 L / (kg⋅μm); is the target penetration concentration of glycine betaine, with a value range of 0.3 ≤ ≤ 0.5 mmol / kg; is the target thickness of the outer layer coating, with a value range of 0.8 ≤ ≤ 1.2 μm.

[0017] Among them, the coefficient a determines the volume of the basic coating solution required for a unit mass of garlic through preliminary experiments. The specific steps are as follows: Experimental design: Select garlic with different masses (such as 1 kg, 5 kg, 10 kg), fix other conditions (such as coating solution concentration, soaking time), and measure the minimum volume of the coating solution required to completely immerse the garlic.

[0018] Result analysis: The experiment shows that about 1.5 L of coating solution is required per kilogram of garlic to ensure uniform coverage of the epidermis while avoiding excessive waste.

[0019] Verification: After optimization through orthogonal experiments, it is confirmed that 1.5 L / kg is the optimal value considering both the coating effect and cost.

[0020] The value of k1 is derived from the osmotic kinetic model of glycine betaine. The specific logic is as follows: Relationship between osmotic concentration and volume: The osmotic concentration of glycine betaine ( ) directly affects the penetration depth of the coating solution. According to Fick's law of diffusion, the penetration volume is linearly related to the concentration gradient: ; Experimental calibration: At a fixed penetration time (8 - 12 min) and epidermal characteristics, by changing (0.3 - 0.5 mmol / kg), the corresponding volume increment of the coating solution is measured, and k1 = 0.5 L / mmol is obtained by fitting.

[0021] Verification: In the example, when = 0.4 mmol / kg, the error between the calculated value and the measured value is < 5%, verifying the applicability of the linear model.

[0022] The coefficient b refers to the relationship between the film-forming characteristics of the sodium alginate coating solution and the surface area of garlic.

[0023] Surface area calculation: Assuming that garlic is approximately spherical (diameter 3 - 4 cm), the surface area per unit mass is about 0.12 m² / kg.

[0024] Coating solution coverage rate: According to the film-forming thickness of the sodium alginate solution (about 1 μm), it is calculated that 1.0 L of the coating solution is required per unit mass to cover the entire surface area.

[0025] Experimental verification: It is confirmed through the spraying test that this volume can form a continuous and uniform film layer.

[0026] The value of k2 is based on the geometric relationship between the film thickness and the amount of coating solution used.

[0027] Film volume formula: The coating volume V2 = surface area × thickness.

[0028] Parameter conversion: Combining the surface area (0.12 m² / kg) and density (the density of the sodium alginate solution ≈ 1 g / mL), it is deduced that: ; Experimental correction: By adjusting the film thickness (0.8 - 1.2 μm), the applicability of the formula is verified, and the error is controlled within ±8%.

[0029] All parameters are calibrated through preliminary experiments, orthogonal experiments or theoretical models to ensure their scientificity and repeatability.

[0030] The present invention has at least the following beneficial effects: The present invention provides a method for prolonging the fresh-keeping storage period of garlic. Through the synergistic effect of the double-layer coating technology and the dynamic regulation process, the fresh-keeping effect of garlic is significantly improved. The inner layer uses a compound coating of betaine and melatonin, which effectively inhibits respiratory metabolism and the accumulation of reactive oxygen species, delays tissue senescence, and maintains relatively high hardness and antioxidant capacity. The outer composite coating forms a dense physical barrier through the modification of sodium alginate, chitosan nanocomposite, and antibacterial treatment with nano-zinc oxide, reducing water loss and inhibiting the reproduction of microorganisms. The staged vacuum precooling and precise air-drying processes optimize the pretreatment process of garlic bulbs, reducing stress damage and maintaining the stability of epidermal moisture. By dynamically adjusting the calcium chloride cross-linking density through the degree of deacetylation, the uniformity and structural stability of the coating are ensured. The precise ratio of the volume of the coating solution to the mass of the garlic bulbs realizes the controllable adjustment of the penetration amount of active ingredients and the film thickness, reducing the risk of chemical residues while improving the treatment efficiency. The overall process prolongs the storage period while maintaining the color, flavor, and nutritional value of the garlic bulbs, significantly inhibiting germination and decay, and achieving the goal of energy-saving and efficient fresh-keeping.

[0031] Other advantages, objectives, and features of the present invention will be partially reflected by the following description and partially understood by those skilled in the art through the research and practice of the present invention. Detailed implementation manners

[0032] The following further elaborates on the present invention in conjunction with specific implementation manners, enabling those skilled in the art to implement it with reference to the text of the specification.

[0033] It should be understood that the terms such as "having", "comprising", and "including" used herein do not exclude the presence or addition of one or more other elements or their combinations.

[0034] It should be noted that the experimental methods described in the following implementation examples are all conventional methods unless otherwise specified, and the reagents and materials can be obtained from commercial channels unless otherwise specified.

[0035] Example 1 A method for prolonging the fresh-keeping storage period of garlic includes the following steps: Step 1: Select 100 kg of fresh garlic without mechanical damage and pests and diseases, and use a vacuum precooling machine for precooling. Set the vacuum degree to 7 kPa and cool down in three stages: In the first stage, cool the garlic from room temperature (about 25°C) to 11°C within 0.5 h; In the second stage, cool down at a rate of 1.8°C / h to 5°C; In the third stage, maintain the temperature at 3°C and the relative humidity at 70% for 36 hours. After pre-cooling is completed, transfer the garlic to a drying room and use natural ventilation combined with a dehumidifier. During the rapid dehydration stage, control the temperature at 22 °C, humidity at 45%, and wind speed at 2.5 m / s. When the surface moisture content drops to 21%, switch to the equilibrium dehydration stage (temperature 18 °C, humidity 55%, wind speed 0.8 m / s) until the moisture content stabilizes at 17%. Step 2: Calculate the required volumes of the inner coating solution and the outer coating solution. The target parameters are set as follows: the osmotic concentration of glycine betaine = 0.4 mmol / kg, and the target thickness of the outer coating = 1 μm.

[0036] V1 = 100 kg × (1.5 L / kg + 0.5 L / mmol × 0.4 mmol / kg) = 170 L; V2 = 100 kg × (1.0 L / kg + 0.25 L / (kg⋅μm) × 1 μm) = 125 L.

[0037] Mix 10 mmol / L glycine betaine and 500 μmol / L melatonin in a volume ratio of 1:1 to prepare a total of 170 L of the inner coating solution. Outer coating solution: Dissolve sodium alginate (the DA value is determined by infrared spectroscopy to be 85%) in deionized water to prepare a solution with a concentration of 2.0 wt%. When the DA value is between 80% and 90%, the volume ratio of the sodium alginate solution to the calcium chloride solution is selected as 4.5:0.5.

[0038] Mix 2 wt% sodium alginate, 1.2 wt% hydroxypropyltrimethylammonium chloride chitosan, 0.3 wt% nano-zinc oxide, and 0.2 wt% calcium chloride in a volume ratio of 4.5:2.5:1:0.5 to prepare a total of 125 L of the outer coating solution.

[0039] Completely immerse the garlic in the inner coating solution for 10 min, drain it, and then immerse it in the outer coating solution for 8 min, and drain the excess liquid on the surface. Step 3: Put the processed garlic into a plastic mesh bag with a pore size of 0.1 cm and store it in a cold storage at a temperature of 0.5 °C and a humidity of 70%. Example 2 A method for prolonging the fresh-keeping storage period of garlic, which is different from Example 1 in that the sodium alginate in Step 2 is pretreated before use, specifically: Dissolve sodium alginate in deionized water to prepare a solution with a mass fraction of 2.5%. Add 0.8% of the mass of sodium alginate of citric acid in a 45 °C water bath, and then remove the solvent by freeze-drying to obtain the pretreated sodium alginate.

[0040] The remaining steps are the same as those in Example 1.

[0041] Example 3 A method for prolonging the fresh-keeping storage period of garlic, different from Example 2 in that the hydroxypropyltrimethylammonium chloride chitosan in Step 2 is pretreated before use, specifically: Mix hydroxypropyltrimethylammonium chloride chitosan and nano-montmorillonite according to a mass ratio of 1:0.08, add an acetic acid solution with a volume fraction of 1.5%, and treat under ultrasonic conditions of 350 W and 45 kHz for 25 min to form a nano-composite structure, and then perform vacuum drying to obtain the pretreated hydroxypropyltrimethylammonium chloride chitosan. The remaining steps are the same as those in Example 2.

[0042] Example 4 A method for prolonging the fresh-keeping storage period of garlic, different from Example 3 in that the nano-zinc oxide in Step 2 is pretreated before use, specifically: Disperse nano-zinc oxide in absolute ethanol to prepare a suspension with a mass fraction of 7%, add 1.5% of the mass of nano-zinc oxide of silane coupling agent KH-550, reflux and stir in an oil bath at 65 °C for 2.5 h to graft the silane coupling agent onto the surface of nano-zinc oxide, and then perform vacuum drying to obtain the pretreated nano-zinc oxide.

[0043] The remaining steps are the same as those in Example 3.

[0044] Example 5 A method for prolonging the fresh-keeping storage period of garlic, different from Example 4 in that the preparation steps of the outer coating solution are specifically as follows: Prepare a solution with a concentration of 2 wt% of the pretreated sodium alginate, and prepare a solution with a concentration of 1.2 wt% of the pretreated hydroxypropyltrimethylammonium chloride chitosan. Mix the two, and under the condition of 35 °C, stir at a speed of 450 r / min for 1 h to form a preliminary composite system through electrostatic interaction and hydrogen bonding between the two; Prepare a solution with a concentration of 0.3 wt% of the pretreated nano-zinc oxide, and slowly drop it into the composite system obtained in Step a above. The dropping speed is controlled at 1 mL / min, and at the same time, stir at a high speed of 600 r / min for 1.5 h to uniformly disperse the nano-zinc oxide in the composite system to form a nano-composite coating solution; Prepare a solution with a concentration of 0.2 wt% of calcium chloride, and slowly add it to the nano-composite coating solution obtained in Step b above. During the addition process, reduce the stirring speed to 300 r / min, continue stirring for 30 min, and then let it stand at room temperature for 1.5 h to obtain the outer coating solution; The remaining steps are the same as those in Example 4.

[0045] Comparative Example 1 A method for prolonging the fresh-keeping storage period of garlic. Compared with Example 5, only the inner coating solution is used for coating, and the remaining steps are the same as those in Example 5.

[0046] Comparative Example 2 A method for prolonging the fresh-keeping storage period of garlic. Compared with Example 5, only the outer coating solution is used for coating, and the remaining steps are the same as those in Example 5.

[0047] Comparative Example 3 A method for prolonging the fresh-keeping storage period of garlic. Compared with Example 5, in the pre-cooling process, the temperature is not decreased in stages, and only single rapid dehydration is adopted, with a wind speed of 3 m / s until the moisture content reaches 15%. The remaining steps are the same as those in Example 5.

[0048] Comparative Example 4 A method for prolonging the fresh-keeping storage period of garlic. Compared with Example 5, in the air-drying process, it is not in stages, and only a single cooling rate of 1.8 °C / h is adopted to cool down to 3 °C and maintain it, and the entire pre-cooling process lasts for 72 h. The remaining steps are the same as those in Example 5.

[0049] Comparative Example 5 A method for prolonging the fresh-keeping storage period of garlic. Compared with Example 5, the addition amount of calcium chloride is not dynamically adjusted, and the volume ratio of the sodium alginate solution to the calcium chloride solution is fixed at 5.5:0.5. The remaining steps are the same as those in Example 5.

[0050] Comparative Example 6 Compared with Example 5, the volumes of the inner coating solution and the outer coating solution are not dynamically adjusted, and the volumes of both the inner coating solution and the outer coating solution are fixed at 150 L. The remaining steps are the same as those in Example 5.

[0051] Determination and comparison of the fresh-keeping effect of garlic Take garlic of the same batch and carry out fresh-keeping storage by using the methods in each example and comparative example respectively. After 120 days, take the garlic for the following tests: Use the weighing method to determine the weight loss rate, use the drying method to determine the tissue moisture content, and use a GY-1 type hardness tester to determine the fruit hardness.

[0052] Pry open each garlic clove to measure the germ length and the clove length, and the result is recorded as the ratio between the germ and the clove length of each garlic clove, denoted as the bud-clove ratio.

[0053] Statistically process the percentage between the total number of rotten garlic cloves and the total number of garlic cloves in the treatment, denoted as the rot rate.

[0054] Use a commercially available related kit to determine the hydroxyl radical scavenging ability.

[0055] The test results are shown in Table 1.

[0056] Table 1 As can be seen from Table 1, the pretreatment processes in Examples 2-4 carboxylate sodium alginate, nanocomposite chitosan, and graft nanometer zinc oxide coupling agent, respectively improving the stability, antibacterial property, and dispersibility of the coating solution. In Example 5, the calcium chloride ratio (4.5:0.5) was adjusted according to the DA value to balance the crosslinking density and film flexibility, avoiding over-crosslinking or loose structure. And Example 5 (comprehensive pretreatment + dynamic adjustment of the coating solution) performed optimally in all indicators. It significantly inhibited water loss through double-layer coating and dynamic regulation process. The physical barrier effect of the outer layer coating and the antioxidant synergistic effect of the inner layer coating were prominent, reducing the weight loss rate of garlic. Epidermal damage was reduced through staged precooling and air drying, combined with crosslinking modification of sodium alginate, enhancing the mechanical strength of the coating and improving the hardness of garlic. Microbial reproduction was effectively inhibited through pretreatment with nanometer zinc oxide and the chitosan-montmorillonite composite structure, effectively reducing the garlic rot rate. Oxidative damage was delayed through the synergistic effect of melatonin and glycine betaine, effectively improving the antioxidant capacity of garlic.

[0057] In Comparative Examples 1-2, only single-layer coating was used, resulting in a significant increase in the weight loss rate and rot rate of garlic, indicating that the synergistic barrier and antibacterial functions of double-layer coating are indispensable. In Comparative Examples 3-4, staged precooling / air drying was not carried out, resulting in a high weight loss rate of garlic, increased epidermal microcracks leading to mold invasion, and serious deterioration of storage quality. In Comparative Example 5, the calcium chloride ratio was fixed, and over-crosslinking at DA = 85% led to coating embrittlement and a decrease in the hardness of garlic. In Comparative Example 6, the volume of the coating solution was fixed, without adapting to the garlic mass and film thickness requirements, resulting in insufficient penetration of active ingredients and a decrease in antioxidant capacity.

[0058] Using the treatment method of Example 5, garlic was successively immersed in the inner layer coating solution and the outer layer coating solution, and after draining, the residual amount of KH-550 was detected by gas chromatography-mass spectrometry (GC-MS). The result showed that the residual amount of KH-550 < 0.01 ppm (meeting the standard of GB9685-2016).

[0059] In summary, the present invention significantly extends the storage period of garlic and maintains the commercial quality through the synergistic effects of double-layer coating, dynamic regulation, and staged precooling and air drying. In particular, the comprehensive scheme of Example 5 has the best effect in inhibiting weight loss, rot, germination, and oxidative damage, and has the potential for large-scale application.

[0060] Although the embodiments of the present invention have been disclosed as above, they are not limited to the applications listed in the specification and the embodiments. It can be fully applied to various fields suitable for the present invention. For those skilled in the art, additional modifications can be easily made. Therefore, without departing from the general concept defined by the claims and the equivalent scope, the present invention is not limited to the specific details and the examples shown and described herein.

Claims

1. A method for prolonging the fresh-keeping storage period of garlic, characterized in that, It includes the following steps: Step 1: Select garlic without mechanical damage and pests and diseases, and pre-cool and air-dry the epidermis. Step 2: Completely immerse the garlic after pre-cooling and air-drying the epidermis obtained in Step 1 in the inner coating solution for 8 - 12 min, take it out and drain, then immerse the garlic treated with the inner coating in the outer coating solution, soak for 5 - 10 min, and drain. Step 3: Put the drained garlic obtained in Step 2 into a plastic mesh bag with a pore size of 0.08 - 0.12 cm, and store it in a cold storage with a temperature of 0 - 1°C and a humidity of 65% - 75%. Among them, the inner coating solution is prepared by mixing glycine betaine with a concentration of 8 - 12 mmol / L and melatonin with a concentration of 400 - 600 μmol / L in a volume ratio of 0.8 - 1.2:1; the outer coating solution is prepared by mixing sodium alginate with a concentration of 1.5 - 2.5 wt%, hydroxypropyltrimethylammonium chloride chitosan with a concentration of 1 - 1.5 wt%, nano-zinc oxide with a concentration of 0.2 - 0.5 wt% and calcium chloride with a concentration of 0.1 - 0.3 wt%, and the volume ratio of sodium alginate, hydroxypropyltrimethylammonium chloride chitosan, nano-zinc oxide, and calcium chloride is (3 - 5.5):(2 - 3.5):1:(0.35 - 0.65).

2. The method for prolonging the fresh-keeping storage period of garlic as described in claim 1, wherein The pre-cooling process in Step 1 is as follows: Put the selected garlic into a vacuum pre-cooling machine, control the vacuum degree at 6 - 8 kPa, and cool down in stages. In the first stage, cool down to 10 - 12°C within 0.5 h, in the second stage, cool down at a rate of 1.5 - 2°C / h to 4 - 6°C, in the third stage, maintain the temperature at 2 - 3°C, and keep the relative humidity at 60 - 80% for 23 - 48 h to complete the pre-cooling process.

3. The method for prolonging the fresh-keeping storage period of garlic as claimed in claim 1, wherein, The air-drying process in Step 1 is as follows: Use natural ventilation combined with a dehumidifier to air-dry the pre-cooled garlic. The air-drying process is divided into two stages: rapid dehydration and equilibrium dehydration. Use a near-infrared moisture meter to scan the moisture of the garlic epidermis. When the epidermis moisture drops to 20 - 22%, switch to the equilibrium dehydration stage until the epidermis moisture stabilizes at 15 - 20%, and the air-drying process ends; Among them, the temperature in the rapid dehydration stage is 20 - 25°C, the relative humidity is controlled at 40 - 50%, and the wind speed is 2 - 3 m / s; the temperature in the equilibrium dehydration stage is 15 - 20°C, the relative humidity is maintained at 50 - 60%, and the wind speed drops to 0.5 - 1 m / s.

4. The method for prolonging the fresh storage period of garlic according to claim 1, characterized in that, The sodium alginate in the outer coating solution needs to be pretreated before compounding. Specifically: Dissolve sodium alginate in deionized water to make a solution with a mass fraction of 2% - 3%. Under a water bath at 40 - 50°C, add citric acid accounting for 0.5% - 1% of the mass of sodium alginate, and stir at 200 - 300 r / min for 30 - 45 min to make sodium alginate slightly cross-linked and carboxylated. Then remove the solvent by freeze-drying to obtain pretreated sodium alginate.

5. The method for prolonging the fresh storage period of garlic according to claim 4, characterized in that, The hydroxypropyltrimethylammonium chloride chitosan in the outer coating solution needs to be pretreated before compounding. Specifically: Mix hydroxypropyltrimethylammonium chloride chitosan and nano-montmorillonite in a mass ratio of 1:0.05 - 0.1, add an acetic acid solution with a volume fraction of 1% - 2%, and perform ultrasonic treatment at 300 - 400 W and 40 - 50 kHz for 20 - 30 min to disperse the hydroxypropyltrimethylammonium chloride chitosan between the nano-montmorillonite lamellae, forming a nano-composite structure, and then perform vacuum drying to obtain the pretreated hydroxypropyltrimethylammonium chloride chitosan.

6. The method for prolonging the fresh-keeping storage period of garlic as described in claim 5, characterized in that, The nano-zinc oxide in the outer coating liquid needs to undergo a pretreatment process before compounding. Specifically: Disperse nano-zinc oxide in absolute ethanol to make a suspension with a mass fraction of 5% - 8%, add 1% - 2% of the silane coupling agent KH-550 based on the mass of nano-zinc oxide, and perform oil bath reflux stirring at 60 - 70 °C for 2 - 3 h to graft the silane coupling agent onto the surface of nano-zinc oxide, and then perform vacuum drying to obtain the pretreated nano-zinc oxide.

7. The method for prolonging the fresh storage period of garlic according to claim 6, characterized in that, The specific preparation process of the outer coating liquid is as follows: Step a: Prepare a solution with a concentration of 1.5 - 2.5 wt% of the pretreated sodium alginate, and prepare a solution with a concentration of 1 - 1.5 wt% of the pretreated hydroxypropyltrimethylammonium chloride chitosan. Mix the two, and under the condition of 30 - 40 °C, stir at a speed of 400 - 500 r / min for 1 - 1.5 h to form a preliminary composite system through electrostatic interaction and hydrogen bonding between the two; Step b: Prepare a solution with a concentration of 0.2 - 0.5 wt% of the pretreated nano-zinc oxide, and slowly add it to the composite system obtained in step a. The dropping speed is controlled at 1 - 2 mL / min, and at the same time, stir at a high speed of 500 - 600 r / min for 1.5 - 2 h to uniformly disperse the nano-zinc oxide in the composite system, forming a nano-composite coating liquid; Step c: Prepare a solution with a concentration of 0.1 - 0.3 wt% of calcium chloride, and slowly add it to the nano-composite coating liquid obtained in step b. During the addition process, reduce the stirring speed to 200 - 300 r / min, continuously stir for 30 - 45 min, and then let it stand at room temperature for 1 - 2 h to obtain the outer coating liquid.

8. The method for prolonging the fresh storage period of garlic according to claim 7, wherein, The dynamic regulation of the addition amount of calcium chloride in step c is specifically as follows: When the deacetylation degree DA value of the sodium alginate is 70 - 80%, the volume ratio of the sodium alginate solution to the calcium chloride solution is 5 - 5.5:0.5; When the DA value is 80 - 90%, the volume ratio of the sodium alginate solution to the calcium chloride solution is 4 - 5:0.5; When the DA value is 90 - 95%, the volume ratio of the sodium alginate solution to the calcium chloride solution is 3 - 4:0.

5.

9. The method for prolonging the fresh storage period of garlic according to claim 1, characterized in that, The volume relationship between the inner coating liquid and the outer coating liquid and the mass of garlic is as follows: ； Among them, V1 is the volume of the inner coating solution, in L; V2 is the volume of the outer coating solution, in L; m is the mass of garlic, in kg; a is the reference proportion coefficient of the inner coating solution, with a value of 1.5 L / kg; k1 is the proportion coefficient, with a value of 0.5 L / mmol; b is the reference proportion coefficient of the outer coating solution, with a value of 1.0 L / kg; k2 is the proportion coefficient, with a value of 0.25 L / (kg⋅μm); is the target penetration concentration of glycine betaine, and the value range is 0.3 ≤ ≤ 0.5 mmol / kg; is the target thickness of the outer coating, and the value range is 0.8 ≤ ≤ 1.2 μm.

Images