Method for inhibiting bacteria and preserving fresh fruit by using different skin and flesh

Abstract

The application discloses a method for inhibiting bacteria and preserving different edible fruit skins and flesh, relates to the field of postharvest preservation of agricultural products, and solves the problems of rotting, weight loss, softening and flavor deterioration of fruits caused by microbial infection and ethylene ripening after harvesting. The method comprises the following steps: after the surface of different edible fruit skins and flesh is cleaned, the fruit is soaked in a pretreatment liquid containing a food-grade non-ionic surfactant and a phosphate buffer system, then the fruit is soaked in a composite preservative containing chitosan oligosaccharide, calcium disodium ethylenediaminetetraacetate, citric acid and PVA, and is blown dry to form a film, finally, the fruit is placed in a breathable container with a composite ethylene absorption layer in a single layer, and is stored in an environment with controlled temperature, humidity and gas. The method is mainly used for prolonging the shelf life of different edible fruit skins and flesh, and is suitable for high-end brand fruits, organic fruits, e-commerce pretreatment and off-season sales and the like.

Description

Technical Field

[0001] This invention relates to the field of postharvest preservation technology for agricultural products. More specifically, this invention relates to a method for antibacterial preservation of fruits with different skins and flesh. Background Technology

[0002] Post-harvest storage, transportation, and sales of fruits commonly face problems such as rotting, weight loss, softening, and decline in flavor and quality due to their own physiological activities, microbial infection, and the accumulation and effects of endogenous ethylene gas. This directly leads to significant economic losses. Developing effective preservation technologies is crucial for maintaining the profitability of the fruit industry. Currently, several commonly used methods exist in the industry for post-harvest preservation of fruits with different peels and flesh, but each of these methods has its own limitations.

[0003] Chemical fungicide treatment is one of the most widely used techniques for controlling postharvest diseases. For example, synthetic fungicides such as imazalil and thiabendazole are used for soaking or spraying. However, residues of these chemicals on or inside the fruit may raise consumer concerns about food safety. Especially in the production of organic fruits or fruits requiring green certification, relevant regulations and standards typically explicitly prohibit the use of such synthetic fungicides, which greatly limits their application.

[0004] Controlled atmosphere storage (CAS) is another important preservation method. It precisely controls the oxygen and carbon dioxide concentrations in the storage environment to suppress fruit respiration, thereby delaying ripening and senescence. While this method can effectively extend shelf life to some extent, its implementation typically relies on expensive gas control equipment and sophisticated control systems, resulting in high initial investment and operating costs, posing economic challenges for large-scale application. More importantly, traditional CAS technologies primarily focus on controlling the macroscopic gas environment, and their ability to actively remove trace amounts of ethylene gas produced by the fruit's own metabolism is usually limited. Ethylene, a key plant hormone promoting fruit ripening and senescence, accumulates in the storage environment, triggering and accelerating the ripening process. Even under optimized temperature, humidity, and gas atmospheres, trace amounts of ethylene can still initiate a ripening chain reaction, leading to decreased fruit firmness, yellowing, and even excessive softening, ultimately limiting further improvements in the effectiveness of CAS.

[0005] The peels of fruits with different flesh types are often covered with a natural waxy layer, which may also harbor dust, agricultural residues, and some environmental microorganisms. This complex surface condition directly affects the effectiveness of subsequent preservation treatments. Incomplete cleaning not only provides a haven for pathogens to grow and infect, but also hinders the even wetting, spreading, and effective adhesion of preservative solutions to the peel surface, making it difficult for the preservative components to fully exert their effects. Therefore, under current technological conditions, in the field of post-harvest processing of fruits with different flesh types, especially in scenarios requiring safety, efficiency, and consideration of long-distance transportation or long-term storage, there are a series of technical challenges that need to be addressed. Summary of the Invention

[0006] One object of the present invention is to solve at least the above-mentioned problems and to provide at least the advantages that will be described later.

[0007] To achieve these objectives and other advantages according to the present invention, a method for antibacterial preservation of fruits with separate peels and flesh is provided, wherein the fruits with separate peels and flesh are durian, mango, or jackfruit, comprising the following steps:

[0008] S1. Clean the surface of fruits with different peels and flesh;

[0009] S2. Completely immerse fruits with different peels and flesh in a compound preservative solution at a temperature of 20℃-25℃ for 4-8 minutes, while maintaining a stirring speed of 20-30 r / min. After immersion, remove and dry the fruits to form a compound preservative film on their surface. The compound preservative solution includes 0.1%-2% chitosan oligosaccharide, 0.1%-2% calcium disodium EDTA, 0.05%-1% citric acid, and 0.1%-1% PVA by mass fraction. The solvent is drinking water, and the pH value is adjusted to 5.0-6.0.

[0010] S3. After film formation, place the fruits (with different skins and flesh) in a single layer in a breathable container and transfer them to a storage environment with a temperature of 10℃-15℃ and a relative humidity of 80%-90%. The bottom of the breathable container is lined with an ethylene absorption layer, which consists of a lower layer of alumina particles loaded with 5%-8% potassium permanganate solution, a middle layer of activated carbon particles impregnated with 3%-5% zinc palmitate solution, and an upper layer of zeolite molecular sieves loaded with 2%-4% nano-titanium dioxide. Each layer is separated by a stainless steel mesh. A polypropylene microporous plate is placed between the ethylene absorption layer and the fruits. The sidewalls of the storage environment are equipped with LED ultraviolet light sources with an emission wavelength of 365-395nm and a power density of 0.5-2.0mW / cm³. 2 .

[0011] Preferably, the drying method involves placing the air in a clean airflow at 15℃-25℃ with a wind speed of 2.0-4.0m / s for 10-12 minutes. The clean airflow is filtered through a high-efficiency air filter with a filtration accuracy of 0.22μm, and the relative humidity of the airflow is controlled at 45%-55%.

[0012] Preferably, the surface cleaning in step S1 uses atomized spraying with a pressure of 0.15-0.20 MPa, a spray water temperature of 15℃-20℃, and a spraying time of 1-2 min;

[0013] After surface cleaning, before step S2, soak fruits with different peels and flesh in a pretreatment solution for 30-60 seconds at a soaking temperature of 20℃-25℃. Then rinse the fruit surface with drinking water for 5-10 seconds and drain. The pretreatment solution includes an aqueous solution of 0.05%-0.2% food-grade nonionic surfactant and 0.5%-1.5% potassium dihydrogen phosphate-dipotassium hydrogen phosphate buffer system, with the pH value adjusted to 7.5-8.5.

[0014] Preferably, in step S3, the oxygen volume fraction in the storage environment is maintained at 5%-8% and the carbon dioxide volume fraction is maintained at 3%-5%.

[0015] Preferably, in step S3, the mass ratio of the alumina particle layer, the activated carbon particle layer, and the zeolite molecular sieve layer is (2.5-3.5):(1.5-2.5):1, and the total thickness of the ethylene absorption layer is 20-30 mm.

[0016] Preferably, an ethylene concentration monitoring system and a circulating fan are installed in the storage environment. When the ethylene concentration exceeds 0.05 μL / L, the circulating fan is activated to circulate the air.

[0017] Preferably, the airflow of the circulating fan in the storage environment flows from top to bottom, passes over the fruit and then through the ethylene absorption layer, with an airflow velocity of 0.1-0.3 m / s.

[0018] Preferably, the upper surface of the polypropylene microporous plate is covered with a removable non-woven fabric liner.

[0019] Preferably, in step S4, the ventilated container has multiple vent holes on its bottom plate and side wall. The vent holes on the bottom plate have an opening rate of 30%-40% and a hole diameter of 3-5 mm. The vent holes on the side wall have an opening rate of 20%-30% and a hole diameter of 2-4 mm. The inner surface of the bottom plate has multiple raised support points distributed in a grid pattern. The grid unit spacing is 10-15 mm and the support point height is 2-3 mm. The bottom of the ventilated container has a support foot with a height of 5-8 mm. The side wall of the ventilated container has at least 4 symmetrically distributed vent windows near the upper part.

[0020] The present invention has at least the following beneficial effects:

[0021] First, this invention constructs a synergistic preservation system by combining a specific pretreatment solution, a compound preservative treatment, and a storage scheme with an internal compound ethylene absorption layer. Firstly, the pretreatment solution improves the wettability and cleanliness of the fruit peel surface, laying the foundation for subsequent treatments. Then, the compound preservative forms a protective film on the fruit surface, possessing both antibacterial and physical barrier functions, effectively blocking pathogen infection and slowing water transpiration. Finally, during storage, the compound ethylene absorption layer removes ethylene gas through multiple mechanisms. This solution, encompassing surface treatment and environmental control, overcomes the limitations of single technical measures, achieving comprehensive inhibition of microbial spoilage and physiological aging, and significantly extending the postharvest life of fruits with different peels and flesh.

[0022] Secondly, this invention specifies that the clean airflow must be filtered through a high-efficiency filter and its humidity controlled. This feature effectively prevents secondary contamination of the fruit by suspended microorganisms in the ambient air during the film-forming stage when the fruit surface is moist. Simultaneously, precise humidity control avoids uneven film formation and cracking caused by excessively dry air leading to rapid water loss of the preservative solution, or excessively high humidity resulting in excessively long drying times and thinner film layers. This ensures that the composite preservation film can form a continuous, dense, and complete structure, optimizing its physical barrier function.

[0023] Third, surface cleaning is performed using atomized spraying at specific pressures and temperatures. Atomized water droplets offer better penetration and even coverage, effectively dissolving and washing away surface dust, pesticide residues, and some microorganisms while avoiding mechanical damage to the delicate fruit peel from high-pressure water jets. This gentle yet efficient cleaning method provides a clean and activated fruit peel surface for subsequent pretreatment soaking and preservative treatment, forming a fundamental step in ensuring the effectiveness of the entire preservation process.

[0024] Fourth, by combining controlled atmosphere storage with an ethylene absorption layer, a synergistic effect is achieved. The low-oxygen, high-carbon dioxide environment directly inhibits the respiration rate of the fruit and, to some extent, suppresses the growth of aerobic microorganisms. This environment, combined with the efficient ethylene removal, works on two key aspects of postharvest physiological metabolism in the fruit: respiration and ripening. This comprehensively delays the ripening and senescence process of the fruit, achieving a superior preservation effect compared to controlled atmosphere storage or ethylene absorption alone.

[0025] Fifth, by adding a specific wavelength of LED ultraviolet light source to the storage environment and irradiating the zeolite molecular sieve / nano titanium dioxide layer of the ethylene absorption layer, the technical contradiction that the highly efficient photocatalyst nano titanium dioxide could not be activated in a dark storage environment was successfully resolved. The introduction of ultraviolet light activated the photocatalytic properties of nano titanium dioxide, enabling it to continuously decompose and remove adsorbed ethylene gas. This organically combines physical adsorption with chemical and photocatalytic oxidation removal, significantly improving the efficiency and durability of the entire ethylene absorption system under actual storage conditions.

[0026] Other advantages, objectives and features of the present invention will become apparent in part from the following description, and in part from those skilled in the art through study and practice of the invention. Attached Figure Description

[0027] Figure 1 Comparative graphs showing the appearance changes of the compound preservative and the control group during durian preservation from day 0 to day 13 (D0-D13);

[0028] Figure 2 The average weight loss rate of the compound preservative and the control group in durian preservation;

[0029] Figure 3 The comparison of the compound preservative agent and the control group in durian preservation showed the flesh firmness.

[0030] Figure 4 The comparison of the compound preservative agent and the control group in durian preservation showed the peel hardness.

[0031] Figure 5 The color difference of durian pulp between the compound preservative and the control group during durian preservation;

[0032] Figure 6 The color difference of durian peel between the compound preservative and the control group during durian preservation;

[0033] Figure 7 The opening rate of durian in the compound preservative and the control group was compared.

[0034] Figure 8 A picture showing the appearance of a durian that has developed mold.

[0035] Figure 9 Comparison of the appearance changes (spoilage area) of mangoes from day 1 to day 9 in the preservation process between the compound preservative and the control group;

[0036] Figures 10 to 15 The images show a comparison of the appearance of whole mangoes preserved using the compound preservative and the control group on days 0, 2, 4, 6, 8, and 11, respectively.

[0037] Figure 16The comparison of peel firmness between the compound preservative and the control group in mango preservation;

[0038] Figure 17 The peeling firmness of mangoes was compared between the compound preservative and the control group during mango preservation.

[0039] Figure 18 The weight loss rate of the compound preservative and the control group in mango preservation;

[0040] Figure 19 The incidence of black spots in mangoes was compared between the compound preservative and the control group. Detailed Implementation

[0041] The present invention will now be described in further detail with reference to examples, so that those skilled in the art can implement it based on the description.

[0042] It should be noted that, unless otherwise specified, the experimental methods described in the following embodiments are conventional methods, and the reagents and materials described are commercially available. It should be understood that the specific embodiments described herein are for illustrative purposes only and are not intended to limit the scope of the invention.

[0043] <Example 1>

[0044] This embodiment provides a compound preservative for antibacterial and fresh-keeping purposes of fruits with different skins and flesh, which is composed of the following components by weight percentage:

[0045] Chitosan oligosaccharide: 1%, calcium disodium EDTA: 1%, citric acid: 0.5%, polyvinyl alcohol (PVA): 0.1%, balance is drinking water;

[0046] The preparation method is as follows:

[0047] At room temperature, 0.1 g of PVA was dissolved in a portion of drinking water, and the mixture was stirred slowly until it was fully dissolved to form a PVA solution.

[0048] 1g of chitosan oligosaccharide, 1g of calcium disodium ethylenediaminetetraacetate and 0.5g of citric acid were added to the PVA solution in sequence, and the mixture was stirred continuously until it was completely dissolved after each addition.

[0049] The solution was brought to a final volume of 100g and thoroughly mixed to obtain a transparent and homogeneous composite preservative solution, which was then ready for use.

[0050] <Example 2>

[0051] Screening of preservative formulations based on antibacterial experiments (taking postharvest pathogens of jackfruit as an example): This embodiment illustrates the screening process of the core components and their proportions in the compound preservative of the present invention.

[0052] 1. Experimental Method: The growth rate method was used. Mycelial cakes of the tested pathogens (anthrax, Fusarium, and Rhizopus) were placed in the center of PDA plates containing different concentrations of preservatives, with plates without preservatives serving as the control group. After incubation at a suitable temperature, the colony diameter was measured, and the inhibition rate was calculated using the following formula:

[0053] Inhibition rate (%) = [1 - (experimental group colony diameter - mycelial cake diameter) / (control group colony diameter - mycelial cake diameter)] × 100%.

[0054] 2. Screening of Oligosaccharide Components: The antibacterial effects of chitosan oligosaccharide, fucoidan oligosaccharide, and fucoidan oligosaccharide at concentrations of 1% (K1 / Y1 / H1), 0.1% (K2 / Y2 / H2), and 0.01% (K3 / Y3 / H3) were tested. The results showed that 1% chitosan oligosaccharide (K1) had the best antibacterial effect against the three pathogens.

[0055] Table 1. Antibacterial data of chitosan oligosaccharide, fucoidan oligosaccharide, and fucoidan oligosaccharide against anthrax bacteria.

[0056]

[0057] Table 2. Antibacterial data of chitosan oligosaccharide, fucoidan oligosaccharide, and fucoidan oligosaccharide against Fusarium.

[0058]

[0059] Table 3. Antimicrobial data of chitosan oligosaccharide, fucoidan oligosaccharide, and fucoidan oligosaccharide against Rhizopus.

[0060]

[0061] 3. Screening of calcium ion components: The antibacterial effects of disodium ethylenediaminetetraacetate (EDTA), calcium VC, and calcium chloride at concentrations of 1% (E1 / V1 / CL1), 0.1% (E2 / V2 / CL2), and 0.01% (E3 / V3 / CL3) were tested. The results showed that 1% disodium ethylenediaminetetraacetate (E1) had the best antibacterial effect against the three pathogens.

[0062] Table 4. Antibacterial data of calcium disodium EDTA, calcium VC, and calcium chloride against Bacillus anthracis.

[0063]

[0064] Table 5. Antibacterial data of calcium disodium EDTA, calcium VC, and calcium chloride against Fusarium.

[0065]

[0066] Table 6. Antimicrobial data of calcium disodium EDTA, calcium VC, and calcium chloride against Rhizopus.

[0067]

[0068] 4. Compound Optimization: The 1% chitosan oligosaccharide with the best effect was compounded with different concentrations of calcium disodium EDTA (1%, 0.5%, 0.1%). The results showed that the combination of 1% chitosan oligosaccharide + 1% calcium disodium EDTA (K1E1) had the most significant antibacterial effect.

[0069] Table 7. Antimicrobial data of chitosan oligosaccharide combined with different concentrations of calcium disodium EDTA on anthrax.

[0070]

[0071] Table 8. Antibacterial data of chitosan oligosaccharide combined with different concentrations of calcium disodium EDTA on Fusarium oxysporum.

[0072]

[0073] Table 9. Antimicrobial data of chitosan oligosaccharide combined with different concentrations of calcium disodium EDTA on Rhizopus.

[0074]

[0075] 5. Citric Acid Optimization: Based on the K1E1 compound system, 1% (N1), 0.5% (N2), and 0.1% (N3) of citric acid were added, respectively. The results showed that adding 0.5%-1% citric acid further improved the antibacterial rate. Considering both cost and effectiveness, 0.5% citric acid was ultimately selected.

[0076] Table 10. Antimicrobial data of chitosan oligosaccharide combined with calcium disodium EDTA and different concentrations of citric acid against anthrax.

[0077]

[0078] Table 11 Antibacterial data of chitosan oligosaccharide combined with calcium disodium EDTA and different concentrations of citric acid against Fusarium oxysporum.

[0079]

[0080] 6. Film-forming agent addition: In order to further form a protective film on the fruit surface, 0.1% polyvinyl alcohol (PVA) was added to the above optimized system as a film-forming agent, and the final compound preservative formula was determined.

[0081] <Example 3>

[0082] Application of compound preservatives in durian preservation. This embodiment verifies the preservation effect of the preservative of the present invention on durian.

[0083] 1. Treatment method: Select durians of uniform color and size, and randomly divide them into two groups of 8 per group. The control group (CK) received no treatment; the treatment groups were sprayed with the compound preservative prepared in Example 1 until the surface of the fruit was completely covered by the preservative liquid. Then, they were dried in a ventilated place with cool air to form a film.

[0084] 2. Storage conditions: Store the treated durian in a cold storage at a temperature of 13℃ and a relative humidity of 80%.

[0085] 3. Effect Evaluation: Regularly observe and measure various indicators, such as... Figures 1 to 8 As shown. D0 to D13 represent days 0 to 13, and DAY0 to DAY13 represent days 0 to 13.

[0086] Phenomorphology: The control group began to show mold on day 8, while the treatment group did not show mold until day 10, indicating a delayed onset of putrefaction.

[0087] Weight loss rate: Throughout the entire storage period, the weight loss rate of the treatment group was consistently lower than that of the control group.

[0088] Firmness: The treated group maintained better firmness in both the pulp and peel.

[0089] Sensory evaluation: Based on the criteria in Table 12, the treated durian group was significantly superior to the control group in terms of color, aroma, taste, and juice retention. Scoring criteria

[0090] 9 points: Bright color, no water seepage, sweet and juicy, excellent taste;

[0091] 7 points: The color is slightly dull, there is a small amount of water seepage, and the sweetness is slightly weak;

[0092] 5 points: The color is average, and the sweetness and moisture content are significantly reduced.

[0093] 3 points: Dull color, loss of aroma, and excessive water seepage;

[0094] 1 point: The color is black, it is severely softened, and it has a rotten smell.

[0095] Table 12 Sensory Evaluation Table

[0096]

[0097] <Example 4>

[0098] like Figures 9 to 19 As shown, the compound preservative is applied to the preservation of whole mangoes. This embodiment verifies the preservation effect of the preservative of the present invention on mangoes. Wherein, K+E+N+P represents the compound preservative.

[0099] 1. Treatment method: Select mangoes with uniform ripeness and no blemishes, and randomly group them. The control group (CK) received no treatment; the treatment groups were sprayed with the compound preservative prepared in Example 1 and dried with cold air to form a film. All mangoes were individually packaged and stored in a low-temperature warehouse at 18℃.

[0100] Table 13 Data on the area of ​​mango spoilage after preservative treatment

[0101]

[0102] 2. Effect Evaluation:

[0103] The spoilage process: In the control group, some mangoes developed black spots on day 3, and yellow exudate with a pungent odor appeared on day 5. The black spots expanded extensively from day 7 to day 9. In the treatment group, black spots only began to appear on day 5, and although the peel turned black later, there was no pungent rotten odor, and the mango still retained its inherent aroma.

[0104] Black spot incidence: On the 8th day of storage, the incidence of black spots in the treatment group was significantly lower than that in the control group.

[0105] Firmness and weight loss: Measured at 0, 4 and 8 days of storage, the treated group showed a slower decrease in fruit firmness and a lower weight loss rate.

[0106] Examples 2-4 above fully demonstrate that the composite preservative and its application method, composed of 1% chitosan oligosaccharide + 1% calcium disodium EDTA + 0.5% citric acid + 0.1% PVA provided by the present invention, can effectively inhibit the growth of postharvest pathogens in various fruits with different peels and flesh (such as jackfruit, durian, and mango), significantly delay the spoilage process, reduce quality deterioration, and extend shelf life, and has good versatility and application prospects.

[0107] <Example 5>

[0108] Optimized methods for antibacterial preservation of fruits with different peels and flesh include:

[0109] 1. Materials and Equipment

[0110] Test fruit: Mango (Mangifera indica L., variety 'Tainong No. 1'), harvested at commercial maturity, selected for its uniform size and color and free from mechanical damage and pests.

[0111] Pretreatment solution: using drinking water as solvent, containing 0.1% by mass of food-grade nonionic surfactant Tween-80 and 1.0% of potassium dihydrogen phosphate-dipotassium hydrogen phosphate buffer system, and adjusting the pH to 8.0 with 1 mol / L sodium hydroxide solution.

[0112] Compound preservative: using drinking water as a solvent, it contains the following components by mass fraction: 1% chitosan oligosaccharide (degree of deacetylation ≥90%), 1% calcium disodium EDTA, 0.5% citric acid, and 0.1% polyvinyl alcohol (PVA, degree of hydrolysis 87%-89%), with the pH value adjusted to 5.5 using a 1 mol / L hydrochloric acid solution.

[0113] Ethylene absorber layer: from bottom to top, it includes:

[0114] Bottom layer: Alumina particles (particle size 2-4 mm) loaded with 6% potassium permanganate solution.

[0115] Middle layer: Activated carbon particles impregnated with 4% zinc palmitate solution (particle size 3-5 mm, specific surface area ≥1000 m²) 2 / g).

[0116] Top layer: Zeolite molecular sieve (model 4A, particle size 1-3 mm) loaded with 3% nano titanium dioxide (anatase type, particle size about 20 nm).

[0117] The mass ratio of the alumina granular layer, activated carbon granular layer, and zeolite molecular sieve layer is 3:2:1. Each layer is separated by a stainless steel mesh with a pore size of 1.5 mm. The total filling thickness of the ethylene absorber layer is 25 mm.

[0118] Ventilation Container: Injection molded from food-grade polypropylene. Multiple vents are provided on the bottom plate and side walls of the container. The vents on the bottom plate have an opening ratio of 35% and a diameter of 4 mm; the vents on the side walls have an opening ratio of 25% and a diameter of 3 mm. Multiple raised support points are provided on the inner surface of the bottom plate, evenly distributed in a grid pattern with a grid unit spacing of 12 mm and a support point height of 2.5 mm. The bottom of the container has support feet with a height of 6 mm. Four symmetrically distributed vent windows (50 mm × 20 mm) are provided on the upper part of the side wall of the container.

[0119] Polypropylene microporous plate and non-woven fabric liner: A polypropylene microporous plate with an average pore size of 50 μm is laid on top of the ethylene absorption layer. A removable polypropylene non-woven fabric liner is laid on the upper surface of the polypropylene microporous plate.

[0120] Storage system:

[0121] Environmental control: A cold storage facility with an adjustable temperature of 10-15℃, relative humidity of 80%-90%, and gas composition (O2: 5%-8%, CO2: 3%-5%).

[0122] Airflow and filtration: A drying device equipped with a high-efficiency air filter (filtration accuracy 0.22μm) and a circulating fan system in the storage room.

[0123] Ethylene monitoring: Equipped with an electrochemical ethylene concentration sensor, the monitoring range is 0-1 μL / L, and the accuracy is ±0.01 μL / L.

[0124] Ultraviolet light source: An array of LED ultraviolet light sources with an emission wavelength of 380 nm (range 365-395 nm) is installed on the side wall of the storage environment, with a power density of 1.0 mW / cm². 2 (Range 0.5-2.0 mW / cm) 2 The light path of the LED ultraviolet light source is configured to irradiate the bottom area of ​​the ventilated container in a horizontal direction.

[0125] 2. Methods and Steps

[0126] S1. Surface cleaning and pretreatment:

[0127] Mangoes were placed in a misting sprayer and cleaned with clean water at a pressure of 0.18 MPa and a temperature of 18°C ​​for 1.5 minutes. The mangoes were then immersed in the pretreatment solution at 22°C for 45 seconds. After removal, the fruit surface was immediately rinsed with 20°C drinking water for 8 seconds and allowed to drain naturally.

[0128] S2, Composite Preservation Treatment and Film Formation:

[0129] The mangoes treated with S1 were completely immersed in the composite preservative at 22°C for 6 minutes, during which the composite preservative was continuously stirred using a magnetic stirrer at a rate of 25 r / min. After removal, the mangoes were placed in a drying station and blown in a clean airflow at 22°C, 50% relative humidity, and 3.0 m / s for 11 minutes to form a uniform composite preservative film on the mango surface. The clean airflow was filtered through the high-efficiency air filter.

[0130] S3. Storage Management:

[0131] The mangoes, after film formation, are placed in a single layer in the breathable container, ensuring each mango is stably supported by the raised support points. The polypropylene microporous plate and the non-woven fabric liner are then laid on top of the ethylene absorption layer, and the breathable container containing the mangoes is transferred to the storage system. The storage environment is set at 12°C, relative humidity at 85%, oxygen volume fraction at 6%, and carbon dioxide volume fraction at 4%. The ethylene concentration monitoring system and circulating fan are activated. When the ethylene concentration exceeds 0.05 μL / L, the circulating fan automatically starts, forming a downward airflow at a velocity of 0.2 m / s. Simultaneously, the LED ultraviolet light source is turned on, continuously irradiating the bottom of the breathable container.

[0132] 3. Evaluation of Results

[0133] During the 14-day storage period, mangoes were sampled regularly to determine the rate of spoilage, firmness, and weight loss.

[0134] By the 10th day of storage, the mango spoilage rate in the treatment group of this example was 20%.

[0135] By the 14th day of storage, the spoilage rate was 45%.

[0136] Throughout the storage period, the treated mangoes maintained a high firmness rate, and the weight loss rate remained below 5%.

[0137] The results show that the method of the present invention can effectively delay the spoilage process of mangoes and better maintain their post-harvest quality.

[0138] <Comparative Example 1>

[0139] Comparative Example 1 investigated the effect of the pretreatment solution in step S1, including:

[0140] 1. Materials and Equipment

[0141] Except for omitting the pretreatment solution and related steps, the other materials, equipment and storage conditions are exactly the same as in Example 5.

[0142] 2. Methods and Steps

[0143] S1. Surface cleaning (pretreatment omitted): The mangoes are cleaned only by mist spraying, with the same parameters as in Example 5. After spraying, they are drained directly without soaking in the pretreatment solution or rinsing with drinking water.

[0144] S2, Composite preservation treatment and film formation: exactly the same as in Example 5.

[0145] S3. Storage management: exactly the same as in Example 5.

[0146] 3. Evaluation of Results

[0147] Evaluation was conducted under the same storage conditions:

[0148] By the 10th day of storage, the rate of mango spoilage in the comparative treatment group was as high as 50%.

[0149] Obvious bacterial colonies were visible on the surface of the fruit, and the composite plastic wrap was unevenly adhered in some areas, resulting in peeling.

[0150] The results showed that the lack of a pretreatment step could not effectively remove the natural wax, dust, and some potential pathogens on the fruit peel surface, resulting in a decrease in the wettability and film uniformity of the subsequent compound preservative, which significantly weakened the overall antibacterial and preservation effect.

[0151] <Comparative Example 2>

[0152] Comparative Example 2 investigates the effect of the breathable container in step S3, including:

[0153] 1. Materials and Equipment

[0154] Except for the storage container, all other materials, equipment and reagents are the same as in Example 5. This comparative example uses a commercially available ordinary plastic basket (without specific ventilation holes, a solid bottom, only a few simple ventilation seams on the side walls, and no protruding support points or feet).

[0155] 2. Methods and Steps

[0156] S1. Surface cleaning and pretreatment: exactly the same as in Example 5.

[0157] S2, Composite preservation treatment and film formation: exactly the same as in Example 5.

[0158] S3. Storage Management (using ordinary containers): Place the processed mangoes in a single layer in the ordinary plastic basket. Place the ethylene absorption layer, polypropylene microporous plate, and non-woven fabric liner directly at the bottom of the basket. Then transfer the container to the same storage environment as in Example 5, with environmental parameters and control logic kept consistent.

[0159] 3. Evaluation of Results

[0160] Evaluation was conducted under the same storage conditions:

[0161] By the 10th day of storage, the rate of mango spoilage in the comparative treatment group had increased to 60%.

[0162] The mangoes at the bottom of the container showed obvious signs of softening and rotting due to pressure and poor ventilation.

[0163] The airflow circulation in the storage environment is obstructed, and the local ethylene concentration is prone to accumulate. Furthermore, the utilization rate of the ethylene absorption layer is low because the airflow cannot penetrate it effectively.

[0164] The results showed that ordinary containers severely affected the uniformity of the storage microenvironment and the efficiency of gas exchange, resulting in a significant decrease in the preservation effect.

[0165] <Comparative Example 3>

[0166] To investigate the influence of specific structural parameters (pore opening ratio, distribution, and support structure) of the permeable container, including:

[0167] 1. Materials and Equipment

[0168] Except for the storage container, everything else is the same as in Example 5. This comparative example uses a specially made container with a bottom plate vent opening rate of 10% and a hole diameter of 1 mm; no vent windows on the side walls; no protruding support points on the inner surface of the bottom plate; and no support feet at the bottom of the container.

[0169] 2. Methods and Steps

[0170] S1. Surface cleaning and pretreatment: exactly the same as in Example 5.

[0171] S2, Composite preservation treatment and film formation: exactly the same as in Example 5.

[0172] S3. Storage Management (using low-permeability containers): The treated mangoes are placed in a single layer in the specially designed container, and an ethylene absorption layer, a polypropylene microporous plate, and a non-woven fabric liner are laid out as in Example 5. They are then transferred to the same storage system.

[0173] 3. Evaluation of Results

[0174] Evaluation was conducted under the same storage conditions:

[0175] By the 10th day of storage, the rate of mango spoilage in this comparative treatment group was 45%.

[0176] Poor airflow inside the container leads to faster deterioration of the quality of the fruit at the bottom due to its large contact area and insufficient ventilation.

[0177] Despite the presence of an ethylene absorption layer, its absorption efficiency is lower than that of Example 5 due to insufficient airflow exchange.

[0178] The results show that even if the container has basic containment function, if its air permeability structure does not meet the optimized parameters defined in Embodiment 5 of the present invention, the expected gas circulation and physical support effects cannot be achieved, ultimately affecting the overall preservation performance.

[0179] Through the detailed comparison of the above embodiments and comparative examples, it is fully demonstrated that each step of the method of the present invention, especially the pretreatment liquid, the breathable container and its specific structure, plays an irreplaceable synergistic role, and together achieves the purpose of effectively extending the shelf life of fruits with different skins and flesh and reducing post-harvest losses.

[0180] Results analysis:

[0181] The pretreatment solution uses drinking water as a solvent and contains 0.1% by mass of the food-grade nonionic surfactant Tween-80 and a 1.0% potassium dihydrogen phosphate-dipotassium hydrogen phosphate buffer system. The pH value is precisely adjusted to 8.0 using sodium hydroxide solution. This composition aims to systematically solve the technical bottleneck of uneven penetration and poor adhesion of subsequent preservatives caused by the hydrophobic waxy layer, dust, and some potentially attached microorganisms on the surface of the peel of fruits with different flesh (such as mangoes).

[0182] Its mechanism of action can be broken down as follows:

[0183] Wetting and Penetration Effects of Surfactants: Tween-80, as a nonionic surfactant, can significantly reduce the surface tension of the pretreatment solution. When it comes into contact with the fruit peel, it can quickly spread and penetrate into the microscopic gaps in the waxy layer. Through emulsification and solubilization, it effectively removes the aforementioned hydrophobic contaminants, creating a hydrophilic surface for uniform contact with subsequent water-based preservatives.

[0184] Synergistic cleaning and interface regulation effects of the buffer system: The phosphate buffer system not only stabilizes the pretreatment solution within a slightly alkaline range (pH 8.0), helping to neutralize any acidic secretions that may be present on the fruit surface, but more importantly, it provides a stable pH transition interface for the subsequent application of the acidic compound preservative (pH 5.5). This avoids the denaturation of certain fruit peel components or rejection of preservative components that may be caused by drastic pH changes, ensuring the consistency and effectiveness of the treatment process.

[0185] The pretreatment in step S1 fundamentally optimizes the physicochemical state of the fruit peel surface, laying an indispensable foundation for the effective wetting, uniform spreading, and firm adhesion of the compound preservative in step S2. This core function was clearly verified by the negative results of Comparative Example 1 (omitting the pretreatment led to a significant increase in the spoilage rate and uneven film formation).

[0186] The compound preservative is formulated from 1% (w / w) chitosan oligosaccharide, 1% (w / w) disodium calcium EDTA, 0.5% citric acid, and 0.1% polyvinyl alcohol (PVA) in drinking water, with the pH adjusted to 5.5 using hydrochloric acid solution. This specific formula solves the technical challenges of single preservative components having a narrow antibacterial spectrum, short duration of action, and difficulty in forming a stable, functional protective film on the fruit peel surface through multiple synergistic effects among the components.

[0187] The synergistic mechanism is structured as follows:

[0188] The core antibacterial function of chitosan oligosaccharide: In an acidic environment of pH 5.5, the protonation of the amino groups on the chitosan oligosaccharide molecular chain gives it strong cationic properties. It can strongly adsorb onto the cell membrane surface of normally negatively charged pathogens (such as anthrax, Fusarium, and Rhizopus) through electrostatic attraction, disrupting the membrane potential and permeability, leading to the leakage of key intracellular substances, thereby achieving its broad-spectrum and highly efficient antibacterial effect. This effect has been fully verified in the antibacterial experimental data of Example 2.

[0189] The dual enhancing effect of calcium disodium ethylenediaminetetraacetate: Firstly, as a safe calcium source, it releases calcium ions (Ca... 2+ It can cross-link with pectin substances in fruit cell walls, helping to maintain cell wall structural strength and thus delaying the postharvest softening process; secondly, its excellent chelating ability can selectively bind metal ions (such as Mg) necessary for the stability of microbial cell membranes. 2+ Ca 2+ This disrupts membrane integrity, which, combined with the membrane attack mechanism of chitosan oligosaccharide, produces a significant synergistic effect, jointly enhancing the antibacterial efficacy of the system.

[0190] Citric acid plays a multi-functional role in this system: (a) as an acidity regulator, creating and maintaining the acidic environment required for chitosan oligosaccharide to exert its optimal antibacterial activity; (b) it itself has a low pH stress and acidification damage effect on microbial cells; (c) its chelating properties can further enhance the deprivation of micronutrients from microorganisms, complementing calcium disodium EDTA.

[0191] Film-forming and immobilization functions of PVA: Polyvinyl alcohol (PVA) acts as a film-forming agent, forming a continuous, transparent, and dense physical film on the fruit surface during the drying process in step S2. This film not only directly constitutes a physical barrier to limit pathogen infection and excessive water loss and respiration of the fruit, but more importantly, it effectively encapsulates and immobilizes active ingredients such as chitosan oligosaccharides and calcium disodium EDTA on the fruit peel surface, achieving slow release of active ingredients, thereby prolonging the duration of action and providing continuous preservation protection.

[0192] The ethylene absorber layer employs a composite structure consisting of, from bottom to top, a layer of alumina particles loaded with 6% potassium permanganate, a layer of activated carbon particles impregnated with 4% zinc palmitate, and a layer of zeolite molecular sieves loaded with 3% nano-titanium dioxide. Each layer is physically separated by a stainless steel mesh. This design aims to overcome the limitations of single ethylene scavengers, such as rapid saturation of adsorption capacity, insufficient catalytic efficiency for trace amounts of ethylene, and the deactivation of photocatalysts in dark environments.

[0193] The mechanism by which it synergistically removes ethylene is as follows:

[0194] Chemical oxidation of potassium permanganate layer: Potassium permanganate (KMnO4) supported by alumina particles in the lower layer is a strong oxidant that can decompose ethylene (C2H4) into carbon dioxide and water through irreversible oxidation reaction. This is the main way to remove ethylene and has high capacity and reliability.

[0195] Adsorption and catalysis of activated carbon / zinc palmitate layer: The activated carbon in the middle layer physically adsorbs and enriches ethylene molecules due to its large specific surface area. The impregnated zinc palmitate, as a metal soap catalyst, can catalyze the decomposition reaction of some of the adsorbed ethylene at room temperature and pressure, providing a second removal pathway.

[0196] Photocatalytic oxidation of the zeolite molecular sieve / nano-titanium dioxide layer: The upper zeolite molecular sieve has a regular pore structure, which can selectively adsorb and concentrate ethylene molecules around the supported nano-titanium dioxide (anatase type) catalyst. To activate the photocatalytic activity of the nano-titanium dioxide, in the storage environment of step S3, an emission wavelength of 380 nm and a power density of 1.0 mW / cm² are placed on the sidewall. 2 An LED ultraviolet light source array is used, with the light path precisely configured to horizontally irradiate the bottom of the breathable container. Under this ultraviolet light excitation, nano-titanium dioxide generates electron-hole pairs, which then react with H2O and O2 adsorbed on the surface to generate highly oxidizing hydroxyl radicals (…). ) and superoxide anion ( These active substances can completely degrade enriched ethylene molecules into non-toxic CO2 and H2O. This photocatalytic process constitutes a third efficient and sustainable pathway for ethylene removal.

[0197] The three-stage composite ethylene removal system, in conjunction with the ultraviolet light source, achieves an organic combination of physical adsorption, chemical oxidation, non-photocatalysis, and photocatalysis. This ensures the continuous, efficient, and thorough removal of trace amounts of ethylene released by the fruit throughout the entire storage period, effectively blocking the ripening chain reaction of ethylene.

[0198] The breathable container features ventilation holes with specific opening ratios (35% and 25%, respectively) and pore diameters (4 mm and 3 mm, respectively) on its bottom plate and side walls. The inner surface of the bottom plate has a grid-like distribution of raised support points, 2.5 mm high and spaced 12 mm apart. The container bottom has 6 mm high support legs. This physical structure design is coupled with a forced airflow organization mode of "top-down, 0.2 m / s," solving the problems of uneven storage microenvironment, localized airflow dead zones, and physical damage to the fruit caused by improper container design.

[0199] Its optimization principle is reflected in:

[0200] Optimization of the support structure and airflow channels: The grid-like raised support points stably support the single-layer fruit, creating a uniform gap between the fruit and the container bottom. On the one hand, this avoids direct contact between the fruit and the solid bottom, effectively preventing softening and rotting (pressure damage) of the fruit peel due to long-term static pressure and condensation accumulation; on the other hand, this gap, together with the ventilation holes on the container side walls, bottom, and the bottom space formed by the support legs, constitutes a low-resistance three-dimensional airflow channel network.

[0201] Efficient airflow organization and mass and heat transfer: Driven by a circulating fan, clean, cool air flows downwards at a speed of 0.2 m / s. This airflow first flows evenly over the surface of each fruit, efficiently removing the fruit's respiratory heat, moisture, and released ethylene. The airflow is then forcibly guided through the polypropylene microporous plate and the underlying composite ethylene absorption layer. This directional airflow pattern ensures the uniformity of temperature, humidity, gas composition, and ethylene concentration within the storage space, avoiding the formation of localized hot spots and high-concentration areas. Simultaneously, it significantly enhances the contact efficiency between the airflow and the components of the ethylene absorption layer, promoting the continuous adsorption and reaction processes.

[0202] The test results of Comparative Examples 2 and 3 clearly show that conventional containers without this optimized breathable structure and airflow organization cannot form an effective microenvironment circulation, resulting in accelerated local quality deterioration, low ethylene removal efficiency, and ultimately significantly inferior preservation effect compared to the present invention.

[0203] Although embodiments of the present invention have been disclosed above, they are not limited to the applications listed in the specification and embodiments. They can be applied to various fields suitable for the present invention. Other modifications can be easily made by those skilled in the art. Therefore, without departing from the general concept defined by the claims and their equivalents, the present invention is not limited to the specific details and examples shown and described herein.

Claims

1. A method for inhibiting bacteria and preserving the freshness of fruits with different peels and flesh, wherein the fruits with different peels and flesh are durian, mango, or jackfruit, characterized in that, Includes the following steps: S1. Clean the surface of fruits with different peels and flesh; S2. Completely immerse fruits with different peels and flesh in a compound preservative solution at a temperature of 20℃-25℃ for 4-8 minutes, while maintaining a stirring speed of 20-30 r / min. After immersion, remove and dry the fruits to form a compound preservative film on their surface. The compound preservative solution includes 0.1%-2% chitosan oligosaccharide, 0.1%-2% calcium disodium EDTA, 0.05%-1% citric acid, and 0.1%-1% PVA by mass fraction. The solvent is drinking water, and the pH value is adjusted to 5.0-6.

0. S3. After film formation, place the fruits (with different skins and flesh) in a single layer in a breathable container and transfer them to a storage environment with a temperature of 10℃-15℃ and a relative humidity of 80%-90%. The bottom of the breathable container is lined with an ethylene absorption layer, which consists of a lower layer of alumina particles loaded with 5%-8% potassium permanganate solution, a middle layer of activated carbon particles impregnated with 3%-5% zinc palmitate solution, and an upper layer of zeolite molecular sieves loaded with 2%-4% nano-titanium dioxide. Each layer is separated by a stainless steel mesh. A polypropylene microporous plate is placed between the ethylene absorption layer and the fruits. The sidewalls of the storage environment are equipped with LED ultraviolet light sources with an emission wavelength of 365-395nm and a power density of 0.5-2.0mW / cm³. 2 ; In step S1, the surface cleaning is carried out by atomized spraying with a pressure of 0.15-0.20 MPa, a spray water temperature of 15℃-20℃, and a spraying time of 1-2 min. After surface cleaning, before step S2, soak fruits with different peels and flesh in a pretreatment solution for 30-60 seconds at a soaking temperature of 20℃-25℃. Then rinse the fruit surface with drinking water for 5-10 seconds and drain. The pretreatment solution includes an aqueous solution of 0.05%-0.2% by mass of food-grade nonionic surfactant and 0.5%-1.5% of potassium dihydrogen phosphate-dipotassium hydrogen phosphate buffer system, with the pH value adjusted to 7.5-8.

5. In step S3, the ventilated container has multiple vent holes on its bottom plate and side walls. The vent holes on the bottom plate have an opening rate of 30%-40% and a diameter of 3-5mm. The vent holes on the side walls have an opening rate of 20%-30% and a diameter of 2-4mm. The inner surface of the bottom plate has multiple raised support points distributed in a grid pattern. The grid unit spacing is 10-15mm and the support point height is 2-3mm. The bottom of the ventilated container has support feet with a height of 5-8mm. The side wall of the ventilated container has at least 4 symmetrically distributed vent windows near the top.

2. The method for antibacterial preservation of fruits with different skins and flesh as described in claim 1, characterized in that, The drying method involves placing the air in a clean airflow at 15℃-25℃ with a wind speed of 2.0-4.0m / s for 10-12 minutes. The clean airflow is filtered through a high-efficiency air filter with a filtration accuracy of 0.22μm, and the relative humidity of the airflow is controlled at 45%-55%.

3. The method for antibacterial preservation of fruits with different skins and flesh as described in claim 1, characterized in that, In step S3, the oxygen volume fraction in the storage environment is maintained at 5%-8%, and the carbon dioxide volume fraction is maintained at 3%-5%.

4. The method for antibacterial preservation of fruits with different skins and flesh as described in claim 1, characterized in that, In step S3, the mass ratio of the alumina particle layer, the activated carbon particle layer, and the zeolite molecular sieve layer is (2.5-3.5):(1.5-2.5):1, and the total thickness of the ethylene absorption layer is 20-30 mm.

5. The method for antibacterial preservation of fruits with different skins and flesh as described in claim 1, characterized in that, An ethylene concentration monitoring system and a circulating fan are installed in the storage environment. When the ethylene concentration exceeds 0.05 μL / L, the circulating fan is activated to circulate the air.

6. The method for antibacterial preservation of fruits with different skins and flesh as described in claim 5, characterized in that, The airflow from the circulating fan in the storage environment flows from top to bottom, passing over the fruit and then through the ethylene absorption layer, with an airflow velocity of 0.1-0.3 m / s.

7. The method for antibacterial preservation of fruits with different skins and flesh as described in claim 1, characterized in that, A removable non-woven fabric liner is laid on the upper surface of the polypropylene microporous plate.

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