Method for extracting fruit and vegetable cuticle wax

Abstract

The application provides a fruit and vegetable skin wax extraction method, comprising the following steps: S1: coating a composite functional coating on the surface of fruit and vegetable raw materials to obtain coated fruit and vegetable materials; the composite functional coating comprises a water-soluble film-forming polymer and an inert micro-nano ceramic material; S2: placing the coated fruit and vegetable materials in an inert gas environment to perform low-temperature plasma treatment on the skin of the fruit and vegetable materials to obtain fruit and vegetable materials with etched surfaces; S3: immersing the fruit and vegetable materials with etched surfaces in a wax selective solvent to perform wax extraction to obtain a wax extraction solution; the wax selective solvent is an organic solvent that does not dissolve the film-forming polymer; and S4: filtering the wax extraction solution, drying the filtrate, and obtaining wax. The application can solve the technical problems of the existing fruit and vegetable wax extraction method, i.e., the damage of the fruit and vegetable surface wax is relatively large, and the purity and extraction efficiency are relatively low.

Description

Technical Field

[0001] This invention relates to the field of plant natural component extraction technology, and in particular to a method for extracting waxy substances from the skin of fruits and vegetables. Background Technology

[0002] The natural waxy layer on the surface of fruits and vegetables is a complex mixture composed of long-chain fatty acids, alkanes, alcohols, aldehydes, esters, etc. It is the first barrier for plants to cope with the external environment and plays a vital role in maintaining fruit water balance, preventing pathogen infection, and regulating post-harvest quality. High-complete extraction and analysis of the waxy components and structure are fundamental to in-depth research on its physiological functions and the development of its high-value applications in food preservation, cosmetics, and fine chemicals.

[0003] However, while various methods exist for extracting waxes from fruit and vegetable peels, such as solvent extraction, Soxhlet extraction, high-temperature melting, and mechanical scraping, they all have limitations in terms of extraction efficiency, product purity, and protection of the original wax structure. For example, solvent extraction, the most commonly used method, often uses large amounts of highly polar solvents, extends processing time, or employs high temperatures to maximize extraction rates. This not only results in high wastewater treatment costs and significant environmental pressure but also leads to solvent molecules embedding or interacting with certain wax components, altering the wax structure. Furthermore, it can cause the dissolution of large amounts of lipophilic impurities, such as pigments and terpenes, from the fruit and vegetable peel / flesh cells, leading to a complex composition and low purity of the wax extract, making subsequent purification and precise analysis difficult. Conversely, because the wax layer is firmly bonded to the epidermal cells, using mild conditions to protect the wax structure makes it difficult to effectively extract the inner wax layer that is tightly bound to the cells, resulting in severely low extraction rates and missing wax components. Therefore, it is difficult to achieve both extraction efficiency and product purity simultaneously.

[0004] Extraction methods such as Soxhlet extraction use continuous heating and reflux for extraction, and the entire process may last for several hours or even tens of hours. This is time-consuming and energy-intensive, and it inevitably causes the heat-sensitive components in the wax (such as some unsaturated esters and aldehydes) to degrade or oxidize, resulting in its chemical composition deviating from its natural state and causing structural damage.

[0005] In addition, there are high-temperature melting methods that separate waxes by melting them at high temperatures, and mechanical scraping methods that involve scraping directly with a scraper. While the high-temperature melting method is direct, it is extremely destructive. High temperatures significantly accelerate the oxidation, polymerization, and isomerization reactions of wax components, destroying their natural conformation and biological activity. The extracted wax becomes darker in color, its functionality is severely reduced, and its properties are drastically altered. Mechanical scraping is time-consuming and labor-intensive, and its extraction effect is heavily dependent on the operator's skill level. It is easy to mix in epidermal cell fragments and even fruit pulp tissue, especially when processing fruits with easily damaged surfaces such as plums and grapes, as well as fruits with uneven skin such as cantaloupes. This introduces a large amount of non-waxy impurities (if it is fruit pulp), resulting in lower product purity and extraction efficiency.

[0006] In summary, there is an urgent need for a wax extraction method that can gently and efficiently separate waxes from the surface of fruits and vegetables while minimizing damage to the molecular structure of the waxes, in order to obtain wax products that are closer to their natural state and lay a reliable foundation for subsequent functional research and applications. Summary of the Invention

[0007] (a) Technical problems to be solved

[0008] In view of the above-mentioned shortcomings and deficiencies of the prior art, the present invention provides a method for extracting wax from the surface of fruits and vegetables, which solves the technical problems of large damage, low purity and low extraction efficiency of the wax extracted from the surface of fruits and vegetables in the prior art.

[0009] (II) Technical Solution

[0010] To achieve the above objectives, the main technical solutions adopted by the present invention include:

[0011] This invention provides a method for extracting wax from the skin of fruits and vegetables, comprising the following steps:

[0012] S1: A composite functional coating is applied to the surface of fruit and vegetable raw materials to obtain a film-coated fruit and vegetable material; the composite functional coating contains a water-soluble film-forming polymer and an inert micro-nano ceramic material;

[0013] S2: The coated fruit and vegetable material is placed in an inert gas environment and its skin is subjected to low-temperature plasma treatment to obtain fruit and vegetable material with surface etching.

[0014] S3: Immerse the surface-etched fruit and vegetable materials in a wax-selective solvent to extract the wax and obtain a wax extract; the wax-selective solvent is an organic solvent that does not dissolve film-forming polymers;

[0015] S4: Filter the wax extract and dry the filtrate to obtain the wax.

[0016] According to a preferred embodiment of the present invention, in S1, the film-forming polymer includes at least one of sodium alginate, gellan gum, chitosan, xanthan gum, polyvinyl alcohol, polyethylene oxide, cellulose and its derivatives, and guar gum and its derivatives; the micro / nano ceramic material includes at least one of nano- and / or submicron-sized zirconium oxide particles, alumina particles, titanium dioxide particles, and zinc oxide particles; the dielectric constant of the micro / nano ceramic material is greater than the dielectric constant of the film-forming polymer.

[0017] According to a preferred embodiment of the present invention, in S1, the fruit and vegetable raw materials are immersed in a coating solution containing a film-forming polymer, micro-nano ceramic materials and water, and then dried and cured to obtain coated fruit and vegetable materials; the viscosity of the coating solution is 500-3000 mPa·s; the mass ratio of the film-forming polymer, micro-nano ceramic materials and water in the coating solution is 1-8:0.1-1:80-120.

[0018] According to a preferred embodiment of the present invention, in S1, the thickness of the composite functional coating is 1-5 micrometers; the particle size of the micro-nano ceramic material is 10-200 nm, and the dielectric constant is not less than 12; the dielectric constant of the film-forming polymer is not more than 8; and the fruit and vegetable raw materials are at least one of whole fruits and vegetables, partially damaged fruits and vegetables, and the peel of fruits and vegetables.

[0019] According to a preferred embodiment of the present invention, in S2, the gas in the inert gas environment includes at least one of nitrogen, argon, and helium;

[0020] The low-temperature plasma treatment is a low-frequency low-temperature plasma treatment with a frequency of 5-15kHz, a duty cycle of 10%-50%, a discharge time of 40-240s, and a power density of 0.5-4W / cm³. 2 The surface temperature of the coated fruit and vegetable materials is 30℃-60℃.

[0021] According to a preferred embodiment of the present invention, in S3, the wax-based selective solvent includes at least one selected from ethyl acetate, n-hexane, butyl acetate, ethyl lactate, ethyl levulinate, valerate, dimethyl carbonate, dichloromethane, chloroform, toluene, xylene, and tetrahydrofuran.

[0022] According to a preferred embodiment of the present invention, in S3, the wax selective solvent is a mixed solution of ethyl acetate and n-hexane, and the volume ratio of ethyl acetate to n-hexane is 7-9:3-5.

[0023] According to a preferred embodiment of the present invention, in S3, the mass-to-volume ratio of the surface-etched fruit and vegetable material to the waxy selective solvent is 1 kg: 2-4 L, and the extraction time is 100-300 s.

[0024] According to a preferred embodiment of the present invention, in S3, during wax extraction, intermittent ultrasonic oscillation is used as an auxiliary treatment. The power of the ultrasonic oscillation is 250-350W, the frequency is 20-40kHz, and the intermittent mode is to stop for 1-3 seconds after each oscillation.

[0025] According to a preferred embodiment of the present invention, in S4, the obtained wax extract is filtered to remove solid impurities, resulting in a filtrate containing wax. The wax-selective solvent in the filtrate is then removed to obtain the wax.

[0026] (III) Beneficial Effects

[0027] The beneficial effects of this invention are as follows: The method for extracting wax from the peel of fruits and vegetables of this invention adopts a technical solution of first constructing a composite functional coating with protective properties on the surface of the fruits and vegetables to be extracted, and then using low-temperature plasma treatment and organic solvent extraction. Compared with the prior art, it can completely and cleanly separate the wax from the surface of fruits and vegetables while minimizing damage to the natural wax structure, thus achieving efficient, high-integrity and high-purity wax extraction.

[0028] Specifically, before extracting the wax, this invention first applies a composite functional coating consisting of a film-forming polymer and micro / nano ceramic materials to the surface of fruits and vegetables. During plasma treatment, this composite functional coating, or rather, the energy absorbed and evenly dispersed by the plasma bombardment, weakens the physical bonding force within the wax layer and its adhesion to the epidermal substrate. This loosens the wax layer structure on the fruit and vegetable surface, improving extraction efficiency and preventing the chemical structure of the wax components from being damaged by direct plasma bombardment. Furthermore, since the plasma treatment of fruits and vegetables is performed on the epidermis, the untreated composite functional coating remains intact, thus hindering contact between the selective solvent for wax and the non-epidermal portion during subsequent extraction. This reduces impurities that may dissolve from the fruits and vegetables during extraction, improving the purity of the extracted wax.

[0029] The micro / nano ceramic materials in the composite functional coating, through their high hardness and dielectric constant, can guide and concentrate the energy of plasma bombardment, causing the plasma to erode through the film-forming polymer surrounding the micro / nano ceramic materials and the underlying wax layer. This forms interconnected microchannels within the composite functional coating and the wax layer, creating a porous structure. During solvent extraction, the wax-selective solvent can bypass the dense structure of the wax layer along these microchannels and directly penetrate deep into the wax layer. This significantly improves the efficiency of the wax-selective solvent in contacting and dissolving the wax, thereby enhancing the extraction effect and efficiency of this invention. Furthermore, it avoids excessive extraction time leading to the dissolution of large amounts of intracellular substances, further improving the purity of the extracted wax.

[0030] Furthermore, since this invention selects a wax-selective solvent that does not dissolve the film-forming polymer matrix for wax extraction, this solvent is generally non-polar or weakly polar organic. During the extraction process, the film-forming polymer itself will not dissolve in the wax-selective solvent and form impurities, thus not affecting the purity of the wax extracted by this invention. Simultaneously, since the micro / nano ceramic material is an inert, insoluble inorganic material, it will not affect the purity of the wax extracted by this invention.

[0031] This invention combines film-forming polymers and micro / nano ceramic materials in a composite functional coating with low-temperature plasma treatment and non-polar wax selective solvents. This ensures high extraction efficiency and purity without involving any high-temperature treatment or highly polar environment, and minimizes the damage to the wax structure caused by plasma bombardment, resulting in a wax with high integrity. Detailed Implementation

[0032] To better explain and facilitate understanding of the present invention, the present invention will be described in detail below through specific embodiments.

[0033] This invention provides a method for extracting wax from the skin of fruits and vegetables, comprising the following steps:

[0034] S1: A composite functional coating is applied to the surface of fruit and vegetable raw materials to obtain a film-coated fruit and vegetable material; the composite functional coating contains a water-soluble film-forming polymer and an inert micro-nano ceramic material;

[0035] S2: The coated fruit and vegetable material is placed in an inert gas environment and its skin is subjected to low-temperature plasma treatment to obtain fruit and vegetable material with surface etching.

[0036] S3: Immerse the surface-etched fruit and vegetable materials in a wax-selective solvent to extract the wax and obtain a wax extract; the wax-selective solvent is an organic solvent that does not dissolve film-forming polymers;

[0037] S4: Filter the wax extract and dry the filtrate to obtain the wax.

[0038] This invention achieves efficient, high-purity, and low-damage wax extraction by combining a composite functional coating constructed on the surface of fruit and vegetable raw materials with low-temperature plasma treatment. It is suitable for research extraction of wax from the surface of fruits and vegetables, especially for the extraction of wax from the surface of fruits such as plums, pears, cantaloupes, red dates, and green walnuts, which have thick wax, high cuticle content, and strong wax layer bonding, as well as the extraction of wax from the surface of berries such as grapes and blueberries, whose skins are easily damaged and whose contents are easily leaked.

[0039] Specifically, in S1, the present invention utilizes a water-soluble film-forming polymer with good film-forming properties to form a continuous and uniform coating on the surface of fruits and vegetables. The film-forming polymer is used to load nano- or submicron-sized ceramic particles to form a composite functional coating and to create weak points in the composite functional coating.

[0040] In S2, during low-temperature plasma treatment (referred to as plasma treatment), the composite functional coating is first bombarded by the plasma. The film-forming polymer in the coating absorbs and consumes most of the particle kinetic and chemical energy through etching processes such as molecular chain breakage, cross-linking, or volatilization. This effectively buffers and physically isolates the underlying natural wax layer, ensuring that the wax layer itself is protected from direct bombardment by high-energy particles and preventing direct damage to the chemical bonds of the wax molecules by the plasma, thus protecting the integrity of its chemical structure. Simultaneously, some of the energy generated by the plasma bombardment of the coating is transferred to the wax layer through the coating in the form of reduced mechanical vibration and heat. This buffered energy transfer is insufficient to cause thermal degradation or chemical changes in the wax components, but it effectively weakens the physical bonding forces between the layers within the wax layer, as well as the adhesion between the wax layer and substances such as keratin. This also makes the physical structure of the wax layer more loosely structured, ensuring more efficient extraction during subsequent solvent extraction.

[0041] Meanwhile, in S2, the composite functional coating is not uniformly etched under the uniform bombardment of plasma on its surface. Compared to the film-forming polymer, the inert micro / nano ceramic material has relatively high hardness and chemical stability, and there are significant differences in its electrical conductivity, dielectric constant, and other properties, resulting in a much lower etching rate for the micro / nano ceramic material compared to the film-forming polymer. During the etching process, the micro / nano ceramic material, acting as a hard barrier that is difficult to etch, provides a certain degree of physical shielding to the polymer region directly below it, reducing the direct bombardment received by the micro / nano ceramic material. However, this also causes the plasma to scatter after impacting the micro / nano ceramic material and to generate electric field distortion within the micro / nano ceramic material itself, forming concentrated areas of energy and active particles at the particle edges and sides, leading to faster etching rates in these areas. In addition, the physical interface between the rigid, inorganic micro / nano ceramic material and the flexible, organic film-forming polymer is itself a region with many microscopic defects and relatively weak bonding, i.e., a weak point, making it easy for the plasma to rapidly advance downwards along the particle edge interface, further etching to form channels. The combined action of numerous micro- and nano-ceramic materials in the composite functional coating creates a large number of micropores in both the composite functional coating and the wax layer, transforming the plasma-treated composite functional coating and the underlying wax layer into a porous structure.

[0042] When micro / nano ceramic materials with high dielectric constants are selected, they will also generate significant polarization in the plasma electric field, resulting in a significant enhancement of the local electric field at the particle edges and tips or severe distortion. This attracts and accelerates more charged particles (plasma) to bombard the interface region, thereby greatly enhancing the etching speed and efficiency of plasma on the film-forming polymers and / or waxes around the micro / nano ceramic materials, and dominating the direction of the etching process. This ensures the formation of a composite functional coating that starts from the particle edges, runs through the thickness direction, and extends to the wax layer, especially the micropores that penetrate the surface wax layer.

[0043] In S3, during the wax extraction process using a wax-selective solvent, the micropores formed in S2 provide a dissolution path for the wax-selective solvent to bypass the dense wax surface. This allows the wax-selective solvent to quickly contact and dissolve deep waxes, and to diffuse and transport along the micropores over short distances, resulting in high mass transfer efficiency and extraction rate. It can quickly penetrate and dissolve deep waxes, and the composite functional coating, which has not been etched by plasma, will not be damaged by etching. It can remain intact during the extraction process in S3, limiting the large-area lateral spread of the wax-selective solvent on the fruit and vegetable epidermis. This effectively reduces the contact area between the wax-selective solvent and non-waxy tissues such as epidermal cells, thereby inhibiting the dissolution of intracellular impurities.

[0044] In S4, due to the solubility mismatch between the film-forming polymer and the selective solvent for wax, the composite functional coating itself does not dissolve during extraction, avoiding the introduction of impurities. Even if it breaks down and produces debris under etching, it can be removed by subsequent filtration. The chemical inertness of the micro / nano ceramic material also ensures that it will not contaminate the final extracted wax, and can also be removed by filtration.

[0045] Preferably, in S1, the dielectric constant of the micro / nano ceramic material is greater than that of the film-forming polymer. This ensures a difference in dielectric constant between the micro / nano ceramic material and the film-forming polymer, ensuring that the micro / nano ceramic material can induce significant local electric field changes during plasma processing, and ensuring the precise and controllable formation of the micropore structure.

[0046] In S1, the film-forming polymer is a water-soluble, or rather, hydrophilic, organic polymer material or its composition, ensuring that it does not dissolve in the selective solvent for waxes and thus avoids contaminating the wax. Preferably, in S1, the film-forming polymer includes at least one of sodium alginate, gellan gum, chitosan, xanthan gum, polyvinyl alcohol, polyethylene oxide, cellulose and its derivatives, and guar gum and its derivatives. In actual operation, materials and combinations thereof can be selected from the above raw materials as needed. These materials all possess good water solubility and film-forming properties and are insoluble in selective solvents for waxes.

[0047] Furthermore, to reduce unnecessary adhesion between the composite functional coating and the wax layer, and to avoid excessive bonding that could hinder subsequent wax separation, a polymer with moderate viscosity and safety after film formation should be selected. More preferably, the film-forming polymer is sodium alginate or gellan gum. Both have simple compositions, good film-forming effects, and are edible polysaccharides of natural or biological origin, non-toxic and harmless. The viscosity of their aqueous solutions can also be precisely controlled by selecting products with different viscosity specifications and adjusting the amount added.

[0048] Micro- and nano-ceramic materials need to possess high hardness and chemical inertness to ensure effective plasma guidance during low-temperature plasma treatment and to guarantee etching results. In this invention, preferably, in S1, the micro- and nano-ceramic material is a nano- and / or submicron-sized oxide ceramic, preferably at least one of nano- and / or submicron-sized zirconium oxide particles, alumina particles, titanium dioxide particles, silica particles, zinc oxide particles, and calcium titanate ceramic particles. More preferably, at least one of zirconium oxide particles, alumina particles, titanium dioxide particles, silica particles, and zinc oxide particles. Selecting a single metal oxide ceramic as the micro- and nano-ceramic material generally results in high purity, high hardness, chemical stability, and dielectric constant, enabling more effective directional etching of composite functional coatings and wax layers, ensuring the formation of micropores.

[0049] More preferably, the micro / nano ceramic material is at least one of zirconium oxide particles and titanium dioxide particles. Among them, zirconium oxide and titanium dioxide have high dielectric constants and good biocompatibility, and can more efficiently attract and converge plasma in the alternating electric field of low-temperature plasma, or in other words, converge charged particles, further ensuring that a well-defined and uniformly distributed microporous network can be formed during plasma treatment, penetrating the coating and extending into the interior of the wax layer.

[0050] It should be noted that in actual operation, the appropriate micro / nano ceramic materials can be selected according to the specific experimental purpose or subsequent operation arrangements. If it is necessary to reuse the fruit and vegetable raw materials that have undergone wax extraction using the method of this invention, such as in food-related research or transformation, especially when whole fruits and vegetables are selected as raw materials, although the composite functional coating of this invention can separate from the surface of the fruit and vegetable raw materials after wax extraction, to ensure safety, food-grade high-purity oxide ceramics should be selected to ensure that they are safe to contact with food. Preferably, submicron level alumina particles, zirconium oxide particles, titanium dioxide particles, and zinc oxide particles with a particle size greater than 100 nm and less than 1 micron are selected. These materials are effective but generally not absorbed by the human body, have no obvious toxic effects, and have relatively high safe dosages. When biotransformation is not considered at all, nano- and / or submicron level calcium titanate ceramic particles can also be used as micro / nano ceramic materials, which have higher dielectric constants and can more effectively improve etching efficiency and micropore formation effect.

[0051] Preferably, in step S1, the fruit and vegetable raw materials are immersed in a coating solution containing a film-forming polymer, micro / nano ceramic materials, and water for a certain period of time. After removal, the coated fruit and vegetable materials are obtained. The selected organic polymer material has good film-forming properties and is insoluble in wax-based selective solvents, allowing its molecular chains to fully extend in water. When the fruit and vegetable raw materials are immersed in the coating solution, the polymer molecules and the uniformly dispersed micro / nano ceramic materials adhere to the fruit and vegetable surface. After removal, as water further evaporates, a continuous gel-like or solid film encapsulating the micro / nano ceramic materials is spontaneously formed, providing preliminary covering and isolation effects.

[0052] Preferably, in step S1, the micro / nano ceramic material and water are first mixed and subjected to a first ultrasonic dispersion to obtain a micro / nano ceramic dispersion. Then, the film-forming polymer is immediately mixed with the micro / nano ceramic dispersion and subjected to a second ultrasonic dispersion to obtain a coating solution. By controlling the mixing sequence and using continuous ultrasonic dispersion, it is ensured that the micro / nano ceramic material can be evenly distributed in the coating solution without the addition of dispersants or other materials. More preferably, after obtaining the coating solution, the fruit and vegetable raw materials are quickly immersed in the coating solution for coating to avoid problems such as sedimentation of the micro / nano ceramic material, which could affect the forming effect of the composite functional coating and lead to uneven distribution of the micro / nano ceramic material inside.

[0053] More preferably, in step S1, the fruit and vegetable raw materials are immersed in the coating solution for a certain period of time, then removed and dried to allow the film-forming polymer on them to solidify, thus completing the coating process and obtaining the coated fruit and vegetable raw materials. Drying can be done using ambient temperature ventilation or hot air drying. When using hot air drying, the temperature should not exceed 50°C, and the drying time can be determined according to actual conditions, ensuring that the composite functional coating is dried and formed. Through drying and curing, the moisture in the coating solution is completely evaporated, ultimately solidifying into a continuous, solid composite functional coating, and the micro / nano ceramic materials are firmly embedded or inlaid in the polymer. The dried and cured composite functional coating has a more stable microstructure and better mechanical strength, enabling it to more uniformly and effectively withstand and disperse energy during subsequent low-temperature plasma treatment, and serving as a more effective physical barrier in step S3 when extracting wax, ensuring its structural integrity and functional reliability.

[0054] More preferably, the fruit and vegetable raw materials are immersed in the coating solution for no less than 10 seconds to ensure that the fruit and vegetable skins can be fully wetted by the coating solution, so that the water-soluble film-forming polymer molecules and micro-nano ceramic materials have enough time to diffuse and adhere to the skin surface, ensuring that a continuous and defect-free composite functional coating can be formed subsequently.

[0055] This invention does not impose a strict upper limit on the soaking time of fruit and vegetable raw materials. In practice, provided that the raw materials do not undergo tissue softening, rotting, or deterioration during soaking and subsequent processing, which would negatively impact their integrity and the effectiveness of subsequent extraction, the upper limit of the soaking time can be flexibly adjusted according to the type, physiological state, and environmental conditions of the raw materials. For example, for fruits and vegetables with dense, uneven, and easily damaged skin, such as cantaloupe, the soaking time can be appropriately extended to ensure sufficient coverage by the coating solution. For fruits and vegetables with regular, delicate skin that are easily perishable, such as blueberries, the next processing step should be carried out as soon as possible.

[0056] Preferably, in S1, before immersing the fruit and vegetable raw materials in the coating solution, the raw materials need to be washed and dried to ensure that the surface of their wax layer is clean.

[0057] Preferably, in step S1, when immersing the fruit and vegetable raw materials in the coating solution, a vibration treatment is also required. This vibration treatment can be conventional mechanical vibration, such as horizontal reciprocating or rotary vibration at a frequency of 1-5 Hz, or low-frequency ultrasonic vibration, such as ultrasonic vibration at a frequency of 20-40 kHz and a power of 50-200 W. The vibration treatment removes air bubbles adhering to the surface of the fruit and vegetables and in the coating solution, while simultaneously promoting the flow of the coating solution along complex surface contours, and further ensuring the uniform distribution of the micro / nano ceramic materials, thus ensuring the formation of a composite functional coating with uniform thickness and uniform dispersion of ceramic particles. The specific vibration intensity and duration are determined based on actual conditions, ensuring effective defoaming without damaging the surface of the fruit and vegetable raw materials.

[0058] Preferably, in step S1, the viscosity of the coating solution is 500-3000 mPa·s, more preferably 1000-1800 mPa·s, ensuring that the coating solution can fully wet the complex surface and form a continuous coating of suitable thickness. Too low a viscosity may result in insufficient adhesion of the coating solution, failing to form a continuous and complete film. Too low a viscosity may also lead to uneven coating distribution and problems such as cracking.

[0059] Preferably, in S1, the mass ratio of the film-forming polymer, micro / nano ceramic material, and water in the coating solution is 1-8:0.1-1:80-120, more preferably 2-5:0.1-1:80-100. It is important to note that while adjusting the mass ratio of the film-forming polymer to water to ensure the viscosity and film-forming effect of the coating solution, it is also necessary to control the ratio of the film-forming polymer to the micro / nano ceramic material. This avoids situations where the content of the micro / nano ceramic material is too low, resulting in sparse etching sites during subsequent processing and insufficient micropores, leading to a significant decrease in extraction efficiency. Conversely, excessive content can cause particle agglomeration, affecting the uniformity of the composite functional coating and interfering with the normal interface etching process, potentially leading to problems such as the inability to form micropores.

[0060] Preferably, in S1, the thickness of the composite functional coating is 0.5-10 micrometers, more preferably 1-5 micrometers. If the thickness of the composite functional coating is too thin, such as less than 1 micrometer, the possibility of coating discontinuity gradually increases, which may result in insufficient energy buffering and barrier layer effects, and its reliability is also lower. If the coating thickness is too high, such as greater than 5 micrometers, although the composite functional coating can provide more adequate protection, the intensity or duration of the subsequent plasma treatment in S2 needs to be significantly increased to achieve effective penetrating etching, and its effect on the physical loosening of the wax will gradually decrease. This will increase the corresponding process energy consumption and time costs, and the thick film is more prone to defects during drying and curing.

[0061] Preferably, in S1, the particle size of the micro / nano ceramic material is 10-200 nm, more preferably 100-200 nm. The particle size of a single micro / nano ceramic material needs to be smaller than the thickness of the composite functional coating to ensure that the micro / nano ceramic material can be uniformly dispersed and embedded in the polymer. Simultaneously, it is also necessary to avoid excessively small particle sizes of the micro / nano ceramic material to ensure that it can efficiently guide plasma energy to generate localized etching rather than causing uniform etching, and to ensure that the pore size of the final microchannels is not too small, thus affecting mass transfer.

[0062] Preferably, in S1, the dielectric constant of the micro / nano ceramic material is not less than 12, and the dielectric constant of the film-forming polymer is not more than 8. It is necessary to ensure a sufficiently large difference in dielectric constant between the two materials to ensure that the micro / nano ceramic material has sufficient ability to guide the plasma for directional etching during plasma treatment, thus ensuring the stable formation of micropores.

[0063] Preferably, in S1, the fruit and vegetable raw materials are at least one of whole fruits and vegetables, partially damaged fruits and vegetables, and fruit and vegetable peels. This invention can extract wax from various forms of waxy fruit and vegetable raw materials. It should be noted that partially damaged fruits and vegetables refer to fruits and vegetables with partial defects due to rot, mold, or mechanical damage. Mechanically damaged fruits and vegetables can still have their wax extracted using the method of this invention. If extraction is to be performed on fruits and vegetables with defects caused by non-mechanical reasons such as mold or rot, these parts need to be removed (cut off) first to avoid contaminating the coating solution or affecting the wax extraction effect. The fruit and vegetable peel refers to the peel removed from whole or partially damaged fruits and vegetables by methods such as cutting or peeling, such as the peel of a cantaloupe obtained by cutting.

[0064] Preferably, in S2, the inert gas environment includes at least one of nitrogen, argon, and helium. It should be noted that in S2, since the plasma treatment is performed under an inert atmosphere, etching is primarily achieved through bombardment by high-energy particles. This avoids adverse chemical reactions such as film polymerization and severe oxidation or degradation of the wax itself, and prevents the generation of substances that contaminate the wax, effectively ensuring the purity of the wax obtained by this invention. Furthermore, during the etching process that forms micropores, the etching effect of the plasma on the wax is strictly limited to an extremely small local space guided by the micro / nano ceramic material. Only a very small portion of the wax within the ultimately formed micropores is affected by etching, while the wax in the vast majority of the area between and below the micropores remains intact under the protection of the composite functional coating, which effectively buffers and isolates the wax.

[0065] More preferably, the oxygen content in the inert gas environment is not higher than 5%, and more preferably not higher than 2%, to ensure that the oxygen content in the inert gas environment of S2 is at a low level, suppress possible oxidation side reactions, and avoid problems such as excessive oxidation of wax or film-forming polymer, which would affect the purity of the wax extracted by the present invention.

[0066] Preferably, in S2, during processing, only the portions of the coated fruit and vegetable material (hereinafter referred to as fruit and vegetable material) from which wax needs to be extracted are subjected to low-temperature plasma treatment. For example, by adjusting the fixed angle of the nozzle in the plasma generator and its relative position to the surface of the fruit and vegetable material, the plasma can bombard only the epidermal area from which wax needs to be extracted after generation, minimizing the impact on non-target areas such as stems, fruit stalk depressions, the side of the removed peel near the pulp, and areas with fruit defects or mechanical damage. This further reduces process energy consumption and avoids unnecessary physical or physiological impacts on the non-epidermal tissues of the fruit and vegetables. At the same time, the composite functional coating in the areas not treated by plasma can remain intact, effectively preventing the contact between the wax selective solvent and non-target areas, thus avoiding impurities in these areas. If cell fragments, hydrophilic or lipophilic contents within the cells (such as sugars, organic acids, pigments, proteins, etc.) and soluble components between the pulp tissues are dissolved in the wax selective solvent, the purity of the wax extracted by this invention is ensured.

[0067] Preferably, in S2, the low-temperature plasma treatment is a low-frequency low-temperature plasma treatment with a frequency of 5-15kHz and a duty cycle of 10%-50%, resulting in a surface temperature of 30℃-60℃ for the coated fruit and vegetable materials. The selection of a treatment frequency of 5-15kHz, where the plasma generated in the kHz low-frequency stage has higher physical impact and etching capabilities compared to plasma generated at MHz high frequencies, ensures etching effectiveness while also applying a stronger impact to the wax layer under the protection of the composite functional coating, resulting in a looser structure of the wax layer. Simultaneously, the lower treatment frequency, combined with the 10%-50% duty cycle selected in this invention (equivalent to 50%-90% of the time being in an off state during plasma treatment), effectively reduces heat accumulation on the fruit surface, effectively controls the surface temperature of the coated fruit and vegetable materials, and prevents damage to the wax layer due to excessively high surface temperatures.

[0068] More preferably, in S2, during low-temperature plasma treatment, the discharge time is 40-240 seconds, the treatment distance is 8-12 cm, the treatment voltage is 120-180 V, and the power density is 0.5-4 W / cm². 2The working air pressure is 100-500 Pa, and the gas flow rate is 0.01-5 L / min. It should be noted that the above range is only the preferred range of the present invention. In actual operation, more appropriate plasma treatment parameters can be selected according to the specific thickness and composition of the composite functional coating and the specific plasma treatment equipment selected. This can ensure that the plasma has sufficient energy to erode the composite functional coating and form an effective microporous network in the wax layer, and ensure that the surface temperature of the coated fruit and vegetable material is always controlled within a low temperature range of 30℃-60℃ to avoid heat damage to the wax.

[0069] Preferably, in step S3, the selective solvent for the wax is a non-polar or weakly polar solvent, or a mixture of both. It is preferably composed of at least one of ethyl acetate, n-hexane, butyl acetate, ethyl lactate, ethyl levulinate, valerate, dimethyl carbonate, dichloromethane, chloroform, toluene, xylene, and tetrahydrofuran. This solvent has good solubility for the components of the wax (long-chain alkanes, alcohols, aldehydes, esters, etc.), but does not dissolve water-soluble film-forming polymers, or its solubility is extremely low, preventing the coating itself from dissolving as an impurity. In practice, the solvent can be selected and combined from the above sources according to the specific circumstances to ensure effective dissolution.

[0070] More preferably, in S3, the wax-selective solvent is at least one selected from ethyl acetate, dimethyl carbonate, n-hexane, ethyl levulinate, ethyl lactate, and valproic acid. These solvents have low toxicity and high biodegradability, which can effectively reduce the potential health hazards to operators during the extraction process, and reduce the difficulty of subsequent waste liquid treatment and the potential negative impact on the environment.

[0071] More preferably, in S3, the wax-selective solvent is a mixed solution of ethyl acetate and n-hexane, with a volume ratio of ethyl acetate to n-hexane of 7-9:3-5. Hexane, as a non-polar solvent, has a strong dissolving ability for long-chain alkanes and other components in waxes; ethyl acetate, a weakly polar ester solvent with a certain degree of polarity, has a good dissolving ability for esters, alcohols, and other slightly more polar components in waxes. The mixture of the two in the above ratio can produce a strong synergistic effect, resulting in an extraction effect significantly higher than that of conventional single or mixed solvents. It can also broaden the dissolution range and effect of the wax-selective solvent of this invention on complex wax components, achieving more complete and efficient extraction. This makes the extracted wax components more comprehensive and has a faster dissolution rate without the need for heating.

[0072] Preferably, in step S3, the mass-to-volume ratio of the surface-etched fruit and vegetable material to the wax-selective solvent is 1 kg: 2-4 L, and the extraction time is 100-300 s. It is crucial to control the amount of wax-selective solvent used, ensuring sufficient solvent to fully wet, penetrate, and dissolve the wax released from the micropores while avoiding excessive use and waste. The extraction time needs to be determined based on the specific fruit and vegetable species, the estimated thickness of the wax layer, and prior experimental results (if any). Too short a time may prevent the wax-selective solvent from fully utilizing the micropores to achieve adequate contact and dissolution of the deep wax layer; too long a time may lead to excessive diffusion and penetration of the wax-selective solvent into the fruit and vegetable tissue, increasing the risk of dissolving intracellular non-waxylipophilic impurities (such as certain pigments and terpenes), thus affecting product purity.

[0073] Preferably, in step S3, during wax extraction, intermittent ultrasonic oscillation is used as an auxiliary treatment. The power of the ultrasonic oscillation is 250-350W, the frequency is 20-40kHz, and the intermittent mode involves oscillation for 1-3 seconds followed by a 1-3 second pause. The cavitation effect and mechanical disturbance generated by the intermittent, low-frequency ultrasound in the liquid effectively promote the penetration and filling of the wax-selective solvent into the depths of the micropores, and enhance the exchange rate between the wax-selective solvent and wax within the micropores, as well as between the wax-selective solvent and the solvent that has not entered the micropores, further improving the wax extraction rate of this invention. Simultaneously, the use of a lower-power, gentler intermittent pulse working mode effectively prevents the temperature of the wax-selective solvent from rising or damaging the fruit and vegetable skin due to continuous ultrasonic vibration, avoiding the dissolution of intracellular or pulp substances and the generation of impurities.

[0074] Preferably, in step S4, the obtained wax extract is filtered to remove solid impurities, resulting in a filtrate containing wax. The wax-selective solvent in the filtrate is then removed to obtain the wax. Filtration can be performed using conventional filtration methods such as quantitative filter paper or a conventional microfiltration membrane, as long as insoluble matter in the filtrate is removed.

[0075] Preferably, in step S4, air drying at room temperature is used, such as placing the filtrate in a fume hood or other air drying equipment at room temperature, allowing the wax-selective solvent in the filtrate to evaporate, thus obtaining the wax. Air drying at room temperature effectively avoids potential heat damage during the removal of the wax-selective solvent. Of course, to ensure drying speed, the filtrate can be concentrated before air drying using methods such as vacuum concentration, membrane separation, or other low-temperature concentration techniques to accelerate the subsequent air drying process and recover some of the wax-selective solvent.

[0076] To better understand the above technical solutions, exemplary embodiments of the present invention will be described in more detail below. However, it should be understood that the present invention can be implemented in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided to enable a clearer and more thorough understanding of the present invention and to fully convey the scope of the invention to those skilled in the art.

[0077] Example 1

[0078] This invention provides a method for extracting wax from the skin of fruits and vegetables, comprising the following steps:

[0079] Raw material preparation: In this example, a number of 80% ripe plums (Gashi New Plums) from a farm in Tumushuke City, Xinjiang Uygur Autonomous Region were selected. The plums were intact without obvious scars, uniform in size, with a longitudinal diameter of 4.0-5.0 cm, a transverse diameter of 3.5-4.5 cm, a hardness of 3.0-3.6 N, and a soluble solids content of 23.5%-25.5%. After being heated to room temperature, the plums were washed, dried, and weighed as raw materials for fruits and vegetables.

[0080] S1: Zirconia particles were mixed with sterile water, ultrasonically dispersed, and then sodium alginate was added. The mixture was then ultrasonically dispersed again to obtain a uniform coating solution. Washed and dried plums were immersed in this coating solution for 15 seconds, accompanied by mechanical vibration at a frequency of 3 Hz. The fruit was then removed and dried with hot air at 35°C for 10 minutes to solidify and form a composite functional coating with a thickness of 3 micrometers. The coating solution, by weight, comprises 2.5 parts sodium alginate, 0.3 parts zirconia particles, and 100 parts sterile water. The average particle size of the zirconia particles is 150 nm, and the dielectric constant is 25. The viscosity of the prepared coating solution at room temperature is 1500 mPa·s.

[0081] S2: Place the coated plums in the reaction chamber of the low-temperature plasma equipment, evacuate to 200 Pa, then introduce nitrogen gas, maintaining a gas flow rate of 1 L / min, at a power density of 1.5 W / cm³. 2 Low-temperature plasma treatment was performed for 110 seconds under the following conditions: pulse frequency of 10kHz, duty cycle of 30%, processing voltage of 150V, and nozzle distance of 10cm from the fruit surface. During the treatment, the fruit surface temperature was maintained below 45℃.

[0082] S3: Immediately immerse the plasma-treated fruit in a mixed organic solvent with a volume ratio of ethyl acetate to n-hexane of 2:1, and control the mass-volume ratio of the fruit to the mixed organic solvent to be 1 kg: 3 L. Extract at room temperature for 150 s to obtain an extract containing wax.

[0083] S4: Filter the wax-containing extract with quantitative filter paper. After the filtrate is concentrated by rotary evaporation at 40°C to remove most of the solvent, transfer it to a pre-weighed glass dish and allow it to evaporate naturally at room temperature to constant weight in a fume hood to obtain a pale yellow solid wax, thus completing the wax extraction.

[0084] The mass of the wax obtained in this embodiment was weighed, and the wax extraction rate of this embodiment was calculated to be 39.2 mg / 100g (the wax extraction rate is the total weight of extracted wax / the total weight of plum raw material). Gas chromatography-mass spectrometry analysis was performed on the wax obtained in this embodiment, and the relative contents of characteristic long-chain alkanes (mainly C29 and C31) and primary alcohols (mainly C28), or wax characteristic components, were found to be 85.7%, and the relative contents of oxidation products such as short-chain carboxylic acids were 0.9%, indicating that the wax extracted by this invention has high chemical purity and good structural integrity.

[0085] Note: In this invention, the characteristic components of wax are those that are clearly contained in the wax obtained in this embodiment and can be identified by gas chromatography-mass spectrometry analysis. Their relative content, or the relative area ratio of the chromatographic peaks, can reflect the abundance of the target components that can be clearly identified in the wax extracted by this invention, so as to reflect the integrity and consistency of the chemical composition of the wax extracted by this invention.

[0086] The relative content ratio of oxidation products refers to the relative area ratio of chromatographic peaks that can be clearly attributed to the degradation products of wax components (such as short-chain carboxylic acids) in gas chromatography-mass spectrometry analysis. It is used to reflect the degree of damage to the wax structure caused by oxidation, decomposition, etc. during the extraction process.

[0087] Apart from the aforementioned identifiable characteristic components and oxidation products, the remaining components are mostly other inherent wax components that have not been identified or quantified individually (such as homologues, isomers, inherent components of aldehyde, ketone, and ester waxes with different carbon chain lengths, as well as trace amounts of natural wax components that have not been fully identified). These are all natural components of the wax itself, and no obvious impurities, such as sodium alginate residue, were observed.

[0088] Example 2

[0089] This embodiment provides a method for extracting wax from the skin of fruits and vegetables. Prunes are selected as the raw material, and the source, batch, and selection criteria of the prunes are the same as in Example 1. The difference from Example 1 is that in S3 of this embodiment, intermittent ultrasonic treatment is performed: after the fruit treated with plasma is immersed in a solvent, it is treated with ultrasonic vibration with a power of 250W and a frequency of 28kHz. The working mode is to stop for 2 seconds after every 2 seconds of vibration, and the total extraction time is still 150 seconds.

[0090] The wax extraction rate was 40.8 mg / 100g, the total relative content of characteristic components was 85.5%, and the proportion of oxidation products was 1.1%, all tested using the same method as in Example 1.

[0091] Example 3

[0092] This embodiment provides a method for extracting wax from the peel of fruits and vegetables. Prunes are selected as the raw material, and the source, batch, and selection criteria of the prunes are the same as in Example 1. The difference from Example 1 is that in S1, the coating solution includes 2.5 parts sodium alginate, 0.3 parts titanium dioxide particles, and 100 parts sterile water. The average particle size of the titanium dioxide particles is 120 nm, and the dielectric constant is 80. In S2, the plasma treatment time is 80 s.

[0093] The test was performed using the same method as in Example 1. The wax extraction rate was 41.5 mg / 100 g, the total relative content of characteristic components was 86.8%, and the proportion of oxidation products was 0.7%.

[0094] Example 4

[0095] This embodiment provides a method for extracting wax from the skin of fruits and vegetables. Prunes are selected as the raw material, and the source, batch, and selection criteria of the prunes are the same as in Example 1. The difference from Example 1 is that in S1, the coating solution includes 1.2 parts sodium alginate, 0.3 parts zirconium oxide particles, and 100 parts sterile water. In S2, the plasma treatment time is 80 seconds.

[0096] The same method as in Example 1 was used for testing, and the wax extraction rate was 36.0 mg / 100g, the total relative content of characteristic components was 84.2%, and the proportion of oxidation products was 1.5%.

[0097] Example 5

[0098] This embodiment provides a method for extracting wax from the skin of fruits and vegetables. Prunes are selected as the raw material, and the source, batch, and selection criteria of the prunes are the same as in Example 1. The difference from Example 1 is that in S2, the power density is increased to 2.5 W / cm². 2 At the same time, the processing time is reduced to 80 seconds.

[0099] The same method as in Example 1 was used for testing, and the wax extraction rate was 38.5 mg / 100 g, the total relative content of characteristic components was 85.0%, and the proportion of oxidation products was 1.3%.

[0100] Example 6

[0101] This embodiment provides a method for extracting wax from the skin of fruits and vegetables. Prunes are selected as the raw material, and the source, batch, and selection criteria of the prunes are the same as those in Example 1. The difference from Example 1 is that only ethyl acetate is selected as the selective solvent for wax.

[0102] The test was performed using the same method as in Example 1. The wax extraction rate was 32.5 mg / 100 g, the total relative content of characteristic components was 80.3%, and the proportion of oxidation products was 1.0%.

[0103] Example 7

[0104] This embodiment provides a method for extracting wax from the skin of fruits and vegetables. Prunes are selected as the raw material. The source, batch and selection criteria of the prunes are the same as those in Example 1. The difference from Example 1 is that the ratio of ethyl acetate and n-hexane in the selective solvent for wax is 1:2.

[0105] The same method as in Example 1 was used for testing, and the wax extraction rate was 36.2 mg / 100g, the total relative content of characteristic components was 86.0%, and the proportion of oxidation products was 0.9%.

[0106] Example 8

[0107] This embodiment provides a method for extracting wax from the skin of fruits and vegetables. The difference from Embodiment 1 is that the skin of Hami melon is selected as the raw material. Mature Hami melons (Golden Honey No. 25) produced by a farm in Hami City, Xinjiang Uygur Autonomous Region are taken. The skin is golden yellow, with clear netting and free from pests and diseases. The outer skin with a thickness of about 1 mm is peeled off with a stainless steel peeler to obtain the raw material of Hami melon skin.

[0108] The test was performed using the same method as in Example 1. The wax extraction rate was 155 mg / 100 g tan weight, the total relative content of characteristic components was 86.6%, and the proportion of oxidation products was 1.1%.

[0109] Comparative Example 1

[0110] This comparative example provides a method for extracting wax from the skin of fruits and vegetables. Prunes are selected as the raw material. The source, batch and selection criteria of the prunes are the same as those in Example 1. The difference from Example 1 is that the low-temperature plasma treatment is not performed on the washed and dried prunes in S1 and S2.

[0111] The test was performed using the same method as in Example 1. The wax extraction rate was 32.0 mg / 100g, the total relative content of characteristic components was 78.0%, and the proportion of oxidation products was 6.5%.

[0112] Comparative Example 2

[0113] This comparative example provides a method for extracting wax from the skin of fruits and vegetables. Prunes are selected as the raw material, and the source, batch, and selection criteria of the prunes are the same as those in Example 1. The difference from Example 1 is that S1 and S2 are not included. In S3, the prunes are directly immersed in an organic mixed solvent to extract the wax.

[0114] The test was performed using the same method as in Example 1. The wax extraction rate was 25.5 mg / 100 g, the total relative content of characteristic components was 84.0%, and the proportion of oxidation products was 1.0%.

[0115] Comparative Example 3

[0116] This comparative example provides a method for extracting wax from the skin of fruits and vegetables. Prunes are selected as the raw material. The source, batch and selection criteria of the prunes are the same as those in Example 1. The difference from Example 2 is that S1 and S2 are not included. In S3, the prunes are directly immersed in an organic mixed solvent and subjected to intermittent ultrasonic vibration treatment.

[0117] The test was performed using the same method as in Example 1. The wax extraction rate was 30.5 mg / 100 g, the total relative content of characteristic components was 81.5%, and the proportion of oxidation products was 1.2%.

[0118] Comparative Example 4

[0119] This comparative example provides a method for extracting wax from the skin of fruits and vegetables. Prunes are selected as the raw material, and the source, batch, and selection criteria of the prunes are the same as those in Example 1. The difference from Example 1 is that, in S1, the coating solution does not contain zirconium oxide particles; and the plasma treatment time is 180s.

[0120] The test was performed using the same method as in Example 1. The wax extraction rate was 23.0 mg / 100g, the total relative content of characteristic components was 84.2%, and the proportion of oxidation products was 1.4%.

[0121] Based on the above, it can be seen that in Example 1 of the present invention, the technical solution of first constructing a protective sodium alginate-zirconia composite functional coating on the surface of the plum to be extracted, and then using low-temperature plasma treatment and an organic solvent of ethyl acetate-n-hexane for wax extraction, not only has a high extraction rate, but also effectively retains the natural components of the wax. The extracted wax has a relatively high content of wax characteristic components and a low content of oxidized components.

[0122] Compared to Example 1, Example 2 introduced intermittent ultrasonic treatment in S3, which enhanced the convection and mass transfer between the solute and solvent, resulting in a certain improvement in the extraction efficiency of waxes and an increase in the extraction rate. However, the weak thermal effect and mechanical disturbance generated by the ultrasonic waves may also cause changes in a small number of wax components, and the oxidation products increased slightly.

[0123] Compared to Example 1, Example 3 utilizes titanium dioxide particles with a higher dielectric constant, which have a stronger guiding effect during plasma treatment. This results in more efficient and regular micropore formation and faster wax extraction. Furthermore, Example 3 appropriately shortens the plasma treatment time to avoid excessive wax loss and further reduces the disturbance to the overall wax structure during the etching process. The combination of these two factors leads to a significant increase in the content of characteristic components in the obtained wax, while reducing the content of oxidation products.

[0124] Compared to Example 1, Example 4 reduced the content of film-forming polymer in the coating, resulting in a thinner coating. This reduced the coating's ability to buffer plasma energy, made the wax layer more susceptible to plasma effects, decreased the extraction rate, and increased the content of oxidation products.

[0125] Compared to Example 1, Example 5 increases the power density of plasma treatment, which not only leads to faster etching but also reduces the uniformity and controllability of plasma treatment. This may cause some points to be etched through prematurely. Even if the processing time is shortened, the plasma bombardment will still affect the wax, resulting in a higher content of oxidation products in the wax.

[0126] Compared to Example 1, Example 6 uses only ethyl acetate as a selective solvent for waxes, which has a lower degree of matching between its solubility range and the complete composition of the waxes. In particular, it is not good at extracting non-polar components in the waxes, and its polarity is also low, resulting in a decrease in both extraction rate and content of characteristic components.

[0127] Compared to Example 1, Example 7 increased the proportion of n-hexane in the solvent, which enhanced the solvent system's solubility selectivity for non-polar wax components. The extraction was more targeted but the coverage was insufficient, resulting in a decrease in the extraction rate. At the same time, the proportion of identifiable non-polar components in the extracted wax increased.

[0128] Compared to Example 1, Example 8 selected a larger cantaloupe for wax extraction and extracted the wax from the cantaloupe peel obtained by cutting according to the method of the present invention. This effectively prevented the exposed inner components of the peel from contaminating the wax, and the resulting wax had high purity and high content of characteristic components.

[0129] Compared to Example 1, Comparative Example 1 did not have a composite functional coating, so the plasma directly bombarded the wax layer. Although it could also destroy the structure of the wax layer and promote extraction, it also caused significant damage to the wax, resulting in a significant increase in the content of oxidation products and a decrease in the integrity of characteristic components.

[0130] Compared to Example 1, Comparative Example 2, due to the absence of a composite functional coating and plasma treatment, although its wax damage was lower, it was difficult to effectively overcome the wax layer barrier (such as keratin) during solvent extraction, resulting in a slower dissolution rate and a lower extraction rate.

[0131] Compared to Example 2, Comparative Example 3, although it uses ultrasonic assistance but lacks the composite functional coating and plasma treatment of the present invention, still needs to overcome the dense structure of the wax layer to dissolve it, and its extraction effect cannot reach a high level. Furthermore, the direct action of ultrasonic waves also causes some damage to its wax components.

[0132] Compared to Example 1, Comparative Example 4, due to the absence of micro- and nano-ceramic materials in its composite functional coating, cannot form oriented micropores through etching by plasma treatment. Instead, it can only extend the plasma treatment time to preferentially etch through thinner coating points, poorly bonded interfaces, or protrusions to form large-area open points, thereby reducing the interference of the composite functional coating on wax extraction. However, it cannot construct an efficient solvent penetration path, resulting in a significant reduction in the extraction rate of Comparative Example 4 and greater damage to the wax.

[0133] In summary, this invention solves the technical problems of significant damage to the surface wax of fruits and vegetables, and low purity and extraction efficiency in existing technologies.

[0134] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for extracting wax from the skin of fruits and vegetables, comprising the following steps: S1: A composite functional coating is applied to the surface of fruit and vegetable raw materials to obtain a film-coated fruit and vegetable material; the composite functional coating comprises a water-soluble film-forming polymer and an inert micro-nano ceramic material; S2: The coated fruit and vegetable material is placed in an inert gas environment and its surface is subjected to low-temperature plasma treatment to obtain a surface-etched fruit and vegetable material. S3: Immerse the surface-etched fruit and vegetable materials in a wax-selective solvent to extract the wax and obtain a wax extract; the wax-selective solvent is an organic solvent that does not dissolve the film-forming polymer; S4: Filter the wax extract and dry the filtrate to obtain wax.

2. The method for extracting wax from fruit and vegetable peels as described in claim 1, characterized in that, In S1, the film-forming polymer includes at least one of sodium alginate, gellan gum, chitosan, xanthan gum, polyvinyl alcohol, polyethylene oxide, cellulose and its derivatives, and guar gum and its derivatives; the micro / nano ceramic material includes at least one of nano- and / or submicron-sized zirconium oxide particles, alumina particles, titanium dioxide particles, and zinc oxide particles; the dielectric constant of the micro / nano ceramic material is greater than the dielectric constant of the film-forming polymer.

3. The method for extracting wax from fruit and vegetable peels as described in claim 1, characterized in that, In step S1, the fruit and vegetable raw materials are immersed in a coating solution containing the film-forming polymer, micro-nano ceramic materials, and water. After being removed, they are dried and cured to obtain the coated fruit and vegetable materials. The viscosity of the coating solution is 500-3000 mPa·s. The mass ratio of the film-forming polymer, micro-nano ceramic materials, and water in the coating solution is 1-8:0.1-1:80-120.

4. The method for extracting wax from fruit and vegetable peels as described in claim 1, 2, or 3, characterized in that, In S1, the thickness of the composite functional coating is 1-5 micrometers; the particle size of the micro-nano ceramic material is 10-200 nm, and the dielectric constant is not less than 12; the dielectric constant of the film-forming polymer is not more than 8; the fruit and vegetable raw materials are at least one of whole fruits and vegetables, partially damaged fruits and vegetables, and the peel of fruits and vegetables.

5. The method for extracting wax from fruit and vegetable peels as described in claim 1, characterized in that, In S2, the gas in the inert gas environment includes at least one of nitrogen, argon, and helium; The aforementioned low-temperature plasma treatment is a low-frequency low-temperature plasma treatment with a frequency of 5-15kHz, a duty cycle of 10%-50%, a discharge time of 40-240s, and a power density of 0.5-4W / cm³. 2 The surface temperature of the coated fruit and vegetable material is 30℃-60℃.

6. The method for extracting wax from fruit and vegetable peels as described in claim 1, characterized in that, In S3, the wax-based selective solvent includes at least one of ethyl acetate, n-hexane, butyl acetate, ethyl lactate, ethyl levulinate, valerate, dimethyl carbonate, dichloromethane, chloroform, toluene, xylene, and tetrahydrofuran.

7. The method for extracting wax from fruit and vegetable peels as described in claim 1 or 6, characterized in that, In S3, the selective solvent for the wax is a mixed solution of ethyl acetate and n-hexane, with a volume ratio of ethyl acetate to n-hexane of 7-9:3-5.

8. The method for extracting wax from fruit and vegetable peels as described in claim 1 or 6, characterized in that, In step S3, the mass-to-volume ratio of the surface-etched fruit and vegetable material to the waxy selective solvent is 1 kg: 2-4 L, and the extraction time is 100-300 s.

9. The method for extracting wax from fruit and vegetable peels as described in claim 1, characterized in that, In S3, during wax extraction, intermittent ultrasonic oscillation is used as an auxiliary treatment. The power of the ultrasonic oscillation is 250-350W, the frequency is 20-40kHz, and the intermittent mode is to stop for 1-3 seconds after each oscillation.

10. The method for extracting wax from fruit and vegetable peels as described in claim 1, characterized in that, In step S4, the obtained wax extract is filtered to remove solid impurities, resulting in a filtrate containing wax. The wax-selective solvent in the filtrate is then removed to obtain the wax.