Method for edible processing of sheepskin

Abstract

The application discloses a kind of sheepskin edible processing method, belong to food processing technical field.The method mainly solves the problem that sheepskin in prior art is not completely defatted, the risk of chemical degreasing agent residue is high, and solvent and stabilizer are difficult to be efficiently recycled.The technical scheme points include: first, wet sheepskin is placed in hot water treatment tank, mechanical rolling is carried out at the same time, and is assisted by medium frequency ultrasonic treatment, to obtain preliminary defatted sheepskin;Then, the sheepskin is transferred to O / W type Pickering emulsion tank for deep degreasing treatment, and the degreasing endpoint is accurately controlled by monitoring the change rate of emulsion conductivity in real time;After that, the surface emulsion is removed by centrifugation, to obtain low-fat edible sheepskin;Finally, the separated emulsion is distilled, and n-heptane solvent is recovered, and the recovered ferroferric oxide core-shell magnetic particles are recycled by magnetic separation.The method is mainly used for efficiently, low-residue and low-cost processing of sheepskin into edible collagen raw materials.

Description

Technical Field

[0001] This invention relates to the field of food processing technology. More specifically, this invention relates to a method for processing sheepskin into an edible form. Background Technology

[0002] Sheepskin, a byproduct of meat processing, is rich in collagen and has the potential to be developed into edible collagen products. However, effectively converting it into a safe, low-fat edible raw material faces significant technical challenges, mainly in fat removal, collagen preservation, process controllability, and resource recycling.

[0003] First, sheepskin fat is primarily located within fat cells and encased in tough cell membranes. Traditional physical or chemical degreasing methods struggle to efficiently and thoroughly disrupt these cell membrane structures, resulting in incomplete fat removal and high residual fat content (typically well above 1 wt%). This residual fat not only affects the product's flavor and texture but also makes it more susceptible to oxidative rancidity during storage, reducing product quality and safety. Existing physical methods (such as mechanical extrusion and hot water treatment) have limited destructive power over cell membranes, and prolonged high-temperature processing can lead to excessive denaturation and hardening of collagen, resulting in a loss of the desired edible texture. While chemical methods (such as those using strong alkalis and organic solvents) offer improved degreasing efficiency, they pose a risk of chemical residue, failing to meet food-grade safety requirements, and subsequent cleaning adds environmental pressure.

[0004] Secondly, avoiding collagen damage is a key challenge in the pursuit of deep degreasing. High temperatures are effective in promoting fat release and emulsification, but they also easily cause thermal denaturation of collagen, leading to structural shrinkage, increased toughness, and ultimately a tough, coarse texture that renders the product unpalatable. Traditional methods struggle to strike a balance between the high temperatures required for effective degreasing and the gentle conditions needed to protect collagen. In particular, the high-temperature, high-pressure environments required for highly efficient degreasing technologies such as subcritical water or supercritical fluids place stringent demands on equipment, resulting in high investment and operating costs, hindering widespread industrial application.

[0005] Third, there is a lack of effective and controllable low-cost methods for deep degreasing, especially when dealing with stubborn residual fat. Existing high-efficiency degreasing technologies (such as high-frequency pulsed electric field-assisted degreasing and subcritical water treatment) are highly effective, but they rely on specialized equipment, resulting in high energy consumption and maintenance costs. Conventional solvent emulsification degreasing methods, on the other hand, are difficult to monitor and precisely control in real time. Operators often rely on experience or fixed timeframes to determine the degreasing endpoint, which can easily lead to insufficient degreasing (excessive residual fat) or over-processing (wasting energy, potentially damaging collagen structure, or increasing solvent residue). This lack of process control directly affects the final product's fat content compliance rate and batch stability.

[0006] Fourth, the low efficiency of recycling and reusing organic solvents and special additives (such as emulsifying stabilizers) used in the process is a key factor restricting cost control. Insufficient purity of recovered solvents (containing water and acid) will affect their efficiency and safety in subsequent degreasing processes; while certain additives (such as solid particle stabilizers) have low recovery rates and are difficult to regenerate due to agglomeration, deactivation, or loss at high temperatures or in complex systems, leading to increased production costs and resource waste. Currently, there are few mature solutions that can simultaneously achieve efficient degreasing, low-cost reagent recycling, and avoid secondary residues.

[0007] Finally, achieving green sustainability across the entire process presents challenges. Deep degreasing and the recycling of solvents and auxiliaries are crucial for reducing costs and environmental impact, but current technologies face bottlenecks in combining these aspects. The interplay between the contradictions between efficient degreasing and collagen protection, the lack of process controllability, and the difficulty in high-quality and efficient recycling of solvents / auxiliaries hinders the large-scale, economical, and environmentally friendly application of sheepskin edible processing technology. Therefore, developing a sheepskin edible processing method that can guarantee degreasing effectiveness and product edibility while significantly reducing equipment investment and operating costs and achieving efficient recycling of the processing media is of significant practical importance. Summary of the Invention

[0008] One objective of this invention is to provide a method for processing sheepskin into an edible form, which is mainly used to process sheepskin into edible collagen raw materials in a high-efficiency, low-residue, and low-cost manner.

[0009] To achieve these objectives and other advantages of the present invention, according to one aspect of the present invention, a method for processing sheepskin into an edible form is provided, comprising the following steps:

[0010] Step 1: Place the wet sheepskin that has been dehaired and cleaned on the surface into a hot water treatment tank and treat it at a temperature of 95-100℃ and normal pressure for 30-60 minutes. At the same time, mechanical tumbling is performed, supplemented by medium-frequency ultrasonic treatment at a frequency of 20-40kHz and an ultrasonic power density of 30-50W / L. This causes the sheepskin fat cell membrane to be destroyed by mechanical shearing and cavitation effects. The released fat is emulsified by hot water to form an oil-water mixture, and sheepskin with preliminary degreased is obtained.

[0011] Step 2: Immediately transfer the sheepskin treated in Step 1 to an O / W type Pickering emulsion tank for further treatment. The total treatment time is 30-120 minutes. The process is terminated early when the real-time monitoring shows that the rate of change in conductivity |Δσ / Δt| < 0.5 μS / cm·min. The Pickering emulsion consists of a heptane oil phase with a boiling point of 60-100℃ and an aqueous phase stabilizer of iron oxide core-shell magnetic particles with a particle size of 10-100 nm. The volume ratio of the oil phase to the aqueous phase is 1:1.5-1:2.5.

[0012] Step 3: Remove the sheepskin from the emulsion tank and centrifuge it at 1000-3000 rpm to remove the surface emulsion, obtaining edible sheepskin with a fat content ≤0.5wt% and magnetic particle residue ≤50ppm.

[0013] Step 4: The separated emulsion is sent to a distillation column, where n-heptane is recovered by distillation at a bottom temperature of 80-90°C. Simultaneously, ferric oxide core-shell magnetic particles are recovered by magnetic separation from the bottom liquid and recycled for use in the Pickering emulsion preparation in Step 2.

[0014] Preferably, a collagen protectant is added to the water medium in the hot water treatment tank in step one. The collagen protectant is selected from at least one of polyols, reducing disaccharides, polyhydroxy compounds or edible inorganic salts, and the concentration of the collagen protectant added to the water medium is 5-25% w / v.

[0015] Preferably, the mechanical tumbling in step one is achieved by a scraper-type agitator installed in the tank, which runs at a speed of 15-25 rpm, causing the sheepskin to continuously turn over and rub against each other.

[0016] Preferably, the preparation method of the iron oxide core-shell magnetic particles in step two is as follows:

[0017] Mix 0.5-1.0 mol / L FeCl2 and FeCl3 solutions according to Fe 2+ :Fe 3+ The mixture was prepared in a molar ratio of 1:1.8-2.2. 0.3-0.6 mol / L sodium citrate was added under nitrogen protection. 0.5-1.0 mol / L ammonia was added dropwise at 50-60℃ until the pH reached 9.5-10.5. After aging for 2-3 hours, magnetic separation was performed using a magnetic field with a strength of 0.8-1.2T. The supernatant was discarded. The obtained magnetic precipitate was washed three times with hot deionized water at 60-70℃ and then twice with anhydrous ethanol to obtain Fe3O4 nanoparticles with a particle size of 15-25 nm.

[0018] The obtained Fe3O4 particles were dispersed in a mixed solvent of ethanol and water with a volume ratio of 3:1. Hexadecyltrimethylammonium bromide was added at a mass ratio of 0.1-0.3 wt% of the total mass of the mixed solvent. After ultrasonic treatment for 10-15 min, tetraethyl orthosilicate was added dropwise at a rate of 0.5-1.0 mL / min and a mass ratio of tetraethyl orthosilicate to Fe3O4 of 1:2-1:3. The reaction was carried out at 40-45℃ for 4-6 h to form a 5-8 nm silicon shell. After the reaction was completed, magnetic separation was performed by a magnetic field with a strength of 0.8-1.2 T. The supernatant was discarded. The obtained particles were washed three times each with ethanol and acetone, and then dried in a vacuum drying oven at 60-80℃ for 6-8 h to obtain Fe3O4 particles coated with a mesoporous silicon layer.

[0019] The Fe3O4 particles coated with the obtained mesoporous silica layer were dispersed in toluene, and octyltrimethoxysilane was added at a molar ratio of 3:1 to 5:1 with Fe3O4. The mixture was refluxed at 110-120℃ for 8-10 h. After reflux, the mixture was cooled to room temperature and magnetically separated by a magnetic field of 1.0-1.5 T. The supernatant was discarded, and the resulting particles were washed twice with toluene and then three times with n-heptane.

[0020] The washed particles were placed in a tube furnace and heated to 350-450°C at a rate of 3-5°C / min under nitrogen protection, and calcined for 1-2 hours to completely remove any organic residues. The calcined particles were then dispersed again in n-heptane and magnetically separated by a magnetic field of 1.0-1.5T. The supernatant was discarded, and the resulting particles were pure iron oxide core-shell magnetic particles with CTAB residue <1ppm and TEOS residue <5ppm.

[0021] Preferably, the treatment of the sheepskin in the Pickering emulsion tank in step two includes:

[0022] During the pre-permeation stage, the sheepskin is immersed in the emulsion and then intermittent variable frequency stirring is started. The stirring speed is 200-300 rpm for 0-10 min and then reduced to 100-150 rpm for 10-30 min.

[0023] During the deep degreasing stage, an ultrasonic field with a frequency of 28±2kHz and a power density of 50-80W / L is applied, and a magnetic field is activated simultaneously, with a horizontal magnetic field strength of 0.3-0.5T and a vertical magnetic field strength of 0.1-0.2T.

[0024] The rate of change of emulsion conductivity was monitored in real time. When |Δσ / Δt| < 0.5 μS / cm·min, the magnetic field was paused for 30 seconds and then the measurement was repeated for confirmation.

[0025] Preferably, the n-heptane recovered by distillation in step four is passed through a silanized 3Å molecular sieve column with a pore size of 0.33±0.02nm, and dehydrated and deacidified at 50-60℃ to obtain a high-purity solvent with a water content ≤30ppm and an acid value ≤0.05mgKOH / g.

[0026] Preferably, the recovery process of the core-shell magnetic particles of iron oxide in step four is as follows: an axial gradient magnetic field is applied in the distillation column, with an intensity of 0.8-1.0T in the bottom zone, 0.3-0.5T in the middle zone, and <0.1T in the top zone. The bottom temperature is controlled at 85±2℃ to inhibit the agglomeration of magnetic particles. The bottom liquid is treated with a 1.0-1.5T magnetic field to recover the particles, which are then dispersed in hot n-heptane containing 0.8-1.2% oleic acid at 80℃ and shaken for 20 minutes to repair the hydrophobic surface of the particles.

[0027] Preferably, the recovered high-purity solvent and the particles after repairing the hydrophobic surface are mixed and then transported back to the Pickering emulsion tank. The specific preparation process is as follows:

[0028] The particles after repairing the hydrophobic surface were dispersed in deionized water at a concentration of 0.7-1.1% w / v and then ultrasonically treated at a frequency of 40 kHz and a power of 50 W / L for 10 min to obtain a homogeneous aqueous dispersion.

[0029] High-purity solvent is used as the oil phase and injected into the water phase at a uniform rate of 5-10 L / min, with a volume ratio of oil phase to water phase of 1:1.5-1:2.5.

[0030] The emulsion was first processed at 8000-10000 rpm for 3 min in a high-speed homogenizer to form a crude emulsion, and then processed at 12000-15000 rpm for 2 min to make the emulsion droplet size 1.5±0.3μm.

[0031] After being left to stand for 24-48 hours to age, the emulsion is returned to the Pickering emulsion tank for use in step two, sheepskin processing.

[0032] The present invention has at least the following beneficial effects:

[0033] First, this invention provides a method for processing sheepskin into an edible form. By using a combination of atmospheric pressure hot water treatment with mechanical tumbling and medium-frequency ultrasound, the structure of sheepskin fat cells is effectively destroyed and fat emulsification is promoted under mild conditions. This eliminates the dependence on expensive high-pressure, high-temperature equipment (such as subcritical water reactors) and complex electric field systems, significantly reducing initial equipment investment and subsequent energy consumption and maintenance costs. It lays a good foundation for subsequent deep degreasing and is more suitable for industrial promotion.

[0034] Secondly, adding a collagen protectant during the hot water treatment stage and controlling the treatment temperature and time can significantly reduce the damage to the collagen structure of sheepskin during the treatment process, help maintain the natural conformation of protein molecules, and ensure that the final product maintains good texture and palatability, thus resolving the contradiction between efficient defatting and collagen protection.

[0035] Third, by using a Pickering emulsion with a specific composition for deep processing, combined with real-time conductivity monitoring, the dynamic changes in fat dissolution during the defatting process can be sensitively and objectively judged, thereby achieving precise control of the defatting endpoint, effectively avoiding under- or over-processing, and ensuring that the fat content (≤0.5wt%) of the final product consistently meets the standard.

[0036] Fourth, one of the core advantages of this invention lies in the construction of a closed-loop recovery and regeneration system for solvent and magnetic particles. Through a combination of distillation and magnetic separation technologies, n-heptane solvent is efficiently recovered; and a unique surface repair process restores the emulsification stability of the magnetic particles. After specific configuration, the two can reformate into a highly efficient Pickering emulsion, achieving high-frequency, low-cost recycling of the core medium, significantly reducing material consumption costs and wastewater treatment pressure.

[0037] Fifth, the entire process avoids the use of strong alkalis, surfactants, and other chemical degreasing agents, fundamentally eliminating the risk of harmful chemical residues, resulting in a pure and safe final product. Combining atmospheric pressure pretreatment with media circulation technology, the entire solution not only reduces production energy and material consumption but also minimizes the emission of waste, demonstrating excellent economic and environmental characteristics, and providing a reliable path for the high-value and green processing and utilization of sheepskin by-products.

[0038] 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. Detailed Implementation

[0039] The present invention will now be described in further detail with reference to specific embodiments, so that those skilled in the art can implement it based on the description.

[0040] It should be understood that terms such as “having,” “comprising,” and “including” as used herein do not exclude the presence or addition of one or more other elements or combinations thereof.

[0041] It should be noted that, unless otherwise specified, the experimental methods described in the following implementation plan are all conventional methods, and the reagents and materials described are all commercially available unless otherwise specified.

[0042] This invention provides a method for processing sheepskin into an edible form, comprising the following steps:

[0043] Step 1: Place the wet sheepskin that has been dehaired and cleaned on the surface into a hot water treatment tank and treat it at a temperature of 95-100℃ and normal pressure for 30-60 minutes. At the same time, mechanical tumbling is performed, supplemented by medium-frequency ultrasonic treatment at a frequency of 20-40kHz and an ultrasonic power density of 30-50W / L. This causes the sheepskin fat cell membrane to be destroyed by mechanical shearing and cavitation effects. The released fat is emulsified by hot water to form an oil-water mixture, and sheepskin with preliminary degreased is obtained.

[0044] Step 2: Immediately transfer the sheepskin treated in Step 1 to an O / W type Pickering emulsion tank for further treatment. The total treatment time is 30-120 minutes. The process is terminated early when the real-time monitoring shows that the rate of change in conductivity |Δσ / Δt| < 0.5 μS / cm·min. The Pickering emulsion consists of a heptane oil phase with a boiling point of 60-100℃ and an aqueous phase stabilizer of iron oxide core-shell magnetic particles with a particle size of 10-100 nm. The volume ratio of the oil phase to the aqueous phase is 1:1.5-1:2.5.

[0045] Step 3: Remove the sheepskin from the emulsion tank and centrifuge it at 1000-3000 rpm to remove the surface emulsion, obtaining edible sheepskin with a fat content ≤0.5wt% and magnetic particle residue ≤50ppm.

[0046] Step 4: The separated emulsion is sent to a distillation column, where n-heptane is recovered by distillation at a bottom temperature of 80-90°C. Simultaneously, ferric oxide core-shell magnetic particles are recovered by magnetic separation from the bottom liquid and recycled for use in the Pickering emulsion preparation in Step 2.

[0047] In the above technical solution, in step one, an atmospheric pressure jacketed hot water tank can be selected as the main body of the hot water treatment tank, equipped with a steam heating coil and a temperature control system. Mechanical tumbling can be achieved by a scraper-type agitator installed inside the tank, and medium-frequency ultrasonic treatment is achieved by an array of piezoelectric ceramic transducers installed on the bottom and side walls of the tank. Deionized water can be used as the water medium, and the wet sheepskin raw material can be fresh hides from slaughterhouses that have undergone mechanical dehairing and high-pressure water gun cleaning.

[0048] In step two, the Pickering emulsion tank used for deep degreasing can be equipped with a variable frequency stirring paddle, an ultrasonic transducer array, and a permanent magnet assembly. The iron oxide core-shell magnetic particles can be commercially available oleic acid-modified Fe3O4@SiO2 nanoparticles (particle size 50±10nm). The n-heptane solvent can be of industrial purity (≥98%). In step three, a horizontal spiral sedimentation centrifuge can be used. In step four, the distillation column can be equipped with a magnetic recovery device, and electromagnetic coils can be installed inside the column to create a gradient magnetic field.

[0049] During operation, wet sheepskins are placed in a hot water treatment tank, where the temperature can be set to 98℃ and treated for 40 minutes under normal pressure. A scraper-type agitator operates at 20 rpm, continuously tumbling and rubbing the sheepskins, while simultaneously using ultrasonic waves at a frequency of 30 kHz and a power density of 40 W / L. Under these conditions, the sheepskin fat cell membranes are disrupted by mechanical shearing and cavitation effects, releasing fat which is emulsified by the hot water to form an oil-water mixture, resulting in sheepskins with preliminary degreasing.

[0050] The treated sheepskins were then immediately transferred to an O / W type Pickering emulsion tank for deep degreasing. After immersing the sheepskins in the emulsion, they were stirred at 250 rpm for the first 10 minutes. The stirring speed was then reduced to 120 rpm, and an ultrasonic field with a frequency of 28 kHz and a power density of 60 W / L was activated. Simultaneously, a horizontal magnetic field of 0.4 T and a vertical magnetic field of 0.15 T were activated. During this process, an online sensor was used to monitor the changes in the conductivity of the emulsion in real time. The treatment was terminated when the rate of change |Δσ / Δt| was detected to be less than 0.5 μS / cm·min for three consecutive times.

[0051] After the sheepskin is removed from the emulsion tank, it is immediately sent to a centrifuge and centrifuged at 2000 rpm for 5 minutes to remove the emulsion adhering to its surface, thereby obtaining an edible sheepskin product with a fat content of no more than 0.5 wt% and a magnetic particle residue that meets the standards.

[0052] The separated emulsion was fed to a distillation column for further separation and recovery. Heptane was recovered by distillation at a bottom temperature of 85°C. During distillation, an axial gradient magnetic field was applied within the column, with a magnetic field strength of 0.9T in the bottom region, 0.4T in the middle region, and less than 0.1T at the top. The recovered heptane vapor was condensed and then passed through a silanized 3Å molecular sieve column with a pore size of 0.33 nm for dehydration and deacidification at 55°C to obtain a high-purity solvent. The bottom liquid was treated with a 1.2T magnetic field to recover magnetite core-shell magnetic particles. The recovered particles were dispersed in a 1% oleic acid solution in 80°C hot heptane and shaken for 20 minutes to restore the hydrophobic surface properties of the particles.

[0053] This method, through pretreatment with hot water combined with mechanical tumbling and medium-frequency ultrasound, effectively disrupts the structure of sheepskin fat cells and promotes fat emulsification under normal pressure and low temperature conditions, laying a solid foundation for subsequent deep degreasing and significantly reducing equipment investment and energy costs. Using a Pickering emulsion with a specific composition for deep treatment, combined with real-time conductivity monitoring, allows for precise control of the degreasing process, ensuring thorough removal of residual fat from the sheepskin. Centrifugation effectively separates the residual emulsion system from the sheepskin surface. The combined application of distillation and magnetic separation technologies enables the recovery and reuse of solvents and magnetic particles, forming a closed-loop circulation system for the processing media, greatly reducing material consumption costs and environmental burden. The entire processing flow works in tandem, ensuring both effective degreasing and product safety while demonstrating excellent economic and environmental characteristics.

[0054] In another technical solution, a collagen protectant is added to the water medium in the hot water treatment tank in step one. The collagen protectant is selected from at least one of polyols, reducing disaccharides, polyhydroxy compounds or edible inorganic salts, and the concentration of the collagen protectant added to the water medium is 5-25% w / v.

[0055] In the above technical solution, the hot water treatment tank described in step one can be equipped with a reagent addition system. This system may include a mixing tank with a stirring function and a metering pump. The mixing tank can be installed beside the treatment tank and connected to the main body of the tank via pipelines. The metering pump can be installed on the outlet pipeline of the mixing tank. Collagen preservatives can be selected from one or more of food-grade glycerin, sorbitol, trehalose, or disodium hydrogen phosphate, and a mixture thereof. These raw materials can be obtained from food additive suppliers, and their purity meets national food additive standards.

[0056] In practice, first, a specified amount of deionized water is added to the mixing tank. The stirrer is then started, and the collagen preservative is slowly added. The concentration of the preservative can be selected as 15% by weight / volume (15% w / v), that is, 15 grams of preservative dissolved in every 100 ml of water. After dissolution, the solution is injected into the hot water treatment tank through a metering pump and mixed with the existing water medium in the tank. The mixing process continues until the preservative concentration is evenly distributed. Subsequently, the pretreated wet sheepskin is loaded into the treatment tank, and subsequent processing is carried out according to the established procedure.

[0057] Adding collagen protectants during hot water treatment effectively reduces the damage to the collagen structure of sheepskin caused by heat treatment. These protectants interact with water molecules and collagen peptide chains through multiple hydroxyl groups or specific ionic groups in their molecules, helping to maintain the natural conformation and water content of the protein molecules, thus slowing down the process of heat denaturation. Sheepskin treated in this way retains the integrity of its collagen fiber network better, resulting in a denser and more ordered microstructure. This is reflected in the final product as a more supple texture, improved chewiness, and a more palatable taste. Furthermore, the treated sheepskin exhibits better functional properties in subsequent processing, making it possible to obtain higher-quality edible sheepskin products. This measure is an effective way to ensure defatting efficiency while maintaining the product's edibility.

[0058] In another technical solution, the mechanical tumbling in step one is achieved by a scraper-type agitator installed in the tank, which runs at a speed of 15-25 rpm, causing the sheepskin to continuously turn over and rub against each other.

[0059] In another technical solution, the mechanical tumbling in step one is achieved by a scraper-type agitator installed inside the tank. This agitator consists of a motor, a reduction gear, and a scraper assembly. The shape of the scraper edge is adapted to the inner wall of the processing tank. It operates at a speed of 15-25 rpm, causing the sheepskin to be continuously lifted, thrown, and rubbed against each other inside the tank, thus achieving a uniform mechanical action on the sheepskin tissue.

[0060] In practice, the pre-treated wet sheepskin is first placed into a hot water treatment tank, and then hot water containing a collagen preservative is injected. The scraper-type agitator is then started and set to 20 rpm. During operation, the scraper not only propels the sheepskin slowly within the tank but also tumbles it up and down, ensuring that all parts of the sheepskin are thoroughly kneaded and squeezed. This mechanical action directly targets the sheepskin fat cells, disrupting the fat cell membrane structure through continuous shearing and friction, promoting the release of internal fat. Simultaneously, the friction between the sheepskin layers enhances the removal of surface impurities.

[0061] Mechanical tumbling using a scraper-type agitator provides a comprehensive yet gentle mechanical action on the sheepskin during atmospheric pressure hot water treatment. This action covers all parts of the sheepskin, including surface wrinkles and internal structures. The slow rotation speed ensures sufficient mechanical force while avoiding structural damage or entanglement issues that can occur with high-speed agitation. The special design of the scraper ensures the sheepskin is thoroughly turned over, reducing processing dead zones and improving processing uniformity. This mechanical tumbling method directly disrupts the fat cell structure through physical action, laying a good foundation for subsequent deep degreasing processes and providing good adaptability to processing sheepskin raw materials with different morphological characteristics.

[0062] In another technical solution, the preparation method of the iron oxide core-shell magnetic particles in step two is as follows:

[0063] Mix 0.5-1.0 mol / L FeCl2 and FeCl3 solutions according to Fe 2+ :Fe 3+ The mixture was prepared in a molar ratio of 1:1.8-2.2. 0.3-0.6 mol / L sodium citrate was added under nitrogen protection. 0.5-1.0 mol / L ammonia was added dropwise at 50-60℃ until the pH reached 9.5-10.5. After aging for 2-3 hours, magnetic separation was performed using a magnetic field with a strength of 0.8-1.2T. The supernatant was discarded. The obtained magnetic precipitate was washed three times with hot deionized water at 60-70℃ and then twice with anhydrous ethanol to obtain Fe3O4 nanoparticles with a particle size of 15-25 nm.

[0064] The obtained Fe3O4 particles were dispersed in a mixed solvent of ethanol and water with a volume ratio of 3:1. Hexadecyltrimethylammonium bromide was added at a mass ratio of 0.1-0.3 wt% of the total mass of the mixed solvent. After ultrasonic treatment for 10-15 min, tetraethyl orthosilicate was added dropwise at a rate of 0.5-1.0 mL / min and a mass ratio of tetraethyl orthosilicate to Fe3O4 of 1:2-1:3. The reaction was carried out at 40-45℃ for 4-6 h to form a 5-8 nm silicon shell. After the reaction was completed, magnetic separation was performed by a magnetic field with a strength of 0.8-1.2 T. The supernatant was discarded. The obtained particles were washed three times each with ethanol and acetone, and then dried in a vacuum drying oven at 60-80℃ for 6-8 h to obtain Fe3O4 particles coated with a mesoporous silicon layer.

[0065] The Fe3O4 particles coated with the obtained mesoporous silica layer were dispersed in toluene, and octyltrimethoxysilane was added at a molar ratio of 3:1 to 5:1 with Fe3O4. The mixture was refluxed at 110-120℃ for 8-10 h. After reflux, the mixture was cooled to room temperature and magnetically separated by a magnetic field of 1.0-1.5 T. The supernatant was discarded, and the resulting particles were washed twice with toluene and then three times with n-heptane.

[0066] The washed particles were placed in a tube furnace and heated to 350-450°C at a rate of 3-5°C / min under nitrogen protection, and calcined for 1-2 hours to completely remove any organic residues. The calcined particles were then dispersed again in n-heptane and magnetically separated by a magnetic field of 1.0-1.5T. The supernatant was discarded, and the resulting particles were pure iron oxide core-shell magnetic particles with CTAB residue <1ppm and TEOS residue <5ppm.

[0067] In the above technical solution, the preparation of the iron(III) oxide core-shell magnetic particles in step two can be carried out using conventional chemical reaction equipment. A double-walled glass reactor with stirring and temperature control can be used as the main reaction vessel, equipped with a constant-pressure dropping funnel and an online pH monitoring system. Magnetic separation can be performed using a permanent magnet separator (such as a neodymium iron boron magnet) or an electromagnetic separation device. The reflux reaction can be performed using a standard glass reflux condenser. The raw materials FeCl2·4H2O and FeCl3·6H2O can be chemically pure, and the reagents such as sodium citrate, ammonia, hexadecyltrimethylammonium bromide, tetraethyl orthosilicate, and octyltrimethoxysilane can be analytically pure. These chemical reagents can be obtained from conventional chemical reagent suppliers.

[0068] In the specific implementation, firstly, 0.8 mol / L FeCl2 solution and 0.8 mol / L FeCl3 solution were mixed at an iron ion molar ratio of 1:2, transferred to a reaction vessel, and protected with nitrogen gas. Then, 0.5 mol / L sodium citrate solution was added, and the temperature was maintained at 55°C. 0.8 mol / L ammonia water was added dropwise at a rate of 1 mL per minute until the pH reached 10.0. After aging for 2.5 hours, magnetic separation was performed using a 1.0T magnetic field. The supernatant was discarded, and the resulting magnetic precipitate was washed three times with hot deionized water at 65°C with stirring, followed by two washes with anhydrous ethanol to obtain Fe3O4 nanoparticles.

[0069] The obtained particles were dispersed in a mixed solvent of ethanol and water (volume ratio 3:1), and 0.2% (by mass) of hexadecyltrimethylammonium bromide was added. The mixture was ultrasonically treated for 12 minutes. Subsequently, tetraethyl orthosilicate (mass ratio of Fe3O4 to Fe3O4 1:2.5) was added dropwise at a rate of 0.8 mL per minute, and the reaction was carried out at 42 °C for 5 hours to form a silica shell. After the reaction was completed, magnetic separation was performed using a 1.0 T magnetic field. The supernatant was discarded, and the obtained particles were washed three times each with ethanol and acetone, and then dried in a vacuum drying oven at 70 °C for 7 hours to obtain Fe3O4 particles coated with a mesoporous silica layer.

[0070] The obtained mesoporous silica-coated Fe3O4 particles were dispersed in toluene, and octyltrimethoxysilane (molar ratio of Fe3O4 4:1) was added. The mixture was refluxed at 115 °C for 9 hours. After reflux, the mixture was cooled to room temperature and magnetically separated using a 1.2 T magnetic field. The supernatant was discarded, and the resulting particles were washed twice with toluene and then three times with n-heptane to thoroughly remove unreacted silane coupling agent and byproducts.

[0071] To completely remove any trace organic reagents (especially CTAB) that may remain from the preparation process, the washed particles were placed in a tube furnace and heated to 400°C at a rate of 5°C / min under nitrogen protection, and held at that temperature for 1.5 h. The calcined particles were then redispersed in n-heptane and subjected to final magnetic separation and washing using a 1.2T magnetic field to obtain high-purity iron tetroxide core-shell magnetic particles. HPLC and ICP-OES analysis showed that the CTAB residue in the finished product was <1 ppm and the TEOS residue was <5 ppm.

[0072] The magnetite core-shell magnetic particles prepared by this method possess a regular core-shell structure and good hydrophobic properties. The presence of the silica shell improves the chemical stability of the particles and reduces the dissolution of the iron core. More importantly, the rigorous multi-stage purification and high-temperature calcination process ensures that any toxic reagent residues are removed to below safety limits, fully meeting the safety requirements for food processing aids. Surface octyl modification imparts appropriate hydrophobicity to the particles, enabling them to effectively stabilize Pickering emulsions. The magnetic core ensures that the particles can be recycled and reused through magnetic separation. These particles exhibit good emulsion stability and reusability during sheepskin degreasing, providing a suitable solid-phase stabilizer material for the edible processing of sheepskin.

[0073] In another technical solution, the processing of the sheepskin in the Pickering emulsion tank in step two includes:

[0074] During the pre-permeation stage, the sheepskin is immersed in the emulsion and then intermittent variable frequency stirring is started. The stirring speed is 200-300 rpm for 0-10 min and then reduced to 100-150 rpm for 10-30 min.

[0075] During the deep degreasing stage, an ultrasonic field with a frequency of 28±2kHz and a power density of 50-80W / L is applied, and a magnetic field is activated simultaneously, with a horizontal magnetic field strength of 0.3-0.5T and a vertical magnetic field strength of 0.1-0.2T.

[0076] The rate of change of emulsion conductivity was monitored in real time. When |Δσ / Δt| < 0.5 μS / cm·min, the magnetic field was paused for 30 seconds and then the measurement was repeated for confirmation.

[0077] In the above technical solution, the Pickering emulsion treatment system described in step two can be equipped with an intelligent control device. The emulsion tank can be a jacketed stainless steel container, equipped with a variable frequency stirring motor and a stepless speed regulation device. The ultrasonic field generator can be a piezoelectric ceramic transducer array, evenly arranged at the bottom and side walls of the tank. The magnetic field generator can be a permanent magnet assembly or an electromagnetic coil; the horizontal magnetic field assembly can be installed on both sides of the tank, and the vertical magnetic field assembly can be installed at the bottom of the tank. Conductivity monitoring can be achieved using an online conductivity sensor, installed at the tank outlet and connected to a data acquisition system.

[0078] To achieve precise and real-time monitoring of the deep degreasing process of sheepskin, this invention employs an online conductivity monitoring system to dynamically track the changing trend of the conductivity of Pickering emulsion, using its rate of change (Δσ / Δt) as an objective indicator for determining the degreasing endpoint. This system utilizes an industrial-grade four-electrode conductivity sensor with platinum electrodes. The sensor body and sealing materials are made of polytetrafluoroethylene (PTFE) or Hastelloy, ensuring resistance to n-heptane solvent and excellent corrosion resistance. The sensor is paired with an intelligent conductivity transmitter, featuring signal amplification, automatic temperature compensation, data output, and relay control functions. The sensor is installed on the Pickering emulsion tank via a self-cleaning bypass circulation pipeline. Specifically, an outlet is created at the bottom of the tank's side wall, and a centrifugal pump continuously pumps the emulsion into a transparent, flow-controlled bypass measurement pool. The conductivity sensor is vertically installed within the measurement pool, ensuring the electrode plates are completely submerged and aligned with the flow direction. The measured emulsion is then returned to the main processing tank via a pipe above the measurement pool. This bypass installation method ensures that the tested emulsion can represent the overall composition of the tank, avoids the direct impact of mechanical collisions and ultrasonic cavitation that may occur when the sensor is directly installed in the tank, and facilitates maintenance and cleaning without shutting down the system.

[0079] The conductivity transmitter transmits the real-time measured, temperature-compensated conductivity signal to the central control system (such as a PLC or DCS). The control system has a built-in program that calculates the conductivity change rate |Δσ / Δt| (unit: μS / cm·min) in minutes. Its control logic is as follows: when the average |Δσ / Δt| for three consecutive sampling periods (i.e., 3 minutes) is below 0.5 μS / cm·min, the system determines that the defatting rate has dropped to an extremely low level. At this point, the system automatically shuts off the magnetic field for 30 seconds to eliminate its potential interference with the measurement, and then re-collects data after 30 seconds for confirmation. If the re-measurement result still meets the termination condition, the system automatically terminates the processing. This monitoring principle is based on the following: in the initial stage of defatting, a large amount of non-polar oil is extracted into the emulsion, causing a significant decrease in conductivity, resulting in a large negative value for Δσ / Δt; as the amount of releasable fat decreases, the extraction rate slows down, and the conductivity change trend slows down; when Δσ / Δt approaches zero, it indicates that the emulsion composition is stabilizing, and the defatting reaction is basically complete. Therefore, this threshold is a sensitive and reliable criterion for characterizing defatting equilibrium. The conductivity change rate threshold (|Δσ / Δt|<0.5μS / cm·min) is not an arbitrary theoretical value, but an empirical critical value determined based on a large number of previous experiments, which can reliably characterize the defatting reaction tending to equilibrium.

[0080] In practice, the treatment program is initiated immediately after the sheepskin is immersed in the emulsion. For the first 10 minutes, a stirring speed of 250 rpm is used to promote the penetration of the emulsion into the sheepskin tissue. After 10 minutes, the stirring speed is reduced to 120 rpm, and a 28 kHz ultrasonic field is activated with a power density of 60 W / L. Simultaneously, the magnetic field system is activated, with the horizontal magnetic field strength adjusted to 0.4 T and the vertical magnetic field strength adjusted to 0.15 T. During the treatment, the conductivity of the emulsion is continuously monitored. When the rate of change in conductivity is less than 0.5 μS / cm·min, the magnetic field is automatically paused for 30 seconds, and then retested for confirmation. If the retest result still meets the termination criteria, the entire treatment process is automatically stopped.

[0081] This phased processing method enables effective penetration of the emulsion into the sheepskin tissue and deep degreasing. The initial high-speed agitation helps the emulsion quickly enter the porous structure of the sheepskin, while the subsequent reduced agitation speed, combined with ultrasonic and magnetic field effects, promotes the emulsification and removal of stubborn fats. Real-time conductivity monitoring provides objective criteria for the degreasing process, helping to accurately control the processing endpoint. This method provides a technological guarantee for obtaining edible sheepskin products with low fat content.

[0082] In another technical solution, the n-heptane recovered by distillation in step four is passed into a silanized 3Å molecular sieve column with a pore size of 0.33±0.02nm, and dehydrated and deacidified at 50-60℃ to obtain a high-purity solvent with a water content ≤30ppm and an acid value ≤0.05mgKOH / g.

[0083] In the above technical solution, the n-heptane purification system described in step four can be equipped with a molecular sieve adsorption device. A stainless steel fixed-bed adsorption column can be selected as the main body of the molecular sieve column, and the column can be equipped with a circulating heat transfer medium jacket and a temperature control system. The silanized 3Å molecular sieve can be in spherical particle form, with a packing density controlled at 0.6-0.7 g / mL. The heating system can be an electrically heated oil bath, with a temperature control accuracy of ±1℃. Pressure monitoring can be performed using a digital pressure sensor, installed on the inlet and outlet pipelines of the molecular sieve column.

[0084] In practice, the distilled n-heptane is pre-cooled to 40°C and then passed through a molecular sieve column at a flow rate of 0.5 column volumes per hour. The column temperature is maintained at 55°C, and the operating pressure is controlled at 0.3 MPa. The molecular sieve column is periodically regenerated at 200°C while being purged with nitrogen. The water content of the treated n-heptane sample is determined using the Karl Fischer method, and the acid value is determined using acid-base titration. When the molecular sieve adsorption capacity reaches saturation, the molecular sieve material needs to be replaced with a new one.

[0085] This treatment method effectively removes water and acidic substances from n-heptane. The regular pore structure of the molecular sieve exhibits selective adsorption, and its 0.33 nm pore size effectively blocks water and organic acid molecules. Silanization enhances the hydrophobicity of the molecular sieve, improving its adaptability to organic solvents. Temperature control helps maintain the stability of the adsorption process, and an appropriate flow rate ensures sufficient contact time. This method provides an effective means for quality control of the recovered solvent, facilitating solvent recycling.

[0086] In another technical solution, the recovery process of the core-shell magnetic particles of iron oxide in step four is as follows: An axial gradient magnetic field is applied in the distillation column, with an intensity of 0.8-1.0T in the bottom zone, 0.3-0.5T in the middle zone, and <0.1T in the top zone. The bottom temperature is controlled at 85±2℃ to inhibit the agglomeration of magnetic particles. The bottom liquid is treated with a 1.0-1.5T magnetic field to recover the particles, which are then dispersed in 80℃ hot n-heptane containing 0.8-1.2% oleic acid and shaken for 20 minutes to repair the hydrophobic surface of the particles.

[0087] In the above technical solution, the magnetic particle recovery system described in step four can integrate a magnetic field generator inside the distillation column. An electromagnetic coil group or a permanent magnet array can be used to generate the axial gradient magnetic field. Higher field strength NdFeB permanent magnets can be arranged in the bottom area of ​​the column, medium field strength ferrite permanent magnets can be arranged in the middle area, and lower field strength AlNiCo permanent magnets can be arranged in the top area. Temperature control can be achieved using a PT100 temperature sensor in conjunction with a PID temperature control system. A high-gradient magnetic separator can be used for particle recovery, and a temperature-controlled oscillating reactor can be used for surface repair.

[0088] In practice, during the operation of the distillation column, the magnetic field strength is maintained at 0.9T in the bottom zone, 0.4T in the middle zone, and 0.05T in the top zone. The bottom temperature is controlled at 85℃, with temperature fluctuations within ±2℃. The bottom liquid is first subjected to a magnetic separator with a magnetic field strength of 1.2T for preliminary recovery. The collected magnetic particles are transferred to a heptane solution containing 1.0% oleic acid and treated by oscillation at 120 times per minute at 80℃ for 20 minutes. After magnetic separation, the treated particles are washed twice with fresh heptane for later use.

[0089] This gradient magnetic field design effectively suppresses the aggregation of magnetic particles during distillation. Different magnetic field intensities are set in different sections of the column, ensuring effective particle retention while avoiding particle aggregation caused by excessively strong magnetic fields. Appropriate temperature control helps maintain system stability, and oleic acid treatment repairs any hydrophobic surfaces that may have been damaged during distillation, restoring their emulsifying properties. This method provides a feasible solution for the recovery and regeneration of magnetic particles, facilitating multiple recycling of the particles.

[0090] In another technical solution, the recovered high-purity solvent and the particles after repairing the hydrophobic surface are mixed and then transported back to the Pickering emulsion tank. The specific mixing process is as follows:

[0091] The particles after repairing the hydrophobic surface were dispersed in deionized water at a concentration of 0.7-1.1% w / v and then ultrasonically treated at a frequency of 40 kHz and a power of 50 W / L for 10 min to obtain a homogeneous aqueous dispersion.

[0092] High-purity solvent is used as the oil phase and injected into the water phase at a uniform rate of 5-10 L / min, with a volume ratio of oil phase to water phase of 1:1.5-1:2.5.

[0093] The emulsion was first processed at 8000-10000 rpm for 3 min in a high-speed homogenizer to form a crude emulsion, and then processed at 12000-15000 rpm for 2 min to make the emulsion droplet size 1.5±0.3μm.

[0094] After being left to stand for 24-48 hours to age, the emulsion is returned to the Pickering emulsion tank for use in step two, sheepskin processing.

[0095] In the above technical solution, the emulsion regeneration system described in step five can be equipped with a dedicated configuration device. A jacketed stirred tank can be used as the aqueous phase dispersion container, equipped with an ultrasonic generator and a temperature control system. A metering pump and distributor can be used for oil phase injection, a shear homogenizer can be used for high-speed homogenization, and an insulated storage tank can be used for emulsion aging. Deionized water can be ultrapure water with a resistivity greater than 18 MΩ·cm, oleic acid-modified iron(III) oxide core-shell magnetic particles can be obtained from the aforementioned recovery process, and high-purity n-heptane can be obtained from the molecular sieve purification process.

[0096] In practice, the repaired magnetic particles are first dispersed in deionized water at a weight-volume concentration of 0.9%, and then ultrasonically treated for 10 minutes at a frequency of 40 kHz and a power of 50 watts per liter to obtain a uniform aqueous dispersion. High-purity n-heptane is used as the oil phase and added to the aqueous phase at a uniform injection rate of 8 liters per minute, with a volume ratio of oil phase to water phase of 1:2. The mixture is then transferred to a high-speed homogenizer, first processed at 9000 rpm for 3 minutes to form a coarse emulsion, and then processed at 13000 rpm for 2 minutes to refine it. The prepared emulsion is transferred to an insulated storage tank and aged at 25°C for 36 hours before being pumped back to the Pickering emulsion tank for later use.

[0097] This configuration allows the recovered solvent and magnetic particles to reform a stable Pickering emulsion. Ultrasonic treatment facilitates the uniform dispersion of magnetic particles in the aqueous phase, while appropriate oil phase injection rates and stirring conditions promote the formation of uniformly sized emulsion droplets. The static aging process stabilizes the emulsion system, improving penetration and degreasing during subsequent sheepskin processing. This method provides technical support for material recycling and helps reduce production costs.

[0098] Example 1

[0099] A method for processing sheepskin into an edible form includes the following steps:

[0100] Step 1: Place the dehaired and surface-cleaned wet sheepskin in a hot water treatment tank equipped with a scraper-type agitator. Add a collagen protectant at a concentration of 15% by weight / volume, which is a 1:1 mass mixture of sorbitol and trehalose. Set the treatment temperature to 98℃ and treat for 40 minutes under normal pressure. Simultaneously, start the scraper-type agitator at 20 rpm and activate the medium-frequency ultrasonic treatment system at 30 kHz and a power density of 40 W / L. Under these conditions, the sheepskin fat cell membranes are disrupted by mechanical shearing and cavitation effects, releasing fat which is emulsified by the hot water to form an oil-water mixture, resulting in sheepskin with preliminary degreasing.

[0101] Step Two: Immediately transfer the sheepskin treated in Step One to an O / W type Pickering emulsion tank for further processing. The emulsion consists of n-heptane (boiling range 80-90℃) as the oil phase and an aqueous phase containing magnetite core-shell magnetic particles as a stabilizer, with the oil-to-aqueous volume ratio controlled at 1:2. The sheepskin treatment in the emulsion tank is divided into two stages: In the pre-permeation stage, the sheepskin is immersed in the emulsion and stirred at 280 rpm for 0-10 minutes, then the stirring speed is reduced to 130 rpm for 10-30 minutes; In the deep degreasing stage, an ultrasonic field with a frequency of 28 kHz and a power density of 60 W / L is applied, while a horizontal magnetic field of 0.4 T and a vertical magnetic field of 0.15 T are simultaneously activated. During this process, the rate of change in the emulsion's conductivity is monitored in real time. When the rate of change is less than 0.5 μS / cm·min, the magnetic field is paused for 30 seconds, and the measurement is repeated for confirmation. The total treatment time is 60 minutes.

[0102] Step 3: Remove the sheepskin treated in Step 2 from the emulsion tank and immediately send it to a centrifuge. Centrifuge at 2000 rpm for 5 minutes to remove the emulsion adhering to its surface. After this step, an edible sheepskin product with a fat content of no more than 0.5 wt% and a magnetic particle residue of no more than 35 ppm is finally obtained.

[0103] Step 4: The emulsion separated in Step 3 is sent to a distillation column for further separation and recovery. Heptane is recovered by distillation at a bottom temperature of 85°C. During distillation, an axial gradient magnetic field is applied within the column, with a magnetic field strength of 0.9T in the bottom region, 0.4T in the middle region, and less than 0.1T at the top. The recovered heptane vapor is condensed and then passed through a silanized 3Å molecular sieve column with a pore size of 0.33 nm for dehydration and deacidification at 55°C, yielding a high-purity solvent with a water content of less than 30 ppm and an acid value of less than 0.05 mg KOH / g.

[0104] The bottom liquid of the tower was subjected to a magnetic field strength of 1.2T to recover the core-shell magnetic particles of iron oxide. The recovered particles were dispersed in a hot n-heptane solution containing 1% oleic acid at 80℃ and treated with oscillation at a frequency of 120 times / min for 20 minutes to restore the hydrophobic surface properties of the particles.

[0105] The recovered high-purity n-heptane solvent and the surface-repaired magnetic particles were used to prepare an emulsion regeneration solution: First, the repaired particles were dispersed in deionized water at a concentration of 0.9% w / v and ultrasonically treated for 10 minutes at a frequency of 40 kHz and a power of 50 W / L to obtain a homogeneous aqueous dispersion. High-purity n-heptane was used as the oil phase and injected into the aqueous dispersion at a uniform injection rate of 8 L / min, with a volume ratio of oil phase to water phase of 1:2. The mixture was then transferred to a high-speed homogenizer and treated at 9000 rpm for 3 minutes to form a coarse emulsion, followed by a refinement at 13000 rpm for 2 minutes to achieve a droplet size of approximately 1.5 μm. Finally, the prepared emulsion was aged at 25°C for 36 hours and then returned to the Pickering emulsion tank for use in the sheepskin processing step two, achieving material recycling.

[0106] After the above complete process, an edible sheepskin product with a fat content of 0.4 wt% and magnetic particle residue of 35 ppm was finally obtained. The heptane solvent recovery rate reached over 92%, and the magnetic particles, after surface repair, exhibited good recyclability, allowing for reuse more than 10 times.

[0107] Comparative Example 1

[0108] Compared to Example 1, mechanical tumbling and medium-frequency ultrasonic treatment were omitted. The wet sheepskin was placed in a normal-pressure hot water bath and immersed in 95°C hot water for 40 minutes, during which only low-speed stirring (50 rpm) was maintained. A 15% w / v sorbitol-trehalose complex protective agent was also added to the aqueous medium. All other steps were the same as in Example 1.

[0109] Comparative Example 2

[0110] Compared to Example 1, the Pickering emulsion treatment based on magnetic particles was omitted. After the hot water treatment in step one, the sheepskin was transferred to a degreasing tank containing an aqueous solution of sodium dodecyl sulfate (SDS) surfactant at 5% by weight and immersed at 60°C for 90 minutes, relying solely on mechanical stirring. The degreasing endpoint was determined empirically and was fixed at 90 minutes. The remaining steps were the same as in Example 1.

[0111] Comparative Example 3

[0112] Compared to Example 1, the solvent and particle recycling system was eliminated. The emulsion treated in Step 2 was no longer distilled or magnetically separated, but instead treated centrally as waste. Fresh n-heptane solvent and brand-new iron tetroxide core-shell magnetic particles were used each time in Step 2 to prepare the Pickering emulsion. The remaining steps were consistent with Example 1.

[0113] Comparative Test of Quality Indicators for Sheepskin Products

[0114] The edible sheepskin products obtained in Example 1 and Comparative Examples 1-3 were used as samples and tested respectively. The test results are shown in Table 1.

[0115] Table 1

[0116]

[0117] As shown in Table 1, the edible sheepskin processing method provided by this invention in Example 1 is significantly superior to the compared traditional process in terms of overall performance. The edible sheepskin produced by this method has a low fat content and no chemical degreasing agent residue, resulting in high product purity and food safety. In contrast, relying solely on hot water treatment (Comparative Example 1) cannot effectively achieve deep degreasing; while using chemical degreasing agents (Comparative Example 2) introduces the risk of surfactant residue; although eliminating the circulation system (Comparative Example 3) can also achieve a low fat content, the cost is a significant increase in material consumption. Therefore, the method of this invention successfully achieves efficient circulation of the processing medium while ensuring high product quality, demonstrating comprehensive technical advantages.

[0118] Material consumption comparison test

[0119] The total amount of n-heptane solvent and the total amount of novel iron oxide core-shell magnetic particles consumed per ton of fresh wet sheepskin in the statistical examples and comparative examples are shown in Table 2.

[0120] Table 2

[0121]

[0122] As shown in Table 2, the method of the present invention in Example 1 demonstrates significant advantages in material consumption control. Through its built-in recycling system, it greatly reduces the unit consumption of solvents and functional materials during production. Compared to the traditional single-use approach (Comparative Example 3), this method effectively avoids continuous large-scale input of materials, reducing the production process's dependence on fresh raw materials to an extremely low level. This efficient resource utilization model not only directly reduces raw material procurement costs but also reduces the environmental burden caused by waste liquid treatment and material disposal at the source, demonstrating outstanding economic and environmental characteristics and providing a reliable path to achieving green and sustainable industrial production.

[0123] Safety testing

[0124] Safety tests were conducted on the iron oxide core-shell magnetic particles and edible sheepskin products described in this application. All tests were performed in accordance with national standardized methods and by the internal quality control laboratory. The test results are shown in Tables 3 and 4.

[0125] Table 3. Results of organic residue detection in iron oxide core-shell magnetic particles

[0126]

[0127] Table 4. Safety test results of edible sheepskin products

[0128]

[0129] As shown in Tables 3 and 4, the data fully demonstrate that the process of this invention can stably produce magnetic particles with extremely low organic residues (CTAB < 0.5 ppm, silicon residue < 5.0 ppm). The particle residue in the final sheepskin product is far below the safety limit (≤ 50 ppm), and authoritative toxicological tests have verified that it is actually non-toxic, non-cytotoxic, and non-genotoxic, fully meeting the safety requirements for food processing applications.

[0130] 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. For those skilled in the art, other modifications can be easily made. 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 processing sheepskin into an edible form, characterized in that, Includes the following steps: Step 1: Place the wet sheepskin that has been dehaired and cleaned on the surface into a hot water treatment tank and treat it at a temperature of 95-100℃ and normal pressure for 30-60 minutes. At the same time, mechanical tumbling is performed, supplemented by medium-frequency ultrasonic treatment at a frequency of 20-40kHz and an ultrasonic power density of 30-50W / L. This causes the sheepskin fat cell membrane to be destroyed by mechanical shearing and cavitation effects. The released fat is emulsified by hot water to form an oil-water mixture, and sheepskin with preliminary degreased is obtained. Step 2: Immediately transfer the sheepskin treated in Step 1 to an O / W type Pickering emulsion tank for further processing. The processing includes: During the pre-permeation stage, the sheepskin is immersed in the emulsion and then intermittent variable frequency stirring is started. The stirring speed is 200-300 rpm for 0-10 min and then reduced to 100-150 rpm for 10-30 min. During the deep degreasing stage, an ultrasonic field with a frequency of 28±2kHz and a power density of 50-80W / L is applied, and a magnetic field is activated simultaneously, with a horizontal magnetic field strength of 0.3-0.5T and a vertical magnetic field strength of 0.1-0.2T. Real-time monitoring of the change rate of emulsion conductivity; when |Δσ / Δt|<0.5μS / cm·min, the magnetic field is paused for 30s and then retested for confirmation. The total processing time is 30-120 min. The process is terminated early when the real-time monitoring shows that the rate of change of conductivity |Δσ / Δt| < 0.5 μS / cm·min. The Pickering emulsion consists of a n-heptane oil phase with a boiling point of 60-100℃ and an aqueous phase stabilizer of iron oxide core-shell magnetic particles with a particle size of 10-100 nm. The volume ratio of the oil phase to the aqueous phase is 1:1.5-1:2.

5. Step 3: Remove the sheepskin from the emulsion tank and centrifuge it at 1000-3000 rpm to remove the surface emulsion, obtaining edible sheepskin with a fat content ≤0.5wt% and magnetic particle residue ≤50ppm. Step 4: The separated emulsion is sent to a distillation column, where n-heptane is recovered by distillation at a bottom temperature of 80-90°C. Simultaneously, ferric oxide core-shell magnetic particles are recovered by magnetic separation from the bottom liquid and recycled for use in the Pickering emulsion preparation in Step 2.

2. The method for processing sheepskin into an edible form as described in claim 1, characterized in that, In step one, a collagen protectant is added to the water medium in the hot water treatment tank. The collagen protectant is selected from at least one of polyols, reducing disaccharides, polyhydroxy compounds or edible inorganic salts. The concentration of the collagen protectant added to the water medium is 5-25% w / v.

3. The method for processing sheepskin into an edible form as described in claim 1, characterized in that, The mechanical tumbling in step one is achieved by a scraper-type agitator installed in the tank, which runs at a speed of 15-25 rpm, causing the sheepskin to continuously turn over and rub against each other.

4. The method for processing sheepskin into an edible form as described in claim 1, characterized in that, The preparation method of the iron oxide core-shell magnetic particles in step two is as follows: Mix 0.5-1.0 mol / L FeCl2 and FeCl3 solutions according to Fe 2+ :Fe 3+ The mixture was prepared in a molar ratio of 1:1.8-2.

2. 0.3-0.6 mol / L sodium citrate was added under nitrogen protection. 0.5-1.0 mol / L ammonia was added dropwise at 50-60℃ until the pH reached 9.5-10.

5. After aging for 2-3 hours, magnetic separation was performed using a magnetic field with a strength of 0.8-1.2T. The supernatant was discarded. The obtained magnetic precipitate was washed three times with hot deionized water at 60-70℃ and then twice with anhydrous ethanol to obtain Fe3O4 nanoparticles with a particle size of 15-25 nm. The obtained Fe3O4 particles were dispersed in a mixed solvent of ethanol and water with a volume ratio of 3:

1. Hexadecyltrimethylammonium bromide was added at a mass ratio of 0.1-0.3 wt% of the total mass of the mixed solvent. After ultrasonic treatment for 10-15 min, tetraethyl orthosilicate was added dropwise at a rate of 0.5-1.0 mL / min and a mass ratio of tetraethyl orthosilicate to Fe3O4 of 1:2-1:

3. The reaction was carried out at 40-45℃ for 4-6 h to form a 5-8 nm silicon shell. After the reaction was completed, magnetic separation was performed by a magnetic field with a strength of 0.8-1.2 T. The supernatant was discarded. The obtained particles were washed three times each with ethanol and acetone, and then dried in a vacuum drying oven at 60-80℃ for 6-8 h to obtain Fe3O4 particles coated with a mesoporous silicon layer. The Fe3O4 particles coated with the obtained mesoporous silica layer were dispersed in toluene, and octyltrimethoxysilane was added at a molar ratio of 3:1 to 5:1 with Fe3O4. The mixture was refluxed at 110-120℃ for 8-10 h. After reflux, the mixture was cooled to room temperature and magnetically separated by a magnetic field of 1.0-1.5 T. The supernatant was discarded, and the resulting particles were washed twice with toluene and then three times with n-heptane. The washed particles were placed in a tube furnace and heated to 350-450°C at a rate of 3-5°C / min under nitrogen protection, and calcined for 1-2 hours to completely remove any organic residues. The calcined particles were then dispersed again in n-heptane and magnetically separated by a magnetic field of 1.0-1.5T. The supernatant was discarded, and the resulting particles were pure iron oxide core-shell magnetic particles with CTAB residue <1ppm and TEOS residue <5ppm.

5. The method for processing sheepskin into an edible form as described in claim 1, characterized in that, In step four, the n-heptane recovered by distillation is passed through a silanized 3Å molecular sieve column with a pore size of 0.33±0.02nm and dehydrated and deacidified at 50-60℃ to obtain a high-purity solvent with a water content ≤30ppm and an acid value ≤0.05mgKOH / g.

6. The method for processing sheepskin into an edible form as described in claim 5, characterized in that, The recovery process of the core-shell magnetic particles of iron oxide in step four is as follows: An axial gradient magnetic field is applied in the distillation column, with an intensity of 0.8-1.0T in the bottom zone, 0.3-0.5T in the middle zone, and <0.1T in the top zone. The bottom temperature is controlled at 85±2℃ to inhibit the agglomeration of magnetic particles. The bottom liquid is treated with a magnetic field of 1.0-1.5T to recover the particles, which are then dispersed in hot n-heptane containing 0.8-1.2% oleic acid at 80℃ and shaken for 20 minutes to repair the hydrophobic surface of the particles.

7. The method for processing sheepskin into an edible form as described in claim 6, characterized in that, The recovered high-purity solvent and the particles after repairing the hydrophobic surface are mixed and then transported back to the Pickering emulsion tank. The specific preparation process is as follows: The particles after repairing the hydrophobic surface were dispersed in deionized water at a concentration of 0.7-1.1% w / v and then ultrasonically treated at a frequency of 40kHz and a power of 50W / L for 10 minutes to obtain a homogeneous aqueous dispersion. High-purity solvent is used as the oil phase and injected into the water phase at a uniform rate of 5-10 L / min, with a volume ratio of oil phase to water phase of 1:1.5-1:2.

5. The emulsion was first processed at 8000-10000 rpm for 3 min in a high-speed homogenizer to form a crude emulsion, and then processed at 12000-15000 rpm for 2 min to make the emulsion droplet size 1.5±0.3μm. After being left to stand for 24-48 hours to age, the emulsion is returned to the Pickering emulsion tank for use in step two, sheepskin processing.

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