Method of processing pelt food

Abstract

The application discloses a kind of processing methods of mutton skin food, belong to food processing technical field.For the problems such as not completely removing fishy smell, uneven calcium salt penetration caused by dense tissue, large taste difference between outside and inside of product in existing mutton skin processing, the method comprises the following steps: removing hair, washing and cutting fresh mutton skin into pieces; the skin pieces are placed in a reaction solution containing complex protease and flavour protease for enzymolysis; the enzymolyzed skin pieces are transferred into an aqueous solution containing edible calcium salt and organic acid for soaking; finally, the skin pieces are marinated, cooled, shaped, and packaged.The application effectively removes fishy smell and softens the tissue moderately through complex enzymolysis, and then the skin pieces are treated with calcium salt and organic acid coupling to make them brittle, which significantly improves the texture of the skin pieces by forming a uniform gel network through ion crosslinking.The method is simple and mild, and the mutton skin food prepared has low fishy smell, uniform crisp and tender taste, and full flavor penetration, which is suitable for high-value utilization and industrial production of mutton skin.

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 food products. Background Technology

[0002] Sheepskin is rich in collagen and is a potential food processing ingredient. However, sheepskin itself has a distinct muttony odor, and its dense collagen fiber network structure makes it tough and difficult to chew, resulting in an unpleasant taste when eaten directly. Therefore, when processing it into ready-to-eat foods, it is essential to address both the removal of the muttony odor and the softening process.

[0003] In existing technologies, the deodorization of animal hide raw materials typically involves alkaline soaking or high-temperature cooking. While alkaline treatment can hydrolyze proteins and remove some odorous substances to a certain extent, the harsh conditions can easily lead to excessive dissolution and denaturation of collagen, resulting in a decrease in raw material yield. It also produces unpleasant odor byproducts, and the alkaline residue requires repeated rinsing with large amounts of water, making the process lengthy and generating significant wastewater. Although high-temperature cooking can soften the hide, the odorous substances may be further released or transformed during heating, limiting the deodorization effect. Furthermore, excessive heating can gelatinize collagen, causing it to lose its elasticity and chewiness.

[0004] Regarding the crisping or hardening treatment, known methods for achieving a crisp texture in leather raw materials include soaking in edible calcium salts. This utilizes the cross-linking of calcium ions with collagen or residual acidic groups to form a gel network, thereby increasing the product's crispness and hardness. However, due to the dense structure of sheepskin, traditional static soaking methods rely solely on passive diffusion due to concentration gradients, making it difficult for calcium ions to penetrate evenly into the deeper layers of the hide within a short time. In actual production, excessive calcium deposition on the surface and insufficient penetration in the center are common, resulting in a product that is hard on the outside and soft on the inside, with a significant difference in texture. Attempts to improve penetration have included extending the soaking time or increasing the calcium salt concentration, but these methods easily lead to excessive surface crisping or even hardening, and also increase processing time and costs, with unsatisfactory results.

[0005] Furthermore, sheepskin raw materials naturally vary in thickness, and hides from different parts or individuals also differ in density. During enzymatic softening, if a uniform temperature, time, and enzyme dosage are used, thin and porous sections often undergo over-hydrolysis, becoming soft and losing their supporting structure; while thick and dense sections are under-hydrolyzed, retaining some toughness. This inconsistency in processing endpoints due to raw material variations has long lacked effective online monitoring and control methods, resulting in poor batch-to-batch product stability and hindering industrialized, standardized continuous production.

[0006] In summary, existing sheepskin food processing methods have significant shortcomings in terms of deodorization, penetration uniformity, and textural consistency, and there is an urgent need to develop a processing technology that can address these issues in a coordinated manner. Summary of the Invention

[0007] One object of the present invention is to solve at least the above-mentioned problems and to provide at least the advantages that will be described later.

[0008] To achieve these objectives and other advantages according to the present invention, a method for processing sheepskin food products is provided, comprising the following steps:

[0009] S1. Raw material pretreatment: Remove the hair from the fresh sheepskin, wash it, and cut it into pieces of the predetermined shape;

[0010] S2. Enzymatic deodorization treatment: Place the skin pieces in a reaction solution containing compound protease and flavor protease, and carry out the first stage of enzymatic hydrolysis at pH 5.5-6.5 and temperature 45-55℃ for 30-90 minutes.

[0011] S3, Coupling embrittlement treatment: The leather pieces treated in S2 are transferred to an aqueous solution containing edible calcium salt and organic acid for soaking treatment. The concentration of edible calcium salt is 0.5%-2.0%, the concentration of organic acid is 0.1%-0.5%, the soaking temperature is 20-40℃, and the soaking time is 2-6 hours.

[0012] S4. Cooking and Shaping: The leather pieces treated in S3 are braised until fully cooked, then cooled, shaped, and packaged.

[0013] Specifically, the coupling embrittlement treatment in S3 includes:

[0014] S3a, Primary Infiltration: The leather pieces treated with S2 are immersed in an aqueous solution of edible calcium salt and organic acid. First, the solution is kept at 20-30℃ and 0.08-0.1MPa vacuum for 5-15 minutes to allow air to be released from the pores of the leather pieces and to promote the initial wetting of the solution.

[0015] S3b, Pressure-driven penetration: Subsequently, the vacuum is released within 1-2 minutes and a positive pressure of 0.2-0.5 MPa is applied. This pressure is maintained for 10-20 minutes, using the pressure difference to drive the solution to rapidly penetrate into the deep layers of the skin.

[0016] S3c, Dynamic Release: The pressure is rapidly released to normal pressure within 30 seconds. During this process, the solution in the micropores inside the leather expands slightly due to the sudden drop in external pressure, which helps to form a more uniform micro-embrittlement structure.

[0017] S3d, Cyclic processing: Repeat the vacuum-pressurization-release cycle from S3a to S3c 2-4 times;

[0018] S3e, Equilibrium Embrittlement: Finally, continue soaking under normal pressure and 20-40℃ conditions until the total time meets 2-6 hours to complete ion exchange and stabilize the gel network.

[0019] Preferably, the complex protease in S2 is a mixture of papain and trypsin in a mass ratio of (1-3):1, with a total enzyme activity of 500-1500 U / g sheepskin; the flavor protease has an enzyme activity of 300-800 U / g sheepskin.

[0020] Preferably, the edible calcium salt in S3 is one or more of calcium chloride, calcium lactate, or calcium gluconate; and the organic acid is one or more of citric acid, lactic acid, or malic acid.

[0021] Preferably, after step S3, a rinsing and neutralization step is also included: rinsing the leather piece 1-3 times with clean water, and then soaking and neutralizing it in a sodium bicarbonate solution with a concentration of 0.05%-0.2% for 5-15 minutes.

[0022] Preferably, in step S4, the brine used contains 0.01%-0.1% of natural spice extract, wherein the natural spice extract is cumin extract and / or Sichuan pepper extract.

[0023] Preferably, the enzymatic deodorization treatment in S2 specifically includes:

[0024] S2a. Prepare two independent constant-temperature enzymatic hydrolysis containers, one as a high-temperature enzymatic hydrolysis vessel and the other as a low-temperature enzymatic hydrolysis vessel. Pour equal amounts of reaction solution containing compound protease and flavor protease into each vessel. Maintain the temperature in the high-temperature enzymatic hydrolysis vessel at 50-55℃ and the temperature in the low-temperature enzymatic hydrolysis vessel at 40-45℃. Weigh each pretreated piece of leather, record the initial mass M0 of each piece, and calculate the total mass.

[0025] S2b. Put all the leather pieces into the high-temperature enzymatic hydrolysis tank, start timing and continue to stir gently; when the enzymatic hydrolysis has reached 1 / 3 of the total predetermined time, conduct the first monitoring: take all the leather pieces out of the high-temperature tank, quickly absorb the surface moisture with gauze, weigh them one by one, and record the mass M1 of each piece of leather at this time.

[0026] S2c, Calculate the quality loss rate of each piece of leather from the initial stage to the present: ΔM1 = (M0 - M1) / M0 × 100%; operate according to the following rules:

[0027] All leather pieces with ΔM1 greater than or equal to the preset threshold A were manually transferred to a low-temperature enzymatic hydrolysis tank; leather pieces with ΔM1 less than the preset threshold A were returned to the high-temperature enzymatic hydrolysis tank for further enzymatic hydrolysis; the value of A was in the range of 8%-12%;

[0028] After S2d and the transfer is completed, the leather pieces in the high-temperature tank and the low-temperature tank continue to be enzymatically hydrolyzed at their respective temperatures. When 2 / 3 of the total predetermined time is reached, a second monitoring is performed: the leather pieces in the two tanks are taken out again, dried, and weighed one by one, and the mass M2 is recorded.

[0029] For the leather pieces in the high-temperature enzymatic hydrolysis tank, calculate the mass loss rate ΔM2 in the second stage. Manually transfer all leather pieces with ΔM2 greater than or equal to the preset threshold B to the low-temperature enzymatic hydrolysis tank; return leather pieces with ΔM2 less than the preset threshold B to the high-temperature enzymatic hydrolysis tank for further enzymatic hydrolysis; the value of B ranges from 5% to 8%.

[0030] For the leather pieces in the cryogenic tank, calculate the change in mass since entering the cryogenic tank. If the change rate is less than 0.5% after two consecutive weighings, it can be determined that the endpoint has been reached and the enzymatic hydrolysis can be terminated early.

[0031] S2e: The leather pieces in the high-temperature tank are processed until the end of the total predetermined time; the leather pieces in the low-temperature tank are processed until the quality is stable, but the total time does not exceed the total predetermined time; finally, all leather pieces are merged to proceed to the next step.

[0032] Preferably, before step S3, the following steps are also included:

[0033] S2-1. Immerse the leather pieces that have undergone enzymatic deodorization treatment in clean water at a temperature of 35-45℃, apply a vacuum pressure of -0.075 MPa to -0.090 MPa in the container, and maintain it for 3-8 minutes to allow the leather tissue to fully absorb water and swell under negative pressure.

[0034] S2-2. Within 1-3 seconds, sterile inert gas or steam is rapidly introduced into the container, causing the pressure to rise sharply to 0.4-0.6 MPa, and this high-pressure state is maintained for 5-15 seconds. By using the instantaneous pressure difference impact, a large number of microscopic permeable channels and fissures are formed in the collagen fiber network structure of the skin piece.

[0035] S2-3. Release the container pressure to normal pressure within 2-5 seconds, then let the leather block stand in clean water for 5-10 minutes to balance. After draining the surface water, immediately proceed to step S3.

[0036] The present invention has at least the following beneficial effects:

[0037] This invention provides a processing method for sheepskin food products. Through systematic process design and multi-step synergistic effects, it achieves significantly superior comprehensive benefits compared to existing technologies. In the enzymatic deodorization stage, this invention employs a compound system of complex proteases and flavor proteases, which performs specific hydrolysis under mild pH and temperature conditions. This effectively removes the inherent fishy and muttony odor substances from sheepskin while avoiding excessive protein degradation and off-flavor byproducts caused by traditional alkaline treatments. Sensory evaluation data shows that sheepskin food products processed using this invention achieve a fishy and muttony odor score of 3.7 out of 4, while the comparative sample only scores 1.9, indicating an extremely thorough deodorization effect.

[0038] Building upon this foundation, this invention further introduces a zoned, stepped enzymatic hydrolysis control method based on mass loss rate monitoring. Through independent enzymatic hydrolysis in dual temperature zones and dynamic material transfer, precise control of the hydrolysis degree of leather pieces with different thicknesses is achieved. Experimental results show that this process reduces the standard deviation of the degree of hydrolysis between different leather pieces from over 1.75 to 0.43, a reduction of over 75%, completely resolving the problem of inconsistent enzymatic hydrolysis endpoints caused by differences in raw material thickness. The uniform degree of hydrolysis provides homogeneous precursor materials for subsequent crisping treatment, while ensuring the stable formation of flavor precursors, resulting in a significant improvement in the flavor intensity and harmony of the final product.

[0039] In the crisping process, this invention creatively employs a pulsed vacuum-pressurized cyclic soaking process. Through multiple cycles of primary penetration, pressure-driven penetration, and dynamic release, calcium ions and organic acid solution are forced to uniformly penetrate deep into the hide. Calcium ion concentration gradient measurements show that this process drastically reduces the coefficient of variation of calcium content in the surface, subsurface, and central layers of the hide from 57.6% in traditional static soaking to below 7.3%, resulting in a highly consistent crisping effect across the inner and outer layers. Texture analysis results indicate that sheepskin products processed using this method have moderate hardness, excellent elasticity, and suitable chewiness, completely avoiding the defects of traditional processes, such as a hard exterior, tough interior, and uneven texture.

[0040] To further overcome the natural barrier of dense collagen fiber tissue to solution penetration, this invention adds a controllable microporousization pretreatment step before the embrittlement process. Through the synergistic effect of pulsed negative pressure expansion and instantaneous high-pressure impact, a large number of micro-channels and fissures are actively created in the collagen fiber network structure. Mercury porosimetry analysis shows that this pretreatment increases the porosity of the leather by 84.4%, and water absorption kinetics experiments show that its initial water absorption rate increases by 126%, and its saturated liquid holding capacity increases by 29.5%. This physical structural improvement not only lays a solid foundation for the rapid and uniform penetration of the subsequent embrittlement solution, but also significantly enhances the diffusion and adsorption capacity of flavor substances during the braising process, resulting in a rich and lasting aroma and a full-bodied and mellow taste.

[0041] The aforementioned innovative process steps are not simply superimposed, but exhibit a significant synergistic effect: the uniform enzymatic hydrolysis creates a textural basis for uniform embrittlement, the microporous pretreatment opens physical channels for solution penetration, and the pulsed vacuum-pressurized cycle achieves ideal ion distribution through forced driving force. The organic integration of these three elements enables the final sheepskin food to achieve optimal levels in sensory quality, textural characteristics, and microstructural uniformity. The total sensory score increased from 16.7 points (out of 32) in the traditional process to 28.4 points, the hardness decreased from 1680g to 890g, the elasticity increased from 0.58 to 0.86, and the chewiness decreased from 950g to 450g, with all indicators showing significant improvement.

[0042] In summary, this invention provides a complete, synergistic, precise, and controllable solution to a series of long-standing technical problems in sheepskin food processing, such as incomplete deodorization, uneven enzymatic hydrolysis, difficulty in crisping and penetration, and large differences in taste. The resulting products have low fishy smell, a crisp and uniform taste, full flavor penetration, and excellent texture, and have extremely high commercial value and market competitiveness.

[0043] 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

[0044] The present invention will be further described in detail below with reference to embodiments, so that those skilled in the art can implement it based on the description.

[0045] 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.

[0046] <Example 1>

[0047] A method for processing sheepskin food products includes the following steps:

[0048] S1. Raw material pretreatment: Remove the hair from the fresh sheepskin, wash it, and cut it into pieces of the predetermined shape;

[0049] S2. Enzymatic deodorization treatment: Place the hide pieces in a reaction solution containing a complex protease and a flavor protease, and carry out the first stage of enzymatic hydrolysis at pH 6 and 50℃ for 80 minutes. The complex protease is a mixture of papain and trypsin in a mass ratio of 2:1, with a total enzyme activity of 1000 U / g sheepskin; the flavor protease has an enzyme activity of 500 U / g sheepskin.

[0050] S3, Coupling embrittlement treatment: The leather pieces treated in S2 are transferred to an aqueous solution containing edible calcium salt and organic acid for soaking treatment. The concentration of the edible calcium salt is 1.0%, the concentration of the organic acid is 0.3%, the soaking temperature is 30°C, and the soaking time is 5 hours. The edible calcium salt is calcium lactate, and the organic acid is lactic acid.

[0051] S4. Cooking and Shaping: The skin pieces treated in S3 are braised until fully cooked, then cooled, shaped, and packaged. The braising liquid contains 0.1% natural spice extract, which is cumin extract. The cumin extract is extracted at a ratio of 1g:40ml (the ratio of cumin powder to water) at 72℃ for 130 minutes, and the extract is dried.

[0052] <Example 2>

[0053] The process is basically the same as in Example 1, except that after step S3, a rinsing and neutralization step is added: the leather piece is rinsed twice with clean water, and then soaked and neutralized in a 0.1% sodium bicarbonate solution for 10 minutes.

[0054] <Example 3>

[0055] It is basically the same as Example 2, except that:

[0056] The coupling embrittlement process in S3 specifically includes:

[0057] S3a, Primary Infiltration: The leather pieces treated with S2 are immersed in an aqueous solution of edible calcium salt and organic acid. First, they are kept at 25°C and 0.08MPa vacuum for 10 minutes to allow air to be released from the pores of the leather tissue and to promote the initial wetting of the solution.

[0058] S3b, Pressure-driven penetration: Subsequently, the vacuum is released within 1 minute and a positive pressure of 0.3 MPa is applied and maintained for 15 minutes, using the pressure difference to drive the solution to rapidly penetrate into the deep layers of the skin block;

[0059] S3c, Dynamic Release: The pressure is rapidly released to normal pressure within 30 seconds. During this process, the solution in the micropores inside the leather expands slightly due to the sudden drop in external pressure, which helps to form a more uniform micro-embrittlement structure.

[0060] S3d, Cyclic Processing: Repeat the vacuum-pressurization-release cycle from S3a to S3c three times;

[0061] S3e, Equilibrium Embrittlement: Finally, continue soaking under normal pressure and 30°C until the total time meets 4 hours to complete ion exchange and stabilize the gel network.

[0062] <Example 4>

[0063] It is basically the same as Example 3, except that:

[0064] The enzymatic deodorization process in S2 specifically includes:

[0065] S2a. Prepare two independent constant-temperature enzymatic hydrolysis containers, one as a high-temperature enzymatic hydrolysis vessel and the other as a low-temperature enzymatic hydrolysis vessel. Pour equal amounts of reaction solution containing compound protease and flavor protease into each vessel. Maintain the temperature in the high-temperature enzymatic hydrolysis vessel at 52°C and the temperature in the low-temperature enzymatic hydrolysis vessel at 42°C. Weigh each pretreated piece of leather, record the initial mass M0 of each piece of leather, and calculate the total mass.

[0066] S2b. Put all the leather pieces into the high-temperature enzymatic hydrolysis tank, start timing and continue to stir gently; when the enzymatic hydrolysis has reached 1 / 3 of the total predetermined time, conduct the first monitoring: take all the leather pieces out of the high-temperature tank, quickly absorb the surface moisture with gauze, weigh them one by one, and record the mass M1 of each piece of leather at this time.

[0067] S2c, Calculate the quality loss rate of each piece of leather from the initial stage to the present, ΔM1 = (M0 - M1) / M0 × 100%; operate according to the following rules:

[0068] All leather pieces with ΔM1 greater than or equal to 10% of the preset threshold were manually transferred to a low-temperature enzymatic hydrolysis tank; leather pieces with ΔM1 less than 10% of the preset threshold were returned to a high-temperature enzymatic hydrolysis tank for further enzymatic hydrolysis.

[0069] After S2d and the transfer is completed, the leather pieces in the high-temperature tank and the low-temperature tank continue to be enzymatically hydrolyzed at their respective temperatures. When 2 / 3 of the total predetermined time is reached, a second monitoring is performed: the leather pieces in the two tanks are taken out again, dried, and weighed one by one, and the mass M2 is recorded.

[0070] For the leather pieces in the high-temperature enzymatic hydrolysis tank, calculate the mass loss rate ΔM2 = (M1–M2) / M1×100% in the second stage. Manually transfer all leather pieces with ΔM2 greater than or equal to the preset threshold of 5% to the low-temperature enzymatic hydrolysis tank; put the leather pieces with ΔM2 less than the preset threshold of 5% back into the high-temperature enzymatic hydrolysis tank for continued enzymatic hydrolysis.

[0071] For the leather pieces in the cryogenic tank, calculate the change in mass since entering the cryogenic tank. If the change rate is less than 0.5% after two consecutive weighings, it can be determined that the endpoint has been reached and the enzymatic hydrolysis can be terminated early.

[0072] S2e: The leather pieces in the high-temperature tank are processed until the end of the total predetermined time; the leather pieces in the low-temperature tank are processed until the quality is stable, but the total time does not exceed the total predetermined time; finally, all leather pieces are merged to proceed to the next step.

[0073] <Example 5>

[0074] It is basically the same as Example 4, except that:

[0075] Before step S3, the following are also included:

[0076] S2-1. Immerse the leather pieces that have undergone enzymatic deodorization treatment in clean water at a temperature of 40°C, apply a vacuum pressure of -0.080MPa in the container, and maintain it for 5 minutes to allow the leather tissue to fully absorb water and swell under negative pressure.

[0077] S2-2. Within 2 seconds, sterile inert gas or steam is rapidly introduced into the container, causing the pressure to rise sharply to 0.4 MPa, and this high-pressure state is maintained for 10 seconds. By using the instantaneous pressure difference impact, a large number of microscopic permeable channels and fissures are formed in the collagen fiber network structure of the skin piece.

[0078] S2-3. Release the container pressure to normal pressure within 5 seconds, then let the leather block stand in clean water for 10 minutes to balance. After draining the surface water, immediately proceed to step S3.

[0079] <Comparative Example 1>

[0080] A traditional method for processing sheepskin food products includes the following steps:

[0081] S1. Remove the hair from the fresh sheepskin, wash it, and cut it into pieces of the predetermined shape;

[0082] S2. Place the leather pieces in a 1.5% edible alkali solution and soak them at 60°C for 60 minutes, then rinse thoroughly with clean water until neutral.

[0083] S3. Transfer the treated leather pieces into an aqueous solution containing 1.0% calcium chloride and immerse them statically at 30°C for 5 hours.

[0084] S4. Braise the skin pieces until fully cooked, then cool, shape, and package them. Use the same braising liquid formula as in Example 1 during the braising process.

[0085] Sensory evaluation

[0086] Select more than 10 trained sensory evaluators to conduct evaluations in a quiet, odorless, and well-lit independent sensory evaluation room according to the standards in Table 1 below. The samples are cut into pieces of uniform size and shape, randomly numbered, and presented to the evaluators at room temperature. Blind evaluation and independent scoring are adopted.

[0087] Table 1

[0088]

[0089]

[0090] Each evaluator scored each sample and each indicator independently, and calculated the average score and total score for each sample on each indicator. The results are shown in Table 2 below.

[0091] Table 2

[0092]

[0093] Comparative Example 1, employing a traditional alkali treatment + static calcium leaching process, achieved significantly lower sensory scores than the embodiments of this invention, with a total score of only 16.7 points. This was characterized by a strong fishy and muttony odor, a tough and chewy texture, and unevenness between the inside and outside. Examples 1 and 2, representing the basic scheme of this invention, achieved total scores of 22.5 to 23.5 points. The fishy and muttony odor was significantly improved, and the crispness and hardness were moderate, but the uniformity score was low, indicating inconsistent texture. Example 3 introduced pulsed vacuum-pressure cyclic embrittlement, improving uniformity to 2.4 points and crispness and hardness to 3.4 points, demonstrating that this process significantly improved the uniformity of calcium ion penetration. Example 4 further introduced partitioned stepwise enzymatic hydrolysis, improving the fishy and muttony odor score to 3.6 points and the uniformity score to 2.6 points, demonstrating that this process ensured the uniformity of the enzymatic hydrolysis endpoint, laying a good foundation for subsequent processing. Example 5 further introduced controllable microporous pretreatment, and all indicators reached the optimal level, with a total score of 28.4 points. The characteristic aroma, flavor intensity and persistence were significantly better than other groups, proving that microporous pretreatment effectively promoted the penetration and adsorption of flavor substances.

[0094] <Textural Properties Determination>

[0095] The texture analyzer was calibrated, and the hardness, elasticity, chewiness, and resilience of sheepskin products were tested using a TA / 1 in probe and the TPA mode of the analyzer. Parameter settings: pre-test rate 2 mm / s, test rate 1 mm / s, post-test rate 2 mm / s, compression degree 30%, two compressions at 5-second intervals, automatic triggering, trigger force 5 g.

[0096] The textural properties are shown in Table 3 below:

[0097] Table 3

[0098]

[0099] Comparative Example 1 had a hardness as high as 1680g, an elasticity of only 0.58, and a chewiness of 950g, exhibiting excessive hardness, lack of elasticity, and difficulty in chewing. Examples 1-2 had a hardness of approximately 1220-1250g and an elasticity of 0.72-0.73, showing improvement over the comparative example, but still being relatively hard. Example 3 reduced the hardness to 980g, increased the elasticity to 0.81, and reduced the chewiness to 520g, demonstrating a significant uniform embrittlement effect. Example 4 had a hardness of 950g and an elasticity of 0.83, indicating that uniform enzymatic hydrolysis further optimized the textural basis. Example 5 had a hardness of 890g, an elasticity of 0.86, a chewiness of 450g, and a resilience of 0.40, with all textural indicators being optimal, proving a significant synergistic effect between microporous pretreatment, pulsed vacuum-pressure cyclic embrittlement, and partitioned stepwise enzymatic hydrolysis.

[0100] <Calcium Ion Concentration Gradient Measurement>

[0101] The sheepskin food products treated in the examples / comparative examples were immediately frozen and fixed with liquid nitrogen. Then, the surface layer, subsurface layer, and central layer were cut along the thickness direction using a cryostat. Samples of each layer were accurately weighed and, after acid digestion, the calcium ion content (unit: mg / g dry weight) of each sample was determined using atomic absorption spectrometry (AAS). The standard deviation (SD) and coefficient of variation (CV) of the calcium content of each layer were calculated.

[0102] The calcium ion concentration gradient results are shown in Table 4 below:

[0103] Table 4

[0104]

[0105] Comparative Example 1 showed a surface calcium content as high as 4.12 mg / g, while the central layer only had 0.96 mg / g, with a coefficient of variation as high as 57.6%, indicating that traditional static immersion led to severe excessive surface deposition and insufficient central penetration. Examples 1 and 2 showed coefficients of variation ranging from 25.6% to 27.3%, still exhibiting a significant gradient. In Example 3, after introducing a pulsed vacuum-pressurized cycling process, the coefficient of variation plummeted to 7.3%, and the central layer calcium content increased to 2.88 mg / g, proving that this process forced the solution to achieve uniform penetration from the surface inwards. Example 4 further reduced the coefficient of variation to 6.3%, with uniform enzymatic hydrolysis creating a better tissue basis for uniform embrittlement. Example 5 showed a coefficient of variation of only 4.4%, with highly consistent calcium content across the three layers. The microporous pretreatment and coupled embrittlement produced a synergistic effect, achieving near-ideal uniform penetration.

[0106] <Determination of the dispersion of hydrolysis degree>

[0107] The internationally recognized pH-stat method was used to determine the degree of hydrolysis of the samples from the examples / comparative examples after enzymatic hydrolysis. For Examples 1-3 and the comparative example, six sheepskin samples were taken from each example. For Examples 4 and 5, three sheepskin samples were taken from both the high-temperature and low-temperature enzymatic hydrolysis vessels. The standard deviation (SD) of the degree of hydrolysis data for all samples was calculated for each example.

[0108] The dispersion results of the degree of hydrolysis are shown in Table 5 below:

[0109] Table 5

[0110]

[0111] Note: Comparative Example 1 was treated with alkali and did not undergo enzymatic hydrolysis, so it is not suitable for the determination of degree of hydrolysis.

[0112] Examples 1-3 employed traditional single-temperature enzymatic hydrolysis. Although compound proteases and flavor proteases were used, significant differences in the degree of hydrolysis were observed among different pieces of leather, with standard deviations as high as 1.75-1.82, reflecting inconsistencies in the hydrolysis endpoints due to uneven raw material thickness. Examples 4 and 5 introduced a zoned, stepped enzymatic hydrolysis method. Through monitoring of mass loss rate and dynamic zone transfer, the standard deviation of the degree of hydrolysis was reduced from over 1.75 to 0.43 and 0.41, respectively, a reduction of over 75%. This directly demonstrates that the process successfully achieved differentiated and precise enzymatic hydrolysis control for pieces of leather of different thicknesses, resulting in a highly uniform final degree of hydrolysis.

[0113] <Porosity Measurement>

[0114] The total porosity (%) was directly obtained by using mercury porosimetry and a mercury porosimeter to test the leather pieces that were about to enter step S3 in Examples 4 and 5.

[0115] The total porosity results are shown in Table 6 below:

[0116] Table 6

[0117]

[0118] In Example 4, the porosity was 12.8%, mainly due to the natural loosening effect of enzymatic hydrolysis on the collagen fibers. In Example 5, after undergoing controlled microporous pretreatment, the porosity jumped to 23.6%, an increase of 84.4% compared to Example 4. This significant difference directly proves that the synergistic effect of pulsed negative pressure expansion and instantaneous high-pressure impact successfully created a large number of micropores and fissures in the collagen fiber network.

[0119] <Water Absorption Dynamics Test>

[0120] The leather pieces from Examples 4-5 and Comparative Example 1, which were immersed in the embrittlement treatment solution S3, were removed at predetermined time points (1, 5, 15, 30, and 60 minutes), and weighed after the surface solution was quickly blotted dry with filter paper. The water absorption weight gain rate (%) relative to the mass before immersion was calculated.

[0121] The results of water absorption weight gain are shown in Table 7 below:

[0122] Table 7

[0123]

[0124] Comparative Example 1, without any pretreatment, had a dense tissue structure, with a water absorption weight gain of only 14.8% in 60 minutes and a saturation weight gain of 15.2%, indicating high osmotic resistance. Example 4, although not subjected to microporous pretreatment, had a somewhat loose tissue structure due to enzymatic hydrolysis, achieving a water absorption weight gain of 28.5% in 60 minutes, significantly better than the comparative example. Example 5, after microporous pretreatment, achieved a water absorption weight gain of 18.5% in 1 minute, 2.26 times that of Example 4 at the same time; and reached 34.2% in 15 minutes, approaching saturation. The saturation weight gain was 37.8%, an increase of 29.5% compared to Example 4 and 149% compared to Comparative Example 1. These data demonstrate that microporous pretreatment significantly improved the initial water absorption rate and total liquid holding capacity of the hide, creating favorable conditions for the rapid and deep penetration of calcium ions and organic acids during the subsequent S3 embrittlement treatment.

[0125] 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 embodiments shown and described herein.

Claims

1. A method for processing sheepskin food products, characterized in that, Includes the following steps: S1. Remove the hair from the fresh sheepskin, wash it, and cut it into pieces of the predetermined shape; S2. Place the leather pieces in a reaction solution containing complex protease and flavor protease, and carry out the first enzymatic hydrolysis treatment at pH 5.5-6.5 and temperature 45-55℃ for 30-90 minutes. S2-1. Immerse the leather pieces that have undergone enzymatic deodorization treatment in clean water at a temperature of 35-45℃, apply a vacuum pressure of -0.075 MPa to -0.090 MPa in the container, and maintain it for 3-8 minutes to allow the leather tissue to fully absorb water and swell under negative pressure. S2-2. Within 1-3 seconds, sterile inert gas or steam is rapidly introduced into the container, causing the pressure to rise sharply to 0.4-0.6 MPa, and this high-pressure state is maintained for 5-15 seconds. By using the instantaneous pressure difference impact, a large number of microscopic permeable channels and fissures are formed in the collagen fiber network structure of the skin piece. S2-3. Release the container pressure to normal pressure within 2-5 seconds, then let the leather block stand in clean water for 5-10 minutes to balance, drain the surface water and immediately proceed to step S3. S3. The leather pieces treated in S2 are then soaked in an aqueous solution containing edible calcium salt and organic acid. The concentration of the edible calcium salt is 0.5%-2.0%, the concentration of the organic acid is 0.1%-0.5%, the soaking temperature is 20-40℃, and the soaking time is 2-6 hours. S4. Braise the leather pieces processed in S3 until fully cooked, then cool, shape, and package them. Specifically, S3 includes: S3a. Immerse the hide pieces treated in S2 in an aqueous solution of edible calcium salt and organic acid. First, maintain the solution at 20-30℃ and 0.08-0.1MPa vacuum for 5-15 minutes to allow air to be released from the pores of the hide pieces and to promote initial wetting of the solution. S3b. Within 1-2 minutes, release the vacuum and apply a positive pressure of 0.2-0.5 MPa, maintain this pressure for 10-20 minutes, and use the pressure difference to drive the solution to quickly penetrate into the deep layers of the skin. S3c: The pressure is rapidly released to normal pressure within 30 seconds. During this process, the solution in the micropores inside the leather expands slightly due to the sudden drop in external pressure, which helps to form a more uniform micro-embrittlement structure. S3d, Repeat the vacuum-pressurization-release cycle from S3a to S3c 2-4 times; S3e, continue soaking under normal pressure and 20-40℃ conditions until the total time meets 2-6 hours to complete ion exchange and stabilize the gel network; Specifically, the enzymatic deodorization treatment in S2 includes: S2a. Prepare two independent constant-temperature enzymatic hydrolysis containers, one as a high-temperature enzymatic hydrolysis vessel and the other as a low-temperature enzymatic hydrolysis vessel. Pour equal amounts of reaction solution containing compound protease and flavor protease into each vessel. Maintain the temperature in the high-temperature enzymatic hydrolysis vessel at 50-55℃ and the temperature in the low-temperature enzymatic hydrolysis vessel at 40-45℃. Weigh each pretreated piece of leather, record the initial mass M0 of each piece, and calculate the total mass. S2b. Put all the leather pieces into the high-temperature enzymatic hydrolysis tank, start timing and continue to stir gently; when the enzymatic hydrolysis has reached 1 / 3 of the total predetermined time, conduct the first monitoring: take all the leather pieces out of the high-temperature tank, quickly absorb the surface moisture with gauze, weigh them one by one, and record the mass M1 of each piece of leather at this time. S2c, Calculate the quality loss rate of each piece of leather from the initial stage to the present: ΔM1 = (M0 - M1) / M0 × 100%; operate according to the following rules: All leather pieces with ΔM1 greater than or equal to the preset threshold A were manually transferred to a low-temperature enzymatic hydrolysis tank; leather pieces with ΔM1 less than the preset threshold A were returned to the high-temperature enzymatic hydrolysis tank for further enzymatic hydrolysis; the value of A was in the range of 8%-12%; After S2d and the transfer is completed, the leather pieces in the high-temperature tank and the low-temperature tank continue to be enzymatically hydrolyzed at their respective temperatures. When 2 / 3 of the total predetermined time is reached, a second monitoring is performed: the leather pieces in the two tanks are taken out again, dried, and weighed one by one, and the mass M2 is recorded. For the leather pieces in the high-temperature enzymatic hydrolysis tank, calculate the mass loss rate ΔM2 in the second stage. Manually transfer all leather pieces with ΔM2 greater than or equal to the preset threshold B to the low-temperature enzymatic hydrolysis tank; return leather pieces with ΔM2 less than the preset threshold B to the high-temperature enzymatic hydrolysis tank for further enzymatic hydrolysis; the value of B ranges from 5% to 8%. For the leather pieces in the cryogenic tank, calculate the change in mass since entering the cryogenic tank. If the change rate is less than 0.5% after two consecutive weighings, it can be determined that the endpoint has been reached and the enzymatic hydrolysis can be terminated early. S2e: The leather pieces in the high-temperature tank are processed until the end of the total predetermined time; the leather pieces in the low-temperature tank are processed until the quality is stable, but the total time does not exceed the total predetermined time; finally, all leather pieces are merged to proceed to the next step.

2. The processing method for sheepskin food products as described in claim 1, characterized in that, The complex protease in S2 is a mixture of papain and trypsin in a mass ratio of (1-3):1, with a total enzyme activity of 500-1500 U / g sheepskin; the flavor protease has an enzyme activity of 300-800 U / g sheepskin.

3. The processing method for sheepskin food products as described in claim 1, characterized in that, The edible calcium salt in S3 is one or more of calcium chloride, calcium lactate, or calcium gluconate; the organic acid is one or more of citric acid, lactic acid, or malic acid.

4. The processing method of sheepskin food products as described in claim 1, characterized in that, After step S3, there is also a rinsing and neutralization step: rinse the leather piece 1-3 times with clean water, and then soak it in a sodium bicarbonate solution with a concentration of 0.05%-0.2% for 5-15 minutes to neutralize it.

5. The processing method of sheepskin food products as described in claim 1, characterized in that, In S4, the brine used contains 0.01%-0.1% of natural spice extract, which is cumin extract and / or Sichuan pepper extract.

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