Multi-layer milk skin and preparation method thereof

Abstract

The invention belongs to the technical field of dairy food preparation, and relates to a multi-layer milk skin and a preparation method thereof.The preparation method comprises the steps that firstly, fresh milk is subjected to ultrasonic-assisted fermentation and directional enzymolysis, and modified milk slurry rich in flavor precursor substances is prepared; then, a multi-layer structure is constructed in the mode of multi-round layered slurry laying and accurate temperature control superposition, and a gradient functional layer is formed; and finally, performing staged dynamic drying on the multi-layer blank body, and coating the multi-layer blank body with a multifunctional edible film coating liquid. According to the technology, a multi-layer structure with gradient is actively constructed, and the multi-layer taste of the product is achieved; meanwhile, through the cooperation of fermentation, enzymolysis and controlled Maillard reaction, the product is endowed with a compound flavor of interlaced delicate flavor, mellow flavor and scorch aroma; and the outer coating effectively prolongs the shelf life of the product. The technical defects of single structure, insufficient flavor, unstable texture and short shelf life of the traditional milk skin are overcome.

Description

Technical Field

[0001] This invention belongs to the field of dairy food preparation technology, and relates to a layered milk skin and its preparation method. Background Technology

[0002] Milk skin is a traditional dairy product with a long history of consumption. The traditional method of preparing milk skin is relatively simple: fresh cow's or sheep's milk is boiled, then allowed to cool and solidify, forming a thin film rich in fat and protein. This film, once peeled off, is the milk skin. Milk skin produced using this traditional method has a single-layer structure, a relatively uniform texture, and a taste that is either crisp or chewy. Its flavor primarily depends on the quality of the raw milk itself and the limited Maillard reaction that occurs during the heating process.

[0003] With the development of the food industry, some improved milk skin production technologies have emerged. For example, the thickness and firmness of the milk skin are adjusted by controlling the heating temperature and time, or small amounts of thickeners and emulsifiers are added to improve its texture and formability. However, existing technologies and products still generally suffer from the following shortcomings: 1) The structure is simple and the texture is lacking. Most existing milk skin products have a single-layer film structure with a uniform internal texture and lack of layering. When consumers eat them, the taste experience is monotonous, and they cannot simultaneously feel the interweaving and transition of multiple textures such as crispness, crunchiness, chewiness, and smoothness. This makes it difficult to meet the market's diverse sensory demands for high-end and specialty dairy products.

[0004] 2) The flavor lacks depth and complexity. Traditional or existing improved processes mainly rely on the natural flavor of the raw milk and the caramelized aroma during heating, resulting in a passive and singular flavor profile. The application of fermentation technology is mostly limited to products such as yogurt. In the preparation of milk skin, the technical solution of directional fermentation combined with enzymatic hydrolysis to actively construct flavor precursors is rare. As a result, the product has a thin flavor profile and lacks the complex flavor presented by the combined action of amino acids, small molecule peptides, and Maillard reaction products.

[0005] 3) The texture control is unstable, and it is easy to become hard or loose. The existing process relies heavily on experience for the drying process of the final product. If it is over-dried, it is easy to cause a hard shell to form on the surface, hinder the migration of internal moisture, and make the product too hard. If it is under-dried, the product structure is not strong enough, it is easy to break and the product quality is unstable.

[0006] 4) The components have single functions and lack synergistic design. The purpose of adding excipients (such as cream and stabilizers) in existing technologies is mostly to adjust the basic components or provide simple physical stability. The components are mostly physically mixed, and the molecular-level interaction and functional synergy between the components are not achieved through process design. For example, the binding between fat globules and protein matrix is ​​not strong, which can easily lead to a greasy taste or fat precipitation during storage; flavor substances lack effective protection and are prone to volatilization or deterioration during processing and storage.

[0007] 5) The product has a short shelf life. Traditional milk skin has a high water content and lacks an effective protective coating, making it prone to absorbing moisture, softening, or growing microorganisms, resulting in a short shelf life. Even with packaging, it is difficult to prevent oxygen penetration, leading to significant problems such as fat oxidation and rancidity, as well as flavor loss, which limits the product's distribution range and shelf life. Summary of the Invention

[0008] To address the above problems, this invention provides a layered milk skin and its preparation method, specifically including the following steps: Step 1: Heat raw milk with a solids content ≥12.5% ​​and a fat content ≥3.8% to 35-45℃, add a compound fermentation agent, and sonicate at 25-30kHz for 10-20 minutes. The cavitation effect of ultrasound not only achieves the miniaturization of fat globules to submicron levels, but more importantly, it forms instantaneous micropores on the surface of casein micelles. This allows the fermentation bacteria and their metabolites to penetrate into the micelles, increasing the fermentation rate. At the same time, the fermentation bacteria create a slightly acidic environment, ultimately yielding an activated whey rich in active peptides and flavor precursors.

[0009] Step two involves cooling the activated whey to 30-35℃, adding a complex protease, and hydrolyzing at 35-45 rpm for 20-30 minutes under inert gas protection. The complex protease not only cleaves the peptide bonds within the protein to produce medium-length flavor peptides, but also releases hydrophobic amino acids (such as leucine and phenylalanine) from the peptide chain ends. This step converts milk proteins into peptides and free amino acids. After hydrolysis, the temperature is increased to 80-90℃ at a rate of 1.5-2.5℃ / min and held for 2-3 minutes to inactivate the protein. This gradient heating initiates the initial stage of the Maillard reaction. The free amino acids produced by hydrolysis combine with lactose to form Maillard intermediates, laying the foundation for the layered color and aroma development during subsequent layered heating.

[0010] Step 3: Cool the enzymatically hydrolyzed milk mixture to 55-65℃, then add light cream (35-40% fat content), flavor protectant, structure modifier, and salt sequentially. Shear at 4500-5500 rpm for 3-5 minutes. This high-temperature, high-speed shearing forces the structure modifier to partially dissolve and instantly bind to the exposed hydrophobic regions of the proteins and the fat globule membrane proteins. The mixture is then allowed to stand at 3-5℃ for 14-16 hours to mature, yielding the modified milk slurry. At low temperature, the structure modifier completely hydrates and forms a three-dimensional gel network throughout the entire system. The flavor protectant, in its stable glassy state, fills the protein-fat interface, while the hydrophobic peptides and amino acids produced during enzymatic hydrolysis and fermentation are selectively adsorbed onto the interface membrane of the light cream fat globules. At the end of maturation, the system is not a homogeneous, stable emulsion, but rather a pre-structured slurry with micro-regional structures formed due to differences in component interactions.

[0011] Preferably, the mass ratio of the raw milk, compound fermentation agent, compound protease, light cream, flavor protectant, structure modifier and salt is (800-900):(0.2-0.3):(0.07-0.08):(140-150):(7-9):(5-7):(0.8-1.2).

[0012] Preferably, the total number of viable bacteria in the compound fermentation agent is ≥1×10⁻⁶. 9 CFU / g, including Streptococcus thermophilus and Lactobacillus plantarum, in a mass ratio of (1-3):(1-3).

[0013] Preferably, the complex protease comprises a neutral protease and a flavor protease in a mass ratio of (1-3):(1-2).

[0014] Preferably, the flavor protectant is trehalose.

[0015] Preferably, the structural modifier is inulin.

[0016] Step 4: Spread the initial amount of modified milk slurry evenly on a preheated heating platform to 74-76℃ to form a uniform liquid layer of 3-4mm. After the slurry is heated, a high-temperature zone is formed at the bottom first. Due to the presence of inulin network in the pretreatment, the upward migration of water and fat is partially inhibited. When heated for 5-8 minutes, the bottom temperature reaches 68-70℃. At this time, the whey protein close to the bottom surface will denature and aggregate, and combine with calcium ions to form an extremely dense initial protein film with a thickness of about 0.08mm. This film can serve as the base of the entire multilayer structure.

[0017] After the basement membrane is formed, the heating platform is cooled to 64-65°C at a rate of 0.8-1°C / min and maintained for 8-12 minutes. The slow cooling process is key to the formation of the first peelable thick skin. As the temperature gradient at the bottom slows down, the fat globules in the middle of the slurry begin to selectively and slowly migrate and attach to the existing basement membrane at the bottom. At the same time, some casein micelles bound to inulin are further deposited on the basement membrane at this temperature, gradually forming a loosely structured, porous, and fat-rich first functional layer.

[0018] Step 5: Remove the first functional layer and air dry it naturally at 45-55℃ and 65-75%RH for 80-100 seconds. Add modified milk slurry to the heating platform, with an initial to replenished amount at a mass ratio of (2-3):1. Cover the replenished slurry surface with the first functional layer and heat the platform to 75-77℃ for 5-8 minutes. During this stage, a new protein film forms at the bottom of the new slurry due to heating, while the bottom of the first functional layer softens locally due to heat and the action of moisture below.

[0019] The heating platform is cooled to 63-64℃ at a rate of 0.8-0.9℃ / min and held for 10-15 minutes. During this process, components in the new slurry below precipitate upwards, forming a new second functional layer. The precipitated substances (especially Maillard reaction intermediates and hydrophobic peptides) undergo strong molecular interactions (mainly hydrophobic interactions and hydrogen bonds) with the softened parts of the first functional layer at 63-64℃, achieving molecular bonding between the two layers. At the same time, this temperature range is precisely the optimal temperature for the Maillard reaction to produce a golden color and flavor.

[0020] Step six: Repeat step five to stack layers three through ten, controlling the parameters for each stack as follows: For each additional layer from the second layer onwards, the amount of modified milk slurry added should be reduced by 1 / 20 of the amount added in the second layer. For each additional layer beyond the second layer, the initial platform temperature increases by 0.8-1.2℃, with a maximum not exceeding 85℃; With each additional layer beyond the second layer, the cooling rate decreases by 0.04-0.06℃ / min. With each additional layer from the second layer onwards, the low-temperature maintenance temperature decreases by 0.4-0.6℃, with a minimum of 60℃. This dynamic parameter system ensures that each functional layer exhibits a continuous gradient difference in porosity, fat content, and Maillard reaction degree due to differences in its thermal history and interfacial chemical environment during formation.

[0021] Step 7: After completing the tenth layer, the embryo is dried at 45-55℃ and 65-75%RH for 20-30 minutes. During this stage, the surface free water evaporates rapidly, but due to the high ambient humidity, the internal water can continue to migrate to the surface, and the surface is not easy to form a hard film. The relative humidity decreased by 38-42% at a rate of 0.4-0.6%RH / min, while the temperature remained constant, and the drying process lasted for 50-60 minutes. As the humidity decreased, the surface moisture evaporation rate began to exceed the internal migration rate, and the drying process entered a deceleration phase. At this time, the inulin gel network began to shrink due to the reduction of moisture, gradually tightening the protein fibers and initially strengthening the layered structure. The temperature is increased to 58-62℃ at a rate of 0.1-0.3℃ / min, while the relative humidity remains constant, and the mixture is dried for 30-40 minutes. The gentle temperature increase allows the Maillard reaction to proceed gently again. The trehalose concentration increases and its viscosity increases due to the reduction of water, which allows it to form binding points between proteins and fats.

[0022] Stop heating, introduce air at 0.7-0.9 m / s, 23-27℃, and 55-65%RH, and allow it to cool naturally for 50-70 minutes to obtain the initial milk skin.

[0023] Step 8: Apply the coating solution to the outer surface of the initial layered milk skin, using 80-120g of coating solution per square meter of the initial layered milk skin surface. Dry at 40-50℃ and 25-35%RH for 3-5 minutes to obtain the finished milk skin.

[0024] Preferably, the coating solution comprises whey protein isolate (WPI90), chitosan (degree of deacetylation ≥90%), acetic acid, rosemary extract, glycerol, and deionized water in a mass ratio of (7-9):(1-3):(18-22):(0.04-0.06):(1-2):70.

[0025] The present invention has the following advantages: (1) The core advantage of this invention lies in overcoming the limitations of the single-layer structure of milk skin. By precisely controlling the spreading and layering of each layer of slurry and the differentiated heat treatment parameters (such as layered cooling and gradient temperature maintenance), a multi-layer functional system has been successfully constructed. Each layer exhibits a continuous gradient difference in porosity, fat enrichment, protein network density, and Maillard reaction degree due to the different heat and humidity formed. This allows the final product to experience multiple texture changes sequentially when chewed, from the relatively dense and crispy surface layer to the loose and moist middle layer, and then to the soft and fragrant bottom layer. The taste is extremely rich and three-dimensional, solving the problem of the monotonous taste of traditional products and providing an unprecedented sensory experience.

[0026] 2) This invention actively and systematically constructs a multi-layered flavor profile. Through ultrasonic-assisted fermentation with a compound fermenting agent, the process is not only accelerated but also microscopically activated in the milk paste, creating flavor precursors. Targeted enzymatic hydrolysis by a compound protease under inert gas protection precisely generates medium-length flavor peptides and key free amino acids (such as leucine and phenylalanine). These products undergo a controlled Maillard reaction with reducing sugars during subsequent layered heating. Due to the precise control of the heating temperature for each layer, the degree of the Maillard reaction and the products vary between layers. The final product not only possesses the inherent rich aroma of dairy products but also incorporates the umami base from peptides, the multi-layered caramel-sweet aroma from the Maillard reaction, and the slightly acidic flavor from fermentation. These various flavors are harmoniously blended, resulting in high complexity and a long-lasting aftertaste, changing the traditional single-flavor profile of milk skin.

[0027] (3) The advantages of this invention lie in the precise control of product texture achieved through pre-structured slurry preparation (combined with inulin gel network, trehalose protective agent, etc.) and a phased dynamic drying process. The three-dimensional network formed by inulin inhibits the uneven migration of components in the early stages of ripening and heating, laying the foundation for the layered structure. In the drying stage, a procedure of high humidity followed by gradient dehumidification and then gentle heating is adopted to ensure that moisture is evenly lost from the inside to the outside, avoiding surface hardening. At the same time, the concentration of trehalose increases in the later stage, forming natural binding points between proteins and fats. The inulin network gently shrinks as the moisture decreases, further tightening the protein fibers and strengthening the interlayer bonding and overall structural toughness. Therefore, the resulting milk skin has a uniform texture, is not easily broken, and has both appropriate crispness and flexibility, overcoming the disadvantages of traditional products being prone to hardening or loosening.

[0028] 4) This invention is not simply a mixture of raw materials, but rather guides each component to achieve functional positioning and synergy through process sequence and parameter design. For example, the flavor protectant trehalose fills the interface in a glassy state, effectively locking in flavor and preventing spoilage; the structure modifier inulin constructs a network that runs through the gel; and the hydrophobic peptides generated by enzymatic hydrolysis selectively adsorb onto the fat globule interface, enhancing the binding between the fat and protein matrix. This synergistic component design results in a robust internal structure, anchored flavor substances, and a smooth, non-greasy texture, solving the problems of single-function and loosely bound components in traditional products.

[0029] 5) In the final process, this invention utilizes a specially formulated coating solution (containing whey protein isolate, chitosan, rosemary extract, etc.) to form a thin, dense, edible protective film on the surface of the finished product. This film possesses excellent barrier properties, effectively preventing the product from absorbing moisture and softening, blocking oxygen penetration, and thus delaying fat oxidation. Simultaneously, the rosemary extract provides natural antioxidant protection. The coating process is rapid and gentle, without affecting the original texture and flavor of the product. This measure significantly enhances the physical and chemical stability of the product, substantially extending its shelf life, making it more suitable for industrial production, long-distance transportation, and commercial sales, thus solving the problems of short shelf life and easy spoilage associated with traditional milk skin. Detailed Implementation

[0030] The technical solutions in the embodiments of the invention are described clearly and completely below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0031] Example 1 Raw material preparation: Compound fermentation agent: total viable count ≥ 1×10 9CFU / g, including Streptococcus thermophilus (purchased from Jinan Shenghe Chemical Co., Ltd.) and Lactobacillus plantarum (purchased from Zhengzhou Yukong Biotechnology Co., Ltd.), with a mass ratio of 2:3.

[0032] Complex protease: neutral protease (purchased from Sichuan Huanxu Biotechnology Co., Ltd.) and flavor protease (purchased from Hebei Jiuyu Biotechnology Co., Ltd.), with a mass ratio of 3:2.

[0033] The coating solution consisted of whey protein isolate (WPI90), chitosan (degree of deacetylation ≥90%), acetic acid, rosemary extract (purchased from Lanzhou Waterles Biotechnology Co., Ltd.), glycerol, and deionized water in a mass ratio of 8:2:20:0.05:1.5:70.

[0034] Specific preparation steps: Step 1: Heat raw milk with a solid content ≥12.5% ​​and a fat content ≥3.8% to 40°C, add a compound fermentation agent, sonicate at 28kHz for 15 minutes, cool to 32°C, add a compound protease, stir at 40rpm for 25 minutes under nitrogen protection, heat to 85°C at a rate of 2°C / min, hold for 2.5 minutes to inactivate, cool to 60°C, add light cream with a fat content of 38%, trehalose, inulin and salt in sequence, shear at 5000rpm for 4 minutes, let stand at 4°C for 15 hours to mature, and obtain modified milk slurry.

[0035] The mass ratio of the raw milk, compound fermentation agent, compound protease, light cream, trehalose, inulin and salt is 850:0.25:0.075:145:8:6:1.

[0036] Step 2: Spread the initial amount (300g) of modified milk slurry evenly on the heating platform that has been preheated to 75℃ to form a uniform liquid layer of 3.5mm. Heat for 7min, then cool the heating platform to 64℃ at a rate of 0.9℃ / min and maintain for 10min to obtain the first functional layer. Step 3: Remove the first functional layer and air dry it naturally at 50℃ and 70%RH for 90 seconds. Add 100g of modified milk slurry to the heating platform and cover the surface of the added slurry with the first functional layer. Heat the heating platform to 76℃ for 7 minutes. Then, cool the heating platform to 63℃ at a rate of 0.8℃ / min and hold for 13 minutes to obtain the second functional layer. Step four, repeat the process of step three to stack layers three through ten, with the parameters controlled as follows for each stack: For each additional layer from the second layer onwards, the amount of modified milk paste added is reduced by 5g. For each additional layer from the second layer onwards, the initial platform temperature increases by 1°C, with a maximum not exceeding 85°C. With each additional layer beyond the second layer, the cooling rate decreases by 0.05℃ / min. For each additional layer beyond the second layer, the low-temperature maintenance temperature decreases by 0.5℃, with a minimum of 60℃.

[0037] Step 5: After completing the tenth layer stacking, the embryo is obtained and dried at 50℃ and 30%RH for 25 minutes. The relative humidity was reduced by 40% at a rate of 0.5%RH / min, while the temperature remained constant, and the drying time was 55 minutes. The temperature was increased to 60℃ at a rate of 0.2℃ / min, while the relative humidity remained constant, and the drying process lasted for 35 minutes. Introduce air at 0.8 m / s, 25°C, and 60% RH, and allow it to cool naturally for 60 minutes to obtain the initial milk skin. Step 6: Apply the coating solution to the outer surface of the initial layered milk skin, using 100g of coating solution per square meter of the initial layered milk skin surface, and dry at 45℃ and 30%RH for 4 minutes to obtain the finished milk skin.

[0038] Experimental Example 1 Experimental group: Layered milk skin prepared in Example 1.

[0039] Control group: Commercially available Inner Mongolia Chaolu brand milk skin.

[0040] Each group had 3 parallel samples, and all samples were equilibrated in the same environment (25℃, 50%RH) for 2 hours before the experiment.

[0041] Sensory evaluation experiment: Ten trained sensory evaluators were invited to conduct blind evaluations in a standard sensory laboratory. They scored the products based on four aspects: appearance, aroma, taste, and overall acceptability. Each aspect was scored out of 10. The scores of each evaluator were recorded and the average score was calculated.

[0042] Texture analysis (TPA test): Total texture analysis (TPA) was performed using a texture analyzer with a P / 36R probe, a test speed of 1 mm / s, a compression ratio of 50%, and a trigger force of 5 g. Hardness, elasticity, chewiness, and resilience were measured, and each group was repeated 5 times.

[0043] Preservation performance test: The two groups of samples were placed under accelerated storage conditions of 35℃ and 75%RH, and samples were taken on days 0, 7, 14 and 21 to determine the total number of colonies, peroxide value, water activity and color change.

[0044] Table 1 Sensory evaluation results

[0045] Table 2 Comparison of textural properties

[0046] Table 3 Quality changes during accelerated storage

[0047] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for preparing layered milk skin, characterized in that, Includes the following steps: Step 1: Heat raw milk to 35-45℃, add compound fermentation agent, sonicate, cool to 30-35℃, add compound protease, stir and enzymatically hydrolyze for 20-30 minutes under inert gas protection, heat to 80-90℃ at a rate of 1.5-2.5℃ / min, hold for 2-3 minutes to inactivate, cool to 55-65℃, add light cream, flavor protectant, structure modifier and salt in sequence, cut, and let stand at 3-5℃ for 14-16 hours to mature, to obtain modified milk slurry; The mass ratio of the raw milk, compound fermentation agent, compound protease, light cream, flavor protectant, structure modifier and salt is (800-900):(0.2-0.3):(0.07-0.08):(140-150):(7-9):(5-7):(0.8-1.2); Step 2: Spread the initial amount of modified milk slurry evenly on a heating platform that has been preheated to 74-76℃ to form a uniform liquid layer of 3-4mm. Heat for 5-8 minutes, then cool the heating platform to 64-65℃ at a rate of 0.8-1℃ / min and maintain for 8-12 minutes to obtain the first functional layer. Step 3: Remove the first functional layer and air dry it naturally at 45-55℃ and 65-75%RH for 80-100 seconds. Add modified milk slurry to the heating platform with an initial mass ratio of (2-3):

1. Cover the surface of the added slurry with the first functional layer. Heat the heating platform to 75-77℃ for 5-8 minutes. Then, cool the heating platform to 63-64℃ at a rate of 0.8-0.9℃ / min and hold for 10-15 minutes to obtain the second functional layer. Step four, repeat the process of step three, and stack the third to tenth layers to obtain the embryo; Step 5: Dry the embryo at 45-62℃ and 38-75%RH for 100-130 minutes, introduce air at 0.7-0.9m / s, 23-27℃ and 55-65%RH, and allow it to cool naturally for 50-70 minutes to obtain the initial milk skin. Step 6: Apply the coating solution to the outer surface of the initial layered milk skin, using 80-120g of coating solution per square meter of the initial layered milk skin surface. Dry at 40-50℃ and 25-35%RH for 3-5 minutes to obtain the finished milk skin.

2. The method for preparing a layered milk skin according to claim 1, characterized in that, The total viable count of the compound fermentation agent mentioned in step one is ≥1×10⁻⁶. 9 CFU / g, including Streptococcus thermophilus and Lactobacillus plantarum, in a mass ratio of (1-3):(1-3).

3. The method for preparing a layered milk skin according to claim 1, characterized in that, The complex protease mentioned in step one includes neutral protease and flavor protease in a mass ratio of (1-3):(1-2).

4. The method for preparing a layered milk skin according to claim 1, characterized in that, The flavor protectant mentioned in step one is trehalose.

5. The method for preparing a layered milk skin according to claim 1, characterized in that, The structural modifier mentioned in step one is inulin.

6. The method for preparing a layered milk skin according to claim 1, characterized in that, The parameters for each superposition in step four are controlled as follows: For each additional layer from the second layer onwards, the amount of modified milk slurry added should be reduced by 1 / 20 of the amount added in the second layer. For each additional layer beyond the second layer, the initial platform temperature increases by 0.8-1.2℃, with a maximum not exceeding 85℃; With each additional layer beyond the second layer, the cooling rate decreases by 0.04-0.06℃ / min. For each additional layer from the second layer onwards, the low-temperature maintenance temperature decreases by 0.4-0.6℃, with a minimum of 60℃.

7. The method for preparing a layered milk skin according to claim 1, characterized in that, In step five, the embryos are dried at 45-55℃ and 25-35%RH for 20-30 minutes. The relative humidity decreases by 38-42% at a rate of 0.4-0.6%RH / min, while the temperature remains constant, and the drying process lasts for 50-60 minutes. The temperature is increased to 58-62℃ at a rate of 0.1-0.3℃ / min, while the relative humidity remains constant, and the drying process lasts for 30-40 minutes. Introduce air at 0.7-0.9 m / s, 23-27℃, and 55-65%RH, and allow it to cool naturally for 50-70 minutes to obtain the initial milk skin.

8. The method for preparing a layered milk skin according to claim 1, characterized in that, The coating solution mentioned in step six includes whey protein isolate, chitosan, acetic acid, rosemary extract, glycerol and deionized water in a mass ratio of (7-9):(1-3):(18-22):(0.04-0.06):(1-2):

70.

9. The method for preparing a layered milk skin according to claim 8, characterized in that, The whey protein isolate is WPI90 whey protein isolate, and the degree of deacetylation of the chitosan is ≥90%.

10. The layered milk skin prepared by the method according to any one of claims 1-9.

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