Freeze-dried fruit food containing dairy product coating and preparation method of freeze-dried fruit food

Abstract

The invention belongs to the technical field of food processing, and particularly relates to a freeze-dried fruit food containing a dairy product coating and a preparation method of the freeze-dried fruit food. According to the freeze-dried fruit food containing the dairy product coating, the freeze-dried fruit is used as a core material, other chocolate materials, milk powder, dietary fibers, cheese powder, a stabilizer, a sweetening agent and edible essence are added as raw materials to form the coating, and the prepared freeze-dried fruit food not only can be stored for 12 months at normal temperature, but also is crisp in taste and unique in flavor.

Description

Technical Field

[0001] The invention belongs to the technical field of food processing, and in particular relates to a freeze-dried dried fruit food containing a dairy product coating and a preparation method thereof. Background Art

[0002] Leisure food is a common type of fast-moving consumer goods, usually referring to the food that people eat during their leisure time and rest. It has always been a popular food among the general public. The main categories of leisure food include: dried fruits, puffed food, candy, meat products, etc. With the improvement of people's living standards, leisure food is gradually becoming a daily necessity for the people, and with the development of the economy and the improvement of consumption levels, consumers' demand for the variety and quality of leisure food is growing.

[0003] At present, most of the solid coated leisure products on the market are chocolate coated products, such as Maltesers, Hawthorn Cake and other products. However, this type of product generally has problems such as high fat content, low protein index and low nutritional value. In particular, the outer layer of chocolate skin is easy to melt at room temperature or in summer, which brings great difficulties to the preservation and stability of the product. Some products that use high melting point chocolate (≥34℃) as raw materials have poor solubility in the mouth, which affects the waxy texture of the product and the overall taste of the product is poor. Another type of coating product on the market usually uses water and powder as the coating layer. This type of product is not easy to melt at room temperature, but the moisture of the surface coating will migrate to the core material, seriously affecting the crispness of the product, resulting in a poor taste of the product.

[0004] Therefore, the art expects to develop a freeze-dried fruit food containing a dairy coating that is easy to store stably and has good taste stability to meet market demand. Summary of the invention

[0005] To this end, the first object of the present invention is to provide a freeze-dried fruit food containing a dairy coating that is easy to store stably and has good taste stability, so as to solve the problem of poor taste stability of coated leisure foods in the prior art;

[0006] The second object of the present invention is to provide a method for preparing the freeze-dried dried fruit food containing the dairy product coating.

[0007] In order to solve the above technical problems, the freeze-dried dried fruit food containing a dairy product coating according to the present invention comprises a freeze-dried dried fruit core and a coating containing a dairy product;

[0008] The raw materials for preparing the coating layer include the following components in parts by weight: 25-35 parts by weight of chocolate material, 10-15 parts by weight of sweetener, 15-20 parts by weight of milk powder, 3-5 parts by weight of dietary fiber, 11-15 parts by weight of cheese powder, 0.1-0.4 parts by weight of edible flavor, and 0.3-1.0 parts by weight of stabilizer.

[0009] Specifically, the freeze-dried fruit food containing a dairy coating comprises, based on its total amount, the following raw material components in terms of mass content: 20-30wt% freeze-dried fruit, 25-35wt% chocolate material, 10-15wt% sweetener, 15-20wt% milk powder, 3-5wt% dietary fiber, 11-15wt% cheese powder, 0.1-0.4wt% edible flavor, and 0.3-1.0wt% stabilizer.

[0010] Specifically, in the freeze-dried dried fruit food containing a dairy coating, the stabilizer comprises a mixture of mono- and di-glycerol fatty acid esters, phospholipids, and polyglycerol fatty acid esters;

[0011] The stabilizer, calculated on the total amount, comprises the following components in mass content: 20-50 wt % of mono- and di-glycerol fatty acid esters, 30-40 wt % of phospholipids, and 10-40 wt % of polyglycerol fatty acid esters.

[0012] Specifically, the freeze-dried dried fruit food containing a dairy coating:

[0013] The chocolate material comprises one or a mixture of cocoa butter substitute, cocoa butter, white chocolate or white chocolate products; preferably, the cocoa butter substitute comprises cocoa butter substitute with a melting point of 30°C-32°C, the product has good solubility in the mouth, good taste and no waxy texture; and the product does not melt at room temperature below 42°C; and / or,

[0014] The milk powder comprises one or a mixture of skim milk powder, whole milk powder, reconstituted milk powder or buttermilk powder; and / or,

[0015] The dietary fiber includes one or a mixture of resistant dextrin, polydextrose or inulin; and / or,

[0016] The sweetener includes one or a mixture of white sugar, glucose, maltitol, xylitol or erythritol; and / or,

[0017] The cheese powder comprises processed cheese powder or cheese product powder or a mixture of the two or more thereof; preferably, the cheese content of the cheese powder is greater than 15%; and / or,

[0018] The freeze-dried dried fruit includes one or a mixture of freeze-dried strawberries, freeze-dried blueberries, freeze-dried apples, freeze-dried pears or freeze-dried bananas.

[0019] The present invention also discloses a method for preparing the freeze-dried dried fruit food containing the dairy product coating, comprising the following steps:

[0020] (1) Mixing: Mixing selected amounts of the chocolate material, stabilizer and edible flavor to obtain a first mixed material; mixing selected amounts of the sweetener, milk powder, dietary fiber and cheese powder to obtain a second mixed material;

[0021] (2) Rolling coating of the surface coating: Mixing a selected amount of the freeze-dried dried fruit with the first mixed material and the second mixed material in sequence and rolling coating the mixture to obtain the surface coating.

[0022] Specifically, the preparation method of the freeze-dried dried fruit food containing the dairy product coating is as follows:

[0023] The step (1) further comprises heating the chocolate material to 45-65° C.; and / or,

[0024] The step (1) further comprises cooling the first mixed material to 36-40° C.; and / or,

[0025] In the step (2), the rotation speed of the roller coating step is 6-10 rpm.

[0026] Specifically, in the method for preparing the freeze-dried dried fruit food containing a dairy product coating, in the step (2), the rolling coating step specifically comprises:

[0027] (a) Grease absorption: After adding the first mixed material, roll coating is performed, and then the material temperature is adjusted to 28-30° C. and roll coating is continued;

[0028] (b) Powder adhesion: continue to add the second mixed material, mix and roll-coat;

[0029] (c) Shaping: Adjust the material temperature to 32-34°C and continue rolling;

[0030] (d) Reinforcement: Adjust the material temperature to 20-28℃ and continue rolling.

[0031] Specifically, in the method for preparing the freeze-dried dried fruit food containing a dairy product coating, in the step (2), the rolling coating step specifically comprises:

[0032] (a) Grease absorption: After adding the first mixed material, roll coating is performed for 1-2 minutes, and then cold air is blown in to adjust the material temperature to 28-30° C. After stopping the cold air blowing, roll coating is continued for 1-2 minutes;

[0033] (b) Powder adhesion: continue to add the second mixed material, mix, and roll-coat for 3-5 minutes;

[0034] (c) Shaping: Blow hot air to adjust the material temperature to 32-34°C, and continue rolling for 1-2 minutes;

[0035] (d) Reinforcement: Blow in cold air to adjust the material temperature to 20-28°C and continue rolling for 2-4 minutes.

[0036] Specifically, in the method for preparing the freeze-dried dried fruit food containing a dairy product coating, in the step (2), the first mixed material and the second mixed material are added in batches and rolled;

[0037] The first rolling addition amount of the first mixed material accounts for 20-30wt% of the freeze-dried dried fruit core;

[0038] The first rolling addition amount of the second mixed material accounts for 30-40wt% of the freeze-dried dried fruit core.

[0039] Specifically, the method for preparing the freeze-dried dried fruit food containing the dairy product coating layer, in the step (2), further comprises the step of rolling the thickened coating layer;

[0040] The thickening coating rolling step includes repeating the step of rolling the surface coating on the mixture remaining after the first rolling and the second mixture according to the operation of step (2).

[0041] Specifically, in the method for preparing the freeze-dried dried fruit food containing the dairy product coating, in the thickening coating rolling step:

[0042] The thickening coating rolling step is to repeat the skin coating rolling 4-6 times; and / or,

[0043] The thickening coating rolling step also includes the step of adjusting the rolling speed to 12-15 rpm.

[0044] The freeze-dried fruit food containing a dairy coating of the present invention uses freeze-dried fruit as a core material, and adds other chocolate materials, milk powder, dietary fiber, cheese powder, stabilizer, sweetener, and edible flavor as raw materials to form a coating. The moisture content of the obtained freeze-dried fruit food is 2-2.5%, and it can not only be stored at room temperature for 12 months, but also has a crisp taste and unique flavor. The freeze-dried fruit food containing a dairy coating of the present invention has a melting point of up to 42° C. and does not melt. During transportation and the shelf life, the product does not brown or discolor, the coating and the core material do not fall off or delaminate, and the moisture does not migrate during the shelf life, and the core material maintains a crisp taste.

[0045] The freeze-dried dried fruit food containing dairy product coating of the present invention preferably uses skim milk powder, resistant dextrin (dietary fiber), white sugar, cheese powder and other powder materials to replace more than 50% of oil in the coating, and the moisture content of the obtained dairy product is 2.0-2.5%, and the water activity is controlled within the range of 0.20-0.23AW. At the same time, the melting point of the product is increased, and the product can be stored at room temperature for 12 months. The product has a crisp taste and a unique flavor.

[0046] The freeze-dried dried fruit food containing dairy product coating of the present invention preferably comprises a mixture of mono- and di-glycerol fatty acid esters, phospholipids and polyglycerol fatty acid esters as the compound stabilizer. The compound stabilizer allows the powder and the cocoa butter product to adhere well to each other, and the melting point is as high as 42° C. without melting. The water activity is controlled within the range of 0.20-0.23AW, so that the product does not change color, brown or absorb oil during the shelf life, and the shelf life stability is effectively guaranteed. Furthermore, the moisture of the product does not migrate during the shelf life, and the core material maintains a crisp taste.

[0047] The preparation method of the freeze-dried dried fruit food containing a dairy coating of the present invention uses a rolling coating production method of adding powder and cocoa butter multiple times, so that the core material, oil and powder are tightly combined, and the powder and cocoa butter raw materials are firmly coated on the surface of the freeze-dried dried fruit and tightly combined with the freeze-dried dried fruit core material. The melting point is as high as 42°C and it will not melt. The product will not absorb oil during the shelf life, and will not fall off or delaminate during the shelf life. In particular, by controlling the temperature during the rolling coating process and controlling the amount of powder added each time, the product can be formed into a rounder shape with a smooth surface, thereby ensuring the product shape.

[0048] The preparation method of the freeze-dried dried fruit food containing a dairy product coating of the present invention utilizes a method of "blowing cold air → hot air → cold air" to control the material temperature during the rolling coating process, so that the coating is smoother, stronger and more rounded. BRIEF DESCRIPTION OF THE DRAWINGS

[0049] In order to make the content of the present invention more clearly understood, the present invention is further described in detail below according to specific embodiments of the present invention in conjunction with the accompanying drawings, wherein:

[0050] Figure 1 The present invention is a processing flow chart of the freeze-dried dried fruit food. DETAILED DESCRIPTION

[0051] Examples 1-5

[0052] The present invention implements schemes 1-5 as follows. The raw material ratio of the freeze-dried dried fruit food containing a dairy product coating is shown in Table 1 below, wherein the cocoa butter substitute is selected with a melting point of 30° C.-32° C.

[0053] Table 1 Raw material selection and formulation of Examples 1-5

[0054]

[0055] like Figure 1 The method for preparing the freeze-dried dried fruit food containing the dairy product coating layer described in Examples 1-5 of the present invention comprises the following steps:

[0056] (1) Mixing: heating a selected amount of cocoa butter to 55° C., adding a selected amount of stabilizer and edible flavor, stirring for 15 minutes, cooling to 38° C. after the stabilizer is dissolved, to obtain a first mixed material; crushing white sugar and premixing with other powder materials, namely skim milk powder, resistant dextrin, and cheese powder, for 10 minutes to obtain a second mixed material;

[0057] (2) Roll coating of the skin coating: a selected amount of freeze-dried fruit core material is placed in a sugar coating machine, the speed of the sugar coating machine is adjusted to 8 rpm, and then the first mixed material is added, the amount of which is 30 wt % of the core material;

[0058] Grease absorption: After adding the first mixed material, roll coating for 2 minutes, then blow in cold air, control the material temperature at 28°C, stop blowing in cold air, and roll coating for 1 minute;

[0059] Powder adhesion: then add the second mixed material, the single addition amount is 30wt% of the core material, and roll coating is performed for 4 minutes;

[0060] Shaping: Then blow in hot air, control the material temperature at 34°C, and roll-coat for 2 minutes;

[0061] Reinforcement: Then blow in cold air, control the material temperature at 20°C, and roll for 2 minutes;

[0062] Thickening the coating: adjusting the speed of the sugar coating machine to 15 rpm, rolling the remaining first mixture and the second mixture for 5 times according to the operation method of the above step (2), controlling the first mixture and the second mixture to be evenly added in each rolling; and packaging the thickened coating product.

[0063] Example 6

[0064] like Figure 1 As shown in the flow chart, the ingredients of the freeze-dried dried fruit food containing a dairy product coating in this embodiment are the same as those in Example 2, except that the preparation method of the freeze-dried dried fruit food containing a dairy product coating comprises the following steps:

[0065] (1) Mixing: heating a selected amount of cocoa butter to 55° C., adding a selected amount of stabilizer and edible flavor, stirring for 15 minutes, cooling to 38° C. after the stabilizer is dissolved, to obtain a first mixed material; crushing white sugar and premixing with other powder materials, namely skim milk powder, resistant dextrin, and cheese powder, for 10 minutes to obtain a second mixed material;

[0066] (2) Roll coating of the skin coating: a selected amount of freeze-dried fruit core material is placed in a sugar coating machine, the speed of the sugar coating machine is adjusted to 6 rpm, and then the first mixed material is added, the amount of which is 20 wt % of the core material;

[0067] Grease absorption: After adding the first mixed material, roll coating for 1 minute, then blow in cold air, control the material temperature at 30°C, stop blowing in cold air, and roll coating for 2 minutes;

[0068] Powder adhesion: Then add the second mixed material, the single addition amount is 40wt% of the core material, and roll coating for 3 minutes;

[0069] Shaping: Then blow in hot air, control the material temperature at 32°C, and roll coat for 1 minute;

[0070] Reinforcement: Then blow in cold air, control the material temperature at 28°C, and roll for 4 minutes;

[0071] Thickening the coating: adjusting the speed of the sugar coating machine to 12 rpm, rolling the remaining first mixture and the second mixture for 5 times according to the operation method of the above step (2), controlling the first mixture and the second mixture to be evenly added in each rolling; and packaging the product with thick coating.

[0072] Comparative Examples 1-14

[0073] like Figure 1 As shown in the flow chart, in the following comparative examples 1-14 of the present invention, the raw material composition, proportion and preparation method parameter control of the freeze-dried dried fruit food containing dairy coating are as shown in the following Table 2.

[0074] Table 2 Comparative Examples 1-14 Raw material selection and proportion

[0075]

[0076] The differences between the comparative examples and the examples 1-5 are as follows:

[0077] In the comparative example 1, cocoa butter substitute with a melting point of 38°C is selected as the raw material;

[0078] In the comparative example 2, the coating process of step (2) was not performed in the order of "cold air → hot air → cold air", but the entire coating roller coating operation was performed at 30°C.

[0079] In the comparative example 3, cocoa butter substitute with a melting point of 26°C is selected as the raw material;

[0080] In the comparative example 4, the proportion of mono- and di-glycerol fatty acid esters in the stabilizer system is more than 60 wt%, and the phospholipids are less than 30 wt%;

[0081] In the comparative example 5, in the first rolling operation, the amount of the first mixed material added was 18 wt% of the amount of the core material;

[0082] In the scheme of comparative example 6, in the first rolling operation, the amount of the first mixed material added was 32wt% of the amount of the core material;

[0083] In the scheme of comparative example 7, in the first rolling operation, the amount of the second mixed material added was 27wt% of the amount of the core material;

[0084] In the scheme of comparative example 8, in the first rolling operation, the amount of the second mixed material added was 43wt% of the amount of the core material;

[0085] In the comparative example 9, the speed of the sugar coater was adjusted to 17 rpm during the roller coating step;

[0086] In the scheme of comparative example 10, the proportion of phospholipid in the stabilizer system is selected to be more than 40wt%;

[0087] In the comparative example 11, the proportion in the stabilizer system is selected to be higher than 40wt%;

[0088] In the comparative example 12, only mono- and di-glycerol fatty acid esters were selected as stabilizers;

[0089] In the scheme of comparative example 13, the coating process of step (2) is not performed in the order of "cold air → hot air → cold air", but the entire coating roller coating operation is performed in a cold air environment of 20°C;

[0090] In the comparative example 14, the coating process of step (2) was not performed in the order of "cold air → hot air → cold air", and the product temperature of the hot air step was adjusted to 36°C.

[0091] Experimental example

[0092] The properties of the freeze-dried dried fruit products obtained in the above Examples 1-5 and Comparative Examples 1-14 were measured respectively, and the changes in the shelf life (12 months) of the products were observed, and the results are recorded in Table 3 below.

[0093] Compression hardness test method: Use TA.XT.plus texture analyzer, and use P / 45 disc probe as probe; Test mode: measure compression deformation 5mm, record the maximum force during the process as compression hardness. Options: Pre-test speed: 30.0mm / s; Test speed: 30.0mm / s; Post-test speed: 100.0mm / s, distance: 5mm. Among them, products with compressive hardness (N) ≥ 50.100 are stable, the skin and core material are tightly combined, the coating does not fall off, and the product is not easy to break or break.

[0094] Table 3 Test results of freeze-dried dried fruit food

[0095]

[0096]

[0097] It can be seen that the freeze-dried dried fruit food containing dairy product coating of the present invention uses freeze-dried dried fruit as the core material, and adds other chocolate materials, milk powder, dietary fiber, cheese powder, stabilizer, sweetener, and edible flavor as raw materials to form a coating. Through the screening and optimization of the preparation raw materials, the coating is replaced by more than 50% of oil with skim milk powder, resistant dextrin (dietary fiber), white sugar, cheese powder and other powders. In particular, the compound stabilizer is preferably a mixture of mono- and di-glycerol fatty acid esters, phospholipids, and polyglycerol fatty acid esters. The compound stabilizer makes the powder and the cocoa butter product adhere well. The moisture content of the obtained dairy product is 2.0-2.5%, and the water activity is controlled within the range of 0.20-0.23AW. At the same time, the melting point of the product is improved, and it can be stored at room temperature for 12 months. The product has a crisp taste and a unique flavor.

[0098] In the comparative schemes, due to the poor melting point of the raw materials of cocoa butter substitutes selected in comparative examples 1 and 3, the product taste is poor; in comparative examples 2, 13 and 14, since the coating process adopts a single temperature control, the product absorbs oil and the product surface morphology is poor; in comparative examples 4 and 10-12, due to the inappropriate selection of stabilizers, the product absorbs water and oil, and the surface of the product melts at room temperature; in comparative examples 5-8, due to the influence of the feed amount during the roll coating process, the product coating is unstable or absorbs oil, and the surface morphology of the product is poor; and in comparative example 9, the parameters of the roll coating step will also affect the morphology and stability of the product.

[0099] In summary, the freeze-dried dried fruit food containing a dairy product coating of the present invention has good properties and taste, and the product has a low water activity, which is conducive to stable storage.

[0100] Obviously, the above embodiments are merely examples for the purpose of clear explanation, and are not intended to limit the implementation methods. For those skilled in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all the implementation methods here. The obvious changes or modifications derived therefrom are still within the scope of protection of the invention.

Claims

1. A freeze-dried dried fruit food containing a dairy product coating, characterized in that: including a freeze-dried dried fruit core and a coating containing a dairy product; The raw materials for preparing the coating layer include the following components in parts by weight: 25-35 parts by weight of chocolate material, 10-15 parts by weight of sweetener, 15-20 parts by weight of milk powder, 3-5 parts by weight of dietary fiber, 11-15 parts by weight of cheese powder, 0.1-0.4 parts by weight of edible flavor, and 0.3-1.0 parts by weight of stabilizer.

2. The freeze-dried dried fruit food containing a dairy product coating according to claim 1, characterized in that: The freeze-dried fruit food comprises the following raw material components in total weight: 20-30wt% of freeze-dried fruit, 25-35wt% of chocolate, 10-15wt% of sweetener, 15-20wt% of milk powder, 3-5wt% of dietary fiber, 11-15wt% of cheese powder, 0.1-0.4wt% of edible flavor, and 0.3-1.0wt% of stabilizer.

3. The freeze-dried dried fruit food containing a dairy product coating according to claim 1 or 2, characterized in that: The stabilizer includes a mixture of mono- and di-glycerol fatty acid esters, phospholipids and polyglycerol fatty acid esters; The stabilizer, calculated on the total amount, comprises the following components in mass content: 20-50 wt % of mono- and di-glycerol fatty acid esters, 30-40 wt % of phospholipids, and 10-40 wt % of polyglycerol fatty acid esters.

4. The freeze-dried dried fruit food containing a dairy product coating according to claim 1 or 2, characterized in that: The chocolate material comprises one or a mixture of cocoa butter substitute, cocoa butter, white chocolate or white chocolate products; and / or, The milk powder comprises one or a mixture of skim milk powder, whole milk powder, reconstituted milk powder or buttermilk powder; and / or, The dietary fiber includes resistant dextrin; and / or, The sweetener includes one or a mixture of white sugar, glucose, maltitol, xylitol or erythritol; and / or The cheese powder includes processed cheese powder or cheese product powder or a mixture of the two or more thereof; and / or, The freeze-dried dried fruit includes one or a mixture of freeze-dried strawberries, freeze-dried blueberries, freeze-dried apples, freeze-dried pears or freeze-dried bananas.

5. A method for preparing a freeze-dried dried fruit food containing a dairy product coating as claimed in any one of claims 1 to 4, characterized in that: The steps include: (1) Mixing: Mixing selected amounts of the chocolate material, stabilizer and edible flavor to obtain a first mixed material; mixing selected amounts of the sweetener, milk powder, dietary fiber and cheese powder to obtain a second mixed material; (2) Rolling coating of the surface coating: Mixing a selected amount of the freeze-dried dried fruit with the first mixed material and the second mixed material in sequence and rolling coating the mixture to obtain the surface coating.

6. The method for preparing the freeze-dried dried fruit food containing a dairy product coating according to claim 5, characterized in that: The step (1) further comprises heating the chocolate material to 45-65° C.; and / or, The step (1) further comprises cooling the first mixed material to 36-40° C.; and / or, In the step (2), the rotation speed of the roller coating step is 6-10 rpm.

7. The method for preparing freeze-dried dried fruit food containing dairy product coating according to claim 6, characterized in that: In the step (2), the roll coating step specifically comprises: (a) Grease absorption: After adding the first mixed material, roll coating is performed, and then the material temperature is adjusted to 28-30° C. and roll coating is continued; (b) Powder adhesion: continue to add the second mixed material, mix and roll-coat; (c) Shaping: Adjust the material temperature to 32-34°C and continue rolling; (d) Reinforcement: Adjust the material temperature to 20-28℃ and continue rolling.

8. The method for preparing freeze-dried dried fruit food containing dairy product coating according to claim 7, characterized in that: In the step (2), the roll coating step specifically comprises: (a) Grease absorption: After adding the first mixed material, roll coating is performed for 1-2 minutes, and then cold air is blown in to adjust the material temperature to 28-30° C. After stopping the cold air blowing, roll coating is continued for 1-2 minutes; (b) Powder adhesion: continue to add the second mixed material, mix, and roll-coat for 3-5 minutes; (c) Shaping: Blow hot air to adjust the material temperature to 32-34°C, and continue rolling for 1-2 minutes; (d) Reinforcement: Blow in cold air to adjust the material temperature to 20-28°C and continue rolling for 2-4 minutes.

9. The method for preparing the freeze-dried dried fruit food containing a dairy product coating according to any one of claims 5 to 8, characterized in that: In the step (2), the first mixture and the second mixture are added in batches and then rolled; The first rolling addition amount of the first mixed material accounts for 20-30wt% of the freeze-dried dried fruit core; The first rolling addition amount of the second mixed material accounts for 30-40wt% of the freeze-dried dried fruit core.

10. The method for preparing freeze-dried dried fruit food containing dairy product coating according to claim 9, characterized in that: The step (2) also includes the step of rolling the thickened coating; The thickening coating rolling step includes repeating the step of rolling the surface coating on the mixture remaining after the first rolling and the second mixture according to the operation of step (2).

11. The method for preparing freeze-dried dried fruit food containing dairy product coating according to claim 10, characterized in that: In the thickening coating rolling step: The thickening coating rolling step is to repeat the skin coating rolling 4-6 times; and / or, The thickening coating rolling step also includes the step of adjusting the rolling speed to 12-15 rpm.

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