Milk skin roll and preparation method thereof

Abstract

The invention belongs to the technical field of dairy food, and relates to a milk skin roll and a preparation method thereof.The method comprises the steps that cow milk is subjected to short-time fermentation and composite enzymolysis modification and then subjected to synergistic treatment with a structure stabilizer, and modified cow milk is obtained; the preparation method comprises the following steps: spreading the milk skin, standing at 55-60 DEG C to form a gel substrate, and applying hot air at 80-85 DEG C to promote densification of a surface layer, so as to prepare the composite milk skin with a gradient structure; coating a coconut water-gellan gum solution on the bottom layer, cooling and gelling, then coating flavor paste, rolling and curing to obtain a primary product; finally, the outer surface is coated with pullulan polysaccharide-based edible film liquid, and a finished product is obtained. Through biological modification, gradient skin forming and multi-layer construction technologies, the defects that a traditional milk skin roll is fragile in texture, single in flavor and prone to water loss and deterioration are overcome; the prepared product has the comprehensive advantages of tough outer layer, soft inner layer, rich flavor levels and prolonged shelf life, and is high in process controllability and suitable for standardized production.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of dairy products, and relates to a milk roll and a preparation method thereof. BACKGROUND

[0002] As a derivative form of traditional dairy products, the basic process of milk roll is mostly derived from the formation principle of natural milk skin, that is, after the surface layer of milk is heated to make the protein and fat aggregate and coagulate to form a film, it is rolled into a roll. In the prior art, the preparation method of milk roll is generally simple and extensive, and most of them rely on directly heating milk to form a single milk skin layer, and then rolling up after smearing simple filling (if sauce, syrup, etc.). Although this method is simple to operate, it has significant limitations in product texture, flavor, nutrient retention and shelf life:

[0003] 1) The texture is single, easy to break and rough in taste. The milk skin layer of traditional milk roll often relies on the thermal denaturation of milk protein to form, which has a dense but fragile structure, lacks elasticity and toughness, and is easy to break and break during rolling, storage and consumption. At the same time, since the milk protein is not pretreated, the formed milk skin is often rough, uneven in hardness, and lacks level in taste.

[0004] 2) The flavor is monotonous, and the filling and milk skin have poor combination. The existing milk roll often smears flavor filling in the outer milk skin, but the filling is often simply attached to the surface and cannot be deeply integrated with the milk skin structure, resulting in the filling being easy to fall off and unevenly distributed when cutting or chewing. In addition, the milk skin itself has a single flavor, lacking the rich milk fragrance and complex flavor brought by fermentation or enzymolysis.

[0005] 3) Short shelf life, easy to lose water or deteriorate. Since the traditional milk roll does not introduce an effective structure stabilizing and moisturizing system, it is still prone to problems such as hard and dry surface, inner filling exuding water, sticky texture, etc. under cold storage conditions. At the same time, due to the lack of effective microbial control or coating protection, the product is prone to mold or rancidity, and the shelf life is usually short.

[0006] 4) Single nutritional function, and the value of milk raw materials is not fully utilized. The existing process of milk is often limited to heating, and cannot improve its digestibility, bioactive peptide content or probiotic function through biological techniques such as fermentation or enzymolysis. The utilization rate of milk protein is low, the nutritional composition of the product is simple, and the synergistic design of functional ingredients is lacking.

[0007] 5) Poor process controllability and unstable product quality. The process relying on natural skinning is greatly affected by factors such as milk composition, heating conditions, environmental temperature and humidity, and it is difficult to accurately control the thickness, strength and film uniformity of the milk skin, resulting in significant differences between batches of products and difficulty in achieving standardized production. SUMMARY

[0008] In order to solve the above problems, the present application provides a milk skin roll and a preparation method thereof, specifically comprising the following steps:

[0009] Step one, heat the milk to 38-42℃, add the compound starter, and ferment at 38-42℃ for 80-120min. The purpose of this process is not complete fermentation, but to adjust the pH to create a slightly acidic environment, activate the optimal activity of the subsequent compound enzyme, and subtly change the charge of milk protein (especially casein micelles), making it more susceptible to enzyme attack. At the same time, the extracellular polysaccharide produced by fermentation naturally thickens, providing initial suspension stability for the emulsion and preventing uneven distribution of the subsequent added stabilizer.

[0010] After fermentation, heat to 44-46℃, add compound enzyme, and hydrolyze at 44-46℃ and 120-150rpm for 15-20min. The milk protein adjusted in pH and structure by the previous step is cut into large molecular weight polypeptide fragments in a specific compound enzyme and time, and these fragments have amphiphilic properties, which are the key materials for forming high-strength and high-gloss milk skin. After enzyme hydrolysis, heat to 78-82℃ and maintain for 2-3min to inactivate, then add a structure stabilizer, shear at 2000-3000rpm for 1-2min, heat to 85-90℃, and maintain for 5-10min. First, use 78-82℃ to make the structure stabilizer initially disperse and bind to the polypeptide, providing immediate protection, then raise the temperature to 85-90℃ to make the structure stabilizer completely dissolve and form a gel precursor with the calcium ion protein polypeptide network. Finally, store at 3-5℃ for 7-9h to mature, and obtain modified milk.

[0011] Preferably, the compound starter is Streptococcus thermophilus and Lactobacillus plantarum, with a mass ratio of (1-3):(1-3).

[0012] Preferably, the compound enzyme is bromelain (200,000 U / g) and papain (300,000 U / g), with a mass ratio of (2-4):(6-8).

[0013] Preferably, the structure stabilizer is trehalose and carrageenan, with a mass ratio of (10-15):(0.5-1).

[0014] Step two, spread the modified milk with a thickness of 3-4mm, and keep it at 55-60℃ for 30-40min. The temperature is higher than the gelling temperature of carrageenan (40-45℃), but lower than the denaturation temperature of milk protein (above 70℃), so the carrageenan and polypeptides produced by enzymatic hydrolysis will form a gel network at the bottom to create a porous hydrogel base with elasticity, and then apply hot air with a temperature of 80-85℃ and a speed of 0.7-0.9m / s on the top of the modified milk for 15-25min. The high temperature of 80-85℃ will make the surface layer of milk protein denature rapidly and thoroughly, and deeply integrate with the existing carrageenan-polypeptide network to form an extremely dense "surface film". Hot air accelerates the evaporation of water in the surface layer, causing water in the lower network to migrate upward by capillary action. Because the carrageenan-polypeptide network at the bottom has strong water retention, the water migration is orderly and slow. Finally, a composite milk skin is formed, which has a dense and tough surface layer (thickness of 0.3mm) and a loose and porous bottom layer rich in water (thickness of about 2.7mm).

[0015] Step three, mix coconut water and gellan gum with a mass ratio of (350-450):(1-2), heat to 90-95℃ to dissolve, and then cool to 30-40℃ to obtain a coconut water-gellan gum solution. Mix almond paste, whey protein and inulin with a mass ratio of (65-75):(8-12):(4-6) to obtain a flavor paste.

[0016] Coat the coconut water-gellan gum solution on the bottom layer of the composite milk skin. Because the bottom layer is loose and the temperature of the coconut water-gellan gum solution is higher than its gelling temperature, the solution will quickly penetrate the milk skin. Then cool the whole thing at 4-6℃ for 10-20min, and the gellan gum quickly coagulates into a gel layer, locking the water and coconut flavor inside the composite milk skin. Then coat the flavor paste on the gel layer, cool it at 10-12℃ for 10-20min, and then roll it into a cylindrical shape. Keep it at 4-6℃ for 10-15h to mature, and obtain the initial product milk skin roll.

[0017] Preferably, the gellan gum is low-acyl gellan gum.

[0018] Preferably, the whey protein is WPC80 whey protein. Most preferably, the WPC80 whey protein is modified in step one to obtain modified WPC80 whey protein, which is then mixed with almond paste and inulin to obtain the flavor paste.

[0019] Step four, coat the surface film solution on the outer surface of the initial milk skin roll. For every square decimeter of the outer surface area of the initial milk skin roll, use 1.8-2.2g of surface film solution, and store it at 4-6℃ to obtain the finished product milk skin roll.

[0020] Preferably, the mass ratio of the cow milk, the composite fermenting agent, the composite enzyme, the structure stabilizer, the coconut water-konjac gum solution, and the flavor paste is 1000:(0.1-0.2):(0.03-0.04):(12-13):(75-85):(80-90).

[0021] Preferably, the surface film solution comprises pullulan, citrus pectin, hydroxypropyl distarch phosphate, sorbitol, glycerol, and water, and the mass ratio is (2-3):(0.8-1.2):(3-5):(1-2):(0.7-0.9):100.

[0022] The present application has the following advantages:

[0023] (1) The present application builds a gradient milk skin structure with a dense and tough surface layer and a loose and porous bottom layer through staged temperature control and directional hot air drying. The high-temperature hot air on the surface layer makes the protein denature deeply and fuse with the carrageenan-polypeptide network to form a strong and tough protective layer. The bottom layer forms an elastic gel substrate with strong water retention through the carrageenan and enzymatic polypeptide. This structure not only makes the milk skin not easy to break during rolling, but also presents a complex taste of "tough outer layer and soft inner layer" when eaten, completely overcoming the problem of easy breakage and single texture of traditional milk skin.

[0024] (2) The present application introduces short-time fermentation and composite enzymolysis. Not only does it activate enzyme activity and regulate protein charge through a slightly acidic environment, but also it produces large-molecule polypeptides with amphiphilic properties through specific enzyme cutting. These polypeptides become the key structural units of the milk skin network, and at the same time, they give the product a natural fermented aroma and a delicate aftertaste. Compared with the traditional simple heating process, the present application makes the milk skin flavor richer and the taste smoother, and generates bioactive peptide segments that are easy to absorb, thereby improving the nutritional added value of the product.

[0025] (3) The present application uses a coconut water-konjac gum solution to penetrate the bottom layer and gel at low temperature. Not only does it firmly lock the water and coconut flavor inside the milk skin, preventing texture separation caused by water migration, but also it provides a stable adhesion base for the subsequent flavor paste. The flavor paste mainly uses almond paste as the main body, and is matched with modified whey protein and inulin. The almond aroma and milk aroma are gradually released in the mouth with chewing, forming a flavor gradient from the outside to the inside and from light to strong, which solves the defects of traditional products such as easy separation of filling and flavor separation.

[0026] (4) The present application builds a multiple protection system from the inside to the outside: the structure stabilizer (trehalose + carrageenan) forms a gel precursor to maintain the water retention of the system, and the konjac gum gel layer blocks water evaporation; the surface film solution (pullulan composite system) forms an oxygen and moisture resistant edible film. The multiple layers of protection work together to effectively inhibit product dehydration, drying, and deterioration, extend the cold storage shelf life, and improve the adaptability of commodity circulation.

[0027] (5) From fermentation time, enzymatic hydrolysis temperature, hot air flow rate to the addition ratio of each component, the present application has a clear process window and quantitative index (such as rpm, temperature gradient, ratio range) at each link. This fine control ensures the high consistency of milk skin thickness, strength, flavor penetration depth and final product texture, which is suitable for large-scale, standardized production, and significantly improves the industrial applicability and quality stability of the product.

[0028] (6) Raw material modification and reuse, improve the overall compatibility and functionality of the product, the present application focuses on the synergistic modification of raw materials, for example, the whey protein is modified synchronously in step one and then used in the flavor paste, so that its structure is more compatible with the main body milk skin; low-acyl gellan gum is selected to realize low-temperature rapid gelation without affecting the original texture of the milk skin. This systematic raw material treatment enhances the interaction between components, making the product show high integration in taste, flavor and nutrition. DETAILED DESCRIPTION

[0029] The technical solutions in the embodiments of the application will be described below in a clear and complete manner. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the scope of protection of the present application.

[0030] Embodiment 1

[0031] Raw material preparation:

[0032] Compound fermenting agent: Streptococcus thermophilus (purchased from Jinan Shenghe Chemical Co., Ltd.) and Lactobacillus plantarum (purchased from Zhengzhou Yuke Biological Technology Co., Ltd.), mass ratio 2:1.

[0033] Compound enzyme: 200,000 U / g of bromelain and 300,000 U / g of papain, mass ratio 3:7.

[0034] Structure stabilizer: trehalose and carrageenan, mass ratio 12:0.75.

[0035] Coconut water-gellan gum solution: coconut water and low-acyl gellan gum are mixed in a mass ratio of 400:1.5, heated to 92°C to dissolve, and then cooled to 35°C.

[0036] Flavor paste: almond paste, WPC80 whey protein and inulin, mass ratio 70:10:5.

[0037] Surface film solution: pullulan, citrus pectin, hydroxypropyl distarch phosphate, sorbitol, glycerol and water, mass ratio 2.5:1:4:1.5:0.8:100.

[0038] Specific preparation method:

[0039] Step 1: Heat the milk to 40℃, add the compound fermentation agent, ferment at 40℃ for 100 minutes. After fermentation, raise the temperature to 45℃, add the compound enzyme, and enzymatically hydrolyze at 45℃ and 135 rpm for 18 minutes. After enzymatic hydrolysis, raise the temperature to 80℃ and hold for 2.5 minutes to inactivate the enzyme. Then add the structure stabilizer, shear at 2500 rpm for 2 minutes, raise the temperature to 88℃, hold for 8 minutes, and then refrigerate at 4℃ for 8 hours to obtain modified milk.

[0040] Step 2: Spread the modified milk in a 4mm thick layer, let it stand at 57℃ for 35 minutes, and then apply hot air at 82℃ and 0.8m / s above the modified milk for 20 minutes to obtain a composite milk skin with a dense surface and a loose bottom layer.

[0041] Step 3: Coat the bottom layer of the composite milk skin with coconut water-gellan gum solution, cool at 5°C for 15 minutes to form a gel layer, then coat the gel layer with flavor paste, cool at 10°C for 15 minutes, roll it into a cylindrical shape, and let it stand at 5°C for 12 hours to mature, and obtain the initial milk skin roll.

[0042] Step 4: Apply the surface film liquid to the outer surface of the initial milk skin roll, using 2g of surface film liquid per square decimeter of the outer surface area of ​​the initial milk skin roll, and store at 2℃ to obtain the finished milk skin roll.

[0043] The mass ratio of the milk, compound starter culture, compound enzyme, structural stabilizer, coconut water-gellan gum solution and flavor paste is 1000:0.15:0.035:12.5:80:85.

[0044] Experimental Example 1

[0045] Experimental group: Milk skin rolls prepared according to the method in Example 1.

[0046] Control group: The milk was heated to 85°C and left to stand to form a skin, while the rest of the method was the same as in Example 1.

[0047] Three parallel samples were prepared for each group and tested under the same conditions.

[0048] Test steps: 1. Use a texture analyzer (model: TA.XT Plus) equipped with a P / 36R cylindrical probe, pre-compression speed 1mm / s, test speed 2mm / s, compression ratio 50%, trigger force 5g, take the middle uniform segment (length 2cm) of each sample, repeat the test 5 times, take the average value, and the results are shown in Table 1.

[0049] 2. Drop the milk skin roll from a height of 1 meter onto a flat stainless steel plate and record whether it breaks, the degree of breakage, and the extent of filling loss. The results are shown in Table 1.

[0050] 3. Using a stereomicroscope (10× magnification), observe the layered structure of the cross-section of the milk skin roll, record the surface thickness, bottom pore structure and filling penetration, and the results are shown in Table 1.

[0051] Table 1 Comparison of Product Texture and Structure

[0052] Experimental Example 2

[0053] Experimental group: Milk skin rolls prepared in Example 1;

[0054] Control group: Xilinhu milk skin rolls purchased from the market;

[0055] Evaluators: 10 trained sensory evaluators;

[0056] Evaluation method: blind test scoring, with a maximum score of 10 points for each item.

[0057] Experimental procedure: Cut all samples into 2 cm segments, number them, and provide them randomly. Evaluation items include richness of milky aroma, flavor complexity, texture, sweetness balance, and overall acceptability.

[0058] Scoring criteria: 1 point (very poor) to 10 points (excellent);

[0059] Statistical method: The highest and lowest scores were removed, and the average score was taken. The results are shown in Table 2.

[0060] Table 2 Flavor and Sensory Evaluation

[0061] Experimental Example 3

[0062] Experimental group: Milk skin rolls prepared in Example 1;

[0063] Control group: Xilinhu milk skin rolls purchased from the market;

[0064] Storage conditions: Refrigerate at 4℃, relative humidity 85%;

[0065] Test periods: 0, 7, 14, 21, 28 days.

[0066] Moisture content determination: The oven drying method (105℃ to constant weight) was used, and three parallel samples were taken at each time point.

[0067] Total bacterial count determination: Performed according to GB 4789.2-2016.

[0068] Texture tracking test: Same as in Experiment 1, test the changes in hardness and elasticity.

[0069] Appearance record: Observe daily for signs of mold, cracking, seepage, etc. The results are shown in Table 3.

[0070] Table 3 Shelf life test data

[0071] 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 milk skin rolls, characterized in that, Includes the following steps: Step 1: Heat the milk to 38-42℃, add the compound starter culture and ferment for 80-120 minutes, raise the temperature to 44-46℃, add the compound enzyme and hydrolyze for 15-20 minutes, after hydrolysis, raise the temperature to 78-82℃ and hold for 2-3 minutes to inactivate the enzyme, add the structure stabilizer, shear at 2000-3000 rpm for 1-2 minutes, raise the temperature to 85-90℃ and hold for 5-10 minutes, then refrigerate at 3-5℃ for 7-9 hours to obtain modified milk; Step 2: Spread the modified milk evenly and let it stand at 55-60℃. Then apply hot air at 80-85℃ above it and maintain for 15-25 minutes to obtain the composite milk skin. Step 3: Coat the bottom layer of the composite milk skin with coconut water-gellan gum solution, cool at 4-6℃ for 10-20 minutes, then coat with flavor paste, cool at 10-12℃ for 10-20 minutes, roll into a cylindrical shape, and let stand at 4-6℃ for 10-15 hours to obtain the initial milk skin roll. Step 4: Apply the surface film liquid to the outer surface of the initial milk skin roll. Use 1.8-2.2g of surface film liquid per square decimeter of the outer surface area of ​​the initial milk skin roll. Store at 4-6℃ to obtain the finished milk skin roll. The mass ratio of the milk, compound starter culture, compound enzyme, structural stabilizer, coconut water-gellan gum solution and flavor paste is 1000:(0.1-0.2):(0.03-0.04):(12-13):(75-85):(80-90).

2. The method for preparing a milk skin roll according to claim 1, characterized in that, The compound fermentation agent mentioned in step one is Streptococcus thermophilus and Lactobacillus plantarum in a mass ratio of (1-3):(1-3).

3. The method for preparing a milk skin roll according to claim 1, characterized in that, The complex enzymes mentioned in step one are bromelain and papain, with a mass ratio of (2-4):(6-8).

4. The method for preparing a milk skin roll according to claim 1, characterized in that, The structural stabilizer mentioned in step one is trehalose and carrageenan in a mass ratio of (10-15):(0.5-1).

5. The method for preparing a milk skin roll according to claim 1, characterized in that, The method for preparing the coconut water-gellan gum solution in step three is as follows: mix coconut water and gellan gum at a mass ratio of (350-450):(1-2), heat to 90-95℃ to dissolve, and then cool to 30-40℃ to obtain the solution.

6. The method for preparing a milk skin roll according to claim 5, characterized in that, The gellan gum is a low-acyl gellan gum.

7. The method for preparing a milk skin roll according to claim 1, characterized in that, The flavor paste described in step three includes almond paste, whey protein, and inulin in a mass ratio of (65-75):(8-12):(4-6).

8. The method for preparing a milk skin roll according to claim 7, characterized in that, After the whey protein is modified in step one, modified whey protein is obtained, which is then mixed with almond paste and inulin to obtain a flavor paste.

9. The method for preparing a milk skin roll according to claim 1, characterized in that, The surface film solution mentioned in step four includes pullulan, citrus pectin, hydroxypropyl distarch phosphate, sorbitol, glycerol and water, in a mass ratio of (2-3):(0.8-1.2):(3-5):(1-2):(0.7-0.9):

100.

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

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