Low-fat milk skin yoghourt and preparation method thereof

Abstract

The invention discloses low-fat milk skin yoghourt and a preparation method thereof. The raw materials comprise the following components in parts by mass: 12-30 parts of concentrated skimmed milk, 1.5-4 parts of a milk fat product with the fat content of 80%-100%, sweet substances, oil-soluble beta-carotene, a leavening agent and water in terms of 100 parts. The total fat content of the yoghourt disclosed by the invention can be in a range of 1.6%-4%; through a specific process, the particle size of fat globules, membrane protein composition and floating speed of the fat globules are accurately regulated and controlled, collaborative floating of fat and protein is promoted, a stable milk skin layer with the thickness of about 1-2 mm is formed, oil-soluble beta-carotene is synchronously migrated in the floating process of fat, and the low-fat milk skin yoghourt with a cream yellow milk skin layer is successfully formed. The low-fat milk skin yoghurt disclosed by the invention has the traditional flavor and modern health requirements, and endows the product with richer nutritional value and market potential.

Description

Technical Field

[0001] This invention belongs to the field of dairy processing technology, specifically relating to a low-fat milk skin yogurt and its preparation method. Background Technology

[0002] Milk skin yogurt is a fermented dairy product with a unique double-layer structure. The upper layer is a fat-rich milk skin layer (concentrated milk fat layer), and the lower layer is a set yogurt layer. Traditional milk skin yogurt relies on fat globules to rise and form a dense milk skin during natural fermentation. Its typical characteristics are a milky yellow and thick surface, and a smooth and even yogurt curd at the bottom. It is loved by consumers for its rich flavor and unique taste.

[0003] However, commercially available milk skin yogurt generally has a high fat content because it requires fat globules to rise and form a thick, yellowish milk skin layer. Market research data shows that the fat content of mainstream milk skin yogurt products is typically between 6.5% and 10%. In contrast, the fat content of regular set yogurt is mostly around 3%, meaning that milk skin yogurt's fat content exceeds the national standard for flavored fermented milk by 2-3 times. In recent years, with the increasing number of people suffering from cardiovascular and cerebrovascular diseases and obesity, more and more consumers are inclined to choose low-fat or fat-free foods to prevent chronic diseases caused by excessive fat intake. The high-fat nature of milk skin yogurt significantly limits its popularity and application in the health-conscious consumer market.

[0004] Currently, there is a relative lack of patented technologies for optimizing yogurt with milk skin. For example:

[0005] CN119423163A discloses a formula for yogurt with milk skin and its preparation method. This yogurt formula, by weight, contains 450-550 parts fresh milk, 70-75 parts milk skin, 15-18 parts sugar, 75-85 parts cream, 40-50 parts condensed milk, 14-16 parts milk powder, 8-12 parts cheese powder, 6-9 parts protein powder, and 4-7 parts carotene. This method provides a fat layer by adding various high-fat ingredients such as milk skin, cream, condensed milk, and cheese powder. However, the complex ingredient composition and diverse fat sources fail to address the issue of high base fat content.

[0006] CN118415237A discloses a fermented milk with milk skin and its preparation method. The raw materials of the fermented milk with milk skin include a fermentation base and a starter culture. The fermentation base, by mass percentage, contains 6-7% sweetened condensed milk, 3-4% white sugar, 0.1-0.5% light cream, 0.6-0.7% stabilizer, and 0.1-0.2% agar, with the remainder made up to 100% with raw milk. The preparation method involves stirring and dissolving the sweetened condensed milk, white sugar, light cream, stabilizer, agar, and raw milk to obtain the fermentation base. The fermentation base is continuously stirred and heated to a high temperature for sterilization. After cooling, the starter culture is inoculated and stirred. The mixture is then bottled and fermented at a constant temperature, avoiding shaking. After fermentation is complete, the mixture is cooled to obtain the fermented milk with milk skin. This patent allows fat to rise and form a skin layer by omitting the homogenization step. Although it can also produce yogurt with a skin, the formation of the skin depends on the addition of high-fat condensed milk and light cream. If the amount added is too small, it may not be enough to form a skin. At the same time, the product stability is also highly dependent on the added stabilizers. It fails to innovate from the perspective of raw materials and does not solve the problem of high fat content.

[0007] CN119032993A discloses a set-type milk skin yogurt and its preparation method. The set-type milk skin yogurt, by total weight, contains 5.0-8.0% sweetener, 0.5-1.0% compound stabilizer, 4.0-8.0% cream, and 1-5×10... 6 The result is CFU / g lactic acid bacteria, with the remainder being filtered, impurities removed, but not homogenized fresh milk. This method, like many others, still relies on high-fat formulas and stabilizers.

[0008] CN119097019A discloses a fermented milk with a milk skin flavor and its preparation method. The raw materials for this fermented milk with a milk skin flavor, based on the total mass of the base material and light cream, contain 80-90 wt% raw milk with a fat content of 0.01-1.5 wt%, 0.01-10.0 wt% sweetener, and 5.0-15.0 wt% light cream. It may also contain 0.4-2.0 wt% whey protein powder and 0.3-2.0 wt% thickener, etc. The preparation method is as follows: the base material is mixed, homogenized at 60-65℃ / 18-20MPa, sterilized at 90-95℃ for 5-10 min, cooled to 42-45℃, and inoculated with starter cultures to obtain a mixed base material; the light cream is sterilized at 90-95℃ for 5-10 min to obtain sterilized light cream; the two are mixed and fermented at 42-45℃ for 4-7 h until the acidity reaches 65-75°T, then cooled and matured to obtain the final product. This method is sensitive to the amount of cream added. The proportion of cream needs to be precisely controlled between 5.0-15.0 wt%. If the proportion is less than 5%, the milk skin cannot cover the surface and the layering effect is poor. At the same time, the process is complicated. The mixing time after the base material is inoculated with bacteria needs to be precisely controlled. If it is too long, it will cause curdling. If the curd and cream ferment together, the milk skin cannot be formed.

[0009] In summary, existing technologies often rely on directly adding high-fat ingredients (such as butter, condensed milk, and cheese powder) or using stabilizers (such as agar and compound colloids) to form and maintain the milk skin layer. This not only results in a consistently high overall fat content in the product but also complicates the ingredient list, falling short of current consumer trends that favor clean labels, simple ingredients, and low-fat, healthy options. This problem urgently needs to be addressed. Summary of the Invention

[0010] The technical problem to be solved by the present invention is to overcome the defects of the existing technology in the preparation of milk skin yogurt, which mostly relies on the direct addition of high-fat raw materials (such as cream, condensed milk, cheese powder) or on stabilizers (such as agar, compound colloids) to form and maintain the milk skin layer, resulting in a high overall fat content of the product and a complicated ingredient list. The present invention provides a low-fat milk skin yogurt and its preparation method.

[0011] Despite the flavor advantages of milk skin yogurt, its high fat content has become a major technical bottleneck restricting the product's adaptation to health-conscious consumption trends. Existing processes rely on natural fat rising to form a milk skin, resulting in a product that cannot simultaneously maintain traditional taste while meeting low-fat demands. Research has found that reducing the fat content in low-fat yogurt leads to problems such as a loose texture, whey separation, and reduced milk fat content. This invention achieves effective reduction of fat content while stably forming a high-quality milk skin layer through raw material and process innovation, ensuring the overall texture and flavor of the product. This invention's low-fat milk skin yogurt enhances health attributes while retaining its unique sensory appeal, meeting the new national standards and consumer demand for low-fat, clean-label fermented dairy products.

[0012] The present invention solves the above-mentioned technical problems through the following technical solutions.

[0013] This invention provides a low-fat milk skin yogurt, the raw materials of which include the following components by weight:

[0014] Based on 100 parts, it consists of 12-30 parts concentrated skim milk, 1.5-4 parts milk fat products with a fat content of 80%-100%, sweeteners, oil-soluble beta-carotene, starter culture, and water.

[0015] In this invention, the concentrated skim milk is generally a product obtained by separating the skim milk portion from raw milk, pasteurizing it, concentrating it to remove some water, and then filling and packaging it. The concentrated skim milk is generally stored frozen or refrigerated.

[0016] In this invention, the preferred content of each component in the concentrated skim milk is: dry matter of about 45-47%, protein content of about 16.0-18.5%, fat content of ≤0.6%, and carbohydrate content of ≥20%.

[0017] In some preferred embodiments, the concentrated skim milk may be 4x concentrated skim milk. If other concentrations of skim milk are selected, the amount added can be calculated based on the dry matter content.

[0018] In this invention, the milk fat product with a fat content of 80%-100% can be butter and / or anhydrous butter. The butter typically has a fat content of 80%. The anhydrous butter is generally a milk fat product with a fat content of not less than 99.9% made from milk, cream, or whipped cream.

[0019] In this invention, the milk fat product with a fat content of 80%-100% is typically remodeled into fat globules and uniformly dispersed in water during subsequent processing. If light cream is used, its fat content is generally 40%. This oil-in-water system is more stable because the fat globules are already relatively uniformly dispersed, making it unsuitable for this invention.

[0020] In this invention, the sweetener can be one or more of the following conventional sweeteners: white sugar, fructose syrup, glucose, maltitol, erythritol, xylitol, sucralose, acesulfame potassium, and steviol glycosides, such as white sugar.

[0021] In this invention, the oil-soluble β-carotene generally refers to a product in which β-carotene powder crystals are dissolved and dispersed in edible vegetable oil, with edible vegetable oil as the carrier.

[0022] In some preferred embodiments, 30% β-carotene (oil-soluble) purchased from BASF (China) Co., Ltd. is used. This comprises 30g of pure β-carotene per 100g, with the remainder being vegetable oil (corn oil, rapeseed oil) and antioxidants (vitamin E).

[0023] In this invention, the fermenting agent generally refers to a mesophilic / thermophilic lactic acid bacteria fermenting agent prepared by freeze-drying and concentration, which can improve the viscosity of the finished product.

[0024] In some preferred embodiments, the starter culture SC-101, purchased from Danisco (China) Co., Ltd., is used, and its composition is: Lactococcus lactis subsp. lactis, Lactococcus cremoris subsp. cremoris, and Streptococcus salivarius subsp. thermophilus.

[0025] In this invention, preferably, the raw materials of the milk skin yogurt also include inulin.

[0026] Inulin is a naturally occurring reserve polysaccharide found in various plants. It belongs to the fructan family and is also a natural water-soluble dietary fiber. It is primarily composed of linearly polymerized D-fructose residues linked by β-(1→2) glycosidic bonds, typically ending with a glucose residue. Its degree of polymerization (DP) ranges widely, usually between 2 and 60.

[0027] The amount of inulin can be 0.5 parts, 1 part, 2 parts, 3 parts, 3.5 parts, 4 parts or 5 parts, preferably 0-5 parts, more preferably 0.5-4 parts, for example 1-3 parts.

[0028] In this invention, preferably, the raw materials of the milk skin yogurt also include whey protein powder.

[0029] The whey protein powder is generally a powdered product with a protein content of not less than 70%, made from whey through processes such as separation, concentration, and drying.

[0030] The amount of whey protein powder used can be 0.5 parts, 1 part, 2 parts, 3 parts, 3.5 parts, 4 parts or 5 parts, preferably 0-5 parts, more preferably 0.5-4 parts, for example 1-3 parts.

[0031] In this invention, the amount of concentrated skim milk can be 15 parts, 18 parts, 20 parts, 22 parts, 25 parts, 28 parts, 30 parts or 32 parts, preferably 15-28 parts, more preferably 16-24 parts, and even more preferably 18-22 parts.

[0032] In this invention, the amount of the milk fat product with a fat content of 80%-100% can be 2 parts, 2.5 parts, 3 parts, 3.5 parts or 4 parts, preferably 2-4 parts, more preferably 2.5-3.5 parts.

[0033] When adding anhydrous butter, if the amount used is greater than 4 parts, it can result in a high fat content in the final product, which does not meet the requirements for low fat.

[0034] In this invention, the amount of sweetener added can be adjusted according to the usual sweetness level.

[0035] When the sweetener is white sugar, the amount of white sugar used is preferably 6-14 parts, and can be 8 parts, 8.5 parts, 9 parts, 9.5 parts, 10 parts, 10.5 parts, 11 parts, 11.5 parts or 12 parts, more preferably 8-12 parts, and even more preferably 8.5-11.5 parts, for example 9-11 parts.

[0036] In this invention, the amount of water used can be 59-75 parts, for example 59 parts, 60 parts, 62 parts, 64 parts, 66 parts, 67 parts, 68 parts, 70 parts, 72 parts or 75 parts, preferably 60 parts-69 parts, more preferably 61 parts-66 parts.

[0037] In this invention, the amount of oil-soluble β-carotene used can be calculated based on its purity or specifications and the effective content of the target β-carotene.

[0038] In this invention, the amount of oil-soluble β-carotene used, based on the effective content of β-carotene, can be 0.0009‰, 0.0012‰, 0.0015‰, or 0.0018‰, preferably 0.0009-0.0018‰, more preferably 0.0012-0.0018‰. The above percentages represent the effective content of β-carotene as a percentage of the mass of the fermentation substrate. In the percentage of oil-soluble β-carotene, the fermentation substrate refers to the sum of all other components except the fermenting agent.

[0039] In some preferred embodiments, an oil-soluble β-carotene with a concentration of 30% is used, and the amount of the oil-soluble β-carotene can be 0.003‰, 0.004‰, 0.005‰ or 0.006‰, preferably 0.004-0.006‰.

[0040] In this invention, the amount of the fermenting agent can be 0.02‰, 0.03‰, 0.04‰, or 0.05‰, preferably 0.02-0.05‰, and more preferably 0.03‰-0.05‰. The above percentages represent the mass percentage of the fermentation substrate. In the percentage of the fermenting agent, the fermentation substrate refers to the sum of all other components besides the fermenting agent.

[0041] In some preferred embodiments, the ingredients of the low-fat milk skin yogurt include: 15-25% (e.g., 20%) of the concentrated skim milk, 2-4% (e.g., 3%) of the milk fat product with a fat content of 80%-100%, 8-12% (e.g., 10%) of the sweetener, 0-4% (e.g., 0-3%) of the inulin, 0-4% (e.g., 0-3%) of the whey protein powder, and 59-75% of the water; the percentages are the mass percentages of each component relative to the total amount of the above substances.

[0042] The milk fat product with a fat content of 80%-100% is preferably anhydrous butter, and the sweetener is preferably white sugar;

[0043] The oil-soluble β-carotene, based on the effective content of β-carotene, has a dosage of 0.0009-0.0018‰, where the above percentages represent the effective content of β-carotene as a percentage of the mass of the fermentation substrate.

[0044] The fermenting agent is 0.02-0.05‰ of the fermentation substrate, where the above percentages are percentages by mass of the fermentation substrate.

[0045] In some preferred embodiments, the ingredients of the low-fat milk skin yogurt include: 20% of the concentrated skim milk, 3% of the milk fat product with a fat content of 80%-100%, 10% of the sweetener, 3% of the inulin, and 64% of the water; the percentages are the mass percentages of each component relative to the total amount of the above substances; the milk fat product with a fat content of 80%-100% is preferably anhydrous butter, and the sweetener is preferably white sugar;

[0046] The oil-soluble β-carotene, based on the effective content of β-carotene, has a dosage of 0.0015‰, and the above percentage is the effective content of β-carotene as a percentage of the mass of the fermentation substrate.

[0047] The fermenting agent is 0.03‰, where the percentage is the mass percentage of the fermentation substrate.

[0048] In some preferred embodiments, the ingredients of the low-fat milk skin yogurt include: 20% of the concentrated skim milk, 3% of the milk fat product with a fat content of 80%-100%, 10% of the sweetener, 3% of the whey protein powder, and 64% of the water; the percentages are the mass percentages of each component relative to the total amount of the above substances.

[0049] The milk fat product with a fat content of 80%-100% is preferably anhydrous butter, and the sweetener is preferably white sugar;

[0050] The oil-soluble β-carotene, based on the effective content of β-carotene, has a dosage of 0.0015‰, and the above percentage is the effective content of β-carotene as a percentage of the mass of the fermentation substrate.

[0051] The fermenting agent is 0.03‰, where the percentage is the mass percentage of the fermentation substrate.

[0052] In the percentage of oil-soluble β-carotene or the fermenting agent, the fermentation base refers to the sum of all other components except the fermenting agent.

[0053] The present invention also provides a method for preparing the low-fat milk skin yogurt, which includes the following steps: cutting, homogenizing, sterilizing, and inoculating the mixture to obtain the low-fat milk skin yogurt;

[0054] The mixture includes raw materials other than the fermenting agent; the homogenization pressure is 6-10 MPa.

[0055] In this invention, the preparation method of the mixture can be conventional in the art, and is preferably obtained through the following steps:

[0056] S1 First, the concentrated skim milk, the water, and the sweetener are stirred, mixed, and dissolved to obtain a premix;

[0057] S2 After melting the milk fat product with a fat content of 80%-100%, it is stirred and mixed with the oil-soluble β-carotene. The resulting material is then mixed with the premix to obtain the mixture.

[0058] In S1, it is preferable to mix the concentrated skim milk and the water and preheat it to 60°C-75°C (e.g., 72°C) before mixing it with the sweetener.

[0059] When the raw material contains inulin or whey protein powder, the inulin or whey protein powder may be added simultaneously with the sweetener.

[0060] In step S2, the milk fat product with a fat content of 80%-100% is typically heated to 60℃-65℃ (e.g., 62℃) to melt before the oil-soluble β-carotene is added. The stirring and mixing is generally stopped when the β-carotene is completely dissolved and there are no pigment particles or layering phenomena.

[0061] In this invention, the shearing speed is preferably 6000-8000 rpm, for example 6000 rpm, 7000 rpm or 8000 rpm.

[0062] In this invention, the cutting time is preferably 1-3 min, for example 1 min, 2 min or 3 min.

[0063] In this invention, the fat content in the sheared material can be 1.6-4.0%, for example 2.0%.

[0064] In this invention, the homogenization temperature is preferably 65-75°C, for example 65°C, 70°C or 75°C.

[0065] In this invention, the homogenization pressure can be 6 MPa, 8 MPa or 10 MPa, preferably 6.5-9 MPa.

[0066] In this invention, the sterilization operation and conditions can be conventional in the art. The sterilization temperature is preferably 90-100℃, for example, 90℃, 95℃, or 100℃. The sterilization holding time is preferably 5-10 minutes, for example, 5 minutes, 6 minutes, or 10 minutes.

[0067] In this invention, after sterilization, the sterilized material is generally cooled to the fermentation temperature. The fermentation temperature is preferably 30-40℃, more preferably 37-40℃.

[0068] In this invention, the inoculation method and operation can be conventional in the art, generally involving adding the fermenting agent to the material and mixing it evenly.

[0069] In this invention, the fermentation conditions are preferably sealed and at a constant temperature. In a preferred embodiment, the material is filled into a cup, sealed, and fermented at a constant temperature of 37-40°C.

[0070] In this invention, the fermentation endpoint is preferably an acidity of 70-80°T (e.g., 72°T).

[0071] In this invention, after the fermentation is completed, the resulting product is generally transferred to a refrigerator or cold storage to be cooled to 2-6°C, for example, 2-4°C.

[0072] The present invention also provides a low-fat milk skin yogurt prepared by the preparation method described above.

[0073] In this invention, the fat content of the low-fat milk skin yogurt can be 1.6-4.0%, for example 2.0%.

[0074] Based on common knowledge in the field, the above-mentioned preferred conditions can be combined arbitrarily to obtain various preferred embodiments of the present invention.

[0075] The reagents and raw materials used in this invention are all commercially available.

[0076] The positive and progressive effects of this invention are as follows:

[0077] This invention uses concentrated skim milk as the main raw material. By adding milk fat products with a fat content of 80%-100%, the total fat content of the product can be controlled within the range of 2%-4%, significantly reducing the fat level. To further enhance the visual quality of the milk skin, a specific process (e.g., homogenization at 6-10 MPa) is used to precisely control the size of fat globules, their membrane protein composition, and the floating speed, promoting the synergistic floating of fat and protein to form a stable milk skin layer with a thickness of approximately 1-2 mm. During the fat floating process, oil-soluble β-carotene migrates simultaneously, successfully forming a low-fat milk skin yogurt with a milky yellow milk skin layer. This invention's low-fat milk skin yogurt combines traditional flavor with modern health needs, giving this product category richer nutritional value and market potential.

[0078] In some preferred embodiments, to ensure the smooth texture of the yogurt layer, auxiliary materials such as whey protein and inulin can be added to enhance the gel network structure and texture stability, maintain the firm texture of the yogurt after the fat content is reduced, reduce whey separation, retain the milky feel, and improve the overall taste and texture. Attached Figure Description

[0079] Figure 1-14The images are real photos taken from different angles of the low-fat milk skin yogurt in Examples 1-5 and Comparative Examples 1-9. Detailed Implementation

[0080] The present invention is further illustrated below by way of embodiments, but the invention is not limited to the scope of the embodiments described herein. Experimental methods in the following embodiments that do not specify specific conditions were performed according to conventional methods and conditions, or as selected according to the product instructions.

[0081] In the following embodiments and comparative examples:

[0082] 1. The main sources of raw and auxiliary materials are as follows:

[0083] Frozen concentrated skim milk (4x concentrated skim milk, dry matter content around 45-47%, protein content around 16.0-18.5%, fat content ≤0.6%, carbohydrate content ≥20%), raw milk, 40% cream, and skim milk were all purchased from Heilongjiang Feihe Dairy Co., Ltd.

[0084] Anhydrous butter was purchased from Nestlé (China) Co., Ltd.

[0085] The white sugar was purchased from COFCO (Tangshan) Sugar Co., Ltd.

[0086] 30% β-carotene (oil-soluble) was purchased from BASF (China) Co., Ltd.

[0087] 1% β-carotene (water-soluble) was purchased from DSM-Firmfield.

[0088] Inulin was purchased from Hebei Weilefu Agricultural Technology Co., Ltd.

[0089] Concentrated whey protein powder (generally a powdered product with a protein content of not less than 70%) was purchased from Hilmar Company in the United States.

[0090] The starter culture SC-101 was purchased from Danisco (China) Co., Ltd., and its composition is: Lactococcus lactis subsp. lactis, Lactococcus cremoris subsp. cremoris, and Streptococcus salivarius subsp. thermophilus.

[0091] 2. Main instruments and equipment

[0092] IKA cantilever mechanical stirrer, IKA digital display disperser, APV 1000 homogenizer, clean bench (biosafety cabinet) (THERMO), electronic balance (Sartorius), electric thermostatic incubator, centrifuge (TDL-60B), Microtrac laser particle size analyzer S3500.

[0093] A low-fat yogurt with a milk skin, the ingredients of which include the following components by weight:

[0094] Based on 100 parts, it consists of 12-30 parts concentrated skim milk, 1.5-4 parts milk fat products with a fat content of 80%-100%, sweeteners, oil-soluble beta-carotene, starter culture, and water.

[0095] In this invention, the raw materials for the milk skin yogurt may also include inulin.

[0096] In this invention, the raw materials for the milk skin yogurt may also include whey protein powder.

[0097] A method for preparing the low-fat milk skin yogurt includes the following steps: cutting, homogenizing, sterilizing, and inoculating the mixture to obtain the low-fat milk skin yogurt;

[0098] The mixture includes raw materials other than the fermenting agent; the homogenization pressure is 6-10 MPa.

[0099] In this invention, the preparation method of the mixture can be conventional in the art, for example:

[0100] S1 First, the concentrated skim milk, the water, and the sweetener are stirred, mixed, and dissolved to obtain a premix; when the raw materials contain inulin or whey protein powder, the inulin or whey protein powder can be added simultaneously with the sweetener;

[0101] S2 After melting the milk fat product with a fat content of 80%-100%, it is stirred and mixed with the oil-soluble β-carotene. The resulting material is then mixed with the premix to obtain the mixture.

[0102] The recipes for low-fat milk skin yogurt in Examples 1-5 are shown in Table 1.

[0103] Table 1. Recipes for Low-Fat Milk Skin Yogurt in Examples 1-5 (by weight percentage)

[0104]

[0105] The percentages of 30% β-carotene (oil-soluble) and starter culture SC-101 are the respective mass percentages of the fermentation substrate. The fermentation substrate refers to the sum of all other components except the starter culture (including β-carotene). The percentages of other components are the percentages of each component relative to the total mass of all other components except the starter culture and β-carotene.

[0106] Example 1

[0107] The preparation method of low-fat milk skin yogurt includes the following steps:

[0108] 1. Mix 15% of pre-thawed frozen concentrated skim milk and 75% water, then preheat to 60°C; add 8% white sugar and stir until dissolved to obtain the mixture;

[0109] 2. Melt 2% anhydrous butter at 60℃, add 0.003‰ β-carotene, and stir until the β-carotene is completely dissolved and there are no pigment particles or layering.

[0110] 3. Add anhydrous butter to the mixture and shear at 6000 rpm for 1 min to initially disperse it, resulting in a pre-dispersed material with a fat content of 2.0%.

[0111] 4. Homogenize the initially dispersed material at 65℃ and 6 MPa;

[0112] 5. Sterilize the homogenized material: sterilization temperature 90℃, sterilization holding time 5 min, and then rapidly cool to fermentation temperature 30℃.

[0113] 6. Add the fermenting agent to the cooled material and mix well. The addition amount is 0.02‰. Fill the material into cups and seal them. Ferment at a constant temperature of 37℃.

[0114] 7. Stop fermentation when the acidity reaches 70°T, transfer to a refrigerator or cold storage to cool to 2°C, and you will get low-fat milk skin yogurt.

[0115] Example 2

[0116] The preparation method of low-fat milk skin yogurt includes the following steps:

[0117] 1. Mix 25% of pre-frozen, thawed, concentrated skim milk with 60% water and preheat to 75°C; add 12% white sugar and stir until dissolved to obtain the mixture;

[0118] 2. Melt 4% anhydrous butter at 65°C, add 0.006‰ β-carotene, and stir until the β-carotene is completely dissolved and there are no pigment particles or layering.

[0119] 3. Add anhydrous butter to the mixture and shear at 8000 rpm for 3 minutes to initially disperse it, resulting in a pre-dispersed material with a fat content of 4.0%.

[0120] 4. Homogenize the initially dispersed material at 75℃ and 10 MPa;

[0121] 5. Sterilize the homogenized material: sterilization temperature 100℃, sterilization holding time 10min, and then rapidly cool to fermentation temperature 40℃.

[0122] 6. Add the fermenting agent to the cooled material and mix well. The addition amount is 0.05‰. Fill the material into cups and seal them. Ferment at a constant temperature of 40℃.

[0123] 7. Stop fermentation when the acidity reaches 80°T, transfer to a refrigerator or cold storage to cool to 6°C, and you will get low-fat milk skin yogurt.

[0124] Example 3

[0125] The preparation method of low-fat milk skin yogurt includes the following steps:

[0126] 1. Mix 20% of pre-frozen, thawed, concentrated skim milk with 67% water and preheat to 72°C; add 10% white sugar and stir until dissolved to obtain the mixture;

[0127] 2. Melt 3% anhydrous butter at 62℃, add 0.005‰ β-carotene, and stir until the β-carotene is completely dissolved and there are no pigment particles or layering.

[0128] 3. Add anhydrous butter to the mixture and shear at 7000 rpm for 2 minutes to initially disperse it, resulting in a pre-dispersed material with a fat content of 3.0%.

[0129] 4. Homogenize the initially dispersed material at 70℃ and 8 MPa;

[0130] 5. Sterilize the homogenized material: sterilization temperature 95℃, sterilization holding time 6 min, and then rapidly cool to fermentation temperature 37℃.

[0131] 6. Add the fermenting agent to the cooled material and mix well. The addition amount is 0.03‰. Fill the material into cups and seal them. Ferment at a constant temperature of 37℃.

[0132] 7. Stop fermentation when the acidity reaches 72°T, transfer to a refrigerator or cold storage to cool to 4°C, and you will get low-fat milk skin yogurt.

[0133] Example 4

[0134] The preparation method of low-fat milk skin yogurt includes the following steps:

[0135] 1. Mix 20% of pre-frozen, thawed, concentrated skim milk with 64% water and preheat to 72°C; add 10% white sugar and 3% whey protein powder and stir to dissolve to obtain the mixture;

[0136] 2. Melt 3% anhydrous butter at 62℃, add 0.005‰ β-carotene, and stir until the β-carotene is completely dissolved and there are no pigment particles or layering.

[0137] 3. Add anhydrous butter to the mixture and shear at 7000 rpm for 2 minutes to initially disperse it, resulting in a pre-dispersed material with a fat content of 3.0%.

[0138] 4. Homogenize the initially dispersed material at 70℃ and 8 MPa;

[0139] 5. Sterilize the homogenized material: sterilization temperature 95℃, sterilization holding time 6 min, and then rapidly cool to fermentation temperature 37℃.

[0140] 6. Add the fermenting agent to the cooled material and mix well. The addition amount is 0.03‰. Fill the material into cups and seal them. Ferment at a constant temperature of 37℃.

[0141] 7. Stop fermentation when the acidity reaches 72°T, transfer to a refrigerator or cold storage to cool to 4°C, and you will get low-fat milk skin yogurt.

[0142] Example 5

[0143] The preparation method of low-fat milk skin yogurt includes the following steps:

[0144] 1. Mix 20% of pre-frozen, thawed, concentrated skim milk and 64% of water, and preheat to 72°C; add 10% of granulated sugar and 3% of inulin, and stir thoroughly to dissolve to obtain the mixture;

[0145] 2. Melt 3% anhydrous butter at 62℃, add 0.005‰ β-carotene, and stir until the β-carotene is completely dissolved and there are no pigment particles or layering.

[0146] 3. Add anhydrous butter to the mixture and shear at 7000 rpm for 2 minutes to initially disperse it, resulting in a pre-dispersed material with a fat content of 3.0%.

[0147] 4. Homogenize the initially dispersed material at 70℃ and 8 MPa;

[0148] 5. Sterilize the homogenized material: sterilization temperature 95℃, sterilization holding time 6 min, and then rapidly cool to fermentation temperature 37℃.

[0149] 6. Add the fermenting agent to the cooled material and mix well. The addition amount is 0.03‰. Fill the material into cups and seal them. Ferment at a constant temperature of 37℃.

[0150] 7. Stop fermentation when the acidity reaches 72°T, transfer to a refrigerator or cold storage to cool to 4°C, and you will get low-fat milk skin yogurt.

[0151] Comparative Example 1

[0152] Based on Example 3, the 30% β-carotene (oil-soluble) was replaced with 1% β-carotene (water-soluble), and the remaining steps were the same as in Example 3.

[0153] Comparative Example 2

[0154] Based on Example 3, the concentrated skim milk, anhydrous butter, and water were replaced with an equal amount (i.e., 90%) of pasteurized pure milk, while the remaining steps remained the same as in Example 3.

[0155] Comparative Example 3

[0156] Based on Example 3, the homogenization pressure was changed to 3 MPa, and the remaining steps remained the same as in Example 3.

[0157] Comparative Example 4

[0158] Based on Example 3, the homogenization pressure was changed to 13 MPa, and the remaining steps remained the same as in Example 3.

[0159] Comparative Example 5

[0160] Based on Example 3, the amount of anhydrous butter added was reduced to 1%, and water was used to make up the difference. The remaining steps were the same as in Example 3.

[0161] Comparative Example 6

[0162] Based on Example 3, the concentrated skim milk and water were replaced with an equal amount (i.e., 87%) of skim milk, and the remaining steps were the same as in Example 3.

[0163] Comparative Example 7

[0164] Based on Example 3, anhydrous butter was replaced with pasteurized light cream (40% fat content) that provides the same amount of added fat, with an addition amount of 7.5% and water addition amount of 62.5%. The addition amounts of other ingredients remained unchanged, and the remaining steps were consistent with Example 3.

[0165] Comparative Example 8

[0166] Based on Example 3, the amount of frozen concentrated skim milk added was reduced to 10% and made up with water, while the remaining steps remained the same as in Example 3.

[0167] Comparative Example 9

[0168] Based on Example 3, the amount of frozen concentrated skim milk added was increased to 35%, and the amount of water added was 52%, while the remaining steps remained the same as in Example 3.

[0169] Example 1: Sensory Analysis and Real-World Photos

[0170] A team of more than 20 professionals conducted blind tests and scored the low-fat milk skin yogurts prepared in Examples 1-5 and Comparative Examples 1-9, and the average score was taken. The scoring rules are shown in Table 2, with higher scores indicating greater satisfaction. The scoring results are shown in Table 3.

[0171] Table 2 Sensory Evaluation Criteria for Milk Skin Yogurt

[0172]

[0173] Table 3 Sensory scores of the milk skin yogurt in the examples and comparative examples

[0174]

[0175] Real photos of low-fat yogurt with milk skin

[0176] Figure 1-14 The images are real photos taken from different angles of the low-fat milk skin yogurt in Examples 1-5 and Comparative Examples 1-9.

[0177] In Examples 1-3, the fermented milk with milk skin flavor that has been refrigerated and then fermented has a layer of milk skin on the surface, with a smooth and delicate texture and a rich milky aroma. The yogurt at the bottom has a silky and delicate texture and a sweet and sour taste. The combination of the two makes the taste even richer.

[0178] In Example 4, the fermented milk with milk skin flavor that has been refrigerated and then cooked has a layer of milk skin on the surface, with a smooth and delicate texture and a rich milky aroma. The yogurt at the bottom has a silky and delicate texture and a sweet and sour taste. The addition of whey protein can enhance its thickness and fullness, and maintain the firm texture of the yogurt after the fat content is reduced.

[0179] In Example 5, the fermented milk with milk skin flavor, after being refrigerated and cooked, has a layer of milk skin on the surface, with a smooth and delicate texture and a rich milky aroma. The addition of inulin can effectively optimize the texture of the lower yogurt layer, reduce whey separation, maintain a good milk fat feel, and make the taste more delicate and mellow.

[0180] The product prepared in Comparative Example 1 did not have a noticeable milky yellow skin on its surface because the water-soluble pigments could not float to the surface with the fat.

[0181] The product prepared in Comparative Example 2 did not have any milk skin on the surface because the fat globules in pasteurized pure milk are small in size and are wrapped with a complete natural interfacial membrane, resulting in high emulsification stability and preventing them from agglomerating and floating to form milk skin.

[0182] The product prepared in Comparative Example 3 had a thicker, rougher milk skin on the surface, a yellower color, and would break when scooped with a spoon, resulting in whey separation. This was because the lower homogenization pressure caused the fat globules to be too large, carrying less surface protein and excessively high fat content during the upward movement.

[0183] The product prepared in Comparative Example 4 did not have any milk skin on the surface because the homogenization pressure was too high, resulting in small fat globules that could not aggregate and float to form milk skin.

[0184] The product prepared in Comparative Ratio 5 did not have a milk skin on the surface because the amount of anhydrous butter added was too low, resulting in a low fat content that prevented the formation of a milk skin.

[0185] The product obtained in Comparative Example 6 had a milk skin on the surface, but the yogurt layer was soft and watery. The core reason is that skim milk has a low protein and solids content—even though the formula contains only skim milk except for anhydrous butter and sugar, the solids and protein it provides are still insufficient to support the stable texture required for yogurt. This comparative example effectively highlights the advantage of concentrated skim milk in improving the texture stability of yogurt. In actual production, the texture of the yogurt layer can be specifically optimized by increasing the amount of concentrated skim milk added.

[0186] The product prepared in Comparative Example 7 showed no milk skin on the surface. This is because, under low-fat conditions, although the added cream provided a small amount of fat, the emulsification stability of the fat globules was relatively high, and the surface of the fat globules in the cream was covered with a complete natural interfacial film. This ensured that the fat globules remained evenly dispersed in the yogurt matrix during fermentation, preventing them from aggregating into larger fat globules and migrating upwards, ultimately making it difficult to form a milk skin of a certain thickness on the product surface. In other words, the fat in the cream was too stable to float and form a milk skin.

[0187] The product prepared in Comparative Example 8 had a skin on the surface, but insufficient concentrated skim milk resulted in a softer yogurt texture and watery consistency. This is because concentrated skim milk provides the main solids and protein content in the system; if the solids and protein content is also low under low-fat conditions, the yogurt texture will be softer and more prone to watery consistency.

[0188] The product prepared in Comparative Example 9 did not form a sufficiently thick milk skin on the surface, and the milk skin was light in color, appearing as a pale milky white. Furthermore, the excessive amount of concentrated skim milk resulted in a noticeable defect in the texture of the yogurt layer, with a pronounced powdery feel and insufficient smoothness. This was because the amount of concentrated skim milk added to the formula was too high, causing the solids and protein content to exceed the appropriate range. On the one hand, the excessive protein and solids significantly increased the viscosity of the yogurt system, significantly increasing the system resistance encountered by fat globules during fermentation, making it difficult for them to migrate upwards and resulting in an insufficiently thick milk skin on the surface, and a lighter-colored milk skin. On the other hand, the excessively high concentration of casein from the concentrated skim milk resulted in an overly dense casein network structure after fermentation, leading to a noticeable powdery feel and ruining the smooth texture that the yogurt layer should have.

[0189] Table 4. Thickness of milk skin in yogurt from the examples and comparative examples.

[0190]

[0191] Results analysis: Based on the sensory evaluation results and photos of the milk skin, it can be seen that the texture and flavor of each embodiment and preferred embodiment of this technical solution are significantly better than those of the comparative proportions.

[0192] Example 2: Acidity and water-holding capacity analysis

[0193] Test methods: Acidity (GB 5009.239), water holding capacity (refer to the following literature: Study on the application characteristics of pea protein from different sources in set-type yogurt and the development of low-fat yogurt [D]. Chinese Academy of Agricultural Sciences, 2022.). The test results are shown in the table below.

[0194] Table 5. Water-holding capacity of the examples and comparative examples

[0195]

[0196] Results analysis: The water-holding capacity data show that Example 5 (with added inulin) and Example 4 (with added whey protein) are more effective at maintaining the water-holding capacity of the samples compared with the comparative examples and other examples.

[0197] In Comparative Example 9, the water-holding capacity was higher. This was due to the excessive amount of concentrated skim milk added, resulting in solids and protein content exceeding the appropriate range. In other words, the excessive concentrated skim milk caused a noticeable defect in the yogurt layer's texture, with a pronounced powdery feel and insufficient smoothness. However, for yogurt, better water-holding capacity does not necessarily mean better product quality and taste. Higher solids content generally indicates better water-holding capacity, but it results in a poorer, dry, and unpleasant texture.

[0198] Example 3: Particle Size Analysis

[0199] Test method: Particle size was determined according to the Microtrac S3500 laser particle size analyzer wet dispersion test operation guide, and deionized water was used as the dispersion medium. The test results are shown in the table below.

[0200] Table 6 Particle size of examples and comparative examples

[0201]

[0202] Results Analysis: D90 represents the particle size corresponding to 90% of the cumulative volume (i.e., 90% of the particles have a diameter less than or equal to this value). The D90 data shows that D90 decreases with increasing homogenization pressure, indicating that homogenization effectively refines particle size. This patent controls the particle size of fat globules in the mixed system to meet the D90 requirement of 2.6-1.5 μm through homogenization, allowing the fat globules to float during fermentation and form a uniform milk skin with a thickness of 1.5-2.0 mm.

Claims

1. A type of yogurt with a milk skin, characterized in that, Its raw materials include the following components by mass: Based on 100 parts, it consists of 12-30 parts concentrated skim milk, 1.5-4 parts milk fat products with a fat content of 80%-100%, sweeteners, oil-soluble beta-carotene, starter culture, and water.

2. The yogurt with milk skin as described in claim 1, characterized in that, The milk skin yogurt meets one or more of the following conditions: (1) The amount of the concentrated skim milk used is 15-28 parts; (2) The amount of the milk fat product with a fat content of 80%-100% is 2-4 parts; (3) When the sweetener is white sugar, the amount of white sugar used is 6-14 parts; (4) The amount of water used is 59-75 parts; (5) The oil-soluble β-carotene, based on the effective content of β-carotene, has a dosage of 0.0009-0.0018‰, and the above percentage is the effective content of β-carotene as a percentage of the mass of the fermentation substrate; (6) The amount of the fermenting agent is 0.02-0.05‰, and the above percentage is the mass percentage of the fermentation substrate; In the percentage of oil-soluble β-carotene or the fermentation agent, the fermentation substrate refers to the sum of all components except the fermentation agent; (7) The ingredients of the milk skin yogurt also include inulin; and, (8) The raw material of the milk skin yogurt is whey protein powder.

3. The yogurt with milk skin as described in claim 2, characterized in that, The milk skin yogurt meets one or more of the following conditions: (1) The amount of the concentrated skim milk used is 16-25 parts, preferably 18-22 parts; (2) The amount of the milk fat product with a fat content of 80%-100% used is 2.5-3.5 parts; (3) When the sweetener is white sugar, the amount of white sugar used is 8-12 parts, preferably 8.5-11.5 parts, and more preferably 9-11 parts; (4) The amount of water used is 60-69 parts, preferably 61-66 parts; (5) The oil-soluble β-carotene, based on the effective content of β-carotene, has a dosage of 0.0012-0.0018‰; Preferably, a 30% concentration of oil-soluble β-carotene is used, and the amount of oil-soluble β-carotene used is 0.004-0.006‰; (6) The amount of inulin used is 0-5 parts, preferably 0.5-4 parts, and more preferably 1-3 parts; (7) The amount of whey protein powder used is 0-5 parts, preferably 0.5-4 parts, more preferably 1-3 parts; and, (8) The amount of the fermentation agent is 0.03‰-0.05‰.

4. The yogurt with milk skin as described in any one of claims 1-3, characterized in that, The milk skin yogurt meets one or more of the following conditions: (1) The concentrated skim milk contains the following components: dry matter content 45-47%, protein content 16.0-18.5%, fat content ≤0.6%, and carbohydrate content ≥20%; (2) The milk fat products with a fat content of 80%-100% are butter and / or anhydrous butter; (3) The sweetener is selected from one or more of the following: white sugar, fructose syrup, glucose, maltitol, erythritol, xylitol, sucralose, acesulfame potassium, and steviol glycosides; and, (4) The fermentation agent is a mesophilic or thermophilic lactic acid bacteria fermentation agent prepared by freeze drying and concentration.

5. The yogurt with milk skin as described in any one of claims 1-4, characterized in that, The milk skin yogurt meets the following conditions (1) and / or (2): (1) The sweetener is white sugar; (2) The starter culture is a starter culture containing Lactococcus lactis subsp. lactis, Lactococcus cremoris subsp. cremoris and Streptococcus salivarius subsp. thermophilus.

6. The yogurt with milk skin as described in claim 1, characterized in that, The ingredients of the milk skin yogurt include: 15-25% concentrated skim milk, 2-4% milk fat products with a fat content of 80%-100%, 8-12% sweeteners, 0-4% inulin, 0-4% whey protein powder, and 59-75% water; the percentages are the mass percentages of each component relative to the total amount of the above substances. The milk fat product with a fat content of 80%-100% is preferably anhydrous butter, and the sweetener is preferably white sugar; The oil-soluble β-carotene, based on the effective content of β-carotene, has an amount of 0.0009-0.0018‰, where the above percentage is the effective content of β-carotene as a percentage of the mass of the fermentation substrate; the fermentation agent has an amount of 0.02-0.05‰, where the above percentage is a percentage of the mass of the fermentation substrate.

7. A method for preparing yogurt with milk skin as described in any one of claims 1-6, characterized in that, It includes the following steps: cutting, homogenizing, sterilizing, and inoculating the mixture to produce the milk skin yogurt; The mixture includes raw materials other than the fermenting agent; the homogenization pressure is 6-10 MPa.

8. The preparation method according to claim 7, characterized in that, The preparation method of the mixture includes the following steps: S1 First, the concentrated skim milk, the water, and the sweetener are stirred, mixed, and dissolved to obtain a premix; S2 The milk fat product with a fat content of 80%-100% is melted and then mixed with the oil-soluble β-carotene. The resulting material is then mixed with the premix to obtain the mixture. Preferably, in step S1, the concentrated skim milk and the water are mixed and preheated to 60°C-75°C before being mixed with the sweetener; when the raw material contains inulin or whey protein powder, the inulin or whey protein powder is added simultaneously with the sweetener. Preferably, in step S2, the milk fat product with a fat content of 80%-100% is heated to 60℃-65℃ to melt and then mixed with the oil-soluble β-carotene.

9. The preparation method according to claim 7 or 8, characterized in that, It meets one or more of the following conditions: (1) The shearing speed is 6000-8000 rpm; (2) The shearing time is 1-3 min; (3) The fat content in the sheared material is 1.6-4.0%; (4) The temperature of the homogenization is 65-75℃; (5) The pressure of the homogenized material is 6.5-9 MPa; (6) The sterilization temperature is 90-100℃; (7) The sterilization holding time is 5-10 min; (8) The fermentation temperature is 30-40℃, preferably 37-40℃; (9) The fermentation conditions are sealed, constant-temperature fermentation; and, (10) The fermentation endpoint is when the acidity reaches 70-80°T.

10. A low-fat yogurt with a milk skin prepared by the method described in any one of claims 7-9; The low-fat milk skin yogurt contains 1.6-4.0% fat.

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