Fermented milk and method for preparing the same

Abstract

The present application relates to the technical field of dairy processing, in particular to a fermented milk and a preparation method thereof. The preparation method comprises the following steps: separating skimmed milk by using a microfiltration membrane and / or an ultrafiltration membrane to obtain casein liquid and whey protein liquid; controlling the lactose content in the whey protein liquid to be less than 5%, and then performing microparticulation on the whey protein liquid to obtain microparticulated whey protein; and taking the microparticulated whey protein, the casein liquid and whipped cream as fermentation raw materials to obtain fermented milk. The fermented milk product prepared by the preparation method has a smooth taste and no obvious powder or particle feeling. Moreover, the texture and rheological properties of the final product can be controlled by adjusting the microparticulation process parameters, so that different types of fermented milk products can be developed by enterprises, and the present application is suitable for popularization and application.

Description

Technical Field

[0001] This invention relates to the field of dairy processing technology, specifically to a fermented milk and its preparation method. Background Technology

[0002] Fermented milk is an acidic dairy product made primarily from cow's milk, which is pasteurized, cooled, and then fermented with lactic acid bacteria. Long-term consumption of fermented milk can promote the absorption of phosphorus, calcium, and iron, maintain B vitamin balance, alleviate lactose intolerance, lower cholesterol, prevent cardiovascular and liver diseases, and help prevent constipation and bacterial diarrhea. Fermented milk can also enhance immunity, inhibit cancer, slow aging, and has beauty benefits such as strengthening teeth and promoting healthy hair.

[0003] Taste, flavor, and texture are important sensory evaluations of fermented milk quality, directly related to consumer acceptance. Some fermented milk products may provide consumers with unpleasant experiences such as a powdery feel in the mouth (feeling small particles like flour or starch), or even visible "particles." It's important to note that stirred fermented milk doesn't actually contain individual particles, but rather clusters of proteins connected by weak bonds, forming the weak gel system. The stirring and dilution during particle size testing disrupt this weak gel network, creating the so-called "particles." The weak gel structure of stirred fermented milk depends primarily on two steps: gel formation during fermentation and the disruption of the gel by subsequent mechanical processing. Casein micelles, with diameters between 50 and 300 nm, are small structural elements dispersed in a colloidal state, also known as substructures. During fermentation, the decrease in pH causes casein micelles to aggregate, forming a uniform gel network. Simultaneously, due to acidification, some casein micelles become free and no longer maintain their original state within the gel network. During processing, mechanical stress disrupts the structure of the gel network, forming microgel particles with diameters ranging from 2 to 200 μm. These particles are dispersed in the whey phase, forming a microgel suspension. Other theories suggest that heating milk causes whey protein peptide chains to unfold, leading to protein denaturation and exposing sulfhydryl groups that cross-link with κ-casein on casein micelles via disulfide bonds. Simultaneously, whey proteins may undergo other reactions, resulting in the formation of dimers and other small soluble protein aggregates. As the pH decreases, the denatured whey protein-casein complexes gradually precipitate, while the denatured whey proteins tend to aggregate, forming large, insoluble complexes. Ultimately, this gives fermented milk a "granular" or "powdery" texture, especially noticeable in low-fat and skim fermented milk.

[0004] To improve the smoothness and reduce powdery or grainy texture, most existing fermented milk products add micronized whey protein to their formulas. For example, CN102550669A balances the texture and mouthfeel of low-fat, high-protein fermented milk by adding a certain proportion of exogenous micronized whey protein and gelling whey protein. CN103583688B improves the texture of low-fat yogurt by adding exogenous micronized whey protein (particle size 1-10 μm). However, directly adding exogenous micronized whey protein is costly, and the product's texture is still not ideal. Summary of the Invention

[0005] The purpose of this invention is to provide a fermented milk and its preparation method. In the raw milk pretreatment stage, the whey protein and casein in the milk are separated online, and the lactose content in the whey protein solution is controlled to be below 5% (w / w). Then, the whey protein is micronized to improve the micronization effect of the whey protein, so that the fermented milk product has a smooth taste and no obvious powdery or grainy texture or other unpleasant taste experience.

[0006] First, the present invention provides a method for preparing fermented milk, comprising: separating skim milk using a microfiltration membrane and / or an ultrafiltration membrane to obtain casein liquid and whey protein liquid; controlling the lactose content in the whey protein liquid to be below 5%, and then micronizing it to obtain micronized whey protein; and then using the micronized whey protein, the casein liquid, and light cream as fermentation raw materials to obtain fermented milk.

[0007] The fermented milk product prepared by the method of this invention has a smooth texture and no noticeable powdery or grainy feel. By controlling the lactose content in the whey protein solution before micronization to below 5%, it helps to form micronized whey protein particles with smaller particle sizes, thereby improving the delicate and silky texture of the fermented milk product. Simultaneously, because the whey protein undergoes a specific degree of denaturation before fermentation, the degree of cross-linking with casein and itself during the pre-fermentation heat treatment is effectively reduced, thus decreasing the size of the gel microparticles after fermentation. The fermented milk prepared by the method of this invention has a delicate and smooth texture, and the texture and rheological properties of the final product can be controlled by adjusting the micronization process parameters, facilitating the development of different types of fermented milk products by enterprises.

[0008] In the specific implementation process, the separation of microfiltration membrane and / or ultrafiltration membrane is carried out at 7–12°C.

[0009] In the specific implementation process, the separated casein solution is cooled to 4-7°C and then temporarily stored.

[0010] As a preferred embodiment of the present invention, the preparation method further includes: concentrating the whey protein solution using an ultrafiltration membrane or microfiltration membrane of 10-30 kDa before micronization;

[0011] Preferably, the concentrated whey protein solution is washed with water to control its lactose content to below 5%; more preferably, it is washed with water more than 3 times.

[0012] Through further concentration and washing processes, lactose in whey protein liquid can be effectively removed or reduced, which helps to form smaller micronized whey protein particles during the micronization process, thereby improving the delicate and silky texture of fermented milk products.

[0013] In the specific implementation process, purified water or RO water can be used for cleaning.

[0014] In a preferred embodiment of the present invention, when concentrating the whey protein solution, the concentrated whey protein solution and lactose solution are collected; the lactose solution is hydrolyzed using lactase to obtain a hydrolysate; and then the concentrated whey protein solution and the hydrolysate are mixed and micronized.

[0015] Using lactase to hydrolyze lactose helps form micronized whey proteins with smaller particle sizes, thereby further enhancing the delicate and silky texture of fermented milk products.

[0016] In a preferred embodiment of the present invention, when hydrolyzing the lactose solution, the lactose solution is first concentrated twice using a nanofiltration membrane of 100-1000 Da, and then the concentrated lactose solution is hydrolyzed using lactase to obtain the hydrolysate.

[0017] In a preferred embodiment of the present invention, the concentration ratio of the secondary concentration is 2 to 6.

[0018] In a preferred embodiment of the present invention, the mass-to-volume ratio of lactase to concentrated lactose solution in the hydrolysis is 3-5:1000.

[0019] As a preferred embodiment of the present invention, the hydrolysis is carried out at 5-7°C for 10-15 hours.

[0020] In a preferred embodiment of the present invention, the microparticle temperature is 75-90°C and the shear rate is 3500-5500 rpm.

[0021] In the specific implementation process, those skilled in the art can select a micronization time of 300s to 18min as needed.

[0022] In a preferred embodiment of the present invention, the weight ratio of casein to whey protein in the fermentation raw materials is 2 to 6:1.

[0023] In a preferred embodiment of the present invention, the cream is separated from the raw milk during the preparation of skim milk.

[0024] In practice, the amount of light cream used can be added according to the product's fat content requirements.

[0025] As a preferred embodiment of the present invention, the preparation method includes the following steps:

[0026] Skim milk was separated using microfiltration and / or ultrafiltration membranes to obtain casein and whey protein solutions.

[0027] The lactose content in the whey protein solution is controlled to be below 5%, and then it is micronized to obtain micronized whey protein.

[0028] Then, the micronized whey protein, the casein liquid, and the light cream are used as fermentation raw materials. After homogenization, sterilization, fermentation, demulsification, secondary homogenization, and secondary sterilization, fermented milk is obtained.

[0029] In the specific implementation process, the raw milk can be purified to remove impurities and somatic cells from the milk, with the separation temperature being 45-65℃.

[0030] In the specific implementation process, the separation of light cream can be carried out by a self-cleaning airtight separator, with the temperature being 50-70℃, the rotation speed being 5000-7500 rpm, and the time being 20-40 seconds.

[0031] In the specific implementation process, the separated cream can be sterilized; the sterilization temperature is 85-100℃, and the sterilization time is 10-50 seconds. The sterilized milk is then cooled to 4-7℃ for temporary storage.

[0032] In a preferred embodiment of the present invention, whey protein liquid is micronized and then mixed with casein liquid and light cream as fermentation raw material to obtain fermented milk; the fermentation strains are selected from at least two of Streptococcus thermophilus, Lactobacillus bulgaricus, Lactococcus lactis, Leuconostoc mesenteroides, Pediococcus, Bifidobacterium and Enterococcus, preferably with a weight ratio of 1:1 between different strains.

[0033] In the specific implementation process, other raw materials may be added to the fermentation raw materials. These other raw materials may be at least one of the following: granulated sugar, hydroxypropyl starch, agar, low-fat pectin, and gellan gum.

[0034] In the specific implementation process, all raw materials are mixed and homogenized at 55–65°C, with a total pressure of 140–160 bar and a secondary pressure of 30–40 bar. After homogenization, ultrapasteurization is performed at 85–133°C for 2–500 seconds. Then, the mixture is cooled to 30–45°C for fermentation. When the lactic acidity reaches above 70° and the pH value is below 4.6, the milk is broken up, stirred for 1–2 minutes, and then cooled to 20–25°C. The broken-up fermented milk is then homogenized without pressure, i.e., at a homogenization pressure of 0 bar. For producing long-shelf-life yogurt (room temperature yogurt), a secondary pasteurization and dynamic smoothing process is performed. The secondary pasteurization temperature is preferably 70-75°C and the time is 20-30 seconds. The dynamic smoothing process is preferably performed at a temperature of 20-40°C and a shear frequency of 30-70Hz. For producing short-shelf-life yogurt (low-temperature yogurt), the secondary pasteurization and dynamic smoothing process is not required. The yogurt can be directly filled after cooling.

[0035] As a preferred embodiment of the present invention, the specific steps include:

[0036] (1) Cleanse milk

[0037] The raw milk is purified and separated at a temperature of 45–65°C.

[0038] (2) Fat separation

[0039] Fat separation was performed using a self-cleaning, airtight separator at a temperature of 50–70°C, a rotation speed of 5000–7500 rpm, and a time of 20–40 seconds to produce light cream and skim milk.

[0040] (3) Sterilize, cool, and temporarily store light cream.

[0041] The cream obtained in (2) was sterilized at a temperature of 85–100°C for 10–50 seconds. The sterilized milk was then cooled to 4–7°C and stored temporarily.

[0042] (4) Skim milk microfiltration or ultrafiltration

[0043] At 7–12°C, a 0.1 μm microfiltration membrane or ultrafiltration membrane is used to separate casein and whey protein solutions. The casein solution is further washed 1–3 times with purified water or RO water, and the separated casein solution is cooled to 4–7°C and then temporarily stored.

[0044] (5) Ultrafiltration

[0045] The whey protein solution obtained in step (4) was concentrated using an ultrafiltration membrane of 10-30 kDa. The concentrated whey protein solution was then washed 3-5 times with purified water or RO water.

[0046] (6) Nanofiltration

[0047] The lactose solution obtained in step (5) was concentrated a second time using a nanofiltration membrane with a density of 100 to 1000 Da, with a concentration ratio of 2 to 6.

[0048] (7) Lactase hydrolysis

[0049] The concentrated lactose solution was hydrolyzed with 3-5‰ lactase at 5-7℃ for 10-15 hours to obtain the hydrolysate.

[0050] (8) Mixing

[0051] The concentrated whey protein solution obtained in step (5) and the hydrolysate obtained in step (7) are mixed, wherein the lactose content is controlled to be below 5% (w / w).

[0052] (9) Microparticles

[0053] The mixture obtained in step (8) is subjected to micronization treatment to obtain micronized whey protein solution; the micronization treatment temperature is 75-90℃, the time is 300s-18min, and the shear rate is 3500rpm-5500rpm.

[0054] (10) Mixing

[0055] The light cream obtained in step (3), the casein liquid obtained in step (4), and the micronized whey protein liquid obtained in step (9) are mixed to prepare the fermentation raw material; in the fermentation raw material, the weight ratio of casein to whey protein is 2 to 6:1.

[0056] (11) Mixing

[0057] Mix 880-895 parts of fermentation raw materials, 80-90 parts of white sugar, 2-6 parts of whey protein powder, 10-12 parts of hydroxypropyl starch, 1.45-1.65 parts of agar, 1.45-1.65 parts of low-fat pectin, 0.2-1.3 parts of gellan gum, and 100U of bacterial strain from step (10). The bacterial strains used in fermentation are selected from at least two of Streptococcus thermophilus, Lactobacillus bulgaricus, Lactococcus lactis, Leuconostoc mesenteroides, Pediococcus, Bifidobacterium, and Enterococcus, and the weight ratio between different strains is 1:1.

[0058] (12) Homogeneous

[0059] The mixed milk base material is homogenized at 55-65℃, with a total pressure of 140-160 bar and a secondary pressure of 30-40 bar.

[0060] (13) Superbus

[0061] After homogenization, ultrapasteurization is carried out at 85–133℃ for 2–500 seconds.

[0062] (14) Fermentation after cooling

[0063] The liquid material is cooled to 30-45℃ and then fermented.

[0064] (15) Delaying milk production

[0065] Once the fermentation acidity reaches above 70° and the pH value is below 4.6, the emulsion can be broken. Stir for 1 to 2 minutes and cool to 20 to 25°C.

[0066] (16) Secondary homogenization

[0067] After demulsification, the fermented milk is homogenized without pressure, i.e., the homogenization pressure is 0 bar. If producing long-shelf-life yogurt (room temperature yogurt), continue with steps (17) to (19). If producing short-shelf-life yogurt (low-temperature yogurt), proceed directly to step (19).

[0068] (17) Secondary sterilization

[0069] The homogenized fermented milk is subjected to a second pasteurization treatment at a temperature of 70-75℃ for 20-30 seconds.

[0070] (18) Dynamic smoothing

[0071] The fermented milk after secondary sterilization was subjected to dynamic smoothing treatment at a temperature of 20–40℃ and a shear frequency of 30–70Hz.

[0072] (19) Filling

[0073] The liquid is cooled before being filled.

[0074] Furthermore, the present invention also provides fermented milk prepared according to any of the above embodiments.

[0075] The beneficial effects of this invention are as follows:

[0076] The fermented milk prepared by the method of this invention has a delicate and silky texture, a pure fermented flavor, and good system stability, without whey separation or other problems during its shelf life. Furthermore, by adjusting the micronization process parameters, the texture and rheological properties of the final product can be controlled, facilitating the development of different types of fermented milk products and making it suitable for widespread application. Attached Figure Description

[0077] Figure 1 This is a process flow diagram of Embodiment 1 of the present invention. Detailed Implementation

[0078] The following examples are used to illustrate the present invention, but are not intended to limit the scope of the invention.

[0079] Unless otherwise specified, all methods used in the examples were conventional or performed according to techniques or conditions described in the literature in this field, or in accordance with the product instructions. Reagents and instruments used without specified manufacturers were all conventional products that could be purchased from legitimate channels.

[0080] Example 1

[0081] This embodiment provides a fermented milk, the preparation method of which includes the following steps:

[0082] (1) Cleanse milk

[0083] The raw milk is purified at a separation temperature of 55℃.

[0084] (2) Fat separation

[0085] Fat separation was performed using a self-cleaning, airtight separator at a temperature of 60℃, a rotation speed of 6800 rpm, and a time of 35 seconds, yielding light cream and skim milk.

[0086] (3) Sterilize, cool, and temporarily store light cream.

[0087] The cream obtained in (2) was sterilized at a temperature of 95°C for 20 seconds. The sterilized milk was then cooled to 4-7°C and stored temporarily.

[0088] (4) Skim milk microfiltration

[0089] At 10°C, a 0.1 μm microfiltration membrane was used to separate casein and whey protein solutions. The casein solution was further washed once with purified water, and the separated casein solution was cooled to 4–7°C and then temporarily stored.

[0090] (5) Ultrafiltration

[0091] The whey protein solution obtained in step (4) was concentrated using a 20 kDa ultrafiltration membrane, and the concentrated whey protein solution was further washed 5 times with purified water.

[0092] (6) Nanofiltration

[0093] The lactose solution obtained in step (5) was concentrated a second time using a 300 Da nanofiltration membrane, with a concentration ratio of 4.

[0094] (7) Lactase hydrolysis

[0095] The concentrated lactose solution was hydrolyzed with 4‰ lactase at 6℃ for 12 hours to obtain the hydrolysate.

[0096] (8) Mixing

[0097] Mix the concentrated whey protein solution obtained in step (5) with the hydrolysate obtained in step (7).

[0098] (9) Microparticles

[0099] The mixture obtained in step (8) is subjected to micronization treatment to obtain micronized whey protein solution; the micronization treatment temperature is 80℃, the time is 15min, and the shear rate is 4500rpm.

[0100] (10) Mixing

[0101] Mix the light cream obtained in step (3), the casein liquid obtained in step (4), and the micronized whey protein liquid obtained in step (9).

[0102] (11) Mixing

[0103] The following formula was used for mixing (1t): 892.4 kg of the mixture liquid in step (10), 88 kg of white sugar, 4 kg of whey protein powder, 12 kg of hydroxypropyl starch, 1.65 kg of agar, 1.65 kg of low-fat pectin, 0.3 kg of gellan gum, and 100 U of bacterial strain. The bacterial strains used for fermentation were selected from Streptococcus thermophilus and Lactobacillus bulgaricus, and the weight ratio between the strains was 1:1.

[0104] Heat the mixture in step (10) to 50°C, turn on the mixer, and slowly add the other ingredients (Note: first mix the low-fat pectin and white sugar in a 1:3 weight ratio). The order of addition is: remaining white sugar, whey protein powder, low-fat pectin and white sugar mixture, starch, agar, and gellan gum. After adding the ingredients, circulate for 1 minute, push the mixture into the mixing tank and stir for 15 minutes. Check the mixture in a steel basin; if there are no abnormalities, cool it down at 25°C.

[0105] (12) Homogeneous

[0106] The mixed milk base was homogenized at 62°C with a total pressure of 160 bar and a secondary pressure of 40 bar.

[0107] (13) Superbus

[0108] After homogenization, ultrapasteurization was carried out at 93℃ for 300s.

[0109] (14) Fermentation after cooling

[0110] The liquid was cooled to 43°C and then fermented.

[0111] (15) Delaying milk production

[0112] Once the fermentation acidity reaches 80° and the pH value is 4.4, break the emulsion, stir for 1 minute, and cool to 25°C.

[0113] (16) Secondary homogenization

[0114] The fermented milk after demulsification is homogenized without pressure, i.e., the homogenization pressure is 0 bar.

[0115] (17) Secondary sterilization

[0116] The homogenized fermented milk was subjected to a second pasteurization treatment at a temperature of 72℃ for 25 seconds.

[0117] (18) Dynamic smoothing

[0118] The fermented milk after secondary sterilization was subjected to dynamic smoothing treatment at a temperature of 20℃ and a shear frequency of 50Hz.

[0119] (19) Filling

[0120] Cool the liquid to 20°C before filling.

[0121] The process flow diagram of this embodiment is as follows: Figure 1 As shown.

[0122] Example 2

[0123] This embodiment provides a fermented milk, the preparation method of which differs from that of Example 1 only in that:

[0124] (4) Skim milk microfiltration

[0125] At 10°C, a 0.1 μm microfiltration membrane was used to separate casein and whey protein solutions. The casein solution was further washed twice with purified water, and the separated casein solution was cooled to 4–7°C and then temporarily stored.

[0126] Example 3

[0127] This embodiment provides a fermented milk, the preparation method of which differs from that of Example 1 only in that:

[0128] (5) Ultrafiltration

[0129] The whey protein solution obtained in step (4) was concentrated using a 20 kDa ultrafiltration membrane, and the concentrated whey protein solution was further washed four times with purified water.

[0130] (11) Mixing

[0131] The following formula was used for mixing (1t): 892.6kg of the mixed liquid in step (10), 87kg of white sugar, 6kg of whey protein, 11kg of hydroxypropyl starch, 1.55kg of agar, 1.45kg of low-fat pectin, 0.4kg of gellan gum, and 100U of bacterial strains. The fermentation strains were Streptococcus thermophilus, Lactobacillus bulgaricus, and Leuconostoc mesenteroides, with a weight ratio of 1:1:1 between the different strains.

[0132] Example 4

[0133] This embodiment provides a fermented milk, the preparation method of which differs from that of Example 1 only in that:

[0134] (5) Ultrafiltration

[0135] The whey protein solution obtained in step (4) was concentrated using a 20 kDa ultrafiltration membrane, and the concentrated whey protein solution was further washed three times with purified water.

[0136] (11) Mixing is the same as in Example 3.

[0137] Example 5

[0138] This embodiment provides a fermented milk, the preparation method of which differs from that of Example 1 only in that:

[0139] (7) Lactase hydrolysis

[0140] The concentrated lactose solution was hydrolyzed with 3‰ lactase at 7°C for 15 hours to obtain the hydrolysate.

[0141] Example 6

[0142] This embodiment provides a fermented milk, the preparation method of which differs from that of Example 1 only in that:

[0143] (7) Lactase hydrolysis

[0144] The concentrated lactose solution was hydrolyzed with 5‰ lactase at 5℃ for 15 hours to obtain the hydrolysate.

[0145] Example 7

[0146] This embodiment provides a fermented milk, the preparation method of which differs from that of Example 1 only in that:

[0147] (9) Microparticles

[0148] The mixture obtained in step (8) is subjected to micronization treatment to obtain micronized whey protein solution; the micronization treatment temperature is 85℃, the time is 10min, and the shear rate is 5000rpm.

[0149] Example 8

[0150] This embodiment provides a fermented milk, the preparation method of which differs from that of Example 1 only in that:

[0151] (9) Microparticles

[0152] The mixture obtained in step (8) is subjected to micronization treatment to obtain micronized whey protein solution; the micronization treatment temperature is 78℃, the time is 18min, and the shear rate is 4000rpm.

[0153] Example 9

[0154] This embodiment provides a fermented milk, the preparation method of which differs from that of Example 1 only in that:

[0155] (4) Skim milk microfiltration

[0156] At 10°C, a 0.1 μm microfiltration membrane was used to separate casein and whey protein solutions. The casein solution was further washed five times with purified water, and the separated casein solution was cooled to 4–7°C and then temporarily stored.

[0157] Example 10

[0158] This embodiment provides a fermented milk, the preparation method of which differs from that of Example 1 only in that:

[0159] (5) Ultrafiltration

[0160] The whey protein solution obtained in step (4) was concentrated using a 20 kDa ultrafiltration membrane, and the concentrated whey protein solution was further washed once with purified water.

[0161] (11) Mixing is the same as in Example 3.

[0162] Example 11

[0163] This embodiment provides a fermented milk, the preparation method of which differs from that of Example 1 only in that:

[0164] (9) Microparticles

[0165] The mixture obtained in step (8) is subjected to micronization treatment to obtain micronized whey protein solution; the micronization treatment temperature is 95℃, the time is 10min, and the shear rate is 5000rpm.

[0166] Comparative Example 1

[0167] This embodiment provides a fermented milk, the preparation method of which differs from that of Example 1 only in that:

[0168] Step (7) lactase hydrolysis is omitted, and the lactose concentrate obtained by nanofiltration in step (6) is directly mixed with the concentrated whey protein solution obtained in step (5).

[0169] Comparative Example 2

[0170] This comparative example provides a fermented milk, the preparation method of which differs from that of Example 1 only in that:

[0171] Skim the skim milk microfiltration step (4) and directly perform the skim milk separated in step (2) ultrafiltration step (5).

[0172] Comparative Example 3

[0173] This comparative example provides a fermented milk, the preparation method of which differs from that of Example 1 only in that:

[0174] Skip step (9) micronization, and directly proceed to step (10) mixing after step (8) mixing.

[0175] Comparative Example 4

[0176] This comparative example provides a fermented milk, the preparation method of which differs from that of Example 1 only in that:

[0177] (5) Ultrafiltration

[0178] The whey protein solution obtained in step (4) is concentrated using a reverse osmosis membrane without washing the retentate.

[0179] (11) Mixing is the same as in Example 3.

[0180] Comparative Example 5

[0181] This comparative example provides a fermented milk, the preparation method of which differs from that of Example 1 only in that:

[0182] (5) Ultrafiltration: The whey protein solution obtained in step (4) is concentrated using a 20 kDa ultrafiltration membrane. The concentrated whey protein solution is not washed with purified water.

[0183] Test case

[0184] The fermented milk prepared in the examples and comparative examples was tested.

[0185] (1) Particle size testing method: The particle size of whey protein and fermented milk before and after micronization treatment was tested using a HORIBA LA 960 nm laser particle size analyzer. 1 g of liquid sample was pre-dispersed in 10 mL of deionized water and pre-dispersed at 450 rpm for 15 min using a magnetic stirrer. A few drops of the dispersion were then transferred to the laser diffraction particle analyzer unit. The parameters were set as follows: refractive index 1.52, absorptivity 0.1, refractive index 10%, and stirring speed 2000 rpm.

[0186] (2) Protein content detection method: The method specified in GB5009.5—2016 National Food Safety Standard for Determination of Protein in Food is adopted.

[0187] (3) Method for detecting fat content: The method specified in GB5009.5—2016 National Food Safety Standard for Determination of Fat in Food shall be adopted.

[0188] (4) Lactose content detection method: The method specified in GB5009.8—2016 National Food Safety Standard for the Determination of Fructose, Glucose, Sucrose, Maltose and Lactose in Food shall be adopted.

[0189] (5) Method for detecting the texture of fermented milk: The consistency of yogurt was tested using a Universal TA texture analyzer from Shanghai Tengba Instrument Technology Co., Ltd., with an A / BE probe. The parameters were set as follows: probe descent rate 1 mm / s before test, probe descent rate 1 mm / s during test, probe ascent rate 30 mm / s after test, and trigger force 5.0 g.

[0190] (6) Method for detecting the centrifugal dehydration rate of fermented milk: On the day the product is produced, weigh 20g of yogurt sample in a 25ml centrifuge tube, centrifuge at 3500rpm / min for 15min, discard the supernatant, weigh the remaining yogurt m, and calculate the centrifugal dehydration rate using the following formula: Centrifugal dehydration rate (%) = [(20-m) / m]*100%.

[0191] (7) Sensory testing method during shelf life: 50 professional tasters were invited to score the product’s liking level 5 months after it was taken off the production line. The scoring range was 1 to 10 points. The higher the score, the higher the liking level. The average of the scores was calculated to obtain the sensory liking test results. At the same time, the product’s texture, appearance particle size and taste particle size were scored. The evaluation criteria are shown in Table 1.

[0192] (8) Shelf life test:

[0193] The test results are shown in Tables 2 and 3.

[0194] Table 1 Sensory Evaluation Criteria for the Granularity of Fermented Milk

[0195]

[0196]

[0197] Table 2. Lactose content before micronization and protein and fat content in fermented milk.

[0198]

[0199] Table 3. Particle size and fermented milk properties of whey protein before and after micronization

[0200]

[0201]

[0202] Although the present invention has been described in detail above with general descriptions and specific embodiments, modifications or improvements can be made to it, which will be obvious to those skilled in the art. Therefore, all such modifications or improvements made without departing from the spirit of the present invention fall within the scope of protection claimed by the present invention.

Claims

1. A method for preparing fermented milk, characterized in that, include: The skim milk was separated using a microfiltration membrane to obtain casein and whey protein solutions; The lactose content in the whey protein solution is controlled to be below 5%, and then it is micronized to obtain micronized whey protein. Then, the micronized whey protein, the casein liquid, and the light cream are used as fermentation raw materials to obtain fermented milk; Before micronization, the whey protein solution is concentrated using an ultrafiltration membrane with a strength of 10-30 kDa. The concentrated whey protein solution is then washed with water, and the concentrated whey protein solution and lactose solution are collected. The lactose solution is then concentrated a second time using a nanofiltration membrane with a strength of 100-1000 kDa. Finally, the concentrated lactose solution is hydrolyzed using lactase to obtain the hydrolysate. Then, the concentrated whey protein solution and the hydrolysate are mixed and micronized. The concentration ratio of the secondary concentration is 2 to 6; In the hydrolysis, the mass-to-volume ratio of lactase to concentrated lactose solution is 3-5:1000, and the hydrolysis is carried out at 5-7°C for 10-15 hours. The microparticle formation temperature is 75~90℃, and the shear rate is 3500rpm~5500rpm; In the fermentation raw materials, the weight ratio of casein to whey protein is 2~6:

1.

2. The preparation method according to claim 1, characterized in that, The cream is obtained from the process of preparing skim milk from raw milk.

3. The preparation method according to claim 1 or 2, characterized in that, Includes the following steps: The skim milk was separated using a microfiltration membrane to obtain casein and whey protein solutions; The lactose content in the whey protein solution is controlled to be below 5%, and then it is micronized to obtain micronized whey protein. Then, the micronized whey protein, the casein liquid, and the light cream are used as fermentation raw materials. After homogenization, sterilization, fermentation, demulsification, secondary homogenization, and secondary sterilization, fermented milk is obtained.

4. A fermented milk, characterized in that, It is prepared by any one of claims 1 to 3.

Images