阅读说明：本技术 一种低脂高蛋白发酵乳及其生产方法 (Low-fat high-protein fermented milk and production method thereof ) 是由 周偏 李洪亮 李树森 康正雄 荆培培 于 2020-05-22 设计创作，主要内容包括：本发明公开了一种低脂高蛋白发酵乳及其生产方法,该低脂高蛋白发酵乳的原料包括：生牛乳、脱脂乳粉和发酵菌种；所述发酵乳的粘度为9000cp～15000cp；所述发酵乳的蛋白质含量为8％～14％。本发明在降低脂肪、提高蛋白含量的情况下,制备出蛋白含量高、粘度低、风味纯正且具有清爽口感的低脂高蛋白发酵乳。(The invention discloses low-fat high-protein fermented milk and a production method thereof, and the raw materials of the low-fat high-protein fermented milk comprise: raw milk, skim milk powder and fermentation strains; the viscosity of the fermented milk is 9000-15000 cp; the protein content of the fermented milk is 8-14%. The low-fat high-protein fermented milk with high protein content, low viscosity, pure flavor and fresh taste is prepared under the conditions of reducing fat and improving protein content.)

1. A low-fat high-protein fermented milk is characterized by comprising the following raw materials: raw milk, skim milk powder and fermentation strains;

the viscosity of the fermented milk is 9000-15000 cp; the protein content of the fermented milk is 8-15%.

2. The low-fat high-protein fermented milk according to claim 1, wherein the ratio of the raw milk to the skim milk powder is 85: 15-65: 35;

the fermentation strain is lactobacillus bulgaricus and lactobacillus thermophilus, and the addition amount of the fermentation strain is 50-100U/T.

3. A low-fat and high-protein fermented milk according to claim 1 or 2, wherein the raw milk is defatted raw milk.

4. A low-fat and high-protein fermented milk according to any one of claims 1 to 3, wherein the fat content of the skim milk powder is not more than 1 wt% and the protein content is not less than 36 wt%.

5. A method for producing low-fat high-protein fermented milk, which is characterized by comprising the following steps:

degreasing raw milk: degreasing raw milk to obtain degreased raw milk;

first homogenizing: carrying out primary homogenization treatment on the skim raw milk, wherein the primary homogenization condition is 15-18 MPa, and the temperature during primary homogenization is 55-65 ℃;

hydration: mixing skim raw milk and skim milk powder, and hydrating to obtain fermentation base material; (ii) a

And (3) homogenizing and sterilizing for the second time: carrying out secondary homogenization on the fermentation base material and then carrying out sterilization treatment, or carrying out secondary homogenization on the fermentation base material after carrying out sterilization treatment; the second homogenization is carried out under the condition of 20-25 MPa, and the temperature during the second homogenization is 60-70 ℃;

inoculation and fermentation: adjusting the temperature of the fermentation base material, then inoculating fermentation strains, uniformly stirring, fermenting until the final acidity is 120-130 DEG T;

demulsifying and smoothing: and demulsifying after the fermentation is finished, smoothing the demulsified fermented milk, and cooling to obtain the low-fat high-protein fermented milk with the viscosity of 9000-15000 cp and the protein content of 8-14%.

6. The production method according to claim 5, wherein the ratio of the raw milk to the skim milk powder is 85: 15-65: 35;

the fermentation strain is lactobacillus bulgaricus and lactobacillus thermophilus, and the addition amount of the fermentation strain is 50-100U/T;

the protein content of the skim raw milk is more than or equal to 3.1 wt%, and the fat content of the skim raw milk is less than or equal to 0.8 wt%.

7. The production method according to claim 5, wherein the skim raw milk after the first homogenization is cooled to 35-45 ℃; in the hydration step, the stirring speed is 400-600 r/min, the stirring time is more than 30min, the initial stirring temperature is 45-55 ℃, and the hydration temperature after stirring is 40-50 ℃.

8. The production method according to claim 5, wherein the stirring speed after inoculation and before fermentation is 100-300 r/min, and the stirring time is 15-20 min.

9. The production method according to claim 5, wherein the smoothing treatment is carried out under a treatment condition of 300 to 700 rpm.

10. The production method according to claim 5, wherein the fermentation temperature is 42 ± 1 ℃, and the cooling temperature after the smoothing treatment is 7-10 ℃;

the sterilization conditions are as follows: 133 +/-2 ℃ and 4-6S.

Technical Field

The invention relates to the field of dairy products, in particular to fermented milk and a production method thereof.

Background

In recent years, people have increasingly strengthened food safety awareness and health awareness, and fermented milk is popular among people as a product having both delicious taste and high nutritional value. With the improvement of living standard of people, the nutritional requirement on dairy products is higher and higher, and the low-fat high-protein fermented milk contains more abundant protein than common fermented milk and has lower fat content, so that the probiotic effect of the fermented milk and the nutritional health effect of high protein can be combined, and the low-fat high-protein fermented milk has important physiological effects on maintaining the health of human bodies and enhancing the immunity of people.

At present, for increasing the protein content in fermented milk, the production methods mainly comprise a concentration method and an external addition method.

The concentration method mainly comprises a membrane filtration method and a centrifugation method, and has three disadvantages: 1. the production cost is high: capital costs for the purchase of membrane separation systems or concentration centrifuges are invested; 2. the production efficiency is low: because the concentration process determines that the output is less than the feeding amount, longer equipment operation time is needed; 3. the pollution is large: the large amount of whey produced during the concentration process has a detrimental effect on the environment.

The external addition method is mainly used for improving the protein content of the fermented milk by adding protein powder, but the conventional protein powder addition method can cause the problems of poor sense such as granular feeling, obvious powder taste, coarse texture and the like of the yogurt, and the improper selection and application of the protein powder can cause additional damage to production equipment. Especially in the external addition method, the more protein is added, the more obvious the granular feeling and powdery taste of the yoghurt are, and the high protein content causes the product to be more viscous, which is more difficult for the yoghurt with fresh mouthfeel to further increase the protein content in the yoghurt.

For low fat content in fermented milk, the demand for "low fat" and "zero fat" fermented milk is also expanding. However, although low-fat and low-fat dairy products with a low milk fat content have a very light, thin and less intense taste, and low-fat type fermented milks are usually supplemented with sweeteners at present, it is difficult to achieve a strong milk flavor of the fermented milk by this method, and the flavor of the fermented milk is greatly affected.

Disclosure of Invention

Therefore, the technical problem to be solved by the invention is how to ensure the flavor of the fermented milk by optimizing the formula or/and the process under the condition of reducing fat and increasing protein content; provides pure and refreshing low-fat and high-protein fermented milk and a preparation process of the low-fat and high-protein fermented milk.

A low-fat high-protein fermented milk comprises the following raw materials: raw milk, skim milk powder and fermentation strains;

the viscosity of the fermented milk is 9000-15000 cp; the protein content of the fermented milk is 8-15%.

The adding amount ratio of the raw milk to the skim milk powder is 85: 15-65: 35;

the fermentation strain is lactobacillus bulgaricus and lactobacillus thermophilus, and the addition amount of the fermentation strain is 50-100U/T.

The raw milk is degreased raw milk.

In the skim milk powder, the fat content is not more than 1 wt%, and the protein content is not less than 36 wt%.

A method for producing low-fat high-protein fermented milk, comprising:

degreasing raw milk: degreasing raw milk to obtain degreased raw milk;

first homogenizing: carrying out primary homogenization treatment on the skim raw milk, wherein the primary homogenization condition is 15-18 MPa, and the temperature during primary homogenization is 55-65 ℃;

hydration: mixing skim raw milk and skim milk powder, and hydrating to obtain fermentation base material;

and (3) homogenizing and sterilizing for the second time: carrying out secondary homogenization on the fermentation base material and then carrying out sterilization treatment, or carrying out secondary homogenization on the fermentation base material after carrying out sterilization treatment; the second homogenization is carried out under the condition of 20-25 MPa, and the temperature during the second homogenization is 60-70 ℃;

inoculation and fermentation: adjusting the temperature of the fermentation base material, then inoculating fermentation strains, uniformly stirring, fermenting until the final acidity is 120-130 DEG T; the addition amount of the fermentation strain is based on the amount of the fermentation base material, namely 50-100U of the fermentation strain is added into each ton of the fermentation base material;

demulsifying and smoothing: and demulsifying after the fermentation is finished, smoothing the demulsified fermented milk, and cooling to obtain the low-fat high-protein fermented milk with the viscosity of 9000-15000 cp and the protein content of 8-14%.

The ratio of the raw milk to the skim milk powder is 85: 15-65: 35;

the fermentation strain is lactobacillus bulgaricus and lactobacillus thermophilus, and the addition amount of the fermentation strain is 50-100U/T;

the protein content of the skim raw milk is more than or equal to 3.1 wt%, and the fat content of the skim raw milk is less than or equal to 0.8 wt%.

Cooling the defatted raw milk subjected to primary homogenization to 35-45 ℃; in the hydration step, the stirring speed is 400-600 r/min, the stirring time is more than 30min, the initial stirring temperature is 45-55 ℃, and the hydration temperature after stirring is 40-50 ℃.

The sterilization conditions are as follows: 133 +/-2 ℃ and 4-6S.

The stirring speed after inoculation and before fermentation is 100-300 r/min, and the stirring time is 15-20 min.

The processing condition of the smoothing treatment is 300-700 rpm.

The fermentation temperature is 42 +/-1 ℃, and the cooling temperature after the smoothing treatment is 7-10 ℃.

The technical scheme of the invention has the following advantages:

1. the raw material selection of the low-fat high-protein fermented milk is optimized, the raw milk is used as the fermentation raw material, and only the skim milk powder is used as the exogenous protein, so that the low-fat high-protein fermented milk with the protein content of 8-14% and the viscosity of 9000-15000 cp can be effectively prepared, and the low-fat high-protein fermented milk has the advantages of high protein content, low viscosity, fresh mouthfeel and the like.

2. According to the invention, the ratio of raw milk to skim milk powder is further optimized to 85: 15-65: 35, the type and the amount of fermentation strains are optimized, the addition amount of the fermentation strains is optimized to 50-100U/T, and the fermentation strains are optimized to lactobacillus bulgaricus and lactobacillus thermophilus. After the optimization, the defect of common whey precipitation in the fermented milk can be successfully overcome on the premise of not adding any stabilizer, thickener and sweetener completely, and the low-fat high-protein fermented milk with high protein content, low viscosity, good stability and fresh mouthfeel can be effectively prepared. Since it is known to those skilled in the art that in low-fat fermented milk, the sweetener has not only a better effect on flavor improvement but also a promoting effect on system stability, if no stabilizer, thickener or sweetener is added, the effect on flavor is not only great, but also the system stability is more challenging; according to the invention, the skim milk powder is selected as the exogenous added protein, and the adding amount of the skim milk powder and the types and adding amounts of the strains are optimized, so that the strong milk flavor of the fermented milk can be effectively realized, the flavor of the fermented milk can be ensured, the separation of whey in the fermented milk in the shelf life can be maximally avoided, the high stability is obtained, and the effect is very remarkable.

3. The fermentation steps and parameters of the fermented milk are optimized, and the steps of the method specifically comprise the following steps: the method comprises the following steps of raw milk degreasing, primary homogenization, hydration, secondary homogenization, sterilization, inoculation, fermentation, demulsification and smoothing, wherein the fermentation raw materials are treated by adopting a two-time homogenization method, and the low-fat high-protein fermented milk with stable system, good flavor, low viscosity and fresh taste can be effectively prepared by controlling the homogenization conditions; specifically, as is known to those skilled in the art, the viscosity is inevitably and effectively increased while the protein content is increased, the preparation process in the application can effectively overcome the problem of high viscosity caused by high protein content, and the product with lower viscosity is obtained while the protein content is increased, so that the product has fresh mouthfeel, and the effect is very remarkable.

4. The fermented milk with low viscosity and fresh and cool taste can be effectively obtained by optimizing the types and the proportion of the raw materials and matching the fermentation inoculation amount, the fermentation conditions and the fermentation end point. Namely, the low-fat high-protein fermented milk with fresh taste, stable body system in shelf life and good flavor can be effectively obtained after comprehensive control through mutual matching of parameter conditions, raw material types and raw material contents of all the steps.

5. In the preparation process of the fermented milk, parameters in the whole fermentation process are strictly controlled, after the fermented milk is prepared, the fermented milk is subjected to soft stirring and cooling demulsification, the defect of common whey precipitation in the fermented milk is successfully overcome on the premise of not adding any stabilizer, thickener or sweetener, the effect of successfully regulating and controlling the stability of the product is achieved, and the low-fat high-protein fermented milk with fine quality, fresh taste, fine texture, no whey precipitation in the quality guarantee period and high nutritive value is obtained.

Drawings

In order to show the invention more clearly, the invention also provides the following figures.

Fig. 1 is an electronic nose sensor response intensity radar chart of fermented milk in example 1.

Fig. 2 is an electronic nose sensor response intensity radar chart of fermented milk in example 2.

Fig. 3 is an electronic nose sensor response intensity radar chart of fermented milk in example 3.

Fig. 4 is an electronic nose sensor response intensity radar chart of the fermented milk in example 4.

Fig. 5 is an electronic nose sensor response intensity radar chart of the fermented milk in example 5.

Fig. 6 is an electronic nose sensor response intensity radar chart of fermented milk in comparative example 1.

Fig. 7 is an electronic nose sensor response intensity radar chart of fermented milk in comparative example 2.

Fig. 8 is an electronic nose sensor response intensity radar chart of fermented milk in comparative example 3.

Fig. 9 is an electronic nose sensor response intensity radar chart of fermented milk in comparative example 4.

Detailed Description

The following examples are provided to further understand the present invention, not to limit the scope of the present invention, but to provide the best mode, not to limit the content and the protection scope of the present invention, and any product similar or similar to the present invention, which is obtained by combining the present invention with other prior art features, falls within the protection scope of the present invention.

The examples do not show the specific experimental steps or conditions, and can be performed according to the conventional experimental steps described in the literature in the field. The reagents or instruments used are not indicated by the manufacturer, and are all conventional reagent products or instruments that are commercially available.

Example 1

A low-fat high-protein fermented milk and a production method thereof comprise the following steps:

firstly, the product formula is as follows:

85% of raw milk, 15% of skim milk powder and 100U/T of fermentation strains, wherein the fermentation strains comprise lactobacillus bulgaricus and lactobacillus thermophilus, and the fat content and the protein content in the skim milk powder are respectively 1% and 36%. The performance indexes of the raw materials meet the requirements of the conventional quality standard in the field.

Secondly, the specific process flow is as follows:

(1) standardized degreasing treatment: the step adopts the conventional process in the field, generally, in order to adjust milk fat and milk protein to reach the product nutrition index, in the embodiment, the raw milk is subjected to degreasing treatment to obtain standardized degreased raw milk with protein more than or equal to 3.1 wt% and fat less than or equal to 0.8 wt%;

(2) homogenizing and cooling: the defatted raw milk is preheated to 65 ℃ and homogenized under 15MPa of homogenization pressure. Then cooled to 40 ℃.

(3) Hydration: putting skim raw milk into a mixing tank, heating to 50 ℃, adding skim milk powder under the condition of stirring speed of 500r/min, stirring at 45 ℃ for more than 30min, stopping stirring, hydrating the skim milk powder for 30min, and preparing a fermentation base material;

(4) sterilization, homogenization, inoculation and fermentation: preheating the fermented base material to 70 deg.C, homogenizing under 20MPa, and sterilizing at 133 + -2 deg.C for 6S. Cooling to 42 +/-1 ℃, inoculating 100U/T of lactobacillus bulgaricus and streptococcus thermophilus fermentation strains, stirring at a stirring speed of 200r/min for 20min, stopping stirring, and starting fermentation for 6 h;

(5) demulsifying, smoothing and cooling: demulsifying after fermenting to the end point acidity of 125 degrees T. Smoothing the demulsified fermented milk at the rotation speed of a smoothing pump of 400rpm, and then cooling to 8 ℃;

(6) filling: and filling the cooled low-fat high-protein fermented milk into a specific container by a clean filling machine to obtain the product.

The low-fat high-protein fermented milk 1 produced by the method has a protein content of 8% and a fat content of 0.8%.

Example 2

A low-fat high-protein fermented milk and a production method thereof comprise the following steps:

firstly, the product formula is as follows:

80% of raw milk, 20% of skim milk powder and 80U/T of fermentation strains, wherein the fermentation strains comprise lactobacillus bulgaricus and lactobacillus thermophilus, and the fat content and the protein content in the skim milk powder are respectively 1% and 36%. The performance indexes of the raw materials meet the requirements of the conventional quality standard in the field.

Secondly, the specific process flow is as follows:

(1) standardized degreasing treatment: the step adopts the conventional process in the field, generally, in order to adjust milk fat and milk protein to reach the product nutrition index, in the embodiment, the raw milk is subjected to degreasing treatment to obtain standardized degreased raw milk with protein more than or equal to 3.1 wt% and fat less than or equal to 0.8 wt%;

(2) homogenizing and cooling: the defatted raw milk is preheated to 65 ℃ and homogenized under 15MPa of homogenization pressure. Then cooled to 40 ℃.

(3) Hydration: putting skim raw milk into a mixing tank, heating to 50 ℃, adding skim milk powder under the condition of stirring speed of 500r/min, stirring at 45 ℃ for more than 30min, stopping stirring, hydrating the skim milk powder for 30min, and preparing a fermentation base material;

(4) sterilization, homogenization, inoculation and fermentation: preheating the fermented base material to 70 deg.C, homogenizing under 20MPa, and sterilizing at 133 + -2 deg.C for 6S. Cooling to 42 +/-1 ℃, inoculating fermentation strains of lactobacillus bulgaricus and streptococcus thermophilus with the addition of 80U/T, stirring at the stirring speed of 200r/min for 20min, stopping stirring, and starting fermentation for 6 h;

(5) demulsifying, smoothing and cooling: demulsifying after fermenting to the end point acidity of 125 degrees T. Smoothing the demulsified fermented milk at the rotation speed of a smoothing pump of 400rpm, and then cooling to 8 ℃;

(6) filling: and filling the cooled low-fat high-protein fermented milk into a specific container by a clean filling machine to obtain the product.

The low-fat high-protein fermented milk 2 prepared by the method has the protein content of 9.6% and the fat content of 0.8%.

Example 3

A low-fat high-protein fermented milk and a production method thereof comprise the following steps:

firstly, the product formula is as follows:

75% of raw milk, 25% of skim milk powder and 70U/T of fermentation strains, wherein the fermentation strains comprise lactobacillus bulgaricus and lactobacillus thermophilus, and the fat content and the protein content in the skim milk powder are respectively 1% and 36%. The performance indexes of the raw materials meet the requirements of the conventional quality standard in the field.

Secondly, the specific process flow is as follows:

(1) standardized degreasing treatment: the step adopts the conventional process in the field, generally, in order to adjust milk fat and milk protein to reach the product nutrition index, in the embodiment, the raw milk is subjected to degreasing treatment to obtain standardized degreased raw milk with protein more than or equal to 3.1 wt% and fat less than or equal to 0.8 wt%;

(2) homogenizing and cooling: the defatted raw milk is preheated to 65 ℃ and homogenized under the homogenization pressure of 18 MPa. Then cooled to 40 ℃.

(3) Hydration: putting skim raw milk into a mixing tank, heating to 50 ℃, adding skim milk powder under the condition of stirring speed of 500r/min, stirring at 45 ℃ for more than 30min, stopping stirring, hydrating the skim milk powder for 30min, and preparing a fermentation base material;

(4) sterilization, homogenization, inoculation and fermentation: preheating the fermented base material to 65 deg.C, homogenizing under 22MPa, and sterilizing at 133 + -2 deg.C for 6S. Cooling to 42 +/-1 ℃, inoculating 70U/T of lactobacillus bulgaricus and streptococcus thermophilus fermentation strains, stirring at a stirring speed of 220r/min for 20min, stopping stirring, and starting fermentation for 6 h;

(5) demulsifying, smoothing and cooling: demulsifying after fermenting to the end point acidity of 125 degrees T. Smoothing the demulsified fermented milk at the rotation speed of a smoothing pump of 400rpm, and then cooling to 8 ℃;

(6) filling: and filling the cooled low-fat high-protein fermented milk into a specific container by a clean filling machine to obtain the product.

The low-fat high-protein fermented milk 3 prepared by the method has the protein content of 11.2% and the fat content of 0.8%.

Example 4

A low-fat high-protein fermented milk and a production method thereof comprise the following steps:

firstly, the product formula is as follows:

70% of raw milk, 30% of skim milk powder and 60U/T of fermentation strains, wherein the fermentation strains comprise lactobacillus bulgaricus and lactobacillus thermophilus, and the fat content and the protein content in the skim milk powder are respectively 1% and 36%. The performance indexes of the raw materials meet the requirements of the conventional quality standard in the field.

Secondly, the specific process flow is as follows:

(1) standardized degreasing treatment: the step adopts the conventional process in the field, generally, in order to adjust milk fat and milk protein to reach the product nutrition index, in the embodiment, the raw milk is subjected to degreasing treatment to obtain standardized degreased raw milk with protein more than or equal to 3.1 wt% and fat less than or equal to 0.8 wt%;

(2) homogenizing and cooling: the defatted raw milk is preheated to 60 ℃ and homogenized under 16MPa homogenizing pressure. Then cooled to 40 ℃.

(3) Hydration: putting skim raw milk into a mixing tank, heating to 45 ℃, adding skim milk powder under the condition of stirring speed of 600r/min, stirring at 45 ℃ for more than 30min, stopping stirring, hydrating the skim milk powder for 30min, and preparing a fermentation base material;

(4) sterilization, homogenization, inoculation and fermentation: preheating the fermented base material to 70 deg.C, homogenizing under 24MPa, and sterilizing at 133 + -2 deg.C for 6S. Cooling to 42 +/-1 ℃, inoculating 60U/T of lactobacillus bulgaricus and streptococcus thermophilus fermentation strains, stirring at a stirring speed of 250r/min for 20min, stopping stirring, and starting fermentation for 5 h;

(5) demulsifying, smoothing and cooling: demulsifying after fermenting to the end point acidity of 125 degrees T. Smoothing the demulsified fermented milk at the rotation speed of a smoothing pump of 400rpm, and then cooling to 8 ℃;

(6) filling: and filling the cooled low-fat high-protein fermented milk into a specific container by a clean filling machine to obtain the product.

The low-fat high-protein fermented milk 4 produced by the method has a protein content of 13% and a fat content of 0.8%.

Example 5

A low-fat high-protein fermented milk and a production method thereof comprise the following steps:

firstly, the product formula is as follows:

65% of raw milk, 35% of skim milk powder and 50U/T of fermentation strains, wherein the fermentation strains comprise lactobacillus bulgaricus and lactobacillus thermophilus, and the fat content and the protein content in the skim milk powder are respectively 1% and 36%. The performance indexes of the raw materials meet the requirements of the conventional quality standard in the field.

Secondly, the specific process flow is as follows:

(1) standardized degreasing treatment: the step adopts the conventional process in the field, generally, in order to adjust milk fat and milk protein to reach the product nutrition index, in the embodiment, the raw milk is subjected to degreasing treatment to obtain standardized degreased raw milk with protein more than or equal to 3.1 wt% and fat less than or equal to 0.8 wt%;

(2) homogenizing and cooling: the defatted raw milk is preheated to 60 ℃ and homogenized under 16MPa homogenizing pressure. Then cooled to 40 ℃.

(3) Hydration: putting skim raw milk into a mixing tank, heating to 45 ℃, adding skim milk powder under the condition of stirring speed of 600r/min, stirring at 45 ℃ for more than 30min, stopping stirring, hydrating the skim milk powder for 30min, and preparing a fermentation base material;

(4) sterilization, homogenization, inoculation and fermentation: preheating the fermented base material to 70 deg.C, homogenizing under 25MPa, and sterilizing at 133 + -2 deg.C for 6S. Cooling to 42 +/-1 ℃, inoculating fermentation strains of lactobacillus bulgaricus and streptococcus thermophilus with the addition of 50U/T, stirring at the stirring speed of 250r/min for 20min, stopping stirring, and starting fermentation for 5 h;

(5) demulsifying, smoothing and cooling: demulsifying after fermenting to the end point acidity of 125 degrees T. Smoothing the demulsified fermented milk at the rotation speed of a smoothing pump of 400rpm, and then cooling to 8 ℃;

(6) filling: and filling the cooled low-fat high-protein fermented milk into a specific container by a clean filling machine to obtain the product.

The low-fat high-protein fermented milk 5 produced by the method for producing low-fat high-protein fermented milk had a protein content of 14.6% and a fat content of 0.9%.

Comparative example 1

The comparative example is that the concentrated milk protein powder is added to improve the protein of the fermentation base material by an external addition method to prepare the low-fat high-protein fermented milk with 9 percent of protein content and 0.7 percent of fat content, and the method comprises the following steps:

firstly, the product formula is as follows:

90% of raw milk, 10% of concentrated milk protein powder (the protein content is 62%), 100U/T of fermentation strain, wherein the fermentation strain comprises lactobacillus bulgaricus and lactobacillus thermophilus. The performance indexes of the raw materials meet the requirements of the conventional quality standard in the field.

Secondly, the specific process flow of the process is as follows:

(1) and (3) standardization: degreasing raw milk to obtain standardized degreased raw milk with protein more than or equal to 3.1% and fat less than or equal to 0.8%, wherein the contents are mass percent;

(2) homogenizing and cooling: the degreased raw milk is preheated to 60 ℃, and is homogenized under the homogenization pressure of 15 MPa. Then cooled to 35 ℃.

(3) Hydration: putting skim raw milk into a mixing tank, heating to 55 ℃, adding concentrated milk protein powder under the condition of stirring speed of 500r/min, stirring at 400 ℃ for more than 30min, stopping stirring, hydrating the concentrated milk protein powder for 30min, and preparing a fermentation base material;

(4) sterilization, homogenization, inoculation and fermentation: preheating the fermented base material to 70 deg.C, homogenizing under 20MPa, and sterilizing at 133 + -2 deg.C for 6S. Cooling to 42 +/-1 ℃, inoculating 100U/T of lactobacillus bulgaricus and streptococcus thermophilus fermentation strains, stirring at a stirring speed of 200r/min for 20min, stopping stirring, and fermenting for 7 h;

(5) demulsifying, smoothing and cooling: demulsifying after fermenting to the end point acidity of 125 degrees T. Smoothing the demulsified fermented milk at the rotation speed of a smoothing pump of 400rpm, and then cooling to 10 ℃;

(6) filling: and filling the cooled low-fat high-protein fermented milk into a specific container by a clean filling machine to obtain the product.

Comparative example 2

The comparative example is that concentrated whey protein powder is added to improve the protein of a fermentation base material by an external addition method to prepare the low-fat high-protein fermented milk with 12 percent of protein content and 1 percent of fat content, and the method comprises the following steps:

firstly, the product formula is as follows:

80% of raw milk, 20% of concentrated whey protein powder (the protein content is 50%), 80U/T of fermentation strain, wherein the fermentation strain comprises lactobacillus bulgaricus and lactobacillus thermophilus. The performance indexes of the raw materials meet the requirements of the conventional quality standard in the field.

Secondly, the specific process flow of the process is as follows:

(1) and (3) standardization: degreasing raw milk to obtain standardized degreased raw milk with protein more than or equal to 3.1% and fat less than or equal to 0.8%;

(2) homogenizing and cooling: the degreased raw milk is preheated to 60 ℃, and is homogenized under the homogenization pressure of 15 MPa. Then cooled to 35 ℃.

(3) Hydration: putting the skim raw milk into a mixing tank, heating to 55 ℃, adding the concentrated whey protein powder under the condition of stirring speed of 500r/min, stirring for more than 30min at 400 ℃, stopping stirring, hydrating the concentrated whey protein powder for 30min, and preparing a fermentation base material;

(4) sterilization, homogenization, inoculation and fermentation: preheating the fermented base material to 70 deg.C, homogenizing under 20MPa, and sterilizing at 133 + -2 deg.C for 6S. Cooling to 42 +/-1 ℃, inoculating 80U/T of lactobacillus bulgaricus and streptococcus thermophilus fermentation strains, stirring at a stirring speed of 200r/min for 20min, stopping stirring, and starting fermentation for 6 h;

(5) demulsifying, smoothing and cooling: demulsifying after fermenting to the end point acidity of 125 degrees T. Smoothing the demulsified fermented milk at the rotation speed of a smoothing pump of 400rpm, and then cooling to 10 ℃;

(6) filling: and filling the cooled low-fat high-protein fermented milk into a specific container by a clean filling machine to obtain the product.

Comparative example 3

The comparative example is that through the external addition method, add skim milk powder, concentrated whey protein powder and casein powder to improve the protein of fermented base material, make the fermented milk of low fat and high protein of 8.8% of protein content, the fat content is 1.0%, including the following steps:

firstly, the product formula is as follows:

91.5 percent of raw milk, 2 percent of skim milk powder (the protein content is 34 percent and the fat content is 0.8 percent), 2 percent of concentrated whey protein (the protein content is 82 percent), 4.5 percent of casein (the protein content is 82 percent), and 150U/T of fermentation strain, wherein the fermentation strain comprises lactobacillus bulgaricus and streptococcus thermophilus. The performance indexes of the raw materials meet the requirements of the conventional quality standard in the field.

Secondly, the specific process flow of the process is as follows:

(1) and (3) standardization: degreasing raw milk to obtain standardized degreased raw milk with protein more than or equal to 3.1% and fat less than or equal to 0.8%;

(2) hydration: putting skim raw milk into a mixing tank, heating to 55 ℃, adding skim milk powder, concentrated whey protein and casein under the condition of stirring speed of 500r/min, stirring at 400 ℃ for more than 30min, stopping stirring, hydrating the skim milk powder, the concentrated whey protein and the casein for 30min, and preparing a fermentation base material;

(3) sterilization, homogenization, inoculation and fermentation: preheating the fermented base material to 70 deg.C, homogenizing under 20MPa, and sterilizing at 133 + -2 deg.C for 6S. Cooling to 42 +/-1 ℃, inoculating fermentation strains of lactobacillus bulgaricus and streptococcus thermophilus with the addition of 150U/T, stirring at the stirring speed of 200r/min for 20min, stopping stirring, and starting fermentation for 6 h;

(4) demulsifying, smoothing and cooling: demulsifying after fermenting to the end point acidity of 125 degrees T. Smoothing the demulsified fermented milk at the rotation speed of a smoothing pump of 400rpm, and then cooling to 10 ℃;

(5) filling: and filling the cooled low-fat high-protein fermented milk into a specific container by a clean filling machine to obtain the product.

Comparative example 4

The comparative example is that through an external addition method, skim milk powder is added to improve protein of a fermentation base material, and the low-fat high-protein fermented milk with 5 percent of protein content and 0.8 percent of fat content is prepared, and the method comprises the following steps:

firstly, the product formula is as follows:

93% of raw milk, 7% of skim milk powder (the protein content is 36% and the fat content is 0.8%), 100U/T of fermentation strain, wherein the fermentation strain comprises lactobacillus bulgaricus and lactobacillus thermophilus. The performance indexes of the raw materials meet the requirements of the conventional quality standard in the field.

Secondly, the specific process flow of the process is as follows:

(1) and (3) standardization: degreasing raw milk to obtain standardized degreased raw milk with protein more than or equal to 3.1% and fat less than or equal to 0.8%;

(2) homogenizing and cooling: the skim raw milk was preheated to 60 ℃, homogenized under 15MPa homogenization pressure, and then cooled to 35 ℃.

(3) Hydration: putting skim raw milk into a mixing tank, heating to 55 ℃, adding skim milk powder under the condition of stirring speed of 500r/min, stirring at 40 ℃ for more than 30min, stopping stirring, hydrating the skim milk powder for 30min, and preparing a fermentation base material;

(4) sterilization, homogenization, inoculation and fermentation: preheating the fermented base material to 70 deg.C, homogenizing under 20MPa, and sterilizing at 133 + -2 deg.C for 6S. Cooling to 42 +/-1 ℃, inoculating 100U/T of lactobacillus bulgaricus and streptococcus thermophilus fermentation strains, stirring at a stirring speed of 200r/min for 20min, stopping stirring, and fermenting for 7 h;

(5) demulsifying, smoothing and cooling: demulsifying after fermenting to the end point acidity of 125 degrees T. Smoothing the demulsified fermented milk at the rotation speed of a smoothing pump of 400rpm, and then cooling to 10 ℃;

(6) filling: and filling the cooled low-fat high-protein fermented milk into a specific container by a clean filling machine to obtain the product.

The contents of the above examples are all mass percent contents.

Test examples

1. Sensory testing

Sensory tests were conducted on the products of examples 1-5 and comparative examples 1-4. The sensory test comprises that 30 professional sensory evaluation persons form a sensory evaluation group, the tissue state, the flavor and the taste are comprehensively scored, the average value is taken, meanwhile, the number of people who like the whole sample is statistically analyzed, and the evaluation indexes of the tissue state, the flavor and the taste are shown in table 1.

TABLE 1

After professional sensory evaluation, the evaluation results are shown in table 2.

TABLE 2

Item	Flavor (I) and flavor (II)	Tissue state	Taste of the product	Total score
					Example 1	25	27	37	89
Example 2	26	25	36	87
					Example 3	26	27	35	88
Example 4	27	26	36	89
					Example 5	26	25	36	87
Comparative example 1	18	18	26	62
					Comparative example 2	18	24	20	62
Comparative example 3	16	20	30	66
					Comparative example 4	15	10	26	51

2. Analysis of volatile substance flavor

Volatile flavor substance analysis is carried out on the products in examples 1-5 and comparative examples 1-4 by combining with an electronic nose detection technology, the difference of flavors in different fermented milk samples is revealed, and samples with pure and excellent flavors are screened, wherein the names and the performances of various sensors of the electronic nose are described in table 3.

The electronic nose detection method comprises the following steps: weighing 10g of fermented milk product, sealing in a 50ml headspace bottle, bathing at 42 deg.C for 30min, inserting an electronic nose probe, and measuring with 10 metal sensors.

Electronic nose measurement conditions: sensor cleaning time 60 s; sample preparation time 5 s; the measuring time is 90s, the internal flow rate is 300mL/min, and the sample injection flow rate is 200 mL/min.

TABLE 3 PEN3 electronic nose sensor name and Performance description

Serial number	Sensor name	Description of Performance
			1	W1C	Fragrance ingredient
2	W5S	High sensitivity and sensitivity to nitrogen oxides
			3	W3C	Ammonia, sensitive to aromatic components
4	W6S	Is selective for hydrogen gas
			5	W5C	Aromatic components of alkanes
6	W1S	Sensitive to methyl groups
			7	W1W	Para sulfurSensitive to chemical compounds
8	W2S	Sensitive to alcohols and aldehydes and ketones
			9	W2W	Aromatic components, sensitive to organic sulfides
10	W3S	Sensitive to alkanes

The flavor test results of the samples are shown in fig. 1-9. Among them, five sensors of W5S, W2W, W1W, W2S and W1S are sensitive to nitrogen oxides, aromatics, sulfides, alcohols, aldehydes and ketones, respectively. The five sensors are proved to contribute greatly in the process of detecting the flavor of the fermented milk.

The data show that: examples 1-5 the overall flavor contribution of the samples was mainly W5S, W2W, W1W and significantly higher than the other sensors, indicating a pure flavor, mainly nitrogen oxides, aromatics, sulfides, etc. Meanwhile, compared with comparative examples 1-4, the induction value is larger, which shows that the flavor is rich and outstanding; the samples in comparative examples 1 to 3 mainly contribute to more sensors and have no obvious difference, which shows that the products have more flavor substances, and have more and impure flavors, while the sample in comparative example 4 has purer and more positive flavors and mainly contributes to W5S and W2S, but has smaller induction value and weaker overall flavor.

3. Viscosity test and particle size test

Viscosity test method: testing with 92# rotor of viscometer BROOKFIELD DV2T at 20 + -0.5 deg.C and 2rpm for 10s at test interval, and taking 5 parallel samples and the average value;

and (3) particle size testing: the method is characterized in that a BECKMAN COULTER LS13320 laser diffraction particle size analyzer is adopted to measure, 5 parallel samples are taken from each sample, and an average particle size value is taken.

The results of the above viscosity and particle size tests are shown in table 4.

TABLE 4 sample viscosity and particle size

Item	Viscosity (cp)	Particle size (um)
			Example 1	11009	15
Example 2	11443	16
			Example 3	13082	18
Example 4	13454	17
			Example 5	13533	19
Comparative example 1	18232	20
			Comparative example 2	23579	23
Comparative example 3	20988	28
			Comparative example 4	7034	16

4. Surface whey yield test

The products of examples 1-5 and comparative examples 1-4 were subjected to a whey precipitation test. From the fermented milk products prepared in examples and comparative examples, samples of the same mass were taken, respectively using sterile bottles, and left in a refrigerator at 4 ℃ for 2 weeks, and the weight of the sample W1 and the weight of the collected whey precipitated on the surface W2 were weighed, and 5 replicates of each sample were taken. The amount of whey precipitated on the surface of each sample was calculated in the following manner, and the results of the measurement are shown in table 5.

The surface whey deposition amount (%) [ W2/W1] x 100%.

TABLE 5 whey deposition of samples

Item	Amount of whey separated (%)
		Example 1	0.10
Example 2	0.08
		Example 3	0.09
Example 4	0.11
		Example 5	0.12
Comparative example 1	0.19
		Comparative example 2	0.20
Comparative example 3	0.15
		Comparative example 4	0.21

The results of the above-described measurements in FIG. 1 and tables 2 to 5 show that:

according to the invention, the skim milk powder is used as the exogenous added protein, and the addition amount of the skim milk powder, the types of the strains and the addition amount of the strains are optimized, so that after the process steps are combined, the strong milk fragrance of the fermented milk can be effectively realized, the flavor of the fermented milk is ensured, the protein content is improved, the low viscosity of the fermented milk is ensured, and the refreshing taste of the fermented milk is ensured. In addition, under the condition of not adding a stabilizing agent and a thickening agent, the separation of whey in the fermented milk in the shelf life is avoided to the maximum extent, higher stability is obtained, and the effect is very obvious.

It should be understood that the above examples are only for clarity of illustration and are not intended to limit the embodiments. Other variations and modifications will be apparent to persons skilled in the art in light of the above description. And are neither required nor exhaustive of all embodiments. And obvious variations or modifications therefrom are within the scope of the invention.