A room-temperature yogurt and its preparation method

Abstract

The present invention relates to the technical field of room-temperature yogurt, and specifically relates to a room-temperature yogurt and a preparation method thereof. By combining dual-frequency ultrasonic treatment with ultra-high pressure treatment and applying ultrasonic treatment during the second-stage fermentation between the first-stage fermentation and the third-stage fermentation, the drawability of the yogurt can be greatly improved on the basis of maintaining a low bacterial count or even sterility, so that the yogurt can be stored at room temperature and has a good drawability effect. If the ultra-high pressure treatment pressure is too high or the treatment time is too long, the structure of the yogurt will be damaged and it cannot be drawn into filaments. If the ultra-high pressure treatment pressure is too low and the treatment time is too short, there will be too many lactic acid bacteria in the yogurt, resulting in the inability to store at room temperature and only being able to store at low temperature. In this application, by controlling the pressure and time of the ultra-high pressure treatment within the above range, a good drawability effect is obtained while maintaining a low bacterial count or even sterility of the yogurt.

Description

Technical Field

[0001] The present invention relates to the technical field of ambient temperature yogurt, and particularly relates to an ambient temperature yogurt and a preparation method thereof. Background Art

[0002] With the continuous improvement of consumers' health awareness, the market demand for high-quality, natural and functional dairy products is increasing day by day. The traditional dairy processing technology has been difficult to meet consumers' diverse pursuits of taste, nutrition and health. At present, it is urgent to accelerate the pace of process technology innovation.

[0003] Pulled yogurt has successfully attracted the favor of a large number of consumers with its unique taste, healthy image, high-end market positioning and the communication advantages on social media. The reason for the pulled texture of yogurt is that a closer cross-linking is formed between proteins and polysaccharides during the fermentation process. However, at present, most of the pulled yogurt is low-temperature yogurt, because the preparation process of ambient temperature yogurt will destroy the pulling characteristics and lead to the loss of the pulling effect. Summary of the Invention

[0004] Therefore, what the present invention needs to solve is the defect that the preparation process of ambient temperature yogurt in the prior art destroys the pulling characteristics and causes the yogurt to lose the pulling effect, and further provides an ambient temperature yogurt and a preparation method thereof.

[0005] To solve the above technical problems, the technical solutions adopted by the present invention are as follows:

[0006] The present application provides a preparation method of ambient temperature yogurt, including fermenting and demulsifying the milk base material, then performing dual-frequency ultrasonic treatment, and then performing ultra-high pressure treatment at a pressure of 200-400 MPa for 3-10 min to obtain ambient temperature yogurt, wherein the fermentation sequentially includes a first-stage fermentation, a second-stage fermentation and a third-stage fermentation, and a first ultrasonic treatment is applied during the second-stage fermentation.

[0007] Further, the pressure of the ultra-high pressure sterilization treatment is 300-400 Mpa, and the time is 3-8 min.

[0008] Further, the ultrasonic frequencies of the dual-frequency ultrasonic treatment include a first ultrasonic frequency of 15-25 kHz and a second ultrasonic frequency of 45-55 kHz; the ultrasonic time is 3-5 min; the ultrasonic power is 600-800 W.

[0009] Further, a step of cooling and / or aseptic filling is also included between the dual-frequency ultrasonic treatment and the ultra-high pressure treatment.

[0010] Further, the demulsification is carried out by a stirring method.

[0011] Further, the time of the first-stage fermentation is 80 - 100 min; and / or, the ultrasonic frequency of the first ultrasonic treatment is 15 - 25 kHz, the ultrasonic power is 100 - 200 W, and the ultrasonic time is 15 - 25 min.

[0012] Further, the time of the second-stage fermentation is the same as the ultrasonic time of the first ultrasonic treatment, that is, the first ultrasonic treatment is carried out throughout the second-stage fermentation.

[0013] Further, no ultrasonic treatment is carried out during the first-stage fermentation and the third-stage fermentation.

[0014] In some preferred embodiments, the ultrasonic frequency of the first ultrasonic treatment is 18 - 22 kHz, the ultrasonic power is 120 - 180 W, and the ultrasonic time is 15 - 25 min.

[0015] Further, a fermentation strain is added to the milk base material to initiate the first-stage fermentation.

[0016] Further, the fermentation strains used in the fermentation include a combined strain of one or more of YO-MIX883 starter culture (Danisco starter culture), FD-DVS Yoflex® Premium 5.0 starter culture (Chr. Hansen starter culture), YS-242 starter culture (DSM starter culture), PYS-V141 starter culture (Keyto Starter Culture) and Streptococcus salivarius; and / or, the mass ratio of the fermentation strain used in the fermentation to the milk base material is 0.03 - 0.05:900 - 1100; and / or, the fermentation end point of the third-stage fermentation is that the acidity reaches 70 - 80 °T; and / or, the stirring speed during the demulsification process is 25 - 30 r / min, and the time is 3 - 5 min.

[0017] Further, the Streptococcus salivarius cells are Streptococcus thermophilus subsp. salivarius, such as Streptococcus thermophilus subsp. salivarius MN-ZLW-002, with the deposit number of CGMCC No. 3817.

[0018] Further, the fermentation temperatures of the first-stage fermentation, the second-stage fermentation and the third-stage fermentation are 38 - 40 °C.

[0019] Further, by weight, the milk base material includes 810 - 870 parts by weight of milk raw materials, 30 - 75 parts by weight of sweeteners, 10 - 15 parts by weight of stabilizers, 6 - 8 parts by weight of protein in protein raw materials, and 40 - 100 parts by weight of water; and / or, the preparation method of the milk base material includes mixing milk raw materials, sweeteners, stabilizers and proteins, and homogenizing and sterilizing to obtain the milk base material.

[0020] Further, the preparation method also satisfies one or more of the following A - E:

[0021] A. The temperature of homogenization is 58 - 62°C. The homogenization includes primary homogenization and secondary homogenization. The pressure of primary homogenization is 130 - 150 bar, and the pressure of secondary homogenization is 30 - 40 bar.

[0022] B. The temperature of sterilization is 120 - 122°C, and the time is 6 - 8 s.

[0023] C. The milk raw material includes raw cow milk or reconstituted whole milk powder; and / or, the sweetener includes one or more of white granulated sugar, fructose, glucose, xylitol, erythritol, stevioside, sucralose, isomaltooligosaccharide, fructooligosaccharide, xylooligosaccharide, galactooligosaccharide, trehalose; and / or, the stabilizer includes one or more of corn starch, tapioca starch, glutinous rice starch; and / or, the source of protein includes one or more of whey protein, fibrillated whey protein.

[0024] D. Before mixing to prepare the milk base material, the milk raw material also includes steps of filtration, homogenization, and sterilization.

[0025] E. Before mixing to prepare the milk base material, the protein also includes a step of fibrillization treatment.

[0026] The addition amount of the sweetener in the yogurt product of the present invention all complies with the standard provisions of GB2760 - 2014.

[0027] Further, when the source of the protein is fibrillated whey protein, fibrillated whey protein liquid with a protein content of 7 - 13% (especially fibrillated whey protein liquid with a protein content of 8 - 12%) can be used to be mixed with the milk raw material, sweetener, and stabilizer, and after homogenization and sterilization, the milk base material is obtained. The fibrillated whey protein liquid is prepared by fibrillization treatment using a protein liquid formed by dispersing whey protein powder in water as the raw material. After the fibrillization treatment of the prepared protein liquid, the protein content remains unchanged, only the protein structure and properties change. That is to say, the protein content in the protein liquid is the same as that in the prepared fibrillated whey protein liquid. The fibrillated whey protein liquid can be prepared by fibrillization treatment of a protein liquid with a protein content of 7 - 13%. The prepared protein liquid can use commercially available conventional whey protein powder, such as whey protein powder with a protein content > 55%, specifically, whey protein powder with a protein content of 56% - 65% can be used.

[0028] In this application, the protein content in the product or raw material refers to the mass percentage content of the protein in the product or raw material.

[0029] Further, the mixing time of the milk base material is 10 - 15 min, and the mixing stirring speed is 35 - 45 r / min.

[0030] Further, before mixing to prepare the milk base material, the milk raw material further includes steps of filtration, homogenization, and sterilization. For example, the temperature of homogenization is 50 - 65°C. The homogenization includes primary homogenization and secondary homogenization. The primary homogenization pressure is 180 - 200 bar, and the secondary homogenization pressure is 40 - 50 bar. For example, the temperature of sterilization is 73 - 78°C, and the sterilization time is 15 - 20 s.

[0031] Further, before mixing to prepare the milk base material, the protein further includes a step of fibrillation treatment.

[0032] Further, the fibrillation treatment includes:

[0033] Step S1: Disperse whey protein in water to obtain a protein solution;

[0034] Step S2: Use an acidity regulator to adjust the pH of the protein solution obtained in Step S1 to 4.2 - 5.5, perform heat treatment, and cool down with stirring to obtain a mixed solution;

[0035] Step S3: Use an acidity regulator to adjust the pH of the mixed solution obtained in Step S2 to 6.5 - 7.0 to obtain a fibrillated whey protein solution.

[0036] Further, in Step S1, the protein content in the protein solution is 7 - 13%.

[0037] Further, in Step S1, the protein content in the protein solution is 8 - 12%.

[0038] Further, in Step S2, the temperature of heat treatment is 83 - 90°C, and the time is 50 - 100 s.

[0039] Further, the acidity regulator includes one or more of citric acid and sodium tripolyphosphate.

[0040] Further, the dispersion process includes steps of stirring and static hydration. Among them, the stirring time is 15 - 20 min, and the static hydration time is 25 - 35 min; and / or, the stirring speed is 350 - 400 rpm, and the temperature is cooled down to 1 - 7°C for the liquid material.

[0041] This application also provides a room-temperature yogurt prepared by the preparation method described in any one of the above.

[0042] Compared with the prior art, the present invention has the following beneficial effects:

[0043] (1)Research findings show that heat sterilization treatment and high-intensity shearing after the fermentation of room-temperature yogurt will damage the cross-linked structure, resulting in a significantly deteriorated drawing effect. Adjusting the preparation process will lead to a low bacterial count or inability to ensure sterility in yogurt, and it cannot be stored at room temperature. The preparation method of room-temperature yogurt provided by the present invention includes subjecting the milk base material to fermentation and demulsification, then performing dual-frequency ultrasonic treatment, and then performing ultra-high pressure treatment at a pressure of 200-400 MPa for 3-10 minutes to obtain room-temperature yogurt. Among them, the fermentation sequentially includes the first-stage fermentation, the second-stage fermentation, and the third-stage fermentation. During the second-stage fermentation, the first ultrasonic treatment is applied. By combining dual-frequency ultrasonic treatment with ultra-high pressure treatment and applying ultrasonic treatment during the second-stage fermentation between the first-stage fermentation and the third-stage fermentation, the drawing characteristics of yogurt can be greatly improved on the basis of maintaining a low bacterial count or even sterility, so that the yogurt can be stored at room temperature and has a good drawing effect. Excessive ultra-high pressure treatment pressure or too long treatment time will cause the yogurt structure to be damaged and unable to be drawn, while too low ultra-high pressure treatment pressure and too short treatment time will cause too many lactic acid numbers in the yogurt, resulting in the inability to be stored at room temperature and can only be stored at low temperature. By controlling the pressure and time of ultra-high pressure treatment within the above range in this application, a good drawing effect is obtained, and the low bacterial count or even sterility of yogurt is maintained, and finally room-temperature yogurt is obtained. Applying ultrasonic treatment to the lactic acid bacteria that have initially grown after the first-stage fermentation can effectively enrich the exopolysaccharides of lactic acid bacteria and promote the synthesis of longer-chain polysaccharides with larger molecular weights, improving the drawing effect of yogurt.

[0044] Currently, the commonly used drawing yogurt usually requires the use of a large amount of chemical stabilizers, resulting in problems such as high additive usage, seriously affecting the consumer experience and the further upgrading of product quality, and the drawing effect is not excellent. Adopting the technical solution of this application also avoids the addition of a large amount of chemical stabilizers.

[0045] (2)The preparation method of room-temperature yogurt provided by the present invention can further improve the drawing effect of yogurt and obtain sterile yogurt by controlling the pressure of ultra-high pressure treatment to be 300-400 Mpa and the time to be 3-8 minutes.

[0046] (3)In the preparation method of room-temperature yogurt provided by the present invention, the ultrasonic frequencies of the dual-frequency ultrasonic treatment include a first ultrasonic frequency of 15-25 kHz and a second ultrasonic frequency of 45-55 kHz; the ultrasonic time is 3-5 minutes; the ultrasonic power is 600-800 W. By controlling the first ultrasonic frequency, the second ultrasonic frequency, the ultrasonic time, and the ultrasonic power within the above range, the drawing effect of yogurt can be further improved, the bacterial count of yogurt can be reduced, the texture of yogurt can be stabilized, and the shelf-life stability of yogurt can be improved.

[0047] (4) In the method for preparing room temperature yogurt provided by the present invention, the ultrasonic frequency is 15-25 kHz, the ultrasonic power is 100-200 W, and the ultrasonic time is 15-25 min. In particular, the use of low-frequency and low-power ultrasound (for example, the ultrasonic frequency is 18-22 kHz, the ultrasonic power is 120-180 W, and the ultrasonic time is 15-25 min) can effectively enrich the extracellular polysaccharides of lactic acid bacteria and promote the synthesis of long-chain polysaccharides with larger molecular weight, thereby further improving the drawing effect of room temperature yogurt.

[0048] (5) The method for preparing room temperature yogurt provided by the present invention comprises, by weight, 810-870 parts by weight of milk raw material, 30-75 parts by weight of sweetener, 10-15 parts by weight of stabilizer, 6-8 parts by weight of protein, and 40-100 parts by weight of water. The present application uses the above-mentioned formula of milk base to make yogurt have good shelf life stability.

[0049] (6) The preparation method of room temperature yogurt provided by the present invention, the fiberization treatment comprises: step S1: dispersing whey protein in water to obtain a protein solution; step S2: adjusting the pH of the protein solution obtained in step S1 to 4.2-5.5 with an acidity regulator, heating the solution, and cooling the solution under stirring to obtain a mixed solution; step S3: adjusting the pH of the mixed solution obtained in step S2 to 6.5-7.0 with an acidity regulator to obtain a fiberized whey protein solution. The fiberization treatment of the protein by the above method and then mixing it into the milk base can further improve the shelf life stability of the yogurt, especially controlling the protein content in the protein solution to 8-12%, which can further improve the wire drawing effect and shelf life stability of the yogurt. BRIEF DESCRIPTION OF THE DRAWINGS

[0050] In order to more clearly illustrate the specific implementation methods of the present invention or the technical solutions in the prior art, the following is a brief introduction to the drawings required for use in the specific implementation methods or the description of the prior art. It is obvious that the drawings described below are some implementation methods of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0051] Figure 1 is a schematic diagram of the yogurt wire drawing test device used in Experimental Example 1;

[0052] 1. Liquid storage component; 2. Camera component; 3. Computer. DETAILED DESCRIPTION

[0053] The technical solution of the present invention will be described clearly and completely below. Obviously, the described embodiments are part of the embodiments of the present invention, rather than all of them. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts belong to the scope of protection of the present invention.

[0054] For those embodiments in which specific experimental steps or conditions are not specified, the operations or conditions of the conventional experimental steps described in the literature in this field can be followed. For the reagents or instruments whose manufacturers are not specified, they are all conventional reagent products that can be obtained through commercial purchase. The protein content in the fibrillar whey protein solution is the theoretically calculated value, and the protein content = (protein content in whey protein powder × addition amount of whey protein powder) / (addition amount of whey protein powder + water amount); where the addition amount of whey protein powder and the water amount are the masses of whey protein powder and water added during the fibrillization of whey protein, respectively.

[0055] Example 1

[0056] This example provides a method for preparing room-temperature yogurt, and the raw materials are as follows: raw milk: 869.97 kg, granulated sugar: 65 kg, corn starch: 4.5 kg, glutinous rice starch: 10.5 kg, fibrillar whey protein solution: 50 kg (protein content 12%), bacterial strains: 0.03 kg (YO-MIX883 starter: 0.02 kg; MN-ZLW-002: 0.01 kg).

[0057] The above method for preparing room-temperature yogurt includes first-stage fermentation, second-stage fermentation, third-stage fermentation, demulsification, dual-frequency ultrasonic treatment, cooling, aseptic filling, and ultra-high pressure treatment of the milk base material. Specifically: cool the milk base material to 38°C, add the bacterial strains, and ferment in a fermentation tank. After starting fermentation for 90 min (first-stage fermentation), apply low-frequency ultrasonic treatment with an ultrasonic frequency of 20 kHz and an ultrasonic power of 150 W for 20 min (second-stage fermentation). Continue fermentation at 38°C (third-stage fermentation). When the fermentation acidity reaches 75°T, demulsify and stir for 1 min at a stirring speed of 25 r / min. After the stirring is completed, apply dual-frequency ultrasonic treatment with ultrasonic frequencies of 25 kHz and 55 kHz, an ultrasonic power of 600 W, and a treatment time of 3 min. Then quickly cool to below 10°C and perform aseptic filling. The filled yogurt samples are subjected to ultra-high pressure treatment at a pressure of 300 Mpa for 5 min.

[0058] Among them, the method for preparing the above milk base material in this example includes the following steps:

[0059] (1) Raw milk pretreatment: Raw milk is filtered through a primary filter with a pore size of 1.0 mm and a secondary filter with a pore size of 0.5 mm, preheated to 55°C for separation and sterilization, and then homogenized with a primary homogenization pressure of 180 bar and a secondary pressure of 50 bar. The temperature is then raised to 75°C for pasteurization for 15 seconds and cooled to 4°C.

[0060] (2) Whey protein fibrillation: The water was heated to 45°C, the shear mixing pump was turned on, and whey protein powder was added to prepare a protein solution with a protein content of 12%. The solution was stirred for 20 minutes, allowed to stand for hydration for 30 minutes, and cooled to 4°C. Then, stirring was turned on and citric acid was added to adjust the pH of the protein solution to 4.2. The solution was heated to 83°C and kept warm for 80 seconds. Then, stirring was turned on while the temperature was lowered and shear dispersion was performed at a speed of 400 rpm. The solution was cooled to 4°C, and sodium tripolyphosphate was added to adjust the pH of the solution to 6.7 to obtain a fibrillated whey protein solution.

[0061] (3) Ingredients: The raw milk treated in step (1) is heated to 45°C, the shear mixer pump is turned on, and white sugar, corn starch, glutinous rice starch, and fibrous whey protein liquid are added in sequence through a high-efficiency online mixer. After the feeding is completed, the shear pump is turned off, the mixture is circulated for 5 minutes, and the stirring is continued for 15 minutes at a stirring speed of 40 r / min. The homogenization temperature is 60°C, the first-level homogenization pressure is 150 bar, and the second-level homogenization pressure is 30 bar. After that, ultra-high temperature sterilization is performed at a sterilization temperature of 121±1°C and a time of 8 seconds to obtain a milk-based material.

[0062] Example 2

[0063] The present embodiment provides a method for preparing room temperature yogurt, and the raw materials are as follows: raw milk: 846.97 kg, white sugar: 40 kg, erythritol: 35 kg, corn starch: 3.6 kg, glutinous rice starch: 8.4 kg, fibrous whey protein liquid: 66 kg (protein content 12%), bacterial strain: 0.03 kg (FD-DVS Yoflex® Premium 5.0: 0.02 kg; MN-ZLW-002: 0.01 kg).

[0064] The preparation method of the above-mentioned ambient temperature yogurt involves first-stage fermentation, second-stage fermentation, third-stage fermentation, demulsification, dual-frequency ultrasonic treatment, cooling, aseptic filling, and ultra-high pressure treatment of the milk base material, specifically as follows: Cool the milk base material to 38°C, add the strain, and ferment in a fermentation tank. After starting fermentation for 90 min (first-stage fermentation), apply low-frequency ultrasonic treatment with an ultrasonic frequency of 20 kHz, an ultrasonic power of 150 W, and a treatment time of 20 min (second-stage fermentation). Continue fermentation at 38°C (third-stage fermentation). When the fermentation acidity reaches 75°T, perform demulsification and stir for 1 min at a stirring speed of 25 r / min. After stirring is completed, apply dual-frequency ultrasonic treatment with ultrasonic frequencies of 20 kHz and 50 kHz, an ultrasonic power of 600 W, and a treatment time of 5 min. Then quickly cool to below 10°C and perform aseptic filling. Subject the filled yogurt sample to ultra-high pressure treatment at a pressure of 300 Mpa and hold the pressure for 8 min.

[0065] Among them, the preparation method of the above-mentioned milk base material in this embodiment includes the following steps:

[0066] (1) Pretreatment of raw milk: Raw cow milk is filtered through a primary filter with a pore size of 1.0 mm and a secondary filter with a pore size of 0.5 mm, preheated to 55°C for separation and sterilization, then homogenized with a primary homogenization pressure of 180 bar and a secondary pressure of 50 bar, and then heated to 75°C for pasteurization for 15 s and cooled to 4°C.

[0067] (2) Fibrosis of whey protein: Heat water to 45°C, turn on the shear mixing pump, and add whey protein powder to prepare a protein solution with a protein content of 12%. Continuously stir for 17 min, stand for hydration for 30 min, and cool to 4°C. Then turn on the stirrer and add citric acid to adjust the pH of the protein solution to 4.7, heat to 85°C, and keep warm for 80 s. Then while cooling, turn on the stirrer and perform shear dispersion at a speed of 400 rpm. Cool the liquid material to 4°C, add sodium tripolyphosphate to adjust the pH of the solution to 6.7 to obtain the fibrotic whey protein liquid.

[0068] (3) Ingredient preparation: Heat the raw cow milk treated in step (1) to 45°C, turn on the shear mixing pump, and sequentially add granulated sugar, erythritol, corn starch, glutinous rice starch, and fibrotic whey protein liquid through an efficient online mixer. After the feeding is completed, turn off the shear pump, circulate for 5 minutes, and continue stirring for 15 min at a stirring speed of 40 r / min. The homogenization temperature is 60°C, the primary homogenization pressure is 150 bar, and the secondary homogenization pressure is 30 bar. Then perform ultra-high temperature sterilization at a sterilization temperature of 121 ± 1°C for 8 s to obtain the milk base material.

[0069] Example 3

[0070] This embodiment provides a method for preparing room-temperature yogurt, with the following raw materials: raw milk: 849.92 kg, granulated sugar: 40 kg, sucralose: 0.05 kg, corn starch: 3 kg, glutinous rice starch: 7 kg, fibrillated whey protein solution: 100 kg (protein content 8%), strains: 0.03 kg (YS-242: 0.02 kg; MN-ZLW-002: 0.01 kg).

[0071] For the above method for preparing room-temperature yogurt, the milk base is subjected to first-stage fermentation, second-stage fermentation, third-stage fermentation, demulsification, dual-frequency ultrasonic treatment, cooling, aseptic filling, and ultra-high pressure treatment. Specifically: The milk base is cooled to 38°C, and strains are added and fermented in a fermentation tank. After starting fermentation for 90 min (first-stage fermentation), low-frequency ultrasonic treatment is applied, with an ultrasonic frequency of 20 kHz, an ultrasonic power of 150 W, and a treatment time of 20 min (second-stage fermentation). Fermentation continues at 38°C (third-stage fermentation). When the fermentation acidity reaches 75°T, demulsification and stirring are carried out for 1 min, with a stirring speed of 25 r / min. After the stirring is completed, dual-frequency ultrasonic treatment is applied, with ultrasonic frequencies of 15 kHz and 45 kHz, an ultrasonic power of 600 W, and a treatment time of 5 min. Then, it is quickly cooled to below 10°C for aseptic filling. The filled yogurt samples are subjected to ultra-high pressure treatment at a pressure of 300 Mpa and a pressure holding time of 5 min.

[0072] Among them, the method for preparing the above milk base in this embodiment includes the following steps:

[0073] (1) Pretreatment of raw milk: Raw milk is filtered through a primary filter with a pore size of 1.0 mm and a secondary filter with a pore size of 0.5 mm, preheated to 55°C for separation and sterilization, then homogenized, with a primary homogenization pressure of 180 bar and a secondary pressure of 50 bar. Then, it is heated to 75°C for pasteurization for 15 s and cooled to 4°C.

[0074] (2) Fibrillation of whey protein: Water is heated to 45°C, the shear mixing pump is turned on, and whey protein powder is added to prepare a protein solution with a protein content of 8%. Stirring is continued for 15 min, and then static hydration is carried out for 30 min and cooled to 4°C. Then, stirring is started and citric acid is added to adjust the pH of the protein solution to 5.5, heated to 90°C, and kept warm for 80 s. Then, while cooling, stirring is started and shear dispersion is carried out at a speed of 350 rpm. The liquid material is cooled to 4°C, and sodium tripolyphosphate is added to adjust the pH of the solution to 6.7 to obtain a fibrillated whey protein solution.

[0075] (3) Ingredients: The raw milk after being processed in step (1) is heated to 45°C, the shearing and mixing pump is turned on, and white granulated sugar, sucralose, corn starch, glutinous rice starch, and fibrillated whey protein solution are sequentially added through an efficient online mixer. After the feeding is completed, the shearing pump is turned off, circulated for 5 minutes, and continuously stirred for 15 minutes at a stirring speed of 40 r / min. The homogenization temperature is 60°C, the primary homogenization pressure is 150 bar, and the secondary homogenization pressure is 30 bar. Then, ultra-high temperature sterilization is carried out at a sterilization temperature of 121 ± 1°C for 8 s to obtain the milk base material.

[0076] Example 4

[0077] This example provides a method for preparing room-temperature yogurt, and the raw materials are as follows: raw milk: 849.92 kg, white granulated sugar: 40 kg, sucralose: 0.05 kg, corn starch: 3 kg, glutinous rice starch: 7 kg, fibrillated whey protein solution: 100 kg (protein content 8%), bacterial strains: 0.03 kg (PYS-V141: 0.02 kg; MN-ZLW-002: 0.01 kg).

[0078] For the above method for preparing room-temperature yogurt, the milk base material is subjected to the first-stage fermentation, second-stage fermentation, third-stage fermentation, demulsification, dual-frequency ultrasonic treatment, cooling, aseptic filling, and ultra-high pressure treatment. Specifically: The milk base material is cooled to 39°C, the bacterial strains are added, and fermentation is carried out in a fermentation tank. After starting fermentation for 90 minutes (the first-stage fermentation), low-frequency ultrasonic treatment is applied, the ultrasonic frequency is 20 kHz, the ultrasonic power is 150 W, and the treatment time is 15 minutes (the second-stage fermentation). Fermentation continues at 38°C (the third-stage fermentation). When the fermentation acidity reaches 75°T, demulsification and stirring are carried out for 1 minute at a stirring speed of 25 r / min. After the stirring is completed, dual-frequency ultrasonic treatment is applied, the ultrasonic frequencies are 20 kHz and 50 kHz, the ultrasonic power is 600 W, and the treatment time is 5 minutes. Then, it is quickly cooled to below 10°C for aseptic filling. The filled yogurt samples are subjected to ultra-high pressure treatment at a pressure of 300 Mpa for 5 minutes.

[0079] Among them, the method for preparing the above milk base material in this example includes the following steps:

[0080] (1) Pretreatment of raw milk: The raw milk is filtered through a primary filter with a pore size of 1.0 mm and a secondary filter with a pore size of 0.5 mm, preheated to 55°C for separation and sterilization, then homogenized, with a primary homogenization pressure of 180 bar and a secondary pressure of 50 bar, and then heated to 75°C for pasteurization for 15 s and cooled to 4°C.

[0081] (2) Whey protein fibrillation: The water was heated to 45°C, the shear mixing pump was turned on, whey protein powder was added, and a protein solution with a protein content of 8% was prepared. The mixture was stirred for 17 minutes, allowed to stand for hydration for 30 minutes, and cooled to 4°C. Then, stirring was turned on and citric acid was added to adjust the pH of the protein solution to 4.7. The mixture was heated to 85°C and kept warm for 80 seconds. Then, stirring was turned on while the mixture was cooled and sheared and dispersed at a speed of 350 rpm. The mixture was cooled to 4°C, and sodium tripolyphosphate was added to adjust the pH of the solution to 6.7 to obtain a fibrillated whey protein solution.

[0082] (3) Ingredients: The raw milk treated in step (1) is heated to 45°C, the shear mixer pump is turned on, and white sugar, sucralose, corn starch, glutinous rice starch, and fibrous whey protein solution are added in sequence through a high-efficiency online mixer. After the feeding is completed, the shear pump is turned off, the mixture is circulated for 5 minutes, and stirring is continued for 15 minutes at a stirring speed of 40 r / min. The homogenization temperature is 60°C, the first-level homogenization pressure is 150 bar, and the second-level homogenization pressure is 30 bar. After that, ultra-high temperature sterilization is performed at a sterilization temperature of 121±1°C for 6 seconds to obtain a milk-based material.

[0083] Example 5

[0084] The present embodiment provides a method for preparing room temperature yogurt, the raw materials are as follows: raw milk: 849.9 kg, white sugar: 40 kg, sucralose: 0.05 kg, cassava starch: 10 kg, fibrous whey protein solution: 100 kg (protein content 8%), bacterial strain: 0.05 kg (PYS-V141: 0.03 kg; MN-ZLW-002: 0.02 kg).

[0085] The preparation method of the above-mentioned room temperature yogurt is to perform the first stage fermentation, the second stage fermentation, the third stage fermentation, demulsification, dual-frequency ultrasonic treatment, cooling, aseptic filling and ultra-high pressure treatment on the milk base material, specifically: the milk base material is cooled to 40°C, the bacteria are added, and fermented in a fermentation tank. After starting the fermentation for 90 minutes (first stage fermentation), low-frequency ultrasonic treatment is applied, the ultrasonic frequency is 20kHz, the ultrasonic power is 150W, and the treatment time is 15min (second stage fermentation). Fermentation is continued at 38°C (third stage fermentation). When the fermented milk acidity reaches 75°T, the demulsification is stirred for 1min, the stirring speed is 30r / min, and after the stirring is completed, dual-frequency ultrasonic treatment is applied, the ultrasonic frequency is 20kHz and 50kHz, the ultrasonic power is 800W, and the treatment time is 3min, and then it is quickly cooled to below 10°C and aseptic filling is performed. The yogurt sample after filling is subjected to ultra-high pressure treatment, the pressure is 400Mpa, and the pressure is maintained for 3min.

[0086] The method for preparing the milk-based material in this embodiment comprises the following steps:

[0087] (1)Raw milk pretreatment: Raw cow milk is filtered through a primary filter with a pore size of 1.0 mm and a secondary filter with a pore size of 0.5 mm, preheated to 55 °C for separation and sterilization, then homogenized. The primary homogenization pressure is 180 bar and the secondary pressure is 50 bar. Then it is heated to 75 °C for pasteurization for 15 s and cooled to 4 °C.

[0088] (2)Whey protein fibrillation: Water is heated to 45 °C, the shear mixing pump is turned on, and whey protein powder is added to prepare a protein solution with a protein content of 8%. Stir continuously for 17 min, let it stand for hydration for 30 min, and cool to 4 °C. Then turn on the stirrer and add citric acid to adjust the pH of the protein solution to 4.7. Heat it to 85 °C and keep it warm for 80 s. Then start stirring while cooling and perform shear dispersion at a speed of 350 rpm. The liquid material is cooled to 4 °C, and sodium tripolyphosphate is added to adjust the pH of the solution to 6.7 to obtain the fibrillated whey protein liquid.

[0089] (3)Formulation: The raw cow milk treated in step (1) is heated to 45 °C, the shear mixing pump is turned on, and sucrose, sucralose, tapioca starch, and fibrillated whey protein liquid are added sequentially through a high-efficiency online mixer. After the feeding is completed, the shear pump is turned off, and it is circulated for 5 minutes and then stirred continuously for 15 min at a stirring speed of 40 r / min. The homogenization temperature is 60 °C, the primary homogenization pressure is 150 bar, and the secondary homogenization pressure is 30 bar. Then ultra-high temperature sterilization is carried out at a sterilization temperature of 121 ± 1 °C for 8 s to obtain the milk-based material.

[0090] Example 6

[0091] This example provides a method for preparing room-temperature yogurt, which is basically the same as Example 1, except that the pressure and time of ultra-high pressure treatment are different. In this example, the pressure of ultra-high pressure treatment is 200 Mpa and the holding time is 10 min.

[0092] Example 7

[0093] This example provides a method for preparing room-temperature yogurt, which is basically the same as Example 1, except that the ultrasonic treatment conditions in the second-stage fermentation are different. In this example, the ultrasonic frequency is 25 kHz, the ultrasonic power is 200 W, and the treatment time is 20 min.

[0094] Example 8

[0095] This example provides a method for preparing room-temperature yogurt, which is basically the same as Example 3, except that the protein content in the protein solution prepared during the whey protein fibrillation process is different. In this example, a protein solution with a protein content of 7% is prepared.

[0096] Example 9

[0097] This example provides a method for preparing room-temperature yogurt, which is basically the same as Example 1, except that the protein content in the protein solution prepared during the whey protein fibrosis process is different. In this example, a protein solution with a protein content of 13% is prepared.

[0098] Comparative Example 1

[0099] This comparative example provides a method for preparing room-temperature yogurt, which is basically the same as Example 1, except that the dual-frequency ultrasonic treatment is omitted, and instead, it is directly cooled, aseptically filled, and ultra-high pressure treated after demulsification. Specifically: Cool the milk base to 38 °C, add the strain, and ferment in a fermenter. After starting fermentation for 90 min, apply low-frequency ultrasonic treatment with an ultrasonic frequency of 20 kHz, an ultrasonic power of 150 W, and a treatment time of 20 min. When the fermentation acidity reaches 75 °T, demulsify and stir for 1 min at a stirring speed of 25 r / min, then quickly cool to below 10 °C and perform aseptic filling. Ultra-high pressure treat the filled yogurt sample at a pressure of 300 Mpa for 5 min.

[0100] Comparative Example 2

[0101] This comparative example provides a method for preparing room-temperature yogurt, which is basically the same as Example 1, except that the ultra-high pressure treatment is omitted.

[0102] Comparative Example 3

[0103] This comparative example provides a method for preparing room-temperature yogurt, which is basically the same as Example 1, except that the pressure and time of the ultra-high pressure treatment are different. In this comparative example, the pressure of the ultra-high pressure treatment is 500 Mpa and the holding time is 2 min.

[0104] Comparative Example 4

[0105] This comparative example provides a method for preparing room-temperature yogurt, which is basically the same as Example 1, except that the pressure and time of the ultra-high pressure treatment are different. In this comparative example, the pressure of the ultra-high pressure treatment is 100 Mpa and the holding time is 15 min.

[0106] Comparative Example 5

[0107] This comparative example provides a method for preparing room-temperature yogurt, which is basically the same as Example 1, except that single-frequency ultrasonic treatment is used instead of dual-frequency ultrasonic treatment. The ultrasonic frequency of the single-frequency ultrasonic treatment is 50 kHz, the ultrasonic power is 600 W, and the treatment time is 5 min.

[0108] Comparative Example 6

[0109] This comparative example provides a method for preparing room-temperature yogurt, which is basically the same as that of Example 1, except that single-frequency ultrasonic treatment is used instead of dual-frequency ultrasonic treatment. The ultrasonic frequency of the single-frequency ultrasonic treatment is 70 kHz, the ultrasonic power is 600 W, and the treatment time is 10 min.

[0110] Comparative Example 7

[0111] This comparative example provides a method for preparing room-temperature yogurt, which is basically the same as that of Example 1, except that pasteurization is used instead of dual-frequency ultrasonic treatment, and the ultra-high pressure treatment is omitted at the same time. Specifically: the milk base material is cooled to 38 °C, the strain is added, and fermentation is carried out in a fermentation tank. After starting fermentation for 90 min, low-frequency ultrasonic treatment is applied, the ultrasonic frequency is 20 kHz, the ultrasonic power is 150 W, and the treatment time is 20 min. When the fermentation acidity reaches 75 °T, demulsification and stirring are carried out for 1 min, the stirring speed is 25 r / min, and after the stirring is completed, pasteurization is carried out, the sterilization temperature is 75 °C, the time is 25 seconds, and then it is quickly cooled to below 10 °C for aseptic filling. The filled yogurt sample is subjected to ultra-high pressure treatment, the pressure is 300 Mpa, and the pressure is maintained for 5 min.

[0112] Comparative Example 8

[0113] This comparative example provides a method for preparing room-temperature yogurt, which is basically the same as that of Example 1, except that the fermentation process is different. This comparative example includes a first-stage fermentation and a second-stage fermentation. Ultrasonic treatment is applied during the first-stage fermentation, while ultrasonic treatment is not applied during the second-stage fermentation. Specifically: the milk base material is cooled to 38 °C, the strain is added for fermentation, and low-frequency ultrasonic treatment is immediately applied, the ultrasonic frequency is 20 kHz, the ultrasonic power is 150 W, and the treatment time is 20 min (first-stage fermentation), and then the ultrasonic is turned off and fermentation continues (second-stage fermentation). When the fermentation acidity reaches 75 °T, demulsification is carried out.

[0114] Comparative Example 9

[0115] This comparative example provides a method for preparing room-temperature yogurt, which is basically the same as that of Example 1, except that ultrasonic treatment is not applied during the whole fermentation process. Specifically: the milk base material is cooled to 38 °C, the strain is added, and fermentation is carried out in a fermentation tank. When the fermentation acidity reaches 75 °T, demulsification is carried out.

[0116] Experimental Example 1

[0117] 1. Test the drawing properties of the room-temperature yogurt prepared by the methods of Examples 1-9 and Comparative Examples 3, 6-9.

[0118] For the drawing property test device, see Figure 1As shown, the yogurt drawing test device includes a liquid storage component 1, a camera component 2 and a computer 3. The liquid storage component 1 is suitable for storing yogurt samples, and the liquid storage component 1 is provided with a liquid outlet, which is used to discharge the yogurt sample stored in the liquid storage component 1 and enable it to form yogurt drawing. The liquid storage component 1 can be a funnel. The funnel is provided with a funnel piston for blocking or opening the liquid outlet. The camera component 2 is arranged on one side of the liquid storage component 1, and there is a certain distance between the camera component 2 and the yogurt drawing, so that the entire process of yogurt drawing can be photographed by the camera component 2, so that the camera component 2 can obtain the image information of the yogurt sample discharged by the liquid storage component 1. The computer 3 is electrically connected to the camera component 2, and is suitable for generating the time and length information of the yogurt sample flowing out from the liquid outlet to the formation of the drawing breakpoint according to the image information of the yogurt sample discharged by the liquid storage component 1, and the drawing performance of the yogurt is evaluated by the obtained breakpoint appearance time and initial drawing length. This application configures the openCV image processing system in computer 3 to perform algorithm processing and fitting on the collected image data, and can quickly identify the wire drawing breakpoint position and breakpoint time, and output them to the user through the computer, avoiding the risks of large system errors and strong subjectivity caused by relying entirely on human visual observation and manual operation, and quickly and scientifically giving experimental results, improving the accuracy of the data and meeting the application needs in the product development process.

[0119] Test method: Pour 50 mL of yogurt sample into the funnel of the equipment and let it stand for 3 minutes. After the sample structure is fully restored, open the funnel piston and turn on the camera device at the same time. At this time, the camera captures dynamic images of the yogurt filamentous structure flowing out of the funnel at a collection frequency of 150 times / s. When the yogurt sample in the funnel has flowed out, the photo test stops. The camera device automatically transmits the collected image information to the computer connected to the equipment. The image processing system openCV configured on the computer recognizes, processes, calculates and outputs the data values ​​of the fracture position (i.e., the drawing length) L (cm) and the fracture time T (s) when the yogurt sample is first drawn and broken. The results are shown in Table 1.

[0120] 2. Test the lactic acid bacteria content of the room temperature yogurts prepared by the methods of Examples 1-9 and Comparative Examples 1-6.

[0121] According to GB4789.35 National Food Safety Standard - Food Microbiology Test - Lactic Acid Bacteria Test Method, the number of thermophilic streptococci and lactobacilli were tested 72 hours after the product was offline. The results are shown in Table 2.

[0122] The results in Table 1 show that the wire drawing properties of the room temperature yogurt prepared by the methods of Comparative Examples 3 and 6-9 are significantly reduced. Among them, in Comparative Example 6, single-frequency ultrasonic treatment is used. Although increasing the intensity of ultrasonic sterilization treatment will improve the sterilization ability to a certain extent, it will seriously damage the wire drawing structure of the yogurt. The results in Table 2 show that Comparative Example 1 does not perform dual-frequency ultrasonic sterilization, and Comparative Example 2 does not perform ultra-high pressure sterilization, and the number of live bacteria retained is relatively large. Comparative Example 5 only performs single-frequency ultrasonic sterilization, and Comparative Example 6 increases the intensity of single-frequency ultrasonic sterilization, but lactic acid bacteria cannot be effectively inactivated. Comparative Example 4 reduces the ultra-high pressure sterilization pressure and prolongs the sterilization time, and there are still more lactic acid bacteria retained.

[0123] Table 1 Wire drawing performance test results

[0124]

[0125] Table 2 Lactic acid bacteria test results

[0126]

[0127] Compared with the comparative examples, the room temperature yogurt prepared in the embodiments of the present application can better balance the drawing performance and aseptic properties, especially the embodiments 1-5, 8 and 9 have better effects. Compared with embodiment 1, embodiment 6 reduces the ultra-high pressure sterilization treatment pressure and prolongs the treatment time, which will weaken the drawing effect to a certain extent. In embodiment 7, increasing the ultrasonic frequency and power in the second fermentation stage will reduce the extracellular polysaccharide yield and molecular weight to a certain extent, thereby reducing the drawing performance to a certain extent.

[0128] Experimental Example 2 Determination of the yield and molecular weight of crude polysaccharides in room temperature yogurt

[0129] 1. Determination of crude polysaccharide yield and molecular weight in room temperature yogurt

[0130] Heat the room temperature yogurt to 90℃ for 5 minutes, cool to 4℃, centrifuge at 8000r / min for 15min, and retain the supernatant. Add trichloroacetic acid to the supernatant to a final concentration of 5%, let stand at 4℃ overnight, centrifuge at 8000r / min for 15min, and retain the supernatant. Add 3 times the volume of 4℃ anhydrous ethanol to the supernatant, let stand at 4℃ overnight, centrifuge at 8000r / min for 15min, and retain the precipitate. Dissolve the precipitate in deionized water, put it into a 8000~12000Da dialysis bag and dialyze it for 48h. The dialysis medium is water, and the water is changed every 12h. After dialysis, evaporate and concentrate, and freeze-dry to obtain crude polysaccharide.

[0131] Crude polysaccharide yield = freeze-dried crude polysaccharide weight / yogurt weight.

[0132] 2. Determination of polysaccharide molecular weight

[0133] The crude polysaccharide was formulated into a 5 mg / mL sugar solution with distilled water, filtered through a 0.45 μm water-based filter membrane, and then subjected to Sepharose CL-6B gel column chromatography. The sample loading volume was 4 mL, and it was eluted at a constant speed with 0.05 mol / L NaCl. The elution rate was 0.8 mL / min, and 8 mL fractions were collected in each tube. The polysaccharide content of each tube was detected (determined by the phenol-sulfuric acid method at A490 nm). The peak tubes were collected according to the detected polysaccharide content values, placed in a dialysis bag with a molecular weight cut-off of 8000 - 12000 Da, and dialyzed for 48 h, with the water changed every 12 h. After dialysis, it was evaporated and concentrated, and then freeze-dried to obtain the purified polysaccharide. The molecular weight of the purified polysaccharide was detected using gel permeation chromatography combined with multi-angle laser light scattering (GPC / MALLS). The results are shown in Table 3.

[0134] Table 3 Test results of the yield of crude polysaccharide and the molecular weight of polysaccharide in yogurt

[0135]

[0136] After inoculation in Examples 1 - 7 to initiate the first-stage fermentation (fermentation for 80 - 100 min), that is, when the lactic acid bacteria began to enter the logarithmic growth phase, low-frequency ultrasonic treatment was applied. In Comparative Example 8, low-frequency ultrasonic treatment was carried out immediately after inoculation, and in Comparative Example 9, no ultrasonic treatment was applied during the fermentation stage. The extracellular polysaccharide yields in Examples 1 - 7 were much higher than those in Comparative Example 8 and Comparative Example 9, proving that the fermentation regulation technology of this patent can effectively enrich the extracellular polysaccharide of lactic acid bacteria and promote the synthesis of longer-chain polysaccharides with larger molecular weights. In Example 7, higher-frequency and higher-power ultrasonic parameters were used for fermentation regulation, and the polysaccharide content was enriched to a certain extent, but the molecular weight of the polysaccharide was lower than that in Examples 1 - 6, indicating that further increasing the intensity of ultrasonic treatment is not conducive to the synthesis of longer-chain polysaccharides. In Comparative Example 7, although it had a higher crude polysaccharide content, due to the influence of heat sterilization after fermentation, the polysaccharide molecular chain was broken and the molecular weight decreased, resulting in the loss of the drawability of the product.

[0137] Experimental Example 3 Evaluation of the stability of fermented milk and observation of the shelf life

[0138] The centrifugal water loss rate of the room-temperature yogurt prepared by the methods of Examples 1 - 9 and Comparative Examples 3 and 6 was measured. The specific method was as follows: The room-temperature sodium alginate was centrifuged at 4000 r / min for 15 min, and the mass of the product before and after the test was measured. The centrifugal water loss rate was calculated by the formula:

[0139]

[0140] The room-temperature yogurt prepared by the methods of Examples 1 - 9 and Comparative Examples 3 and 6 was stored at room temperature for 5 months. The state of the product was observed. The results are shown in Table 4.

[0141] Table 4 Stability results of yogurt products

[0142]

[0143] The results show that, compared with Comparative Examples 3 and 6, the stability of the products of Examples 1-9 of the present invention is significantly improved. Among them, the centrifugal water loss rate of the products of Examples 1-5 is lower than 3.5%. After storage at room temperature for 5 months, the product system is stable, no water separation or local thinning is observed, and the tissue state is uniform. In Example 6, the ultra-high pressure treatment time was extended, and the gel shrank under force, resulting in some water floating out of the network structure, and slight water separation occurred during storage for 5 months. In Example 7, the extracellular polysaccharide yield was low and the polysaccharide molecular weight was low, and the product system showed slight water separation, and slight water separation occurred during storage for 5 months. In Example 9, the process parameters for preparing fibrillar whey protein were not within the preferred range of this patent. The prepared protein had a high degree of cross-linking and partial gelation, and could not be evenly dispersed, resulting in an uneven tissue state of the product. Since the fibrillar protein did not fully participate in the formation of the yogurt gel structure, it could not play a role in stabilizing the texture, resulting in water separation during the shelf life of the product. In Comparative Example 6, the single-frequency ultrasonic sterilization frequency was increased, which damaged the gel structure to a certain extent, resulting in a decrease in water holding capacity and inducing non-enzymatic browning, resulting in product discoloration. The present invention provides a method for preparing room-temperature yogurt that can enhance the stretching effect of yogurt, ensure sterility and maintain good stability during storage at room temperature. This method does not add raw materials with stretching properties, and the stretching texture can be produced by lactic acid bacteria fermentation, and it can ensure that the stretching texture is not damaged during the processing. By modifying the structure of whey protein to play a thickening and stabilizing effect, the stability of the system within the shelf life of room-temperature yogurt can be achieved without adding hydrocolloids, achieving the effect of reducing ingredients.

[0144] Obviously, the above examples are only for clear illustration and not a limitation of the implementation manners. For those of ordinary skill in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to enumerate all the implementation manners here. And the obvious changes or modifications derived therefrom are still within the protection scope of the present invention.

Claims

1. A method for preparing room temperature yogurt, characterized in that: The method comprises the following steps: fermenting and demulsifying a milk-based material, subjecting the milk-based material to dual-frequency ultrasonic treatment, and then subjecting the milk-based material to ultra-high pressure treatment at a pressure of 200-400 MPa for 3-10 minutes to obtain room temperature yogurt, wherein the fermentation comprises a first stage fermentation, a second stage fermentation and a third stage fermentation in sequence, wherein the first ultrasonic treatment is applied during the second stage fermentation; in terms of weight parts, the milk-based material comprises 810-870 parts by weight of milk raw material, 30-75 parts by weight of sweetener, 10-15 parts by weight of stabilizer, 6-8 parts by weight of protein, and 40-100 parts by weight of water; the ultrasonic frequency of the dual-frequency ultrasonic treatment comprises a first ultrasonic frequency of 15-25 kHz and a second ultrasonic frequency of 45-55 kHz; the ultrasonic time is 3-5 minutes; the ultrasonic power is 600-800 W; and the source of the protein comprises fibrotic whey protein.

2. The method for preparing room temperature yogurt according to claim 1, characterized in that: The fermentation time of the first stage is 80-100 min; and / or, the ultrasonic frequency of the first ultrasonic treatment is 15-25 kHz, the ultrasonic power is 100-200 W, and the ultrasonic time is 15-25 min.

3. The method for preparing room temperature yogurt according to claim 1, characterized in that: The fermentation bacteria used in the fermentation include a combination of one or more of YO-MIX883 fermentation agent, FD-DVS Yoflex®Premium 5.0 fermentation agent, YS-242 fermentation agent, PYS-V141 fermentation agent and Streptococcus salivarius; and / or, the mass ratio of the fermentation bacteria used in the fermentation to the milk base material is 0.03-0.05:900-1100; and / or, the fermentation endpoint of the third stage fermentation is that the acidity reaches 70~80°T; and / or, the stirring speed during the demulsification process is 25~30r / min, and the time is 3~5min.

4. The method for preparing room temperature yogurt according to any one of claims 1 to 3, characterized in that: The preparation method of the milk-based material comprises mixing milk raw materials, a sweetener, a stabilizer and a fibrotic whey protein solution, homogenizing, and sterilizing to obtain the milk-based material. The preparation method of the fibrotic whey protein solution comprises: Step S1: dispersing whey protein in water to prepare a protein solution; Step S2: adjusting the pH of the protein solution obtained in step S1 to 4.2-5.5 with an acidity regulator, heating, and cooling under stirring to obtain a mixed solution; Step S3: adjusting the pH of the mixed solution obtained in step S2 to 6.5-7.0 with an acidity regulator to obtain a fibrotic whey protein solution.

5. The method for preparing room temperature yogurt according to claim 1, characterized in that: The milk raw material includes raw cow's milk or reconstituted milk with whole milk powder; and / or the sweetener includes one or more of white sugar, fructose, glucose, xylitol, erythritol, steviol glycoside, sucralose, isomaltooligosaccharide, fructooligosaccharide, xylo-oligosaccharide, galacto-oligosaccharide, and trehalose; and / or the stabilizer includes one or more of corn starch, tapioca starch, and glutinous rice starch.

6. The method for preparing room temperature yogurt according to claim 4, characterized in that: The preparation method also satisfies one or more of the following AC: A. The homogenization temperature is 58-62°C. The homogenization includes primary homogenization and secondary homogenization. The primary homogenization pressure is 130-150 bar, and the secondary homogenization pressure is 30-40 bar. B. The sterilization temperature is 120-122°C and the time is 6-8s; C. The milk raw materials also include the steps of filtering, homogenizing and sterilizing before being mixed to prepare the milk base.

7. The method for preparing room temperature yogurt according to claim 4, characterized in that: In step S1, the protein content in the protein solution is 7-13%.

8. The method for preparing room temperature yogurt according to claim 4, characterized in that: In step S2, the heating treatment temperature is 83-90°C for 50-100s; and / or the stirring speed is 350-400rpm, and the temperature is lowered to 1-7°C.

9. A room temperature yogurt obtained by the preparation method according to any one of claims 1 to 8.

Images