Normal-temperature yoghourt and preparation method thereof

Abstract

The invention relates to the technical field of normal-temperature yoghurt, in particular to normal-temperature yoghurt and a preparation method thereof. By combining double-frequency ultrasonic treatment and ultrahigh pressure treatment and applying ultrasonic treatment in the second-stage fermentation process between the first-stage fermentation and the third-stage fermentation, the drawing characteristic of the yoghourt can be greatly improved on the basis of maintaining relatively low bacterial count and even sterility of the yoghourt; the yogurt can be stored at normal temperature and has a good wire drawing effect. Excessive high-pressure treatment pressure or too long treatment time can cause damage to the structure of the yogurt and incapability of drawing the yogurt, and too low high-pressure treatment pressure and too short treatment time can cause excessive lactic acid content of the yogurt, so that the yogurt cannot be stored at normal temperature and only can be stored at low temperature. According to the invention, the pressure and time of the ultrahigh pressure treatment are controlled within the range, so that a good wire drawing effect is obtained, and the low bacterial count and even sterility of the yoghourt are maintained.

Description

Technical Field

[0001] The invention relates to the technical field of room-temperature yogurt, and in particular to room-temperature yogurt and a preparation method thereof. Background Art

[0002] As consumers' health awareness continues to improve, the market demand for high-quality, natural and functional dairy products is growing. Traditional dairy processing technology can no longer meet consumers' diverse pursuits for taste, nutrition and health. There is an urgent need to accelerate the pace of process technology innovation.

[0003] With its unique taste, healthy image, high-end market positioning and communication advantages on social media, stringy yogurt has successfully attracted the favor of a large number of consumers. The reason why yogurt has a stringy texture is that the protein and polysaccharide form a tighter cross-linking during the fermentation process. However, most of the current stringy yogurt is low-temperature yogurt, because the preparation process of room-temperature yogurt will destroy the stringy characteristics, resulting in the loss of the stringy effect. Summary of the invention

[0004] To this end, the present invention aims to solve the defect that the preparation process of room temperature yogurt in the prior art destroys the wire drawing properties and causes the yogurt to lose the wire drawing effect, and further provides a room temperature yogurt and a preparation method thereof.

[0005] In order to solve the above technical problems, the technical solution adopted by the present invention is as follows: The present application provides a method for preparing room temperature yogurt, comprising fermenting and demulsifying a milk base material, subjecting the milk base material to dual-frequency ultrasonic treatment, and then subjecting the milk base 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 sequentially comprises a first stage fermentation, a second stage fermentation, and a third stage fermentation, wherein the first ultrasonic treatment is applied during the second stage fermentation.

[0006] Furthermore, the pressure of the ultra-high pressure sterilization treatment is 300~400Mpa, and the time is 3~8min.

[0007] Furthermore, the ultrasonic frequency of the dual-frequency ultrasonic treatment includes a first ultrasonic frequency of 15-25 kHz and a second ultrasonic frequency of 45-55 kHz; the ultrasonic time is 3-5 min; and the ultrasonic power is 600-800 W.

[0008] Furthermore, the steps of cooling and / or aseptic filling are included between the dual-frequency ultrasonic treatment and the ultrahigh pressure treatment.

[0009] Furthermore, the emulsion is broken by stirring.

[0010] Furthermore, 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.

[0011] Furthermore, the fermentation time of the second stage is the same as the ultrasonic treatment time of the first stage, that is, the first ultrasonic treatment is performed throughout the fermentation of the second stage.

[0012] Furthermore, the first stage fermentation and the third stage fermentation were not subjected to ultrasonic treatment.

[0013] In certain preferred embodiments, the first ultrasonic treatment has an ultrasonic frequency of 18-22 kHz, an ultrasonic power of 120-180 W, and an ultrasonic time of 15-25 min.

[0014] Furthermore, fermentation bacteria are added to the milk base to initiate the first stage of fermentation.

[0015] Furthermore, the fermentation bacteria used in the fermentation include one or more of YO-MIX883 fermentation agent (Danisco fermentation agent), FD-DVS Yoflex®Premium 5.0 fermentation agent (Chr. Hansen fermentation agent), YS-242 fermentation agent (DSM fermentation agent), PYS-V141 fermentation agent (Kentuo Hengtong fermentation agent) and a combination of Streptococcus salivarius; and / or, the mass ratio of the fermentation bacteria used in the fermentation to the milk base 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.

[0016] Furthermore, the Streptococcus salivarius cells use Streptococcus salivarius thermophilic subspecies, such as Streptococcus salivarius thermophilic subspecies MN-ZLW-002, with a preservation number of CGMCC No. 3817.

[0017] Furthermore, the fermentation temperature of the first stage fermentation, the second stage fermentation and the third stage fermentation is 38-40°C.

[0018] Furthermore, in terms of weight parts, the milk base comprises 810-870 weight parts of milk raw material, 30-75 weight parts of sweetener, 10-15 weight parts of stabilizer, 6-8 weight parts of protein in the protein raw material, and 40-100 weight parts of water; and / or, the preparation method of the milk base comprises mixing the milk raw material, sweetener, stabilizer and protein, homogenizing and sterilizing to obtain the milk base.

[0019] Furthermore, the preparation method also satisfies one or more of the following AE: 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 material includes raw cow milk or whole milk powder reconstituted milk; 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; and / or, the source of the protein includes one or more of whey protein and fibrous whey protein; D. The milk raw materials further include the steps of filtering, homogenizing and sterilizing before being mixed to prepare the milk base; E. The protein also includes a step of fiberization before mixing to prepare the milk base.

[0020] The added amount of the sweetener in the yogurt product of the present invention complies with the standard provisions of GB2760-2014.

[0021] Further, when the source of the protein is fibrotic whey protein, a fibrotic whey protein solution with a protein content of 7 to 13% (especially a fibrotic whey protein solution with a protein content of 8 to 12%) can be used to mix with milk raw materials, sweeteners, and stabilizers, and the milk base material is obtained after homogenization and sterilization. Fibrotic whey protein solution is prepared by fibrotic treatment of a protein solution formed by dispersing whey protein powder in water as a raw material. The protein content of the prepared protein solution remains unchanged after fibrotic treatment, but the protein structure and properties change, that is, the protein content in the protein solution is the same as the protein content of the prepared fibrotic whey protein solution. Fibrotic whey protein solution can be prepared by fibrotic treatment of a protein solution with a protein content of 7 to 13%. The prepared protein solution can be prepared using commercially available conventional whey protein powder, such as whey protein powder with a protein content of >55%, and specifically, whey protein powder with a protein content of 56%-65% can be used.

[0022] In the present application, the protein content in a product or raw material refers to the mass percentage of the protein in the product or raw material.

[0023] Furthermore, the milk base material is mixed for 10-15 minutes, and the mixing speed is 35-45 r / min.

[0024] Furthermore, the milk raw materials further include the steps of filtering, homogenizing, and sterilizing before mixing to prepare the milk base. For example, the homogenization temperature 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 sterilization temperature is 73-78°C, and the sterilization time is 15-20 seconds.

[0025] Furthermore, the protein also includes a step of fiberization before mixing to prepare the milk base.

[0026] Furthermore, the fibrosis treatment includes: 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.

[0027] Furthermore, in step S1, the protein content in the protein solution is 7-13%.

[0028] Furthermore, in step S1, the protein content in the protein solution is 8-12%.

[0029] Furthermore, in step S2, the temperature of the heating treatment is 83-90° C., and the time is 50-100 s.

[0030] Furthermore, the acidity regulator includes one or more of citric acid and sodium tripolyphosphate.

[0031] Furthermore, the dispersion process includes stirring and standing hydration steps, wherein the stirring time is 15-20 minutes, the standing hydration time is 25-35 minutes; and / or the stirring speed is 350-400 rpm, and the temperature is lowered to 1-7°C.

[0032] The present application also provides room temperature yogurt prepared by any of the above-mentioned preparation methods.

[0033] Compared with the prior art, the present invention has the following beneficial effects: (1) The study found that heat sterilization and high-intensity shearing after room temperature yogurt fermentation will destroy the cross-linking structure, resulting in a significant deterioration in the drawing effect. Adjusting the preparation process will result in the low bacterial count or aseptic properties of the yogurt being unable to be guaranteed, and the yogurt cannot be stored at room temperature. The preparation method of room temperature yogurt provided by the present invention comprises fermenting and demulsifying a milk base material, and then subjecting the milk base material to dual-frequency ultrasonic treatment and then subjecting the milk base 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 sequentially comprises a first stage fermentation, a second stage fermentation and a third stage fermentation, wherein the first ultrasonic treatment is applied during the second stage fermentation, and by combining the dual-frequency ultrasonic treatment with the ultra-high pressure treatment and applying the ultrasonic treatment during the second stage fermentation between the first stage fermentation and the third stage fermentation, the drawing properties of the yogurt can be greatly improved on the basis of maintaining a low bacterial count or even aseptic properties, so that the yogurt can be stored at room temperature and has a good drawing effect. If the ultra-high pressure treatment is too high or the treatment time is too long, the yogurt structure will be destroyed and cannot be drawn. If the ultra-high pressure treatment is too low or the treatment time is too short, the yogurt lactic acid content will be too high, which will make it impossible to store at room temperature and can only be stored at low temperature. The present application achieves a good drawing effect and maintains a low bacterial count or even aseptic yogurt by controlling the pressure and time of the ultra-high pressure treatment within the above range, and finally obtains room temperature yogurt. Ultrasonic treatment of the initially grown lactic acid bacteria after the first stage of fermentation can effectively enrich the lactic acid bacteria extracellular polysaccharides and promote the synthesis of long-chain polysaccharides with larger molecular weight, thereby improving the drawing effect of yogurt.

[0034] The current wire drawing yogurt usually needs to use a large amount of chemical stabilizers, resulting in high additive usage and other problems, which seriously affects the consumer experience and further upgrading of product quality, and the wire drawing effect is not excellent. The technical solution of the present application also avoids the addition of a large amount of chemical stabilizers.

[0035] (2) The method for preparing room temperature yogurt provided by the present invention can further improve the wire drawing effect of yogurt by controlling the pressure of ultra-high pressure treatment to 300-400 MPa and the time to 3-8 min, and the obtained yogurt is aseptic.

[0036] (3) In the method for preparing room temperature yogurt provided by the present invention, the ultrasonic frequency of the dual-frequency ultrasonic treatment includes a first ultrasonic frequency of 15-25 kHz and a second ultrasonic frequency of 45-55 kHz; the ultrasonic time is 3-5 min; and the ultrasonic power is 600-800 W. By controlling the first ultrasonic frequency and the second ultrasonic frequency, the ultrasonic time and the ultrasonic power within the above range can further improve the wire drawing effect of the yogurt, reduce the number of bacteria in the yogurt, stabilize the texture of the yogurt, and improve the shelf life stability of the yogurt.

[0037] (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.

[0038] (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.

[0039] (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

[0040] 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.

[0041] Figure 1 is a schematic diagram of the yogurt wire drawing test device used in Experimental Example 1; 1. Liquid storage component; 2. Camera component; 3. Computer. DETAILED DESCRIPTION

[0042] The technical solution of the present invention is described clearly and completely below. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0043] If the specific experimental steps or conditions are not specified in the embodiments, the operation or conditions of the conventional experimental steps described in the literature in this field can be carried out. The reagents or instruments used without indicating the manufacturer are all conventional reagent products that can be obtained commercially. The protein content in the fibrotic whey protein solution is a theoretical calculated value, protein content = (protein content in whey protein powder × amount of whey protein powder added) / (amount of whey protein powder added + amount of water); wherein the amount of whey protein powder added and the amount of water are the mass of whey protein powder and water added during the whey protein fibrillation process, respectively.

[0044] Example 1 The present embodiment provides a method for preparing room temperature yogurt, and the raw materials are as follows: raw milk: 869.97 kg, white sugar: 65 kg, corn starch: 4.5 kg, glutinous rice starch: 10.5 kg, fibrous whey protein liquid: 50 kg (protein content 12%), bacterial strain: 0.03 kg (YO-MIX883 starter: 0.02 kg; MN-ZLW-002: 0.01 kg).

[0045] The preparation method of the above-mentioned room temperature yogurt includes the following steps: 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: cooling the milk base material to 38°C, adding bacteria, and fermenting in a fermentation tank. After starting the fermentation for 90 minutes (first stage fermentation), low-frequency ultrasonic treatment is applied, with an ultrasonic frequency of 20kHz, an ultrasonic power of 150W, and a treatment time of 20 minutes (second stage fermentation). Continue fermentation at 38°C (third stage fermentation), and when the fermented milk acidity reaches 75°T, demulsification is stirred for 1 minute, with a stirring speed of 25r / min. After stirring, dual-frequency ultrasonic treatment is applied, with ultrasonic frequencies of 25kHz and 55kHz, an ultrasonic power of 600W, and a treatment time of 3 minutes, and then rapidly cooled to below 10°C for aseptic filling. The filled yogurt sample is subjected to ultra-high pressure treatment, with a pressure of 300Mpa and a pressure maintenance of 5 minutes.

[0046] The method for preparing the milk-based material in this embodiment comprises the following steps: (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.

[0047] (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.

[0048] (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.

[0049] Example 2 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).

[0050] 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 38°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 20min (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 25r / min, and after the stirring is completed, dual-frequency ultrasonic treatment is applied, the ultrasonic frequency is 20kHz and 50kHz, the ultrasonic power is 600W, and the treatment time is 5min, 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 300Mpa, and the pressure is maintained for 8min.

[0051] The method for preparing the milk-based material in this embodiment comprises the following steps: (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.

[0052] (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 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 solution was heated to 85°C and kept warm for 80 seconds. Then, stirring was turned on while the temperature was lowered and shear dispersion was performed at 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.

[0053] (3) Ingredients: The raw milk treated in step (1) is heated to 45°C, the shear mixer pump is turned on, and white sugar, erythritol, 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 and a time of 8 seconds to obtain a milk-based material.

[0054] Example 3 The present embodiment provides a method for preparing room temperature yogurt, wherein the raw materials are as follows: raw milk: 849.92 kg, white sugar: 40 kg, sucralose: 0.05 kg, corn starch: 3 kg, glutinous rice starch: 7 kg, fibrous whey protein solution: 100 kg (protein content 8%), bacterial strain: 0.03 kg (YS-242: 0.02 kg; MN-ZLW-002: 0.01 kg).

[0055] 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 38°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 20min (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, and the stirring speed is 25r / min. After the stirring is completed, dual-frequency ultrasonic treatment is applied, the ultrasonic frequency is 15kHz and 45kHz, the ultrasonic power is 600W, and the treatment time is 5min. 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 300Mpa, and the pressure is maintained for 5min.

[0056] The method for preparing the milk-based material in this embodiment comprises the following steps: (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.

[0057] (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 8%. The solution was stirred for 15 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 5.5. The solution was heated to 90°C and kept warm for 80 seconds. Then, stirring was turned on while cooling and shearing and dispersing was performed at a speed of 350 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.

[0058] (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 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.

[0059] Example 4 The present embodiment provides a method for preparing room temperature yogurt, wherein the raw materials are as follows: raw milk: 849.92 kg, white sugar: 40 kg, sucralose: 0.05 kg, corn starch: 3 kg, glutinous rice starch: 7 kg, fibrous whey protein solution: 100 kg (protein content 8%), bacterial strain: 0.03 kg (PYS-V141: 0.02 kg; MN-ZLW-002: 0.01 kg).

[0060] 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 39°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 25r / min, and after the stirring is completed, dual-frequency ultrasonic treatment is applied, the ultrasonic frequency is 20kHz and 50kHz, the ultrasonic power is 600W, and the treatment time is 5min, and then it is quickly cooled to below 10°C and aseptically filled. The yogurt sample after filling is subjected to ultra-high pressure treatment, the pressure is 300Mpa, and the pressure is maintained for 5min.

[0061] The method for preparing the milk-based material in this embodiment comprises the following steps: (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.

[0062] (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.

[0063] (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.

[0064] Example 5 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).

[0065] 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.

[0066] The method for preparing the milk-based material in this embodiment comprises the following steps: (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.

[0067] (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.

[0068] (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, tapioca 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. Ultra-high temperature sterilization is then performed at a sterilization temperature of 121±1°C for 8 seconds to obtain a milk-based material.

[0069] Example 6 This embodiment provides a method for preparing room temperature yogurt, which is basically the same as that of Embodiment 1, except that the pressure and time of the ultra-high pressure treatment are different. In this embodiment, the pressure of the ultra-high pressure treatment is 200 MPa, and the pressure holding time is 10 min.

[0070] Example 7 This embodiment provides a method for preparing room temperature yogurt, which is basically the same as that of Example 1, except that the ultrasonic treatment conditions of the second stage fermentation are different. In this embodiment, the ultrasonic frequency is 25 kHz, the ultrasonic power is 200 W, and the treatment time is 20 min.

[0071] Example 8 This embodiment provides a method for preparing room temperature yogurt, which is basically the same as that of Example 3, except that the protein content in the protein solution prepared during the whey protein fibrillation process is different. In this embodiment, a protein solution with a protein content of 7% is prepared.

[0072] Example 9 This embodiment provides a method for preparing room temperature yogurt, which is basically the same as that of Example 1, except that the protein content in the protein solution prepared during the whey protein fibrillation process is different. In this embodiment, a protein solution with a protein content of 13% is prepared.

[0073] Comparative Example 1 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 the emulsion is directly cooled, aseptically filled and treated with ultra-high pressure after demulsification. Specifically: the milk base is cooled to 38°C, the bacteria are added, and fermented in a fermentation tank. After starting the fermentation for 90 minutes, low-frequency ultrasonic treatment is applied, with an ultrasonic frequency of 20kHz, an ultrasonic power of 150W, and a treatment time of 20 minutes. When the acidity of the fermented milk reaches 75°T, the emulsion is stirred for 1 minute, and the stirring speed is 25r / min, and then it is quickly cooled to below 10°C and aseptically filled. The filled yogurt sample is subjected to ultra-high pressure treatment, with a pressure of 300Mpa and a pressure maintenance of 5 minutes.

[0074] Comparative Example 2 This comparative example provides a method for preparing room temperature yogurt, which is basically the same as that of Example 1, except that the ultrahigh pressure treatment is omitted.

[0075] Comparative Example 3 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 pressure holding time is 2 min.

[0076] Comparative Example 4 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 pressure holding time is 15 min.

[0077] Comparative Example 5 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.

[0078] Comparative Example 6 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 70 kHz, the ultrasonic power is 600 W, and the treatment time is 10 min.

[0079] Comparative Example 7 This comparative example provides a method for preparing room temperature yogurt, which is basically the same as Example 1, except that pasteurization is used instead of dual-frequency ultrasonic treatment, and ultra-high pressure treatment is omitted, specifically: the milk base is cooled to 38°C, the bacteria are added, and fermented in a fermenter. After starting the fermentation for 90 minutes, low-frequency ultrasonic treatment is applied, the ultrasonic frequency is 20kHz, the ultrasonic power is 150W, and the treatment time is 20min. When the acidity of the fermented milk reaches 75°T, the emulsion is stirred for 1min, and the stirring speed is 25r / min. 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 and aseptic filling is carried out. The filled yogurt sample is subjected to ultra-high pressure treatment, the pressure is 300Mpa, and the pressure is maintained for 5min.

[0080] Comparative Example 8 The present comparative example provides a method for preparing room temperature yogurt, which is basically the same as Example 1, except that the fermentation process is different. The present comparative example includes a first stage fermentation and a second stage fermentation. Ultrasonic treatment is applied during the first stage fermentation, but no ultrasonic treatment is applied during the second stage fermentation. Specifically, the milk base is cooled to 38°C, bacteria are added for fermentation, and low-frequency ultrasonic treatment is immediately applied, with an ultrasonic frequency of 20kHz, an ultrasonic power of 150W, and a treatment time of 20min (first stage fermentation), and then the ultrasound is turned off and the fermentation is continued (second stage fermentation), and the emulsion is broken when the acidity of the fermented lactic acid reaches 75°T.

[0081] Comparative Example 9 This comparative example provides a method for preparing room temperature yogurt, which is basically the same as Example 1, except that no ultrasonic treatment is applied during the entire fermentation process. Specifically, the milk base is cooled to 38°C, bacteria are added, and fermented in a fermentation tank. The fermented milk is demulsified when the acidity reaches 75°T.

[0082] Experimental Example 1 1. Test the wire drawing properties of room temperature yogurts prepared by the methods of Examples 1-9 and Comparative Examples 3 and 6-9.

[0083] Wire drawing performance 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.

[0084] 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.

[0085] 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.

[0086] 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.

[0087] 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.

[0088] Table 1 Wire drawing performance test results

[0089] Table 2 Lactic acid bacteria test results

[0090] 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.

[0091] Experimental Example 2 Determination of the yield and molecular weight of crude polysaccharides in room temperature yogurt 1. Determination of crude polysaccharide yield and molecular weight in room temperature yogurt 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.

[0092] Crude polysaccharide yield = freeze-dried crude polysaccharide weight / yogurt weight.

[0093] 2. Determination of polysaccharide molecular weight The crude polysaccharide was prepared into 5 mg / mL sugar solution with distilled water, filtered with a 0.45 μm water filter membrane, and then chromatographed on a Sepharose CL-6B gel column. The sample volume was 4 mL and eluted at a constant rate of 0.05 mol / L NaCl at a rate of 0.8 mL / min. 8 mL of each tube was collected, and the polysaccharide content was detected tube by tube (A490 nm was determined by the phenol-sulfuric acid method). The peak tube was collected according to the polysaccharide content detection value, and placed in an 8000-12000Da dialysis bag for 48 hours, with water changed every 12 hours. After dialysis, the purified polysaccharide was evaporated and concentrated, and freeze-dried to obtain the purified polysaccharide. The molecular weight of the purified polysaccharide was detected by gel permeation chromatography combined with multiangle laser light scattering (GPC / MALLS). The results are shown in Table 3.

[0094] Table 3 Test results of crude polysaccharide yield and polysaccharide molecular weight in yogurt

[0095] After the inoculation of Examples 1 to 7 to start the first stage of fermentation (fermentation 80-100min), low-frequency ultrasonic treatment was applied when the lactic acid bacteria began to enter the logarithmic growth phase. Comparative Example 8 was subjected to low-frequency ultrasonic treatment immediately after inoculation, and no ultrasonic treatment was applied during the fermentation stage of Comparative Example 9. The extracellular polysaccharide yield of Examples 1-7 is much higher than that of Comparative Examples 8 and 9, proving that the fermentation regulation technology of this patent can effectively enrich the extracellular polysaccharides of lactic acid bacteria and promote the synthesis of long-chain polysaccharides with larger molecular weight. In Example 7, the fermentation regulation uses higher frequency and higher power ultrasonic parameters, and the polysaccharide content is enriched to a certain extent, but the molecular weight of the polysaccharide is lower than that of Examples 1-6, proving that further increasing the intensity of ultrasonic treatment is not conducive to the synthesis of long-chain polysaccharides. Although Comparative Example 7 has a higher crude polysaccharide content, due to the influence of heat sterilization after fermentation, the molecular weight of the polysaccharide molecular chain is reduced, causing the product to lose its wire drawing properties.

[0096] Experimental Example 3 Evaluation of the stability of fermented milk and observation of its shelf life 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 tested. The specific method was as follows: the room temperature sodium syrup was placed at 4000r / min, centrifuged for 15min, and the quality of the product before and after was tested. The centrifugal water loss rate was calculated by the formula:

[0097] The room temperature yogurts prepared by the methods of Examples 1-9 and Comparative Examples 3 and 6 were stored at room temperature for 5 months. The product status was observed. The results are shown in Table 4.

[0098] Table 4 Stability results of yogurt products

[0099] The results show that compared with comparative examples 3 and 6, the stability of the products of Examples 1 to 9 of the present invention is significantly improved, among which the centrifugal water loss rate of the products of Examples 1 to 5 is less than 3.5%, and the product system is stable after being stored at room temperature for 5 months, without water separation and local thinning, and the tissue state is uniform. Example 6 prolongs the ultra-high pressure treatment time, and the gel shrinks under stress, causing some water to float out of the network structure, and slightly dehydrates after being stored for 5 months. Example 7 has a small yield of extracellular polysaccharides, a low molecular weight of polysaccharides, and a slight dehydration of the product system, which is slightly dehydrated after being stored for 5 months. Example 9 The process parameters for preparing fibrotic whey protein are not within the preferred range of this patent. The obtained protein has a high degree of cross-linking, and some gels cannot be evenly dispersed, resulting in uneven product tissue state. Because the fibrotic protein does not fully participate in the formation of the yogurt gel structure, it cannot play a role in stabilizing the texture, resulting in water separation during the shelf life of the product. Comparative Example 6 increases the frequency of single-frequency ultrasonic sterilization, destroys the gel structure to a certain extent, causes a decrease in water holding capacity, and induces non-enzymatic browning, causing the product to change color. The present invention provides a method for preparing room-temperature yogurt that can enhance the stringiness of yogurt, ensure aseptic properties, and maintain good stability during storage at room temperature. The method does not add raw materials with stringiness properties, but relies on lactic acid bacteria fermentation to produce stringiness texture, and can ensure that the stringiness texture is not destroyed during processing. By modifying the whey protein structure to exert thickening and stabilizing effects, the system stability of room-temperature yogurt during the shelf life can be achieved without adding hydrophilic colloids, thereby achieving the effect of reducing ingredients.

[0100] Obviously, the above embodiments are merely examples for the purpose of clear explanation, and are not intended to limit the implementation methods. For those skilled 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 list all the implementation methods here. The obvious changes or modifications derived therefrom are still within the scope of protection of the invention.

Claims

1. A method for preparing room temperature yogurt, characterized in that: The method comprises the steps of 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 sequentially comprises a first stage fermentation, a second stage fermentation and a third stage fermentation, wherein the first ultrasonic treatment is applied during the second stage fermentation.

2. The method for preparing room temperature yogurt according to claim 1, characterized in that: The ultrasonic frequency of the dual-frequency ultrasonic treatment includes a first ultrasonic frequency of 15-25 kHz and a second ultrasonic frequency of 45-55 kHz; the ultrasonic time is 3-5 minutes; and the ultrasonic power is 600-800W.

3. 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.

4. 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.

5. The method for preparing room temperature yogurt according to any one of claims 1 to 4, characterized in that: In terms of weight, the milk base comprises 810-870 weight parts of milk raw material, 30-75 weight parts of sweetener, 10-15 weight parts of stabilizer, 6-8 weight parts of protein in the protein raw material, and 40-100 weight parts of water; and / or, The method for preparing the milk base material comprises the steps of mixing milk raw materials, a sweetener, a stabilizer and protein, homogenizing and sterilizing the mixture to obtain the milk base material.

6. The method for preparing room temperature yogurt according to claim 5, characterized in that: The preparation method also satisfies one or more of the following AD: 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 material includes raw cow milk or whole milk powder reconstituted milk; 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; and / or, the source of the protein includes one or more of whey protein and fibrous whey protein; D. The milk raw materials further include the steps of filtering, homogenizing and sterilizing before being mixed to prepare the milk base; E. The protein also includes a step of fiberization before mixing to prepare the milk base.

7. The method for preparing room temperature yogurt according to claim 6, characterized in that: The fibrosis treatment 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.

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

9. The method for preparing room temperature yogurt according to claim 7, 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.

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

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