Yoghourt preparation method based on ultrahigh pressure sterilization technology

Abstract

The invention relates to the technical field of dairy product preparation, in particular to a yoghurt preparation method based on an ultrahigh pressure sterilization technology. The preparation method of the yoghourt provided by the invention comprises the following steps: burdening, fermenting and performing ultrahigh-pressure sterilization. The mass ratio of the fat content to the protein content is 1.2-1.8, and the mass ratio of the whey protein to the casein content is 0.25-0.4 in the mixed feed liquid obtained by burdening; the ultra-high pressure sterilization temperature is 4-15 DEG C, the pressure is 400-800 Mpa, and the treatment time is 4-7 min. According to the invention, by controlling the types, contents and proportions of protein and fat components in the feed liquid before fermentation and combining with an ultrahigh pressure sterilization process, the yoghourt with more sufficient reservation of nutritional ingredients, more stable product system and finer taste is provided.

Description

Technical Field

[0001] The present invention relates to the technical field of dairy product preparation, and particularly relates to a method for preparing yogurt based on ultra-high pressure sterilization technology. Background Art

[0002] Yogurt (fermented milk) is an acidic dairy product mainly made from cow's milk. After pasteurization, it is cooled to an appropriate temperature and then added with lactic acid bacteria for fermentation. Long-term consumption of yogurt can promote the absorption of phosphorus, calcium, and iron by the human body, maintain the balance of B vitamins, relieve lactose intolerance, reduce cholesterol, prevent the occurrence of cardiovascular and liver diseases, regulate the intestinal balance, and play a preventive role in constipation and bacterial diarrhea.

[0003] Consumers' demand for yogurt is not only due to the bacterial activity in yogurt and the bioavailability of the nutrients produced, but also the taste, flavor, texture, and appearance of yogurt are important factors. The sensory characteristics of yogurt are determined by many variables, such as milk composition, starter culture, production method, heat treatment, fermentation temperature, final fermentation pH value, cooling process, etc., as well as the precise sequence and duration of these steps.

[0004] Typical sensory characteristics of yogurt include: creamy / white, soft / smooth semi-solid structure, spreadable / spoonable colloidal network, and slightly acidic sour taste. The enrichment of milk proteins, high protein content, application of new technologies, processes and gel structures, and the interaction of structures can change the structure and sensory characteristics of yogurt.

[0005] Ultra-high pressure sterilization technology is a new type of non-thermal processing technology. By sealing food materials in elastic materials or placing them in a sterile pressure system, usually using water or other fluid media as the medium for transmitting pressure, after acting for a period of time under a pressure of 100 MPa - 1000 MPa, protein denaturation, starch gelatinization, enzyme inactivation, and bacteria and other microorganisms are killed, so as to meet the sterilization requirements. Ultra-high pressure does not break the covalent bonds of food components, thus reducing the loss of nutrients and the deterioration of color, aroma, and taste caused by high temperature.

[0006] During the production of room-temperature yogurt, usually after fermentation, pasteurization is required to kill lactic acid bacteria to prevent post-acidification during room-temperature storage and transportation, which affects the product quality. However, during the pasteurization of yogurt, due to a certain degree of heat treatment, it will cause protein aggregation, resulting in adverse experiences such as a powdery feeling and astringency (feeling fine particles in the mouth when tasting, like the feeling of putting flour or starch in the mouth, and even visible "particles" may appear). And ultra-high pressure sterilization, as a non-thermal sterilization technology, can better retain or even enhance the taste of the product. Therefore, ultra-high pressure sterilization technology is introduced into the post-fermentation sterilization link of room-temperature yogurt. However, ultra-high pressure sterilization technology has a great impact on the stability of yogurt products during the production process. Summary of the Invention

[0007] In the prior art of using ultra-high pressure sterilization technology to prepare yogurt, the ultra-high pressure technology is mainly used as a secondary sterilization process after fermentation and filling. However, after ultra-high pressure sterilization, some yogurt products will lose their delicate taste, and the viscosity and stability effects during the shelf life are poor. Therefore, most of the existing yogurt products overcome the defects in the taste and stability of yogurt caused by ultra-high pressure sterilization by adding stabilizers.

[0008] The present invention provides a method for preparing yogurt based on ultra-high pressure sterilization technology by controlling the types, contents, proportions of components such as protein and fat, and adopting a specific ultra-high pressure sterilization process, and obtains yogurt with more fully retained nutritional components, a more stable product system, and a more delicate taste.

[0009] In a first aspect, the present invention provides a method for preparing yogurt, including: batching, fermentation, and ultra-high pressure sterilization; in the mixed material liquid obtained by batching, the mass ratio of the total fat content to the total protein content is 1.2 - 1.8, and the mass ratio of the whey protein content to the casein content is 0.25 - 0.4; the temperature of the ultra-high pressure sterilization is 4 - 15°C, the pressure is 400 - 800 Mpa, and the treatment time is 4 - 7 min.

[0010] The stability of yogurt is mainly maintained by a gel network composed of protein, fat, stabilizers, etc. The types, contents, and proportions of protein and fat in the yogurt system have an important impact on the product quality and shelf life of yogurt. The present invention discovers that without external addition, by adjusting the proportions of total protein, total fat, and protein types in the liquid material before fermentation, the defects in taste and stability caused by ultra-high pressure sterilization can be overcome, and the optimal ultra-high pressure sterilization conditions in a yogurt system without external addition are provided.

[0011] Specifically, in the method for preparing yogurt provided by the present invention, the temperature of the ultra-high pressure sterilization is 4 - 10°C, and the pressure is 600 - 700 Mpa.

[0012] In the method for preparing yogurt provided by the present invention, the ultra-high pressure sterilization is a single treatment or multiple treatments; when the ultra-high pressure sterilization is a single treatment, the treatment time is 4 - 7 min; when the ultra-high pressure sterilization is multiple treatments, the treatment time for each treatment is 1 - 3 min.

[0013] In the method for preparing yogurt provided by the present invention, when the ultra-high pressure sterilization is a single treatment, the treatment time is 5 - 7 min.

[0014] In the yogurt preparation method provided by the present invention, the temperature of the ultra-high pressure sterilization is 4°C, and the pressure is 600 Mpa; when the ultra-high pressure sterilization is a single treatment, the treatment time is 5 min; or when the ultra-high pressure sterilization is two treatments, the treatment time for each treatment is 2 min.

[0015] In the yogurt preparation method provided by the present invention, the fermented milk after the fermentation is completed is filled and then ultra-high pressure sterilization is carried out.

[0016] In the yogurt preparation method provided by the present invention, no exogenous stabilizer or other additive is added. Only raw milk is used as the raw material, and the mass ratio of the total fat content to the total protein content in the mixed liquid is 1.2 - 1.8, and the mass ratio of the whey protein to the casein content is 0.25 - 0.4 through the ratio of the fat and protein components in the raw milk. The obtained yogurt product is a yogurt without additives, which better meets the needs of the yogurt market.

[0017] Specifically, in the yogurt preparation method provided by the present invention, the batching includes: using raw milk as the raw material, obtaining skim milk, casein concentrate, whey protein concentrate, permeate or cream for batching to obtain a mixed liquid;

[0018] The mixed liquid is preheated, degassed and homogenized, and then fermented.

[0019] More specifically, the batching includes:

[0020] (1) After the raw milk is clarified and sterilized, the fat is separated to obtain cream and skim milk, and the cream is sterilized for later use;

[0021] (2) The skim milk is microfiltered and sterilized, and a part of the obtained skim milk is reserved for later use;

[0022] (3) Another part of the skim milk obtained by microfiltration and sterilization is microfiltered and concentrated to obtain casein concentrate, whey protein concentrate and permeate;

[0023] (4) Using the skim milk, casein concentrate, whey protein concentrate, permeate or cream obtained in steps (2) - (3) for batching to obtain a mixed liquid.

[0024] When batching in the present invention, through the raw milk sterilization process and separation process, only raw milk is used as the raw material to control the ratio of protein and fat in the yogurt system. Combining with the ultra-high pressure sterilization technology, the flexibility of the product system is improved, the addition of stabilizers and sweeteners is avoided, the production cost is reduced, and the market demand is better met.

[0025] In the yogurt preparation method provided by the present invention, the starter used for fermentation includes: Lactobacillus bulgaricus and Streptococcus thermophilus; the addition amount of the starter is 1×10 6 -1×108 CFU / mL; the fermentation temperature is 35 - 45°C; the acidity value at the end of fermentation is 70 - 140°T, and the pH is controlled at 4.3 - 4.7.

[0026] In the yogurt preparation method provided by the present invention, the starter also includes: one or more of probiotics such as Lactobacillus casei, Lactobacillus acidophilus, Bifidobacterium, Lactobacillus plantarum, etc.;

[0027] The fermentation temperature is 37 - 42°C; the acidity at the end of fermentation is 80 - 100°T, and the pH is controlled at 4.5.

[0028] As a specific embodiment of the present invention, the yogurt preparation method provided by the present invention includes:

[0029] (1) Pass the raw milk through a milk clarifier at a separation temperature of 4 - 10°C to remove impurities contained in the milk.

[0030] (2) Pass the raw milk obtained in step (1) through a self - cleaning airtight double - effect sterilization separator at a separation temperature of 50 - 65°C, preferably 55°C; rotation speed 6000 - 7000 rpm, preferably 6500 rpm; time 30 - 40 s, preferably 35 s, to remove most bacteria and spores.

[0031] (3) Pass the raw milk obtained in step (2) through a fat separator to separate the fat to obtain cream and skim milk; the cream is sterilized, preferably by a coil sterilizer, at a sterilization temperature of 85 - 137°C, preferably 85°C; time is 2 - 15 s, preferably 15 s; and then enter the tank to be filled.

[0032] (4) Pass the skim milk obtained in step (3) through micro - filtration sterilization (0.6 - 1.2 μm, preferably 0.8 μm; 4 - 15°C, preferably 10°C), and part of it enters the tank to be filled.

[0033] (5) Pass another part of the skim milk obtained in step (4) through micro - filtration (0.1 μm, 4 - 15°C, preferably 10°C) to obtain a casein concentrate (retentate) and a whey protein solution.

[0034] (6) Pass the whey protein solution obtained in step (5) through ultra - filtration / reverse osmosis to obtain a whey protein concentrate (retentate) and a permeate.

[0035] (7) Mix the skim milk, casein concentrate, whey protein concentrate, permeate and / or cream obtained in the above steps to obtain a mixed liquid; the mass ratio of the fat content to the protein content in the mixed liquid is 1.2 - 1.8, and the mass ratio of the whey protein content to the casein content is 0.25 - 0.4.

[0036] (8) The obtained mixed material liquid is subjected to dynamic / static mixing, preheated (45 - 60 °C, preferably 50 °C), degassed (55 - 75 °C, preferably 65 °C; vacuum degree -0.4 to -0.7 bar, preferably -0.6 bar), and homogenized (55 - 75 °C, preferably 65 °C; primary pressure 130 - 220 bar, preferably 200 bar; secondary pressure 20 - 50 bar, preferably 25 bar); then fermentation is carried out.

[0037] Fermentation; the fermentation strains are Lactobacillus bulgaricus and Streptococcus thermophilus, and the addition amount of the ferment is 1×10 7 CFU / ml. The fermentation temperature is 40 °C. The fermentation duration is judged by the acidity value at the end of fermentation, which is 80 °T, and the pH value is controlled at 4.3 - 4.7.

[0038] (9) After fermentation is completed, demulsification (stirring for 15 min), cooling, addition of sterile jam and filling are carried out; the cooling temperature is 15 °C; PET prefabricated cups can be used for filling. The filling volume accounts for 95% of the packaging volume for filling.

[0039] (10) After filling, ultra-high pressure sterilization treatment is carried out. The temperature of the ultra-high pressure sterilization is 4 - 15 °C, preferably 4 - 10 °C; the pressure of the ultra-high pressure sterilization is 400 - 800 Mpa, preferably 600 - 700 Mpa, and the best is 600 Mpa.

[0040] The ultra-high pressure sterilization is single treatment and double treatment; when it is single treatment of ultra-high pressure, the time is 4 - 8 min, preferably 5 - 7 min, and the best is 5 min; when it is double treatment, the time is 1 - 3 min, preferably 2 min.

[0041] In the second aspect, the present invention provides a kind of yogurt prepared by the above preparation method. As described above, only raw milk is used as the raw material in the present invention, and no exogenous stabilizer or other additives are added. The yogurt prepared by the present invention is a yogurt without additives.

[0042] The beneficial effects of the present invention are as follows:

[0043] The present invention discovers that only by controlling the ratio of total protein to total fat in the liquid material before fermentation, the defects of yogurt taste and stability brought by ultra-high pressure sterilization can be overcome without exogenous addition, and the optimized ultra-high pressure sterilization conditions are provided under the yogurt system with the mass ratio of total fat content to total protein content being 1.2 - 1.8 and the mass ratio of whey protein to casein content being 0.25 - 0.4.

[0044] The yogurt system provided by the present invention has a mass ratio of total fat content to total protein content of 1.2 - 1.8, and a mass ratio of whey protein to casein content of 0.25 - 0.4, which improves the flexibility of the product system, and at the same time solves the problems of astringency, powdery feeling, and after - acidity commonly existing in room - temperature yogurt, and obtains a preservative - free yogurt with good stability, delicate taste, and high retention rate of nutrients. Brief Description of the Drawings

[0045] In order to more clearly illustrate the technical solutions in the present invention or the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, the drawings in the following description are some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0046] Figure 1 It is a schematic flow chart of the yogurt preparation method provided by the present invention. Detailed Embodiments

[0047] To make the objectives, technical solutions, and advantages of the present invention clearer, the following will clearly and completely describe the technical solutions in the present invention in conjunction with the drawings in the present invention. Obviously, the described embodiments are some, but not all, of the embodiments of the present invention. Based on the embodiments in the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts fall within the scope of protection of the present invention.

[0048] The raw milk used in the embodiments of the present invention is sourced from: raw cow milk; the starter cultures used are sourced from: Chr. Hansen and IFF. In the embodiments of the present invention, the total protein in the skim milk is 3.1 g / 100 mL, the casein is 2.5 g / 100 mL, and the whey protein is 0.6 g / 100 mL; the concentration of the casein concentrate is 13% (negligible trace amounts of whey protein); the concentration of the whey protein concentrate is 15%, and the concentration of the light cream is 35%.

[0049] The test methods used in the embodiments of the present invention are as follows:

[0050] (1) Sensory test method: Invite 50 professional tasters to score the degree of preference for the products 3 days after production. The higher the score, the higher the degree of preference. Calculate the average value of the obtained scores to obtain the result of the sensory preference test. The inspection items are color, texture, flavor, and taste. The average score is taken for each item. The higher the score, the closer it is to the best characteristics of the product.

[0051] (2) Method for determining clarification index based on a stability analyzer: Use a LUMiSizer X65 (SEPView 6) stability analyzer to perform stability analysis on the product 7 days after production. Test conditions: temperature 25°C, 300 profile lines, time interval 25 s, rotation speed 2000 rpm, light factor 1.0.

[0052] (3) Method for measuring shear viscosity: Use an Anton Paar MCR302 rheometer to perform a rotational test shear rate scan on the product 3 days and 90 days after production. Test conditions: temperature 25°C, monitor viscosity at a rate of 0 - 100 s-1, and take the viscosity at 50 s-1 as the monitoring index.

[0053] (4) Method for detecting viable lactic acid bacteria count: Detect according to "GB 4789.35-2016 National Food Safety Standard - Microbiological Examination of Foods - Examination of Lactic Acid Bacteria".

[0054] (5) Method for detecting nutritional components of yogurt: α-lactalbumin: T / TDSTIA 002-2021 Determination of α-lactalbumin in milk and milk products - High performance liquid chromatography method; β-lactoglobulin: T / TDSTIA 007-2019 Determination of β-lactoglobulin in milk and milk products - Liquid chromatography method.

[0055] Figure 1 is a schematic flow chart of the yogurt preparation method provided by the present invention.

[0056] Example 1

[0057] This example provides a yogurt preparation method based on ultra-high pressure sterilization technology, and its raw materials include raw milk; the preparation method provided in this example includes the following steps:

[0058] (1) Raw milk passes through a milk clarifier, with a separation temperature of 4 - 10°C, to remove impurities contained in the milk.

[0059] (2) Then it passes through a self-cleaning airtight double-effect sterilization and separation machine, with a separation temperature of 55°C, a rotation speed of 6000 rpm, and a time of 35 s, to remove most bacteria and spores.

[0060] (3) Pass through a fat separator to separate the fat to obtain cream and skim milk; the cream passes through a coil sterilizer, with a sterilization temperature of 85°C and a time of 15 s; and then enters the tank to be filled.

[0061] (4) The skim milk is sterilized by microfiltration through a 0.8 μm filter at 10°C, and part of it enters the tank to be filled.

[0062] (5) Another part of the skim milk that has been sterilized by microfiltration passes through a 0.1 μm microfilter at 10°C to obtain a casein concentrate (retentate) and a whey protein solution.

[0063] (6) Subject the whey protein solution obtained in step (5) to ultrafiltration / reverse osmosis to obtain a whey protein concentrate (retentate) and a permeate.

[0064] (7) Ingredients: Mix and blend 80 parts by weight of the skim milk obtained above, 2.85 parts by weight of the casein concentrate, 2.34 parts by weight of the whey protein concentrate, 0.81 parts by weight of the permeate, and 14 parts by weight of the fresh cream, so that the total protein content in the blended liquid is 3.2 g / 100 mL, the mass ratio of whey protein to casein is 0.35, and the fat content is 4.8 g / 100 mL; Mix and preheat to 45 °C, shear and stir for 20 min; The degassing temperature is 65 °C and the vacuum degree is -0.7 bar; The homogenization temperature is 65 °C and the homogenization pressure is 150 bar; Cool to 37 °C to obtain a blended liquid.

[0065] (8) Add a starter culture (a total of 1×10 7 CFU / mL of Lactobacillus bulgaricus and Streptococcus thermophilus) to the blended liquid, ferment at 40 °C until the acidity reaches 80 °T, break the emulsion and stir, and cool to 15 °C to terminate the fermentation.

[0066] (9) Fill into PET cups, and sterile jam can be added during filling. The filling volume accounts for 95% of the packaging capacity.

[0067] (10) After filling, perform ultra-high pressure sterilization treatment. The temperature of the ultra-high pressure sterilization is 4 °C, the pressure is 600 Mpa, and the treatment time is 5 min. Then the stirred yogurt is obtained.

[0068] Example 2

[0069] (1) The steps before ingredient blending are the same as in Example 1;

[0070] (2) Ingredients: Mix and blend 80 parts by weight of the skim milk obtained above, 0.53 parts by weight of the casein concentrate, 1.6 parts by weight of the whey protein concentrate, 5.87 parts by weight of the permeate, and 12 parts by weight of the fresh cream, so that the total protein content in the blended liquid is 2.8 g / 100 mL, the mass ratio of whey protein to casein is 0.35, and the fat content is 4.2 g / 100 mL; Mix and preheat to 45 °C, shear and stir for 20 min; The degassing temperature is 65 °C and the vacuum degree is -0.7 bar; The homogenization temperature is 65 °C and the homogenization pressure is 150 bar; Cool to 37 °C to obtain a blended liquid.

[0071] (3) Add a starter culture (a total of 1×10 7 CFU / mL of Lactobacillus bulgaricus and Streptococcus thermophilus) to the blended liquid, ferment at 40 °C until the acidity reaches 80 °T, break the emulsion and stir, and cool to 15 °C to terminate the fermentation.

[0072] (4) Fill it with a PET cup. Sterile jam can be added during filling. The filling volume accounts for 95% of the packaging capacity. After filling, perform ultra-high pressure sterilization treatment. The temperature of the ultra-high pressure sterilization is 4°C, the pressure is 600 Mpa, and the treatment time is 5 minutes. Then the stirred yogurt is obtained.

[0073] Example 3

[0074] (1) The steps before ingredient preparation are the same as those in Example 1;

[0075] (2) Ingredient preparation: Mix 80 parts by weight of the skim milk obtained above, 2.87 parts by weight of casein concentrate, 2.23 parts by weight of whey protein concentrate, 0.9 part by weight of permeate, and 14 parts by weight of light cream for ingredient preparation to meet the total protein content in the mixed liquid of 3.2 g / 100 mL, where the mass ratio of whey protein to casein is 0.4 and the fat content is 4.8 g / 100 mL; Mix and preheat to 45°C, shear and stir for 20 minutes; The degassing temperature is 65°C, and the vacuum degree is -0.7 bar; The homogenization temperature is 65°C, and the homogenization pressure is 150 bar; Cool to 37°C to obtain the mixed liquid;

[0076] (3) Add a starter (a total of 1×10 7 CFU / mL of Lactobacillus bulgaricus and Streptococcus thermophilus) to the mixed liquid and ferment at 40°C until the acidity reaches 80°T. Then break the emulsion and stir, and cool to 15°C to terminate fermentation.

[0077] (4) Fill it with a PET cup. Sterile jam can be added during filling. The filling volume accounts for 95% of the packaging capacity. After filling, perform ultra-high pressure sterilization treatment. The temperature of the ultra-high pressure sterilization is 4°C, the pressure is 600 Mpa, and the treatment time is 5 minutes. Then the stirred yogurt is obtained.

[0078] Example 4

[0079] The difference between this example and Example 1 is that after filling, perform ultra-high pressure sterilization treatment. The temperature of the ultra-high pressure sterilization is 10°C, the pressure is 600 Mpa, and the treatment time is 7 minutes. Then the stirred yogurt is obtained.

[0080] Example 5

[0081] The difference between this example and Example 1 is that after filling, perform ultra-high pressure sterilization treatment twice. The temperature of the ultra-high pressure sterilization is 4°C, the pressure is 600 Mpa, and the treatment time for each time is 2 minutes. Then the stirred yogurt is obtained.

[0082] Comparative Examples 1 - 4

[0083] The preparation method of Comparative Example 1 is the same as that of Example 1, except that after fermentation, demulsification and cooling in step (3), the material is pasteurized at 75° C. for 15 seconds.

[0084] The preparation method of Comparative Example 2 is the same as that of Example 1, except that the fat content and protein content in the mixed liquid obtained by compounding the ingredients are the same, both being 3.2 g / 100 mL.

[0085] The preparation method of Comparative Example 3 is the same as that of Example 1, except that the mass ratio of whey protein to casein in the mixed liquid obtained by batching is 0.2.

[0086] The preparation method of Comparative Example 4 is the same as that of Example 4, except that the ultrahigh pressure is 600 MPa, the treatment time is 4 min, and the treatment is performed twice.

[0087] Experimental Example 1

[0088] In this experimental example, the yogurts prepared in the embodiment of the present invention and comparative examples 1-4 were subjected to taste and flavor evaluation experiments.

[0089] The sensory evaluation scoring criteria are shown in Table 1.

[0090] Table 1 Sensory evaluation standards

[0091]

[0092] The results of sensory evaluation are shown in Table 2.

[0093] Table 2 Sensory analysis scores

[0094]

[0095]

[0096] In this experimental example, the viscosity, stability (clarification index) and lactic acid bacteria count of the yogurt samples obtained in the embodiment and the comparative example were tested. The results are shown in Table 3.

[0097] Table 3

[0098] Item Viscosity (Pa·s) Stability (Clarification Index) Number of lactic acid bacteria (CFU / g) Example 1 0.56 0.003 3200 Example 2 0.48 0.008 2700 Example 3 0.52 0.005 2500 Example 4 0.42 0.009 1900 Example 5 0.43 0.008 2000 Comparative Example 1 0.34 0.012 0 Comparative Example 2 0.36 0.005 2500 Comparative Example 3 0.50 0.010 3000 Comparative Example 4 0.75 0.015 1500

[0099] Table 4 Test results of nutrient composition of yogurt

[0100] Item β-Lactoglobulin (mg / L) α-Lactalbumin (mg / L) Example 1 1988 862 Example 2 1752 759 Example 3 2192 950 Example 4 1491 663 Example 5 1572 690 Comparative Example 1 2485 995 Comparative Example 2 1838 742 Comparative Example 3 1325 580 Comparative Example 4 986 450

[0101] From the data in Table 2, Table 3 and Table 4, we can see that:

[0102] (1) Under the ultra-high pressure sterilization process, for yogurt systems composed of different ingredients, as long as the mass ratio of total fat to total protein is 1.2 - 1.8 and the mass ratio of whey protein to casein is 0.25 - 0.4, the tissue state of the yogurt product is more popular, the stability is better, and the sensory score is higher. That is, the yogurt formula and preparation method provided by the embodiments of the present invention have a good effect on improving the quality of yogurt. The formula provided by the present invention is more flexible and controllable, meeting the needs of products with different component compositions.

[0103] (2) During the preparation of yogurt, performing appropriate ultra-high pressure sterilization after fermentation can not only kill some lactic acid bacteria and reduce the post-acidification during yogurt storage, but also enhance the stability of the yogurt system and improve the taste of the product. Among them, the preference degrees of the parameters of 600 Mpa - 5 min and 600 Mpa - 2 min repeated twice are significantly higher than those of the samples treated with thermal sterilization and excessive ultra-high pressure sterilization.

[0104] (3) Traditional yogurt usually uses ultra-pasteurization, which will cause almost complete denaturation of whey protein, so the retention rate of active protein in the yogurt product is low. The results in Table 4 show that while adjusting the fat content, protein content, and the mass ratio of whey protein to casein in the milk system in this application, microfiltration sterilization combined with ultra-high pressure sterilization treatment retains more active proteins (β-lactoglobulin and α-lactalbumin) in yogurt.

[0105] In addition, it should be noted that although pasteurization can also achieve a relatively high retention degree of active protein in yogurt, the disadvantage of pasteurization is that the obtained yogurt has a poor taste and causes greater damage to the texture and flavor. Therefore, overall, by optimizing the yogurt formula and ultra-high pressure sterilization treatment conditions in this application, it is possible to retain more active proteins in yogurt and provide a yogurt product with a better sensory experience.

[0106] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit them. Although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions recorded in the foregoing embodiments or perform equivalent replacements for some of the technical features. However, such modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing yogurt, characterized in that, Including: Ingredient preparation, fermentation, and ultra-high pressure sterilization; in the mixed liquid obtained from the ingredient preparation, the mass ratio of the total fat content to the total protein content is 1.2 - 1.8, and the mass ratio of the whey protein content to the casein content is 0.25 - 0.4; the temperature of the ultra-high pressure sterilization is 4 - 15°C, the pressure is 400 - 800 Mpa, and the treatment time is 4 - 7 min.

2. The method for preparing yogurt according to claim 1, wherein The temperature of the ultra-high pressure sterilization is 4 - 10°C, and the pressure is 600 - 700 Mpa.

3. The method for preparing yogurt according to any one of claims 1-2, characterized in that, The ultra-high pressure sterilization is a single treatment or multiple treatments; when the ultra-high pressure sterilization is a single treatment, the treatment time is 4 - 7 min; when the ultra-high pressure sterilization is multiple treatments, the treatment time for each treatment is 1 - 3 min.

4. The method for preparing yogurt according to claim 3, wherein When the ultra-high pressure sterilization is a single treatment, the treatment time is 5 - 7 min.

5. The method for preparing yogurt according to any one of claims 1-4, characterized in that, The temperature of the ultra-high pressure sterilization is 4°C, and the pressure is 600 Mpa; when the ultra-high pressure sterilization is a single treatment, the treatment time is 5 min; or when the ultra-high pressure sterilization is two treatments, the treatment time for each treatment is 2 min.

6. The method for preparing yogurt according to any one of claims 1-5, characterized in that The fermented milk after fermentation is filled and then ultra-high pressure sterilization is carried out.

7. The method for preparing yogurt according to any one of claims 1-6, characterized in that, The ingredients include: using raw milk as raw material, obtaining skim milk, casein concentrate, whey protein concentrate, permeate, or cream for ingredient preparation to obtain a mixed liquid; The mixed liquid is preheated, degassed, and homogenized, and then fermented.

8. The method for preparing yogurt according to any one of claims 1-7, characterized in that, The starter culture used for the fermentation includes: Lactobacillus bulgaricus and Streptococcus thermophilus; the addition amount of the starter culture is 1×10 6 -1×10 8 CFU / mL; The fermentation temperature is 35 - 45°C; the acidity value at the end of fermentation is 70 - 140 °T, and the pH is controlled at 4.3 - 4.

7.

9. The preparation method according to claim 8, characterized in that, The fermenting agent also includes: one or more of Lactobacillus casei, Lactobacillus acidophilus, Bifidobacterium, Lactobacillus plantarum; The fermentation temperature is 37 - 42°C; the acidity at the end of fermentation is 80 - 100 °T, and the pH is controlled at 4.

5.

10. A yogurt, characterized in that, Prepared by the preparation method according to any one of claims 1 - 9.

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