A high casein content yoghurt and a method for preparing the same

Abstract

This invention relates to the field of food technology, and more particularly to a high-casein-content yogurt and its preparation method. The yogurt preparation method provided by this invention includes: mixing raw milk, membrane-separated casein concentrate, and inorganic salts; subjecting the mixed raw material liquid to hydraulic cavitation treatment, then inoculating with a starter culture for fermentation; and, while fermenting to a certain pH level, applying ultrasonic treatment simultaneously with fermentation. The high-casein-content yogurt prepared by the method provided by this invention has suitable viscosity, hardness, and cohesiveness, a smooth and stable texture, good water retention, and a low whey separation rate, exhibiting superior stability and excellent sensory evaluation in terms of taste and aroma. The yogurt provided by this invention is characterized by high protein and high casein content. Due to the high casein content, it is naturally low in fat and high in calcium, with a strong feeling of satiety, better meeting the needs of fitness enthusiasts, those seeking weight loss, and those supplementing calcium.

Description

Technical Field

[0001] This invention relates to the field of food technology, and in particular to a yogurt with high casein content and its preparation method. Background Technology

[0002] With the continuous growth of global consumers' demand for health and nutrition, high-protein dairy products are gaining popularity. As a widely popular fermented dairy product, yogurt's high-protein upgrade has become a core focus of current industry research and development. However, the traditional high-protein yogurt production process relying on whey removal not only wastes whey but also causes environmental pollution; while the method of increasing yogurt protein content using micellar casein concentrate (MCC) generally faces problems such as coarse product texture, grainy feel, excessively hard gel, poor flavor, and poor stability.

[0003] Casein accounts for 80% of the protein content in cow's milk. Although the price of basic casein products is low, there is still considerable room for development in high-value-added product areas. Micellar casein, obtained through membrane separation, also known as membrane-separated casein, retains the natural micellar structure and can form a denser and more uniform gel network with whey protein. However, when the proportion of casein in yogurt is too high, it generally tends to form an overly dense and hard gel network, resulting in a hard, brittle texture and a loss of smoothness. Furthermore, a gel network with excessive casein content can also lead to decreased water-holding capacity and severe whey separation during shelf life. In addition, the viscosity of high-protein base materials increases dramatically during fermentation, posing significant challenges to processing steps such as pumping, mixing, and filling, and potentially resulting in a sticky and unpleasant final product.

[0004] Therefore, the traditional method of producing high-protein yogurt simply by adding membranes to separate casein is no longer sufficient to meet the demands of the high-quality market. There is an urgent need to develop new high-casein yogurt production processes to address the key issues of solubility, texture, stability, and mouthfeel. Summary of the Invention

[0005] This invention provides a yogurt with high casein content and a method for preparing the same.

[0006] Specifically, the present invention provides the following technical solutions.

[0007] In a first aspect, the present invention provides a method for preparing yogurt, the method comprising: mixing raw milk, membrane-separated casein concentrate and inorganic salts; subjecting the mixed raw liquid to hydraulic cavitation treatment, then inoculating with a starter culture for fermentation, and starting when the pH drops to 5.0-6.0, while simultaneously applying ultrasonic treatment; wherein the amount of inorganic salts added is 0.2%-0.5% of the total mass of the raw milk and membrane-separated casein concentrate.

[0008] The yogurt of this invention is a high-casein yogurt, using membrane-separated casein concentrate and raw milk as the main ingredients. During the ingredient formulation process, a low dose of the aforementioned inorganic salt is added, causing slight depolymerization of the micelles without causing protein aggregation and precipitation due to excessive salt concentration and destruction of colloidal calcium phosphate, while maintaining sensory appeal. Hydraulic cavitation technology is used to treat the feed solution, further reducing the particle size and viscosity of the system after fermentation, thus improving the smoothness of the texture. Furthermore, ultrasonic treatment is incorporated during fermentation to make the formed gel more delicate and uniform. The combination of these multiple processes—salt dissolution, hydraulic cavitation, and ultrasonic intervention during fermentation—results in a higher casein content yogurt with a better taste, lower whey separation rate, and a richer, more delicate sensory quality.

[0009] Specifically, in the low-concentration inorganic salt treatment process developed in this invention, the salt-dissolving effect can improve the properties of casein micelles in the feed solution. The effect of low-concentration salt is concentrated on the micelle surface, which can slightly disrupt the hydration layer of κ-casein on the micelle surface, causing some aggregated small micelles to deaggregate and redisperse into monodisperse micelles. Controlling the salt concentration in the system at 0.2%-0.5% will not damage the core structure of the micelles, thereby reducing the particle size and particle size distribution of the feed solution and lowering the viscosity of the feed solution. Low-concentration inorganic salt treatment provides a more suitable feed solution state basis for subsequent hydraulic cavitation treatment, and also promotes the formation of excellent yogurt texture during subsequent fermentation.

[0010] Hydraulic cavitation technology utilizes a hydraulic cavitation reactor to generate millions of tiny bubbles through the instantaneous pressure changes produced by fluid flowing through a diffusing pipe. The collapse of these bubbles generates enormous local shear forces, shock waves, and microjets. This energy effectively breaks up difficult-to-disperse aggregates in concentrated micelle casein, allowing the whey protein structure to unfold and improving gelation properties. The cavitation shock waves further break up the micelle aggregates while slightly shearing the κ-casein glycan chains on the micelle surface. This process avoids damaging casein calcium phosphate (CCP), a key structural component that maintains the stable structure of the micelles and affects casein solubility, while reducing the attraction between micelles, resulting in more uniform micelle dispersion, improved gelation properties of the casein solution, and a finer, more uniform gel texture. Hydraulic cavitation combined with low-concentration inorganic salt treatment facilitates the formation of a denser gel network in yogurt with high casein and low whey protein content, improving water retention and gel stability, thus laying the foundation for subsequent fermentation. Simultaneously, it imparts a creamy texture and mouthfeel to the whey protein, mitigating the rough texture caused by low-fat yogurt to some extent. Furthermore, the temperature increase and shear force during cavitation can replace pasteurization and homogenization processes, reducing processing steps and improving production efficiency.

[0011] In conjunction with low-concentration inorganic salt treatment and hydraulic cavitation, this invention also employs ultrasound to treat the fermentation broth during fermentation to assist in the homogenization of the gel network. This treatment step extends the application of physical field technology from the raw material pretreatment stage to the critical stage of yogurt gel formation. After inoculation with the starter culture, a low-intensity, specific-frequency online ultrasonic field is applied to the yogurt broth. This reduces excessive aggregation of casein and the formation of coarse, uneven particles as the pH gradually decreases and the proteins begin to aggregate and form a gel network. This ensures that the gel precursor is evenly distributed throughout the system, resulting in a smaller, more uniform, and delicate gel network structure. This optimizes the yogurt's texture, improves its water-holding capacity and viscosity, and significantly reduces whey separation.

[0012] Preferably, the fermentation begins when the pH drops to 5.0-5.5 (more preferably 5.0-5.2), and ultrasonic treatment is applied simultaneously with the fermentation.

[0013] The inorganic salt is added at a rate of 0.2%-0.3% of the total mass of the raw milk and the membrane-separated casein concentrate.

[0014] In the above method, mixing the raw milk, membrane-separated casein concentrate, and inorganic salt can be done by mixing the raw milk and membrane-separated casein concentrate first, and then mixing with the inorganic salt; or by mixing the membrane-separated casein concentrate and inorganic salt first, and then mixing with the raw milk.

[0015] Preferably, the raw milk and membrane-separated casein concentrate are mixed before being mixed with inorganic salts. This mixing method is more conducive to improving the sensory properties, such as the taste, of the prepared yogurt.

[0016] In the above method, the inorganic salt preferably includes one or more selected from sodium chloride, potassium chloride, sodium sulfate, and calcium chloride.

[0017] In some embodiments of the present invention, the inorganic salt is sodium chloride or potassium chloride.

[0018] In the above method, the mixing with inorganic salt is carried out under stirring conditions.

[0019] In some embodiments of the present invention, inorganic salts are added to the mixture of raw milk and membrane-separated casein concentrate while stirring, and stirring is continued for 10-30 minutes after the addition is completed.

[0020] In the above method, the ultrasonic treatment ends when fermentation reaches pH 4.2-4.8.

[0021] Preferably, the ultrasonic treatment ends when fermentation reaches pH 4.4-4.6.

[0022] If the final pH of fermentation is not reached by the end of the ultrasonic treatment, fermentation will continue until the final pH is reached without ultrasonic treatment.

[0023] In the above method, the frequency of the ultrasonic treatment is 25-50kHz and the power is 100-200W.

[0024] In the above method, the ultrasonic treatment is performed for 0.8-1.5 minutes every 5 minutes.

[0025] In the above method, the temperature of the hydraulic cavitation treatment is 55-70℃, and the cycle is 1-3 times. Hydraulic cavitation treatment under these conditions is more beneficial for improving the properties of casein and whey protein. A more preferred temperature is 60-70℃, with 2 cycles.

[0026] Preferably, the inlet pressure of the hydraulic cavitation treatment is 6-8 bar and the rotation speed is 3000-4000 rpm.

[0027] Preferably, the rotor gap of the hydraulic cavitation treatment is 1-2 mm.

[0028] Hydraulic cavitation treatment can achieve both sterilization and homogenization simultaneously, eliminating the need for further sterilization or homogenization.

[0029] After hydraulic cavitation treatment, the temperature is lowered to 40℃-43℃, and then a fermentation agent is inoculated for fermentation. The fermentation is a static fermentation.

[0030] In principle, there are no special restrictions on the starter culture. Any strain that can be used for yogurt fermentation can be used, including but not limited to Streptococcus thermophilus, Lactobacillus bulgaricus, Bifidobacterium, Lactobacillus acidophilus, Lactobacillus casei, Lactobacillus rhamnosus, Lactobacillus plantarum, and Lactobacillus reuteri.

[0031] In some embodiments of the present invention, the fermenting agent comprises Lactobacillus bulgaricus and Streptococcus thermophilus. Preferably, the ratio of the effective viable counts of Lactobacillus bulgaricus to Streptococcus thermophilus is 1:(3-5).

[0032] Preferably, the fermentation temperature is 40℃-43℃.

[0033] After fermentation, the mixture is cooled and demulsified to obtain yogurt with a high casein content.

[0034] In the above method, the raw milk and the membrane-separated casein concentrate are mixed at a ratio calculated as 6%-12% of total protein.

[0035] Preferably, the raw milk and the membrane-separated casein concentrate are mixed in a ratio calculated as 6%-10% total protein and 1.5%-2.0% total fat.

[0036] Preferably, the mass ratio of the raw milk to the membrane-separated casein concentrate is (40-50):(50-60). More preferably, it is (45-50):(50-55).

[0037] The mixing of raw milk and membrane-separated casein concentrate is carried out at 45-55℃. The mixing of the raw milk and membrane-separated casein concentrate with inorganic salts is also carried out at 45-55℃.

[0038] In this invention, the raw milk is raw milk, preferably raw cow's milk.

[0039] In this invention, the membrane-separated casein concentrate is a liquid concentrated micelle casein, wherein the total protein content is 15%-20%.

[0040] Secondly, the present invention provides a yogurt, which is prepared by the preparation method described in the first aspect above.

[0041] The above-mentioned yogurt meets any one or more of the following conditions: (1) total protein content is 6%-12%; (2) casein accounts for more than 90% of the total protein; (3) total fat content is 1.5%-2.0%; (4) viscosity cp is 4500-6200; (5) particle size is 10-20μm; (6) hardness is 200-380g.

[0042] Among the above indicators, viscosity (cp) is the viscosity measured at 25°C using a viscometer. Particle size is the median particle size measured using a laser particle size analyzer. Hardness is measured using a texture analyzer, with the speed set to 1.0 mm / s before, during, and after the test, the trigger force to be 5 g, and the depth to be 10 mm.

[0043] Preferably, the whey separation rate of the yogurt is ≤7%. The whey separation rate is determined by centrifugation at 3000×g for 5 minutes.

[0044] The beneficial effects of this invention include at least the following: the high casein content yogurt prepared by the method provided by this invention has suitable viscosity, hardness, and cohesiveness, can achieve gel network homogenization, has an average particle size of 10-20 μm, a smooth and stable texture, good water retention, and a low whey separation rate (centrifuged whey separation rate ≤7%), resulting in better stability. Furthermore, it exhibits excellent sensory evaluation in terms of taste and aroma, effectively solving the problems of coarse texture, poor taste, and poor stability associated with high casein content yogurt. The yogurt provided by this invention is characterized by high protein and high casein content. Due to its high casein content, it is naturally low in fat, high in calcium, and has a strong feeling of satiety, conforming to modern health concepts and meeting the needs of people who are fitness enthusiasts, those trying to lose weight, and those seeking calcium supplementation. Detailed Implementation

[0045] A specific embodiment of the present invention provides a method for preparing yogurt with high casein content, which includes the following steps:

[0046] (1) Preparation: Mix the membrane-separated casein concentrate and raw milk at 45-55°C. While stirring at 45-55°C, add inorganic salts (preferably sodium chloride or potassium chloride) according to the concentration, and keep warm and stir for 10-30 minutes; or, mix the membrane-separated casein concentrate and inorganic salts (preferably sodium chloride or potassium chloride) at 45-55°C, keep warm and stir for 10-30 minutes; then mix with raw milk;

[0047] (2) Hydraulic cavitation treatment: inlet pressure 6-8 bar, speed 3000-4000 rpm, rotor gap 1-2 mm, temperature 50-60℃, 1-3 cycles;

[0048] (3) Quickly cool down to 40-43℃, inoculate with the starter culture, and let it stand at 40-43℃ for fermentation;

[0049] (4) When the pH drops to 5.0-6.0, start online ultrasound intervention at a frequency of 25-50kHz and a power of 100-200W. Immerse the probe in the fermentation broth and treat for 1-1.5 minutes every 5 minutes until the pH drops to 4.4-4.7.

[0050] (5) Rapid cooling to break the emulsion.

[0051] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of this invention, not all embodiments. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0052] The experimental materials and equipment used in the following examples are as follows:

[0053] Raw materials: Membrane-separated casein concentrate (total protein content 17.0%); raw milk (protein 3.2%, fat 3.8%); starter culture (the ratio of effective viable bacteria of Lactobacillus bulgaricus to Streptococcus thermophilus is 1:4).

[0054] Equipment: Hydraulic cavitation reactor (inlet pressure 2-6 bar); online ultrasonic fermenter (25 kHz, power adjustable); Analytical equipment: Malvern particle size analyzer, texture analyzer, dairy analyzer, etc.

[0055] Example 1

[0056] This embodiment provides a method for preparing yogurt with high casein content, which includes the following steps:

[0057] (1) Preparation of ingredients: The ingredients are prepared according to the following proportions: total protein 10% and total fat 1.8%, that is, the amount of raw milk is about 46.5% and the amount of membrane-separated casein concentrate is about 53.5%. The membrane-separated casein concentrate is heated to 50°C, and after adding raw milk, it is preheated to 50°C. While stirring, 0.3% of sodium chloride (dissolved in a small amount of water in advance and slowly added to the center of the stirring vortex to prevent local high concentration from causing salting out) is added. The mixture is kept warm and stirred for 20 minutes.

[0058] (2) Hydraulic cavitation treatment: inlet pressure 6 bar, speed 3000 rpm, rotor clearance 1 mm, temperature 70℃, 2 cycles;

[0059] (3) Quickly cool down to about 40°C, add the pre-activated starter culture, and let it stand at 42°C for fermentation;

[0060] (4) When the pH drops to 5.2, start online ultrasound intervention at a frequency of 25kHz and a power of 100W. Immerse the probe in the fermentation broth and treat for 1 minute every 5 minutes until the pH drops to 4.6.

[0061] (5) Continue fermentation until the pH of the yogurt reaches 4.4-4.5, then stop fermentation;

[0062] (6) Cool quickly, stir at 300 rpm for 5 min to break the emulsion, and store at 4℃.

[0063] Example 2

[0064] This embodiment provides a method for preparing yogurt with high casein content, which includes the following steps:

[0065] (1) Preparation of ingredients: The ingredients are prepared according to the following proportions: total protein 10% and total fat 1.8%, that is, the amount of raw milk is 46.5% and the amount of membrane-separated casein concentrate is 53.5%. The membrane-separated casein concentrate is heated to 50°C, raw milk is added and the mixture is preheated to 50°C. While stirring, 0.2% of potassium chloride (dissolved in a small amount of water in advance and slowly added to the center of the stirring vortex to prevent local high concentration from causing salting out) is added. The mixture is kept warm and stirred for 20 minutes.

[0066] (2) Hydraulic cavitation treatment: inlet pressure 6 bar, speed 3000 rpm, rotor clearance 1 mm, temperature 70℃, 2 cycles;

[0067] (3) Quickly cool down to about 40°C, add the starter culture after pre-activating it with pasteurized milk, and let it stand at 42°C for fermentation;

[0068] (4) When the pH drops to 5.2, start online ultrasound intervention at a frequency of 25kHz and a power of 100W. Immerse the probe in the fermentation broth and treat for 1 minute every 5 minutes until the pH drops to 4.6.

[0069] (5) Continue fermentation until the pH of the yogurt reaches 4.4-4.5, then stop fermentation;

[0070] (6) Cool quickly, stir at 300 rpm for 5 min to break the emulsion, and store at 4℃.

[0071] Example 3

[0072] This embodiment provides a method for preparing yogurt with high casein content, which includes the following steps:

[0073] (1) Preparation of ingredients: The ingredients are prepared according to 6% total protein and 2% total fat, that is, the amount of raw milk is about 48.7% and the amount of membrane-separated casein concentrate is about 51.3%; the membrane-separated casein concentrate is heated to 50°C, raw milk is added and the mixture is preheated to 50°C, and while stirring, 0.3% of sodium chloride (dissolved in a small amount of water in advance and slowly added to the center of the stirring vortex to prevent local high concentration from causing salting out) is added and kept warm and stirred for 20 minutes;

[0074] (2) Hydraulic cavitation treatment: inlet pressure 6 bar, speed 3000 rpm, rotor clearance 1 mm, temperature 70℃, 2 cycles;

[0075] (3) Quickly cool down to about 40°C, add the pre-activated starter culture, and let it stand at 42°C for fermentation;

[0076] (4) When the pH drops to 5.2, start online ultrasound intervention at a frequency of 25kHz and a power of 100W. Immerse the probe in the fermentation broth and treat for 1 minute every 5 minutes until the pH drops to 4.4 and the fermentation ends.

[0077] (5) Cool quickly, stir at 300 rpm for 5 min to break the emulsion, and store at 4℃.

[0078] Example 4

[0079] This embodiment provides a method for preparing yogurt with high casein content, which includes the following steps:

[0080] (1) Preparation of ingredients: The ingredients are prepared according to 10% total protein and 1.8% total fat, that is, the amount of raw milk is 46.5% and the amount of membrane-separated casein concentrate is 53.5%; the membrane-separated casein concentrate is heated to 50°C, raw milk is added and the mixture is preheated to 50°C, and while stirring, 0.3% of sodium chloride (dissolved in a small amount of water in advance and slowly added to the center of the stirring vortex to prevent local high concentration from causing salting out) is added and kept warm and stirred for 20 minutes;

[0081] (2) Hydraulic cavitation treatment: inlet pressure 6 bar, speed 3000 rpm, rotor gap 1 mm, temperature 60℃, 2 cycles;

[0082] (3) Quickly cool down to about 40°C, add the pre-activated starter culture, and let it stand at 42°C for fermentation;

[0083] (4) When the pH drops to 5.2, start online ultrasound intervention at a frequency of 25kHz and a power of 100W. Immerse the probe in the fermentation broth and treat for 1 minute every 5 minutes until the pH drops to 4.6.

[0084] (5) Continue fermentation until the pH of the yogurt reaches 4.4-4.5, then stop fermentation;

[0085] (6) Cool quickly, stir at 300 rpm for 5 min to break the emulsion, and store at 4℃.

[0086] Example 5

[0087] This embodiment provides a method for preparing yogurt with high casein content, which includes the following steps:

[0088] (1) Preparation of ingredients: The ingredients are prepared according to 10% total protein and 1.8% total fat, that is, the amount of raw milk is 46.5% and the amount of membrane-separated casein concentrate is 53.5%; the membrane-separated casein concentrate is heated to 50°C, raw milk is added and the mixture is preheated to 50°C, and while stirring, 0.3% of sodium chloride (dissolved in a small amount of water in advance and slowly added to the center of the stirring vortex to prevent local high concentration from causing salting out) is added and kept warm and stirred for 20 minutes;

[0089] (2) Hydraulic cavitation treatment: inlet pressure 8 bar, speed 4000 rpm, rotor clearance 1 mm, temperature 70℃, 2 cycles;

[0090] (3) Quickly cool down to about 40°C, add the pre-activated starter culture, and let it stand at 42°C for fermentation;

[0091] (4) When the pH drops to 5.2, start online ultrasound intervention at a frequency of 25kHz and a power of 100W. Immerse the probe in the fermentation broth and treat for 1 minute every 5 minutes until the pH drops to 4.6.

[0092] (5) Continue fermentation until the pH of the yogurt reaches 4.4-4.5, then stop fermentation;

[0093] (6) Cool quickly, stir at 300 rpm for 5 min to break the emulsion, and store at 4℃.

[0094] Example 6

[0095] This embodiment provides a method for preparing yogurt with high casein content, which includes the following steps:

[0096] (1) Preparation of ingredients: The ingredients are prepared according to 10% total protein and 1.8% total fat, that is, the amount of raw milk is 46.5% and the amount of membrane-separated casein concentrate is 53.5%; the membrane-separated casein concentrate is heated to 50°C, raw milk is added and the mixture is preheated to 50°C, and while stirring, 0.3% of sodium chloride (dissolved in a small amount of water in advance and slowly added to the center of the stirring vortex to prevent local high concentration from causing salting out) is added and kept warm and stirred for 20 minutes;

[0097] (2) Hydraulic cavitation treatment: inlet pressure 6 bar, speed 3000 rpm, rotor clearance 1 mm, temperature 70℃, 2 cycles;

[0098] (3) Quickly cool down to about 40°C, add the pre-activated starter culture, and let it stand at 42°C for fermentation;

[0099] (4) When the pH drops to 5.0, start online ultrasound intervention at a frequency of 50kHz and a power of 200W. Immerse the probe in the fermentation broth and treat for 1 minute every 5 minutes until the pH drops to 4.6.

[0100] (5) Continue fermentation until the pH of the yogurt reaches 4.4-4.5, then stop fermentation;

[0101] (6) Cool quickly, stir at 300 rpm for 5 min to break the emulsion, and store at 4℃.

[0102] Comparative Example 1

[0103] This comparative example provides a method for preparing yogurt with high casein content. The only difference between this method and the method in Example 1 is that the membrane-separated casein concentrate is replaced with membrane-separated casein powder (prepared by spray drying of the membrane-separated casein concentrate). Step (1) is as follows: dissolve the membrane-separated casein powder in water at 55°C, adjust the protein content to 17.0%, stir and hydrate for 1 hour to obtain casein reconstituted solution; add raw milk to the casein reconstituted solution, preheat to 50°C, and add 0.3% sodium chloride (dissolved in a small amount of water in advance and slowly added to the center of the stirring vortex to prevent local high concentration from causing salting out) while stirring. Keep warm and stir for 20 minutes.

[0104] Comparative Example 2

[0105] This comparative example provides a method for preparing yogurt with high casein content, which differs from the method in Example 1 only in that inorganic salts are not added during ingredient preparation.

[0106] Comparative Example 3

[0107] This comparative example provides a method for preparing yogurt with high casein content. The only difference between this method and the method in Example 1 is that: after the hydraulic cavitation treatment in step (2), ultrasonic treatment is performed: the probe is immersed in the liquid surface, the frequency is 25kHz and the power is 100W, and the treatment is performed for 1 minute every 5 minutes for 5 hours (the same as the ultrasonic treatment time in Example 1); then fermentation is carried out under the same conditions as in Example 1, and ultrasonic intervention is no longer used during the fermentation process.

[0108] Comparative Example 4

[0109] This comparative example provides a method for preparing yogurt with high casein content. The only difference between this method and the method in Example 1 is that the same conditions as in Example 1 are used for fermentation, but no ultrasonic intervention is performed during the fermentation process. After demulsification in step (6), ultrasonic treatment is performed: the probe is immersed in the liquid surface, the frequency is 25kHz and the power is 100W, and the treatment is performed for 1 minute every 5 minutes for 5 hours (the same as the ultrasonic treatment time in Example 1). After the treatment, the yogurt is stored at 4°C.

[0110] Comparative Example 5

[0111] This comparative example provides a method for preparing yogurt with high casein content. The only difference between this method and the method in Example 1 is that hydraulic cavitation treatment is not performed. Instead, the yogurt solution after chemical treatment is homogenized and pasteurized (heated to 60°C, homogenized at 60 / 200 bar, sterilization intensity 75°C±2°C / 300s) and then directly fermented.

[0112] Comparative Example 6

[0113] This comparative example provides a method for preparing yogurt with high casein content, which differs from the method in Example 1 only in the addition of inorganic salts. The specific steps are as follows:

[0114] (1) Mixing ingredients: Mix the ingredients according to 10% total protein and 1.8% total fat, that is, the amount of raw milk is 46.5% and the amount of membrane-separated casein concentrate is 53.5%; heat the membrane-separated casein concentrate to 50°C, stir and add raw milk, and continue to preheat to 50°C and mix evenly.

[0115] (2) Hydraulic cavitation treatment, inlet pressure 6 bar, speed 3000 rpm, rotor clearance 1 mm, temperature 70℃, 2 cycles;

[0116] (3) Quickly cool down to 50°C, and while stirring, add 0.3% sodium chloride (dissolved in a small amount of water beforehand and slowly added to the center of the stirring vortex to prevent excessive local concentration from causing salting out), keep warm and stir for about 20 minutes; continue to cool down to 40°C, add the pre-activated fermenting agent, and let it stand at 42°C for fermentation.

[0117] (4) When the pH drops to 5.2, start online ultrasound intervention at a frequency of 25kHz and a power of 100W. Immerse the probe in the fermentation broth and treat for 1 minute every 5 minutes until the pH drops to 4.6.

[0118] (5) Continue fermentation until the pH of the yogurt reaches 4.4-4.5, then stop fermentation;

[0119] (6) Cool quickly, stir at 300 rpm for 5 min to break the emulsion, and store at 4℃.

[0120] Experimental Example

[0121] The yogurts prepared using the methods of the above embodiments and comparative examples were tested, and the specific methods and results are as follows.

[0122] (1) Basic property testing: The yogurt prepared according to the methods of each embodiment and comparative example was tested for basic properties. The viscosity of the sample at 25°C was tested with a viscometer, the median particle size was tested with a laser particle size analyzer, and the gel hardness and cohesiveness of the yogurt were tested with a texture analyzer (P / 50 cylindrical stainless steel probe, the speed was set to 1.0 mm / s before, during and after the test, the trigger force was 5 g, and the depth was 10 mm).

[0123] (2) Stability test: The stability of the yogurt prepared according to the methods of each embodiment and comparative example was evaluated, and the stability was expressed as whey separation rate. An appropriate amount of demulsified yogurt was placed in a 50 mL centrifuge tube with a known mass m1, and the mass of the yogurt added to the centrifuge tube was recorded as m2. Centrifuged at 3000×g for 5 minutes, and after centrifugation, the supernatant was discarded, and the mass of the precipitate added to the centrifuge tube was recorded as m3. The whey separation rate of the sample was calculated according to the following formula: whey separation rate = (m2-m3) / (m2-m1).

[0124] (3) Sensory evaluation: Yogurt samples prepared by the methods of each embodiment and comparative example were tasted and scored by 20 tasters in turn. The samples were tested by rinsing their mouths with water, and the average score was taken to avoid individual bias. The evaluation criteria and scores are shown in Table 1.

[0125] Table 1

[0126]

[0127] The test results are shown in Table 2.

[0128] Table 2

[0129]

[0130] The results showed that, compared with Example 1, Comparative Example 2 did not add inorganic salts, resulting in casein forming a gel with high hardness, poor stability, and a rough texture. This indicates that adding an appropriate amount of salt can make casein form a finer, water-retaining gel network.

[0131] Comparative Example 5 used traditional pasteurization and homogenization instead of hydraulic cavitation. The fermented yogurt had a larger viscosity and particle size, a severe pasty and rough texture, and an overly thick product texture, resulting in a low sensory evaluation score.

[0132] Comparative Example 6 changed the steps of adding inorganic salts. Compared with Example 1, it shows that adding salt first and then performing hydraulic cavitation treatment can enhance the effect of salt on improving the texture of yogurt. Under the same amount of salt added, the yogurt prepared by the method of Example 1 with salt added first has a more delicate and soft texture and a lower whey separation rate.

[0133] Comparative Example 1 used membrane-separated casein powder instead of membrane-separated casein concentrate for processing and fermentation. The resulting yogurt had an excessively thick texture and a high whey separation rate after demulsification. Sensory evaluation revealed problems such as uneven color, poor texture, and off-odor.

[0134] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions 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, The method includes: mixing raw milk, membrane-separated casein concentrate, and inorganic salts; subjecting the mixed raw liquid to hydraulic cavitation treatment, then inoculating it with a starter culture for fermentation, and starting the fermentation process when the pH drops to 5.0-6.0, while simultaneously applying ultrasonic treatment. The inorganic salt is added at a rate of 0.2%-0.5% of the total mass of the raw milk and the membrane-separated casein concentrate. The total protein content of the yogurt is 6%-12%, with casein accounting for more than 90% of the total protein.

2. The method for preparing yogurt according to claim 1, characterized in that, The inorganic salt includes one or more selected from sodium chloride, potassium chloride, sodium sulfate, and calcium chloride.

3. The method for preparing yogurt according to claim 1, characterized in that, The ultrasonic treatment was completed when fermentation reached a pH of 4.2-4.

8.

4. The method for preparing yogurt according to any one of claims 1 to 3, characterized in that, The ultrasonic treatment has a frequency of 25-50 kHz and a power of 100-200 W.

5. The method for preparing yogurt according to claim 4, characterized in that, The ultrasonic treatment is performed for 0.8-1.5 minutes every 5 minutes.

6. The method for preparing yogurt according to any one of claims 1 to 3 and 5, characterized in that, The temperature of the hydraulic cavitation treatment is 55-70℃, and the cycle is 1-3 times.

7. The method for preparing yogurt according to any one of claims 1 to 3 and 5, characterized in that, The starter culture includes Lactobacillus bulgaricus and Streptococcus thermophilus; And / or, the fermentation temperature is 40℃-43℃.

8. The method for preparing yogurt according to any one of claims 1 to 3 and 5, characterized in that, The raw milk and the membrane-separated casein concentrate are mixed at a ratio calculated as 6%-12% of total protein. And / or, the mass ratio of the raw milk to the membrane-separated casein concentrate is (40-50):(50-60).

9. A type of yogurt, characterized in that, The yogurt is prepared by the preparation method according to any one of claims 1 to 8.

10. The yogurt according to claim 9, characterized in that, The total fat content of the yogurt is 1.5%-2.0%, and / or the viscosity (cp) of the yogurt is 4500-6200, and / or the particle size of the yogurt is 10-20μm, and / or the hardness of the yogurt is 200-380g.

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