Preparation method of special yoghurt for curing dysphagia

Abstract

The invention discloses a preparation method of special dry dysphagia yoghurt for baking, relates to the technical field of food processing, and aims to solve the problems that traditional yoghurt is not suitable for high-temperature baking due to high water activity and thermal instability, and is easy to cause unstable form and bleeding. The preparation method comprises the following steps: pretreatment of a fermentation substrate and temperature-controlled gradient fermentation; preparing a basic material of the dysphagia-relieving yoghurt with the total solid content of 28-35% through low-temperature centrifugal filter-pressing dehydration; preparing and compounding a stable system of xanthan gum, carrageenan and modified starch; and homogenizing and compounding. According to the scheme, the liquid yogurt is successfully converted into the solid material with high solid content and low water activity, so that the product has excellent baking resistance and freezing resistance, is stable in form and free of water separation under high-temperature baking, retains rich fermentation flavor and meets the baking application requirement.

Description

Technical Field

[0001] The invention belongs to the technical field of food processing, and in particular relates to a method for preparing dry yogurt specially used for baking. Background Art

[0002] In the modern baking industry, fillings are key components that impart core flavor, texture, and added value to products. Their variety and quality directly determine the market competitiveness and consumer acceptance of the final product. With consumers' increasing demand for healthy diets and flavorful experiences, the development of new baking fillings that combine excellent sensory properties with nutritional and health attributes has become a key area of ​​technological innovation in the industry. To meet the basic requirements of baking production for heat resistance and stability of fillings, the existing technology generally uses traditional filling systems represented by high-sugar jams or high-fat creams. Specifically, jam fillings significantly reduce the water activity of the system by adding large amounts of sugar, and supplemented with thickeners such as pectin, to build a gel network structure that can maintain a stable shape under high-temperature baking conditions, effectively preventing the filling from losing during the baking process or causing the pastry to collapse. Similarly, cream fillings, whether animal or vegetable, are based on a stable water-in-oil or water-in-oil emulsion system. The fat phase provides excellent thermal stability and a smooth taste, making it a widely used type of baking filling. These technical solutions effectively solved the basic stability problem of baked fillings in a specific historical period and provided support for the diversified development of baked products.

[0003] However, as the market's pursuit of healthier, more natural, and more authentic products continues to escalate, the inherent characteristics of these traditional filling systems are increasingly revealing insurmountable limitations in meeting these new consumer demands. This is because the technical approaches used to achieve physical stability, whether for high-sugar jam or high-fat cream, fundamentally conflict with the unique health attributes and natural flavor of yogurt. Yogurt's core value stems from the unique protein gel network formed by lactic acid bacteria fermentation, active probiotics, and a rich variety of flavor compounds such as organic acids and alcohols. Maintaining these valuable properties relies heavily on a high water activity system. If these traditional yogurts are directly used in baking, their high water activity inevitably triggers intense moisture migration, resulting in a soggy dough and disintegrating finished product. Furthermore, the high temperatures of baking immediately and irreversibly denature the delicate casein micelle network, completely destroying its structure and accompanied by the precipitation of large amounts of whey, a phenomenon known as "bursting" or "watery," completely losing its desired texture. Furthermore, high temperatures can inactivate active bacteria and cause large amounts of delicate flavor substances to evaporate or degrade, eliminating the nutritional and health value of yogurt and its unique flavor. Therefore, existing technologies face a deep-seated technical contradiction: on the one hand, the market urgently needs to introduce the health concept and flavor of yogurt; on the other hand, the physical and chemical conditions that maintain the core characteristics of yogurt are inherently contradictory to the heat resistance and low moisture migration characteristics required by the baking process. Attempts to modify traditional yogurt by simply adding thickeners or stabilizers can often only improve its fluidity to a limited extent, but cannot fundamentally solve the problems of protein denaturation and water extraction at high temperatures and excessive water activity. Instead, they may introduce additional additives, affecting the natural properties and pure taste of the product.

[0004] In summary, existing technologies are unable to provide a filling product that can withstand extreme processing conditions such as high-temperature baking and low-temperature freezing, while maintaining a stable physical and chemical form, preventing moisture migration and textural deterioration, and maximally retaining the rich fermented yogurt flavor, smooth mouthfeel, and nutritional value. Therefore, how to overcome the inherent physical barriers of traditional yogurt in thermal processing applications and, through fundamental physical transformation of the fermentation base, create a baking-specific yogurt-based filling with a stable texture, resistance to baking and freezing, rich flavor, and a long shelf life has become a key challenge and a technical problem that needs to be solved urgently by those skilled in the art. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to overcome the fundamental defect of traditional yogurt in the prior art that it is not suitable for high-temperature baking processes due to its high water activity and thermally unstable protein gel network. The existing technical solutions are unable to provide a baking-specific filling that can maintain a stable physical form, does not undergo significant water migration, does not precipitate whey, and can retain the inherent fermented flavor and texture characteristics of yogurt to the greatest extent after undergoing high-temperature baking or low-temperature freezing treatment. Therefore, the field urgently needs a new preparation method that can create a baking-specific dry yogurt product with excellent baking resistance, frost resistance, rich flavor and stable shelf life through fundamental phase transformation and structural reorganization of yogurt.

[0006] To achieve the above-mentioned object of the invention, the present invention provides a method for preparing dry yogurt for baking, comprising:

[0007] Choose bacterial powder containing Lactobacillus bulgaricus and Streptococcus thermophilus, which are the basic bacteria for yogurt fermentation; add warm milk at about 40°C into the sterilized container, sprinkle in the bacterial powder and stir evenly, and let it stand for 5 minutes to activate the bacteria.

[0008] Add the remaining milk, stir evenly and put it into a yogurt machine or a constant temperature environment to ferment for 8-12 hours; the refrigerated fermented plain yogurt is cold-extracted and compressed to make a solid dry yogurt base material with a mellow and solid texture, and two types of colloids are compounded: yellow gum and carrageenan, and the mixture is neutralized with water and subjected to a heat gelatinization process. After the colloid is ground and homogenized, the dry yogurt base material is added to form a stable plain dry yogurt raw material for baking. On the basis of the plain flavor, a modified starch cake that has been subjected to heat gelatinization is added to form a dry yogurt raw material for baking. On the basis of the plain dry yogurt raw material, it is cut into 0.8 mm granules through a freeze-drying and pressing process to form dry yogurt particles for baking. On the basis of the original dry yogurt ingredients for baking, add fruit and vegetable sauces or fruit and vegetable purees, preserved fruit cubes (purple sweet potato, taro puree, red bean, jujube puree, mountain slag puree, pumpkin, purple rice, strawberry, blueberry, durian, white peach, cherry, apple, mango, mango sago, guava, raspberry, pistachio, cranberry, fig, mulberry, chocolate, caramel walnut sauce, caramel biscuit sauce) to make dry yogurt ingredients for baking with various flavors.

[0009] The product comes in four varieties: plain dry yogurt for baking, plain shredded dry yogurt for baking, plain dry yogurt cubes for baking, and various flavors of dry yogurt for baking. Specifications: 1 kg per barrel. Refrigerated storage: Refrigerated. Shelf life: 120 days. Applications: Fillings and fillings for various baked breads, yogurt cakes, Chinese pastries, and steamed buns. Highly nutritious, with a rich milky flavor ten times that of cow's milk, it offers stable baking and frost resistance.

[0010] Furthermore, the preparation method of the dry yogurt for baking comprises the following technical steps:

[0011] Step 1: pretreatment and standardization of fermentation substrate;

[0012] Step 2: temperature-controlled gradient fermentation;

[0013] Step 3: Dehydration by low-temperature centrifugation and filter pressing to prepare a dry yogurt base material;

[0014] Step 4, preparation of composite colloid stabilization system;

[0015] Step five: homogenizing, compounding and preparing the finished product.

[0016] As a preferred embodiment of the present invention, the pretreatment and standardization of the fermentation substrate in step 1 specifically includes the following operations: selecting whole milk with a total solid content of 12.0% to 14.5%, a protein content of 3.2% to 3.8% (by weight), and a fat content of 3.5% to 4.2% (by weight) as the fermentation substrate raw material. The fermentation substrate raw material is pumped into a standardized tank with a jacket, preheated to 60°C to 65°C, and homogenized by a two-stage high-pressure homogenizer, wherein the first stage homogenization pressure is set to 15 MPa to 20 MPa and the second stage homogenization pressure is set to 3 MPa to 5 MPa. The purpose of the homogenization is to break up the fat globules in the milk and micronize them to an average particle size of less than 2 microns, so as to enhance the uniformity and stability of the subsequent fermentation gel network and prevent fat from floating. The homogenized liquid is then transferred to a pasteurizer, where it undergoes a heat treatment at 90°C to 95°C for 300 to 600 seconds. This treatment completely kills any bacteria in the raw milk and denatures the whey protein, allowing it to participate in the construction of the casein gel network, thereby improving the final product's water retention and gel strength. After the pasteurization process, the liquid is rapidly cooled to the inoculation temperature of 43°C to 45°C and transferred to a clean, sterile stainless steel fermenter for later use.

[0017] As a preferred embodiment of the present invention, the temperature-controlled gradient fermentation in step 2 specifically includes the following operations: selecting a direct-vaccine (DVS) freeze-dried starter culture composed of Lactobacillus delbrueckii subsp. bulgaricus and Streptococcus thermophilus with a strain activity ratio of 1:1 to 1:2. The total number of viable bacteria in the starter culture is not less than 1×10 10CFU / gram. The freeze-dried starter culture is added directly to a standardized liquid at a temperature of 43°C to 45°C at a ratio of 20 to 40 grams of starter culture per 100 kg of fermentation substrate, and stirred at a low speed of 30 to 50 rpm for 5 to 10 minutes to ensure that the starter culture is evenly dispersed in the liquid. Subsequently, stirring is stopped and the fermentation tank is sealed, and the first stage of constant temperature fermentation begins. The fermentation temperature is precisely controlled at 42°C to 44°C. This temperature range is conducive to the rapid proliferation of thermophilic Streptococcus, thereby achieving rapid acid production. The pH value of the fermentation liquid is monitored in real time. When the pH value drops to 5.0 to 5.2, the first stage of fermentation ends. This process usually lasts 3.0 to 4.0 hours. The second stage of cooling fermentation is then started. The temperature of the fermentation liquid is gradually reduced to 38°C to 40°C within 30 minutes using jacket cooling water and maintained there. This temperature range is more conducive to the growth of Lactobacillus bulgaricus and the production of characteristic flavor substances (mainly acetaldehyde). Fermentation continues until the pH of the fermentation broth reaches 4.4 to 4.6 and the titrated acidity reaches 85°T to 95°T, which is the end of the fermentation process. The total fermentation time is controlled to be 8 to 12 hours. After fermentation is completed, the jacket cooling is immediately activated to rapidly cool the fermented solidified yogurt to 2°C to 4°C within 1 to 2 hours. After that, it is post-ripened at this temperature for 12 to 24 hours to fully shrink and solidify the gel network, making the structure more compact and further accumulating flavor substances.

[0018] As a preferred embodiment of the present invention, the low-temperature centrifugal-filter press coupled dehydration in step 3 specifically comprises the following operations: the post-ripened, set yogurt maintained at a temperature of 2°C to 4.0°C is pumped via a low-shear screw pump with wide-channel blades into a clot-breaking device with a mesh size of 5 mm to 10 mm, where the intact gel blocks are gently mechanically broken to form a uniform suspension of clot particles. The suspension is then continuously pumped into a horizontal spiral-discharge decanter centrifuge (Decanter Centrifuge) for primary dehydration. During operation, the internal temperature of the centrifuge drum is strictly controlled by a cooling jacket to below 5°C, and the drum speed is set to generate a centrifugal force of 2000 to 3000 g. Under this centrifugal force, the denser set yogurt particles are flung toward the drum wall, forming a solid phase layer, while the less dense whey collects in the inner layer and is continuously discharged from the solid phase outlet and liquid phase outlet, respectively. The collected solids are concentrated yogurt with a high-solids content of 20% to 25%. To achieve further dehydration, the concentrated yogurt is transferred to a membrane filter press for secondary filtration and dehydration. The material is evenly packed into a filter press chamber composed of a polypropylene filter plate and filter cloth. The hydraulic system is activated, applying pressure to the material using a pre-programmed pressure curve: an initial pressure of 0.5 bar is maintained for 20 minutes; the pressure is then gradually increased by 0.5 bar every 10 minutes to 6.0 bar, and the final pressure is maintained at 6.0 bar for 30 to 60 minutes. The entire filtration process is carried out at a temperature below 8°C to prevent protein denaturation due to frictional heat. After the filtration is complete, the pressure is released and the filter plates are opened, resulting in a flaky, firm solid material, which is the dry yogurt base. The technical parameters of the dry yogurt base are strictly controlled as follows: total solid content of 28% to 35% (weight percentage), protein content of 12% to 18% (weight percentage), fat content of 10% to 15% (weight percentage), and water activity (Aw) value of 0.90 to 0.94.

[0019] As a preferred embodiment of the present invention, the preparation of the composite colloid stabilization system in step 4 specifically includes the following operations: adding measured deionized water to a batching tank with a heating jacket and a high shear dispersion device. Under high-speed stirring (rotation speed 1000 to 1500 rpm), the following dry powder raw materials are added in order by weight percentage: 0.5% to 1.5% xanthan gum (80 mesh food grade), 0.3% to 0.8% κ-type carrageenan, and 2.0% to 4.0% acetylated distarch adipate (a freeze-thaw resistant modified starch). The powder is completely dispersed to form a suspension without lumps. Subsequently, food-grade sodium bicarbonate or potassium carbonate powder is added, and the pH value of the suspension is adjusted to a neutral range of 6.8 to 7.2 to ensure that each colloidal molecular chain can fully extend and be fully hydrated during the subsequent heating process. Turn on the heating jacket and heat the liquid to 88°C to 92°C. Maintain constant stirring at this temperature for 5 to 10 minutes to allow all colloids and modified starch to complete the thermal gelatinization process, forming a uniform, transparent gelatin solution. While still hot, pump the gelatin solution into a two-stage high-shear homogenizer and homogenize it at a pressure of 25 MPa in the first stage and 5 MPa in the second stage to obtain a highly uniform and stable composite colloidal solution at molecularly dispersed levels. The homogenized gelatin solution is then rapidly cooled to 8°C to 12°C via a plate heat exchanger and set aside.

[0020] As a preferred embodiment of the present invention, the homogenized compounding and finished product preparation in step 5 specifically comprises the following steps: the dry yogurt base prepared in the previous step and at a temperature of 2°C to 4°C and the composite colloidal stabilizer solution at a temperature of 8°C to 12°C are placed in a vacuum mixing tank equipped with a planetary agitator and a wall scraper in a weight ratio of 80:20 to 90:10. The agitator is activated and mixing is carried out at a low speed of 20 to 40 rpm. Simultaneously, the vacuum system is activated and the tank pressure is reduced to below -0.08 MPa to remove air introduced during mixing, prevent cavitation in the finished product, and reduce oxidation. Mixing is continued for 15 to 30 minutes until a uniform, smooth, and non-granular paste is formed. This material is the plain dry yogurt for baking. The finished product is then filled into pre-sterilized polypropylene drums using a plunger filler under clean conditions. After sealing, it is immediately stored in a cold storage at 2°C to 6°C.

[0021] Furthermore, the present invention provides a method for preparing a stringy dry yogurt specifically for baking, characterized in that during the homogenization and compounding process in step 5, a pre-treated, heat-gelatinized, stringy modified starch dough is added. The dough is prepared by mixing a high-amylose modified potato starch with water and a sorbitol solution in a weight ratio of 1:1.2:0.1. The mixture is then cooked in a twin-screw extruder at 130°C to 140°C under high shear to align the starch molecules. The extruded strips are cooled and shaped, and then cut into 3 mm x 3 mm x 5 mm pellets to form the dough. During the homogenization and compounding step, the dough is added to a mixing tank along with a dry yogurt base and a composite colloidal stabilizer at a ratio of 10% to 15% of the total weight of the finished product and mixed at a low speed until uniform. The resulting product exhibits a distinct melting and stringy effect after baking.

[0022] Furthermore, the present invention provides a method for preparing dry yogurt granules for baking, characterized by freeze-drying and forming the plain dry yogurt for baking. Specifically, the prepared plain dry yogurt is squeezed through an extruder to form strips with a diameter of 3 mm. The strips are then rapidly frozen at -40°C. The frozen strips are then fed into a vacuum freeze dryer (lyophilizer). The freeze-drying process parameters are as follows: a pre-freezing temperature of -35°C for the plate layer; a temperature ramp from -20°C to +20°C during the main drying phase, with the chamber vacuum maintained below 50 Pa; and a temperature increase to +30°C during the desorption drying phase until the product moisture content is below 3%. After drying, the resulting loose, porous dry yogurt strips are crushed and sieved through a granulator equipped with a screen with a specific aperture to produce granular products with an average particle size of 0.8 to 1.0 mm, i.e., the dry yogurt granules for baking.

[0023] Furthermore, the present invention also provides a method for preparing flavored dry yogurt for baking, characterized in that one or more flavor adjuvants are additionally added during the homogenization and compounding process of step five. The flavor adjuvants are all pretreated before being added to adjust their water activity (Aw) to 0.90 to 0.94 and their total sugar content (Brix) to 35 to 50, so as to match the physicochemical parameters of the dry yogurt base material to prevent water migration and osmotic pressure imbalance. The flavor adjuvants include but are not limited to: vacuum-concentrated fruit and vegetable purees (such as purple potato puree, pumpkin puree), candied and hot-air-dried preserved fruit granules (such as cranberry cubes, mango cubes), or sauces prepared from raw materials such as cocoa, nuts, and caramel. The amount of flavor adjuvant added is 10% to 25% of the total weight of the finished product, and it is added in the final stage of homogenization and compounding and mixed evenly at a low speed.

[0024] In summary, the present invention successfully transforms liquid yogurt with a high water content into a solid material with a high total solid content, low water activity, a tight protein network structure and effective protection by stabilizers through precise control of the fermentation process, the application of innovative low-temperature physical dehydration technology, and the scientific construction of a composite colloid stabilization system. When the material is baked at high temperature, the internal bound water is difficult to migrate, and the protein network and the colloid network work together to maintain the morphological stability of the filling, and there will be no "bursting" or "water precipitation" phenomenon. At the same time, because the low-temperature dehydration process retains the flavor substances produced by fermentation to the maximum extent, the finished product has a rich yogurt flavor. Its anti-freeze-thaw performance is due to the effective inhibition of ice crystal formation by the composite colloid system. Therefore, the product prepared by the method provided by the present invention completely solves the contradictions of the existing technology and meets the urgent demand of the baking industry for new healthy flavor fillings. DETAILED DESCRIPTION

[0025] In order to make the purpose, technical solutions and advantages of the present invention clearer, the following will combine specific examples to provide a detailed and reproducible description of the preparation method of a special dry yogurt for baking provided by the present invention. It should be noted that the specific embodiments described herein are only used to explain the present invention, and do not constitute any form of limitation on the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention. Those skilled in the art should understand that all the specific parameters, process flows and equipment selections given in the following description are preferred implementation methods of the present invention. Without departing from the core idea of ​​the present invention, there are a variety of alternative configurations and operating methods, which do not affect the ultimate technical effect of the present invention.

[0026] The core technical idea of ​​the preparation method of dry yogurt for baking provided by the present invention is to systematically transform the traditional, high-water-activity coagulated yogurt into a new material system with low water activity, high solid content, and synergistic stability of protein network and composite colloidal network through a series of precisely controlled physical and chemical processes. This system fundamentally solves the problems of structural collapse, water migration and flavor loss caused by water evaporation and protein denaturation and shrinkage in traditional yogurt in a high-temperature baking environment, while giving the product excellent freeze-thaw stability, making it widely adaptable to the full-chain application requirements of the modern baking industry from frozen dough to finished product baking. The entire preparation process is systematically divided into key technical units such as pretreatment and standardization of fermentation matrix, temperature-controlled gradient fermentation, low-temperature centrifugation-filter press coupling dehydration, preparation of composite colloidal stabilization system, and homogenization compounding and finished product preparation. Each unit is closely linked to ensure the excellent performance of the final product.

[0027] In a specific embodiment, the starting point of the preparation method is the pretreatment and standardization of the fermentation matrix. This step is intended to provide an ideal substrate with uniform physical properties, standard chemical composition and a pure microbial environment for the subsequent microbial fermentation process. Specifically, whole milk with a total solid content accurately controlled within the range of 12.0% to 14.5% is selected as the basic raw material. There are further requirements for the components of the raw milk, among which the protein content is preferably 3.2% to 3.8% (weight percentage), and the fat content is preferably 3.5% to 4.2% (weight percentage). Selecting raw milk within this range can ensure that the gel has sufficient strength and water retention after fermentation, and provide the final product with a rich frankincense flavor and delicate taste.

[0028] The raw milk is pumped into a jacketed standardized tank through sanitary stainless steel pipes. Hot water circulates through the jacket to preheat the emulsion to 60°C to 65°C. This temperature not only reduces the viscosity of the emulsion, facilitating subsequent homogenization, but also activates some heat-insensitive enzymes, preparing for subsequent processing. The preheated liquid is then sent to a two-stage high-pressure homogenizer for processing. The homogenization process is a key pre-step in building a stable gel network. Its purpose is to break up and micronize the naturally occurring fat globules in cow's milk with uneven particle size distribution. In a preferred embodiment of the present invention, the first-stage homogenization pressure is set to a high pressure of 15 MPa to 20 MPa, which is sufficient to break up most of the fat globules; the second-stage homogenization pressure is set to a lower pressure of 3 MPa to 5 MPa, whose main function is to prevent the reaggregation of the broken fine fat particles. After this double-stage homogenization process, the average particle size of the milk fat globules is stably less than 2 microns. They are encapsulated by the newly formed casein-whey protein composite membrane and evenly dispersed in the whey phase. This effectively prevents fat from floating up during subsequent static fermentation and storage. It also allows these micronized fat globules to serve as active or inactive fillers embedded in the protein gel network, enhancing the network's uniformity, density, and stability.

[0029] After homogenization, the liquid is then transported to a set of plate or tubular pasteurization equipment for heat treatment. Unlike the low-temperature long-time (LTLT) or high-temperature short-time (HTST) sterilization processes used in conventional yogurt production, the present invention adopts a more stringent heat treatment condition, that is, maintaining a heat treatment time of 300 seconds to 600 seconds under high temperature conditions of 90°C to 95°C. The selection of these process parameters has a dual purpose: first, to completely kill various miscellaneous bacteria, bacteriophages and heat-resistant spores that may exist in the raw milk, and provide a non-competitive, pure growth environment for the subsequent inoculated starter, ensuring the specificity and controllability of the fermentation process; second, and more critically, the heat treatment intensity is sufficient to fully denature heat-sensitive whey proteins (such as β-lactoglobulin and α-lactalbumin). After denaturation, the whey protein chains unfold, exposing internal hydrophobic and sulfhydryl groups. This allows them to bind to the κ-casein proteins of the casein micelles through covalent bonds (such as disulfide bonds) or non-covalent bonds (such as hydrophobic interactions). They then participate in the construction of the three-dimensional network structure of the casein gel formed during the subsequent acid coagulation process. This participation of whey proteins significantly increases the crosslink density and water-holding capacity of the gel network, making the resulting gel stronger and more delicate. It also reduces the risk of excessive whey separation during the subsequent dehydration process, laying the structural foundation for the preparation of a high-solids dry yogurt base. After sterilization, the liquid must be rapidly cooled to prevent Maillard reactions or burning and to reach a temperature suitable for starter growth. This is typically achieved using cooling water or ethylene glycol solution in a plate heat exchanger to quickly reduce the liquid temperature to the inoculation temperature of 43°C to 45°C. Subsequently, the cooled standardized liquid is transferred to a stainless steel fermentation tank with a temperature-controlled jacket and a stirring device that has been strictly steam sterilized or treated with chemical disinfectants, sealed and maintained at a temperature, waiting for inoculation.

[0030] Next comes the temperature-controlled gradient fermentation step, which is a key stage in giving the product a unique yogurt flavor and core acid gel structure. The present invention preferably uses a direct-vat set (DVS) freeze-dried starter culture composed of two classic yogurt fermentation strains, Lactobacillus delbrueckiisubsp.bulgaricus and Streptococcus thermophilus. Compared with traditional mother bacteria fermentation broth, the selection of DVS starter has the advantages of high bacterial viability, accurate strain ratio, and no risk of bacteriophage contamination. The total number of viable bacteria in the starter culture is required to be no less than 1×10 10The activity ratio of the two strains is precisely controlled within the range of 1:1 to 1:2, meaning that the number of thermophilic Streptococcus is slightly dominant or equivalent to that of Lactobacillus bulgaricus. This ratio is designed to take advantage of the rapid acid production of thermophilic Streptococcus in the early stages of fermentation.

[0031] The amount of starter added is calculated based on the weight of the liquid in the fermenter, usually at a ratio of 20 to 40 grams per 100 kilograms of fermentation substrate. The measured freeze-dried starter powder is directly sprinkled onto the surface of the liquid maintained at a temperature of 43°C to 45°C, and the stirring paddle in the fermenter is immediately started, stirring slowly at a low speed of 30 to 50 rpm for 5 to 10 minutes. The purpose of low-speed stirring is to ensure that the starter powder can be fully wetted, dissolved, and evenly dispersed throughout the liquid system, avoiding excessively high or low local bacterial concentrations, and preventing excessive shear forces from destroying the weak gel precursor structure that has begun to form. After the stirring is completed, the stirring is stopped, the fermenter is sealed, and a strict temperature-controlled gradient fermentation is started.

[0032] The fermentation process is programmed into two stages. The first stage is constant temperature fermentation, in which the temperature inside the fermentation tank jacket is precisely controlled at 42°C to 44°C. This temperature range is the optimal growth temperature for thermophilic Streptococcus, which is conducive to its rapid proliferation and metabolism of lactose to produce lactic acid, resulting in a rapid drop in the pH value of the fermentation broth. During this stage, it is necessary to monitor the pH changes of the fermentation broth in real time using an online pH electrode. When the pH value drops from the initial value of approximately 6.7 to the range of 5.0 to 5.2, it marks the end of the first stage of fermentation. At this point, the electrostatic repulsion of the casein micelles has been significantly weakened due to the establishment of an acidic environment, and aggregation begins to occur, forming a preliminary gel network. This process usually lasts 3.0 to 4.0 hours.

[0033] The system then automatically or manually initiates the second stage of cooled fermentation. By introducing cooling water into the fermenter jacket, the fermentation broth temperature gradually decreases from 42-44°C to 38-40°C over approximately 30 minutes, maintaining a constant temperature at this new temperature plateau. This temperature range is closer to the optimal growth temperature of Lactobacillus bulgaricus. Lactobacillus bulgaricus not only continues to produce acid, further strengthening the gel network, but more importantly, its metabolic activity produces volatile compounds such as acetaldehyde and acetoin, which are crucial for the characteristic flavor of yogurt. Therefore, the core purpose of the second stage is flavor accumulation and maturation. During this stage, pH and acidity are continuously monitored. Fermentation is considered to have reached its endpoint when the pH of the fermentation broth reaches 4.4 to 4.6 and the acidity, measured by titration with 0.1 mol / L sodium hydroxide solution, reaches 85°T to 95°T (degrees T). The total duration of the two-stage fermentation process is controlled to be 8 to 12 hours. Accurate judgment of the fermentation endpoint is crucial to the texture and flavor of the final product. Insufficient fermentation will result in weak gel and bland flavor, while excessive fermentation will result in excessive sourness, rough texture and severe whey precipitation.

[0034] After fermentation is complete, microbial physiological activity must be terminated immediately to lock in the product's current physical, chemical, and sensory characteristics. Operationally, a low-temperature cooling medium (such as 2°C ice water) is immediately introduced into the fermentation tank jacket to rapidly cool the entire block of solidified yogurt formed within the tank to 2°C to 4°C within 1 to 2 hours. Subsequently, a post-ripening treatment is carried out under these low-temperature conditions for 12 to 24 hours. Post-ripening is a crucial step in the production of fermented yogurt. A low temperature environment promotes further contraction and rearrangement of the gel network, expelling a small amount of free whey and making the gel structure more compact and dense. At the same time, some flavor precursors continue to undergo slow chemical transformations at low temperatures, making the yogurt's flavor more mellow, balanced, and harmonious.

[0035] The inherently high water content of fermented and post-ripened set yogurt makes it completely unsuitable for baking. Therefore, the subsequent low-temperature centrifugation-filter-press dehydration step is the core innovation of the present invention, aiming to transform the set yogurt into a high-solids, firm solid material. The entire dehydration process is strictly carried out at low temperatures to preserve the natural conformation of proteins and the stability of fermented flavor compounds. First, the ripened yogurt, maintained at a temperature of 2°C to 4.0°C, is gently pumped from the fermenter using a low-shear screw pump with wide-channel blades. This low-shear pump is chosen to minimize severe mechanical damage to the delicate yogurt gel network during transportation. The material is then pumped into a curd-breaking device equipped with a 5-10 mm mesh or cutting wire. As the yogurt curd passes through, it is gently cut into a relatively uniform suspension of curd particles. This pretreatment step enhances the efficiency and uniformity of the subsequent centrifugal dehydration process.

[0036] The crushed yogurt suspension is then continuously pumped into a horizontal spiral decanter centrifuge (Decanter Centrifuge) for primary dehydration. This highly efficient solid-liquid separation device maintains a strict temperature control of below 5°C during operation by refrigerating the centrifuge drum's outer casing. The centrifuge's drum speed is set to generate a centrifugal force of 2,000 to 3,000 times the acceleration of gravity. Under this powerful centrifugal force, the denser yogurt solids (solid phase) are rapidly flung toward the inner wall of the drum and continuously pushed toward the solid phase outlet via an internal spiral conveyor. The less dense whey (liquid phase) collects in the inner layer of the drum and is continuously discharged through an overflow outlet. This step effectively removes most of the free water and dissolved small molecules such as lactose and salts. The collected solid phase is a high-solids concentrated yogurt with a total solids content of 20% to 25%.

[0037] However, concentrated yogurt that undergoes centrifugal dehydration alone still has a high water activity and a soft texture, failing to meet baking resistance requirements. Therefore, a secondary, deep dehydration step is required. The concentrated yogurt discharged from the centrifuge is transferred to a membrane filter press. The filter press consists of multiple parallel sets of polypropylene filter plates covered with specialized filter cloth. These plates, when closed, form sealed filter chambers. The concentrated yogurt is pumped evenly into these chambers until they are full. Then, a hydraulic system is activated, applying mechanical pressure to the contents of the chambers using a pre-programmed pressure profile. In a preferred pressure profile, the initial pressure is set to a low 0.5 bar and maintained for 20 minutes to facilitate the gradual discharge of free water without over-compacting the filter cake surface and forming a dense layer. The pressure is then gradually increased at a steady rate of 0.5 bar every 10 minutes to a final pressure of 6.0 bar. The 6.0 bar pressure is maintained for 30 to 60 minutes to squeeze out as much water as possible from the tighter interstices between the protein networks. The entire filter pressing process is carried out in an environmentally controlled room with a temperature below 8°C to prevent the frictional heat generated by prolonged mechanical extrusion from causing thermal denaturation of the protein, which would affect the texture and flavor of the final product. After the pressing is completed, the hydraulic pressure is released and the filter plates are pulled apart one by one to obtain a flaky, firm, soft cheese-like solid material. This material is the core intermediate of the present invention - the dry yogurt base. Through precise process control, the technical parameters of the dry yogurt base are strictly limited to a specific range: the total solids content is 28% to 35% (weight percentage), the protein content is 12% to 18%, the fat content is 10% to 15%, and the critical water activity (Aw) value is controlled between 0.90 and 0.94. This low water activity is key to ensuring that the product does not undergo significant moisture migration with other materials such as dough during the baking process.

[0038] After obtaining the dry yogurt base material, it is necessary to construct a composite colloidal stabilization system to improve its processing performance, enhance its thermal stability, and impart a specific mouthfeel. This step is specifically as follows: In a stainless steel batching tank equipped with a heating jacket and a high-shear dispersion device, first add measured deionized water. While turning on high-speed stirring (the speed is set at 1000 to 1500 rpm), the following accurately weighed dry powder raw materials are added in order by weight percentage: 0.5% to 1.5% xanthan gum (preferably 80 mesh food grade), 0.3% to 0.8% kappa-type carrageenan, and 2.0% to 4.0% acetylated distarch adipate. Xanthan gum, a pseudoplastic fluid, provides excellent suspension stability and static structure, preventing material delamination during standing. κ-carrageenan forms a thermoreversible, rigid gel upon cooling, helping to maintain the filling's shape during baking. Acetylated distarch adipate, a modified starch with excellent freeze-thaw resistance, traps moisture and inhibits ice crystal growth during freezing, thereby improving the product's freeze-thaw stability. These powders are thoroughly dispersed in cold water to form a suspension free of visible lumps.

[0039] Subsequently, food-grade sodium bicarbonate or potassium carbonate powder is slowly added to the suspension to adjust the pH. The pH is precisely adjusted to a neutral range of 6.8 to 7.2. This is because anionic polysaccharide colloids such as xanthan gum and carrageenan maximize their molecular chain extension in a neutral to slightly alkaline environment, facilitating subsequent hydration. After the pH is adjusted, the heating jacket of the batching tank is opened and the liquid is heated to 88°C to 92°C. This temperature is maintained constant while stirring at low speed for 5 to 10 minutes. This process, known as thermal gelatinization, ensures that all colloids and modified starch granules fully absorb water, swell, and dissolve, forming a uniform, transparent gelatin solution with a certain viscosity. To achieve a higher degree of dispersion of the colloidal molecules, the hot gelatin solution is pumped into a two-stage high-shear homogenizer, where homogenization is performed at a pressure of 25 MPa in the first stage and 5 MPa in the second stage. Homogenization breaks down any aggregates between the colloidal molecules, forming a molecularly dispersed, highly uniform, and stable composite colloidal solution. Finally, the homogenized high-temperature glue liquid is passed through a plate heat exchanger and quickly cooled with cooling water to reduce its temperature to 8°C to 12°C for use.

[0040] Finally, the components prepared above are combined into the final product through homogenization, compounding, and finished product preparation steps. The dry yogurt base prepared in the previous steps, maintained at a temperature of 2°C to 4°C, and the composite colloidal stabilizer solution, maintained at a temperature of 8°C to 12°C, are placed together in a preferred weight ratio of 80:20 to 90:10 in a vacuum mixing tank equipped with a planetary agitator and a wall scraper. The planetary agitator system achieves efficient macroscopic mixing without dead angles, while the wall scraper continuously removes material adhering to the tank walls to ensure uniform mixing. The agitator system is activated and mixing is continued at a low speed of 20 to 40 rpm. This low speed is used to avoid excessive shearing that disrupts the already formed, compact protein network structure of the dry yogurt base. While mixing, the vacuum system is activated to reduce the pressure within the tank to below -0.08 MPa. The purpose of vacuuming is to remove the air introduced during the feeding and mixing process, to prevent the formation of fine air pockets in the finished product that affect the texture and appearance, and to reduce the oxygen content, thereby slowing down the oxidative deterioration of the product during its shelf life. The entire low-speed vacuum mixing process lasts for 15 to 30 minutes, until the system forms a paste-like material with a uniform texture, fine and smooth texture, and no granularity. This material is the basic product of the present invention - plain dry yogurt for baking. Finally, the finished product is quantitatively filled into polypropylene packaging barrels (e.g., 1 kg specification) that have been pre-sterilized with ozone or ultraviolet light using a sanitary plunger filling machine in an environment with a cleanliness level that meets food production requirements. The barrels are sealed with heat-sealed film or a pressure cap, and then immediately sent to a finished product cold storage controlled at a temperature of 2°C to 6°C for storage. Under these conditions, the product has a refrigerated shelf life of up to 120 days.

[0041] Furthermore, the present invention provides a method for preparing a specially prepared, stringy, dry yogurt specifically for baking, capable of achieving a unique stringy effect. This method comprises adding a specially pretreated, heat-gelatinized, stringy modified starch dough during the homogenization and compounding step. The dough preparation method comprises selecting a modified potato starch with a high amylose content and mixing it with purified water and a sorbitol solution as a humectant and plasticizer in a precise weight ratio of 1:1.2:0.1 to produce a wet powder with a moderate moisture content. This wet powder is continuously fed into a twin-screw extruder via a feeder. Within the extruder barrel, the material undergoes deep gelatinization and maturation under the intense shearing and compression of the screws at temperatures of 130°C to 140°C, simultaneously aligning the starch molecular chains under the high shear forces. The maturated material is then extruded through a specifically shaped die to form strips. After the extrudate leaves the die, it passes through a cooling air duct for rapid cooling and shaping, and is then cut into uniform particles of approximately 3 mm × 3 mm × 5 mm in size by an online pelletizer, which is the described wire-drawn modified starch cake. During the homogenization and compounding step, this prefabricated cake is added to a vacuum mixing tank together with the dry choked yogurt base material and the composite colloid stabilizer at a ratio of 10% to 15% of the total weight of the finished product, and mixed at a low speed until evenly distributed. Because the cake has hot melt properties and a special molecular structure, the resulting wire-drawn dry choked yogurt product can exhibit an obvious melting and wire-drawing effect similar to cheese after baking and heating, which greatly enriches the application scenarios and fun of the product.

[0042] Furthermore, in order to meet the market demand for room temperature storage and ready-to-use ingredients, the present invention also provides a method for preparing dry yogurt particles for baking. It is characterized in that the aforementioned prepared plain dry yogurt for baking is subsequently freeze-dried and formed. The specific operation process is: the freshly prepared plain dry yogurt is squeezed out into continuous strips with a diameter of 3 mm through an extrusion device with a circular die hole, and is directly dropped onto a stainless steel conveyor belt running in a quick-freezing tunnel at -40°C for rapid single-unit freezing. Rapid freezing helps to form fine ice crystals, thereby maximizing the protection of the microstructure of the material. The completely frozen material strips are collected and sent to the material tray of a vacuum freeze dryer (freeze dryer). The parameters of the freeze-drying process are precisely set: first, the pre-freezing temperature of the plate layer is reduced to -35°C and maintained for a period of time to ensure that the center of the material is completely frozen. The main drying stage then begins, where the plate temperature is slowly and gradually raised from -20°C to +20°C using a programmed temperature ramp. Meanwhile, the vacuum level in the drying chamber is maintained below 50 Pa. Under these conditions, solid ice in the material sublimates into water vapor and is extracted. Following the main drying phase, the plate temperature is further raised to +30°C to remove residual moisture, which is more tightly bound to the material, until the final moisture content of the product is controlled below 3%. After drying, the vacuum is released, and the loose, porous dried yogurt strips are removed. These strips are crushed and sieved through a granulator equipped with a screen of a specific aperture, resulting in a granular product with an average particle size of 0.8 mm to 1.0 mm, providing good flowability. These are the dried yogurt granules specifically for baking. These products can be stored sealed at room temperature and have an extremely long shelf life. They can be sprinkled directly on dough or mixed into fillings.

[0043] In addition, in order to greatly enrich the product line and meet consumers' demand for diversified tastes, the present invention also provides a series of methods for preparing flavor-based dry yogurts for baking. The core technology is to add one or more strictly pre-treated flavor adjuvants in the homogenization and compounding step. Before adding, these flavor adjuvants must undergo a special process treatment so that their two key physicochemical parameters - water activity (Aw) and total sugar content (Brix) - match the parameters of the dry yogurt base material. Specifically, the water activity of the flavor adjuvant needs to be adjusted to a range of 0.90 to 0.94, and the total sugar content needs to be adjusted to 35 to 50. This consistency in parameters is the key to preventing moisture migration and osmotic pressure imbalance between the flavor adjuvant and the yogurt base during storage of the finished product, thereby avoiding quality problems such as the yogurt becoming dry and hard, and the yogurt base material losing water. These flavoring ingredients come in a wide variety, including but not limited to: fruit and vegetable purees processed through vacuum low-temperature concentration (e.g., purple sweet potato puree, taro puree, pumpkin puree, and jujube puree); diced preserved fruit (e.g., cranberry puree, mango puree, and fig puree) candied and hot-air dried; and specialty sauces carefully brewed from ingredients like cocoa, nuts, and caramel (e.g., chocolate sauce, caramel walnut sauce, and caramel biscuit sauce). These flavoring ingredients are typically added in amounts ranging from 10% to 25% of the total weight of the finished product. They are then briefly mixed at a low speed to ensure even distribution, without prolonged stirring to prevent the integrity of the fruit and other ingredients from being compromised.

[0044] In order to objectively and quantitatively verify the technical effects of the present invention, the following comparative experiments of the embodiments and comparative examples are carried out.

[0045] Example 1: Preparation of the original dry yogurt for baking of the present invention

[0046] 1000 kg of whole milk with a total solids content of 13.5%, protein content of 3.5%, and fat content of 4.0% was preheated to 62°C, homogenized at 18 MPa / 4 MPa, and then heat treated at 92°C for 450 seconds, followed by cooling to 44°C. 300 g of milk was inoculated with a viable count of 1.2 × 10 10A DVS starter culture with a CFU / g ratio of Lactobacillus bulgaricus to Streptococcus thermophilus of 1:1.5 was stirred at low speed for 8 minutes. Fermentation was continued at 43°C for 3.5 hours to a pH of 5.15, then cooled to 39°C for another 4.5 hours, ending when the pH reached 4.5 and the titratable acidity reached 90°F. The fermentation was then rapidly cooled to 3°C and post-ripened for 18 hours. The post-ripened yogurt was crushed using an 8mm mesh and pumped into a horizontal screw discharge centrifuge with a drum temperature controlled at 4°C and a centrifugal force of 2500g to produce a concentrated yogurt with a total solids content of 23%. This concentrated yogurt was then pumped into a membrane filter press and pressed at an ambient temperature of 6°C using a programmable pressure increase from 0.5 bar to 6.0 bar, with the pressure maintained for 45 minutes. The obtained dry yogurt base material has a total solid content of 32.5%, a protein content of 15.8%, a fat content of 13.2% and a water activity of 0.92.

[0047] In another mixing tank, 1.0% xanthan gum, 0.5% kappa-carrageenan and 3.0% acetylated distarch adipate were dispersed in deionized water, the pH was adjusted to 7.0, the mixture was heated to 90°C for gelatinization for 10 minutes, homogenized at 25 MPa / 5 MPa, and then cooled to 10°C to prepare a composite colloidal stabilizer.

[0048] 85 kg of dry yogurt base material and 15 kg of composite colloid stabilizer were mixed at a low speed in a vacuum mixing tank at a vacuum degree of -0.085 MPa for 20 minutes to obtain the product of Example 1.

[0049] Comparative Example 1: Preparation of a simple improved yogurt filling using traditional technology

[0050] 100 kg of commercially available Greek yogurt (approximately 18% total solids content, approximately 0.97 water activity) prepared by bag filtration was placed in a mixing tank. 5 kg of white sugar and 3 kg of pregelatinized corn starch were directly added and stirred at room temperature for 15 minutes until uniform. The resulting material was the product of Comparative Example 1.

[0051] The products of Example 1 and Comparative Example 1 were used as fillings, respectively, and bread was made using the same recipe and process, and baked in an oven at 180°C for 15 minutes. Various performance indicators of the fillings were evaluated before and after baking, and the results are recorded in Table 1.

[0052] Table 1

[0053]

[0054] The data in the table above clearly demonstrates that the dry yogurt for baking prepared using the present invention significantly outperforms products produced using conventional improved methods in key physical and chemical properties, such as total solids content and water activity. This fundamental phase difference directly leads to its unparalleled performance advantages in actual baking applications. Its exceptional morphological stability, resistance to moisture migration, rich flavor retention, and excellent freeze-thaw stability demonstrate that the present invention successfully addresses the existing challenges of yogurt's ineffective application in high-temperature baking applications, providing the baking industry with a high-value, innovative filling with reliable performance and unique flavor.

[0055] The foregoing description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Those skilled in the art will readily appreciate that various modifications and variations of the present invention are possible. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention are intended to be within the scope of protection of the present invention.

Claims

1. A method for preparing dry yogurt for baking, characterized in that: include: Pre-treating and standardizing the fermentation substrate to obtain a standardized feed solution; performing temperature-controlled gradient fermentation on the standardized liquid to obtain set yogurt; The method comprises the steps of: performing low-temperature physical dehydration treatment on the set yogurt to obtain a dry yogurt base material, wherein the total solid content of the dry yogurt base material is controlled to be 28% to 35% by weight, and the water activity value is 0.90 to 0.94; preparing a composite colloid stabilizer solution; and mixing and compounding the dry yogurt base material and the composite colloid stabilizer solution to obtain the dry yogurt for baking.

2. The preparation method according to claim 1, characterized in that The process of subjecting the set yogurt to low-temperature physical dehydration includes: gently mechanically crushing the set yogurt to form a suspension of curd particles; pumping the suspension of curd particles into a horizontal spiral discharge sedimentation centrifuge for primary centrifugal dehydration, wherein the internal temperature of the centrifuge drum is controlled below 5°C during operation, and the drum speed is set to generate a centrifugal force of 2000 to 3000g, thereby separating and obtaining a concentrated yogurt with a total solids content of 20% to 25%; and conveying the concentrated yogurt into a diaphragm filter press for secondary pressure filtration dehydration, wherein the concentrated yogurt is pressurized using a programmed pressure curve, wherein the pressure curve includes maintaining an initial pressure of 0.5 bar for 20 minutes, then gradually increasing the pressure to 6.0 bar at a rate of 0.5 bar per 10 minutes, and maintaining the final pressure of 6.0 bar for 30 to 60 minutes, and the entire pressure filtration process is carried out in an environment with a temperature below 8°C, thereby obtaining the dry yogurt base.

3. The preparation method according to claim 1, characterized in that The process of performing temperature-controlled gradient fermentation on the standardized feed liquid comprises: Inoculating the standardized liquid with a direct-injection freeze-dried starter culture consisting of Lactobacillus bulgaricus and Streptococcus thermophilus; The first stage of constant temperature fermentation is carried out, and the fermentation temperature is precisely controlled at 42°C to 44°C until the pH value of the fermentation liquid drops to 5.0 to 5.2; Then, the second stage of cooling fermentation is started, and the temperature of the fermentation liquid is gradually lowered to 38°C to 40°C and maintained there, and the fermentation is continued until the pH value of the fermentation liquid reaches 4.4 to 4.6 and the titrated acidity reaches 85°T to 95°T; and the set yogurt after fermentation is quickly cooled to 2°C to 4°C and subjected to post-ripening treatment at this temperature for 12 to 24 hours.

4. The preparation method according to claim 3, characterized in that The process of preparing the composite colloidal stabilizer solution specifically includes: In deionized water, 0.5% to 1.5% xanthan gum, 0.3% to 0.8% kappa-carrageenan, and 2.0% to 4.0% acetylated distarch adipate are sequentially added under high-speed stirring until the powders are completely dispersed to form a suspension; adding a food-grade alkali agent to the suspension to adjust the pH value of the suspension to a neutral range of 6.8 to 7.2; The pH-adjusted liquid is heated to 88° C. to 92° C., and maintained at this temperature with constant stirring for 5 to 10 minutes to allow all colloids and modified starch to complete the thermal gelatinization process to form a glue solution; and the glue solution is subjected to high-pressure homogenization and then quickly cooled to 8° C. to 12° C. for use.

5. The preparation method according to claim 3, characterized in that The process of pretreating and standardizing the fermentation matrix specifically includes: selecting whole raw cow's milk with a total solid content of 12.0% to 14.5%, a protein content of 3.2% to 3.8%, and a fat content of 3.5% to 4.2% as the fermentation matrix raw material; preheating the fermentation matrix raw material to 60°C to 65°C, and homogenizing it through a two-stage high-pressure homogenizer, wherein the first-stage homogenization pressure is set to 15 MPa to 20 MPa, and the second-stage homogenization pressure is set to 3 MPa to 5 MPa; and sterilizing the homogenized liquid at a temperature of 90°C to 95°C for 300 seconds to 600 seconds, and then rapidly cooling it to an inoculation temperature of 43°C to 45°C to obtain the standardized liquid.

6. The preparation method according to claim 1, characterized in that During the process of mixing and compounding the dry yogurt base material and the composite colloid stabilizer solution, a heat-gelatinized, wire-drawn, modified starch cake is additionally added, and the added amount of the cake is 10% to 15% of the total weight of the finished product; wherein, the preparation method of the heat-gelatinized, wire-drawn, modified starch cake is: a potato modified starch with a high amylose content is mixed with water and a sorbitol solution in a weight ratio of 1:1.2:0.1, and the mixture is subjected to a cooking process at a temperature of 130°C to 140°C and high shear force through a twin-screw extrusion machine. After the extruded material is cooled and shaped, it is cut into granules to obtain the cake.

7. The preparation method according to claim 1, characterized in that The method further includes a subsequent processing step of the plain dry yogurt for baking to prepare dry yogurt particles for baking. The subsequent processing step specifically includes: passing the plain dry yogurt for baking through an extruder to extrude a strip having a diameter of 3 mm, and then rapidly freezing the strip at -40°C to obtain a frozen strip; The frozen material strips are fed into a vacuum freeze dryer and freeze-dried under the following process parameters: a plate pre-freezing temperature of -35°C, a plate temperature programmed from -20°C to +20°C during the main drying phase, a plate temperature raised to +30°C during the desorption drying phase, and a chamber vacuum maintained below 50 Pa, until the product moisture content is less than 3%; and The dried yogurt strips obtained after drying are crushed and sieved to obtain granular finished products with an average particle size of 0.8 mm to 1.0 mm.

8. The preparation method according to claim 1, characterized in that During the process of mixing and compounding the dry yogurt base material and the composite colloid stabilizer solution, one or more flavor adjuvants are additionally added, and the amount of the flavor adjuvant added is 10% to 25% of the total weight of the finished product; wherein, before being added, the flavor adjuvants are all pretreated so that their water activity is adjusted to the range of 0.90 to 0.94, and their total sugar content is adjusted to 35 to 50, so as to match the physicochemical parameters of the dry yogurt base material, thereby preventing moisture migration during storage of the finished product.

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