Solidified yoghurt with reversible thixotropic rheological property and preparation method thereof

Abstract

The invention relates to the technical field of food fermentation and dairy product processing, in particular to set yoghurt with reversible thixotropic rheological characteristics and a preparation method of the set yoghurt. The set yogurt with the reversible thixotropic rheological property comprises the following components in parts by mass: 1000 parts of raw milk, 30-50 parts of natural edible medicinal powder, 50-80 parts of white granulated sugar and 1-3 parts of a leavening agent, the natural edible medicine powder is composed of gordon euryale seed superfine powder, lotus seed superfine powder, Chinese yam superfine powder and poria cocos superfine powder. The set yoghurt provided by the invention has thixotropic shear thinning fluid characteristics, is a uniform fluid during pumping and filling, and is in a set gel state after packaging and standing, so that the basic conversion of the set yoghurt from a first-filling and second-fermentation intermittent process to a first-fermentation and second-filling continuous assembly line work is realized. The natural compound prepared from the Chinese yam, the poria cocos, the gordon euryale seeds and the lotus seeds according to a specific proportion has a health-care function and a structure regulation effect, and no additional additive is needed.

Description

Technical Field

[0001] This invention relates to the field of food fermentation and dairy processing technology, and in particular to a set-type yogurt with reversible thixotropic rheological properties and its preparation method. Background Technology

[0002] Based on their texture, yogurt can be divided into two main categories: set yogurt and stirred yogurt. Yogurt processing relies on the growth and metabolism of lactic acid bacteria in milk. Lactic acid bacteria break down lactose to produce lactic acid and other organic acids, causing the pH of the milk to gradually decrease until casein aggregates near its isoelectric point, forming a homogeneous gel system. If this gel system is consumed directly as a finished product, it is called set yogurt. This type of yogurt has a thick, gel-like texture and is usually eaten with a spoon. Set yogurt is close to the form of yogurt before the advent of modern food industry, hence it is also known as "old-fashioned yogurt." However, because the casein gel structure is relatively fragile, if industrial bottling is performed after fermentation, the pumping and shearing processes can easily damage its gel network. This type of yogurt, whose gel structure is damaged during bottling, is called stirred yogurt. Although stirred yogurt may thicken slightly during storage, it cannot return to its pre-bottling gel state. Therefore, stirred yogurt has better fluidity and can be consumed with a straw.

[0003] In modern dairy production, to maintain the unique texture of set yogurt, a "fill-first, ferment-later" process is often used. This involves pre-filling the liquid into retail containers after sterilization and inoculation, then placing them in a fermentation chamber for static cultivation, allowing them to form a complete gel structure within the containers. This "fill-first, ferment-later" process suffers from significant bottlenecks in production efficiency and flexibility. First, the process is intermittent; after filling, a large number of individual retail containers must be placed in a temperature-controlled fermentation chamber, occupying a huge amount of space and resulting in low production efficiency. Second, during ripening and storage, the microenvironment of individual retail containers is difficult to achieve absolute uniformity, affecting the consistency of product quality within the same batch. More importantly, once the final gel forms in the container, its physical form is completely fixed, eliminating the possibility of subsequent centralized reprocessing. For example, it is impossible to evenly mix in fruit pieces, jams, or other ingredients after fermentation, severely limiting the product's flavor diversity.

[0004] Currently, the mainstream type of yogurt on the market is stirred yogurt, which follows a "fermentation first, then packaging" process. After the yogurt undergoes overall fermentation in large fermentation tanks to form curd, the gel structure is broken down by mechanical stirring, transforming it into a pumpable viscous fluid. It is then cooled, flavored, and packaged. This process significantly improves production continuity and equipment utilization, allows for the flexible addition of various flavorings before packaging, and easily maintains product quality stability. However, stirring and packaging irreversibly disrupt the three-dimensional gel network formed by casein. Although food additives can be used to reshape the viscosity and texture of the system, the sensory characteristics of the final product still differ significantly from traditional set yogurt. More importantly, the consumer group for "traditional yogurt" generally dislikes the use of food additives.

[0005] To address the aforementioned contradictions, existing technologies have made numerous attempts and improvements regarding the textural modification of yogurt. For example, existing technologies disclose a "set-type yogurt that is easy to drink with a straw." By adjusting the formula and process, the cohesive strength of the gel is reduced, allowing it to flow locally under the suction of a straw. This technology gives set-type yogurt the drinkable characteristics of stirred yogurt. However, this product, which simply reduces gel strength to compromise processing performance, will still have its casein gel network completely broken down under the high shear forces required for industrial pumping, making continuous production of "fermentation first, then filling" impossible.

[0006] Existing technology also discloses "a form-controllable yogurt and its preparation method," the core of which involves adding specific types of chemically modified starch (such as glutinous rice hydroxypropyl distarch phosphate) and supplementing it with protein powder and stabilizers to control the yogurt's form. This method does not provide conclusive evidence that its gel system can spontaneously recover its original network structure under static conditions after shear failure. More importantly, the use of chemically modified starch and stabilizers contradicts the current "clean label" consumer trend and fails to fundamentally solve the bottleneck of continuous production processes.

[0007] There are also inventions that add yam powder and other food-medicine homologous ingredients to yogurt, but the focus of this type of invention is on utilizing the health benefits of the ingredients, without systematically studying the interaction mechanism between natural polysaccharides and casein, nor involving innovation in the core rheological properties of the product and the production model.

[0008] Overall, existing technologies either sacrifice the texture of set yogurt in exchange for fluidity or rely on food additives for "irreversible" viscosity adjustment, failing to achieve intelligent and reversible "gel-fluid-gel" transformation during production. Although using polysaccharides to regulate the rheological properties of food is a common industry practice, current yogurt-related research and applications are mostly limited to using polysaccharides as simple gelling agents, thickeners, or compounding them with hydrocolloids to improve stability. There are no reports of constructing a "protein-polysaccharide" composite gel system with thixotropic self-recovery properties by precisely controlling the polysaccharide composition and ratio of various natural ingredients.

[0009] To date, no publicly available technical solution has been found that can precisely regulate the yogurt gel network through the precise combination of natural ingredients (rather than food additives), utilizing the synergistic effect of polysaccharides and casein, thereby endowing it with intelligent thixotropic properties such as "gel formation during fermentation, flowability under shear, and self-recovery upon rest." Existing technologies cannot simultaneously achieve the typical texture of set yogurt while meeting the requirements of "zero-additive" clean labeling and the industrial continuous production demands of "fermentation before packaging," exhibiting significant limitations in unifying functionality, naturalness, and processing convenience. This technological gap constitutes the core problem that this invention aims to solve. Summary of the Invention

[0010] The purpose of this invention is to provide a set-type yogurt with reversible thixotropic rheological properties and a preparation method thereof. By adding specific natural food and medicinal powders and using specific processes, it combines excellent set-type yogurt texture with reversible pumpability, making it suitable for continuous production.

[0011] To achieve the above-mentioned objectives, the present invention provides the following technical solution: One of the technical solutions of this invention provides a set-type yogurt with reversible thixotropic rheological properties, comprising the following components in parts by mass: 1000 parts raw milk, 30-50 parts natural food and medicinal powder, 50-80 parts white sugar, and 1-3 parts starter culture; The natural food and medicine powder is composed of ultra-fine powder of fox nuts, ultra-fine powder of lotus seeds, ultra-fine powder of yam, and ultra-fine powder of poria cocos.

[0012] The second technical solution of this invention provides a method for preparing the above-mentioned set-type yogurt with reversible thixotropic rheological properties, comprising the following steps: (1) Mix the fine powder of Euryale ferox and the fine powder of lotus seeds with 10 to 30 times their weight of raw milk, soak them and then pregelatinize them. After the pregelatinization is completed, add the fine powder of yam and the fine powder of Poria cocos to obtain the pregelatinized slurry. (2) Mix the pregelatinized slurry, the remaining raw milk and white sugar, homogenize, sterilize and cool to obtain the fermentation base material; (3) Add starter culture to the fermentation base, ferment, and stir after reaching the fermentation endpoint to obtain thin yogurt; (4) After the diluted yogurt is filled and sealed, it is ripened to obtain a set-type yogurt with reversible thixotropic rheological properties.

[0013] Compared with the prior art, the present invention has the following beneficial effects: The set-type yogurt provided by this invention possesses thixotropic shear-thinning fluid characteristics. During pumping and filling, it is a homogeneous fluid; after packaging and settling, it solidifies into a gel. This fundamentally transforms the set-type yogurt production process from an intermittent "fill first, ferment later" route to a continuous "ferment first, fill later" production line. Existing continuous filling equipment for stirred yogurt can be used for set-type yogurt production without modification. This significantly improves equipment utilization and unit area capacity, while substantially reducing production energy consumption and time costs. It allows for uniform addition of ingredients "after fermentation and before filling," enabling diverse innovations in the flavor and ingredients of set-type yogurt.

[0014] This invention utilizes a natural compound formulated with specific proportions of yam, poria cocos, euryale ferox, and lotus seeds. This compound possesses both health benefits and structural regulation functions, requiring no additional thickeners or stabilizers, achieving "zero additives." The composite gel network exhibits high water retention, prevents whey separation, maintains stable form throughout its shelf life, and has a rich flavor. While ordinary set-type yogurt may suffer structural damage during transportation due to severe vibrations, the yogurt described in this invention recovers its gel structure after a period of rest. Consistent fermentation conditions across batches ensure stable product quality. The addition of medicinal and edible ingredients enhances the yogurt's inherent function of regulating the intestinal microecology. Attached Figure Description

[0015] Figure 1 This is a schematic diagram of the sample from Example 1; Figure 2 This is a schematic diagram of the sample from Example 2; Figure 3 This is a schematic diagram of the sample in Example 3; Figure 4 This is a texture scan of Example 3; Figure 5 These are texture scans of comparative examples 1-6; Figure 6 These are texture scan images of Examples 1 and 2. Detailed Implementation

[0016] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as a limitation of the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0017] It should be understood that the terminology used in this invention is merely for describing particular embodiments and is not intended to limit the invention. Furthermore, with respect to numerical ranges in this invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Every smaller range between any stated value or intermediate value within a stated range, and any other stated value or intermediate value within said range, is also included in this invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0018] Unless otherwise stated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. While only preferred methods and materials have been described herein, any methods and materials similar or equivalent to those described herein may be used in the implementation or testing of this invention. All references to this specification are incorporated by way of citation to disclose and describe methods and / or materials associated with those references. In the event of any conflict with any incorporated reference, the content of this specification shall prevail.

[0019] Various modifications and variations can be made to the specific embodiments described in this specification without departing from the scope or spirit of the invention, as will be apparent to those skilled in the art. Other embodiments derived from this specification will also be obvious to those skilled in the art. This application specification and embodiments are merely exemplary.

[0020] The terms “include,” “including,” “have,” “contain,” etc., used in this article are all open-ended terms, meaning that they include but are not limited to.

[0021] All raw materials used in this invention can be obtained commercially or prepared using existing technologies.

[0022] This invention provides a set-type yogurt with reversible thixotropic rheological properties, comprising the following components in parts by weight: 1000 parts raw milk, 30-50 parts natural food and medicinal powder, 50-80 parts white sugar, and 1-3 parts starter culture; The natural food and medicine powder is composed of ultra-fine powder of fox nuts, ultra-fine powder of lotus seeds, ultra-fine powder of yam, and ultra-fine powder of poria cocos.

[0023] In this invention, the proportion of amylose in the gorgon fruit powder is very high, which easily forms a very hard gel with a high elastic modulus. Its interpenetration or intercalation with the casein network can significantly enhance the mechanical strength of the composite gel. Gelatinized gorgon fruit starch will rapidly age at the storage temperature of yogurt (around 4°C), causing the product to gradually harden, separate into water, and deteriorate in taste during its shelf life. Therefore, without modification or blending with other ingredients, gorgon fruit is not suitable for foods requiring a long-term soft and delicate texture. The main chain of Poria cocos polysaccharide is β-1,3-glucan; its water-retaining and steric hindrance properties can inhibit the aging of gorgon fruit starch, keeping the product soft.

[0024] The addition of lotus seed powder can appropriately reduce the proportion of amylose and adjust the gel strength of the product. The viscosity peak of the mixture of lotus seed powder and fox nut powder is low, and the thermal viscosity stability is good (i.e., the viscosity does not decrease significantly under prolonged heating or shearing). The addition of yam powder can adjust its viscosity to suit the textural characteristics of set yogurt. The gel formed by fox nut and lotus seed powder is opaque and milky white; this characteristic is not a disadvantage when used in yogurt.

[0025] The gelatinization temperatures of various starch components in natural compound formulations differ. Components with high gelatinization temperatures and good thermal stability are pre-gelatinized, followed by pasteurization to gelatinize all starches, resulting in a stable and uniform cross-linked structure. Before the formation of cross-links in milk proteins and Poria cocos polysaccharides, the starches of Euryale ferox and lotus seeds are kept at relatively high temperatures, preventing starch retrogradation. After fermentation to form the cross-linked structure, the product is then stored at low temperatures, effectively preventing starch retrogradation.

[0026] In this invention, the set-type yogurt with reversible thixotropic rheological properties includes 30 to 50 parts of natural food and medicinal powder, for example, 30 parts, 35 parts, 40 parts, 45 parts or 50 parts, etc.

[0027] In this invention, the set-type yogurt with reversible thixotropic rheological properties includes 50 to 80 parts of white sugar, for example, 50, 55, 60, 70, 75 or 80 parts.

[0028] In this invention, the set-type yogurt with reversible thixotropic rheological properties includes 1 to 3 parts of starter, for example, 1 part, 2 parts or 3 parts, etc.

[0029] In some embodiments of the present invention, the fermenting agent is selected from Chuanxiu lactic acid bacteria yogurt starter.

[0030] In this invention, the raw milk includes fresh milk or reconstituted milk.

[0031] In this invention, lotus seeds are dried after removing the core and seed coat, then pulverized into a very fine powder and sieved to obtain lotus seed powder; yam is peeled, sliced, dried, then pulverized into a very fine powder and sieved to obtain yam powder; Poria cocos is cleaned and purified, then pulverized into a very fine powder and sieved to obtain Poria cocos powder; Euryale ferox is dried, coarsely ground to remove the brown substance on the surface, then pulverized into a very fine powder and sieved to obtain Euryale ferox powder.

[0032] In some embodiments of the present invention, the four raw materials—lotus seeds, fox nuts, yam, and poria cocos—should avoid high-temperature drying, and are preferably dried at a low temperature of 40-50°C or sun-dried until the moisture content is ≤8%. Alternatively, commercially available decorated lotus seeds, dried fox nuts, poria cocos slices, and yam slices can be selected, but it must be ensured that they are all naturally sun-dried or dried at a low temperature.

[0033] In this invention, the ultrafine grinding process is as specified in the Chinese Pharmacopoeia, and the resulting powder passes through an 8-mesh sieve (150 mesh) and contains at least 95% of the material that can pass through a 9-mesh sieve (200 mesh).

[0034] In this invention, the total mass ratio of the ultrafine powder of foxnut and lotus seed to the total mass ratio of ultrafine powder of yam and poria is 1:1.5 to 3, for example, it can be 1:1.5, 1:2, 1:2.5 or 1:3, etc.; the mass ratio of ultrafine powder of foxnut to ultrafine powder of lotus seed is 1:1 to 1.5, for example, it can be 1:1, 1:1.2, 1:1.4 or 1:1.5, etc.; the mass ratio of ultrafine powder of poria to ultrafine powder of yam is 1:2 to 3, for example, it can be 1:2, 1:2.5 or 1:3, etc.

[0035] This invention also provides a method for preparing the above-mentioned set-type yogurt with reversible thixotropic rheological properties, comprising the following steps: (1) Mix the fine powder of Euryale ferox and the fine powder of lotus seeds with 10 to 30 times their weight of raw milk, soak them and then pregelatinize them. After the pregelatinization is completed, add the fine powder of yam and the fine powder of Poria cocos to obtain the pregelatinized slurry. (2) Mix the pregelatinized slurry, the remaining raw milk and white sugar, homogenize, sterilize and cool to obtain the fermentation base material; (3) Add starter culture to the fermentation base, ferment, and stir after reaching the fermentation endpoint to obtain thin yogurt; (4) After the diluted yogurt is filled and sealed, it is ripened to obtain a set-type yogurt with reversible thixotropic rheological properties.

[0036] Step (1) of this invention is to first weigh the ultrafine powder of yam, ultrafine powder of poria cocos, ultrafine powder of foxnut, and ultrafine powder of lotus seed according to a specific formula ratio, take the weighed ultrafine powder of foxnut and ultrafine powder of lotus seed and mix them with 10 to 30 times their weight of raw material milk, soak them to make them swell, and then pregelatinize them. After the pregelatinization is completed, wait for the temperature to drop below 55°C and then add ultrafine powder of yam and ultrafine powder of poria cocos to obtain pregelatinized slurry.

[0037] In this invention, the soaking time in step (1) is 10-15 min, for example, 10 min, 12 min, 14 min or 15 min; stirring can be performed during soaking and swelling; the pregelatinization temperature is 80-90℃, for example, 80℃, 85℃, 87℃ or 90℃, and the time is 15-20 min, for example, 15 min, 18 min or 20 min; the stirring speed during the pregelatinization process is 200-300 rpm, for example, 200 rpm, 250 rpm or 300 rpm; when adding yam powder and poria powder, the temperature is ≤55℃, preferably 55℃.

[0038] In this invention, the temperature of the liquid must be controlled below 55°C when adding yam powder to avoid gelatinization of the yam powder before homogenization.

[0039] Step (2) of this invention is to mix the pregelatinized slurry with the remaining raw milk, add white sugar, stir until the white sugar is completely dissolved, then homogenize, sterilize, pump to a fermentation tank, cool, and obtain fermentation base material.

[0040] In this invention, the homogenization, sterilization and cooling in step (2) can be performed using conventional methods and conditions in the art.

[0041] In some embodiments of the present invention, the homogenization is preferably single-stage homogenization; the homogenization temperature is 60~65℃, for example, 60℃, 63℃ or 65℃, and the pressure is 19~21MPa, for example, 19MPa, 20MPa or 21MPa; the sterilization method is preferably pasteurization, and pasteurization conditions with a temperature lower than 85℃ are not used to ensure that the whey protein is fully denatured; the sterilization temperature is preferably 85~95℃, for example, 85℃, 90℃, 93℃ or 95℃, and the time is 5min; the cooling temperature in step (2) is 40~44℃, for example, 40℃, 43℃ or 44℃.

[0042] Step (3) of this invention is to add a starter culture to the fermentation base, stir gently for 1 minute, ferment, and stir after reaching the fermentation endpoint to break the milk gel and obtain thin yogurt.

[0043] In this invention, the fermentation temperature in step (3) is 38~42℃, for example, it can be 38℃, 40℃ or 42℃, etc. The fermentation endpoint is the acidity of the fermentation system is 70~120°T, for example, it can be 70°T, 80°T, 90°T, 100°T, 110°T or 120°T, etc., or the pH value of the fermentation system is 4.45~4.6, for example, it can be 4.45, 4.46, 4.5, 4.52, 4.56 or 4.6, etc. Setting the acidity or pH of the fermentation system within the above range can keep the product moderately sweet and sour.

[0044] In this invention, step (3) is to break down the milk gel. The stirring speed is 300~400 rpm, for example, 300 rpm, 350 rpm or 400 rpm, etc., until the viscosity of the thin yogurt is below 3000 mPa·s that can be pumped.

[0045] Step (4) of the present invention is to fill the diluted yogurt into a packaging container and quickly allow it to stand for post-ripening to obtain a set-type yogurt with reversible thixotropic rheological properties.

[0046] In this invention, the filling process can be carried out using conventional methods and conditions in the field, and the product is rapidly subjected to low-temperature post-curing after filling is completed.

[0047] In this invention, the temperature of post-ripening in step (4) is 4~10℃, for example, it can be 4℃, 6℃, 8℃ or 10℃, and the time is 10~24h, for example, it can be 10h, 12h, 14h, 16h, 18h or 20h.

[0048] This invention introduces a specific proportion of medicinal and edible ingredients and optimizes the fermentation process. Utilizing the polysaccharides and mucoproteins contained within, the gel network formed during yogurt fermentation transforms from a single casein structure into a stable "protein-polysaccharide" composite gel system. This composite gel exhibits significant thixotropic shear-thinning properties. Under external shear force, the gel structure reversibly breaks down, viscosity decreases, resulting in good pumpability. After standing, the gel structure gradually rebuilds over time, viscosity recovers, and the product reverts to a gel state. This reversible "gel-fluid-gel" transformation mechanism endows the product with excellent processing adaptability, enabling it to be compatible with the widely adopted "fermentation before filling" production process, providing a new technological path for the industrial manufacturing of set-type yogurt.

[0049] The technical solutions provided by the present invention will be described in detail below with reference to the embodiments, but they should not be construed as limiting the scope of protection of the present invention.

[0050] Example 1 The set-type yogurt with reversible thixotropic rheological properties is composed of the following ingredients in parts by weight: 1000 parts by weight of fresh milk, 30 parts by weight of natural food and medicine powder, 60 parts by weight of white sugar, and 2 parts by weight of yogurt starter. The natural food and medicine powder consists of: 12 parts by weight of ultrafine yam powder, 6 parts by weight of ultrafine poria cocos powder, 6 parts by weight of ultrafine euryale ferox powder, and 6 parts by weight of ultrafine lotus seed powder.

[0051] Preparation method of set-type yogurt with reversible thixotropic rheological properties: Step A. Remove the core and seed coat from the lotus seeds, dry them, grind them into a very fine powder, and pass them through a 200-mesh sieve to obtain very fine lotus seed powder; peel the yam, slice it, dry it, grind it into a very fine powder, and pass it through a 200-mesh sieve to obtain very fine yam powder; remove impurities from the poria cocos, wash it, grind it into a very fine powder, and pass it through a 200-mesh sieve to obtain very fine poria cocos powder; dry the foxnut, coarsely grind it to remove the brown substances on the surface, grind it into a very fine powder, and pass it through a 200-mesh sieve to obtain very fine foxnut powder.

[0052] Step B. In a mixing tank, add 330 parts by weight of fresh milk, followed by pre-weighed ultrafine powder of fox nuts and lotus seeds. After soaking for 10 minutes, heat to 87°C and maintain this temperature, stirring at 250 rpm for 20 minutes. Then, cool the slurry to 55°C, and add ultrafine powder of yam and poria cocos to obtain a pregelatinized slurry.

[0053] Step C. Mix the pregelatinized slurry with the remaining fresh milk, add granulated sugar, stir until the sugar dissolves, and simultaneously heat to 63°C. Then, perform single-stage homogenization at 20 MPa pressure, sterilize the homogenized liquid at 93°C for 5 minutes, pump it to a fermentation tank, and rapidly cool it to 43°C to obtain the fermentation base.

[0054] Step D. Add the starter culture and stir gently for 1 minute. Ferment at a constant temperature of 42°C until the pH value is 4.52 and the yogurt solidifies. Then start the agitator and stir at 350 rpm until the viscosity reaches below 3000 mPa·s to obtain thin yogurt.

[0055] Step E. Pour the diluted yogurt into a packaging container, quickly transfer it to a 4°C cold storage, and let it stand for 14 hours to ripen, thus obtaining the set-type yogurt with reversible thixotropic rheological properties.

[0056] Example 2 The set-type yogurt with reversible thixotropic rheological properties is composed of the following ingredients in parts by weight: 1000 parts by weight of reconstituted milk, 50 parts by weight of natural food and medicine powder, 60 parts by weight of white sugar, and 3 parts by weight of yogurt starter. The natural food and medicine powder is composed of: 23 parts by weight of yam ultrafine powder, 9.5 parts by weight of poria cocos ultrafine powder, 7 parts by weight of euryale ferox ultrafine powder and 10.5 parts by weight of lotus seed ultrafine powder.

[0057] The fermentation endpoint (pH 4.50) was achieved, and the remaining preparation methods were exactly the same as in Example 1.

[0058] Example 3 The set-type yogurt with reversible thixotropic rheological properties is composed of the following ingredients in parts by weight: 1000 parts by weight of fresh milk, 40 parts by weight of natural food and medicine powder, 60 parts by weight of white sugar, and 3 parts by weight of yogurt starter. The natural food and medicine powder is composed of: 18 parts by weight of yam ultrafine powder, 6 parts by weight of poria cocos ultrafine powder, 6.5 parts by weight of euryale ferox ultrafine powder and 9.5 parts by weight of lotus seed ultrafine powder.

[0059] The fermentation endpoint (pH 4.56) was achieved, and the remaining preparation process was exactly the same as in Example 1.

[0060] Comparative Example 1 Set-type yogurt is composed of the following ingredients in parts by weight: 1000 parts by weight of fresh milk, 60 parts by weight of white sugar, and 2 parts by weight of yogurt starter. Preparation method of set-type yogurt: No pregelatinization is required; the fermentation endpoint (pH 4.62) is achieved; the remaining preparation process is exactly the same as in Example 1.

[0061] Comparative Example 2 Set-type yogurt is composed of the following ingredients in parts by weight: 1000 parts fresh milk, 40 parts fine yam powder, 60 parts white sugar, and 2 parts yogurt starter. Preparation method of set-type yogurt: No pregelatinization is required. The fermentation endpoint (pH 4.48) and the rest of the preparation process are exactly the same as in Example 1.

[0062] Comparative Example 3 Set-type yogurt is composed of the following ingredients in parts by weight: 1000 parts fresh milk, 40 parts finely powdered Poria cocos, 60 parts white sugar, and 2 parts yogurt starter. Preparation method of set-type yogurt: No pregelatinization is required; the fermentation endpoint (pH 4.54) is achieved; the remaining preparation process is exactly the same as in Example 1.

[0063] Comparative Example 4 Set-type yogurt is composed of the following ingredients in parts by weight: 1000 parts fresh milk, 40 parts fine powder of fox nuts, 60 parts white sugar, and 2 parts yogurt starter. Preparation method of set-type yogurt: No pregelatinization is required; the fermentation endpoint (pH 4.57) is achieved; the remaining preparation process is exactly the same as in Example 1.

[0064] Comparative Example 5 Set-type yogurt is composed of the following ingredients in parts by weight: 1000 parts fresh milk, 40 parts ultrafine lotus seed powder, 60 parts white sugar, and 2 parts yogurt starter. Preparation method of set-type yogurt: No pregelatinization is required; the fermentation endpoint (pH 4.54) is achieved; the remaining preparation process is exactly the same as in Example 1.

[0065] Comparative Example 6 Set-type yogurt is composed of the following ingredients in parts by weight: 1000 parts fresh milk, 40 parts natural food and medicinal powder, 60 parts white sugar, and 2 parts yogurt starter. The natural food and medicine powder consists of: 10 parts by weight of ultrafine yam powder, 10 parts by weight of ultrafine poria cocos powder, 10 parts by weight of ultrafine euryale ferox powder, and 10 parts by weight of ultrafine lotus seed powder.

[0066] Preparation method of set-type yogurt: The fermentation endpoint (pH 4.49) was achieved, and the remaining preparation process was exactly the same as in Example 1.

[0067] Comparative Example 7 The difference from Example 1 is that in step B, pregelatinization is not performed. The pre-weighed ultrafine powder of foxnut, lotus seed, yam and poria, as well as all the fresh milk, are added to the mixing tank, stirred evenly at room temperature, and allowed to absorb water and swell for 10 minutes to obtain the mixture.

[0068] The pH at the end of fermentation was 4.30, and the rest of the preparation process was exactly the same as in Example 1.

[0069] Comparative Example 8 The difference from Example 1 is that in step B, 330 parts by weight of fresh milk are mixed with pre-weighed fine powders of fox nuts, lotus seeds, yam and poria cocos, soaked for 10 minutes, heated to 87°C and maintained, and stirred at 250 rpm for 20 minutes to obtain a pregelatinized slurry.

[0070] The pH at the end of fermentation was 4.41, and the rest of the preparation process was exactly the same as in Example 1.

[0071] Comparative Example 9 The difference from Example 1 is that the sterilization conditions in step C are changed to 63°C for 30 minutes, while the other process conditions are exactly the same as in Example 1.

[0072] Comparative Example 10 The difference from Example 1 is that the lotus seeds, yam, poria cocos, and euryale seeds are only ordinary pulverized (passed through an 80-mesh sieve). When proceeding to step C, the natural food and medicine powder particles after absorbing water and swelling are too large, and single-stage homogenization cannot continue. In order to avoid damaging the homogenizer, the experiment is terminated.

[0073] Comparative Example 11 Lotus seeds are dried after removing the core and seed coat, then ground into a very fine powder and passed through a 200-mesh sieve to obtain very fine lotus seed powder; yam is peeled, sliced, dried, ground into a very fine powder, and passed through a 200-mesh sieve to obtain very fine yam powder; Poria cocos is cleaned and purified, then ground into a very fine powder and passed through a 200-mesh sieve to obtain very fine Poria cocos powder; Euryale ferox is dried, coarsely ground to remove the brown substance on the surface, then ground into a very fine powder and passed through a 200-mesh sieve to obtain very fine Euryale ferox powder.

[0074] Take 12 parts by weight of ultrafine yam powder, 6 parts by weight of ultrafine Poria cocos powder, 6 parts by weight of ultrafine Euryale ferox powder, and 6 parts by weight of ultrafine lotus seed powder, mix them with 1000 parts by weight of water and 60 parts by weight of white sugar, heat to 87°C and maintain, and stir at 250 rpm for 20 minutes. Heat to 93°C and sterilize for 5 minutes, then cool to 43°C, stir until the viscosity drops below 3000 mPa·s, and refrigerate at 4°C for 14 hours to obtain a natural medicinal food paste.

[0075] Test case Comparative Examples 7, 8, and 9 all showed significant and substantial whey separation in their final products, failing to maintain the normal form of yogurt. According to GB / T 5009.1-2003, "products failing sensory evaluation do not require physicochemical testing and are directly judged as unqualified products," therefore, no testing was conducted. However, this demonstrates that the processing technology (gelatinization and sterilization conditions) plays a crucial role in the formation of the final product.

[0076] Comparative Example 10 could not be homogenized, making it technically infeasible. This indicates that the natural food and medicinal powders added to the fermentation base must be extremely finely pulverized.

[0077] In Comparative Example 11, although an aqueous solution of the natural food and medicinal powder composition could form a thermal gel, the gel could not recover under refrigeration after stirring and shearing. This indicates that without the participation of milk proteins, the natural food and medicinal paste does not possess reversible thixotropic rheological properties.

[0078] The finished products obtained in Examples 1-3 and Comparative Examples 1-6 were subjected to the following tests: 1) Water holding capacity test: Weigh 10.0g of sample, centrifuge at 3500r / min for 15min, and calculate the mass percentage of precipitate.

[0079] 2) Apparent viscosity determination: The viscosity of the product was measured using an NDJ-1 viscometer with a No. 4 rotor at a speed of 12 rpm. The apparent viscosity of the yogurt was measured at 4℃ for 60 seconds.

[0080] 3) Sensory evaluation: A sensory evaluation group of 20 young students tasted the products and scored them according to Table 1 below. The average value was calculated.

[0081] Table 1 Sensory Rating Table

[0082] Table 2 Yogurt Performance Data

[0083] As shown in Table 2, the yogurt performance data, all examples (1-3) exhibited high water-holding capacity (>80%) and suitable apparent viscosity (25,000~35,000 mPa·s), exhibiting a set-like texture. Comparative Example 1 showed low water-holding capacity and low viscosity, resulting in a thin texture. While the single components in Comparative Examples 2-5 slightly improved water-holding capacity, their viscosity was either too high or too low, failing to form the gel structure characteristic of set-type yogurt, or, although they could form a gel, the sensory quality was poor. In Comparative Example 6, the equal proportions of the four components improved water-holding capacity, viscosity, and sensory scores, but still fell short of the examples. This demonstrates that only a specific ratio of compounded system, combined with a specific process, can synergistically optimize the texture, stability, and flowability of the product during filling, as described in this invention.

[0084] 4) Texture Analysis (TPA): A physical property analyzer with a cylindrical probe was used. The test conditions were: pre-compression speed 1.0 mm / s, test speed 1.0 mm / s, compression ratio 50%, and trigger force 5 g. The hardness (g), viscosity (g·sec), elasticity, adhesiveness, and chewiness of the sample were determined.

[0085] Table 3. Texture Properties Data

[0086] Figure 4 , Figure 5 The scan images are those of Example 3 and Comparative Examples 1-6, respectively. Figure 6The images shown are scanned images of Examples 1 and 2. Texture analysis results indicate that the components, at the specific proportions of this invention, produced a synergistic effect in constructing an ideal gel network. As a flexible linker, the abundant hydroxyl groups of yam polysaccharide provide numerous hydrogen bond sites, resulting in a significant improvement in hardness compared to Comparative Example 1 (without additives). However, using yam powder alone (Comparative Example 2) resulted in a rigid gel with excessive hardness (288.5 g), demonstrating that excessive cross-linking of its flexible long chains alone leads to an overly hard texture and decreased palatability. β-glucan in Poria cocos acts as a rigid framework, stabilizing the network, but its use alone (Comparative Example 3) fails to generate sufficient cohesion (although the absolute value of negative viscosity is high, the network is fragile). When Euryale ferox and lotus seed starch are used alone (Comparative Examples 4 and 5), the final product exhibits insufficient gel hardness and cohesion due to starch aging during refrigeration, highlighting the limitations of pure starch gel structures.

[0087] This invention achieves an optimal balance between the hardness (232.3~266.5 g) and negative viscosity (-392.1 to -526.8 g·sec) of the samples by compounding ultrafine powders of yam, poria cocos, euryale ferox, and lotus seeds in a specific ratio. This demonstrates that at this ratio, the proportion of flexible bonding to rigid support is appropriate, avoiding both excessive cross-linking of starch, polysaccharides, and casein that would harden the gel, and starch aging that would weaken the structure, thus synergistically producing an ideal texture with moderate strength and strong cohesion. A mixture of the four ultrafine powders in equal proportions (Comparative Example 6) failed to achieve the optimal balance, further confirming that "specific proportions" rather than "simple mixing" is the key to producing this effect.

[0088] 5) Rheological property testing: ①Thixotropic test (thixotropic ring area): A rotational rheometer with a flat plate fixture was used, and the test temperature was 4℃. The test procedure was as follows: the shear rate increased from 0 s in 3 minutes. -1 Linearly increase to 300 s -1 Then in 300 seconds -1 Hold for 1 minute, then reduce to 300 seconds within 3 minutes. -1 linearly reduced to 0 s -1 Record the area under the curve of shear stress as a function of shear rate.

[0089] ②Structural recovery dynamics test (recovery time curve): Time-scan tests were performed using the same rheometer. First, a 300-second time-scan was applied to the sample. -1 A high shear rate was applied for 60 seconds to simulate a pump-filling process. The shear rate was then immediately reduced to 0.1 s. -1(Simulating static state), and continuously monitor the change of storage modulus (G', characterizing gel elasticity) over time for 240 min.

[0090] Table 4. Rheological and Thixotropic Property Data Table

[0091] Rheological data confirm that the product of this invention achieves the ideal balance between "easy pumping" and "easy recovery to a solidified state." While the size of the thixotropic ring area does not directly correlate with the "actual viscosity" of the fluid, it directly quantifies the ease and scale of reversible damage to the gel network under shear force; a larger value indicates easier shear thinning. Recovery time represents the speed at which the gel network rebuilds to its original robust state after shearing ceases; a smaller value indicates a stronger structural recovery ability, enabling the system to quickly achieve the desired solidified texture of the final product.

[0092] The products obtained in Examples 1-3 of this invention have undergone a "gel-fluid-gel" transformation process in processing steps D and E. Thixotropic tests show that they all possess relatively high thixotropic ring areas (13506.4~15624.8 Pa / s) and relatively short recovery times (107~123 min). This indicates that the set-type yogurt with reversible thixotropic rheological properties is an ideal "intelligent" thixotype: even if it becomes thinner due to external shear vibration during storage and transportation, it can gradually recover its set state during shelf display.

[0093] None of the comparative examples achieved the ideal balance described above. Comparative Example 1 (traditional stirred type) exhibited an extremely high thixotropic ring area, but its recovery was confirmed to be irreversible (unrecoverable after >240 min). This means that although the traditional stirred yogurt can partially coagulate during its shelf life due to the growth of lactic acid bacteria, each shearing action further thins the yogurt, and the destruction of its gel structure is irreversible. Comparative Examples 2 and 3 (single components) had lower thixotropic ring areas (<5000 Pa / s), indicating that the newly formed gel network during the ripening stage no longer possesses pumpable shear-thinning properties, and their apparent viscosity and hardness are too high (Tables 2 and 3), more closely resembling an irreversible elastic gel in the form of pudding. Comparative Examples 4 and 5 showed better thixotropy than Comparative Examples 2 and 3, but their hardness and viscosity were lower (Tables 2 and 3), lacking a thick texture. Comparative Example 6 outperformed Comparative Examples 2-5 in all aspects, indicating that the addition of a compound is superior to the addition of a single component. However, it still did not reach the level of the Example. Its thixotropy (10693.3 Pa / s) was worse than that of the Example, but its recovery time (137 min) was longer. This proves that it is not a simple mixing of components, but rather the specific proportions defined by this invention that allow for precise control and the optimal synergy between high thixotropy and rapid reversibility. Therefore, the unique rheological properties achieved by this invention are beyond the expectations of those skilled in the art based on conventional knowledge.

[0094] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A set-type yogurt with reversible thixotropic rheological properties, characterized in that, The components include the following parts by mass: 1000 parts raw milk, 30-50 parts natural food and medicinal powder, 50-80 parts white sugar, and 1-3 parts starter culture; The natural food and medicine powder is composed of ultra-fine powder of fox nuts, ultra-fine powder of lotus seeds, ultra-fine powder of yam, and ultra-fine powder of poria cocos.

2. The set-type yogurt with reversible thixotropic rheological properties according to claim 1, characterized in that, All of the ultrafine powder passes through a 150-mesh sieve, and no less than 95% of it passes through a 200-mesh sieve.

3. The set-type yogurt with reversible thixotropic rheological properties according to claim 1, characterized in that, The total mass ratio of the fine powder of foxnut and lotus seed to the fine powder of yam and poria is 1:1.5~3; the mass ratio of the fine powder of foxnut and lotus seed is 1:1~1.5; and the mass ratio of the fine powder of poria and yam is 1:2~3.

4. The method for preparing the set-type yogurt with reversible thixotropic rheological properties according to any one of claims 1 to 3, characterized in that, Includes the following steps: (1) Mix the fine powder of Euryale ferox and the fine powder of lotus seeds with 10 to 30 times their weight of raw milk, soak them and then pregelatinize them. After the pregelatinization is completed, add the fine powder of yam and the fine powder of Poria cocos to obtain the pregelatinized slurry. (2) Mix the pregelatinized slurry, the remaining raw milk and white sugar, homogenize, sterilize and cool to obtain the fermentation base material; (3) Add starter culture to the fermentation base, ferment, and stir after reaching the fermentation endpoint to obtain thin yogurt; (4) After the diluted yogurt is filled and sealed, it is ripened to obtain a set-type yogurt with reversible thixotropic rheological properties.

5. The preparation method according to claim 4, characterized in that, The soaking time in step (1) is 10~15 min; the pregelatinization temperature is 80~90℃ and the time is 15~20 min; the stirring speed during the pregelatinization process is 200~300 rpm; the temperature is ≤55℃ when adding yam powder and poria powder.

6. The preparation method according to claim 4, characterized in that, The homogenization temperature in step (2) is 60~65℃ and the pressure is 19~21MPa; the sterilization temperature in step (2) is 85~95℃ and the time is 5min; the cooling temperature in step (2) is 40~44℃.

7. The preparation method according to claim 4, characterized in that, The fermentation temperature in step (3) is 38~42℃, and the fermentation endpoint is when the acidity of the fermentation system is 70~120°T or the pH value of the fermentation system is 4.45~4.

6.

8. The preparation method according to claim 4, characterized in that, In step (3), the stirring speed is 300~400 rpm and the viscosity of the thin yogurt is ≤3000 mPa·s.

9. The preparation method according to claim 4, characterized in that, In step (4), the temperature for post-ripening is 4~10℃ and the time is 10~24h.

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