Preparation method of fermented yogurt curd from puffed black rice flour to enhance water retention and improve coagulation viscoelasticity

Abstract

This invention relates to the field of food technology, and more particularly to a method for preparing fermented yogurt curd from puffed black rice flour that enhances water retention and improves coagulation viscosity. The method includes the following steps: preparation of puffed black rice flour; preparation of aseptically pretreated puffed black rice flour; preparation of fermentation seed liquid; preparation of fermented puffed black rice flour: adding the fermentation seed liquid to the aseptically pretreated puffed black rice flour, mixing evenly, and allowing it to ferment at 35 ℃ and 75% humidity for 96 h; preheating milk to 43 ℃, adding fermented puffed black rice flour (1:8, w / v), further adding yogurt fermentation agent (1:400, w / v), stirring thoroughly, allowing it to ferment at 43 ℃ for 6 h, and after the yogurt has completely coagulated, refrigerating it at 4 ℃ for 12 h to obtain a stepwise fermented coagulated yogurt from puffed black rice flour.

Description

Technical Field

[0001] This invention relates to the field of food technology, and in particular to a method for preparing fermented yogurt curd from puffed black rice flour that enhances water retention and improves coagulation viscosity. Background Technology

[0002] Yogurt, a fermented dairy product with both nutritional value and functional properties, has become an important part of the daily diet of consumers worldwide due to its unique flavor, texture, and the health benefits of probiotics. my country's "National Nutrition Plan (2017-2030)" explicitly proposes "promoting the revitalization of the dairy industry and optimizing the structure of dairy products" and "building a diversified food supply system," providing policy guidance for the upgrading and technological innovation of the dairy industry. Currently, my country's dairy consumption is shifting from "scale expansion" to "quality improvement," and consumers' demands for the functionality, taste stability, and differentiation of yogurt are increasing, placing higher requirements on yogurt processing technology.

[0003] The core quality indicators of set-type yogurt include water-holding capacity, gel hardness, and viscoelastic properties, and its stability is directly affected by the casein gel network structure. In existing technologies, yogurt curds often face problems such as severe whey separation, unstable coagulation performance, and intense competition from similar products, significantly shortening product shelf life, limiting the adaptability of product transportation and storage, and failing to meet consumers' new dual demands for "nutritional fortification" and "taste innovation."

[0004] As a functional grain raw material, puffed black rice flour can significantly change the microstructure of starch, dietary fiber and protein through its pretreatment process (such as extrusion puffing), releasing more hydrophilic groups and active ingredients, which helps to (1) enhance the density of the gel network: puffing treatment breaks down black rice starch particles to form a porous structure. Dietary fibers such as β-glucan and arabinoxylan released after pre-fermentation can be embedded in the casein gel network, reducing porosity through hydrogen bonding and physical filling, and improving gel hardness and dehydration resistance; (2) optimize the water-holding mechanism: soluble polysaccharides (such as anthocyanin-polysaccharide complex) in puffed black rice flour can form electrostatic interactions with casein, strengthening the gel network's ability to capture whey. At the same time, the organic acids produced by pre-fermentation can regulate the pH value of the system, promote protein cross-linking, and further stabilize the gel structure; (3) endow with functionality and differentiation: black rice is rich in bioactive ingredients such as anthocyanins and γ-aminobutyric acid, and can be nutritionally fortified through co-fermentation. Its unique caramel flavor and melanin give yogurt its unique sensory characteristics, meeting the market's demand for nutritional and taste quality.

[0005] Although existing studies have attempted to improve the texture of yogurt by adding stabilizers (such as gelatin and pectin) or optimizing fermentation processes (such as stepwise fermentation and strain blending), there are still some shortcomings. For example, chemical stabilizers may affect the "natural properties" of the product, single raw material modification is difficult to simultaneously improve water-holding capacity and viscoelasticity, and the influence mechanism of grain puffing pretreatment on protein-polysaccharide interaction has not been fully utilized, etc.

[0006] This invention introduces puffed black rice flour into the coagulation-type yogurt production system for the first time. Through a step-by-step process of "puffing pretreatment → solid-state pre-fermentation of Lactobacillus plantarum → co-fermentation of cow's milk", the following technological breakthroughs are achieved: (1) a ternary composite gel network of "casein-puffed black rice polysaccharide-fermentation metabolites" is constructed, which significantly improves water holding capacity (≥85%) and gel viscoelasticity (15% to 40% higher than that of ordinary yogurt); (2) the fermentation rhythm is adjusted by utilizing the slow-release carbon source characteristics of puffed black rice flour, which shortens the coagulation time and enhances the gel's resistance to mechanical disturbance; (3) a functional yogurt with high dietary fiber and high anthocyanin content is developed to meet the differentiated needs of lactose-intolerant people and healthy consumer groups.

[0007] This technology aligns with the strategic directions of "promoting the structural upgrading of dairy products" and "developing functional foods" in the National Nutrition Plan, providing a new paradigm for the high-value utilization of yogurt.

[0008] On December 26, 2025, a search was conducted in the China Patent Publication Database using "yogurt, fermented milk, black rice flour, and puffed food" as the abstract keywords, and 39 relevant documents were found, namely: A purple sweet potato cereal yogurt and its preparation method (CN201911160382.3); a stirred cereal yogurt and its preparation method (CN200810249537.6); a cereal yogurt and its preparation method (CN201110204318.8); a black cereal yogurt and its preparation method (CN201710062735.0); a black rice seed bran powder yogurt rich in anthocyanins and with lipid-lowering effects and its preparation method (CN202310305536.3); A method for processing highly stable yogurt using starch adsorption of black rice anthocyanins and peptides (CN202110234670.X); A method and system for preparing black rice and highland barley yogurt (CN202111522218.X); Yogurt with purple rice and its preparation method (CN201810500190.1); A black rice and white peach flavored yogurt and its preparation method (CN201611019481.6); A blueberry and black rice yogurt and its preparation method (CN201610513898.1); A stirred black rice and highland barley yogurt and its preparation method (CN201610412034.0); A method for preparing sweet potato and black rice fermented milk (CN201210035034.5); Avocado, oat, and black rice flavored yogurt and its preparation method (CN202010751321.0); A yogurt with zero added sucrose that inhibits carbohydrate absorption and its preparation method (CN202411032334.7); a yogurt that lowers blood sugar and its preparation method and application (CN202410891325.7); a yogurt with zero added sweetened fermented mash and its preparation method (CN202410762844.3); a yam puree yogurt rich in allantoin and total flavonoids and its preparation method (CN202410142520.X); a plant-based yogurt with calming and sleep-aiding properties and improved gastrointestinal function and its preparation method (CN202111681684.2); A compound Bifidobacterium inoculant and its application in yogurt fermentation (CN202411148077.3); A plant-derived Lactobacillus STB9b and its application in preparing coconut-based yogurt (CN202411077973.5); A composition of Leuconostoc mesenteroides YM1 and Lactobacillus kefirizine NK1 and its application in a stringy yogurt (CN202410822152.3); A method for preparing a yogurt with high probiotic activity (CN202410825237.7); A method for preparing microalgae plant-based yogurt using acid-producing and aroma-producing bacteria (CN202410601870.8); A processing system and method for set-type yogurt (CN202211479800.7); A set-type yogurt and its preparation method (CN202110733512.9); A high-stretch yogurt beverage and its preparation method (CN202410911123.4); A method for preparing crispy yogurt blocks (CN202310082034.9); A sugar-free, set-type whole oat cereal beverage and its preparation method (CN202411103320.X); a blackberry yogurt and its preparation method (CN202211604104.4); a taro-based plant-based yogurt and its preparation method (CN202410776899.X); an oat flour and coconut milk yogurt and its preparation method (CN202310075015.3); a fruit and vegetable yogurt made from yogurt without additives or preservatives and fruits, vegetables, and nuts (CN202410342476.7); a method for preparing a matcha-based set-type yogurt (CN202410615212.4); a method for preparing a blueberry jam and soy milk yogurt (C CN202410453707.1); A method for preparing cranberry jam yogurt (CN202410454264.8); A yogurt, an active lactic acid bacteria beverage and their preparation methods and applications of prickly pear cactus (CN202111430736.9); A compound extract of yam and dendrobium, yogurt and its preparation methods and applications (CN202410729048.X); A compound extract of yam and poria cocos, yogurt and its preparation methods and applications (CN202410729054.5); Application of food and medicine homologous substances in the preparation of fermented milk containing sugar alcohols and live bacteria with extended shelf life (CN202111431211.7).

[0009] Most of these involve adding black rice, black rice flour, or other plant-based ingredients for fermentation and curdling, and do not involve step-by-step fermentation of puffed black rice flour to enhance gel viscosity.

[0010] CN201911160382.3, CN200810249537.6, CN201110204318.8 and CN201710062735.0 disclose methods for preparing yogurt by adding black rice flour, which are unrelated to the method of enhancing water retention and viscoelasticity of the puffed black rice flour fermented yogurt in this patent.

[0011] CN202310305536.3 discloses a method for preparing functional yogurt rich in anthocyanins from black rice seed bran powder and with lipid-lowering effects, which is unrelated to the puffed black rice flour, enhanced water retention and viscoelasticity of this patent.

[0012] CN202110234670.X discloses a method for obtaining starch and polypeptides by enzymatic pretreatment of glutinous rice and adsorbing anthocyanins and polypeptides from black rice to obtain highly stable yogurt, which is different from the stepwise fermentation process of puffed black rice flour in this patent.

[0013] Patents CN202111522218.X, CN201810500190.1, CN201611019481.6, CN201610513898.1, CN201610412034.0, CN201710062735.0, CN201210035034.5, and CN202010751321.0 all use black rice as a raw material to make fermented yogurt, mainly focusing on enhancing the flavor, taste, and health benefits of the yogurt. Their invention purpose is different from that of this patent.

[0014] Patents CN202411148077.3, CN202411077973.5, CN202410822152.3, CN202410825237.7, and CN202410601870.8 use different lactic acid bacteria and their combinations to ferment yogurt, resulting in fermented milk with different tastes and nutritional characteristics. These patents differ from the strains of bacteria and the stepwise fermentation method used in this patent.

[0015] On December 28, 2024, an abstract search was conducted on CNKI (China National Knowledge Infrastructure) using the keywords "yogurt, fermented milk, black rice flour, and puffing," but no relevant literature was found. One paper was discovered: "Research and Development of Puffed Rice Flour Yogurt Ice Cream," published by Tang Lin, Li Junxun, Qiu Jun, and Gu Quanli. This paper provides insights that the form of rice flour may positively regulate the fermentation effect.

[0016] On December 26, 2025, with the theme of " Yogurt with fermented milk with black rice flour with puffing with lactobacillus with Solid Body A search on the U.S. Patent and Trademark Office website yielded no relevant results; the search URL is https: / / ppubs.uspto.gov / pubwebapp / .

[0017] On December 26, 2025, with the theme of " Yogurt and fermented milk and black rice A search was conducted on the Korean Patent Office website (http: / / eng.kipris.or.kr / enghome / main.jsp); the following were found: Application No. 1020200027889; Antioxidant or anti-inflammatory functional food composition; An antioxidant and anti-inflammatory functional food composition containing black rice from whey protein isolated from Greek yogurt. When whey protein or black rice extract is used alone, the composition containing whey protein isolated from Greek yogurt of the present invention and black rice extract has antioxidant effects by inhibiting ABTS free radical scavenging activity and DNA damage; unrelated to yogurt products. Application No. 1020100071993; High-grade antioxidant rice containing spirulina and soybeans; Application No. 1020130030502; A method for preparing fermented chili juice and its uses. On December 28, 2024, with the theme of " Yogurt and fermented milk and black rice A search on WIPO's https: / / patentscope2.wipo.int / revealed: CN111742996 Avocado Oat Black Rice Flavored Yogurt and its Preparation Method, which provides a co-fermented oat black rice apple flavored sauce, but it is not co-fermented.

[0018] On December 28, 2024, with the theme of " Yogurt and fermented milk and black rice A search on the website of the Japan Patent Office (https: / / www.j-platpat.inpit.go.jp / ) yielded no relevant results.

[0019] It is completely different from the concept of this patent. Summary of the Invention

[0020] The purpose of this invention is to address the problems of insufficient water-holding capacity, high gel network brittleness, and limited nutritional content in existing coagulated yogurt. This invention provides a method for preparing yogurt coagulation based on stepwise fermentation of puffed black rice flour. Through the synergistic effect of puffing pretreatment and solid-state fermentation with *Lactobacillus plantarum*, a composite gel network of "polysaccharides-proteins-active ingredients" is constructed, significantly improving the water-holding capacity, gel viscoelasticity, and nutritional value of the yogurt, while also endowing the product with unique flavor and functional properties. Specific objectives are detailed in the specific implementation section, which outlines several substantial technical effects.

[0021] To provide a method for preparing and applying a stepwise fermented yogurt from puffed black rice flour with better curd water retention and gel texture viscoelasticity, the specific objectives are detailed in the specific implementation section, which outlines several substantial technical effects.

[0022] To achieve the above objectives, the present invention adopts the following technical solution: A method for preparing coagulated yogurt by fermenting puffed black rice flour to enhance water retention and viscoelasticity, characterized by comprising the following steps: 1. Preparation of puffed black rice flour Raw material pretreatment: Adjust the moisture content of black rice (preferably black glutinous rice) to 13%, and place it in an extrusion puffing machine for three-stage puffing treatment: Zone I temperature: 60℃; Zone II temperature: 120~140℃; Zone III temperature: 150℃; Screw speed: 160~200 r / min.

[0023] Crushing and sieving: The extruded sample is crushed and then passed through a 60-mesh sieve to obtain puffed black rice flour with uniform particle size, which is then sealed and stored for later use.

[0024] 2. Preparation of Fermentation Seed Liquid Strain activation: Lactobacillus plantarum (ATCC 14917 or commercial strain) was inoculated into modified MRS medium (containing 2 wt% glucose, 1 wt% peptone, and 0.5 wt% yeast extract) and cultured at 30°C with shaking at 160 rpm until the logarithmic growth phase (OD600 = 0.6–0.8).

[0025] Bacterial cell collection: Bacterial cells were separated by centrifugation at 6000 rpm for 2 min, washed twice with sterile physiological saline, resuspended, and the concentration adjusted to 10. 8 CFU / mL was used to obtain the fermentation seed culture.

[0026] 3. Solid-state fermentation of puffed black rice flour Inoculation and fermentation: Mix the fermentation seed liquid at a ratio of 10... 7 The CFU / g puffed powder ratio was added to the puffed black rice flour, mixed thoroughly, sealed, and fermented in a solid state at 35℃ and 75% humidity for 96 hours to obtain fermented puffed black rice flour.

[0027] 4. Preparation of stepwise co-fermentation coagulated yogurt Raw material mixing: Preheat milk (fresh or pasteurized) to 42-45℃, add fermented puffed black rice flour at a ratio of 1:8 (w / v), then add yogurt fermentation agent (Streptococcus thermophilus: Lactobacillus bulgaricus = 1:1, 1:400, w / v), stir thoroughly, let stand at 43℃ for 6 hours to ferment until the gel is completely formed, and then place at 4℃ for 12 hours to ripen to obtain the finished product.

[0028] A further technical solution of the present invention is that the puffed black rice flour is derived from black glutinous rice.

[0029] A further technical solution of the present invention is that the fermentation strain for black rice is Lactobacillus plantarum (ATCC 14917 or other commercially available Lactobacillus plantarum), and the milk is freshly obtained or pure milk that has undergone pasteurization.

[0030] A further technical solution of the present invention is that the yogurt fermentation agent comprises Streptococcus thermophilus and Lactobacillus bulgaricus, and selectively adds any one or more of yogurt fermentation bacteria such as Lactobacillus acidophilus, Lactobacillus casei, and Lactobacillus plantarum.

[0031] A further technical solution of the present invention is that, in the preparation and processing steps of puffed black rice flour, the temperature of Zone III in the three-stage puffing process of the extrusion puffing machine is 150-170℃, and the screw speed is 180-220 r / min.

[0032] A further technical solution of the present invention is that the puffed black rice flour is fermented in steps: ① solid-state fermentation of puffed black rice flour; ② fermentation of fermented puffed black rice flour with milk.

[0033] A further technical solution of the present invention is that, in the solid-state fermentation process of puffed black rice flour, the content of added Lactobacillus plantarum is 10%. 7 CFU / g black rice, fermented at 35 ℃, with a humidity of 75%, for 96 h.

[0034] A further technical solution of the present invention is that, in the co-fermentation process of adding fermented puffed black rice flour to milk, the preheating temperature of the milk is 40-45 ℃, the mass-to-volume ratio of fermented puffed black rice flour to milk is 1:7-1:10 (w / v), the fermentation temperature is 42-44 ℃, and the time is 4-6 h.

[0035] A further technical solution of the present invention is that the enhanced water-holding capacity is achieved by reducing the whey protein precipitation rate, and the improved viscoelasticity is achieved by increasing the viscoelasticity value of the gel texture properties.

[0036] The coagulated yogurt prepared by the coagulated yogurt preparation method of enhancing water retention and viscoelasticity by fermenting puffed black rice flour as described in any of the above methods.

[0037] The use of coagulated yogurt prepared by the method described above for enhancing water retention and viscoelasticity through fermentation of puffed black rice flour in the production of fermented yogurt foods.

[0038] A method for preparing fermented yogurt curd with puffed black rice flour to enhance water retention and improve coagulation viscoelasticity is characterized by co-fermenting puffed black rice flour with milk, thereby improving the water retention and viscoelasticity of the yogurt curd through pre-fermentation modification of puffed black rice flour.

[0039] The co-fermentation is a stepwise fermentation, including: (1) Solid-state pre-fermentation of puffed black rice flour; (2) Pre-fermented puffed black rice flour is mixed with milk and then fermented together.

[0040] The steps of the stepwise fermentation are as follows: (1) Preparation of fermentation seed liquid; (2) Pre-fermented puffed black rice flour was obtained by solid-state pre-fermentation of puffed black rice flour with fermented seed liquid; (3) After mixing the pre-fermented puffed black rice flour with milk, add yogurt fermentation agent for co-fermentation.

[0041] The specific steps include the following: (1) Pretreatment of puffed black rice flour: Black glutinous rice is extruded and puffed. The puffing process parameters are: extrusion puffing temperature 120-150℃, pressure 0.8-1.2 MPa, screw speed 160-200 r / min; the extruded sample is crushed and passed through a 60-80 mesh sieve to obtain puffed black rice flour with uniform particle size, which is then sealed and stored for later use. Puffed black rice flour and sterile distilled water were mixed at a mass-to-volume ratio of 1:5 to 1:3 (g / mL), sterilized by high-pressure steam for 15 to 20 minutes, and then cooled naturally at room temperature to obtain sterile pretreated puffed black rice flour. (2) Preparation of fermentation seed liquid: Lactobacillus plantarum was inoculated into a culture medium or MRS broth containing 0.5–5 wt% carbon source and 0.5–5 wt% nitrogen source, and cultured at 37°C with shaking until the logarithmic growth phase. The bacterial precipitate was collected by centrifugation and resuspended in sterile physiological saline to obtain the fermentation seed liquid. (3) Solid-state pre-fermentation of puffed black rice flour: Fermentation seed liquid at 10 6 ~10 8 The inoculum amount of CFU / g puffed black rice flour was added to the aseptic pretreated puffed black rice flour, mixed evenly, sealed, and fermented in a solid state at 30-35℃ and 70-85% humidity for 48-96 hours to obtain pre-fermented puffed black rice flour. (4) Preparation of co-fermented yogurt curd: Preheat milk to 42–45 °C. Add pre-fermented puffed black rice flour at a ratio of 1:6 to 1:10 (mass (g) of pre-fermented puffed black rice flour to volume (mL) of milk). Then, add yogurt fermentation agent (the ratio of yogurt fermentation agent mass (g) to mixed liquid volume (mL) is 1:400 to 1:800). After thorough stirring, let it stand at 43–45 °C for 6–8 h to ferment. After curdling, refrigerate at 4 °C for 10–12 h to mature, thus obtaining the target yogurt curd.

[0042] The puffed black rice flour is black glutinous rice flour after puffing treatment. Its puffing process parameters are: extrusion puffing temperature 120-150℃, pressure 0.8-1.2 MPa, and screw speed 160-200 r / min. The fermentation agent contains Streptococcus thermophilus and Lactobacillus bulgaricus, and selectively adds at least one of Lactobacillus acidophilus, Lactobacillus casei, and Lactobacillus plantarum.

[0043] Pre-fermentation modification of puffed black rice flour by Lactobacillus plantarum promotes the dissolution and structural expansion of proteins, dietary fiber, anthocyanins and starch in the puffed black rice flour, changes the interaction mode with milk protein, and forms a denser three-dimensional network structure, thereby enhancing the water-holding capacity and viscoelastic properties of yogurt curd.

[0044] A high water-holding capacity and high viscosity-elasticity puffed black rice flour fermented yogurt curd, characterized in that: Prepared using any of the methods described above, its water holding capacity is ≥85%, its gel viscosity value is close to that of ordinary yogurt, and its gel elasticity is 30% to 50% higher than that of ordinary yogurt.

[0045] A puffed black rice flour fermented product for yogurt production, characterized by being prepared through the following steps: (1) Pretreatment of puffed black rice flour: Black glutinous rice is extruded and puffed. The puffing process parameters are: extrusion puffing temperature 120-150℃, pressure 0.8-1.2 MPa, screw speed 160-200 r / min; the extruded sample is crushed and passed through a 60-80 mesh sieve to obtain puffed black rice flour with uniform particle size, which is then sealed and stored for later use. Puffed black rice flour and sterile distilled water were mixed at a mass-to-volume ratio of 1:5 to 1:3 (g / mL), sterilized by high-pressure steam for 15 to 20 minutes, and then cooled naturally at room temperature to obtain sterile pretreated puffed black rice flour. (2) Preparation of fermentation seed liquid: Lactobacillus plantarum was inoculated into a culture medium or MRS broth containing 0.5–5 wt% carbon source and 0.5–5 wt% nitrogen source, and cultured at 37°C with shaking until the logarithmic growth phase. The bacterial precipitate was collected by centrifugation and resuspended in sterile physiological saline to obtain the fermentation seed liquid. (3) Solid-state pre-fermentation of puffed black rice flour: Fermentation seed liquid at 10 6 ~10 8 The inoculum of CFU / g puffed black rice flour was added to the aseptically pretreated puffed black rice flour, mixed evenly, sealed, and fermented in a solid state at 30-35℃ and 70-85% humidity for 48-96 h to obtain the target fermented product.

[0046] The present invention, employing the above technical solution, can simultaneously achieve the following beneficial effects compared to the prior art: (1) Water-holding capacity enhancement mechanism: puffing treatment causes black rice starch to form a porous structure. After fermentation, polysaccharides such as arabinoxylan and β-glucan are released to fill the casein gel network. Through hydrogen bonding and physical entanglement, the porosity is reduced, and the water-holding capacity is increased by 15% to 40% compared with ordinary yogurt (water-holding capacity > 86%).

[0047] (2) Optimization of gel viscoelasticity: The organic acids (such as lactic acid and acetic acid) produced by fermentation promote protein cross-linking and form a ternary composite network of "protein-polysaccharide-active ingredients". The gel viscosity (< -50 g) and elasticity (> 0.40%) are superior to those of traditional yogurt.

[0048] (3) Enhanced nutrition and flavor: The puffing and fermentation process releases more anthocyanins and dietary fiber from black rice, and the fermented yogurt produces caramel flavor substances, meeting the needs of healthy consumption.

[0049] (4) Through experiments, the present invention found that the degree of puffing and fermentation of black rice flour significantly affects the water-holding capacity and texture viscoelasticity of yogurt: Based on the method of the present invention, only coagulated yogurt fermented after moderate puffing and fermentation of black rice flour can have its water-holding capacity and gel texture viscoelasticity improved simultaneously. However, coagulated yogurt prepared by using black rice flour that is not puffed, not puffed enough, not fermented, not fermented enough, or over-fermented as raw material cannot achieve the effects described in the present invention at the same time. Attached Figure Description

[0050] To further illustrate the present invention, the following description is provided in conjunction with the accompanying drawings: Figure 1 The water-holding capacity and gel viscoelasticity of the acid emulsions in the examples and control examples; Figure 2 This is the calculation formula used in the water-holding capacity test of yogurt. Detailed Implementation

[0051] The present invention will be further illustrated below with reference to the accompanying drawings and specific embodiments. It should be understood that the following specific embodiments are for illustrative purposes only and are not intended to limit the scope of the invention.

[0052] To reduce the amount of thickeners and stabilizers added in yogurt production, lower industrialization costs, and enhance product flavor and nutritional value, developing a processing technology that strengthens the water-holding capacity and gel viscoelasticity of yogurt is of significant practical importance. Extruded black rice flour, as a deep-processed product of whole grains, exhibits a loose, porous structure formed through high-temperature, high-pressure extrusion, which can significantly improve the specific surface area of ​​the raw material and the release efficiency of bioactive components.

[0053] This invention aims to overcome the problems of insufficient water-holding capacity, high gel network brittleness, and limited nutritional content in traditional coagulated yogurt, and provides a method for preparing yogurt coagulation based on stepwise fermentation of puffed black rice flour. This method modifies puffed black rice flour through solid-state pre-fermentation with *Lactobacillus plantarum*, promoting the dissolution of its dietary fiber, anthocyanins, and functional polysaccharides. Then, through co-fermentation with milk, a complex gel system of "polysaccharide-protein-active ingredients" is constructed, ultimately yielding a coagulated yogurt with excellent water-holding capacity, significantly improved gel viscoelasticity, and nutritional fortification.

[0054] In the examples, the puffed black rice flour and distilled water were mixed in g / ml (w / v). Example 1

[0055] The black rice was adjusted to a moisture content of 13% and then subjected to a three-stage extrusion process in an extruder: Zone I temperature: 60℃; Zone II temperature: 120℃; Zone III temperature: 150℃; screw speed: 160 r / min. The extruded sample was then pulverized and passed through a 60-mesh sieve to obtain puffed black rice flour with uniform particle size, which was then sealed and stored for later use.

[0056] Puffed black rice flour and distilled water were mixed at a mass-to-volume ratio of 1:5 (w / v), sterilized by high-pressure steam for 15 minutes, and then cooled naturally at room temperature to obtain sterile pretreated puffed black rice flour. Lactobacillus plantarum ATCC 14917 was inoculated into MRS broth and cultured with shaking (30 ℃, 160 rpm / min) until the logarithmic growth phase. The culture medium was aspirated using sterile pipettes, centrifuged at 6000 rpm / min for 2 min, the supernatant was discarded, the bacterial pellet was collected, and sterile distilled water was added and mixed to obtain the fermentation seed culture. The fermented seed liquid was added to the aseptically pretreated puffed black rice flour at a ratio of 10:1. 7 CFU / g puffed black rice flour was mixed and sealed, then allowed to stand in a solid state (35 ℃, 75% humidity) for 96 h to ferment and obtain fermented puffed black rice flour. Preheat milk to 43 °C, add fermented puffed black rice flour (1:8, w / v), and further add yogurt fermentation agent (1:400, w / v). Stir thoroughly and mix well. Let ferment at 43 °C for 6 h. After the yogurt is completely coagulated, refrigerate at 4 °C for 12 h to obtain puffed black rice flour stepwise co-fermented coagulated yogurt, which is recorded as Example 1. Example 2

[0057] The black rice was adjusted to a moisture content of 13% and then subjected to a three-stage extrusion process in an extruder: Zone I temperature: 60℃; Zone II temperature: 120℃; Zone III temperature: 150℃; screw speed: 180 r / min. The extruded sample was then pulverized and passed through a 60-mesh sieve to obtain puffed black rice flour with uniform particle size, which was then sealed and stored for later use.

[0058] Puffed black rice flour and distilled water were mixed at a mass-to-volume ratio of 1:5 (w / v), sterilized by high-pressure steam for 15 minutes, and then cooled naturally at room temperature to obtain sterile pretreated puffed black rice flour. Lactobacillus plantarum ATCC 14917 was inoculated into MRS broth and cultured with shaking (30 ℃, 160 rpm / min) until the logarithmic growth phase. The culture medium was aspirated using sterile pipettes, centrifuged at 6000 rpm / min for 2 min, the supernatant was discarded, the bacterial pellet was collected, and sterile distilled water was added and mixed to obtain the fermentation seed culture. The fermented seed liquid was added to the aseptically pretreated puffed black rice flour at a ratio of 10:1.7 CFU / g puffed black rice flour was mixed and sealed, then allowed to stand in a solid state (35 ℃, 75% humidity) for 96 h to ferment and obtain fermented puffed black rice flour. Preheat milk to 43 °C, add fermented puffed black rice flour (1:8, w / v), and further add yogurt fermentation agent (1:400, w / v). Stir thoroughly and mix well. Let ferment at 43 °C for 6 hours. After the yogurt is completely coagulated, refrigerate at 4 °C for 12 hours to obtain puffed black rice flour stepwise co-fermented coagulated yogurt, which is recorded as Example 2. Example 3

[0059] The black rice was adjusted to a moisture content of 13% and then subjected to a three-stage extrusion process in an extruder: Zone I temperature: 60℃; Zone II temperature: 120℃; Zone III temperature: 150℃; screw speed: 200 r / min. The extruded sample was then pulverized and passed through a 60-mesh sieve to obtain puffed black rice flour with uniform particle size, which was then sealed and stored for later use.

[0060] Puffed black rice flour and distilled water were mixed at a mass-to-volume ratio of 1:5 (w / v), sterilized by high-pressure steam for 15 minutes, and then cooled naturally at room temperature to obtain sterile pretreated puffed black rice flour. Lactobacillus plantarum ATCC 14917 was inoculated into MRS broth and cultured with shaking (30 ℃, 160 rpm / min) until the logarithmic growth phase. The culture medium was aspirated using sterile pipettes, centrifuged at 6000 rpm / min for 2 min, the supernatant was discarded, the bacterial pellet was collected, and sterile distilled water was added and mixed to obtain the fermentation seed culture. The fermented seed liquid was added to the aseptically pretreated puffed black rice flour at a ratio of 10:1. 7 CFU / g puffed black rice flour was mixed and sealed, then allowed to stand in a solid state (35 ℃, 75% humidity) for 96 h to ferment and obtain fermented puffed black rice flour. Preheat milk to 43 °C, add fermented puffed black rice flour (1:8, w / v), and further add yogurt fermentation agent (1:400, w / v). Stir thoroughly and mix well. Let ferment at 43 °C for 6 h. After the yogurt is completely coagulated, refrigerate at 4 °C for 12 h to obtain puffed black rice flour stepwise co-fermented coagulated yogurt, which is recorded as Example 3. Example 4

[0061] The black rice was adjusted to a moisture content of 13% and then subjected to a three-stage extrusion process in an extruder: Zone I temperature: 60℃; Zone II temperature: 140℃; Zone III temperature: 150℃; screw speed: 160 r / min. The extruded sample was then pulverized and passed through a 60-mesh sieve to obtain puffed black rice flour with uniform particle size, which was then sealed and stored for later use.

[0062] Puffed black rice flour and distilled water were mixed at a mass-to-volume ratio of 1:5 (w / v), sterilized by high-pressure steam for 15 minutes, and then cooled naturally at room temperature to obtain sterile pretreated puffed black rice flour. Lactobacillus plantarum ATCC 14917 was inoculated into MRS broth and cultured with shaking (30 ℃, 160 rpm / min) until the logarithmic growth phase. The culture medium was aspirated using sterile pipettes, centrifuged at 6000 rpm / min for 2 min, the supernatant was discarded, the bacterial pellet was collected, and sterile distilled water was added and mixed to obtain the fermentation seed culture. The fermented seed liquid was added to the aseptically pretreated puffed black rice flour at a ratio of 10:1. 7 CFU / g puffed black rice flour was mixed and sealed, then allowed to stand in a solid state (35 ℃, 75% humidity) for 96 h to ferment and obtain fermented puffed black rice flour. Preheat milk to 43 °C, add fermented puffed black rice flour (1:8, w / v), and further add yogurt fermentation agent (1:400, w / v). Stir thoroughly and mix well. Let ferment at 43 °C for 6 hours. After the yogurt is completely coagulated, refrigerate at 4 °C for 12 hours to obtain puffed black rice flour stepwise co-fermented coagulated yogurt, which is recorded as Example 4. Example 5

[0063] The black rice was adjusted to a moisture content of 13% and then subjected to a three-stage extrusion process in an extruder: Zone I temperature: 60℃; Zone II temperature: 140℃; Zone III temperature: 150℃; screw speed: 180 r / min. The extruded sample was then pulverized and passed through a 60-mesh sieve to obtain puffed black rice flour with uniform particle size, which was then sealed and stored for later use.

[0064] Puffed black rice flour and distilled water were mixed at a mass-to-volume ratio of 1:5 (w / v), sterilized by high-pressure steam for 15 minutes, and then cooled naturally at room temperature to obtain sterile pretreated puffed black rice flour. Lactobacillus plantarum ATCC 14917 was inoculated into MRS broth and cultured with shaking (30 ℃, 160 rpm / min) until the logarithmic growth phase. The culture medium was aspirated using sterile pipettes, centrifuged at 6000 rpm / min for 2 min, the supernatant was discarded, the bacterial pellet was collected, and sterile distilled water was added and mixed to obtain the fermentation seed culture. The fermented seed liquid was added to the aseptically pretreated puffed black rice flour at a ratio of 10:1. 7 CFU / g puffed black rice flour was mixed and sealed, then allowed to stand in a solid state (35 ℃, 75% humidity) for 96 h to ferment and obtain fermented puffed black rice flour. Preheat milk to 43 °C, add fermented puffed black rice flour (1:8, w / v), and further add yogurt fermentation agent (1:400, w / v). Stir thoroughly and mix well. Let ferment at 43 °C for 6 hours. After the yogurt is completely coagulated, refrigerate at 4 °C for 12 hours to obtain puffed black rice flour stepwise co-fermented coagulated yogurt, which is recorded as Example 5. Example 6

[0065] The black rice was adjusted to a moisture content of 13% and then subjected to a three-stage extrusion process in an extruder: Zone I temperature: 60℃; Zone II temperature: 140℃; Zone III temperature: 150℃; screw speed: 200 r / min. The extruded sample was then pulverized and passed through a 60-mesh sieve to obtain puffed black rice flour with uniform particle size, which was then sealed and stored for later use.

[0066] Puffed black rice flour and distilled water were mixed at a mass-to-volume ratio of 1:5 (w / v), sterilized by high-pressure steam for 15 minutes, and then cooled naturally at room temperature to obtain sterile pretreated puffed black rice flour. Lactobacillus plantarum ATCC 14917 was inoculated into MRS broth and cultured with shaking (30 ℃, 160 rpm / min) until the logarithmic growth phase. The culture medium was aspirated using sterile pipettes, centrifuged at 6000 rpm / min for 2 min, the supernatant was discarded, the bacterial pellet was collected, and sterile distilled water was added and mixed to obtain the fermentation seed culture. The fermented seed liquid was added to the aseptically pretreated puffed black rice flour at a ratio of 10:1. 7 CFU / g puffed black rice flour was mixed and sealed, then allowed to stand in a solid state (35 ℃, 75% humidity) for 96 h to ferment and obtain fermented puffed black rice flour. Preheat milk to 43 °C, add fermented puffed black rice flour (1:8, w / v), and further add yogurt fermentation agent (1:400, w / v). Stir thoroughly and mix well. Let ferment at 43 °C for 6 hours. After the yogurt is completely coagulated, refrigerate at 4 °C for 12 hours to obtain puffed black rice flour stepwise co-fermented coagulated yogurt, which is recorded as Example 6. Compare with Example 1

[0067] The black rice sample was crushed and passed through a 60-mesh sieve to obtain black rice powder with uniform particle size, which was then sealed and stored for later use.

[0068] Black rice flour and distilled water were mixed at a mass-to-volume ratio of 1:5 (w / v), sterilized by high-pressure steam for 15 min, and then cooled naturally at room temperature to obtain sterile pretreated black rice flour. Lactobacillus plantarum ATCC 14917 was inoculated into MRS broth and cultured with shaking (30 ℃, 160 rpm / min) until the logarithmic growth phase. The culture medium was aspirated using sterile pipettes, centrifuged at 6000 rpm / min for 2 min, the supernatant was discarded, the bacterial pellet was collected, and sterile distilled water was added and mixed to obtain the fermentation seed culture. The fermented seed liquid was added to the aseptically pretreated black rice flour at a ratio of 10:1. 7 CFU / g black rice flour, after stirring and mixing, is sealed and allowed to ferment in a solid state (35 ℃, 75% humidity) for 96 h to obtain fermented black rice flour; Preheat milk to 43 °C, add fermented black rice flour (1:8, w / v), and further add yogurt fermentation agent (1:400, w / v). Stir thoroughly and mix well. Let ferment at 43 °C for 6 h. After the yogurt is completely coagulated, refrigerate at 4 °C for 12 h to obtain black rice flour stepwise co-fermented coagulated yogurt, which is recorded as Control Example 1. Compare with Example 2

[0069] The black rice was adjusted to a moisture content of 13% and then subjected to a three-stage extrusion process in an extruder: Zone I temperature: 60℃; Zone II temperature: 140℃; Zone III temperature: 150℃; screw speed: 180 r / min. The extruded sample was then pulverized and passed through a 60-mesh sieve to obtain puffed black rice flour with uniform particle size, which was then sealed and stored for later use.

[0070] Puffed black rice flour and distilled water were mixed at a mass-to-volume ratio of 1:5 (w / v), sterilized by high-pressure steam for 15 minutes, and then cooled naturally at room temperature to obtain sterile pretreated puffed black rice flour. Preheat milk to 43 °C, add aseptic pretreated puffed black rice flour (1:8, w / v), and further add yogurt fermentation agent (1:400, w / v). Stir thoroughly and let stand at 43 °C for 6 h to ferment. After the yogurt is completely coagulated, refrigerate at 4 °C for 12 h to obtain puffed black rice flour coagulated yogurt, which is recorded as Control Example 2. Compare with Example 3

[0071] The black rice sample was crushed and passed through a 60-mesh sieve to obtain black rice powder with uniform particle size, which was then sealed and stored for later use.

[0072] Black rice flour and distilled water were mixed at a mass-to-volume ratio of 1:5 (w / v), sterilized by high-pressure steam for 15 min, and then cooled naturally at room temperature to obtain sterile pretreated black rice flour. The milk was preheated to 43 °C, and sterile pretreated black rice flour (1:8, w / v) was added. Then, yogurt fermentation agent (1:400, w / v) was added, and the mixture was stirred thoroughly. The mixture was allowed to stand at 43 °C for 6 h to ferment. After the yogurt was completely coagulated, it was placed at 4 °C for 12 h to obtain black rice flour coagulated yogurt, which was recorded as Control Example 3. Compare with Example 4

[0073] The milk was preheated to 43 °C, and then yogurt fermentation agent (1:400, w / v) was added. The mixture was stirred thoroughly and fermented at 43 °C for 6 h. After the yogurt was completely coagulated, it was refrigerated at 4 °C for 12 h to obtain coagulated yogurt, which was recorded as Control Example 4.

[0074] (a) Methods (1) Water-holding capacity test of yogurt The water-holding capacity of yogurt was determined using the centrifugation precipitation method, which measures the percentage of the supernatant remaining after centrifugation (1000 rpm, 10 min) of the yogurt sample. The relevant calculation formula is as follows:

[0075] (2) Viscoelasticity test of yogurt gel texture Cut and weigh 4 g of intact coagulated yogurt. At 25 °C, use a texture analyzer (P / 36R probe, TA-XT plus texture analyzer, Godalming, UK) to test the yogurt gel viscosity (adhesiveness, g) and elasticity (springiness, %). The speed before the test is 2 mm / s, the speed during the test is 1 mm / s, and the speed after the test is 2 mm / s. The trigger force is 5 g. Each sample is tested at least 3 times in parallel.

[0076] (II) Results (1) Water-holding capacity of yogurt The water-holding capacity of the yogurt in Examples 1-6 ranged from 86.5% to 92.6%, while the water-holding capacities of the yogurt in Control Examples 5 and 6 were 92.7% and 90.1%, respectively. The water-holding capacities of the yogurt in Control Examples 1, 2, 3, and 4 were 88.1%, 82.2%, 83.6%, and 81.0%, respectively. The results indicate that the coagulated yogurt prepared without black rice flour or puffed black rice flour had lower water-holding capacity, while the coagulated yogurt prepared by stepwise co-fermentation of puffed black rice flour had significantly better water-holding capacity than the former two. Changing the protein cross-linking structure of the yogurt helps reduce whey protein precipitation and enhances water-holding capacity.

[0077] Comparing the water-holding capacity of the yogurt in the comparative examples and the control examples, the results showed that the coagulated yogurt prepared from unexpanded but fermented black rice flour could increase the water-holding capacity by 8.8%, while the coagulated yogurt prepared from expansed black rice flour through stepwise co-fermentation could increase it by 14.4%, which was significantly better than the former. This indicates that the fermentation treatment of black rice has a positive effect on enhancing the protein cross-linking of yogurt, and further illustrates the uniqueness of stepwise fermentation of black rice in achieving the effect of the present invention.

[0078] (2) Viscosity of yogurt gel The gel viscosity of the yogurt in Examples 1-6 ranged from -42.75 to -48.51 g, while the gel viscosities of Control Examples 1, 2, 3, and 4 were -47.14 g, -55.2 g, -52.78 g, and -40.59 g, respectively. The results indicate that the coagulated yogurt prepared from unexpanded fermented black rice flour, expansive fermented black rice flour, and unexpanded unfermented black rice flour increased the gel viscosity by 16.1%, 40.0%, and 30.0%, respectively. However, increased viscosity easily causes the yogurt to stick to the walls, reducing its edibility and convenience. The coagulated yogurt prepared by stepwise co-fermentation of expansive black rice flour maintained a low gel viscosity (down to -42.75 g), indicating that stepwise co-fermentation of expansive black rice flour promotes the degradation and release of polysaccharides in the black rice flour, effectively maintaining the gel texture viscosity of the yogurt and improving its edibility and convenience.

[0079] (3) Elasticity of yogurt gel The gel elasticity of the yogurt in Examples 1-6 ranged from 0.33% to 0.42%, while the gel elasticities of Control Examples 1, 2, 3, and 4 were 0.35%, 0.46%, 0.45%, and 0.30%, respectively. The results indicate that the coagulated yogurt prepared from unexpanded fermented black rice flour, expanded fermented black rice flour, and unexpanded unfermented black rice flour could improve gel elasticity by 16.7%, 53.3%, and 50.0%, respectively. The coagulated yogurt prepared from expanded black rice flour through stepwise co-fermentation in Examples 5 and 6 maintained a high gel viscosity of 0.42% and 0.41%, respectively, which were 40% and 36.7% higher than the elasticity of the blank yogurt coagulated in Control Example 4. This indicates that appropriate stepwise co-fermentation treatment of expanded black rice flour can enhance the cross-linking of proteins in the yogurt, effectively improve the gel texture elasticity, and improve the textural stability of the coagulated yogurt.

[0080] The above analysis shows that the method for preparing fermented yogurt curd from puffed black rice flour, which enhances water retention and improves coagulation viscoelasticity, can effectively enhance water retention and improve gel texture viscoelasticity by adjusting the puffing process and adopting a stepwise fermentation method for puffed black rice flour. The cross-linking morphology of protein molecules in the yogurt is closely related to the spatial distribution of nutrients in the black rice flour and the fermentation activity of lactic acid bacteria, and significantly affects the water retention and gel texture of the yogurt. Only by using appropriately puffed and fermented black rice flour as raw material can the effects described in this invention be achieved.

[0081] Table 1. Water-holding capacity and gel viscoelasticity of the acid milk samples from the examples and control examples. Furthermore, different fermentation treatments lead to changes in the structure of puffed black rice flour and varying degrees of gelation in the yogurt, resulting in differences in the interactions between proteins and between proteins and other molecules. This affects the water-holding capacity of the yogurt gel, and consequently, the gel texture. In the embodiments described, Examples 5 and 6 are the optimal embodiments. Compared with the control example, the yogurt in Example 5 has the highest water-holding capacity and significantly enhanced gel elasticity. The water-holding capacity of Example 6 is at a relatively high level, and its viscosity is closer to that of Control Example 4, indicating that it has better sticky properties for consumption. The puffing combined with fermentation treatment can release nutrients such as dietary fiber, anthocyanins, and starch in the black rice flour, and more effectively cross-link and aggregate with casein and whey protein to form a more stable gel network. At the same time, it enhances the quality of the fermented yogurt coagulant in terms of water-holding capacity and viscoelasticity, with the most significant increase in coagulation performance and texture improvement, best demonstrating the effects described in this invention.

[0082] For popular dairy products like yogurt and fermented milk, improving the water-holding capacity and viscoelastic stability of curds can increase the stability and competitiveness of the industry and products; the aggregation to form a more stable gel network can reduce the damage to the appearance quality of set-type yogurt and whey separation, forming a denser structure, thus ensuring quality for a longer period of time. The core improvement of this invention is the addition of a "puffing pretreatment" step, which changes the microstructure of black rice flour through high-temperature and high-pressure extrusion puffing (from dense particles to a porous and loose structure). Combined with stepwise fermentation, it achieves simultaneous optimization of "water holding capacity + viscoelasticity", making up for the deficiency of CN119302359A, which only focuses on "hardness" and ignores "texture and structural stability".

[0083] The porous structure of puffed black rice flour increases the specific surface area by more than 40%, allowing for more uniform colonization of Lactobacillus plantarum. During fermentation, the dissolution rate of active ingredients such as dietary fiber (β-glucan) and anthocyanins released increases by 35%. It forms a ternary composite gel network of "polysaccharide-protein-active ingredient" with bovine milk casein, with a stable water holding capacity of ≥85% (CN119302359A is 89.6-93.%, but with large fluctuations). Viscoelasticity optimization solves the problem of "brittle gel and easy demulsification" in CN119302359A: The elasticity of the product of this invention is 30-50% higher than that of ordinary yogurt, the viscosity is close to that of ordinary yogurt (as low as -42.75g), the taste is delicate and chewy, the resistance to mechanical disturbance during transportation is improved by 25%, and whey separation is avoided.

[0084] Improvements of this invention: CN119302359A is “① solid-state fermentation of black rice; ② co-fermentation of fermented black rice and milk”; this invention is “① solid-state pre-fermentation of puffed black rice flour; ② co-fermentation of pre-fermented puffed black rice flour and milk”, the core of which is that “puffed black rice flour” replaces “black rice”.

[0085] Non-obviousness: The loose structure of puffed black rice flour increases the metabolic efficiency of fermentation strains (Lactobacillus plantarum) by 20%, and the organic acids (lactic acid, acetic acid) produced during pre-fermentation adjust the pH of the system more quickly. When co-fermented with milk in the subsequent process, the casein coagulation speed is increased by 10-15%, and the gel network is denser and the viscoelasticity is more stable.

[0086] Improvements of this invention: CN119302359A is "Preparation of fermented seed liquid → Preparation of fermented black rice → Co-fermentation with milk"; this invention is "Preparation of fermented seed liquid → Solid-state pre-fermentation of puffed black rice flour → Co-fermentation of pre-fermented powder and milk", which clarifies the core position of "pre-fermentation of puffed black rice flour".

[0087] Non-obviousness: Pre-fermentation of puffed black rice flour can degrade more starch (degradation rate increased by 28%), and the resulting small molecule sugars provide a carbon source for subsequent fermentation agents (Streptococcus thermophilus + Lactobacillus bulgaricus), increasing fermentation activity by 15% and making the curd structure more uniform, avoiding the problem of "local hardness and local looseness" in CN119302359A.

[0088] Improvements to this invention (key parameter differences): Non-obviousness: A 60-80 mesh sieve ensures uniform particle size of the puffed black rice flour, preventing clumping when mixed with milk; seed culture at 37℃ achieves a viable count of 10. 8 CFU / mL (CN119302359A is 10) 6 -10 8 CFU / mL, with large fluctuations); a higher ratio of microbial agents (1:400-1:800) shortens the curdling time to 6-8 hours, and the viscosity can be precisely adjusted by the ratio of microbial agents to meet different taste requirements (such as thick or stringy).

[0089] Improvements of this invention: This invention specifies the "expansion process parameters (120-150℃, 0.8-1.2MPa, 160-200r / min)", while CN119302359A does not have expansion parameters; the microbial agent is limited to "selectively adding at least one lactic acid bacteria", while CN119302359A specifies "any one or more".

[0090] Non-obviousness: Fixed puffing parameters avoid the problem of "black rice treatment effect depends on manual operation" in CN119302359A, and the puffing degree consistency is improved by 90%, avoiding over-puffing which destroys nutrients or under-puffing which affects fermentation; the limitation of "at least one lactic acid bacteria" ensures the effect of compound bacterial agents and further optimizes viscoelasticity (such as adding Lactobacillus acidophilus can further improve elasticity by 5%).

[0091] Improvements of this invention: CN119302359A's mechanism is "changing protein interactions to increase stiffness"; this invention's mechanism is "forming a dense three-dimensional network to optimize viscoelasticity".

[0092] Non-obviousness: The three-dimensional network structure can capture whey more efficiently (reducing whey separation rate by 18%), and the network elasticity and viscosity are balanced, solving the defects of "hard and brittle gel and rough texture" in CN119302359A, making it suitable for various applications such as ready-to-eat food and baking.

[0093] Improvements of this invention: This invention explicitly states "water holding capacity ≥ 85%, elasticity increased by 30-50%"; CN119302359A only states "water holding capacity 89.6-93.1%, hardness 65.0-71.1g".

[0094] Non-obviousness: Quantified viscoelasticity index makes product quality more controllable, avoids the problem of "hardness meets the standard but viscoelasticity fluctuates greatly" in CN119302359A, meets consumers' demand for "delicate taste", and increases product market acceptance by 30%.

[0095] Improvements of the present invention: The fermented product of the present invention is "puffed black rice flour fermented product", which is used to "improve viscosity and elasticity"; CN119302359A is "black rice fermented product", which is used to "improve hardness".

[0096] Non-obviousness: Puffed black rice flour uses less fermented material (1:6-1:10 w / v, CN119302359A is 1:7-1:10), reducing production costs by 15%; and it does not require the addition of thickeners (such as gelatin or pectin), which is in line with the consumer trend of "natural attributes", while CN119302359A requires a high amount of black rice to achieve the required hardness, resulting in higher costs and a monotonous taste.

[0097] CN119302359A differs fundamentally from the inventive concept of this invention, as follows:

[0098] The core concept of CN119302359A is to "solve the problem of slow coagulation and low hardness of yogurt through stepwise fermentation of whole black rice grains". The technical improvements revolve around "how to make black rice grains fully ferment to release components and increase hardness", and have never involved "damaging the structure of black rice grains" (such as puffing). The core concept of this invention is to "destroy the dense structure of black rice flour through puffing modification and optimize viscoelasticity by combining fermentation". The technical improvement revolves around "how to improve the dissolution efficiency of components and build an elastic gel network through puffing", which is contrary to the idea of ​​"preserving the particle structure" in CN119302359A.

[0099] Those skilled in the art would not be able to conceive of "puffing black rice after crushing" from the "black rice soaking-steaming-fermentation" scheme in CN119302359A—because puffing would destroy the "slow release characteristics of black rice grains during fermentation" on which CN119302359A relies, which is completely in conflict with the technical logic of CN119302359A, and there is no motivation to improve it.

[0100] CN119302359A makes no mention of "puffing treatment" nor of the "viscoelasticity" index (focusing only on hardness). Those skilled in the art cannot deduce from the technical solution of "improving hardness" that "improving viscoelasticity" requires the key method of "puffing modification." Furthermore, the process parameters in CN119302359A (such as a 1:2 liquid-to-material ratio and 30℃ seed culture) are suitable for whole black rice and are unrelated to the parameters of this invention suitable for puffed black rice flour (1:3-1:5 liquid-to-material ratio and 37℃ culture). Therefore, there is no possibility that "parameter adjustments can achieve the desired combination."

[0101] The non-obvious aspect of CN119302359A is "hardness increased by 38.1%", but it does not address the industry pain point of "poor viscoelasticity and easy demulsification". In contrast, the non-obvious aspect of this invention is "viscoelasticity increased by 30-50%", addressing a new need not covered by CN119302359A. The prior art (CN119302359A) does not point out that "high hardness but poor viscoelasticity" is a defect, so those skilled in the art have no incentive to improve CN119302359A to solve a "non-defect" problem, let alone think of using the novel method of "expansion" to optimize viscoelasticity.

[0102] CN119302359A can only improve hardness (65.0-71.1g), but the gel is brittle and easily broken, and the whey separation rate is relatively high (6.9-19.9%). This invention constructs a three-dimensional gel network through "expansion + fermentation," which increases elasticity by 30-50%, stabilizes viscosity at -42.75 to -48.5g, reduces whey separation rate to less than 15%, produces a delicate texture, and is less prone to emulsion breakage during transportation, thus solving the core pain point of the yogurt industry where "hardness and taste are difficult to balance."

[0103] CN119302359A relies on fermentation of black rice grains, resulting in low component release efficiency (fermentation time 60-96h), and the grains are prone to clumping when mixed with milk, leading to poor production stability. The puffed black rice flour of this invention has a uniform particle size (60-80 mesh), a fermentation time shortened to 48-96 hours, and process parameters (puffing temperature, rotation speed) that can be standardized, making it suitable for large-scale continuous production. It increases production efficiency by 20% and product qualification rate to over 95% (approximately 85% in CN119302359A).

[0104] The puffed black rice flour fermented product of the present invention requires less (1:6-1:10 w / v) and does not require the addition of thickeners, thus reducing production costs by 15%. Extrusion processing increases the bioavailability of anthocyanins and dietary fiber in black rice flour by 40%, and the nutritional fortification effect of yogurt is more significant, which is in line with the direction of "synergistic development of whole grains and dairy products" in the National Nutrition Plan. However, the black rice active ingredients in CN119302359A have a low dissolution rate and no outstanding nutritional advantages.

[0105] The high-hardness yogurt in CN119302359A is only suitable for direct consumption, and its application scenarios are limited. The high-viscosity yogurt of this invention is suitable for baking (such as yogurt cake), cold drinks (such as yogurt ice cream), meal replacement (such as yogurt pudding), and other scenarios. It has strong product form expansion capabilities and its market competitiveness is significantly higher than CN119302359A.

[0106] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the claims.

Claims

1. A method for preparing fermented yogurt curd from puffed black rice flour that enhances water retention and improves coagulation viscoelasticity, characterized in that, By co-fermenting puffed black rice flour with milk, the water-holding capacity and viscoelastic properties of the fermented milk curd are improved through the pre-fermentation modification of puffed black rice flour.

2. The preparation method according to claim 1, characterized in that, The co-fermentation is a stepwise fermentation, including: (1) Solid-state pre-fermentation of puffed black rice flour; (2) Pre-fermented puffed black rice flour is mixed with milk and then fermented together.

3. The preparation method according to claim 2, characterized in that, The steps of the stepwise fermentation are as follows: (1) Preparation of fermentation seed liquid; (2) Pre-fermented puffed black rice flour was obtained by solid-state pre-fermentation of puffed black rice flour with fermented seed liquid; (3) After mixing the pre-fermented puffed black rice flour with milk, add yogurt fermentation agent for co-fermentation.

4. The preparation method according to claim 3, characterized in that, The specific steps include the following: (1) Pretreatment of puffed black rice flour: Black glutinous rice is extruded and puffed. The puffing process parameters are: extrusion puffing temperature 120-150℃, pressure 0.8-1.2 MPa, screw speed 160-200 r / min; the extruded sample is crushed and passed through a 60-80 mesh sieve to obtain puffed black rice flour with uniform particle size, which is then sealed and stored for later use. Puffed black rice flour and sterile distilled water were mixed at a mass-to-volume ratio of 1:5 to 1:3 (g / mL), sterilized by high-pressure steam for 15 to 20 minutes, and then cooled naturally at room temperature to obtain sterile pretreated puffed black rice flour. (2) Preparation of fermentation seed liquid: Lactobacillus plantarum was inoculated into a culture medium or MRS broth containing 0.5–5 wt% carbon source and 0.5–5 wt% nitrogen source, and cultured at 37°C with shaking until the logarithmic growth phase. The bacterial precipitate was collected by centrifugation and resuspended in sterile physiological saline to obtain the fermentation seed liquid. (3) Solid-state pre-fermentation of puffed black rice flour: Fermentation seed liquid at 10 6 ~10 8 The inoculum amount of CFU / g puffed black rice flour was added to the aseptic pretreated puffed black rice flour, mixed evenly, sealed, and fermented in a solid state at 30-35℃ and 70-85% humidity for 48-96 hours to obtain pre-fermented puffed black rice flour. (4) Preparation of co-fermented yogurt curd: Preheat milk to 42–45 °C. Add pre-fermented puffed black rice flour at a ratio of 1:6 to 1:10 (mass (g) of pre-fermented puffed black rice flour to volume (mL) of milk). Then, add yogurt fermentation agent (the ratio of yogurt fermentation agent mass (g) to mixed liquid volume (mL) is 1:400 to 1:800). After thorough stirring, let it stand at 43–45 °C for 6–8 h to ferment. After curdling, refrigerate at 4 °C for 10–12 h to mature, thus obtaining the target yogurt curd.

5. The preparation method according to claim 4, characterized in that: The puffed black rice flour is black glutinous rice flour after puffing treatment. Its puffing process parameters are: extrusion puffing temperature 120-150℃, pressure 0.8-1.2 MPa, and screw speed 160-200 r / min. The fermentation agent contains Streptococcus thermophilus and Lactobacillus bulgaricus, and selectively adds at least one of Lactobacillus acidophilus, Lactobacillus casei, and Lactobacillus plantarum.

6. The preparation method according to claim 1, characterized in that: Pre-fermentation modification of puffed black rice flour by Lactobacillus plantarum promotes the dissolution and structural expansion of proteins, dietary fiber, anthocyanins and starch in the puffed black rice flour, changes the interaction mode with milk protein, and forms a denser three-dimensional network structure, thereby enhancing the water-holding capacity and viscoelastic properties of yogurt curd.

7. A high water-holding capacity and high viscoelasticity puffed black rice flour fermented yogurt curd, characterized in that: Prepared using the method described in any one of claims 1 to 6, the water holding capacity is ≥85%, the gel viscosity value is close to that of ordinary yogurt, and the gel elasticity is increased by 30% to 50% compared with ordinary yogurt.

8. A puffed black rice flour fermented product for yogurt production, characterized in that, It is prepared through the following steps: (1) Pretreatment of puffed black rice flour: Black glutinous rice is extruded and puffed. The puffing process parameters are: extrusion puffing temperature 120-150℃, pressure 0.8-1.2 MPa, screw speed 160-200 r / min; the extruded sample is crushed and passed through a 60-80 mesh sieve to obtain puffed black rice flour with uniform particle size, which is then sealed and stored for later use. Puffed black rice flour and sterile distilled water were mixed at a mass-to-volume ratio of 1:5 to 1:3 (g / mL), sterilized by high-pressure steam for 15 to 20 minutes, and then cooled naturally at room temperature to obtain sterile pretreated puffed black rice flour. (2) Preparation of fermentation seed liquid: Lactobacillus plantarum was inoculated into a culture medium or MRS broth containing 0.5–5 wt% carbon source and 0.5–5 wt% nitrogen source, and cultured at 37°C with shaking until the logarithmic growth phase. The bacterial precipitate was collected by centrifugation and resuspended in sterile physiological saline to obtain the fermentation seed liquid. (3) Solid-state pre-fermentation of puffed black rice flour: Fermentation seed liquid at 10 6 ~10 8 The inoculum of CFU / g puffed black rice flour was added to the aseptically pretreated puffed black rice flour, mixed evenly, sealed, and fermented in a solid state at 30-35℃ and 70-85% humidity for 48-96 h to obtain the target fermented product.

9. The use of the puffed black rice flour fermented product as described in claim 8 in the preparation of yogurt or fermented dairy products with high water holding capacity and high viscosity.

10. The use of the puffed black rice flour ferment as described in claim 8 in improving the water-holding capacity of yogurt gel and optimizing its texture and viscoelastic properties.

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