A stirred red yeast rice yogurt and its preparation method

Abstract

This invention relates to the field of food fermentation and dairy processing technology, and discloses a stirred red yeast rice yogurt and its preparation method. The preparation method includes the following steps: mixing red yeast rice powder, raw milk, and a sweetener; shearing; ultrasonic treatment; inoculation with a starter culture; fermentation; and stirring to obtain the stirred red yeast rice yogurt; the red yeast rice powder has a particle size of 13-30 μm. The stirred red yeast rice yogurt of this invention has advantages such as uniform color, delicate texture, unique flavor, and stable quality, while significantly shortening the fermentation time compared to conventional methods and increasing the number of live bacteria; furthermore, the preparation method of this invention is simple and suitable for industrial production.

Description

Technical Field

[0001] This invention relates to the field of food fermentation and dairy processing technology, and in particular to a stirred red yeast rice yogurt and its preparation method. Background Technology

[0002] Yogurt is a nutritious and palatable fermented dairy product made primarily from raw milk through lactic acid bacteria fermentation. Stirred yogurt, made using a process of "fermentation in large tanks followed by milk breaking and stirring," boasts advantages such as a smooth texture, convenient consumption, suitability for continuous industrial production, and ease of reconstitution, making it the mainstream category in the current yogurt market. Furthermore, to meet consumers' evolving demands for product diversification, nutritional value, and sensory experiences, the research and development of functional yogurts and specialty fermented dairy products has become a hot topic in the industry in recent years.

[0003] Red yeast rice, also known as red yeast rice, is made from rice (mainly indica rice) through fermentation with Monascus purpureus and other fungi. It typically has a purplish-red or red color. Furthermore, red yeast rice is currently the only natural food coloring produced using microbial fermentation, giving food a vibrant, reddish hue with excellent light and heat stability. It is widely used in fermented bean curd, meat products, beverages, and brewing. Studies have confirmed that red yeast rice is rich in various functional components, including lovastatin, red yeast pigment, γ-aminobutyric acid (GABA), and ergosterol.

[0004] Combining red yeast rice with yogurt has become a significant direction in the research and development of functional dairy products in recent years. By adding red yeast rice powder or extract to yogurt, the natural red pigment of red yeast rice can give the yogurt an appealing strawberry-like color, improving the product's sensory quality and allowing it to meet consumers' demands for natural and healthy foods without relying on artificial colorings. Furthermore, the unique lipid-lowering, blood pressure-lowering, and antioxidant active ingredients of red yeast rice can be introduced into the yogurt system, achieving a dual nutritional synergy of lactic acid bacteria fermentation and red yeast rice metabolites, significantly enhancing the health benefits of yogurt.

[0005] However, red yeast rice powder has the following drawbacks: 1) It inherently suffers from poor water solubility and strong particle aggregation, easily leading to uneven dispersion, particle sedimentation, and bottom clumping when directly added to milk systems; 2) In the acidic environment (pH 4.2-4.6) created during yogurt fermentation, the interaction between red yeast rice particles and casein micelles intensifies, further causing product stratification, water separation, and a rough texture, significantly reducing color uniformity, textural stability, and edible quality, thus limiting the industrial application of red yeast rice in fermented dairy products. Stirred red yeast rice yogurt prepared using conventional methods generally suffers from poor color and flavor consistency, severe whey separation, a gritty texture, and rapid quality degradation over shelf life, making industrialization and marketability difficult.

[0006] Therefore, there is an urgent need to develop a technology that can achieve uniform dispersion and stable suspension of red yeast rice in milk systems, with good taste, to meet the needs of industrial production of red yeast rice yogurt. Summary of the Invention

[0007] In view of the shortcomings of the prior art described above, the purpose of this invention is to provide a stirred red yeast rice yogurt and its preparation method to solve the problems in the prior art.

[0008] To achieve the above and other related objectives, a first aspect of the present invention provides a method for preparing stirred red yeast rice yogurt, comprising the following steps:

[0009] Red yeast rice powder, raw milk and sweetener are mixed, sheared, ultrasonically treated, inoculated with a starter culture, fermented and stirred to obtain the stirred red yeast rice yogurt;

[0010] The particle size of the red yeast rice powder is 13-30 μm.

[0011] Another aspect of the present invention provides stirred red yeast rice yogurt obtained by the preparation method described above.

[0012] As described above, the stirred red yeast rice yogurt and its preparation method of the present invention have the following beneficial effects:

[0013] Compared to regular yogurt without added red yeast rice, this invention adds natural functional components and a unique color of red yeast rice, increasing the product's added value. Compared to existing red yeast rice yogurt technology, it does not require the addition of stabilizers, the ingredients are more natural, and it solves the problems of uneven red yeast rice dispersion and a gritty texture. The product has a unique flavor, uniform color, and more stable quality, making it suitable for industrial production. Attached Figure Description

[0014] Figure 1 The image shown is a real photograph of the stirred red yeast rice yogurt prepared according to the present invention. Detailed Implementation

[0015] This invention provides a method for preparing stirred red yeast rice yogurt, comprising the following steps:

[0016] Red yeast rice powder, raw milk, and sweetener are mixed, sheared, ultrasonically treated, inoculated with a starter culture, fermented, and stirred to obtain the stirred red yeast rice yogurt; the particle size of the red yeast rice powder is 13-30 μm.

[0017] The process sequence of this invention is adjustable, but preferably, a processing sequence of shearing followed by ultrasonication is adopted because it can achieve better dispersion uniformity of red yeast rice pigment and improve the physical stability of the product during storage. Conversely, if an ultrasonication followed by shearing is adopted, there is a risk of secondary agglomeration of red yeast rice particles.

[0018] In this invention, red yeast rice powder refers to red yeast rice, a food additive made from rice fermented and cultured with Monascus purpureus, which is in the form of red granules (or powdered from granules). It conforms to the national standard GB 1886.19-2015 "Food Additives - Red Yeast Rice", and its moisture content is ≤10%.

[0019] In some embodiments, the particle size of the red yeast rice powder can also be 13μm, 15μm, 20μm, 22μm, 25μm, 26μm, 27μm, 28μm, 29μm, or 30μm, i.e., 500 mesh to 1000 mesh. The particle size of the red yeast rice powder of the present invention cannot be too low or too high; too low a particle size leads to poor dispersion stability, while too high a particle size leads to high cost.

[0020] In some embodiments, based on the mass of red yeast rice powder, raw milk, and sweetener, the amount of red yeast rice powder added is 0.02-0.08 wt%, the amount of sweetener added is 6-8 wt%, and the remainder is raw milk. The amount of red yeast rice powder added can also be 0.02 wt%, 0.03 wt%, 0.04 wt%, 0.05 wt%, 0.06 wt%, 0.07 wt%, or 0.08 wt%. The amount of sweetener added can be 6 wt%, 6.2 wt%, 6.5 wt%, 6.8 wt%, 7.0 wt%, 7.2 wt%, 7.4 wt%, 7.8 wt%, or 8.0 wt%. When the amount of red yeast rice powder added is less than 0.02 wt%, the yogurt has poor coloring, weak characteristic flavor, and a shortened shelf life; when the amount added is greater than 0.08 wt%, the product has a dull color, a bitter and rough taste, decreased system stability, and exceeds national standard limits, posing safety and regulatory risks.

[0021] In some embodiments, the raw milk can be any type of raw milk suitable for preparing yogurt in the art. For example, the raw milk can be selected from raw milk, such as one or more of raw cow's milk, raw sheep's milk, and camel's milk, or it can be reconstituted milk. The raw milk conforms to relevant standards such as GB 19301-2010 "National Food Safety Standard - Raw Milk", and the reconstituted milk can conform to relevant standards such as GB19644 "National Food Safety Standard for Milk Powder". The reconstituted milk is preferably whole milk powder. The source of the raw milk is preferably cow and / or sheep.

[0022] In some embodiments, the raw milk is raw cow's milk.

[0023] In some embodiments, the amount of raw milk added is 80–98.9 wt% based on the total mass of red yeast rice powder, raw milk, and sweetener. Preferably, the amount of raw milk added can be 80–83 wt%, 81–83.5 wt%, 82.5–84 wt%, 83.5–85.5 wt%, 85–88.6 wt%, 86.5–89.1 wt%, or 87.5–98.9 wt%, and in a certain preferred embodiment, it is 91.1 wt% or 93.2 wt%.

[0024] In some embodiments, the sweetener is a common sweetener in the art, including natural sweeteners or artificial sweeteners. The natural sweetener is selected from granulated sugar or sucrose. Granulated sugar is generally a variety of edible sugars suitable for preparing yogurt in the food industry. For example, it may meet the requirements of relevant standards such as GB / T 317-2018 granulated sugar. The artificial sweetener is selected from one or more of xylitol and erythritol.

[0025] In some embodiments, the sweetener is selected from sucrose. Sucrose is a preferred raw material in the art for the preparation of fermented milk due to its low overall cost, good performance, and easy availability, and it meets the requirements of relevant standards such as GB 13104—2014 National Food Safety Standard for Sugar.

[0026] In some embodiments, the method for mixing the raw milk, red yeast rice powder, and sweetener can be selected according to conventional methods in the art, and stirring is the preferred method of mixing in this invention. The stirring conditions can be selected according to conventional methods in the art, and the stirring time is preferably 10-20 minutes. The stirring temperature is preferably 50-60°C. The stirring speed is 400-1200 rpm.

[0027] In some embodiments, the shearing speed is 3000-5000 rpm, or it can be 3000 rpm, 3200 rpm, 3500 rpm, 3800 rpm, 4000 rpm, 4200 rpm, 4500 rpm, 4800 rpm, or 5000 rpm. In this invention, the shearing speed cannot be too high or too low. If the shearing speed is higher than 5000 rpm, on the one hand, it will cause excessive breakage of fat globules, causing fat to float to the surface; on the other hand, the violent agitation will introduce a large amount of air, resulting in severe foaming of the liquid. However, if the shearing speed is lower than 3000 rpm, insufficient shearing will result in poor dispersion stability of the red yeast rice powder. Unless otherwise specified, "rpm" in this invention refers to revolutions per minute.

[0028] In some embodiments, the shearing process takes 5-15 minutes, or it can take 3 minutes, 3.2 minutes, 3.5 minutes, 3.8 minutes, 4.0 minutes, 4.2 minutes, 4.5 minutes, 4.8 minutes, or 5 minutes.

[0029] In some embodiments, the power of the ultrasound is 100-300W, or can be 100W, 120W, 150W, 180W, 200W, 220W, 250W, 280W, or 300W. This invention, through ultrasonic treatment, relies on cavitation effect, microjets, and mechanical shearing to help solve the core problems in red yeast rice yogurt, such as uneven dispersion, coarse texture, and insufficient stability. The method of this invention only uses ultrasonic treatment at the raw material stage; subsequent stirring after conventional fermentation achieves a stirred-type red yeast rice yogurt preparation process with uniform red yeast rice dispersion, eliminating the need for additional stabilizers. It also overcomes the shortcomings of poor red yeast rice powder dispersibility in existing processes, simultaneously improving water retention, stability, viable cell count, and shelf life. This has significant theoretical and practical value for enriching the categories of Chinese functional fermented dairy products and promoting the high-value utilization of red yeast rice resources.

[0030] In some embodiments, the ultrasound time is 5-15 minutes, or it can be 5 minutes, 6 minutes, 7 minutes, 8 minutes, 9 minutes, 10 minutes, 11 minutes, 12 minutes, 14 minutes, or 15 minutes. In this invention, the ultrasound time cannot be too long or too short. If the ultrasound time is less than 5 minutes, the ultrasonic cavitation effect is insufficient, resulting in poor red yeast rice dispersion and decreased product stability and water-holding capacity. If the ultrasound time is more than 15 minutes, excessive ultrasonic cavitation causes excessive free fat and milk fat oxidation, leading to decreased water-holding capacity and flavor deterioration in yogurt.

[0031] In some embodiments, the frequency of the ultrasound is 20-40 kHz, or it can be 20 kHz, 25 kHz, 30 kHz, 35 kHz, or 40 kHz. In this invention, the frequency of the ultrasound cannot be too high or too low. If the frequency is below 20 kHz, the cavitation intensity is too high, which can easily cause severe damage to the fat globule membrane, leading to fat floating and deterioration of product color and stability. If the frequency is above 40 kHz, the cavitation mechanical effect is weak, failing to achieve the purpose of improving dispersion and emulsification stability.

[0032] In some embodiments, the starter culture is selected from one or more of the following: *Streptococcus salivarius* subsp. *thermophilus*, *Lactobacillus delbrueckii* subsp. *bulgaricus*, *Lactobacillus acidophilus*, *Lactobacillus plantarum*, *Lactobacillus casei*, *Lactobacillus rhamnosus*, *Lactococcus lactis* subsp. *lactophores*, and *Bifidobacterium animalis* subsp. *lactophores*. The bacterial concentration in the starter culture is (1.5-3) × 10⁻⁶. 11 CFU / g.

[0033] In some embodiments, the starter culture is a combination of *Streptococcus salivarius* subsp. *thermophilus* and *Lactobacillus delbrueckii* subsp. *bulgaricus*. The starter culture of this invention can be selected from Danisco YO-MIX 300 starter culture.

[0034] In some specific embodiments, the mass ratio of *Streptococcus salivarius* subsp. *thermophilus* and *Lactobacillus delbrueckii* subsp. *bulgaricus* is 1:(1-10). In this invention, the mass ratio is based on the weight of the lyophilized powder of each strain.

[0035] In some specific embodiments, the amount of the starter culture added is 0.002-0.008 wt% based on the total mass of red yeast rice powder, raw milk and sweetener, or it can be 0.002 wt%, 0.003 wt%, 0.004 wt%, 0.005 wt%, 0.006 wt% or 0.008 wt%.

[0036] In some embodiments, the fermentation temperature is 35-45°C, or 42-44°C, or 35°C, 38°C, 40°C, 42°C, or 45°C.

[0037] In some embodiments, the acidity at the fermentation endpoint is 70-120°T, or it can be 70°T, 80°T, 90°T, 100°T, 110°T, or 120°T. More preferably, it is 70-73°T, so that the product maintains a balanced sweet and sour taste.

[0038] In some embodiments, the fermentation time is a conventional time in the art, preferably 5-8 hours, more preferably 6-7 hours, and may also be 5 hours, 6 hours, 7 hours, or 8 hours.

[0039] In some embodiments, the stirring speed is 400-1200 rpm, preferably 400 rpm, 600 rpm, 800 rpm, 1000 rpm, or 1200 rpm.

[0040] In some embodiments, the stirring time is 10-30 min, preferably 10-20 min, but can also be 10 min, 15 min, 20 min, 25, or 30 min.

[0041] In some embodiments, the process after ultrasonic treatment and before inoculation with the fermenting agent further includes homogenization, sterilization, and cooling. Homogenization, sterilization, and cooling can be performed using methods and conditions conventional in the art.

[0042] In some embodiments, the homogenization pressure is 160-240 bar, or it can be 160 bar, 180 bar, 200 bar, 220 bar, or 240 bar.

[0043] In some embodiments, the homogenization temperature is 55-65°C, or it can be 55°C, 58°C, 60°C, 62°C, or 65°C.

[0044] In some embodiments, the sterilization temperature is 90-95°C, or it can be 90°C, 92°C, 93°C, or 95°C.

[0045] In some embodiments, the sterilization time is 5-10 minutes, or it can be 5 minutes, 6 minutes, 7 minutes, 8 minutes, 9 minutes, or 10 minutes.

[0046] In some embodiments of the present invention, the cooling method after sterilization is carried out in accordance with conventional methods in the art, and the cooling temperature is preferably 3-50°C, more preferably 42-44°C.

[0047] In another aspect, this invention also provides stirred red yeast rice yogurt prepared by the method described above. The stirred red yeast rice yogurt of this invention does not require the addition of stabilizers and shows no whey separation even after 21 days of storage.

[0048] In some implementations, the number of live lactic acid bacteria in stirred red yeast rice yogurt decreased by no more than 87% after 21 days compared to day 1.

[0049] In some embodiments, the placement conditions are 0-4°C, preferably 4°C.

[0050] In this invention, the decline rate refers to the difference between the number of viable lactic acid bacteria on day 21 and the number of viable lactic acid bacteria on day 1, divided by the number of viable lactic acid bacteria on day 1. The determination of the number of viable lactic acid bacteria is in accordance with GB 4789.35-2023 "Food Microbiology Examination: Lactic Acid Bacteria Examination". The sum of the total number of Lactobacillus spp. and the total number of Streptococcus thermophilus is the number of viable lactic acid bacteria in the stirred red yeast rice yogurt sample.

[0051] The stirred red yeast rice yogurt prepared by the method of this invention has the advantages of uniform color, delicate texture, and unique flavor. Furthermore, it maintains stable quality within a 21-day shelf life, without any separation or water precipitation. The stirred red yeast rice yogurt prepared by this invention not only avoids whey separation, but also shows a decrease in the number of viable lactic acid bacteria at 21 days compared to 1 day, with a decrease rate not exceeding 87%. This effectively solves the problems of uneven dispersion and particle sedimentation caused by the poor water solubility of red yeast rice powder, and also alleviates the significant decline in viable bacteria count during the shelf life of ordinary yogurt.

[0052] The preparation method of this invention improves product quality while significantly shortening fermentation time compared to conventional methods (without shearing or ultrasonic treatment), and significantly increases the number of viable lactic acid bacteria. Specifically, the preparation method of this invention can achieve the endpoint acidity of 70°T and a viable lactic acid bacteria count of 1×10⁻⁶ within 5 hours of fermentation.9 CFU / mL or higher; without adding red yeast rice powder, or only undergoing one of the following treatments: shearing or ultrasonication, or using a shearing rate exceeding the range, achieving the same endpoint acidity (70°T) requires at least 5.2 hours, and the viable lactic acid bacteria count is less than 1×10⁻⁶. 9 CFU / mL, less than one order of magnitude.

[0053] The preparation method of this invention improves product quality while significantly shortening fermentation time and increasing the number of viable lactic acid bacteria compared to conventional methods. The preparation method of this invention is simple in procedure, requires minimal equipment, and is easily scalable and standardized for production, showing promising prospects for industrial application.

[0054] The following specific examples illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and various details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention.

[0055] Before further describing specific embodiments of the present invention, it should be understood that the scope of protection of the present invention is not limited to the specific embodiments described below; it should also be understood that the terminology used in the embodiments of the present invention is for describing specific embodiments and not for limiting the scope of protection of the present invention; in the specification and claims of the present invention, unless otherwise expressly stated in the text, the singular forms "a", "an" and "this" include the plural forms.

[0056] When numerical ranges are given in the embodiments, it should be understood that, unless otherwise stated in the present invention, both endpoints of each numerical range and any value between the two endpoints may be selected. Unless otherwise defined, all technical and scientific terms used in this invention have the same meaning as commonly understood by one of ordinary skill in the art. In addition to the specific methods, apparatus, and materials used in the embodiments, based on the knowledge of the prior art possessed by one of ordinary skill in the art and the description of this invention, any prior art methods, apparatus, and materials similar to or equivalent to those described, apparatus, and materials in the embodiments of this invention may be used to implement the present invention.

[0057] Red yeast rice powder is made by selecting commercially available edible red yeast rice powder, which is purchased from Jiangsu Weipinhui Food Co., Ltd., with a moisture content of 7.2% and a particle size of 150μm (passing through a 100-mesh sieve); then pulverizing it and passing it through a 500-mesh sieve to make its particle size 25-30μm.

[0058] Modified starch and pectin were purchased from Danisco (China) Co., Ltd., and gelatin was purchased from Henan Boyang Biotechnology Co., Ltd.

[0059] The starter culture was purchased from Danisco (China) Co., Ltd., YO-MIX300.

[0060] Example 1: Stirred Red Yeast Rice Yogurt

[0061] This embodiment 1 provides a stirred red yeast rice yogurt and its preparation method, including the following steps:

[0062] 1) Add red yeast rice powder and sweetener to raw milk preheated to 50°C, stir at 400 rpm for 20 minutes until fully mixed to obtain liquid A.

[0063] Based on the total mass of red yeast rice powder, raw milk, and sweetener, the amount of red yeast rice powder added is 0.02 wt%, and the amount of sucrose added is 6 wt%. Specifically, taking a total mass of 100g as an example, the amount of red yeast rice powder added is 0.02g, the amount of sucrose added is 6g, and the amount of raw milk is 93.98g.

[0064] 2) The liquid A obtained in step 1) was sheared and ultrasonically treated in an IKA T25 digital ULTRA-TURRAX® high-speed disperser (IKA (Guangzhou) Instrument Equipment Co., Ltd.), then homogenized at 60℃ and 200 bar, then sterilized at 90℃ for 10 min, and cooled to 42℃ to obtain liquid B.

[0065] The shearing process was performed at a speed of 5000 rpm for 3 minutes; the ultrasonic process was performed at a frequency of 40 kHz, a power of 100 W, and a time of 5 minutes.

[0066] 3) Add the fermentation agent to the liquid B obtained in step 2) and ferment at a constant temperature of 45°C until it reaches 70°T to obtain liquid C.

[0067] The amount of starter culture added is 0.002 wt%, based on the total mass of red yeast rice powder, raw milk (raw milk) and sweetener.

[0068] 4) Stir the liquid C obtained in step 3) at 400 rpm for 20 min, cool it to 18℃ for bottling, and then refrigerate it at 4℃ for 12 h to obtain stirred red yeast rice yogurt.

[0069] Example 2: Stirred Red Yeast Rice Yogurt

[0070] This embodiment 2 provides a stirred red yeast rice yogurt and its preparation method, including the following steps:

[0071] 1) Add red yeast rice powder and sweetener to raw milk preheated to 55°C, stir at 800 rpm for 15 minutes until fully mixed to obtain liquid A.

[0072] Based on the total mass of red yeast rice powder, raw milk (raw milk) and sweetener, the amount of red yeast rice powder added is 0.05 wt%, and the amount of sucrose added is 7 wt%.

[0073] 2) The liquid A obtained in step 1) was sheared and ultrasonically treated in an IKA T25 digital ULTRA-TURRAX® high-speed disperser (same as above), then homogenized at 60°C and 200 bar, then sterilized at 90°C for 10 min, and cooled to 42°C to obtain liquid B.

[0074] The shearing process was performed at a speed of 4000 rpm for 4 minutes; the ultrasonic process was performed at a frequency of 30 kHz, a power of 200 W, and a time of 10 minutes.

[0075] 3) Add the fermentation agent to the liquid B obtained in step 2) and ferment at a constant temperature of 42°C until it reaches 70°T to obtain liquid C.

[0076] The amount of starter culture added is 0.005 wt%, based on the total mass of red yeast rice powder, raw milk (raw milk) and sweetener.

[0077] 4) Stir the liquid C obtained in step 3) at 600 rpm for 15 min, cool it to 21°C for bottling, and then refrigerate it at 4°C for 18 h to obtain stirred red yeast rice yogurt.

[0078] Example 3: Stirred Red Yeast Rice Yogurt

[0079] This embodiment 3 provides a stirred red yeast rice yogurt and its preparation method, including the following steps:

[0080] 1) Add red yeast rice powder and sweetener to raw milk preheated to 60°C, stir at 1200 rpm for 10 minutes until fully mixed to obtain liquid A.

[0081] Based on the total mass of red yeast rice powder, raw milk (raw milk) and sweetener, the amount of red yeast rice powder added is 0.08 wt%, and the amount of sucrose added is 8 wt%.

[0082] 2) The liquid A obtained in step 1) was sheared and ultrasonically treated in an IKA T25 digital ULTRA-TURRAX® high-speed disperser (same as above), then homogenized at 60°C and 200 bar, then sterilized at 90°C for 10 min, and cooled to 42°C to obtain liquid B.

[0083] The shearing process was performed at a speed of 3000 rpm for 5 minutes; the ultrasonic process was performed at a frequency of 20 kHz, a power of 300 W, and a time of 15 minutes.

[0084] 3) Add the fermentation agent to the liquid B obtained in step 2) and place it at a constant temperature of 37°C to ferment until it reaches 70°T.

[0085] The amount of starter culture added is 0.008 wt%, based on the total mass of red yeast rice powder, raw milk (raw milk) and sweetener.

[0086] 4) Stir the liquid C obtained in step 3) at 800 rpm for 10 min, cool it to 24℃ for bottling, and then refrigerate it at 4℃ for 24 h to obtain stirred red yeast rice yogurt.

[0087] Comparative Example 1

[0088] The difference from Example 1 is that no red yeast rice powder is added, but everything else is the same as in Example 1.

[0089] Comparative Example 2

[0090] The difference from Example 1 is that step 2) does not involve shearing or ultrasonic treatment, while the rest is the same as in Example 1.

[0091] Comparative Example 3

[0092] The difference from Example 1 is that in step 2), no shearing is performed, but ultrasonic treatment is performed; otherwise, the process is the same as in Example 1.

[0093] Comparative Example 4

[0094] The difference from Example 1 is that in step 2), shearing is performed, but ultrasonic treatment is not performed; otherwise, it is the same as Example 1.

[0095] Comparative Example 5

[0096] The difference from Example 1 is that the shearing speed is higher than 5000 rpm, specifically 6000 rpm, while the rest is the same as Example 1.

[0097] Comparative Example 6

[0098] The difference from Example 1 is that the shearing speed is lower than 3000 rpm, specifically 2000 rpm, while the rest is the same as Example 1.

[0099] Comparative Example 7

[0100] The difference from Example 1 is that the red yeast rice powder is added directly without sieving; in step 2), no shearing or ultrasonic treatment is performed, and the rest is the same as in Example 1.

[0101] The yogurt samples prepared using the methods of the above embodiments and comparative examples were tested, and the specific methods and results are as follows.

[0102] (1) Water-holding capacity test: Take an appropriate amount of yogurt sample, centrifuge at 3000 g for 15 min, record the mass of the centrifuge tube as m1, and the total mass of the yogurt sample and the centrifuge tube as m2. After centrifugation, remove the supernatant, and record the mass of the precipitate and the centrifuge tube as m3. Calculate the water-holding capacity of the yogurt sample according to the following formula: Water-holding capacity = (m3-m1) / (m2-m1)×100%. Yogurt water-holding capacity (WHC) is one of the important indicators for evaluating yogurt quality, reflecting the ability of the yogurt gel structure to fix water. The stronger the water-holding capacity, the less likely the yogurt is to separate into layers or separate into water, resulting in a more delicate and thicker texture, while also affecting its appearance and flavor stability.

[0103] (2) Determination of viable lactic acid bacteria: Refer to GB 4789.35-2023 "Microbiological Examination of Food - Lactic Acid Bacteria Examination", the sum of the total number of Lactobacillus spp. and the total number of Streptococcus thermophilus is the viable lactic acid bacteria count of the yogurt sample.

[0104] (3) Shelf life stability: The prepared yogurt samples were stored at 4℃ for 21 days, and the overall state of the yogurt and the whey separation were observed.

[0105] (4) Sensory evaluation: The sensory evaluation was conducted by 20 tasters who evaluated the yogurt samples prepared by the methods of each embodiment and comparative example. All tasters rinsed their mouths with purified water during the evaluation, and the final average score was taken. The evaluation criteria and scores are shown in Table 1.

[0106] Table 1

[0107]

[0108] The stirred red yeast rice yogurt obtained in Examples 1-3 was compared with the products of Comparative Examples 1-7. The results are shown in Table 2 below.

[0109] Table 2

[0110]

[0111] As shown in Table 1 above, the stirred red yeast rice yogurts of Examples 1, 2, and 3, which underwent high-speed dispersion and ultrasonic treatment, were superior to the comparative examples in terms of fermentation time, viable lactic acid bacteria count, water holding capacity, shelf-life stability, and sensory evaluation. The stirred red yeast rice yogurts of Examples 1-3 showed a decrease in viable lactic acid bacteria count of 83.8-86.3% at 21 days compared to 1 day, while the stirred red yeast rice yogurts of Comparative Examples 1-7 showed a decrease of over 91% at 21 days; particularly, Comparative Example 1, which did not contain red yeast rice powder, saw a decrease in viable bacteria count of almost two orders of magnitude at 21 days. Furthermore, the stirred red yeast rice yogurts of Examples 1, 2, and 3, which underwent shearing and ultrasonic treatment, showed superior fermentation time, viable lactic acid bacteria count, and water holding capacity compared to Comparative Example 1 (without red yeast rice powder). The high water holding capacity indicates that the addition of red yeast rice powder can improve the water holding capacity of the yogurt. The high number of live lactic acid bacteria in the milk enhances the flavor and functional properties of the product, while the dominant bacterial flora inhibits contamination by other bacteria, extending shelf life. Furthermore, the stirred red yeast rice yogurt of this invention does not exhibit whey separation during storage, even without the addition of stabilizers, whereas traditional stirred yogurt requires stabilizers to prevent whey separation during storage.

[0112] Compared to Example 1, the number of viable lactic acid bacteria in Comparative Example 1 without added red yeast rice powder decreased by 88.0% at 1 day, and the number of viable lactic acid bacteria at 21 days decreased by 98.3% compared to 1 day. In addition, the product had a bland color, weak aroma, and monotonous taste.

[0113] Compared to Example 1, Comparative Example 2, which did not undergo shearing and ultrasonic treatment, showed slight whey separation due to poor dispersion of red yeast rice powder; the number of viable lactic acid bacteria was low at 1 day (down 80.9% compared to Example 1), and at 21 days, the number of viable lactic acid bacteria was 96.3% lower than at 1 day; in addition, the color, flavor and taste of the finished product were significantly deteriorated, with a total score of only 70.4.

[0114] Compared to Example 1, Comparative Example 3, which only underwent ultrasonic treatment without shearing, suffered from poorer homogeneous dispersion of materials due to the omission of the shearing process. The number of viable lactic acid bacteria decreased by 39.4%, and the number of viable bacteria after 21 days was 95.1% lower than that after 1 day. Furthermore, the color, flavor, and texture of the finished product all deteriorated. Similarly, Comparative Example 4, which underwent shearing but not ultrasonic treatment, also suffered from poorer homogeneous dispersion of materials due to the omission of the ultrasonic process. The number of viable lactic acid bacteria decreased by 48.9%, and the number of viable bacteria after 21 days was 91.9% lower than that after 1 day. Furthermore, the color, flavor, and texture of the finished product all deteriorated.

[0115] Compared to the examples, Comparative Example 5, where the shearing speed exceeded 5000 rpm, resulted in excessive breakage of fat globules, causing fat to float to the surface. Furthermore, the vigorous agitation introduced a large amount of air, leading to severe foaming of the liquid. Simultaneously, the number of viable lactic acid bacteria decreased by 83.1%, and the number of viable bacteria after 21 days decreased by 92.4% compared to 1 day. In contrast, Comparative Example 6, where the shearing speed was less than 3000 rpm, exhibited poor red yeast rice dispersion stability due to insufficient shearing, resulting in whey precipitation. Simultaneously, the number of viable bacteria decreased by 88.4% compared to Example 1, and the number of viable bacteria after 21 days decreased by 91.5% compared to 1 day.

[0116] Comparative Example 7, which uses red yeast rice powder that is not sieved, sheared, or ultrasonically treated, compared to Example 1, has a lower number of viable lactic acid bacteria and a dull, uneven color in the finished product due to the coarse and uneven dispersion of the raw red yeast rice powder. Figure 1 The flavor and texture quality deteriorated significantly; at the same time, the number of live bacteria decreased by 56.9%, and the number of live bacteria at 21 days was 98.6% lower than that at 1 day.

[0117] In terms of sensory characteristics, the stirred red yeast rice yogurt produced by this invention is superior to other red yeast rice yogurts in terms of color, aroma, taste and texture. At the same time, compared with ordinary yogurt without added red yeast rice, this invention introduces red yeast rice into the fermentation system to achieve the dual nutritional superposition of lactic acid bacteria fermentation and red yeast rice, thereby enhancing the health value of the yogurt.

[0118] Figure 1 A represents Experimental Example 1, while B, C, D, and E are actual photographs of Comparative Examples 1, 3, 5, and 7, respectively. All samples were fermented in 250mL blue-capped reagent bottles. During the photography, the samples were placed in a small soft-light photography studio with matte white inner walls and photographed using a mobile phone camera. The images only capture the bottom and part of the side area of ​​the reagent bottle, clearly showing the appearance of the different samples.

[0119] from Figure 1 It can be seen that the stirred red yeast rice yogurt obtained in Example 1 has a uniform color; the stirred red yeast rice yogurt obtained in Comparative Example 3, which only undergoes ultrasonic treatment without shearing, has some obvious red yeast rice powder particles in the product; the product of Comparative Example 5, which undergoes excessive shearing, has a lighter overall color, which may be due to the degradation of red yeast rice pigment; the red yeast rice powder in Comparative Example 7, which does not undergo sieving, shearing, or ultrasonic treatment, has red yeast rice sediment at the bottom and obvious red yeast rice powder particles in the system.

[0120] In summary, this invention employs high-speed dispersion combined with ultrasonic pretreatment, which can shorten the fermentation cycle and increase the viable count of lactic acid bacteria. Shearing and ultrasonic cavitation ensure uniform dispersion of red yeast rice powder, promoting the homogeneous binding of milk proteins and milk fats. This process improves the sensory properties of stirred red yeast rice yogurt, enhances gel water-holding capacity, reduces pigment degradation, and improves product stability and batch uniformity.

[0121] The above embodiments are for illustrating the implementation schemes disclosed in this invention and should not be construed as limiting the invention. Furthermore, various modifications and variations of the methods listed herein will be apparent to those skilled in the art without departing from the scope and spirit of the invention. Although the invention has been specifically described in conjunction with various specific preferred embodiments, it should be understood that the invention should not be limited to these specific embodiments. In fact, various modifications as described above that are obvious to those skilled in the art to obtain the invention should be included within the scope of this invention.

Claims

1. A method for preparing stirred red yeast rice yogurt, characterized in that, Includes the following steps: Red yeast rice powder, raw milk and sweetener are mixed, sheared, ultrasonically treated, inoculated with a starter culture, fermented and stirred to obtain the stirred red yeast rice yogurt; The particle size of the red yeast rice powder is 13-30 μm.

2. The preparation method according to claim 1, characterized in that, The raw milk is selected from one or more of raw cow's milk, raw sheep's milk, and camel's milk; And / or, the sweetener is selected from one or more of sucrose, xylitol, fructose syrup and erythritol; And / or, the fermenting agent is selected from one or more of the following: *Streptococcus salivarius* subsp. *thermophilus*, *Lactobacillus delbrueckii* subsp. *bulgaricus*, *Lactobacillus acidophilus*, *Lactobacillus plantarum*, *Lactobacillus casei*, *Lactobacillus rhamnosus*, *Lactococcus lactis* subsp. *lactophores*, and *Bifidobacterium animalis* subsp. *lactophores*.

3. The preparation method according to claim 1, characterized in that, Based on the total mass of red yeast rice powder, raw milk and sweetener, the amount of red yeast rice powder added is 0.02-0.08 wt%, the amount of sweetener added is 6-8 wt%, and the remainder is raw milk; And / or, based on the total mass of red yeast rice powder, raw milk and sweetener, the amount of the starter culture added is 0.002-0.008 wt%.

4. The preparation method according to claim 2, characterized in that, The starter culture is selected from one or both of Streptococcus salivarius subsp. thermophilus and Lactobacillus delbrueckii subsp. bulgaricus.

5. The preparation method according to claim 4, characterized in that, The mass ratio of *Streptococcus salivarius* subsp. *thermophilus* and *Lactobacillus delbrueckii* subsp. *bulgaricus* is 1:(1-10).

6. The preparation method according to claim 1, characterized in that, The rotational speed of the shearing process is 3000-5000 rpm; And / or, the shearing process takes 3-5 minutes.

7. The preparation method according to claim 1, characterized in that, The frequency of the ultrasonic treatment is 20-40kHz; And / or, the duration of the ultrasonic treatment is 5-15 minutes; And / or, the power of the ultrasonic treatment is 100-300 W; And / or, the process after ultrasonic treatment and before inoculation with the fermenting agent further includes homogenization, sterilization, and cooling.

8. The preparation method according to claim 7, characterized in that, The pressure of the homogenized material is 160-240 bar; And / or, the homogenization temperature is 55-65°C; And / or, the sterilization temperature is 90-95℃; And / or, the sterilization time is 5-10 min.

9. The preparation method according to claim 1, characterized in that, The fermentation temperature is 35℃-45℃; And / or, the acidity at the fermentation endpoint is 70-120°T; And / or, the stirring speed is 400-1200 rpm; And / or, the stirring time is 10-30 min; And / or, the mixing temperature is 50-60°C; And / or, the mixing time is 10-20 min; And / or, the mixing method is stirring, and the stirring speed is 400-1200 rpm.

10. The stirred red yeast rice yogurt obtained by the preparation method according to any one of claims 1-9.

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