High-activity matcha yogurt and low-temperature microwave preparation method thereof

Abstract

The present application relates to a kind of high activity Matcha yoghurt and its low-temperature microwave preparation method, belong to food processing technical field.The present application uses organic raw cow milk, Matcha powder, white granulated sugar, corn starch etc.as raw material, using the combination process of adding Matcha before fermentation, low-temperature pre-solution dispersion, microwave low-temperature sterilization, replace traditional high-temperature mixing and high-temperature sterilization, solve the existing Matcha yoghurt chlorophyll browning, tea polyphenol degradation, tea aroma loss, water retention decreases, lactic acid bacteria activity low etc.Problems.The optimal formula of the present application: Matcha powder 10g / 1000mL milk;Using 60~65 ℃ low-temperature dissolution avoids powder agglomeration;Using 40~60 ℃ microwave low-temperature sterilization maximizes to retain heat-sensitive ingredients;Add before fermentation to promote lactic acid bacteria proliferation.The yoghurt prepared has uniform green color, rich tea aroma, delicate and smooth taste, high tea polyphenol retention rate, lactic acid bacteria viable count can reach 8.85×10 8 CFU / mL, water retention ≥80%, sensory score ≥90 points.The process of the present application is simple, and can be industrialized production, suitable for high-quality functional Matcha yoghurt development.

Description

Technical Field

[0001] This invention relates to the field of food processing technology, specifically to a highly active matcha yogurt and its low-temperature microwave preparation method. Background Technology

[0002] Matcha is a type of green tea made from fresh tea leaves through a process of shade cultivation, steaming to kill the green, and ultra-fine grinding. Its nutrients are readily absorbed by the body, giving it a unique advantage over regular green tea. The quality of matcha is closely related to its processing techniques. Shading before harvesting promotes chlorophyll synthesis and reduces the breakdown of theanine, resulting in a vibrant green color and a mellow flavor. Rich in polyphenols, chlorophyll, dietary fiber, and other active ingredients, matcha offers significant nutritional and health benefits.

[0003] Tea polyphenols are the core active ingredients of matcha, accounting for 8% to 15% of its dry weight. Among them, catechins are particularly abundant, exhibiting outstanding antioxidant capabilities, which can scavenge free radicals in the body and reduce oxidative stress damage. Chlorophyll, as the main source of matcha's color, possesses strong antioxidant and anti-inflammatory activities. Dietary fiber can regulate the balance of the intestinal microecology. In recent years, "natural, healthy, and functional" have become the mainstream of food consumption, and matcha has been widely used in baking, beverages, dairy products, and other fields. Its combination with dairy products has become a research hotspot.

[0004] Yogurt, a popular fermented dairy product, is rich in high-quality protein and active lactic acid bacteria, which can regulate intestinal flora, enhance immunity, and provide both nutritional and health benefits. Combining matcha with yogurt can achieve nutritional complementarity and flavor enhancement, aligning with modern food industry development trends. However, most commercially available matcha yogurts currently use physical mixing methods, resulting in poor flavor integration and failing to fully utilize matcha's potential to promote lactic acid bacteria growth. More importantly, heat-sensitive components in matcha, such as chlorophyll and catechins, are easily degraded at high temperatures, leading to color deterioration and reduced nutritional value. Furthermore, the high-temperature steps in traditional yogurt processing severely damage the quality of matcha. Therefore, this study aims to explore the optimal role of matcha in yogurt fermentation, compare the product differences between the two processes, optimize processing parameters, and provide scientific basis and practical guidance for the production of high-quality matcha fermented yogurt.

[0005] However, existing matcha yogurt production processes generally have the following drawbacks: Traditional high-temperature sterilization (90-95℃) severely damages the heat-sensitive components of matcha, leading to chlorophyll browning, significant loss of tea polyphenols, and complete loss of tea aroma. Adding matcha directly to hot-temperature milk easily results in clumping, a grainy texture, and uneven distribution, affecting taste and texture. Furthermore, improper matcha addition methods exist: adding it after fermentation leads to poor flavor integration and fails to promote lactic acid bacteria growth; adding it before fermentation reduces water retention and increases whey separation. There is a lack of a clearly defined optimal addition amount; excessive addition results in a rough texture, dark color, and deteriorated quality. Existing processes cannot simultaneously balance color, aroma, active ingredients, lactic acid bacteria count, and textural stability. Therefore, developing a new matcha yogurt process that can protect the color and activity of matcha, improve the texture and sensory qualities of yogurt, and is suitable for industrial production has significant practical value and market potential. Summary of the Invention

[0006] The purpose of this invention is to solve the above-mentioned problems by providing a highly active matcha yogurt and its low-temperature microwave preparation method. It is a fermented dairy product, specifically a highly active matcha yogurt with high color stability and high tea aroma retention, and its low-temperature microwave preparation method. Through a combination of low-temperature pre-dissolving and dispersion, microwave low-temperature sterilization, and precise addition before fermentation, the matcha yogurt achieves a bright green color, rich tea aroma, delicate texture, high retention of active ingredients, and high activity of lactic acid bacteria.

[0007] The objective of this invention is achieved through the following technical solution: The first objective of this invention is to provide a low-temperature microwave preparation method for highly active matcha yogurt, comprising the following steps: (1) Raw material preparation: The raw materials include organic raw milk, white sugar, corn starch, and matcha powder; (2) Low temperature pre-dissolving: Preheat organic raw milk to 60~65℃ to obtain preheated milk. Take a portion of the preheated milk and stir matcha powder into a paste without granules. Then mix it evenly with the remaining preheated milk, white sugar and corn starch to obtain a mixture. (3) Microwave low-temperature sterilization: The mixture is sterilized by microwave at 40~60℃ to obtain microwave low-temperature sterilized mixture, which replaces the traditional high-temperature sterilization at 90~95℃; (4) Inoculation and fermentation: Cool the microwave-sterilized mixture to 42°C, inoculate with yogurt starter, and ferment at 42°C for 6 hours to obtain the fermented mixture; (5) Cold-cold ripening: The fermented mixture is cold-cold at 2~6℃ for more than 12 hours to obtain highly active matcha yogurt.

[0008] Furthermore, the optimal amount of matcha powder added is 1.0% (w / v) of the volume of organic raw milk, as determined by experiments. Exceeding this ratio will significantly reduce the water-holding capacity of the yogurt and lead to a decline in sensory quality.

[0009] Furthermore, the raw materials contain, based on 1000mL of organic raw milk, 65-75g of white sugar, 10-14g of corn starch, and 8-12g of matcha powder.

[0010] More preferably, the raw materials include, based on 1000mL of organic raw milk, 70g of white sugar, 12g of corn starch, and 10g of matcha powder.

[0011] Furthermore, in step (2), the matcha powder is first made into a paste and then mixed to avoid powder clumping, graininess, and layering.

[0012] Furthermore, the microwave low-temperature sterilization in step (3) strictly controls the temperature to ≤60℃ to prevent browning of tea chlorophyll and oxidation and degradation of tea polyphenols.

[0013] Further, in step (3), the conditions for microwave low-temperature sterilization are: microwave frequency 2450MHz, power density 0.65-0.75kW / L, peak temperature throughout the process ≤60℃, heating stage: single pulse heating for 10s, heating stopped, intermittent for 15s, cycle until the center temperature reaches 55℃; heat preservation stage: single pulse heating for 5s, heating stopped, intermittent for 15s, cycle 8-10 times.

[0014] Furthermore, adding matcha before fermentation can promote the growth of lactic acid bacteria, resulting in a significantly higher number of live bacteria compared to the group that added matcha after fermentation.

[0015] Furthermore, the yogurt starter is a direct-inoculation yogurt starter powder, which contains skim milk powder, as well as YO-MIX300, YO-MIX885-B and YO32.22 strains, which are used in combination.

[0016] Furthermore, an appropriate amount of the yogurt starter (yogurt starter direct-injection powder) is added, specifically 3g per 1000mL of organic raw milk.

[0017] Furthermore, corn starch acts as a stabilizer, improving water retention.

[0018] The second objective of this invention is to provide a highly active matcha yogurt prepared using the method described above.

[0019] Furthermore, the pH of the highly active matcha yogurt is 4.40~4.45.

[0020] Furthermore, the water-holding capacity of the highly active matcha yogurt is ≥80%.

[0021] Furthermore, the viable count of lactic acid bacteria in the highly active matcha yogurt is ≥8.5×10⁻⁶. 8 CFU / mL.

[0022] Furthermore, the highly active matcha yogurt has a uniform bright green color and no browning.

[0023] Furthermore, the highly active matcha yogurt has a rich tea aroma and a delicate, smooth texture.

[0024] Furthermore, the highly active matcha yogurt exhibits no significant whey separation, a delicate and uniform texture, and no grainy or astringent feel, with a total sensory score of ≥90 points.

[0025] Using the above methods, the low-temperature process protects chlorophyll, resulting in a bright green product without browning, and the highly active matcha yogurt prepared with a rich and refreshing tea aroma exhibits improved color and flavor; the loss of tea polyphenols is significantly reduced, resulting in higher nutritional value and high retention of active ingredients; the addition of matcha before fermentation promotes its proliferation, achieving a viable bacteria count of up to 8.85 × 10⁻⁶. 8 CFU / mL, higher lactic acid bacteria activity; water holding capacity ≥80%, no large amount of whey separation, delicate and smooth taste, no grainy or astringent feeling, stable texture; simple process that can be industrialized, no need for complicated equipment, suitable for large-scale production.

[0026] Compared with the prior art, the beneficial effects of the present invention are reflected in the following aspects: 1) This invention provides a high-activity matcha yogurt and its low-temperature microwave preparation method. It uses organic raw milk, matcha powder, white sugar and corn starch as raw materials. It adopts a combination process of adding matcha before fermentation, low-temperature pre-dissolving and dispersion and microwave low-temperature sterilization to replace the traditional high-temperature mixing and high-temperature sterilization. This solves the problems of chlorophyll browning, tea polyphenol degradation, loss of tea aroma, decreased water retention and low lactic acid bacteria activity in existing matcha yogurt.

[0027] 2) This invention provides a highly active matcha yogurt and its low-temperature microwave preparation method, and the optimal formula is obtained by optimization: 10g matcha powder / 1000mL milk; low temperature dissolution at 60~65℃ to avoid powder clumping; low temperature sterilization at 40~60℃ to maximize the preservation of heat-sensitive components; adding before fermentation can significantly promote the proliferation of lactic acid bacteria.

[0028] 3) This invention provides a highly active matcha yogurt and its low-temperature microwave preparation method. The resulting yogurt has a uniform bright green color, a rich tea aroma, a delicate and smooth texture, a high tea polyphenol retention rate, and a lactic acid bacteria viable count of up to 8.85 × 10⁻⁶. 8 CFU / mL, water holding capacity ≥80%, sensory score ≥90 points.

[0029] 4) This invention provides a highly active matcha yogurt and its low-temperature microwave preparation method. The process of this invention is simple, can be industrialized, and is suitable for the development of high-quality functional matcha yogurt. Attached Figure Description

[0030] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0031] Figure 1 The effects of matcha addition method on the physicochemical properties of yogurt were investigated, including (a) pH value, (b) water-holding capacity, (c) lactic acid bacteria count, and (d) tea polyphenol content.

[0032] Figure 2 The effect of adding matcha powder before and after fermentation on the sensory evaluation of yogurt.

[0033] Figure 3 The pH value of yogurt produced by different processes changes with fermentation time.

[0034] Figure 4 The physicochemical indicators of matcha yogurt produced by different processes are: (a) water-holding capacity, (b) lactic acid bacteria count, and (c) tea polyphenols.

[0035] Figure 5 Sensory evaluation of matcha yogurt made using different processes.

[0036] Figure 6 The images show the actual appearance of each group of matcha yogurt samples. Detailed Implementation

[0037] The present invention will now be described in detail with reference to specific embodiments, but this is by no means a limitation thereof. Any preparation methods, materials, structures, or compositional ratios not explicitly described in this technical solution are considered common technical features disclosed in the prior art.

[0038] Unless otherwise specified, the experimental methods described in the following examples and test cases are conventional methods; unless otherwise specified, the reagents and materials are commercially available.

[0039] In the embodiments of the present invention, the matcha was provided by Hangzhou Mingbao Biotechnology Co., Ltd.; the organic raw milk was purchased from the East China Center of Bright Dairy Co., Ltd.; the yogurt starter was specifically a yogurt fermentation direct-inoculation powder (including skim milk powder, YO-MIX 300 strain, YO-MIX885-B strain, and YO32.22 strain), purchased from Beijing Chuanxiu Technology Co., Ltd., model number 100107503900; Yutang white granulated sugar was purchased from Shanghai Sugar, Tobacco & Alcohol (Group) Co., Ltd.; and Zhanyi organic corn starch was purchased from Shanghai Fengwei Industrial Co., Ltd.

[0040] In the embodiments of the present invention, the constant temperature incubator (model: DH-300AB) is from Shanghai Yiheng Scientific Instruments Co., Ltd.; the high-speed refrigerated centrifuge (model: 5427R) is from Eppendorf GmbH, Germany; the pH meter (model: Leici PHS-3C) is from Shanghai Instrument & Electronics Scientific Instruments Co., Ltd.; the electronic balance (model: FA2004B) is from Shanghai Youke Instruments Co., Ltd.; and the ultraviolet-visible spectrophotometer (model: UV-2550) is from Shimadzu Corporation, Japan.

[0041] Example 1 This embodiment includes the following steps: Phase 1: Under a fixed basic formula, design a gradient of matcha powder addition amount, and compare the quality of yogurt with matcha added before fermentation (Group A) and matcha added after fermentation (Group B) to clarify the impact of whether matcha participates in fermentation on the product.

[0042] The second stage: In response to the core issues of damaged matcha color and loss of heat-sensitive components in experimental group A, a low-temperature treatment research method was used to design and improve process group C (i.e., the low-temperature microwave preparation method of high-activity matcha yogurt of the present invention), optimize the temperature control and sterilization method in the matcha addition process, and compare the results at the optimal amount of matcha powder added.

[0043] Basic formula (per 1000mL of milk): 70g granulated sugar, 12g cornstarch. Formula design basis: The amount of granulated sugar added is based on the sweetness of commercially available flavored yogurts; cornstarch is used as a stabilizer to improve the texture of the yogurt and prevent whey separation, and its addition amount also refers to GB 2760-2014; the amount of matcha powder added was determined through preliminary experiments, with groups A and B designed with gradients of 5g, 10g, and 15g, and the amount of matcha powder added in group C determined to be 10g based on the experimental results of groups A and B, to ensure moderate flavor and color. See Table 1 for the specific formula.

[0044] Table 1 Matcha Yogurt Recipe Group A (added before fermentation - traditional process): Matcha powder is added during yogurt fermentation, and traditional mixing and sterilization processes are used. Specifically, the steps include: 1) Preheating: Organic raw milk is preheated to 80℃.

[0045] 2) Mixing: Weigh out all ingredients (white sugar, matcha powder, corn starch) according to the set formula, and dissolve the ingredients in preheated organic raw milk.

[0046] 3) Homogenization and sterilization: The mixture is stirred evenly in a mixer at 80℃ and sterilized at 90℃ for 5 minutes.

[0047] 4) Inoculation and fermentation: When the temperature of the mixture drops to 42℃, add 3g of yogurt starter, stir well, pour the mixture into a sterilized glass bottle, seal it and put it in a constant temperature incubator, set the temperature to 42℃ for fermentation, and ferment for 6 hours.

[0048] 5) Post-fermentation maturation: After fermentation, the yogurt is post-fermented at a refrigeration temperature of 4℃ for more than 12 hours to obtain the finished matcha yogurt product.

[0049] Group B (added after fermentation - traditional process): Organic raw milk is fermented into plain yogurt using traditional methods, and then, under aseptic conditions, an equal amount of matcha powder as in Group A is added and stirred until well combined. The specific steps include: 1) Preheating: Organic raw milk is preheated to 80℃.

[0050] 2) Mixing: Weigh out all the ingredients (white sugar, corn starch) according to the set formula, and dissolve the ingredients in preheated organic raw milk.

[0051] 3) Homogenization and sterilization: The mixture is stirred evenly in a mixer at 80℃ and sterilized at 90℃ for 5 minutes.

[0052] 4) Inoculation and fermentation: When the temperature of the mixture drops to 42℃, add the yogurt starter, stir well, pour the mixture into a sterilized glass bottle, seal it and put it in a constant temperature incubator, set the temperature to 42℃ for fermentation, and ferment for 6 hours.

[0053] 5) Post-fermentation: Immediately after fermentation, add matcha powder and stir. After fermentation at a refrigerated temperature of 4℃ for more than 12 hours, the matcha yogurt product is obtained.

[0054] Matcha powder's color and aroma are significantly damaged at temperatures above 80℃, and its solubility is also noticeably affected by temperature. The original experimental procedure involved mixing matcha powder with organic raw milk at 80-85℃ and then sterilizing the mixture at 90℃. This method suffers from the drawback of high temperatures reducing the matcha's color and flavor. The impact of organic raw milk temperature on the uniformity of matcha powder mixing and the changes in matcha color and flavor under high-temperature conditions should be considered. Without altering the original formula, the operational process was improved by lowering the preheating temperature to 60-65℃. The mixing method was modified by dissolving the matcha in 20mL of preheated organic raw milk until a smooth paste was formed, then adding the remaining organic raw milk and other ingredients, and stirring thoroughly. Microwave sterilization at a strictly controlled temperature of 40-60℃ was used instead of high-temperature sterilization.

[0055] Group C (Pre-fermentation addition - improved process): At the optimal matcha powder content (10g) determined experimentally, a new fermentation process was used, which is the low-temperature microwave preparation method for the high-activity matcha yogurt of this invention. Specifically, it includes the following steps: (1) Raw material preparation: 70g white sugar, 12g corn starch, and 10g matcha powder per 1000mL organic raw milk; (2) Low temperature pre-dissolving: Preheat organic raw milk to 60°C to obtain preheated milk. Take a portion of the preheated milk and stir matcha powder into a paste without granules. Then mix it evenly with the remaining preheated milk, white sugar, and corn starch to obtain a mixture. (3) Microwave low-temperature sterilization: The mixture is sterilized by microwave at 55℃ to obtain microwave low-temperature sterilized mixture. The microwave frequency is 2450MHz, the power density is 0.7kW / L, and the peak temperature of the whole process is ≤60℃. Heating stage: single pulse heating for 10s, heating is stopped, intermittent for 15s, and the cycle is repeated until the center temperature reaches 55℃; heat preservation stage: single pulse heating for 5s, heating is stopped, intermittent for 15s, and the cycle is repeated 10 times. (4) Inoculation and fermentation: Adjust the temperature of the microwave-sterilized mixture to 42°C, inoculate with yogurt starter, and ferment at a constant temperature of 42°C for 6 hours to obtain the fermented mixture; (5) Cold-cold ripening: The fermented mixture is cold-cold at 4℃ for more than 12 hours to obtain highly active matcha yogurt.

[0056] Figure 6 The images show the physical appearance of each group of matcha yogurt samples. Sensory evaluation was conducted based on the prepared matcha yogurt, specifically including the following process: Ten individuals with experience in food sensory evaluation were selected to assess the matcha yogurt based on its color, flavor, texture, and mouthfeel. Each aspect was scored according to a specified scoring standard, with a total score of 100 points. The average score was calculated. The product complies with the relevant provisions of GB19302-2010 "National Food Safety Standard for Fermented Milk". The scoring standard for the matcha yogurt is shown in Table 2.

[0057] Table 2 Sensory Evaluation Criteria for Matcha Yogurt The physicochemical properties of the prepared matcha yogurt were determined, and the specific methods for determining these properties included the following procedures: 1) pH Measurement: Before the experiment, preheat the pH meter in a constant temperature environment of 15℃ for 30 minutes. Perform two-point calibration of the pH meter using standard buffer solutions with pH=4.00 and pH=6.86 respectively. Once calibrated, it is ready for use. Take 50mL of a uniform matcha yogurt sample and place it in a clean beaker. Gently stir to ensure the sample is homogeneous and avoid generating air bubbles that could affect the measurement results. Slowly insert the composite electrode of the pH meter into the sample, ensuring the electrode is completely submerged and does not touch the bottom of the beaker. After the display reading stabilizes (fluctuation range ≤0.02pH), record the current pH value. Each sample is measured in triplicate, and the average of the three measurements is taken as the final pH value of the sample. pH changes are used to assess the fermentation degree, acidity stability, and shelf-life potential of the yogurt. Generally, the pH range of high-quality fermented yogurt is 4.0~4.5. A pH value that is too high indicates insufficient fermentation, while a pH value that is too low may lead to an overly sour taste and decreased stability.

[0058] 2) Water-holding capacity determination: Water-holding capacity is an important physicochemical indicator for evaluating the texture, stability, and sensory quality of yogurt, directly affecting the product's taste, shelf life, and market acceptance. Before the experiment, centrifuge tubes (specification: 50mL) were washed, dried to constant weight, and their mass (m0) was accurately weighed and recorded. 15-20g (accurate to 0.01g) of uniformly fermented matcha yogurt sample was slowly added to the weighed centrifuge tube, and the total mass of the sample was accurately recorded (m1). The centrifuge tube containing the sample was placed in a high-speed refrigerated centrifuge, and the centrifugation conditions were set to 4℃, 10000r / min, and 30min. During centrifugation, the centrifuge tubes were ensured to be placed symmetrically to avoid centrifugal imbalance. After centrifugation, the centrifuge tubes were removed, the supernatant was gently poured off, and the centrifuge tubes were inverted and placed on clean filter paper. The tubes were allowed to stand for 10min to thoroughly drain any remaining supernatant, and then the total mass (m2) of the centrifuge tubes and precipitate was accurately weighed. The water-holding capacity of the yogurt was calculated using the following formula: Yogurt water holding capacity (%) = (m2 - m0) / (m1 - m0) × 100% All weighing operations were accurate to two decimal places. The experiment was conducted in parallel three times. If the relative error of the three measurements was no greater than 5%, the experimental data was deemed qualified. The average of the three results was taken as the final water-holding capacity data of the sample.

[0059] 3) Determination of viable lactic acid bacteria count: Lactic acid bacteria are the core functional component of yogurt, and their viable count directly determines the health benefits and product quality of yogurt. The count was determined according to the national standard GB4789.35-2016 "National Food Safety Standard for Microbiological Examination of Food - Lactic Acid Bacteria Examination". The sample dilution procedure was also optimized based on the characteristics of matcha yogurt. Before the experiment, the sterile operating table, petri dishes, pipettes, and other experimental equipment were autoclaved (121℃, 101kPa, sterilization for 20 min) and cooled to room temperature. 10g of uniform matcha yogurt sample was placed in an Erlenmeyer flask containing 90mL of sterile physiological saline (0.85% NaCl) and thoroughly stirred with a sterile glass rod to prepare a 1:10 sample dilution. Then, a serial dilution method was used to dilute the sample to 1:10. -6 10 -7 10 -8 Three dilution gradients were used, with three replicates for each gradient. Using a sterile pipette, 1 mL of each dilution gradient was injected into a sterile petri dish. MRS medium (pre-sterilized) cooled to 45–50°C was quickly added, and the dish was gently rotated to ensure thorough mixing. After the medium solidified, the dishes were inverted and placed in an incubator at 37°C for 48 hours of anaerobic incubation. After incubation, petri dishes with colony counts between 30 and 300 CFU / mL were selected, and a colony counter was used to count the number of lactic acid bacteria colonies in each dish. The total colony count for each dilution gradient was calculated, and the viable lactic acid bacteria count per gram of matcha yogurt sample was determined. Each sample was tested three times, and the average value was used as the final result.

[0060] 4) Determination of Tea Polyphenol Content: Tea polyphenols are the core active ingredients of matcha, and their content directly reflects the nutritional value and antioxidant capacity of matcha yogurt. Referring to GB / T8313-2018 "Determination Method of Tea Polyphenol and Catechin Content in Tea", and considering the special characteristics of the yogurt matrix, the sample pretreatment method was optimized to ensure accurate and reliable results. Before the experiment, all experimental instruments were washed and dried with distilled water to avoid interference from impurities. 5.00 g of uniform matcha yogurt sample was accurately weighed and placed in a 50 mL centrifuge tube. 20 mL of 70% methanol solution was added, and the mixture was vortexed to ensure full contact between the sample and the extractant. The centrifuge tube was then placed in a constant temperature water bath at 70℃ for 10 minutes, gently shaking the tube every 2 minutes to ensure complete extraction of tea polyphenols. After leaching, remove the centrifuge tubes and allow them to cool to room temperature. Then, place them in a high-speed centrifuge and centrifuge at 3500 rpm for 10 minutes. After centrifugation, use a pipette to aspirate the supernatant and transfer it to a 10 mL volumetric flask. Wash the inner wall of the centrifuge tubes 2-3 times with a small amount of 70% methanol solution. Transfer the washing solution to the volumetric flask and dilute to the mark with 70% methanol solution. Shake well and filter through a 0.45 μm organic filter membrane to remove impurities and macromolecules from the sample, obtaining a clear test solution. The test solution was placed in a UV-Vis spectrophotometer with a wavelength of 765 nm. A 70% methanol solution was used as a blank control. The absorbance of the test solution was measured. The concentration of tea polyphenols in the test solution was calculated according to the tea polyphenol standard curve (y=ax+b, where y is absorbance and x is tea polyphenol concentration). The content of tea polyphenols per gram of matcha yogurt sample (mg / g) was then calculated. The experiment was performed in parallel for 3 times, and the average value was taken as the final result.

[0061] A comparison was made between adding matcha powder after fermentation and adding matcha powder before fermentation.

[0062] Table 3 illustrates the effects of adding matcha powder after fermentation and adding matcha powder before fermentation on the physicochemical properties of yogurt.

[0063] Table 3. Effects of adding matcha powder before and after fermentation on the physicochemical properties of yogurt. Table 4 illustrates the effects of adding matcha powder after fermentation and adding matcha powder before fermentation on the sensory evaluation of yogurt.

[0064] Table 4. Effects of adding matcha powder after fermentation and adding matcha powder before fermentation on the sensory evaluation of yogurt. Compare the process before and after the improvement.

[0065] Table 5 illustrates the effect of fermentation time on the pH changes of matcha yogurt produced by different processes. Table 5 explains that the pH change trends during the fermentation process of groups A and C are similar, and the pH at the fermentation endpoint is similar, which aims to demonstrate that the new process of this invention has no negative impact on pH value, and the final fermentation termination time has been determined to be 6 hours.

[0066] Table 5. Effect of fermentation time on pH changes of matcha yogurt produced by different processes. Table 6 shows the physicochemical indicators of matcha yogurt produced using different processes. Group A2 uses a high-temperature sterilization process with a fermentation time of 6 hours, while Group C uses a microwave low-temperature sterilization process with a fermentation time of 6 hours.

[0067] Table 6 Physicochemical properties of matcha yogurt produced by different processes Table 7 illustrates the sensory evaluation of matcha yogurt produced using different processes.

[0068] Table 7 Sensory evaluation of matcha yogurt produced using different processes The advantage of Group A over Group B lies in the unique flavor of matcha powder during fermentation. Therefore, Group C improved the fermentation process of Group A. Compared with Group B, Group C has similar physicochemical properties and a higher overall score, while retaining its special flavor.

[0069] This invention uses organic raw milk and matcha powder as the main raw materials, and white sugar and corn starch as auxiliary materials. Through comparative experiments, it explores the impact of different matcha addition methods on yogurt quality. Addressing the drawback of traditional high-temperature processes that damage matcha quality, a low-temperature improved process was designed. Product quality was comprehensively evaluated by measuring indicators such as pH value, water retention, viable lactic acid bacteria count, tea polyphenol content, and sensory evaluation, as shown in Tables 3-7. Figures 1-5 As shown, the following conclusions are ultimately drawn: 1) The method of adding matcha has a significant impact on the quality of yogurt. Adding matcha before fermentation can promote the growth of lactic acid bacteria, with the viable count of lactic acid bacteria in group A2 reaching 7.68 × 10⁻⁶. 8 ±0.35×10 8 The CFU / mL of matcha was significantly higher than that of the group that added matcha after fermentation. However, the participation of matcha in fermentation reduced the water-holding capacity of yogurt, and the higher the amount added, the more significant the decrease in water-holding capacity. The water-holding capacity of group A3 was only 73.15±1.52%, which was significantly lower than that of group B3 (84.86±1.31%). At the same time, adding matcha before fermentation made the pH value of yogurt slightly lower than that of the group that added matcha after fermentation, and the pH value gradually decreased with the increase of matcha addition, indicating that the participation of matcha in fermentation can promote the fermentation process of yogurt.

[0070] 2) The amount of matcha added significantly affects the sensory quality and nutritional components of yogurt. Considering all indicators, the optimal product quality is achieved when the amount of matcha added is 10g / 1000mL of milk. At this level, the polyphenol content in group B2 is higher than that in group A2, but the overall sensory score of group A2 is slightly lower than that of group B2. When the amount of matcha added exceeds 10g, whether added before or after fermentation, it leads to a darker yogurt color, a duller taste, increased whey separation, and a significant decrease in sensory score. Therefore, 10g / 1000mL of milk is determined to be the optimal amount of matcha added.

[0071] 3) Low-temperature improved processing effectively enhances the quality of matcha yogurt. Addressing the issues of browning and loss of active ingredients in matcha caused by traditional high-temperature processes, the designed improved process (Group C) significantly improves product quality without altering the original formula. Compared to the traditional process (Group A2), Group C has a slightly higher pH, improved water retention to 80.56±0.85%, and increased viable lactic acid bacteria count to 8.85×10⁻⁶. 8 ±0.42×10 8 The CFU / mL tea polyphenol retention rate was significantly improved. In the sensory evaluation, the color, flavor, texture and taste scores of group C were significantly better than those of group A2, with a total score of 90 points. The product has a bright green color, rich tea aroma and delicate taste, effectively solving the defects of traditional process.

[0072] In summary, this invention optimizes the process of adding matcha before fermentation combined with a low-temperature improvement technique to prepare high-quality matcha fermented yogurt. This process achieves nutritional complementarity between matcha and yogurt, fully preserving the active ingredients and unique flavor of matcha, while ensuring the fermentation characteristics and sensory quality of the yogurt. It provides a theoretical basis and technical reference for the industrial production of high-quality matcha fermented yogurt and also offers new ideas for the in-depth application of matcha in the dairy industry.

[0073] The above description of the embodiments is provided to enable those skilled in the art to understand and use the invention. It will be apparent to those skilled in the art that various modifications can be made to these embodiments, and the general principles described herein can be applied to other embodiments without inventive effort. Therefore, the present invention is not limited to the above embodiments, and any improvements and modifications made by those skilled in the art based on the disclosure of the present invention without departing from the scope of the invention should be within the protection scope of the present invention.

Claims

1. A low-temperature microwave preparation method for highly active matcha yogurt, characterized in that, Includes the following steps: (1) Raw material preparation: The raw materials include organic raw milk, white sugar, corn starch, and matcha powder; (2) Low temperature pre-dissolving: Preheat organic raw milk to 60~65℃ to obtain preheated milk. Take a portion of the preheated milk and stir matcha powder into a paste without granules. Then mix it evenly with the remaining preheated milk, white sugar and corn starch to obtain a mixture. (3) Microwave low-temperature sterilization: The mixture is sterilized by microwave at 40~60℃ to obtain microwave low-temperature sterilized mixture; (4) Inoculation and fermentation: Adjust the temperature of the microwave-sterilized mixture to 42°C, inoculate with yogurt starter, and ferment at a constant temperature of 42°C for 6 hours to obtain the fermented mixture; (5) Cold-cold ripening: The fermented mixture is cold-cold at 2~6℃ for more than 12 hours to obtain highly active matcha yogurt.

2. The low-temperature microwave preparation method according to claim 1, characterized in that, The mass of the added matcha powder is 1.0% w / v relative to the volume of the organic raw milk.

3. The low-temperature microwave preparation method according to claim 1, characterized in that, The ingredients include, based on 1000mL of organic raw milk, 65-75g of white sugar, 10-14g of corn starch, and 8-12g of matcha powder.

4. The low-temperature microwave preparation method according to claim 3, characterized in that, The ingredients include, based on 1000mL of organic raw milk, 70g of white sugar, 12g of corn starch, and 10g of matcha powder.

5. The low-temperature microwave preparation method according to claim 1, characterized in that, In step (3), the conditions for microwave low-temperature sterilization are: microwave frequency 2450MHz, power density 0.65-0.75kW / L, peak temperature throughout the process ≤60℃, heating stage: single pulse heating for 10s, heating stopped, intermittent for 15s, cycle until the center temperature reaches 55℃; heat preservation stage: single pulse heating for 5s, heating stopped, intermittent for 15s, cycle 8-10 times.

6. The low-temperature microwave preparation method according to claim 1, characterized in that, The yogurt starter is a direct-injection yogurt starter powder; The yogurt fermentation direct-inoculation powder contains skim milk powder, as well as YO-MIX 300 strain, YO-MIX885-B strain and YO32.22 strain.

7. A highly active matcha yogurt, characterized in that, Prepared by the method described in any one of claims 1-6.

8. The highly active matcha yogurt according to claim 7, characterized in that, The pH of the highly active matcha yogurt is 4.40~4.45; The water-holding capacity of the highly active matcha yogurt is ≥80%; The high-activity matcha yogurt has a lactic acid bacteria viable count ≥8.5×10 8 CFU / mL.

9. The highly active matcha yogurt according to claim 7, characterized in that, The highly active matcha yogurt has a uniform bright green color and no browning. The highly active matcha yogurt has a rich tea aroma and a smooth, delicate texture.

10. The highly active matcha yogurt according to claim 7, characterized in that, The highly active matcha yogurt showed no obvious whey separation, had a delicate and uniform texture, and no grainy or astringent feeling, with a total sensory score of ≥90 points.

Images