A high-efficiency fermentation process for purple sweet potato rice wine

Abstract

This invention relates to the field of food fermentation technology, specifically to a high-efficiency fermentation process for purple sweet potato rice wine. It aims to solve the technical problems of significant anthocyanin degradation and fading, difficulty in balancing flavor and efficiency, poor strain adaptability, and short shelf life during the fermentation of purple sweet potato rice wine. This invention improves product quality and fermentation efficiency by constructing a specialized compound fermenting agent and employing a two-stage fermentation process with dynamic pH control. The compound fermenting agent consists of *Rhizopus oryzae*, *Monascus purpureus*, *Kluyveromyces martensii*, and *Lactobacillus plantarum*. The fermentation process employs two stages: the first stage is aerobic fermentation, which promotes the stable existence of anthocyanins and facilitates enzyme activity; the second stage is anaerobic fermentation, which further stabilizes the color and inhibits unwanted microorganisms. This invention uses ultra-high pressure sterilization combined with post-treatment with natural antioxidants to sterilize and preserve the purple sweet potato rice wine, which can improve the pigment retention rate and significantly extend the shelf life of the purple sweet potato rice wine.

Description

Technical Field

[0001] This invention relates to the field of food fermentation technology, specifically to a high-efficiency fermentation process for purple sweet potato rice wine. Background Technology

[0002] Purple sweet potatoes, with their purplish-red to purplish-black color due to their rich anthocyanin and other bioactive substances, are a natural food with high nutritional and health value. Using purple sweet potatoes for fermentation to produce a low-alcohol rice wine can yield a brightly colored, mellow, and delicious health wine rich in anthocyanins and other functional components. Traditional purple sweet potato rice wine typically uses purple sweet potatoes and glutinous rice as the main ingredients, fermented by steaming the rice and sweet potatoes, adding yeast or starter culture. Existing patent CN107663481A discloses a method for brewing purple sweet potato glutinous rice wine: first, the purple sweet potatoes and glutinous rice are saccharified separately, then mixed and fermented. The saccharified mash of purple sweet potatoes and glutinous rice is mixed in a specific ratio, yeast is added, the initial pH is adjusted to 4.0, fermentation is carried out at 20℃ for 7 days, followed by aging and pasteurization to obtain the finished wine. This method can produce a product with a certain alcohol content while retaining some of the nutritional components of purple sweet potatoes. However, existing purple sweet potato rice wine fermentation processes have several shortcomings and technical problems that urgently need to be solved.

[0003] 1. Severe Anthocyanin Degradation and Fading: Anthocyanins in purple sweet potatoes are extremely sensitive to pH and oxidation. During traditional fermentation, factors such as long fermentation times, lack of pH control, and subsequent heat sterilization lead to significant anthocyanin degradation. The finished product's color often changes from a bright purple-red to a dull or even brownish hue, severely impacting its sensory quality. Studies indicate that anthocyanins exhibit a stable red to purple-red color in an acidic environment, while an increase in pH causes them to fade. However, conventional processes often only roughly adjust the acidity at the initial stage of fermentation. During fermentation, the pH changes significantly with sugar consumption and microbial metabolism, lacking dynamic control and easily causing anthocyanin instability. Furthermore, while heat sterilization can inhibit microorganisms, it may also accelerate anthocyanin degradation.

[0004] 2. Balancing Flavor and Efficiency: Rice wine fermentation demands both high saccharification and fermentation efficiency to shorten the cycle and increase yield, and the production of a mature and rich flavor. However, traditional processes often use single strains of microorganisms with limited metabolic products, insufficient aroma compounds, and limited acid production, resulting in a less complex flavor profile in the finished product. To achieve a more complex flavor, prolonged fermentation or the addition of other auxiliary materials is often necessary, which can lead to greater anthocyanin loss or the introduction of unwanted microorganisms, reducing efficiency. Therefore, balancing fermentation efficiency with rich flavor and stable anthocyanins presents a difficult challenge in traditional purple sweet potato rice wine brewing.

[0005] 3. Poor strain adaptability: Purple sweet potatoes are rich in polyphenols and dietary fiber, and their substrate is quite unique. Traditionally used single yeast strains may have poor adaptability in this complex substrate, resulting in slow or incomplete fermentation. The naturally occurring antibacterial components and high viscosity of purple sweet potatoes may also affect the growth and reproduction of traditional strains. Furthermore, purple sweet potato starch coexists with glutinous rice starch, requiring a highly efficient saccharifying enzyme system to convert it into fermentable sugars. Traditional fermentation often relies on adding commercial yeast starter, which has a fixed number of molds and yeasts and limited enzyme activity, leading to inconsistent results with different batches of raw materials. If the strain is poorly adapted to the environment, it is easily competed for by other microorganisms or may prematurely stop fermentation, resulting in reduced yield and abnormal flavor.

[0006] 4. Short shelf life: Purple sweet potato rice wine generally has a low alcohol content and limited antibacterial and preservative properties. Furthermore, residual yeast and lactic acid bacteria in the fermentation liquid may continue to ferment or cause spoilage during storage. Therefore, even after pasteurization, the finished product is difficult to store at room temperature for extended periods and often requires refrigeration; otherwise, it is prone to swelling, souring, and color fading. Additionally, the easy oxidation and fading of anthocyanins during storage is also a significant reason for the short shelf life. Consumers generally desire purple sweet potato rice wine that has an appealing color, aroma, and flavor upon opening and can be stored at room temperature for a long time without flavor loss, but traditional processes struggle to meet this requirement.

[0007] In summary, existing technologies cannot simultaneously meet the requirements of anthocyanin stability, rich flavor, efficient fermentation, synergistic effects of microbial strains, and extended shelf life during the fermentation process of purple sweet potato rice wine. A new fermentation process is urgently needed to improve and solve these problems. Summary of the Invention

[0008] This invention provides a highly efficient fermentation process for purple sweet potato rice wine, addressing technical problems in traditional purple sweet potato rice wine fermentation such as significant anthocyanin degradation and fading, difficulty in balancing flavor and efficiency, poor strain adaptability, and short shelf life. By introducing compound fermentation strains and innovative process control methods, the brewing process of purple sweet potato rice wine becomes highly efficient and controllable, ensuring that the finished product has a stable and vibrant color, a rich and harmonious flavor, and a long shelf life.

[0009] The specific technical solution is as follows:

[0010] A highly efficient fermentation process for purple sweet potato rice wine includes the following steps:

[0011] S1: Wash and peel fresh purple sweet potatoes, cut them into chunks, and steam them until soft. Cool the steamed purple sweet potatoes to 30℃, add an equal weight of clean water, and blend into a purple sweet potato paste for later use. Wash glutinous rice thoroughly, soak it in water for 6 hours, drain it, steam it for 1 hour, and spread it out to cool to 30℃ while hot for later use. Add citric acid to adjust the pH while steaming the purple sweet potatoes, and mix the glutinous rice and purple sweet potatoes evenly in the specified proportions to prepare the fermentation substrate.

[0012] Furthermore, the pH was adjusted to 4.0–4.3.

[0013] Furthermore, the weight ratio of glutinous rice to purple sweet potato is 1:0.3 to 1:0.5.

[0014] S2: Cultivate each strain in the compound culture separately. Rhizopus oryzae and Monascus purpureus are cultured on wheat bran medium at 28°C for 5 days; Kluyveromyces martensii is cultured in YPD liquid medium at 30°C with shaking for 24 hours; Lactobacillus plantarum is cultured in MRS medium at 37°C for 24 hours. After cultivation, the compound culture is mixed in proportion to prepare a compound fermentation agent, which is then inoculated into the fermentation substrate prepared in step S1. After thorough mixing, it is placed into a stainless steel fermenter equipped with a pH monitoring device.

[0015] Furthermore, the complex strain consists of Rhizopus oryzae, Monascus purpureus, Kluyveromyces martensii, and Lactobacillus plantarum.

[0016] Furthermore, the proportions of the compound microbial strains added were as follows: Rhizopus oryzae and Monascus purpureus were added at 0.1–0.5% of the total weight of the fermentation substrate, respectively, and the inoculum amounts of Kluyveromyces martensii and Lactobacillus plantarum were 10 g / L. 6 ~10 8 CFU / g.

[0017] S3: The stainless steel fermenter is placed in a temperature-controlled fermentation device for fermentation in two stages. The first stage is aerobic fermentation, in which the container's sealed opening is one-third open; the pH of the fermentation mash is dynamically controlled to maintain it between 4.0 and 4.5. When the pH is below 4.0, 0.5 mol / L NaOH solution is added dropwise to stabilize the pH at 4.2; when the pH rises close to 4.5, citric acid is added dropwise to adjust the pH back to the target range.

[0018] The second stage is anaerobic fermentation. The fermentation container is sealed to remove all air. During this stage, the pH is continuously dynamically controlled between 3.8 and 4.2. When the pH is below 3.8, the pH is stabilized at 4.2 by online monitoring and adding 0.5 mol / L NaOH solution. When the pH rises to close to 4.2, citric acid is added to adjust the pH back to the target range.

[0019] Furthermore, the aerobic fermentation conditions are carried out at 28°C for 12–36 hours.

[0020] Furthermore, the anaerobic fermentation conditions were to continue fermentation at 25°C for 4–6 days.

[0021] S4: After fermentation, the fermented mash is separated into solid and liquid components. The clear, purplish-red liquid is taken as the finished rice wine. A post-treatment method combining ultra-high pressure sterilization and natural antioxidants is used. The rice wine is then packaged into pressure-resistant food containers. During filling, 0.1g of natural antioxidant can be added to each liter of liquid, mixed thoroughly, and the containers are sealed. The containers are then placed in an ultra-high pressure processing device for high-pressure treatment to obtain purple sweet potato rice wine.

[0022] Furthermore, ascorbic acid is chosen as a natural antioxidant.

[0023] Furthermore, the high-pressure treatment involved applying a hydrostatic pressure of 400 MPa at room temperature and holding the pressure for 10 minutes.

[0024] Compared with the prior art, the present invention has the following beneficial effects:

[0025] 1. This invention maintains the environment within the stable acidity range for anthocyanins through dynamic pH control throughout the fermentation process, effectively preventing alkali hydrolysis, degradation, and fading of anthocyanins. Simultaneously, the introduction of pigment-producing *Monascus purpureus* replenishes the color lost during fermentation to a certain extent, resulting in an appealing purplish-red color in the finished product. Ultra-high pressure low-temperature sterilization replaces traditional high-temperature sterilization, further preventing significant anthocyanin degradation under heat conditions. Combined with antioxidants, this ensures that the color does not easily fade during storage, significantly improving anthocyanin retention and resulting in a stable and vibrant color.

[0026] 2. The compound microbial strain of this invention includes molds, yeasts and lactic acid bacteria, which can utilize a variety of nutrients in the raw materials and give full play to their strengths under different environmental parameters, so that the role of the dominant bacteria at each stage can be fully exerted, the fermentation process is stable and rapid, and the saccharification and fermentation efficiency is high, and the fermentation process is controllable and stable.

[0027] 3. This invention employs ultra-high pressure physical sterilization to achieve a near-commercial sterility level in the finished product, eliminating residual bacteria without damaging flavor and nutrients. Antioxidants are added to prevent oxidative deterioration during storage, allowing the finished product to be stored for extended periods without refrigeration, thus extending its shelf life. Attached Figure Description

[0028] Figure 1 This is a flow chart of a high-efficiency fermentation preparation process for purple sweet potato rice wine according to the present invention.

[0029] Figure 2 This is a comparison chart of anthocyanin retention rates at the initial stage and after 30 days in the storage stability experiment of Examples 1-3 and Comparative Examples 1-3.

[0030] Figure 3 This is a comparison chart of the total acid data of Examples 1-3 and Comparative Examples 1-3 at the beginning and after 30 days in the storage stability experiment. Detailed Implementation

[0031] The following embodiments further explain and illustrate the technical solution of the present invention. It is particularly noted that each specific embodiment is a concretization and explanation of the technical solution and should not be considered as a limitation on the scope of protection of the present invention. Those skilled in the art still have the right to modify the technical solutions of these embodiments and make equivalent substitutions for some or all of the technical features, and these modifications or substitutions do not change the essence of the corresponding technical solutions, nor do they cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions described in the present invention. (See attached...) Figure 1 The image shows a highly efficient fermentation process for purple sweet potato rice wine, with detailed preparation steps as follows:

[0032] 1. Raw material pretreatment and saccharification

[0033] Wash and peel fresh purple sweet potatoes, cut them into chunks, and steam them until soft. Cool the steamed purple sweet potatoes to 30°C, add an equal weight of clean water, and blend into a purple sweet potato puree. Rinse glutinous rice thoroughly, soak it in water for 6 hours, drain, and steam for 1 hour. Spread it out while hot and cool to 30°C. Add citric acid during the steaming of the purple sweet potatoes to adjust the pH to 4.0–4.3 to improve anthocyanin stability. Mix the cooled purple sweet potato puree to fermentation temperature evenly with the steamed glutinous rice to prepare the fermentation substrate. The weight ratio of glutinous rice to purple sweet potato should be 1:0.3–0.5 to balance fermentation sugar and anthocyanin content.

[0034] 2. Construction and inoculation of compound fermentation agent

[0035] A compound microbial culture was prepared, consisting of *Rhizopus oryzae*, *Monascus purpureus*, *Kluyveromyces martensii*, and *Lactobacillus plantarum*. Each culture was cultured separately. *Rhizopus oryzae* and *Monascus purpureus* were cultured on wheat bran medium at 28°C for 5 days to obtain mature *Aspergillus* mycelia and spores. *Kluyveromyces martensii* was cultured in YPD (yeast extract peptone glucose) liquid medium at 30°C with shaking for 24 hours. *Lactobacillus plantarum* was cultured in MRS (broth) medium at 37°C for 24 hours. After culturing, the cultures were mixed in a specific ratio to prepare a compound starter culture. The addition ratios were: *Rhizopus oryzae* and *Monascus purpureus* at 0.1–0.5% of the total weight of the fermentation substrate, and the inoculum amounts of *Kluyveromyces martensii* and *Lactobacillus plantarum* were 10 g / L. 6 ~10 8 CFU / g. The above-mentioned compound fermentation agent was evenly inoculated into the fermentation substrate prepared above, and after being thoroughly mixed, it was placed into a stainless steel fermentation tank equipped with a pH monitoring device.

[0036] Rhizopus oryzae and Monascus purpureus grow rapidly in the early stages of fermentation, producing amylase and saccharifying enzymes to efficiently hydrolyze the starch in purple sweet potatoes and glutinous rice into fermentable sugars such as glucose. Monascus purpureus also synthesizes a reddish-purple natural pigment, giving the mash a bright and stable color. Kluyveromyces martensii, as an aroma-producing yeast, can rapidly ferment various sugars produced by Rhizopus oryzae saccharification to produce alcohol, generating various esters and higher alcohols, significantly enhancing the fruit and wine aromas. Lactobacillus plantarum exhibits strong acid tolerance and grows well in the mixed fermentation system. On one hand, it ferments sugars to produce lactic acid and other organic acids, moderately lowering the pH of the environment, inhibiting the growth of unwanted microorganisms, and imparting a mellow sour taste to the mash. On the other hand, its secreted β-glucosidase can gradually hydrolyze the glycosidic bonds of anthocyanins and other phenols in purple sweet potatoes and the bound aromatic precursors in glutinous rice, releasing more aromatic compounds and functional components. The four strains of microorganisms work together in a coordinated manner, each performing its own function, from saccharification and fermentation to wine production, aroma production and acid production for flavoring, achieving multifunctional synergy and significantly improving fermentation performance and product quality.

[0037] 3. Two-stage fermentation with dynamic pH control

[0038] The stainless steel fermenter is placed in a temperature-controlled fermentation device for fermentation in two stages. The first stage is aerobic pre-fermentation, which takes place at 28°C for 12–36 hours. During this stage, one-third of the container's sealed opening is left open. The pH of the fermentation mash is dynamically controlled to maintain it between 4.0 and 4.5. When the pH is below 4.0, 0.5 mol / L NaOH solution is added dropwise to stabilize the pH at 4.2. When the pH rises close to 4.5, citric acid is added dropwise to adjust the pH back to the target range.

[0039] Aerobic conditions are conducive to the growth and enzyme production of Rhizopus oryzae and Monascus purpureus, as well as yeast reproduction. The key is to dynamically maintain the pH of the fermentation mash between 4.0 and 4.5: Since lactic acid bacteria produce acid, the pH will naturally decrease after several hours of fermentation. If it falls below 4.0, it will affect the enzyme activity of Rhizopus oryzae and yeast proliferation. Therefore, it is necessary to monitor the pH online and add 0.5 mol / L NaOH solution to stabilize the pH at 4.2. Conversely, if the initial acidity of the raw materials is insufficient, causing the pH to rise close to 4.5, lactic acid or citric acid can be added to adjust the pH back to the target range. A stable, slightly acidic environment, on the one hand, maximizes the preservation of anthocyanins' stable purple-red color and prevents oxidative fading; on the other hand, it facilitates the function of various microbial enzyme systems, improving saccharification and fermentation efficiency. After 24 hours of pre-fermentation, the starch in the mash is basically completely saccharified, the content of fermentable sugars is significantly increased, yeast cells multiply rapidly, and a certain amount of alcohol and aromatic substances are initially produced.

[0040] The second stage is anaerobic primary fermentation. The fermentation container is sealed to remove all air, and fermentation continues at 25°C for 4–6 days to fully convert sugars into alcohol and flavor products. During this stage, the pH is dynamically controlled between 3.8 and 4.2. When the pH is below 3.8, the pH is stabilized at 4.2 by online monitoring and adding 0.5 mol / L NaOH solution. When the pH rises to near 4.2, citric acid is added to adjust the pH back to the target range.

[0041] Due to the action of lactic acid bacteria, the pH of the mash will further decrease and tend to stabilize in a slightly acidic range close to 4.0. If the pH is below 3.8, it will become too acidic, affecting the later fermentation of yeast and the taste of the finished product. This can be addressed by adding a small amount of NaOH to keep the pH above 3.8. If the pH is above 4.2, citric acid should be added appropriately to inhibit potential contaminating bacteria. In this slightly acidic anaerobic environment, Kluyveromyces macrocarpa fully utilizes its advantages of high temperature and acid resistance to continuously and efficiently produce alcohol through fermentation. Even under conditions close to 4% ethanol, it can still metabolize residual sugars to increase the alcohol content. At the same time, it synthesizes a large amount of esters and other aroma-enhancing substances, making the mash rich and full-bodied in aroma. Lactobacillus plantarum completes lactic acid fermentation, raising the total acidity to a suitable level and stabilizing the anthocyanin structure. After the second stage, fermentation is basically complete. Fermentable sugars are almost completely consumed, the alcohol content reaches the expected value, the total acidity is moderate, and the anthocyanins exhibit a rose-red color under acidic conditions. The mash exudes a rich aroma of alcohol, fruit, and glutinous rice.

[0042] 4. Post-processing

[0043] After fermentation, the fermentation mash is separated into solid and liquid components. The clear, purplish-red liquid is taken as the finished rice wine. A post-treatment method combining ultra-high pressure sterilization and natural antioxidants is used. The rice wine is then packaged into pressure-resistant food containers. During filling, 0.1g of ascorbic acid can be added per liter of liquid, mixed thoroughly, and the containers are sealed. The containers are then placed in an ultra-high pressure processing device, where a hydrostatic pressure of 400MPa is applied at room temperature. After holding the pressure for 10 minutes, the pressure is released, and the purple sweet potato rice wine is obtained.

[0044] The core principles of ultra-high pressure sterilization are Pascal's Law and Le Chatelier's principle. Pascal's Law states that pressure applied to a closed liquid is transmitted uniformly in all directions. This means that regardless of the product's shape, every point inside it experiences the same pressure instantaneously, with no pressure gradient, resulting in uniform and thorough sterilization. Le Chatelier's principle states that high pressure disrupts the non-covalent bonds that maintain the physiological structure of microorganisms, thus inactivating them. Specific effects include: cell membrane damage: High pressure makes the phospholipid bilayer of the cell membrane rigid and disordered, increasing its permeability, leading to leakage of cell contents and loss of organelle function; protein denaturation: High pressure causes reversible or irreversible changes to the three-dimensional and quaternary structures of proteins, leading to the inactivation of functional enzymes and the interruption of microbial metabolic activities; and interference with genetic mechanisms: Extremely high pressure can also interfere with DNA replication and transcription.

[0045] Ultra-high pressure sterilization technology can efficiently kill residual yeast, lactic acid bacteria, and other microorganisms in the fermentation broth at room temperature, with minimal damage to heat-sensitive nutrients such as anthocyanins. High-pressure sterilization avoids anthocyanin degradation and flavor loss caused by traditional heat sterilization. Simultaneously, the addition of antioxidants pre-emptively removes dissolved oxygen and continuously protects anthocyanins from oxidation and discoloration during storage. The product, after high-pressure treatment, is aseptically filled and sealed, extending its shelf life and maintaining stable color and aroma, resulting in a consistent finished purple sweet potato rice wine.

[0046] Example 1

[0047] Table 1 Raw Material Information Table:

[0048]

[0049] A highly efficient fermentation process for purple sweet potato rice wine is as follows:

[0050] S1: Take 2 kg of fresh purple sweet potatoes, wash and peel them, cut them into chunks, and steam them until soft. Cool the steamed purple sweet potatoes to 30℃, add an equal weight of clean water, and blend them into a purple sweet potato puree for later use. Take 5 kg of glutinous rice, wash it clean, soak it in water for 6 hours, drain it, steam it for 1 hour, and spread it out to cool to 30℃ while hot for later use. Add citric acid during the steaming of the purple sweet potatoes to adjust the pH to 4.2 to improve the stability of anthocyanins. Mix the cooled purple sweet potato puree to the fermentation temperature evenly with the steamed glutinous rice to prepare the fermentation substrate;

[0051] S2: Prepare a compound microbial culture consisting of *Rhizopus oryzae*, *Monascus purpureus*, *Kluyveromyces martensii*, and *Lactobacillus plantarum*. Cultivate each microbial strain separately. *Rhizopus oryzae* and *Monascus purpureus* are cultured on wheat bran medium at 28°C for 5 days to obtain mature *Aspergillus* mycelia and spores. *Kluyveromyces martensii* is cultured in YPD liquid medium at 30°C with shaking for 24 hours. *Lactobacillus plantarum* is cultured in MRS medium at 37°C for 24 hours. After cultivation, mix them in a specific ratio to prepare a compound fermentation agent. The addition ratios are: *Rhizopus oryzae* and *Monascus purpureus* at 0.3% of the total weight of the fermentation substrate, and the inoculum amounts of *Kluyveromyces martensii* and *Lactobacillus plantarum* are 1×10⁻⁶. 7 CFU / g. The above-mentioned compound fermentation agent was evenly inoculated into the fermentation substrate prepared in step S1, and after being thoroughly mixed, it was placed into a stainless steel fermentation tank equipped with a pH monitoring device.

[0052] S3: Place the stainless steel fermenter in a temperature-controlled fermentation device and carry out fermentation in two stages. The first stage is aerobic pre-fermentation, which is carried out at 28°C for 24 hours. During this stage, one-third of the container's sealed opening is left open. The pH of the fermentation mash is dynamically controlled to maintain it between 4.0 and 4.5. When the pH is below 4.0, online pH monitoring is used and 0.5 mol / L NaOH solution is added to stabilize the pH at 4.2. When the pH rises close to 4.5, citric acid is added to adjust the pH back to the target range.

[0053] The second stage is anaerobic primary fermentation. The fermentation container is sealed to remove all air, and fermentation continues for 5 days at 25°C to fully convert sugars into alcohol and flavor products. During this stage, the pH is dynamically controlled between 3.8 and 4.2. When the pH is below 3.8, the pH is stabilized at 4.2 by online monitoring and adding 0.5 mol / L NaOH solution. When the pH rises to close to 4.2, citric acid is added to adjust the pH back to the target range.

[0054] S4: After fermentation, the fermentation mash is separated into solid and liquid components. The clear, purplish-red liquid is taken as the finished rice wine. A post-treatment method combining ultra-high pressure sterilization and natural antioxidants is used. The rice wine liquid to be treated is then packaged into pressure-resistant food containers. During filling, 0.1g of ascorbic acid can be added per liter of liquid, mixed thoroughly, and the containers are sealed. The containers are then placed in an ultra-high pressure processing device, where a hydrostatic pressure of 400MPa is applied at room temperature. After holding the pressure for 10 minutes, the pressure is released, and the purple sweet potato rice wine is obtained.

[0055] Example 2

[0056] The fermentation process is the same as in Example 1, except that...

[0057] In step S1: 5 kg of glutinous rice, 1.5 kg of purple sweet potato; adjust the pH value to 4.3;

[0058] In step S2: Rhizopus oryzae and Monascus purpureus were each at 0.1% of the total weight of the fermentation substrate, and the inoculum amounts of Kluyveromyces martensii and Lactobacillus plantarum were 1×10⁻⁶. 8 CFU / g;

[0059] In step S3: the first stage is aerobic pre-fermentation, which is carried out at 28℃ for 12 hours; the second stage is anaerobic main fermentation, which continues fermentation at 25℃ for 4 days.

[0060] Example 3

[0061] The fermentation process is the same as in Example 1, except that...

[0062] In step S1: 5 kg of glutinous rice, 2.5 kg of purple sweet potato; adjust the pH value to 4.0;

[0063] In step S2: Rhizopus oryzae and Monascus purpureus were each at 0.5% of the total weight of the fermentation substrate, and the inoculum amounts of Kluyveromyces martensii and Lactobacillus plantarum were 1×10⁻⁶. 6 CFU / g;

[0064] In step S3: the first stage is aerobic pre-fermentation, which is carried out at 28℃ for 36 hours; the second stage is anaerobic main fermentation, which continues fermentation at 25℃ for 6 days.

[0065] Comparative Example 1

[0066] The fermentation process was followed as in Example 1, but without the two-stage pH adjustment. Instead, the pH of the fermentation substrate was adjusted to 4.2 after inoculation, and the mixture was sealed and fermented continuously at 28°C for 6 days without any pH adjustment. All other steps were the same.

[0067] Comparative Example 2

[0068] The fermentation process is the same as in Example 1, but without the addition of *Monascus purpureus* and *Lactobacillus plantarum* to the compound fermentation agent. All other steps remain the same.

[0069] Comparative Example 3

[0070] The fermentation process was the same as in Example 1, but without high pressure treatment or the addition of antioxidants; instead, pasteurization was performed at 65°C for 30 minutes. All other steps were the same.

[0071] The storage stability test was conducted on the highly efficient fermented purple sweet potato rice wine prepared in combined Examples 1-3 and Comparative Examples 1-3.

[0072] (1) Experimental grouping

[0073] The experiment was divided into 6 groups, with 3 samples of purple sweet potato rice wine in each group. Each group received a different treatment: Example 1 group: The purple sweet potato rice wine prepared in Example 1 was aseptically dispensed into 100mL transparent glass bottles and sealed; Example 2 group: The purple sweet potato rice wine prepared in Example 2 was aseptically dispensed into 100mL transparent glass bottles and sealed; Example 3 group: The purple sweet potato rice wine prepared in Example 3 was aseptically dispensed into 100mL transparent glass bottles and sealed; Comparative Example 1 group: The purple sweet potato rice wine prepared in Comparative Example 1 was aseptically dispensed into 100mL transparent glass bottles and sealed; Comparative Example 2 group: The purple sweet potato rice wine prepared in Comparative Example 2 was aseptically dispensed into 100mL transparent glass bottles and sealed; Comparative Example 3 group: The purple sweet potato rice wine prepared in Comparative Example 3 was aseptically dispensed into 100mL transparent glass bottles and sealed.

[0074] (2) Test conditions

[0075] Accelerated storage tests were conducted to simulate the storage effect of 3 to 6 months at room temperature in 1 month, with the temperature controlled at 37°C and stored away from light.

[0076] (3) Test indicators and methods

[0077] Samples were taken on day 0 (initial), day 14, and day 30 of storage for index testing. Anthocyanin content was determined using the pH differential method, and the anthocyanin retention rate (%) was calculated, with the initial anthocyanin retention rate calculated based on the initial value of Example 1 as 100%. Total acid was expressed as lactic acid and determined by titration. Sensory evaluation was conducted on day 30, with 10 trained sensory evaluators scoring the color, aroma, and taste of the samples (out of 100). The sensory scoring method and score weights are shown in Table 2.

[0078] Table 2 Sensory evaluation method and score weighting for purple sweet potato rice wine:

[0079]

[0080] The specific scoring results are as follows:

[0081] Table 3. Sensory evaluation results of the finished product of purple sweet potato rice wine:

[0082]

[0083] The anthocyanin retention rate and total acid test results are shown in Table 4. Figure 2 , Figure 3 As shown:

[0084] Table 4. Comparison of overall performance between Examples 1-3 and Comparative Examples 1-3:

[0085]

[0086] The comparison results show that in Comparative Example 1, without pH adjustment throughout the fermentation process, the acid produced by microbial metabolism causes a continuous decrease in pH. The excessively acidic environment accelerates anthocyanin degradation. After 30 days, excessive accumulation of organic acids such as lactic acid leads to an overly acidic product and an unbalanced flavor. In Comparative Example 2, no *Monascus purpureus* or *Lactobacillus plantarum* was added to the compound fermentation agent. However, *Monascus purpureus* is a natural pigment producer, and its absence directly results in a low initial pigment content. The absence of *Lactobacillus plantarum* alters the organic acid composition, indirectly affecting pigment stability. This leads to a low anthocyanin retention rate, low total acidity, and an unbalanced flavor after 30 days. In Comparative Example 3, without high-pressure treatment or the addition of antioxidants, the low initial anthocyanin content indicates that the heat sterilization process has already caused anthocyanin loss. The color is not as vibrant as in Example 1 and may have a slight "cooked" taste, as well as flavor loss due to heat processing. After 30 days, the lack of antioxidants leads to even greater anthocyanin loss and a lower sensory evaluation.

Claims

1. A high-efficiency fermentation process applied to purple sweet potato rice wine, characterized in that the purple sweet potato is washed and peeled, cut into pieces, and then cooked by steaming until soft, and the cooked purple sweet potato is cooled to 30℃, and then mixed with an equal amount of clean water to make purple sweet potato pulp; the fermentation process uses a two-stage fermentation with a composite starter and dynamic pH control; the composite starter is composed of Rhizopus oryzae, Monascus purpureus, Kluyveromyces marxianus, and Lactobacillus plantarum; the two-stage fermentation includes a first stage of aerobic fermentation at 28℃ for 12-36 hours, with the pH of the fermentation mash controlled at 4.0-4.5 to promote the stable existence of anthocyanins and facilitate enzyme action; and a second stage of anaerobic fermentation at 25℃ for 4-6 days, with the pH of the fermentation mash controlled at 3.8-4.2 to further stabilize the color and inhibit bacteria; and the fermentation mash is sterilized and preserved by ultra-high pressure sterilization combined with natural antioxidants.

2. The high-efficiency fermentation process applied to purple sweet potato rice wine according to claim 1, characterized in that the ultra-high pressure sterilization is performed by applying a static water pressure of 400MPa for 10 minutes at room temperature.

3. The high-efficiency fermentation process applied to purple sweet potato rice wine according to claim 1, characterized in that the natural antioxidant is ascorbic acid. The process comprises the following specific steps: S1: glutinous rice is cleaned and soaked in water for 6 hours, then drained and steamed for 1 hour, and then spread out while hot and cooled to 30℃ for use; while the purple sweet potato is being cooked, citric acid is added to adjust the pH; the glutinous rice and the purple sweet potato are mixed in proportion to prepare a fermentation substrate; S2: each strain in the composite starter is cultured separately; Rhizopus oryzae and Monascus purpureus are cultured on wheat bran medium at 28℃ for 5 days; Kluyveromyces marxianus is cultured in YPD liquid medium at 30℃ for 24 hours; and Lactobacillus plantarum is cultured in MRS medium at 37℃ for 24 hours; after the culture, the composite starter is prepared by mixing the strains in proportion, and then inoculated into the fermentation substrate prepared in step S1, and then mixed thoroughly and loaded into a fermentation tank with a pH monitoring device; 4. The efficient fermentation process for purple sweet potato rice wine according to any one of claims 1-3, characterized in that, S3: the fermentation tank is placed in a temperature-controlled fermentation equipment, and the fermentation is carried out in two stages with dynamic pH control; the first stage is aerobic fermentation, and the container is sealed with one-third of the opening open; the second stage is anaerobic fermentation, and the fermentation container is sealed to exhaust the air; S4: after the fermentation is completed, the fermentation mash is subjected to solid-liquid separation, and the clear purple-red wine liquid is taken as the finished rice wine; the rice wine to be treated is divided into pressure-resistant food containers, and the natural antioxidant is added and mixed evenly with the wine liquid, and then the container is sealed, and then placed in an ultra-high pressure treatment equipment for high-pressure treatment to prepare the purple sweet potato rice wine.

5. The high-efficiency fermentation process applied to purple sweet potato rice wine according to claim 4, characterized in that the pH in step S1 is adjusted to 4.0-4.

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6. The high-efficiency fermentation process applied to purple sweet potato rice wine according to claim 4, characterized in that ​ ​ ​ ​ The waxy rice and the purple sweet potato are in a weight ratio of 1:0.3-1:0.

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7. The high-efficiency fermentation process applied to the purple sweet potato rice wine according to claim 4, characterized in that, The composite bacteria species in step S2 are mixed in proportion, specifically, the inoculation amount of Rhizopus oryzae and Monascus purpureus is 0.1-0.5% respectively relative to the total weight of the fermentation substrate, and the inoculation amount of Kluyveromyces marxianus and Lactobacillus plantarum is 10 6 -10 8 CFU / g respectively.

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