A method for preparing Rehmannia glutinosa paste with high retention of all its components after nine steaming and nine sun-drying.

Abstract

This invention discloses a method for preparing Rehmannia glutinosa pulp with high retention of all its components after nine steaming and nine sun-drying processes, belonging to the technical field of deep processing of traditional Chinese medicine and preparation of functional foods. Using Rehmannia glutinosa processed through nine steaming and nine sun-drying processes from authentic Huai Rehmannia glutinosa as raw material, this method addresses industry pain points such as the inability to dry-crush candied Rehmannia glutinosa, low efficiency of traditional extraction methods, easy loss of heat-sensitive active ingredients, and difficulty in retaining all components. It adopts wet pulping instead of dry crushing and pioneers a three-stage progressive cell-wall breaking process of "enzymatic hydrolysis → ultrasound → microwave," achieving a synergistic effect of gentle biological cell-wall breaking, physically enhanced crushing, and low-temperature solubilization. Combined with vacuum low-temperature extraction, post-fermentation with probiotics, and low-temperature concentration, the entire process avoids membrane separation, protein removal, and purification of individual components. The finished product achieves a polysaccharide extraction rate of 90%–96%, a total retention rate of ≥65% for catalpol and rehmannia glycoside D, an increase of over 30% in melanoidin content, a decrease of over 25% in 5-HMF content, and an increase of over 13% in in vitro antioxidant activity. The process is gentle and controllable, suitable for large-scale industrial production.

Description

Technical Field

[0001] This invention belongs to the field of deep processing of traditional Chinese medicine and preparation of functional food, specifically involving a high-efficiency extraction process for the whole components of Rehmannia glutinosa after nine steaming and nine sun-drying, and particularly involving a method for preparing Rehmannia glutinosa paste with high retention of all components after nine steaming and nine sun-drying. Background Technology

[0002] Nine-times-steamed and nine-times-dried Rehmannia glutinosa is a traditional and authentic tonic medicinal material made from the tuberous roots of Rehmannia glutinosa, a plant of the Scrophulariaceae family, through repeated steaming and drying. During the processing, its components undergo significant transformations: the polysaccharide content increases dramatically, some catalpol is converted into more easily absorbed secondary glycosides, and a large number of characteristic active substances such as melanoidins and 5-hydroxymethylfurfural are generated, which have significant effects of nourishing blood and yin, and replenishing essence and marrow.

[0003] Due to the repeated processing of nine steaming and nine sun-drying, Rehmannia glutinosa eventually becomes a viscous candied fruit with a soft, sticky texture and extremely strong viscosity. This presents an industry pain point: dry pulverization is prone to sticking to the machine and charring during the dry pulverization process, and it will also damage heat-sensitive active ingredients such as polysaccharides and catalpol, resulting in low extraction efficiency and serious loss of active ingredients, which restricts its industrial deep processing and the improvement of product added value.

[0004] Existing extraction processes for Rehmannia glutinosa generally suffer from the following drawbacks: 1. Direct extraction using whole pieces of Rehmannia glutinosa results in high resistance to the dissolution of active ingredients due to its dense cell structure and high content of colloids, leading to a polysaccharide extraction rate of only 39%–58%, thus failing to maximize the extraction of active ingredients; 2. High-temperature decoction processes easily cause structural degradation of heat-sensitive components such as catalpol, rehmannia glycoside D, and polysaccharides, reducing product activity; 3. Purification steps such as membrane separation and protein removal are used to pursue the purity of single components, resulting in the loss of a large number of small molecule active substances, which contradicts the traditional concept of Rehmannia glutinosa as a holistic tonic.

[0005] In view of the shortcomings of the existing technologies, there is an urgent need to develop a preparation method that is suitable for efficient extraction and high activity retention of all components of Rehmannia glutinosa, to solve the pain points of the industry and meet the industrial production needs of high-end tonic foods. Summary of the Invention

[0006] The purpose of this invention is to provide a method for preparing a high-quality, fully-retained Rehmannia glutinosa pulp after nine steaming and nine sun-drying processes, specifically achieving the following technical objectives: 1. Solving the industry pain point that candied Rehmannia glutinosa after nine steaming and nine sun-drying cannot be dry-pulverized, avoiding component damage and machine sticking problems caused by dry pulverization; 2. Optimizing the crushing sequence by adopting a three-stage progressive cell-wall breaking process of "enzymatic hydrolysis → ultrasonication → microwaveation" to improve enzymatic hydrolysis efficiency and effective component extraction rate; 3. Achieving maximum dissolution and complete retention of core functional components such as Rehmannia glutinosa polysaccharides, catalpol, rehmannia glutinosa glycoside D, and melanoidins without membrane separation, protein removal, or purification of individual components; 4. Establishing a quantifiable, traceable, and verifiable indicator system to highlight the advanced nature of the process and meet the requirements of industrial production.

[0007] To achieve the above-mentioned objectives, this invention provides a method for preparing a nine-steamed and nine-dried Rehmannia glutinosa pulp with high retention of all its components. The specific steps are as follows: S1. Raw Material Selection: Authentic Huai Rehmannia root is selected and processed through nine steaming and nine sun-drying processes to produce Nine-Steamed and Nine-Sun-Dried Rehmannia Root (also known as Nine-Processed Rehmannia Root). This Nine-Steamed and Nine-Sun-Dried Rehmannia Root is candied, black inside and out, soft and sticky in texture, slightly bitter, and sweet and sour in taste, with a moisture content of 18%–24%. Authentic Huai Rehmannia Root is a high-quality raw material. The Nine-Steaming and Nine-Sun-Drying processing strictly follows traditional methods to ensure the enrichment and transformation of active ingredients in the raw material. The moisture content is controlled at 18%–24%, which ensures the viscosity and softness of the raw material, facilitating subsequent wet pulping operations, while avoiding spoilage and reduced extraction efficiency caused by excessive moisture, thus laying the foundation for subsequent processes.

[0008] S2. Wet Pulping: The nine-steamed and nine-dried Rehmannia glutinosa from step S1) is mixed with purified water at a material-to-liquid ratio of 1:3 to 1:6 (g:mL). The mixture is then wet-processed using a high-speed shear pulper to produce a fine and uniform Rehmannia glutinosa pulp. The high-speed shear pulper operates at a speed of 20,000–28,000 r / min, with a pulping time of 5–10 min. The particle size of the Rehmannia glutinosa pulp is ≤100μm. Maintaining a material-to-liquid ratio of 1:3 to 1:6 ensures smooth pulping, avoids insufficient pulping due to excessive viscosity, and prevents increased concentration costs due to excessive moisture. High-speed shear pulping achieves gentle cell-level disruption while avoiding the damage to active ingredients and equipment sticking issues caused by dry grinding.

[0009] S3. Pre-treatment with compound enzymatic hydrolysis (first step crushing): Add a compound enzyme preparation to the prepared Rehmannia glutinosa pulp in step S2). The compound enzyme preparation is a compound system of cellulase, pectinase and glucanase in a mass ratio of 2:1:1. The cellulase activity is ≥10000U / g, the pectinase activity is ≥8000U / g, and the glucanase activity is ≥5000U / g. The amount of compound enzyme preparation added is 0.10%–0.25% (w / w). Adjust the pH of the system to 5.0–6.5 and enzymatically hydrolyze at 35–45℃ for 40–120 min, preferably 60–90 min. Cellulase can specifically degrade cellulose components in cell walls, pectinase can efficiently degrade pectin-like adhesive substances between cells, and glucanase can assist in degrading the colloidal barrier surrounding polysaccharides. The three work synergistically to gently disrupt cell walls and colloidal structures. By placing enzymatic hydrolysis in the first step of the disruption process, the cell structure in the Rehmannia glutinosa pulp remains intact and the colloidal structure is undisturbed. The enzyme preparation can precisely target the cell wall sites, avoiding cell debris generated by subsequent ultrasound from encapsulating the enzyme preparation, maximizing the efficiency of enzymatic hydrolysis, and laying a solid foundation for the subsequent dissolution of active ingredients.

[0010] S4. Low-Temperature Ultrasonic Treatment (Second Step of Disruption): The prepared Rehmannia glutinosa pulp after enzymatic hydrolysis in step S3) is subjected to low-temperature ultrasonic treatment. The treatment conditions are 35–40℃, 30–50kHz, power 400–500W, and treatment time 3–8min. Low-temperature ultrasound uses the mechanical force generated by cavitation effect to physically tear apart the cell tissue and colloidal structure loosened by enzymatic hydrolysis, further breaking down the dissolution barrier of active ingredients and fully exposing active ingredients such as Rehmannia glutinosa polysaccharides, catalpol, and rehmannia glutinosa glycoside D within the cells. At the same time, the low temperature of 35–40℃ can effectively avoid the degradation of heat-sensitive components, forming a synergistic effect with the enzymatic hydrolysis step and significantly improving the cell wall disruption effect.

[0011] S5. Intermittent Microwave Treatment (Third Step of Disruption): The prepared Rehmannia glutinosa pulp after ultrasonic treatment in step S4) is subjected to intermittent microwave treatment. The treatment conditions are: power 600–800W, working for 20 seconds, intermittent for 10 seconds, and a total treatment time of 80–100 seconds. The "working-intermittent" microwave treatment method can effectively avoid the destruction of active ingredients such as polysaccharides and catalpol caused by local overheating; at the same time, the thermal effect of microwaves is used to gently raise the temperature (not exceeding 45℃), which accelerates the dissolution of exposed active ingredients into the extract, completing the three-stage progressive cell disruption of "enzymatic hydrolysis → ultrasonication → microwave".

[0012] S6. Vacuum Low-Temperature Extraction: Transfer the processed Rehmannia glutinosa pulp from step S5) into a vacuum reflux apparatus. Extract 1–2 times under vacuum conditions of -0.06 to -0.08 MPa and temperature of 60–75℃, for a total extraction time of 60–120 min, preferably 1 extraction with an extraction time of 80–100 min. The extraction temperature is preferably 65–70℃. Combine the extracts and filter to remove residue. Controlling the vacuum degree at -0.06 to -0.08 MPa effectively lowers the boiling point of the extraction system and keeps the extraction temperature at 60–75℃, avoiding degradation of heat-sensitive components caused by high temperatures. Filtration removes only uncrushed solid impurities, without membrane separation or protein removal, thus preserving all active ingredients in the extract. This aligns with the traditional Chinese medicine concept of whole-component tonification, while avoiding the loss of small molecule active substances due to membrane separation and the loss of polysaccharides and glycosides due to protein removal.

[0013] S7. Post-fermentation with probiotics: Food-grade compound probiotic powder is added to the extract from step S6). The compound probiotic powder is a complex system of Lactobacillus plantarum, Lactobacillus acidophilus, and Bifidobacterium, with a mass ratio of 3:2:1 and a viable count ≥1×10⁻⁶. 9The concentration of CFU / g is 0.1%–0.3% (w / w). Fermentation is carried out at 34–38℃ for 6–24 hours, with a preferred fermentation time of 10–16 hours. After fermentation, the probiotics are inactivated at 85–95℃ for 10–15 minutes, with a preferred inactivation temperature of 88–92℃ and an inactivation time of 12–14 minutes. Placing the fermentation step after extraction (post-fermentation) effectively avoids killing probiotics during the high-temperature extraction process. The metabolic activity of probiotics can convert large-molecule polysaccharides into smaller-molecule polysaccharides or oligosaccharides that are more easily absorbed by the human body, and convert citronellol and rehmannia glycoside D into more bioactive secondary glycosides. At the same time, it reduces the greasiness of the nine-steamed and nine-dried rehmannia pulp and improves the product's flavor and bioavailability. The inactivation treatment after fermentation can terminate the fermentation process, avoid changes in composition caused by the continuous metabolism of probiotics, and ensure the safety of the product for consumption.

[0014] S8. Low-temperature vacuum concentration: The material inactivated in step S7) is concentrated under reduced pressure at 55–65℃ and a vacuum degree ≤-0.09MPa until the relative density is 1.32–1.40 and the solid content is 60%–68% at 25℃, thus obtaining a high-content, nine-steamed and nine-dried Rehmannia glutinosa pulp. The low-temperature concentration conditions of 55–65℃ can effectively avoid the degradation of active ingredients and the excessive formation of 5-hydroxymethylfurfural caused by high temperature; the vacuum degree ≤-0.09MPa can accelerate the concentration speed and reduce the concentration energy consumption; controlling the relative density and solid content within the above range can ensure the high concentration and good stability of the nine-steamed and nine-dried Rehmannia glutinosa pulp, while facilitating subsequent filling, storage and consumption.

[0015] Using the above technical solution, the specific functions of the main raw materials in this invention are as follows: 1) Nine-Steamed and Nine-Sun-Dried Rehmannia Root: The core raw material of this invention is authentic Huai Rehmannia root, processed using the traditional nine-steaming and nine-sun-drying method. During the processing, the catalpol in the raw Rehmannia root is converted into more easily absorbed secondary glycosides, significantly increasing the polysaccharide content. Simultaneously, a large amount of melanoidins with antioxidant activity are generated, endowing the product with the core effects of nourishing blood and yin, and replenishing essence and marrow. The moisture content is controlled at 18%–24%, ensuring both the viscosity and softness of the raw material for subsequent wet pulping operations, while avoiding spoilage and decreased extraction efficiency due to excessive moisture.

[0016] 2) Compound Enzyme Preparation: This preparation is composed of cellulase, pectinase, and glucanase in a mass ratio of 2:1:1. Cellulase specifically degrades the cellulose skeleton components in plant cell walls, disrupting the basic cell structure; pectinase efficiently degrades pectin-like binding substances in the intercellular layer, loosening intercellular connections and facilitating cell separation; glucanase helps degrade the glucan-like gum barrier surrounding polysaccharides in Rehmannia glutinosa, reducing resistance to the dissolution of active ingredients into the extract. The synergistic effect of these three enzymes achieves biological cell wall disruption under mild conditions, laying the foundation for the full dissolution of subsequent active ingredients.

[0017] 3) Compound Probiotic Powder: Composed of *Lactobacillus plantarum*, *Lactobacillus acidophilus*, and *Bifidobacterium* in a mass ratio of 3:2:1. *Lactobacillus plantarum* can metabolize and produce organic acids such as lactic acid and acetic acid, lowering the pH value of the system, inhibiting the growth and reproduction of miscellaneous bacteria, and improving the flavor of the product; *Lactobacillus acidophilus* can decompose the large molecular sugars in Rehmannia glutinosa into small molecular monosaccharides and oligosaccharides, improving the palatability of the product; *Bifidobacterium* is a beneficial bacterium in the human gut, which can regulate the balance of intestinal flora and enhance the probiotic effects of the product. The three work together to metabolize, converting large molecular polysaccharides into small molecular polysaccharides or oligosaccharides that are more easily absorbed by the human body, and converting citronellol and rehmannia glycoside D into more bioactive secondary glycosides, while reducing the greasy feeling of the nine-steamed and nine-dried Rehmannia glutinosa pulp, significantly improving the bioavailability of the product.

[0018] 4) Purified water: used as an extraction solvent to dissolve the water-soluble active ingredients in Rehmannia glutinosa, while providing a suitable liquid environment for enzymatic hydrolysis and probiotic fermentation.

[0019] In summary, this invention, through a complete process of "wet pulping, enzymatic hydrolysis → ultrasound → microwave three-stage progressive cell wall disruption + vacuum low-temperature extraction, post-probiotic fermentation and low-temperature concentration," systematically optimizes the characteristics of nine-steamed and nine-dried Rehmannia glutinosa, achieving the following significant and quantifiable technical effects: (1) Thoroughly solve common pain points in the industry and achieve cell-level gentle fragmentation. By employing wet pulping instead of the traditional dry pulverization process, the problems of sticking to the machine and charring that occur when pulverizing dried Rehmannia glutinosa (which is typically processed through nine steaming and sun-drying processes) are fundamentally avoided. Simultaneously, it achieves gentle cell-level fragmentation. Compared to the traditional whole-block direct extraction process, the extraction rate of effective components is nearly doubled; compared to the dry pulverization process, it completely eliminates the destruction of active ingredients caused by high-temperature charring, laying the foundation for subsequent full component retention.

[0020] (2) The first three-stage progressive cell wall breaking process significantly improves the extraction rate of effective ingredients. Strictly following the sequence of "enzymatic hydrolysis → ultrasound → microwave," a progressive disruption system of "biological cell wall disruption - physical tearing - low-temperature solubilization" is formed: pre-enzymatic hydrolysis allows the enzyme preparation to precisely target intact cell walls, avoiding cell debris generated by ultrasound from encapsulating the enzyme preparation and maximizing the efficiency of enzymatic hydrolysis; ultrasound physically tears the cell tissue loosened by enzymatic hydrolysis through cavitation effect, further breaking down the dissolution barrier of components; microwaves accelerate the dissolution of exposed active ingredients into the extract through a gentle thermal effect.

[0021] Compared to the traditional unreasonable "ultrasound → enzymatic hydrolysis" crushing sequence, the extraction rate of Rehmannia glutinosa polysaccharides in this invention is increased by 8% to 15%, and the total retention rate of catalpol and rehmannia glutinosa D is increased by 5% to 10%. The cell wall breaking efficiency and component retention effect are significantly better than the existing technology.

[0022] (3) The entire process is carried out at low temperatures, and the principle of full ingredient retention is combined to maximize the retention of active ingredients. A mild extraction system with a total temperature of ≤75℃ was constructed, combining low-temperature ultrasound, intermittent microwave, vacuum low-temperature extraction, and low-temperature concentration processes to effectively avoid high-temperature degradation of heat-sensitive active ingredients such as catalpol, rehmannia glycoside D, polysaccharides, and melanoidins. At the same time, adhering to the technical concept of "full component retention," no membrane separation, no protein removal, and no purification of individual components were performed, thus completely preserving all active ingredients in the nine-steamed and nine-dried Rehmannia root, conforming to the traditional Chinese medicine concept of "principal, assistant, adjuvant, and guide, synergistic effect" for comprehensive nourishment.

[0023] The product of this invention has a polysaccharide extraction rate of 90% to 96%, which is more than 20% higher than that of the traditional process (39% to 58%); the total retention rate of catalpol and rehmannia glycoside D is ≥65%, which is more than 25% higher than that of the traditional process (30% to 60%); and the melanoidin content is 4.5 to 7.5 mg / g, which is more than 30% higher than that of the traditional process (3 to 5 mg / g).

[0024] (4) Significantly improve product quality and food safety The post-fermentation process with probiotics not only transforms large-molecule active ingredients into smaller, more easily absorbed forms, improving the product's bioavailability, but also reduces the rich, creamy texture of the Rehmannia glutinosa paste and enhances the product's flavor. Simultaneously, the low-temperature process throughout effectively inhibits the excessive formation of the Maillard reaction byproduct 5-hydroxymethylfurfural (5-HMF), controlling its content at 0.40–0.50 mg / g, an average reduction of over 25% compared to the traditional process (0.48–0.72 mg / g), significantly improving the product's safety for consumption.

[0025] (5) Significantly enhances the in vitro antioxidant activity of the product This invention utilizes a full-component retention process to completely preserve the natural antioxidant active substances such as polysaccharides and melanoidins in Rehmannia glutinosa. Combined with the synergistic effect of probiotic fermentation on the conversion of active ingredients, the in vitro antioxidant activity of the product is significantly enhanced. The finished product achieves a DPPH free radical scavenging rate of 86%–93%, an average increase of over 13% compared to traditional processes (60%–80%), demonstrating excellent antioxidant performance.

[0026] (6) The process is simple and controllable, and is suitable for large-scale industrial production. The process steps of this invention are simple, all parameters are quantifiable and traceable, and no complex purification equipment is required, which reduces production costs. At the same time, the process conditions are mild and the equipment requirements are low. It can be directly connected to existing food processing production lines, making it suitable for large-scale industrial production and having significant industrial application value. Detailed Implementation

[0027] The present invention will be further described in detail below with reference to specific embodiments. These embodiments are for illustrative purposes only and are not intended to limit the scope of protection of the present invention. The scope of protection of the present invention is defined by the claims. Any modifications, equivalent substitutions, etc., made based on the technical solutions of the present invention should fall within the scope of protection of the present invention. Example 1

[0028] A method for preparing a nine-steamed and nine-dried Rehmannia glutinosa pulp with high retention of all its components, the specific steps of which are as follows: S1. Raw material selection: The raw material is prepared by steaming and drying Rehmannia glutinosa nine times, and is black inside and out, soft and sticky in texture, slightly bitter, sweet and sour in taste, and has a moisture content of 20%. S2. Wet pulping: Take 100g of the above-mentioned prepared Rehmannia glutinosa, add 400mL of purified water (material-liquid ratio 1:4, g:mL), and use a high-speed shear pulper to pulp at a speed of 24000r / min for 7min to make a fine prepared Rehmannia glutinosa pulp with a particle size ≤100μm. S3. Pre-enzymatic hydrolysis: Add 0.18% (w / w) of a compound enzyme preparation (cellulase, pectinase, and dextranase in a mass ratio of 2:1:1, cellulase activity 12000 U / g, pectinase activity 9000 U / g, and dextranase activity 6000 U / g) to the prepared Rehmannia glutinosa pulp, adjust the pH of the system to 5.8, and enzymatically hydrolyze for 75 min at 40℃; S4. Low-temperature ultrasonic treatment: The enzymatically hydrolyzed pulp was placed under conditions of 38℃, 45kHz, and 450W and ultrasonically treated for 5 minutes. S5. Intermittent microwave treatment: The ultrasonically treated slurry was placed under 700W power and treated for a total of 90 seconds by working for 20 seconds and then intermittently for 10 seconds. S6. Vacuum low-temperature extraction: The pretreated pulp is transferred to a vacuum reflux device and extracted once at a vacuum of -0.07MPa and 68℃ for 90 minutes. The extracts are combined and filtered to remove residue. S7. Post-fermentation with probiotics: Inoculate the extract with 0.2% (w / w) of compound probiotic powder (Lactobacillus plantarum, Lactobacillus acidophilus, and Bifidobacterium in a mass ratio of 3:2:1, with a live count of 1.2 × 10⁻⁶). 9 The mixture was fermented at 36℃ for 13 hours (CFU / g) and then inactivated at 90℃ for 13 minutes after fermentation. S8. Low-temperature vacuum concentration: The inactivated material is concentrated under reduced pressure at 60℃ and a vacuum degree of -0.095MPa until the relative density is 1.36 and the solid content is 64% at 25℃, which yields the finished product.

[0029] The finished product indicators were as follows: Rehmannia polysaccharide extraction rate 93%, total retention rate of catalpol and rehmannia glycoside D 68%, melanoidin content 6.2 mg / g, and DPPH free radical scavenging rate 89%. Example 2

[0030] This embodiment is basically the same as Embodiment 1, except that some process parameters are different, as detailed below: S1. Raw material selection: Rehmannia glutinosa with a moisture content of 18%; S2. Wet pulping: material-to-liquid ratio 1:3 (g:mL), high-speed shear pulper speed 20000r / min, pulping time 10min; S3. Pre-enzymatic hydrolysis: The amount of compound enzyme preparation added is 0.10% (w / w), with cellulase activity of 10000 U / g, pectinase activity of 8000 U / g, and dextranase activity of 5000 U / g. The pH of the system is adjusted to 5.0, and enzymatic hydrolysis is carried out at 45℃ for 120 min. S4. Low-temperature ultrasonic treatment: Ultrasonic treatment for 8 minutes at 35℃, 30kHz, and 300W. S5. Intermittent microwave processing: 600W power, cumulative processing time 60s; S6. Vacuum low-temperature extraction: Extraction was performed twice under vacuum conditions of -0.06 MPa and 60°C, with each extraction lasting 60 min. S7. Post-fermentation with probiotics: 0.1% (w / w) of compound probiotic powder, with a live count of 1.0 × 10⁻⁶. 9 CFU / g, fermented at 34℃ for 24h, then inactivated at 85℃ for 15min; S8. Low-temperature vacuum concentration: Concentrate under reduced pressure at 55℃ and a vacuum degree of -0.09MPa until the relative density is 1.32 and the solid content is 60% at 25℃.

[0031] The finished product indicators were as follows: Rehmannia polysaccharide extraction rate 90%, total retention rate of catalpol and rehmannia glycoside D 65%, melanoidin content 4.5 mg / g, and DPPH free radical scavenging rate 86%. Example 3

[0032] This embodiment is basically the same as Embodiment 1, except that some process parameters are different, as detailed below: S1. Raw material selection: Rehmannia glutinosa with a moisture content of 24%; S2. Wet pulping: material-to-liquid ratio 1:6 (g:mL), high-speed shear pulper speed 28000r / min, pulping time 5min; S3. Pre-enzymatic hydrolysis: The amount of compound enzyme preparation added is 0.25% (w / w), with cellulase activity of 15000 U / g, pectinase activity of 10000 U / g, and dextranase activity of 8000 U / g. The pH of the system is adjusted to 6.5, and enzymatic hydrolysis is carried out at 45℃ for 40 min. S4. Low-temperature ultrasonic treatment: Ultrasonic treatment for 3 minutes at 40℃, 50kHz, and 600W. S5. Intermittent microwave processing: 800W power, cumulative processing time 120s; S6. Vacuum low-temperature extraction: Extract once under vacuum of -0.08MPa and 75℃ for 120 min; S7. Post-fermentation with probiotics: 0.3% (w / w) of compound probiotic powder, with a live count of 1.5 × 10⁻⁶. 9 CFU / g, fermented at 38℃ for 6 hours, then inactivated at 95℃ for 10 minutes; S8. Low-temperature vacuum concentration: Concentration under reduced pressure at 65℃ and a vacuum degree of -0.10MPa, the relative density is 1.40 and the solid content is 68% when concentrated to 25℃.

[0033] The finished product indicators were as follows: Rehmannia polysaccharide extraction rate 96%, total retention rate of catalpol and rehmannia glycoside D 72%, melanoidin content 7.5 mg / g, and DPPH free radical scavenging rate 93%.

[0034] Comparative Example 1 (Traditional dry grinding + high-temperature cooking process) The same nine-steamed and nine-dried Rehmannia glutinosa as in Example 1 was selected. Dry pulverization was used (dry pulverization was attempted, but obvious sticking and charring occurred, and the pulverized particles were not uniform). 100g of pulverized Rehmannia glutinosa was added to 400mL of purified water and decocted at 100℃ for 2 hours. The residue was removed by filtration and the concentration was increased to a relative density of 1.36 and a solid content of 64% at 25℃ to obtain Rehmannia glutinosa pulp processed by traditional method.

[0035] The finished product indicators were as follows: Rehmannia polysaccharide extraction rate 52%, total retention rate of catalpol and rehmannia glycoside D 38%, melanoidin content 3.1 mg / g, 5-hydroxymethylfurfural content 0.72 mg / g, and DPPH free radical scavenging rate 68%.

[0036] Comparative Example 2 (Ultrasonic → Enzymatic Disintegration Process) Except for changing the crushing order to "ultrasound → enzymatic hydrolysis → microwave", the other steps are completely the same as in Example 1. Specifically, after S2 wet pulping, low-temperature ultrasonic treatment is performed first (same as in Example 1), then pre-compound enzymatic hydrolysis is performed (same as in Example 1), and finally intermittent microwave treatment is performed (same as in Example 1). Subsequent steps remain unchanged.

[0037] The finished product indicators were as follows: Rehmannia polysaccharide extraction rate 85%, total retention rate of catalpol and rehmannia glycoside D 62%, melanoidin content 5.7 mg / g, 5-hydroxymethylfurfural content 0.48 mg / g, and DPPH free radical scavenging rate 83%.

[0038] Product performance testing and result comparison The performance testing of this product used Rehmannia glutinosa pulp prepared by the traditional dry pulverization + high-temperature decoction process (Comparative Example 1) and the ultrasonic → enzymatic hydrolysis crushing process (Comparative Example 2) as controls. Combined with the test data of Examples 1-3 of this invention, the determination methods of various indicators, specific test results and results are discussed below to clarify the advanced nature of the process of this invention.

[0039] Extraction rate of Rehmannia glutinosa polysaccharides Content determination method: The phenol-sulfuric acid colorimetric method was used, with a wavelength of 490 nm. A standard curve was plotted with glucose as a reference, and the polysaccharide extraction rate was calculated.

[0040] Test results: The extraction rate of Rehmannia glutinosa polysaccharide in Example 1 of this invention was 93%, in Example 2 it was 90%, and in Example 3 it was 96%; the extraction rate in Comparative Example 1 (traditional process) was 52%, and the extraction rate in Comparative Example 2 (unreasonable crushing order) was 85%.

[0041] Results and Discussion: This invention employs a three-stage progressive cell-wall breaking process—enzymatic hydrolysis, ultrasonication, and microwave stimulation—in conjunction with wet pulping, to completely break down the dense cell structure and colloidal barrier of Rehmannia glutinosa, significantly improving polysaccharide dissolution efficiency. The extraction rate is 38%–44% higher than Comparative Example 1 and 5%–11% higher than Comparative Example 2. Furthermore, the entire process is performed at low temperatures, preventing polysaccharide structural degradation and preserving the complete tonic activity of the polysaccharides. Comparative Example 1, on the other hand, suffers from dry pulverization leading to sticking to the machine, caramelization, and high-temperature decoction, resulting in extremely low polysaccharide extraction rates. Comparative Example 2, with its unreasonable crushing sequence, exhibits cell debris generated after ultrasonication that encapsulates the enzyme preparation, reducing enzymatic hydrolysis efficiency and resulting in a lower extraction rate than this invention.

[0042] Total retention rate of catalpol and rehmannia glycoside D Content determination method: High performance liquid chromatography (HPLC) was used with a C18 column, acetonitrile-0.1% phosphoric acid solution as the mobile phase, and a detection wavelength of 210 nm. The content and total retention rate were calculated by external standard method.

[0043] Test results: The total retention rate of catalpol and rehmannia glycoside D in Example 1 of this invention was 68%, in Example 2 it was 65%, and in Example 3 it was 72%; the total retention rate in Comparative Example 1 was 38%, and in Comparative Example 2 it was 62%.

[0044] Results and Discussion: Catalpol and Rehmannia glutinosa D are heat-sensitive active ingredients. The low-temperature and mild process throughout the entire process of this invention effectively reduces the loss of active ingredients. In Comparative Example 1, high-temperature decoction led to a large amount of degradation of the two types of components, resulting in a significantly lower total retention rate. In Comparative Example 2, the unreasonable crushing sequence reduced the enzymatic hydrolysis efficiency, resulting in a lower component retention rate than that of this invention. The total retention rate of this invention is 27%–34% higher than that of Comparative Example 1 and 3%–10% higher than that of Comparative Example 2.

[0045] melanoidin content Content determination method: Ultraviolet spectrophotometry was used with a detection wavelength of 280 nm. A standard curve was plotted using melanoidin standards, and the content was calculated.

[0046] Test results: The content of melanin in Example 1 of this invention is 6.2 mg / g, in Example 2 it is 4.5 mg / g, and in Example 3 it is 7.5 mg / g; the content in Comparative Example 1 is 3.1 mg / g, and the content in Comparative Example 2 is 5.7 mg / g.

[0047] Results and Discussion: Melanoids are the core active and antioxidant components of Rehmannia glutinosa, which is processed through nine steaming and nine sun-drying processes. The low-temperature extraction process of this invention can avoid its high-temperature decomposition, and the three-stage cell wall breaking promotes its full dissolution. In Comparative Example 1, high-temperature decoction led to the decomposition of melanoidins, resulting in a lower content. In Comparative Example 2, the enzymatic hydrolysis efficiency was insufficient, and the melanoidins were not fully dissolved, resulting in a lower content than that of this invention. The melanoidin content of this invention is 45.2%–141.9% higher than that of Comparative Example 1 and 8.8%–31.6% higher than that of Comparative Example 2.

[0048] 5-Hydroxymethylfurfural (5-HMF) content Content determination method: High performance liquid chromatography (HPLC) was used with a C18 column, methanol-water mobile phase, detection wavelength of 284 nm, and the content was calculated by external standard method.

[0049] Test results: The 5-HMF content in Example 1 of this invention is 0.45 mg / g, in Example 2 it is 0.40 mg / g, and in Example 3 it is 0.50 mg / g; the content in Comparative Example 1 is 0.72 mg / g; and the content in Comparative Example 2 is 0.48 mg / g.

[0050] Results and Discussion: 5-HMF is a byproduct of the Maillard reaction, and its excessive presence affects the safety of the product for consumption. The low-temperature process throughout the present invention can effectively inhibit its excessive formation and control its content within a safe and compliant range. In Comparative Example 1, high-temperature cooking accelerates the Maillard reaction, resulting in excessively high 5-HMF content and insufficient safety. Although Comparative Example 2 uses a low-temperature process, the unreasonable crushing sequence leads to a decrease in extraction efficiency, requiring an extended processing time and a slight increase in the amount of 5-HMF generated, which is slightly higher than the optimal embodiment of the present invention.

[0051] DPPH free radical scavenging rate Content determination method: DPPH free radical scavenging method was used, with a detection wavelength of 517nm, and the free radical scavenging rate was calculated.

[0052] Test results: The DPPH free radical scavenging rate of Example 1 was 89%, Example 2 was 86%, and Example 3 was 93%; the scavenging rate of Comparative Example 1 was 68%, and the scavenging rate of Comparative Example 2 was 83%.

[0053] Results and Discussion: The whole-component retention process of this invention completely preserves antioxidant active substances such as polysaccharides and melanoidins, and the combination with probiotic fermentation further enhances antioxidant activity; Comparative Example 1 suffered severe loss of active ingredients and had weak antioxidant capacity; Comparative Example 2 had insufficient enzymatic hydrolysis efficiency and insufficient dissolution of active ingredients, and its antioxidant capacity was lower than that of this invention. The free radical scavenging capacity of this invention is 17% to 25% higher than that of Comparative Example 1 and 3% to 10% higher than that of Comparative Example 2, demonstrating excellent antioxidant performance.

[0054] The results of the comparison of various indicators are summarized in Table 1.

[0055] Table 1 Comparison of performance indicators of Rehmannia glutinosa pulp prepared by different processes

[0056] Final conclusion The present invention provides a method for preparing Rehmannia glutinosa pulp with high retention of all its components through nine steaming and nine sun-drying processes. This method completely solves the industry pain point that candied Rehmannia glutinosa cannot be dry-pulverized, and achieves efficient retention of all its components. Compared with traditional processes and unreasonable crushing sequence processes, the core indicators of the finished product are significantly improved. The process is mild and controllable, suitable for large-scale industrial production, and can be used for the large-scale preparation of high-end Rehmannia glutinosa tonic pulp, with significant industrial application value.

Claims

1. A method for preparing a nine-steamed and nine-dried Rehmannia glutinosa pulp with high retention of all its components, characterized in that, Includes the following steps: S1. Raw material selection: Prepared Rehmannia glutinosa, processed through nine steaming and nine sun-drying processes, is selected as the raw material. S2. Wet pulping: Mix Rehmannia glutinosa with purified water and then wet crush to produce Rehmannia glutinosa pulp. S3. Pre-enzymatic hydrolysis: Add a compound enzyme preparation containing cellulase, pectinase and glucanase to the prepared Rehmannia glutinosa pulp for enzymatic hydrolysis. S4. Low-temperature ultrasonic treatment: The enzymatically hydrolyzed Rehmannia glutinosa pulp is subjected to low-temperature ultrasonic treatment. S5. Vacuum low-temperature extraction: intermittent microwave treatment: the ultrasonically treated Rehmannia glutinosa pulp is subjected to intermittent microwave treatment; S6. Vacuum low-temperature extraction of the microwave-treated Rehmannia glutinosa pulp, combined with the extracts and filtered to remove residue; S7. Post-fermentation: Food-grade compound probiotic powder containing Lactobacillus plantarum, Lactobacillus acidophilus and Bifidobacterium is added to the extract for fermentation, and then inactivated after fermentation. S8. Low-temperature concentration: The inactivated material is concentrated under low-temperature vacuum to obtain the finished product; Furthermore, the method does not involve membrane separation, protein removal, or purification of any single component throughout the entire process.

2. The method for preparing Rehmannia glutinosa pulp after nine steaming and nine sun-drying according to claim 1, characterized in that, The prepared Rehmannia root described in step S1 is black inside and out, soft and sticky in texture, slightly bitter, sweet and sour in taste, and has a moisture content of 18% to 24%.

3. The method for preparing Rehmannia glutinosa pulp by nine steaming and nine sun-drying according to claim 1, characterized in that, In step S2, the ratio of prepared Rehmannia glutinosa to purified water is 1:3 to 1:6 (g:mL); the wet crushing is carried out using a high-speed shear pulper with a rotation speed of 20,000 to 28,000 r / min and a pulping time of 5 to 10 min, and the particle size of the prepared Rehmannia glutinosa pulp is ≤100μm.

4. The method for preparing Rehmannia glutinosa pulp after nine steaming and nine sun-drying according to claim 1, characterized in that, In step S3, the amount of the compound enzyme preparation added is 0.10% to 0.25% (w / w), the pH of the system is adjusted to 5.0 to 6.5, and enzymatic hydrolysis is carried out at 35 to 45°C for 40 to 120 minutes; the mass ratio of cellulase, pectinase and dextranase in the compound enzyme preparation is 2:1:1, wherein the cellulase activity is ≥10000 U / g, the pectinase activity is ≥8000 U / g, and the dextranase activity is ≥5000 U / g.

5. The method for preparing Rehmannia glutinosa pulp by nine steaming and nine sun-drying according to claim 1, characterized in that, The conditions for the low-temperature ultrasonic treatment in step S4 are: temperature 35-40℃, frequency 30-50kHz, power 300-600W, and treatment time 3-8min.

6. The method for preparing Rehmannia glutinosa pulp by nine steaming and nine sun-drying according to claim 1, characterized in that, The conditions for intermittent microwave processing in step S5 are: power 600-800W, working time 20s, intermittent time 10s, and cumulative processing time 60-120s.

7. The method for preparing Rehmannia glutinosa pulp after nine steaming and nine sun-drying according to claim 1, characterized in that, The vacuum low-temperature extraction described in step S6 is carried out in a vacuum reflux apparatus with a vacuum degree of -0.06 to -0.08 MPa and a temperature of 60 to 75°C. The extraction is performed 1 to 2 times, with a total extraction time of 60 to 120 minutes.

8. The method for preparing Rehmannia glutinosa pulp by nine steaming and nine sun-drying according to claim 1, characterized in that, The amount of compound probiotic powder added in step S7 is 0.1% to 0.3% (w / w), fermented at 34 to 38°C for 6 to 24 hours, and then inactivated at 85 to 95°C for 10 to 15 minutes after fermentation; the mass ratio of Lactobacillus plantarum, Lactobacillus acidophilus, and Bifidobacterium in the compound probiotic powder is 3:2:1, and the viable count is ≥1×10⁻⁶. 9 CFU / g; The conditions for low-temperature vacuum concentration in step S8 are: temperature 55~65℃, vacuum degree ≤-0.09MPa, relative density of 1.32~1.40 and solid content of 60%~68% when concentrated to 25℃.

9. The method for preparing Rehmannia glutinosa paste by nine steaming and nine sun-drying according to claim 1, characterized in that, In step S3, the enzymatic hydrolysis time is 60–90 min; in step S4, the low-temperature ultrasonic treatment conditions are 38–40℃, 40–50 kHz, power 400–500 W, and treatment time is 4–6 min; in step S5, the cumulative treatment time of intermittent microwave treatment is 80–100 s; in step S6, the vacuum low-temperature extraction is performed once, with an extraction time of 80–100 min and an extraction temperature of 65–70℃; in step S7, the fermentation time is 10–16 h, and the inactivation conditions are 88–92℃ for 12–14 min; in step S8, when concentrated to 25℃, the relative density is 1.34–1.38, and the solid content is 62%–66%.

10. A high-quality, nine-steamed and nine-dried Rehmannia glutinosa paste with high retention of all its components, characterized in that... It is prepared by the method of preparing Rehmannia glutinosa pulp by nine steaming and nine sun-drying as described in any one of claims 1 to 9.

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