Preparation method of sweet tea instant powder rich in ellagic acid and use thereof

Abstract

The application discloses a preparation method and application of instant sweet tea powder rich in ellagic acid, and comprises the following steps: extraction: crushing dry leaves of sweet tea, stirring and extracting more than three times at room temperature with pure water, and combining the extract; flocculation: adding an organic polymer flocculating agent into the extract, dissolving, stirring, standing, filtering, and obtaining a flocculation liquid; nanofiltration: filtering the flocculation liquid with a nanofiltration membrane, and collecting nanofiltration membrane retentate; impurity removal: adding an adsorbent into the nanofiltration membrane retentate, heating, stirring, filtering, and obtaining an impurity removal liquid; ultrafiltration: filtering the impurity removal liquid with an ultrafiltration membrane, and collecting ultrafiltration membrane permeate; concentration and drying: reducing pressure to concentrate the ultrafiltration membrane permeate, drying, crushing, and obtaining instant sweet tea powder with flavor. The instant sweet tea powder prepared according to the method has obviously improved solubility of ellagic acid in an aqueous solution, can be compounded with a natural sweetener or a synthetic sweetener into a composite sweetener, or be used in food, medicine, condiment, health care product, cosmetic, and essence and flavor.

Description

Technical Field

[0001] This invention relates to the field of plant active ingredient extraction, specifically to a method for extracting catechins and ellagic acid from dried sweet tea leaves, and more specifically to a method for preparing instant sweet tea powder rich in ellagic acid. Background Technology

[0002] Sweet tea (Rubus suavissimu S.Lee), also known as sweet-leaved raspberry, is a perennial deciduous thorny shrub belonging to the genus Rubus in the Rosaceae family. It is mainly distributed in the hilly areas of southern my country, primarily produced in Liuzhou, Guilin, and Wuzhou. It is a rare and precious wild sweet-tasting plant unique to Guangxi, and along with monk fruit and stevia, it is considered one of the three major sweet-tasting plants of Guangxi. Its leaves can be used in medicine and tea. Sweet tea typically grows at altitudes of 500-1000 meters, preferring sunny locations but also tolerating shade, and is highly adaptable. Sweet tea is cool in nature, sweet and neutral in taste, and has the effects of clearing heat, moistening the lungs, resolving phlegm, and relieving cough. Due to its sweet leaves and health benefits, it is commonly consumed as tea in Guangxi, hence the name "sweet tea," also known as "divine tea." Since the 1970s, research has been conducted on sweet tea both domestically and internationally. It has been found that sweet tea is a non-sugar natural sweet plant with high sweetness and low calories. The rubusoside contained in sweet tea leaves has the effects of lowering blood pressure and blood sugar, and can also promote metabolism and treat hyperacidity.

[0003] CN107979977A discloses a sweet tea extract and its uses, which involves using sweet tea as raw material, and then proceeding through steps such as water or solvent extraction, acid adjustment, activated carbon treatment, centrifugation, filtration, concentration, and sterilization to obtain a dried powder. It also discloses a method for manufacturing fermented foods using the sweet tea extract. However, if organic solvents are used in this method, the leaching of water-soluble components will be significantly reduced, resulting in a low extraction rate of the natural active ingredients in the sweet tea. Furthermore, the addition of acidic components will severely affect the flavor of the product.

[0004] CN101069533A discloses a natural sugar-free sweet tea beverage and its preparation method. The method uses fresh sweet tea leaves as raw material, and involves high-temperature fixation, hot water extraction, filtration, and sterilization to obtain the natural sugar-free sweet tea beverage. However, this method does not specifically remove the bitter and astringent components of the sweet tea, resulting in inherent flavor defects. Furthermore, the obtained product is a liquid, making it inconvenient for storage and transportation.

[0005] CN101990968A discloses a sugar-free sweet tea beverage and its preparation method. The method uses sweet tea as a raw material, adds papain, and proceeds through steps such as decoction, microporous membrane filtration, high-temperature sterilization, and bottling to obtain the sugar-free sweet tea beverage. However, this method does not specifically remove the bitter and astringent components of the sweet tea, resulting in inherent flavor defects; the obtained product is a liquid, making it inconvenient to store and transport.

[0006] Sweet tea contains ellagic acid, a polyphenolic dilactone and a dimer derivative of gallic acid. Studies have shown that ellagic acid possesses various biological activities, such as antioxidant, anticancer, antimutagenic properties, and inhibitory effects against human immunodeficiency virus (HIV). In addition, ellagic acid is an effective hemostatic agent, exhibiting good inhibitory effects against various bacteria and viruses, protecting wounds from bacterial invasion, preventing infection, and inhibiting ulceration. Ellagic acid also has hypotensive and sedative effects. Historically, research on sweet tea has focused on sucralose glycosides, with little reporting on ellagic acid. In production practice, the focus has often been solely on the extraction of sucralose glycosides. Furthermore, due to the high degradation rate of ellagic acid in traditional production processes, it is often treated as waste, resulting in significant resource waste.

[0007] The article "Current Status of Research on Physiological Functions and Technological Development of Ellagic Acid" (Natural Product Research and Development, Vol. 13, No. 5, pp. 71-73) describes the synthesis and application of ellagic acid. It suggests that the absorption of ellagic acid from food in the body is limited. For example, oral administration of ellagic acid to mice revealed only a small amount being absorbed, preventing the body tissues from reaching sufficiently high concentrations and thus hindering its effective role as an in vivo anticancer agent. In other words, ellagic acid has poor water and lipid solubility, making it difficult for the human body to absorb and utilize. Therefore, there is an urgent need to develop a method for fully utilizing the active components of sweet tea, especially ellagic acid. Summary of the Invention

[0008] The technical problem to be solved by the present invention is to overcome the above-mentioned defects of the prior art and provide a flavored sweet tea instant powder with high extraction rate of water-soluble components (sweet tea glycosides, ellagic acid) from dried sweet tea leaves, which retains the good flavor of sweet tea itself, has good solubility, no metallic taste, bitter taste, or Chinese medicine taste, low production cost, simple process, safety, environmental protection and no pollution, and is suitable for industrial production, as well as its preparation method.

[0009] The technical solution adopted by this invention to solve its technical problem is as follows: A method for preparing sweet tea instant powder rich in ellagic acid, comprising the following steps:

[0010] (7) Extraction: Crush the dried sweet tea leaves and extract them three or more times with pure water at room temperature, and combine the extracts.

[0011] (8) Flocculation: Add organic polymer flocculant to the extract, dissolve, stir, let stand, filter by plate and frame to obtain flocculent liquid;

[0012] (9) Nanofiltration: Filter the flocculant with a nanofiltration membrane and collect the nanofiltration membrane retentate;

[0013] (10) Impurity removal: Add adsorbent to nanofiltration membrane retentate, heat, keep warm and stir, filter to obtain impurity removed solution;

[0014] (11) Ultrafiltration: Filter the impurity-removed liquid with an ultrafiltration membrane and collect the permeate from the ultrafiltration membrane;

[0015] (12) Concentration and drying: The permeate from the ultrafiltration membrane is concentrated under reduced pressure, dried by microwave, and pulverized to obtain flavored sweet tea instant powder.

[0016] In the instant sweet tea powder prepared by the present invention, the content of ellagic acid is above 3 wt%, preferably above 4 wt%.

[0017] Ellagic acid is a phenolic acid with various physiological activities. Although ellagic acid is well-known, it is rarely noticed that sweet tea also contains it. Ellagic acid is highly unstable, easily decomposing and oxidizing at high temperatures, readily combining with metal ions to form complexes, and exhibiting extreme instability in alkaline environments. Traditional sweet tea production methods typically employ high-temperature extraction, high-temperature concentration, and metal salt flocculation, all of which degrade ellagic acid, making it difficult to preserve. This invention utilizes room-temperature extraction, organic flocculant flocculation, and low-temperature concentration and drying processes, effectively preventing ellagic acid degradation and significantly increasing its yield.

[0018] Preferably, in step (1), the amount of pure water used is 15 to 25 times the weight of the dried sweet tea leaves, more preferably 18 to 22 times, and the extraction time for each stirring is 2 to 5 hours. The extraction is performed three or more times, with the amount of pure water and extraction time decreasing sequentially each time, and the difference in the amount of pure water and extraction time for each time being 1 / 5 to 1 / 2. For example, taking three extractions as an example, the amount of pure water used is 8 to 10 times, 6 to 8 times, and 4 to 5 times the weight of the dried sweet tea leaves, respectively, and the stirring and extraction time is 4 to 5 hours, 3 to 4 hours, and 3 to 4 hours, respectively; if taking four extractions as an example, the amount of pure water used is 5 to 8 times, 4 to 6 times, 3 to 5 times, and 3 to 4 times the weight of the dried sweet tea leaves, respectively, and the stirring and extraction time is 4 to 5 hours, 3 to 4 hours, 3 to 4 hours, and 2 to 3 hours, respectively.

[0019] Room temperature extraction refers to extraction at a temperature of 20-30℃, preferably 23-26℃. The purpose of room temperature extraction is to fully extract the active ingredients while preserving the original flavor of sweet tea, and to prevent ellagic acid from being oxidized and decomposed by heat during the extraction process. If the amount of pure water used is too small, the stirring time is too short, or the number of extractions is too few, these objectives cannot be achieved.

[0020] Preferably, in step (2), the organic polymeric flocculant is chitosan, and the amount of chitosan used is 0.5-5 wt% of the weight of the dried sweet tea leaves, preferably 1-3 wt%. The function of adding flocculant is to coagulate and precipitate macromolecular substances such as proteins and tannins, as well as suspended matter, in the extract, and remove them after filtration. If the amount of flocculant used is too small, the above purpose will not be fully achieved; if the amount of flocculant used is too large, it will result in waste of materials.

[0021] The inventors also discovered that adding a certain amount of chitosan as a flocculant to the extract can not only remove excess proteins and other large molecules, but also effectively retain ellagic acid stably in the system, avoiding the instability and easy precipitation of ellagic acid, which leads to loss. However, the amount of chitosan used should not be too large, otherwise it will make subsequent post-processing difficult, and the yield of ellagic acid will certainly not be guaranteed.

[0022] Preferably, in step (3), the nanofiltration membrane has a molecular weight cutoff of 300–500 Da and a filtration pressure of 0.3–0.5 MPa. The purpose of using a nanofiltration membrane is twofold: first, to remove salt and minerals (derived from dried sweet tea leaves) from the flocculent liquid, thereby eliminating unpleasant tastes such as saltiness and metallic flavor in the product; second, to concentrate the material, reduce its volume, increase the probability of contact between the adsorbent and impurity molecules in subsequent steps, improve the adsorption effect, and reduce the amount of adsorbent used.

[0023] Through extensive experimental research, the inventors discovered that the organic polymer flocculant in step (2) has removed most of the impurities with larger molecular weights. At this point, only nanofiltration, adsorption, and ultrafiltration steps are needed to obtain a clear solution, which is convenient for subsequent drying and concentration.

[0024] Preferably, in step (4), the adsorbent is one or more of alumina, diatomaceous earth, activated clay, and activated carbon, and the amount of adsorbent used is 1-5 wt% of the weight of the dried sweet tea leaves. The purpose of adding the adsorbent is to adsorb pigments and impurities with unpleasant flavors (bitterness, herbal taste), such as flavonoids.

[0025] Preferably, in step (4), the heating temperature is 40-50°C, and the holding and stirring time is 1-2 hours. If the amount of adsorbent is too small, the heating temperature is too low, or the holding and stirring time is too short, the above purpose cannot be fully achieved; if the amount of adsorbent is too large, the heating temperature is too high, or the holding and stirring time is too long, it will result in waste of materials and energy.

[0026] Preferably, in step (5), the ultrafiltration membrane has a molecular weight cutoff of 2000–5000 Da and a filtration pressure of 0.1–0.3 MPa. The purpose of using an ultrafiltration membrane is to remove fine particles remaining in the impurity solution to improve the clarity of the product solution.

[0027] Preferably, in step (6), the temperature of the vacuum concentration is no more than 50°C, generally 40-50°C, the vacuum degree is -0.08 to -0.09 MPa, and the solid concentration of the concentrate is 20% to 40%.

[0028] Preferably, in step (6), the microwave drying temperature is 40–50°C, the microwave drying frequency is 2400–2500 MHz, and the drying time is 20–40 min. The purpose of using microwave drying is to dry the material quickly at a low temperature, preventing ellagic acid and sweet tea flavor components from decomposing at high temperatures during the drying process, thereby producing undesirable flavors such as burnt or bitter tastes.

[0029] The present invention also provides a sweet tea instant powder obtained by the above preparation method. The sweet tea instant powder is rich in ellagic acid, has good solubility, and its aqueous solution is clear and bright with a rich color. It has a mellow, full-bodied, slightly bitter taste with a sweet aftertaste.

[0030] Through testing, the inventors unexpectedly discovered that the concentration of ellagic acid in the saturated solution of the instant sweet tea powder prepared by this invention was above 0.13 g / 100 mL at 21 °C, while the solubility of ellagic acid at 21 °C was only 0.095 g / 100 mL. This indicates that the solubility of ellagic acid in the instant sweet tea powder prepared by this invention is significantly improved. The reason may be that some components in the instant powder have a certain encapsulation effect on ellagic acid, or that some components in the instant powder, after dissolving in water, change the polar environment of the instant powder solution, thus promoting the solubility or miscibility of ellagic acid.

[0031] The present invention also provides the use of the aforementioned sweet tea instant powder, which can be compounded with natural sweeteners or synthetic sweeteners to form novel sweeteners, or used in food, medicine, condiments, health products, cosmetics, and flavorings.

[0032] The beneficial effects of the method of the present invention are as follows:

[0033] I. Sweet tea leaves have a high extraction rate of water-soluble components (sweet tea glycosides, ellagic acid), resulting in good product solubility and low ash content. It does not use inorganic salt flocculants, macroporous resins or ion exchange resins, strong acids or alkalis, or organic solvents, leading to low production costs, simple processes, and safety, environmental friendliness, and no pollution.

[0034] Second, by adding a certain amount of chitosan as an organic polymer flocculant, not only can large molecules such as proteins be effectively removed, but ellagic acid can also be stabilized in the system and will not precipitate, thereby improving the yield of ellagic acid. This makes the instant powder obtained by the present invention have extremely high health, nutritional and economic value.

[0035] Third, the inventors also unexpectedly discovered that the solubility of ellagic acid in the instant sweet tea powder prepared by this invention is significantly improved, thereby increasing the bioavailability of ellagic acid and making it better absorbed and utilized by the human body.

[0036] Fourth, through the synergistic effect of each step, this invention removes the metallic, bitter, and medicinal tastes while retaining the good flavor of sweet tea. The product's flavor is similar to green tea, yet distinct from it, and can perfectly blend and complement various types of tea in terms of flavor. Detailed Implementation

[0037] The present invention will be further described below with reference to the embodiments.

[0038] The dried sweet tea leaves used in the embodiments of this invention were purchased from Guangxi, and contained 3.56% sweet tea glycosides and 1.12% ellagic acid. The ultrafiltration membrane and nanofiltration membrane used in this invention were purchased from Nanjing Fulinde Environmental Protection Technology Co., Ltd. Unless otherwise specified, the raw materials or chemical reagents used in the embodiments of this invention were obtained through conventional commercial channels.

[0039] In this embodiment of the invention, the contents of stevia glycosides and ellagic acid were determined by high performance liquid chromatography (HPLC) with external standard method.

[0040] The concentration of ellagic acid in the solution was determined by referring to the method in "Determination of Equilibrium Solubility and Oil-Water Partition Coefficient of Ellagic Acid, Active Component in Pomegranate Peel", Journal of Xinjiang Medical University, Vol. 39, No. 2, pp. 145-148. The absorbance of the solution at the maximum ultraviolet absorption wavelength of 254 nm was measured and compared with the standard curve to determine the content of ellagic acid in the solution.

[0041] Example 1

[0042] (1) Extraction: Take 10kg of dried sweet tea leaves, crush them, and extract them three times at room temperature with 100L, 80L and 50L of pure water respectively. The extraction time for each extraction is 5h, 3h and 3h respectively. Combine the three extracts.

[0043] (2) Flocculation: Add 0.2 kg of chitosan to the extract, dissolve, stir, let stand, filter by plate and frame to obtain flocculent liquid;

[0044] (3) Nanofiltration: The flocculant was filtered through a nanofiltration membrane with a molecular weight cutoff of 500 Da at a pressure of 0.3 MPa, and the nanofiltration membrane retentate was collected.

[0045] (4) Impurity removal: Add 0.4 kg of diatomaceous earth to the nanofiltration membrane retentate, heat to 40°C, keep warm and stir for 1.5 h, filter to obtain the impurity-removed solution;

[0046] (5) Ultrafiltration: The impurity-removed liquid is filtered through an ultrafiltration membrane with a molecular weight cutoff of 2000 Da at a pressure of 0.2 MPa, and the permeate from the ultrafiltration membrane is collected.

[0047] (6) Concentration and drying: The permeate from the ultrafiltration membrane was concentrated under reduced pressure at a temperature of 45℃ and a vacuum of -0.085MPa until the solid concentration was 25%. The concentrate was microwave-dried at a temperature of 50℃ and a microwave frequency of 2400MHz for 30 minutes, and then pulverized to obtain 2.52kg of flavored sweet tea instant powder.

[0048] According to the high performance liquid chromatography (HPLC) external standard method, the content of stevia glycosides in the flavored sweet tea instant powder obtained in this example was 13.32%, and the yield of stevia glycosides was 94.3%; the content of ellagic acid was 4.02%, and the yield of ellagic acid was 90.5%.

[0049] The flavored sweet tea instant powder obtained in this embodiment is a brownish-brown powder. The concentration of ellagic acid in its saturated solution is 0.13 g / 100 mL. The aqueous solution has a rich color, a fragrant aroma similar to green tea, and a mellow, full-bodied, slightly bitter taste with a sweet aftertaste.

[0050] In the saturated solution of the instant powder obtained in this embodiment, the concentration of ellagic acid is 0.135 g / 100 mL, which significantly improves the solubility and is beneficial for human absorption.

[0051] Example 2

[0052] (1) Extraction: Take 20kg of dried sweet tea leaves, crush them, and extract them three times at room temperature with 160L, 140L and 80L of pure water respectively. The extraction time for each extraction is 4h, 4h and 3h respectively. Combine the three extracts.

[0053] (2) Flocculation: Add 0.6 kg of chitosan to the extract, dissolve, stir, let stand, filter by plate and frame to obtain flocculent liquid;

[0054] (3) Nanofiltration: The flocculant was filtered through a nanofiltration membrane with a molecular weight cutoff of 300 Da at a pressure of 0.5 MPa, and the nanofiltration membrane retentate was collected.

[0055] (4) Impurity removal: Add 0.6 kg of activated clay to the nanofiltration membrane retentate, heat to 45°C, keep warm and stir for 2 hours, filter to obtain the impurity-removed solution;

[0056] (5) Ultrafiltration: The impurity-removed liquid is filtered through an ultrafiltration membrane with a molecular weight cutoff of 3000 Da at a pressure of 0.1 MPa, and the permeate from the ultrafiltration membrane is collected.

[0057] (6) Concentration and drying: The permeate from the ultrafiltration membrane was concentrated under reduced pressure at a temperature of 50°C and a vacuum of -0.08MPa until the solid concentration was 32%. The concentrate was microwave-dried at a temperature of 45°C and a microwave frequency of 2450MHz for 25 minutes, and then pulverized to obtain 4.98 kg of flavored sweet tea instant powder.

[0058] According to the high performance liquid chromatography (HPLC) external standard method, the content of stevia glycosides in the flavored sweet tea instant powder obtained in this example was 13.46%, and the yield of stevia glycosides was 94.1%; the content of ellagic acid was 3.93%, and the yield of ellagic acid was 87.4%.

[0059] The flavored sweet tea instant powder obtained in this embodiment is a brownish-brown powder. After dissolving in water, the aqueous solution has a rich color, a fragrance similar to green tea, and a mellow, full-bodied, slightly bitter taste with a sweet aftertaste.

[0060] In the saturated solution of the instant powder obtained in this embodiment, the concentration of ellagic acid is 0.131 g / 100 mL.

[0061] Example 3

[0062] (1) Extraction: Take 15kg of dried sweet tea leaves, crush them, and extract them three times at room temperature with 150L, ​​90L and 60L of pure water respectively. The extraction time for each extraction is 4h, 3h and 3h respectively. Combine the three extracts.

[0063] (2) Flocculation: Add 0.35 kg of chitosan to the extract, dissolve, stir, let stand, filter by plate and frame to obtain flocculent liquid;

[0064] (3) Nanofiltration: The flocculant was filtered through a nanofiltration membrane with a molecular weight cutoff of 300 Da at a pressure of 0.4 MPa, and the nanofiltration membrane retentate was collected.

[0065] (4) Impurity removal: Add 0.75 kg of alumina to the nanofiltration membrane retentate, heat to 40°C, keep warm and stir for 1.5 h, filter to obtain the impurity-removed solution;

[0066] (5) Ultrafiltration: The impurity-removed liquid is filtered through an ultrafiltration membrane with a molecular weight cutoff of 2000 Da at a pressure of 0.1 MPa, and the permeate from the ultrafiltration membrane is collected.

[0067] (6) Concentration and drying: The permeate from the ultrafiltration membrane was concentrated under reduced pressure at a temperature of 40℃ and a vacuum of -0.09MPa until the solid concentration was 29%. The concentrate was microwave-dried at a temperature of 50℃ and a microwave frequency of 2400MHz for 25 minutes, and then pulverized to obtain 3.46 kg of flavored sweet tea instant powder.

[0068] According to the high performance liquid chromatography (HPLC) external standard method, the content of stevia glycosides in the flavored sweet tea instant powder obtained in this example was 14.20%, and the yield of stevia glycosides was 92.0%; the content of ellagic acid was 4.23%, and the yield of ellagic acid was 87.1%.

[0069] The flavored sweet tea instant powder obtained in this embodiment is a brownish-brown powder. After dissolving in water, the aqueous solution has a rich color, a fragrance similar to green tea, and a mellow, full-bodied, slightly bitter taste with a sweet aftertaste.

[0070] In the saturated solution of the instant powder obtained in this embodiment, the concentration of ellagic acid is 0.135 g / 100 mL.

[0071] Example 4

[0072] The other steps are the same as in Example 1, except that in step (1) extraction, 10 kg of dried sweet tea leaves are taken, crushed, and extracted four times at room temperature with 80 L, 60 L, 50 L, and 40 L of pure water respectively. The extraction time for each extraction is 5 h, 4 h, 3 h, and 2 h respectively. The four extracts are then combined.

[0073] Finally, 2.55 kg of sweet tea instant powder was obtained. High-performance liquid chromatography (HPLC) with external standard method determined that the sweet tea instant powder obtained in this example contained 13.16% stevia glycosides (with a yield of 94.3%) and 4.06% ellagic acid (with a yield of 92.4%). The saturated solution of the instant powder obtained in this example had an ellagic acid concentration of 0.132 g / 100 mL.

[0074] Example 5

[0075] The other steps are the same as in Example 1, except that step (2) involves adding 0.35 kg of chitosan to the extract.

[0076] Finally, 2.54 kg of sweet tea instant powder was obtained. High-performance liquid chromatography (HPLC) with external standard method determined that the sweet tea instant powder obtained in this example contained 13.21% stevia glycosides (with a yield of 94.2%) and 3.51% ellagic acid (with a yield of 79.6%). The saturated solution of the instant powder obtained in this example had an ellagic acid concentration of 0.125 g / 100 mL.

[0077] Example 6

[0078] The other steps are the same as in Example 1, except that step (2) involves adding 0.1 kg of chitosan to the extract.

[0079] Finally, 2.51 kg of sweet tea instant powder was obtained. High-performance liquid chromatography (HPLC) with external standard method determined that the sweet tea instant powder obtained in this example contained 13.46% stevia glycosides (94.9% yield) and 3.68% ellagic acid (82.5% yield). The saturated solution of the instant powder obtained in this example had an ellagic acid concentration of 0.122 g / 100 mL.

[0080] Example 7

[0081] The other steps are the same as in Example 1, except that step (2) involves adding 0.2 kg of β-cyclodextrin to the extract as an organic flocculant.

[0082] Finally, 2.53 kg of sweet tea instant powder was obtained. High-performance liquid chromatography (HPLC) with external standard method determined that the sweet tea instant powder obtained in this example contained 13.31% stevia glycosides (94.6% yield) and 2.84% ellagic acid (64.1% yield). The saturated solution of the instant powder obtained in this example had an ellagic acid concentration of 0.114 g / 100 mL.

[0083] Comparative Example 1

[0084] The other steps were the same as in Example 1, except that in step (1), the stirring and extraction temperature was changed to 60°C. Finally, 2.81 kg of flavored sweet tea instant powder was obtained, with an ellagic acid content of 1.35% and an ellagic acid yield of 33.9%.

[0085] Comparative Example 2

[0086] The other steps are the same as in Example 1, except that in step (2), 0.2 kg of ferric chloride is used as a flocculant. The final product is 2.04 kg of flavored sweet tea instant powder with an ellagic acid content of 0.21% and an ellagic acid yield of 3.8%.

[0087] Comparative Example 3

[0088] The other steps are the same as in Example 1, except that nanofiltration in step (3) is omitted. 2.75 kg of flavored sweet tea instant powder was finally obtained, with a sweet tea glycoside content of 10.38% and a sweet tea glycoside yield of 80.2%; the ellagic acid content was 3.42%, and the ellagic acid yield was 84.0%. The aqueous solution of the obtained sweet tea instant powder had a bitter and astringent taste.

[0089] Comparative Example 4

[0090] The other steps are the same as in Example 1, except that ultrafiltration in step (5) is omitted. A total of 2.63 kg of flavored sweet tea instant powder was obtained, with a sweet tea glycoside content of 12.74% and a sweet tea glycoside yield of 94.1%; the ellagic acid content was 3.74%, and the ellagic acid yield was 87.8%. The aqueous solution of the obtained sweet tea instant powder was relatively turbid, with a small amount of suspended matter, and had a strong metallic taste, being bitter and astringent.

[0091] Comparative Example 5

[0092] The other steps are the same as in Example 1, except that the nanofiltration in step (3) and the ultrafiltration in step (5) are interchanged, i.e., ultrafiltration is performed first, followed by nanofiltration. Finally, 2.26 kg of flavored sweet tea instant powder was obtained, with a sweet tea glycoside content of 12.47% and a sweet tea glycoside yield of 79.1%; the ellagic acid content was 3.41%, and the ellagic acid yield was 68.8%. The aqueous solution of the obtained sweet tea instant powder had a bitter taste.

[0093] The above detailed description is a specific description of one of the feasible embodiments of the present invention. This embodiment is not intended to limit the patent scope of the present invention. All equivalent implementations or modifications that do not depart from the present invention should be included within the scope of the technical solution of the present invention.

Claims

1. A method for preparing a sweet tea instant powder rich in ellagic acid, comprising the following steps: (1) Extraction: The dried sweet tea leaves are crushed and extracted three or more times with pure water at room temperature. The amount of pure water and the extraction time decrease each time, and the difference between the amount of pure water and the extraction time is 1 / 5 to 1 / 2. The extracts are combined. The amount of pure water used is 18-22 times the weight of the dried sweet tea leaves, and the extraction time is 2 to 5 hours each time. The room temperature is 23-26℃. (2) Flocculation: Add an organic polymer flocculant to the extract, dissolve, stir, let stand, filter, and obtain flocculent liquid; the organic polymer flocculant is chitosan, and the amount of chitosan is 2-3 wt% of the weight of the dried sweet tea leaves. (3) Nanofiltration: The flocculant is filtered using a nanofiltration membrane, and the retentate from the nanofiltration membrane is collected; the nanofiltration membrane has a molecular weight cutoff of 300-500 Da and a filtration pressure of 0.3-0.5 MPa; (4) Impurity removal: Add adsorbent to nanofiltration membrane retentate, heat, keep warm and stir, filter to obtain impurity-removed solution; the adsorbent is one or more of alumina, diatomaceous earth, activated clay and activated carbon, and the amount of adsorbent is 1-5 wt% of the weight of dried sweet tea leaves; the heating temperature is 40-50℃, and the keeping and stirring time is 1-2 hours. (5) Ultrafiltration: The impurity-removed liquid is filtered with an ultrafiltration membrane, and the permeate from the ultrafiltration membrane is collected; the molecular weight cutoff of the ultrafiltration membrane is 2000-5000 Da, and the filtration pressure is 0.1-0.3 MPa; (6) Concentration and drying: The permeate from the ultrafiltration membrane is concentrated under reduced pressure, dried, and pulverized to obtain flavored sweet tea instant powder; the content of ellagic acid in the sweet tea instant powder is above 3wt%.

2. The preparation method according to claim 1, characterized in that, In step (6), the temperature of the vacuum concentration is 40-50°C; the drying is microwave drying at a temperature of 40-50°C.

3. The use of the instant sweet tea powder prepared by the preparation method according to claim 1 or 2, which can be compounded with natural sweeteners or synthetic sweeteners to form a compound sweetener, or used to prepare food, medicine, condiments, health products, cosmetics, and flavorings.