Preparation method of highly stable and bioaccessible resveratrol-pectin complex

Abstract

The present invention discloses a method for preparing a high stability and bioaccessible resveratrol-pectin complex, comprising the following steps: step 1, taking high ester pectin and dissolving it in water, adjusting the pH value to 11, reacting at 25 ° C for 20-30 min, maintaining a constant pH value during the reaction, adjusting the pH value to 2 after deesterification, adding anhydrous ethanol to produce precipitation, filtering, washing, drying, and obtaining a low ester pectin with a degree of esterification lower than 30%; step 2, taking the low ester pectin and resveratrol and dissolving them in a solvent respectively, stirring the low ester pectin solution and the resveratrol solution at 30 ° C for 20-40 min in a volume ratio of 2:1, and obtaining a resveratrol-pectin mixed solution; step 3, separating and purifying the resveratrol-pectin mixed solution using a ceramic composite membrane, freeze drying, and obtaining the resveratrol-pectin complex. The present invention can effectively improve the stability and bioaccessibility of resveratrol.

Description

Technical Field

[0001] The present invention relates to the technical field of food, medicine and health care products. More specifically, the present invention relates to a method for preparing a highly stable and bioaccessible resveratrol-pectin complex. Background Art

[0002] Resveratrol (3,5,4'-trihydroxystilbene) is a non-flavonoid polyphenol substance that is widely found in plants such as grapes, peanuts, and knotweed. It has been shown to have multiple physiological activities such as anti-inflammatory, antioxidant, anti-cancer, and hypoglycemic and lipid-lowering. However, problems such as low solubility, poor stability, and low bioavailability of resveratrol limit its application in the food and pharmaceutical industries.

[0003] Constructing a suitable delivery system is one of the effective means to improve the solubility, stability and bioaccessibility of resveratrol. Solid dispersion technology has attracted much attention due to its advantages such as simple process, high embedding efficiency and retention rate. Highly dispersing resveratrol in a water-soluble carrier can not only improve the water solubility of resveratrol, but also shield and protect resveratrol and improve the stability of resveratrol. Therefore, the selection of carrier materials is one of the important factors affecting its effect. Currently, most of the carriers used are chemically synthesized polymers, which will produce side effects and potential safety hazards. Therefore, it is urgent to develop a substance that can improve the water solubility and stability of resveratrol and can synergize with resveratrol to further improve its bioavailability.

[0004] The prior art, such as the invention patent application with Chinese patent number CN201510072466.7, discloses a resveratrol liposome gel and a preparation method thereof, which uses triethanolamine to form the gel. However, triethanolamine is carcinogenic and there is room for improvement. Summary of the invention

[0005] An object of the present invention is to provide a method for preparing a highly stable and bioaccessible resveratrol-pectin complex, which can effectively improve the stability, bioaccessibility and functional activity of resveratrol.

[0006] In order to achieve these objectives and other advantages of the present invention, according to one aspect of the present invention, the present invention provides a method for preparing a highly stable and bioaccessible resveratrol-pectin complex, comprising the following steps:

[0007] Step 1, dissolving high-ester pectin in water, adjusting the pH value to 11, and then reacting at 20-30°C for 20-30 minutes, maintaining a constant pH value during the reaction, and adjusting the pH value to 2 after deesterification, and then adding anhydrous ethanol to produce precipitation, filtering, washing, and drying to obtain low-ester pectin with an esterification degree of less than 30%;

[0008] Step 2: dissolving the low-ester pectin and resveratrol in a solvent respectively, and then stirring the low-ester pectin solution and the resveratrol solution at 25-35° C. for 20-40 minutes to obtain a resveratrol-pectin mixed solution;

[0009] Step three: using a ceramic composite membrane to separate and purify the resveratrol-pectin mixed solution, and freeze-drying it to obtain the resveratrol-pectin complex.

[0010] Preferably, in the step 1, the concentration of high ester pectin after being dissolved in water is 0.05 g / mL.

[0011] Preferably, the specific washing process in the step 1 is: soaking the precipitate with a mixed solvent made of concentrated hydrochloric acid with a mass fraction of 36-38% and an ethanol solution with a volume fraction of 60% in a volume ratio of 1:20, stirring, filtering again, rinsing with the above mixed solvent 3 times, and then rinsing with a volume fraction of 60% ethanol solution until the filtrate contains no chloride ions.

[0012] Preferably, in the step 2, the low-ester pectin is dissolved in water to form a low-ester pectin solution with a concentration of 1 mg / mL.

[0013] Preferably, in step 2, resveratrol is dissolved in ethanol to form a resveratrol solution with a concentration of 0.5 mg / mL; in step 2, the low-ester pectin solution and the resveratrol solution are stirred at a volume ratio of 2:1 at 25-35° C. for 20-40 min.

[0014] Preferably, freeze drying is performed at -80°C and 10Pa in step three.

[0015] Preferably, the method for preparing the ceramic composite membrane comprises the following steps:

[0016] Step a, dissolving polyimide and polyethersulfone in dimethyl sulfoxide to prepare solutions with the same concentration, mixing the polyimide solution and the polyethersulfone solution, heating to 50-80° C. and stirring for 30 minutes, then adding sodium polystyrene sulfonate, stirring, and ultrasonically dispersing for 30 minutes to obtain a mixed solution with a solid content of 8-12%, wherein the weight ratio of the polyimide, polyethersulfone and sodium polystyrene sulfonate is 2:1:0.08;

[0017] Step b, immersing the alumina flat ceramic membrane in a 0.5% by mass aqueous solution of hexadecyltrimethylammonium bromide for 30 minutes, rinsing, and drying to obtain a base membrane;

[0018] Step c, connecting a scraper to an electrostatic generator, setting the electrostatic field strength to 5 kV / cm, and scraping the mixed solution onto the surface of the base film to a thickness of 30 to 50 μm;

[0019] Step d, placing the base film coated with the mixed solution in a vacuum drying oven, heating the temperature to 100°C at a heating rate of 10°C / min, keeping the temperature constant for 1 hour, continuing to heat the temperature to 150°C at a heating rate of 5°C / min, keeping the temperature constant for 1 hour, then heating the temperature to 190°C at a heating rate of 1°C / min, keeping the temperature constant for 3 hours, and cooling to room temperature to obtain the ceramic composite film.

[0020] Preferably, the average pore size of the alumina flat ceramic membrane is 20 μm, and the surface pore size of the ceramic composite membrane is 8-11 μm.

[0021] Preferably, the solid content of the mixed solution in step a is 10%.

[0022] Preferably, the coating thickness in step c is 40 μm.

[0023] The present invention has at least the following beneficial effects:

[0024] First, the present invention provides a method for preparing a highly stable and bioaccessible resveratrol-pectin complex, which uses an anti-solvent precipitation plus freeze-drying method. The technical solution is simple, the operation is safe, the carrier is green, and it is easy to promote.

[0025] Second, the resveratrol-pectin complex prepared by the present invention uses pectin with a low esterification degree as a carrier, and utilizes its outstanding pH stability, thermal stability and anti-digestion properties to increase the bioaccessibility of resveratrol in the complex from 22% to 64-74%, and improve the antioxidant activity of resveratrol in the complex, wherein the DPPH and ABTS free radical scavenging activities are increased by 60% and 50%, respectively.

[0026] Third, the present invention utilizes a self-made ceramic composite membrane to separate and purify the resveratrol-pectin complex, and the obtained resveratrol-pectin complex has high purity and good quality.

[0027] Other advantages, objectives and features of the present invention will be embodied in part through the following description, and in part will be understood by those skilled in the art through study and practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 is a pore size distribution diagram of the ceramic composite membrane of the present invention;

[0029] Figure 2 This is a comparison chart of the average particle sizes of resveratrol, pectin and resveratrol-pectin complex in the present invention;

[0030] Figure 3 This is a comparison diagram of the Zeta potential of resveratrol, pectin and resveratrol-pectin complex in the present invention;

[0031] Figure 4 is a comparison chart of the embedding rate of the resveratrol-pectin complex in the present invention;

[0032] Figure 5 is a scanning electron microscope image of resveratrol, pectin and resveratrol-pectin complex in the present invention;

[0033] Figure 6 The X-RD spectra of resveratrol, pectin and resveratrol-pectin complex in the present invention;

[0034] Figure 7 is a thermogravimetric analysis diagram of resveratrol in the present invention;

[0035] Figure 8 It is the thermogravimetric analysis diagram of T1 and RT1 in the present invention;

[0036] Fig. 9 It is the thermogravimetric analysis diagram of T2 and RT2 in the present invention;

[0037] Fig.10 It is the thermogravimetric analysis diagram of T3 and RT3 in the present invention;

[0038] Fig.11 It is the thermogravimetric analysis diagram of T4 and RT4 in the present invention;

[0039] Fig.12 This is a graph showing the particle size changes of resveratrol and resveratrol-pectin complex under different pH conditions in the present invention;

[0040] Fig.13 The figure is a graph showing the particle size changes of resveratrol and resveratrol-pectin complex under different ionic strengths in the present invention;

[0041] Fig.14 The graph is a graph showing the particle size changes of resveratrol and resveratrol-pectin complex at different temperatures in the present invention;

[0042] Fig.15 DPPH free radical scavenging activity diagram of resveratrol and resveratrol-pectin complex in the present invention;

[0043] Fig.16 ABTS of resveratrol and resveratrol-pectin complex in the present invention + Clearance plot of

[0044] Fig.17 This is a comparison chart of the release rate of resveratrol after in vitro digestion in the present invention;

[0045] Fig.18 The figure is a comparison chart of the bioaccessibility of resveratrol and resveratrol-pectin complex in the present invention. DETAILED DESCRIPTION

[0046] The present invention is further described in detail below in conjunction with the accompanying drawings and specific embodiments so that those skilled in the art can implement the invention with reference to the description.

[0047] It should be understood that the terms such as “having”, “including” and “comprising” used herein do not exclude the existence or addition of one or more other elements or combinations thereof.

[0048] It should be noted that the experimental methods described in the following embodiments are conventional methods unless otherwise specified, and the reagents and materials can be obtained from commercial channels unless otherwise specified.

[0049] Example 1

[0050] A method for preparing a highly stable and bioaccessible resveratrol-pectin complex comprises the following steps:

[0051] Step 1: Dissolve commercially available high-ester pectin (commercial citrus pectin with an esterification degree of 72%) in water to prepare a solution with a concentration of 0.05 g / mL, adjust the pH value to 11 with sodium hydroxide solution, react in a water bath shaker at 25°C for 30 minutes, continuously drop sodium hydroxide solution during the reaction to maintain a constant pH value, add hydrochloric acid solution to adjust the pH value to 2 after deesterification, add anhydrous ethanol in an amount of 2 times the volume of the above mixed solution to produce a precipitate, vacuum filter the filtrate after the precipitate is produced, soak the filter paper with a mixed solvent prepared by a mass fraction of 36% to 38% concentrated hydrochloric acid and a volume fraction of 60% ethanol solution in a volume ratio of 1:20, stir, rinse with the above mixed solvent 3 times, and then rinse with a volume fraction of 60% ethanol solution until the filtrate contains no chloride ions, dry, and obtain low-ester pectin (T1);

[0052] Step 2: dissolving the low-ester pectin in water to prepare a solution with a concentration of 1 mg / mL, dissolving resveratrol in ethanol to prepare a solution with a concentration of 0.5 mg / mL, stirring the low-ester pectin solution and the resveratrol solution at a volume ratio of 2:1 at 30° C. for 30 minutes to obtain a resveratrol-pectin mixed solution;

[0053] Step 3: Separate and purify the resveratrol-pectin mixed solution by using a ceramic composite membrane, and freeze-dry it under the conditions of -80°C and 10Pa to obtain the resveratrol-pectin complex (RT1).

[0054] Wherein, the preparation method of the ceramic composite membrane is:

[0055] Step a, dissolving polyimide and polyethersulfone in dimethyl sulfoxide to prepare solutions with the same concentration, mixing the polyimide solution and the polyethersulfone solution, heating to 60° C. and stirring for 30 minutes, then adding sodium polystyrene sulfonate, stirring, and ultrasonically dispersing for 30 minutes to obtain a mixed solution with a solid content of 10%, wherein the weight ratio of the polyimide, polyethersulfone and sodium polystyrene sulfonate is 2:1:0.08;

[0056] Step b, taking an alumina flat ceramic membrane with an average pore size of 20 μm and immersing it in a 0.5% by mass aqueous solution of hexadecyltrimethylammonium bromide for 30 minutes, rinsing, and drying to obtain a base membrane;

[0057] Step c, connecting a scraper to an electrostatic generator, setting the electrostatic field strength to 5 kV / cm, and scraping the mixed solution onto the surface of the base film to a scraping thickness of 40 μm;

[0058] Step d, placing the base film coated with the mixed solution in a vacuum drying oven, heating the temperature to 100°C at a heating rate of 10°C / min, keeping the temperature constant for 1 hour, continuing to heat the temperature to 150°C at a heating rate of 5°C / min, keeping the temperature constant for 1 hour, then heating the temperature to 190°C at a heating rate of 1°C / min, keeping the temperature constant for 3 hours, and cooling to room temperature to obtain the ceramic composite film.

[0059] Example 2

[0060] A method for preparing a highly stable and bioaccessible resveratrol-pectin complex, which is different from Example 1 in that the method for preparing the ceramic composite membrane is:

[0061] Step a, dissolving polyimide and polyethersulfone in dimethyl sulfoxide to prepare solutions with the same concentration, mixing the polyimide solution and the polyethersulfone solution, heating to 80° C. and stirring for 30 minutes, then adding sodium polystyrene sulfonate, stirring, and ultrasonically dispersing for 30 minutes to obtain a mixed solution with a solid content of 12%, wherein the weight ratio of the polyimide, polyethersulfone and sodium polystyrene sulfonate is 2:1:0.08;

[0062] Step b, taking an alumina flat ceramic membrane with an average pore size of 20 μm and immersing it in a 0.5% by mass aqueous solution of hexadecyltrimethylammonium bromide for 30 minutes, rinsing, and drying to obtain a base membrane;

[0063] Step c, connecting a scraper to an electrostatic generator, setting the electrostatic field strength to 5 kV / cm, and scraping the mixed solution onto the surface of the base film to a scraping thickness of 50 μm;

[0064] Step d, placing the base film coated with the mixed solution in a vacuum drying oven, heating the temperature to 100°C at a heating rate of 10°C / min, keeping the temperature constant for 1 hour, continuing to heat the temperature to 150°C at a heating rate of 5°C / min, keeping the temperature constant for 1 hour, then heating the temperature to 190°C at a heating rate of 1°C / min, keeping the temperature constant for 3 hours, and cooling to room temperature to obtain the ceramic composite film.

[0065] Example 3

[0066] A method for preparing a highly stable and bioaccessible resveratrol-pectin complex, which is different from Example 1 in that the method for preparing the ceramic composite membrane is:

[0067] Step a, dissolving polyimide and polyethersulfone in dimethyl sulfoxide to prepare solutions with the same concentration, mixing the polyimide solution and the polyethersulfone solution, heating to 50° C. and stirring for 30 minutes, adding sodium polystyrene sulfonate, stirring, and ultrasonically dispersing for 30 minutes to obtain a mixed solution with a solid content of 8%, wherein the weight ratio of the polyimide, polyethersulfone and sodium polystyrene sulfonate is 2:1:0.08;

[0068] Step b, taking an alumina flat ceramic membrane with an average pore size of 20 μm and immersing it in a 0.5% by mass aqueous solution of hexadecyltrimethylammonium bromide for 30 minutes, rinsing, and drying to obtain a base membrane;

[0069] Step c, connecting a scraper to an electrostatic generator, setting the electrostatic field strength to 5 kV / cm, and scraping the mixed solution onto the surface of the base film to a scraping thickness of 30 μm;

[0070] Step d, placing the base film coated with the mixed solution in a vacuum drying oven, heating the temperature to 100°C at a heating rate of 10°C / min, keeping the temperature constant for 1 hour, continuing to heat the temperature to 150°C at a heating rate of 5°C / min, keeping the temperature constant for 1 hour, then heating the temperature to 190°C at a heating rate of 1°C / min, keeping the temperature constant for 3 hours, and cooling to room temperature to obtain the ceramic composite film.

[0071] Comparative Example 1

[0072] A method for preparing a highly stable and bioaccessible resveratrol-pectin complex comprises the following steps:

[0073] Step 1: Dissolve commercially available high-ester pectin (commercial citrus pectin with an esterification degree of 72%) in water to prepare a solution with a concentration of 0.05 g / mL, adjust the pH value to 11 with sodium hydroxide solution, react in a water bath shaker at 25°C for 15 minutes, continuously drop sodium hydroxide solution during the reaction to maintain a constant pH value, add hydrochloric acid solution to adjust the pH value to 2 after deesterification, add anhydrous ethanol in an amount of 2 times the volume of the above mixed solution to produce a precipitate, vacuum filter the filtrate after the precipitate is produced, soak the filter paper with a mixed solvent prepared by a mass fraction of 36% to 38% concentrated hydrochloric acid and a volume fraction of 60% ethanol solution in a volume ratio of 1:20, stir, rinse 3 times with the above mixed solvent, and then rinse with a volume fraction of 60% ethanol solution until the filtrate contains no chloride ions, dry, and obtain low-ester pectin (T2);

[0074] Step 2: dissolving the low-ester pectin in water to prepare a solution with a concentration of 1 mg / mL, dissolving resveratrol in ethanol to prepare a solution with a concentration of 0.5 mg / mL, stirring the low-ester pectin solution and the resveratrol solution at a volume ratio of 2:1 at 30° C. for 30 minutes to obtain a resveratrol-pectin mixed solution;

[0075] Step 3: Separate and purify the resveratrol-pectin mixed solution by using a ceramic composite membrane, and freeze-dry it under the conditions of -80°C and 10Pa to obtain the resveratrol-pectin complex (RT2).

[0076] The preparation method of the ceramic composite membrane is the same as that of Example 1.

[0077] Comparative Example 2

[0078] A method for preparing a highly stable and bioaccessible resveratrol-pectin complex comprises the following steps:

[0079] Step 1: Dissolve commercially available high-ester pectin (commercial citrus pectin with an esterification degree of 72%) in water to prepare a solution with a concentration of 0.05 g / mL, adjust the pH value to 9 with sodium hydroxide solution, react in a water bath shaker at 25°C for 20 minutes, continuously drop sodium hydroxide solution during the reaction to maintain a constant pH value, add hydrochloric acid solution to adjust the pH value to 2 after deesterification, add anhydrous ethanol in an amount of 2 times the volume of the above mixed solution to produce a precipitate, vacuum filter the filtrate after the precipitate is produced, soak the filter paper with a mixed solvent prepared by a mass fraction of 36% to 38% concentrated hydrochloric acid and a volume fraction of 60% ethanol solution in a volume ratio of 1:20, stir, rinse 3 times with the above mixed solvent, and then rinse with a volume fraction of 60% ethanol solution until the filtrate contains no chloride ions, dry, and obtain low-ester pectin (T3);

[0080] Step 2: dissolving the low-ester pectin in water to prepare a solution with a concentration of 1 mg / mL, dissolving resveratrol in ethanol to prepare a solution with a concentration of 0.5 mg / mL, stirring the low-ester pectin solution and the resveratrol solution at a volume ratio of 2:1 at 30° C. for 30 minutes to obtain a resveratrol-pectin mixed solution;

[0081] Step 3: Separate and purify the resveratrol-pectin mixed solution by using a ceramic composite membrane, and freeze-dry it to obtain the resveratrol-pectin complex (RT3).

[0082] The preparation method of the ceramic composite membrane is the same as that of Example 1.

[0083] Comparative Example 3

[0084] A method for preparing a highly stable and bioaccessible resveratrol-pectin complex comprises the following steps:

[0085] Commercially available high-ester pectin (commercial citrus pectin T4 with an esterification degree of 72%) was dissolved in water to prepare a solution with a concentration of 1 mg / mL, and resveratrol was dissolved in ethanol to prepare a solution with a concentration of 0.5 mg / mL. The high-ester pectin solution and the resveratrol solution were stirred at a volume ratio of 2:1 at 30°C for 30 minutes to obtain a resveratrol-pectin mixed solution;

[0086] The resveratrol-pectin mixed solution is separated and purified by using a ceramic composite membrane, and freeze-dried under the conditions of -80°C and 10Pa to obtain the resveratrol-pectin complex (RT4).

[0087] The preparation method of the ceramic composite membrane is the same as that of Example 1.

[0088] Comparative Example 4

[0089] A method for preparing a highly stable and bioaccessible resveratrol-pectin complex, which is different from Example 1 in that the method for preparing the ceramic composite membrane is:

[0090] Step a, dissolving polyimide in dimethyl sulfoxide to form a solution with a solid content of 10%, heating to 60° C., stirring for 30 minutes, and ultrasonically dispersing for 30 minutes to obtain a polyimide solution;

[0091] Step b, applying the polyimide solution to the surface of a flat ceramic membrane having an average pore size of 20 μm, with a coating thickness of 40 μm;

[0092] Step c, placing the flat ceramic membrane coated with the mixed solution in a vacuum drying oven, heating the temperature to 100°C at a heating rate of 10°C / min, keeping the temperature constant for 1 hour, continuing to heat the temperature to 150°C at a heating rate of 5°C / min, keeping the temperature constant for 1 hour, then heating the temperature to 190°C at a heating rate of 1°C / min, keeping the temperature constant for 3 hours, and cooling to room temperature to obtain a ceramic composite membrane.

[0093] The resveratrol-pectin mixed solution is separated and purified by using the ceramic composite membrane, and freeze-dried to obtain the resveratrol-pectin complex (RT1-1).

[0094] Comparative Example 5

[0095] A method for preparing a highly stable and bioaccessible resveratrol-pectin complex, which is different from Example 1 in that the method for preparing the ceramic composite membrane is:

[0096] Step a, dissolving polyethersulfone in dimethyl sulfoxide to form a solution with a solid content of 10%, heating to 60° C., stirring for 30 minutes, and ultrasonically dispersing for 30 minutes to obtain a polyethersulfone solution;

[0097] Step b, applying the polyethersulfone solution to the surface of a flat ceramic membrane having an average pore size of 20 μm, with a coating thickness of 40 μm;

[0098] Step c, placing the flat ceramic membrane coated with the mixed solution in a vacuum drying oven, heating the temperature to 100°C at a heating rate of 10°C / min, keeping the temperature constant for 1 hour, continuing to heat the temperature to 150°C at a heating rate of 5°C / min, keeping the temperature constant for 1 hour, then heating the temperature to 190°C at a heating rate of 1°C / min, keeping the temperature constant for 3 hours, and cooling to room temperature to obtain a ceramic composite membrane.

[0099] The resveratrol-pectin mixed solution is separated and purified by using the ceramic composite membrane, and freeze-dried to obtain the resveratrol-pectin complex (RT1-2).

[0100] Comparative Example 6

[0101] A method for preparing a highly stable and bioaccessible resveratrol-pectin complex, which is different from Example 1 in that the method for preparing the ceramic composite membrane is:

[0102] Step a, dissolving polyimide and polyethersulfone in dimethyl sulfoxide to prepare solutions with the same concentration, mixing the polyimide solution and the polyethersulfone solution, heating to 60° C. and stirring for 30 minutes, and ultrasonically dispersing for 30 minutes to obtain a mixed solution with a solid content of 10%, wherein the weight ratio of the polyimide, polyethersulfone and sodium polystyrene sulfonate is 2:1;

[0103] Step b, using a common scraper to scrape the mixed solution onto the surface of an alumina flat ceramic membrane with an average pore size of 20 μm, with a scraping thickness of 40 μm;

[0104] Step d, placing the flat ceramic membrane coated with the mixed solution in a vacuum drying oven, heating the temperature to 100°C at a heating rate of 10°C / min, keeping the temperature constant for 1 hour, continuing to heat the temperature to 150°C at a heating rate of 5°C / min, keeping the temperature constant for 1 hour, then heating the temperature to 190°C at a heating rate of 1°C / min, keeping the temperature constant for 3 hours, and cooling to room temperature to obtain the ceramic composite membrane.

[0105] The resveratrol-pectin mixed solution is separated and purified by using the ceramic composite membrane, and freeze-dried to obtain the resveratrol-pectin complex (RT1-3).

[0106] Membrane pore size distribution determination

[0107] The ceramic composite membranes used in Examples 1 to 3 and Comparative Examples 4 to 6 were used to measure the pore size distribution on the membrane surface using the bubble point method. The test results are as follows: Figure 1 shown.

[0108] The results show that the ceramic composite membranes prepared in Examples 1 to 3 pre-treat the flat ceramic membrane to make it positively charged on the surface, and use polyimide and polyethersulfone to copolymerize with sodium polystyrene sulfonate to make it negatively charged. During the scraping process, the mixed solution is uniformly adsorbed on the surface of the ceramic membrane by electrostatic attraction, which not only helps to improve the uniformity of the scraping thickness, but also enhances the bonding force between the membrane and the substrate, and finally makes the pore size distribution of the prepared ceramic composite membrane uniform, meeting the separation requirements. The ceramic composite membranes prepared in Comparative Examples 4 and 5 only apply a single polyimide or polyethersulfone to the surface of the ceramic membrane, and the pore size distribution is relatively wide. This is mainly because the poor fluidity of polyimide leads to its uneven distribution on the surface of the ceramic membrane, and finally leads to a wide surface pore size distribution of the formed membrane, while the water absorption of polyethersulfone is relatively large, and it is easy to form cracks or generate large pores during the drying process, which makes it difficult to control the size of its pores, so that the pore size distribution is widened. In Comparative Example 6, polyimide and polyethersulfone are mixed to form a coating, which has poor bonding with the ceramic membrane, resulting in poor distribution uniformity on the surface of the base membrane and a wide pore size distribution.

[0109] Purity determination of resveratrol-pectin complex

[0110] The resveratrol-pectin complexes obtained in Examples 1 to 3 and Comparative Examples 4 to 6 were taken and their purity was measured by gel permeation chromatography. The measurement results are shown in Table 1.

[0111] Table 1

[0112] purity(%) Example 1 96.6 Example 2 96.2 Example 3 96.3 Comparative Example 4 75.9 Comparative Example 5 78.4 Comparative Example 6 81.8

[0113] The test results show that the purity of the product finally obtained by separating and purifying the resveratrol-pectin complex through the homemade ceramic composite membrane in Examples 1 to 3 is the highest, because the homemade ceramic composite membrane of the present invention has a narrow pore size distribution and has the best separation effect on impurities and unreacted resveratrol and pectin. The separation membrane used in Comparative Examples 4 to 6 has a wide pore size distribution, poor separation effect, and the purity of the product finally obtained is low.

[0114] Determination of physicochemical properties of pectin

[0115] The pectins in Example 1 and Comparative Examples 1 to 3 were taken and their esterification degree, molecular weight, uronic acid content, total sugar content and protein content were measured respectively. The test method is as follows:

[0116] (1) Determination of esterification degree

[0117] 100 mg of dried pectin was mixed in 2 mL of ethanol and then dissolved in 20 mL of CO2-free 2 distilled water at 40 °C was dripped into the sample using phenolphthalein as an indicator, and then 0.1 M NaOH (V 1 ) until the pink color does not fade for 30 seconds. Then add 10mL of 0.5 M NaOH and stir vigorously to saponify the pectin. Let the solution stand for 20 minutes. Add 10mL of 0.5M HCl and stir until the pink color disappears. Finally, add phenolphthalein and stir with 0.5M NaOH (V 2 ) until it turns slightly red. The calculation method of pectin esterification degree is as follows:

[0118] Degree of esterification (DE) = V 2 / (V 1 +V 2 )×100%;

[0119] V 1 —Original titration volume of sample solution (mL)

[0120] V 2 —Saponification titration volume of sample solution (mL)

[0121] (2) Determination of total sugar content

[0122] Determined by phenol-sulfuric acid method, measured at 490nm with d-glucose as standard. Prepare a 6% phenol solution by mass, and avoid light throughout the process. Draw a standard curve: the glucose concentration is 0mg / mL, 0.02mg / mL, 0.04mg / mL, 0.06mg / mL, 0.08mg / mL, and 0.1mg / mL, respectively. Add 0.5mL of 6% phenol solution and 2.5mL of concentrated sulfuric acid, shake the test tube immediately to mix it thoroughly, let it stand at room temperature for 30min, and measure the absorbance value at a wavelength of 490nm with a spectrophotometer to draw a standard curve. Prepare pectin into a 60μg / mL solution, take 1mL in a clean test tube, measure the absorbance value of pectin according to the above steps, and substitute it into the standard curve to calculate the total sugar content of pectin.

[0123] (3) Determination of galacturonic acid content

[0124] Preparation of galacturonic acid standard curve: Accurately measure 0mL, 0.05mL, 0.10mL, 0.15mL, 0.20mL, and 0.25mL of the freshly prepared galacturonic acid solution in a test tube, and add distilled water to 1mL. The concentrations are 0mg / mL, 0.025mg / mL, 0.05mg / mL, 0.075mg / mL, 0.1mg / mL, and 0.125mg / mL, respectively. Add 6mL of sulfuric acid solution, mix thoroughly, and heat in a boiling water bath for 5min, and cool to room temperature in an ice water bath. Add 0.2mL of carbazole reagent and shake well in a boiling water bath to react in the dark for 2h, and let it stand and cool to room temperature. The spectrophotometer measures the absorbance values ​​at 527nm in turn. Make four parallels for each treatment group, with the horizontal axis being the galacturonic acid content (μg) and the absorbance value being the vertical axis, to obtain the standard curve of galacturonic acid. Prepare pectin solution according to the same method as above, prepare 0.1 mg / mL pectin sample solution, then transfer 1 mL into a test tube, substitute the average of the measured absorbance values ​​into the standard curve, and calculate the pectin uronic acid content according to the standard curve.

[0125] (4) Determination of molecular weight

[0126] The molecular weight of pectin was determined by high performance liquid chromatography coupled with high performance size exclusion chromatography. Dextran was used as the standard for pectin molecular weight. Dextran with different molecular weights (12×10 3 , 25×10 3 , 50×10 3 ,80×10 3 , 270×10 3 ,410×10 3 , 670×10 3) to make standard molecular weight solutions of different masses. The preparation of the standard curve is to weigh 2 mg of standard products of different molecular weights, dissolve the dextran standard product in 1 mL of sodium nitrate solution to make it fully dissolved, and filter the liquid through a 0.45 μm filter membrane. The chromatographic conditions are to use a differential refractive index detector (RID) and an OHpakSB-804HQ column, the mobile phase is 0.05M sodium nitrate solution, the injection volume is 20 μL, the flow rate is 0.45 mL / min, and the column temperature is 35°C. The retention time of the sample is the horizontal axis and the logarithm of the molecular weight (Lg Mw) is the vertical axis to draw a standard curve. Then, according to the above steps, the dextran standard product is replaced with a pectin solution, the molecular weight of pectin is determined, and the molecular weight of pectin can be calculated according to the standard curve.

[0127] The test results are shown in Table 2.

[0128] Table 2

[0129] Pectin Degree of esterification (%) Molecular weight (kDa) Uronic acid (%) Total sugar (%) protein(%) T4 <![CDATA[71±0.33 a ]]> <![CDATA[1099±11.57 a ]]> <![CDATA[68.03±0.04 a ]]> <![CDATA[51.04±0.86 a ]]> <![CDATA[2.61±0.46 b ]]> T3 <![CDATA[52±0.25 b ]]> <![CDATA[929±5.74 b ]]> <![CDATA[64.08±0.2 ab ]]> <![CDATA[48.53±1.1 bc ]]> <![CDATA[3.10±0.94 a ]]> T2 <![CDATA[36±0.22 c ]]> <![CDATA[752±14.05 c ]]> <![CDATA[67.65±0.17 ab ]]> <![CDATA[47.43±0.43 c ]]> <![CDATA[3.05±0.58 a ]]> T1 <![CDATA[26±0.27 d ]]> <![CDATA[394±8.28 d ]]> <![CDATA[62.43±0.52 b ]]> <![CDATA[49.48±0.57 b ]]> <![CDATA[2.40±0.20 c ]]>

[0130] As can be seen from Table 2, the order of esterification degree among the four kinds of pectins in Example 1 and Comparative Examples 1 to 3 is: T4 (71%) > T3 (52%) > T2 (36%) > T1 (26%), and there is a significant difference (P < 0.05). The molecular weight order of the four kinds of pectins is: T4 (1099 kDa) > T3 (929 kDa) > T2 (752 kDa) > T1 (394 kDa), and there is a significant difference between the groups (P < 0.05). The molecular weight of pectin is closely related to the esterification degree. The higher the esterification degree of pectin, the higher the molecular weight, and vice versa. The content of galacturonic acid in the four kinds of pectins is higher than 60%, which are 68.03%, 64.08%, 67.65%, and 62.43% respectively. The total sugar contents were 51.04%, 48.53%, 47.43% and 49.48% respectively, and the protein contents of the four types of pectin were low, at 2.61%, 3.16%, 3.05% and 2.40% respectively.

[0131] Particle size and potential determination

[0132] The average particle size of resveratrol Rsv, four kinds of pectin and four kinds of resveratrol-pectin complexes in Example 1 and Comparative Examples 1 to 3 was measured by laser particle size analyzer. All measurements were carried out at 25°C, equilibrated for 60 seconds before measurement, and each sample was repeated three times. The potential was measured using a Malvern potential meter, and each experiment was repeated three times. Statistical analysis was performed using SPSS Statistics21 software (Zhang et al., 2023). The results are shown in Figure 2 and Figure 3 shown.

[0133] Depend on Figure 2It can be seen that the particle size of resveratrol Rsv is 1.6μm; the particle sizes of T4 pectin, T3 pectin, T2 pectin, and T1 pectin are 2.1μm, 3.7μm, 3.7μm, and 5.2μm, respectively; the particle sizes of RT4 complex, RT3 complex, RT2 complex, and RT1 complex are 16.8μm, 17.6μm, 17.6μm, and 17.8μm, respectively. There is no significant difference in the particle size among the four complexes (p>0.05), but the particle size of the complexes is significantly higher than that of resveratrol and pectin, indicating that resveratrol interacts with pectin. Figure 3 It can be seen that the potential of resveratrol Rsv is -26.73mV, the potentials of T4 pectin, T3 pectin, T2 pectin, and T1 pectin are -84.03mV, -71.13mV, -89.13mV, and -84.5mV, respectively, and the potentials of RT4 complex, RT3 complex, RT2 complex, and RT1 complex are -90.4mV, -73.13mV, -83.93mV, and -93.6mV, respectively. After adding resveratrol, the absolute values ​​of the zeta potential of the four complexes are significantly higher than that of resveratrol, indicating that the construction of the complex significantly improves the stability of resveratrol, among which the absolute value of the zeta potential of the RT1 complex is the largest, indicating that the stability of the RT1 complex in Example 1 is the best.

[0134] Embedding efficiency determination

[0135] The ultraviolet spectrophotometer was used for determination, and the scanning wavelength range was 190-450 nm. 1 mL of the membrane filtrate was added with 9 mL of anhydrous ethanol for precipitation, vortexed for 1 min, centrifuged at 10,000 rpm for 10 min, and the supernatant was analyzed by determining the absorbance at 306 nm (UV1800, Shimadzu, Japan) of the ultraviolet-visible spectrophotometer. The embedding rate of the complex was calculated as follows:

[0136] Embedding rate (%) = (reversatrol addition amount - free resveratrol amount) / resveratrol addition amount × 100%

[0137] The results are as follows Figure 4 As shown. Figure 4 It can be seen that the embedding rates of resveratrol in the four pectins with different esterification degrees are different. The embedding rate of low esterification degree pectin T1 is the highest, reaching 69.29%, and the embedding rate of high esterification degree pectin T4 is the lowest, only 64.39%. The embedding rates of other pectins T3 and T2 are 68.26% and 68.74%, respectively. There is a significant difference in the embedding rate between high esterification degree pectin and low esterification degree pectin, which may be due to the high esterification degree pectin having a large molecular weight, forming a thicker coating, which hinders the movement of resveratrol.

[0138] Micromorphometry

[0139] The microscopic morphology of resveratrol, pectin and the complex was observed using a scanning electron microscope. Figure 5 As shown. Figure 5 It can be seen that resveratrol Rsv has a crystalline structure, which is a rectangle of uneven size. Pectins with different esterification degrees are flaky and filamentous structures. T4 pectin shows a smooth flaky structure with the largest flaky area; T3 and T2 pectins show filamentous and irregular flaky structures, with filaments and flaky structures interlaced with each other, which is smaller than the flaky structure of T4 pectin; T1 pectin shows a larger flaky structure, and the flaky surface is not a smooth structure but a bumpy cluster, which is more conducive to the combination of pectin and resveratrol. When resveratrol is compounded with pectins with different esterification degrees, the complexes all show irregular structural morphology, and the flaky and filamentous structures become smaller at the same magnification. In addition, the structures of pectins with different esterification degrees are looser and more disordered than the corresponding complexes, and the flaky film structure is thinner, which is conducive to the binding of water molecules and improves the water solubility of the complex. This may be that the non-covalent interaction between resveratrol and pectin weakens the intramolecular and intermolecular interactions, but there is no significant difference in the structure of complexes with different esterification degrees.

[0140] Crystallinity determination

[0141] The crystallinity of pectin-resveratrol complex was examined using an X-ray diffractometer (Rigaku SmartLab SE, Japan) at 40 kV and 40 mA with a Cu-Kα source, running at a rate of 4° / min and a step size of 0.02°, with a scanning range of 4–40° to obtain the X-RD patterns. The results are shown in Figure 6 shown.

[0142] Depend on Figure 6 It can be seen that resveratrol Rsv has sharp and narrow crystal diffraction peaks at 2ϴ=6.5°, 13.2°, 16.3°, 19.1°, 22.2°, 23.5°, 25.1°, and 28.2°, indicating that resveratrol is highly crystalline; the four pectins have no sharp diffraction peaks, indicating that pectin exists in an amorphous form; the four complexes have broad and diffuse diffraction peaks at 2ϴ=6.5°, 16.3°, 19.1°, 23.0°, and 28.2°, indicating that the complexes are partially crystallized, but the degree of crystallinity is low and they exist in an amorphous state, indicating that resveratrol is successfully encapsulated with pectin.

[0143] Stability determination

[0144] The thermal stability of the composite was investigated by thermogravimetric analysis (TGA). Figure 7-11 As shown. Figure 7-11It can be seen that the Rsv of resveratrol has a small change trend before 234℃, and the thermogravimetric loss is only 1.17%, which is mainly caused by the dehydration of resveratrol. A sharp weight loss of about 44.78% occurs in the range of 250℃~440℃, which is caused by the degradation of resveratrol. The mass loss of T4 pectin, T3 pectin, T2 pectin and T1 pectin can be divided into two stages. In the first stage, at 30℃~200℃, the mass of the four pectins began to decrease, and the weight loss was 8.97%, 11.3%, 9.8% and 9.36% respectively. This stage is mainly the loss of water in pectin; in the second stage, the mass of pectin decreased sharply during 210℃~300℃, and the mass loss was 34.02%, 26.15%, 28.47% and 21.95% respectively. Among them, T1 pectin has the best thermal stability. The thermogravimetric curves of RT4, RT3, RT2, and RT1 complexes are similar to those of the corresponding pectins, and the weight loss is divided into two stages. In the first stage, at 30℃~200℃, the mass of the four complexes began to decrease, and the weight losses were 6.34%, 7.31%, 5.53%, and 7.53%, respectively. In the second stage, at 210℃~300℃, the mass of the complexes dropped sharply, and the mass losses in this stage were 39.89%, 36.87%, 34.65%, and 31.32%, respectively. The mass loss caused by thermal decomposition of the complexes was significantly lower than that of resveratrol, indicating that the thermal stability of resveratrol was improved after the complex of pectin and resveratrol, and the low esterification degree pectin T1 had the best protective effect on resveratrol.

[0145] Determination of the effect of pH on the stability of the complex: 100 mg of the complex was dissolved in 50 mL of deionized water, and the pH of the freshly prepared complex solution was adjusted with 1 mol / L NaOH or HCL solution to make the pH of the complex solution 2, 4, 6, 8, or 10. The complex solution was allowed to stand at room temperature for 24 h, and the particle size of the nanoparticles under different pH conditions was detected using a particle size analyzer.

[0146] Determination of the effect of ionic strength on the stability of the complex: The complex was dissolved in distilled water with NaCl concentrations of 0, 10, 20, 50, and 100 mM at a concentration of 2 mg / mL and allowed to stand at room temperature for 24 h. The particle size of the solution nanoparticles was detected by a particle size analyzer under different salt ion conditions.

[0147] Determination of the effect of temperature on the stability of the complex: 100 mg of the complex was dissolved in 50 mL of deionized water. The complex solution was heated in a water bath at 60°C, 80°C, and 100°C for 30 min, respectively, and allowed to stand at room temperature for 24 h. The particle size was measured using a particle size analyzer.

[0148] The results are as follows Figure 12-14 As shown. Figure 12-14It can be seen that with the changes in pH value, ionic strength and temperature, the high esterification degree complex has a greater impact, while the particle size of the low ester pectin complex changes less, indicating that the complex formed by low ester pectin is more stable. In summary, the low esterification degree pectin complex RT1 is more stable to the environment.

[0149] Determination of antioxidant capacity

[0150] Determination of DPPH free radical scavenging ability: Weigh 4.00 mg DPPH and dissolve it in anhydrous ethanol to 100 mL to form a DPPH solution (prepared and used immediately), and keep it away from light throughout the process. Dissolve resveratrol, various pectins and their complexes to make a solution for use. Take Vc as a positive control and prepare the same concentration as pectin and the complex. The concentration of all samples is 1 mg / mL. The experimental group is 200 μL of the complex solution and Vc solution into a 2mL test tube, and then add 400 μL of DPPH. Do 3 parallels each time, and the absorbance is recorded as A1. The control group is to take 200 μL of the complex solution and Vc solution into a 2mL test tube, and then add 400 mL of anhydrous ethanol. The absorbance of the sample and Vc is recorded as A2. The blank group is to take 200 μL of deionized water into a 2mL test tube, and then add 400 μL of DPPH. The absorbance is recorded as A0. The experimental group, the control group and the blank group are reacted in the dark for 30 minutes. Then, 200 μL was aspirated into a 96-well plate, and the absorbance was measured at 517 nm using an enzyme reader. The scavenging rate of free radicals (DPPH) was calculated according to the following formula. The results are as follows: Fig.15 shown.

[0151] DPPH clearance rate = 1-(A1-A2) / A0×100;

[0152] Wherein, A1 is the absorbance of the sample and DPPH at 517 nm, A2 is the absorbance of the sample and anhydrous ethanol at 517 nm, and A0 is the absorbance of deionized water and DPPH at 517 nm.

[0153] ABTS + Determination of free radical scavenging ability: Preparation of 7mM ABTS + Solution and 4.9mM potassium persulfate solution, the two solutions were mixed in a 1:1 ratio, and reacted in the dark at 4°C for 18h to produce the required ABTS + Free radical cation, ABTS with deionized water + The solution was diluted to make the absorbance at 734 nm 0.70 + 0.02 (ABTS + Prepare and use immediately). For the experimental group, take 20 μL of the complex solution and 4 μL of resveratrol, then add 180 μL of ABTS +The absorbance is recorded as A1. For the control group, 20 μL of the complex solution and Vc solution were placed in a 96-well plate, and 180 μL of deionized water was added. The absorbance is recorded as A2. For the blank group, 20 μL of deionized water was placed in a 96-well plate, and 180 μL of ABTS was added. + , the absorbance is recorded as A0. After adding, use an enzyme reader to shake and mix, react for 30 minutes in the dark, measure the absorbance at 734nm, and calculate the free radical (ABTS + ) clearance rate, the results are as follows Fig.16 shown.

[0154] ABTS + Clearance rate = 1-(A1-A2) / A0×100%;

[0155] Among them, A1 is the sample and ABTS + The absorbance at 734 nm, A2 is the absorbance of the sample and deionized water at 734 nm, A0 is the absorbance of deionized water and ABTS + Absorbance at 734 nm.

[0156] Depend on Fig.15 It can be seen that the DPPH radical scavenging activity of each complex is significantly higher than that of resveratrol (34%), and pectin itself has a certain antioxidant capacity. The DPPH radical scavenging activities of T4 pectin, T3 pectin, T2 pectin, and T1 pectin are 23.75%, 17.30%, 24.48%, and 23.8%, respectively. The DPPH radical scavenging activities of RT4, RT3, RT2, and RT1 complexes are 91.02%, 85.78%, 87.35%, and 81.15%, respectively. Among them, the DPPH radical scavenging activity of the low esterification degree pectin complex RT1 is the strongest. However, due to the low purity of RT1-1, RT1-2, and RT1-3 complexes, their DPPH radical scavenging activities are lower than RT1.

[0157] Depend on Fig.16 It can be seen that the ABTS of resveratrol alone + The clearance rate was 29.25%, and the ABTS of T4 pectin, T3 pectin, T2 pectin, and T1 pectin + The clearance rates were only 2.13%, 3.03%, 1.89% and 3.8%; the ABTS of RT4, RT3, RT2 and RT1 complexes + The clearance rates were 23.63%, 23.1%, 51.93%, and 68.53%, respectively, and there were significant differences, and they were significantly higher than the corresponding pectins. Among them, the ABTS of the low-ester pectin complex RT1 was +The clearance rate of RT1-1, RT1-2 and RT1-3 complexes was the highest, which may be due to the high content of resveratrol embedded in low-fat pectin. In addition, low-fat pectin may be more conducive to the function of resveratrol phenolic hydroxyl groups. + The clearance rate is lower than that of RT1.

[0158] Determination of resveratrol release in simulated gastrointestinal digestion in vitro

[0159] The dialysis bag method was used to simulate the gastrointestinal digestion process and evaluate the in vitro release characteristics of free resveratrol and complexes. The simulated gastric juice and intestinal juice were incubated to 37°C. The concentration of resveratrol and the four complexes was 10 mg / mL. 3 mL of resveratrol solution and the four complex solutions were mixed with 3 mL of simulated gastric juice and placed in a dialysis bag (3500Da). The dialysis bag was placed in 60 mL of simulated gastric juice for 2 hours. After the simulated gastric digestion was completed, 6 mL of the incubated simulated intestinal juice was added to the dialysis bag of the previous step of simulated gastric digestion, and the dialysis bag was transferred to 120 mL of simulated intestinal juice for 4 hours of dialysis. Every 30 minutes, 1 mL of dialysate outside the bag was taken into a 96-well plate, and free resveratrol was measured at 306 nm. The release amount of resveratrol was calculated according to the following formula:

[0160] Release amount (%) = resveratrol content in supernatant / initial amount of resveratrol × 100%.

[0161] The results are as follows Fig.17 As shown. Fig.17 It can be seen that free resveratrol is rapidly released within 2 hours of gastric digestion, with a release rate of 47.45%. Resveratrol in the complex is slowly released. After 2 hours of gastric digestion, the release rates of RT4, RT3, RT2, and RT1 complexes are 28.62%, 26.26%, 29.46%, and 17.74%, respectively, which are significantly lower than the release rate of resveratrol monomer. Among them, the release rate of low-esterification pectin complex RT1 is the lowest. Further study of the release of resveratrol in simulated intestinal fluid showed that free resveratrol was rapidly released by 59.3% within 0.5 hours of intestinal fluid. The release of the complex was significantly lower than that of free resveratrol. The release of RT4, RT3, RT2, and RT1 complexes was 36.62%, 33.31%, 38.06%, and 25.34%, respectively. The release rate of free resveratrol was significantly higher than that of the complex. After 6 hours of gastrointestinal digestion, the release amount of resveratrol in the low-esterification pectin complex RT1 was the lowest, only 31.2%. From the release amount, the RT1 complex had the best protection effect on resveratrol, which may be due to the better solubility of low-esterification pectin and the encapsulation of more resveratrol.

[0162] Bioaccessibility determination of complexes after digestion

[0163] After the simulated gastrointestinal digestion, the bioaccessibility of resveratrol and the complex was determined by measuring the content of resveratrol in the micelles. Resveratrol and pectin-resveratrol complexes with different esterification degrees were digested in simulated gastric juice for 2 hours and intestinal juice for 4 hours, and then centrifuged at 10,000 rpm / min for 30 minutes. The supernatant was taken and the resveratrol content was detected at 306 nm. The bioaccessibility of resveratrol was calculated according to the following formula:

[0164] Bioaccessibility (%) = resveratrol content in supernatant / resveratrol content before digestion × 100%.

[0165] The results are as follows Fig.18 As shown. Fig.18 It can be seen that the bioaccessibility of resveratrol encapsulated by pectin is significantly improved compared with free resveratrol. The bioaccessibility of free resveratrol is 25.08%, and the bioaccessibility of RT4, RT3, RT2, and RT1 complexes are 64.85%, 66.64%, 70.32%, and 74.36%, respectively. Among them, low-ester pectin has a significantly higher effect on improving the bioaccessibility of resveratrol than other pectins.

[0166] Although the embodiments of the present invention have been disclosed as above, they are not limited to the applications listed in the specification and the implementation modes, and they can be fully applied to various fields suitable for the present invention. For those familiar with the art, additional modifications can be easily implemented. Therefore, without departing from the general concept defined by the claims and the scope of equivalents, the present invention is not limited to the specific details and the illustrations shown and described herein.

Claims

1. A method for preparing a highly stable and bioaccessible resveratrol-pectin complex, characterized in that: The following steps are involved: Step 1, dissolving high-ester pectin in water, adjusting the pH value to 11, and then reacting at 20-30°C for 20-30 minutes, maintaining a constant pH value during the reaction, and adjusting the pH value to 2 after deesterification, and then adding anhydrous ethanol to produce precipitation, filtering, washing, and drying to obtain low-ester pectin with an esterification degree of less than 30%; Step 2: dissolving the low-ester pectin and resveratrol in a solvent respectively, and then stirring the low-ester pectin solution and the resveratrol solution at 25-35° C. for 20-40 minutes to obtain a resveratrol-pectin mixed solution; Step 3: using a ceramic composite membrane to separate and purify the resveratrol-pectin mixed solution, and freeze-drying it to obtain the resveratrol-pectin complex; The method for preparing the ceramic composite membrane comprises the following steps: Step a, dissolving polyimide and polyethersulfone in dimethyl sulfoxide to prepare solutions with the same concentration, mixing the polyimide solution and the polyethersulfone solution, heating to 50-80° C. and stirring for 30 minutes, then adding sodium polystyrene sulfonate, stirring, and ultrasonically dispersing for 30 minutes to obtain a mixed solution with a solid content of 8-12%, wherein the weight ratio of the polyimide, polyethersulfone and sodium polystyrene sulfonate is 2:1:0.08; Step b, immersing the alumina flat ceramic membrane in a 0.5% by mass aqueous solution of hexadecyltrimethylammonium bromide for 30 minutes, rinsing, and drying to obtain a base membrane; Step c, connecting a scraper to an electrostatic generator, setting the electrostatic field strength to 5 kV / cm, and scraping the mixed solution onto the surface of the base film to a thickness of 30 to 50 μm; Step d, placing the base film coated with the mixed solution in a vacuum drying oven, heating the temperature to 100°C at a heating rate of 10°C / min, keeping the temperature constant for 1 hour, continuing to heat the temperature to 150°C at a heating rate of 5°C / min, keeping the temperature constant for 1 hour, then heating the temperature to 190°C at a heating rate of 1°C / min, keeping the temperature constant for 3 hours, and cooling to room temperature to obtain the ceramic composite film.

2. The method for preparing the highly stable and bioaccessible resveratrol-pectin complex according to claim 1, characterized in that: In the step 1, the concentration of high ester pectin after being dissolved in water is 0.05 g / mL.

3. The method for preparing the highly stable and bioaccessible resveratrol-pectin complex according to claim 1, characterized in that: The specific washing process in the step 1 is: soaking the precipitate with a mixed solvent made of concentrated hydrochloric acid with a mass fraction of 36% to 38% and an ethanol solution with a volume fraction of 60% in a volume ratio of 1:20, stirring, filtering again, rinsing with the above mixed solvent 3 times, and then rinsing with an ethanol solution with a volume fraction of 60% until the filtrate does not contain chloride ions.

4. The method for preparing the highly stable and bioaccessible resveratrol-pectin complex according to claim 1, characterized in that: In the step 2, low-ester pectin is dissolved in water to form a low-ester pectin solution with a concentration of 1 mg / mL.

5. The method for preparing the highly stable and bioaccessible resveratrol-pectin complex according to claim 4, characterized in that: In the step 2, resveratrol is dissolved in ethanol to form a resveratrol solution with a concentration of 0.5 mg / mL; in the step 2, the low-ester pectin solution and the resveratrol solution are stirred at a volume ratio of 2:1 at 25-35° C. for 20-40 minutes.

6. The method for preparing the highly stable and bioaccessible resveratrol-pectin complex according to claim 1, characterized in that: In the step three, freeze drying is performed under the conditions of -80°C and 10Pa.

7. The method for preparing the highly stable and bioaccessible resveratrol-pectin complex according to claim 1, characterized in that: The average pore size of the alumina flat ceramic membrane is 20 μm, and the surface pore size of the ceramic composite membrane is 8-11 μm.

8. The method for preparing the highly stable and bioaccessible resveratrol-pectin complex according to claim 1, characterized in that: The solid content of the mixed solution in step a is 10%.

9. The method for preparing the highly stable and bioaccessible resveratrol-pectin complex according to claim 1, characterized in that: The coating thickness in step c is 40 μm.

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