Preparation method of persimmon tannin-pectin compound based on natural eutectic solvent

Abstract

The invention discloses a preparation method of a persimmon tannin-pectin compound based on a natural deep-eutectic solvent, which realizes green, synchronous and efficient extraction of two functional components of persimmon tannin and pectin by reasonably screening and designing the natural deep-eutectic solvent, and also realizes simple recovery and reutilization of the natural deep-eutectic solvent. And the economical efficiency and sustainability of the preparation process are improved. The product prepared by the method disclosed by the invention is a unique compound containing two functional components, namely persimmon tannin and persimmon pectin, and the product shows more excellent capability of stabilizing a high-internal-phase emulsion system than single persimmon pectin, so that the product has potential application value in the fields of food, cosmetics, medicines and the like due to the characteristic.

Description

Technical Field

[0001] The present invention belongs to the technical field of extraction of natural products from persimmons, and particularly relates to a method for preparing persimmon tannin-pectin complex based on natural deep eutectic solvents. Background Art

[0002] In recent years, the research on natural products from persimmons has mainly focused on the single extraction and activity exploration of biological macromolecules such as tannins and pectins in persimmons. At present, the methods for separately extracting persimmon tannins and pectins as two target components mainly include: solvent extraction method (commonly using water or ethanol for extraction), ultrasonic-assisted extraction method, enzymatic hydrolysis method (using enzymes to decompose cell walls to release complexes), etc. Specifically, the extraction of persimmon tannins is carried out by high-temperature reflux extraction using a variety of organic solvents including methanol, ethanol or acetone under the assistance of strong acid (usually hydrochloric acid) and high temperature (usually greater than 90 °C), and multiple repeated operations (usually 3-5 times) are required to achieve a relatively high yield of persimmon tannins; similarly, the extraction of persimmon pectin is usually also completed by long-time leaching (usually 1-3 h) under acidic (adjusting the pH value of the extraction solution by hydrochloric acid, sulfuric acid or citric acid, etc.) and high temperature (greater than 90 °C) environments.

[0003] Persimmon tannin-pectin complex is one of the natural forms of the two functional components, tannins and pectins, in persimmons, and thus has various potential biological activities and application values. At present, there is no report on the extraction method of persimmon tannin-pectin complex. The existing extraction processes for natural products from persimmons generally have problems such as single extraction products (only tannins or pectins can be extracted separately), high extraction costs (requiring high temperature and strong acid environments), cumbersome steps, low extraction efficiency (requiring multiple repeated extractions or long-time leaching), and organic solvent residues, which further limit the further industrial application. Summary of the Invention

[0004] Aiming at the problems existing in the above-mentioned prior art, the purpose of the present invention is to provide a method for preparing persimmon tannin-pectin complex based on natural deep eutectic solvents.

[0005] In order to achieve the above purpose, the present invention adopts the following technical solutions:

[0006] A method for preparing persimmon tannin-pectin complex based on natural deep eutectic solvents, comprising the following steps:

[0007] S1. Perform de-sugaring treatment on persimmons to obtain de-sugared persimmon powder;

[0008] S2. Mix the de-sugared persimmon powder with NADES, carry out leaching, and after the extraction is completed, centrifuge the obtained extraction solution to collect the supernatant;

[0009] S3. Add the obtained supernatant to anhydrous ethanol, mix well, let it stand for precipitation, collect the precipitate by centrifugation, and vacuum freeze-dry to obtain persimmon tannin-pectin complex;

[0010] Preferably, the steps for deglycosylation of persimmons specifically include:

[0011] Perform dehydration treatment on fresh persimmon fruits, powder them to obtain persimmon powder; then add the persimmon powder to 10% ethanol for washing, subsequently collect the precipitate by centrifugation, vacuum freeze-dry, pulverize the freeze-dried powder, and sieve to obtain deglycosylated persimmon powder.

[0012] Preferably, in step S2, the mass-volume ratio of the deglycosylated persimmon powder to NADES is 1 g: 20 - 45 mL.

[0013] Preferably, in step S2, the extraction temperature is 60 - 100 °C.

[0014] Preferably, in step S2, the extraction time is 20 - 45 min.

[0015] Preferably, in step S2, the rotation speed during extraction is 150 - 450 rpm.

[0016] Preferably, the synthesis of NADES includes the following steps:

[0017] Add a hydrogen bond acceptor and a hydrogen bond donor to water, stir at 60 - 90 °C for 3 - 9 h until a clear, homogeneous and transparent liquid is formed to obtain a natural deep eutectic solvent (NADES); wherein, the molar ratio of the hydrogen bond acceptor to the hydrogen bond donor is 5:2 - 1:3; the hydrogen bond acceptor is selected from any one of choline chloride, betaine and L-proline, and the hydrogen bond donor is selected from carboxylic acid, diol, polyol, urea or glucose.

[0018] Preferably, the carboxylic acid is selected from any one of lactic acid, malonic acid, malic acid, tartaric acid and citric acid, the diol is selected from any one of ethylene glycol, 1,2-propanediol, 1,3-propanediol and 1,3-butanediol, the polyol is selected from any one of glycerol, xylitol and sorbitol, and L-proline and glucose cannot be used simultaneously because they will undergo a Maillard reaction at high temperatures.

[0019] Preferably, in step S2, the centrifugal force during centrifugation is 6000 - 10000 × g, and the centrifugation time is 10 - 25 min.

[0020] Preferably, in step S3, the volume ratio of the supernatant to anhydrous ethanol is 1:2 - 6.

[0021] Preferably, in step S3, the standing time is 8 - 24 h, and the cooling temperature is 0 - 4 °C.

[0022] Preferably, in step S3, the vacuum freeze-drying temperature is -50 to -60 °C, and the time is 24 to 48 h.

[0023] Preferably, it further includes: S4, recycling and reuse of NADES:

[0024] The supernatant obtained after centrifugally collecting the precipitate in step S3 is rotary evaporated under negative pressure to remove absolute ethanol, and NADES is recovered.

[0025] Preferably, the negative pressure is -0.08 to -0.1 MPa, the rotary evaporation temperature is 35 to 60 °C, and the rotary evaporation time is 2 to 6 h.

[0026] Compared with the prior art, the present invention has the following beneficial effects:

[0027] (1) The present invention provides a preparation method of persimmon tannin-pectin complex based on natural deep eutectic solvents. This method abandons the traditional idea of using organic reagents, high temperature, multiple times or long time for separate extraction of persimmon tannin and persimmon pectin. Through reasonable screening and design of NADES, green, synchronous and efficient extraction of two functional components, persimmon tannin and pectin, is realized. At the same time, simple recovery and reuse of NADES are also achieved, improving the economy and sustainability of the preparation process.

[0028] (2) The product prepared by the present invention mainly contains a unique complex containing both persimmon tannin and persimmon pectin as two functional components, and this product shows better ability to stabilize high internal phase emulsion systems than single persimmon pectin. This characteristic makes it have potential application value in the fields of food, cosmetics and medicine. Description of the Drawings

[0029] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following will briefly introduce the drawings required to be used in the embodiments. Obviously, the drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can be obtained based on these drawings.

[0030] Figure 1 It is the high performance liquid chromatography of the extract in Example 1;

[0031] Figure 2 It is the ultraviolet-visible spectrum of the product in Example 1;

[0032] Figure 3 It is the infrared spectrum: (a) persimmon tannin; (b) persimmon pectin; (c) persimmon tannin-pectin complex;

[0033] Figure 4Yield results of persimmon tannin-pectin complexes at different extraction temperatures;

[0034] Figure 5 Yield results of persimmon tannin-pectin complexes at different extraction times;

[0035] Figure 6 Yield results of persimmon tannin-pectin complexes at different liquid-solid ratios;

[0036] Figure 7 Emulsifying activities of persimmon pectin and persimmon tannin-pectin complexes at different oil phase volume fractions: (a) persimmon pectin; (b) persimmon tannin-pectin complex. Detailed implementation manners

[0037] In the following description, specific details such as specific system structures and technologies are presented for the purpose of illustration rather than limitation, so as to thoroughly understand the embodiments of the present invention. However, those skilled in the art should clearly understand that the present invention can also be implemented in other embodiments without these specific details.

[0038] Example 1

[0039] (1) Desugaring treatment of persimmons:

[0040] The fresh persimmon fruits were dehydrated by vacuum freeze-drying at -50°C for 48 h, ground into powder and stored at -20°C. Then, the obtained persimmon powder was added to 10% ethanol at a solid-liquid ratio of 1 g:10 mL, washed at 25°C for 2 h, centrifuged at 4°C and 8000×g for 15 min after washing, the precipitate was collected, vacuum freeze-dried at -50°C for 48 h, and the freeze-dried powder was crushed through a 100-mesh sieve to obtain desugared persimmon powder;

[0041] (2) Synthesis of NADES: Betaine was selected as the hydrogen bond acceptor and urea as the hydrogen bond donor. Betaine, urea and water were mixed at a molar ratio of 1:2:12, and stirred at 80°C and 200 rpm for 6 h until a clear, homogeneous and transparent liquid was formed to obtain NADES;

[0042] (3) Synchronous extraction of persimmon tannin and pectin: The obtained desugared persimmon powder was mixed with NADES at a solid-liquid ratio of 1 g:35 mL, extracted in a water bath at 80°C and 200 rpm for 40 min, cooled to 4°C after extraction, and centrifuged at 4°C and 8000×g for 15 min, and the supernatant was collected;

[0043] (4) Isolation of the extracted product persimmon tannin-pectin complex: Mix the supernatant obtained in step (3) with absolute ethanol at a volume ratio of 1:3 (v / v). After mixing, let it stand at 4°C for 12 h, then centrifuge at 4°C and 8000×g for 15 min. Collect the precipitate and vacuum freeze-dry it at -50°C for 24 h to obtain the persimmon tannin-pectin complex;

[0044] (5) Recycling of NADES: Rotate and evaporate the supernatant collected by centrifugation in step (4) at 40°C and -0.1 MPa for 4 h to remove the residual absolute ethanol. The water content of the recycled NADES is measured by a Karl Fischer moisture meter, and then the lost water is supplemented until the molar ratio of betaine, urea and water is 1:2:12, and then it is repeatedly applied to extraction step (3).

[0045] (6) Storage of the extracted product persimmon tannin-pectin complex: Store the obtained persimmon tannin-pectin complex in a three-layer composite octagonal sealed zipper bag. Among them, the inner layer of the three-layer composite octagonal sealed zipper bag is made of food-grade polyethylene material to ensure food safety contact and sealing effect. The middle layer is made of polypropylene material, which can provide overall strength, toughness and moisture-proof effect. The outer layer is made of aluminum foil material, which can provide oxygen barrier, moisture-proof, anti-ultraviolet effect and enhance the anti-tearing and compressive ability of the overall packaging material.

[0046] The yield of the persimmon tannin-pectin complex obtained in this example is 255.4 mg / g of defatted persimmon powder.

[0047] Example 2

[0048] The steps of this example are basically the same as those of Example 1, except that the extraction temperature in step (3) is 60°C.

[0049] The yield of the persimmon tannin-pectin complex obtained in this example is 204.4 mg / g of defatted persimmon powder.

[0050] Example 3

[0051] The steps of this example are basically the same as those of Example 1, except that the extraction temperature in step (3) is 70°C.

[0052] The yield of the persimmon tannin-pectin complex obtained in this example is 223.4 mg / g of defatted persimmon powder.

[0053] Example 4

[0054] The steps of this example are basically the same as those of Example 1, except that the extraction temperature in step (3) is 90°C.

[0055] The yield of the persimmon tannin-pectin complex obtained in this example is 257.6 mg / g of defatted persimmon powder.

[0056] Example 5

[0057] The steps of this example are basically the same as those of Example 1. The difference is that in the synchronous extraction of persimmon tannin and pectin in step (3), the extraction temperature is 100 °C.

[0058] The yield of the persimmon tannin-pectin complex obtained in this example is 221.2 mg / g of defatted persimmon powder.

[0059] Example 6

[0060] The steps of this example are basically the same as those of Example 2. The difference is that in the synchronous extraction of persimmon tannin and pectin in step (3), the solid-liquid ratio of defatted persimmon powder to NADES is 1 g: 40 mL.

[0061] The yield of the persimmon tannin-pectin complex obtained in this example is 197.1 mg / g of defatted persimmon powder.

[0062] Example 7

[0063] The steps of this example are basically the same as those of Example 2. The difference is that in the synchronous extraction of persimmon tannin and pectin in step (3), the solid-liquid ratio of defatted persimmon powder to NADES is 1 g: 45 mL.

[0064] The yield of the persimmon tannin-pectin complex obtained in this example is 186.0 mg / g of defatted persimmon powder.

[0065] Example 8

[0066] The steps of this example are basically the same as those of Example 2. The difference is that in the synchronous extraction of persimmon tannin and pectin in step (3), the solid-liquid ratio of defatted persimmon powder to NADES is 1 g: 20 mL.

[0067] The yield of the persimmon tannin-pectin complex obtained in this example is 180.5 mg / g of defatted persimmon powder.

[0068] Example 9

[0069] The steps of this example are basically the same as those of Example 2. The difference is that in the synchronous extraction of persimmon tannin and pectin in step (3), the solid-liquid ratio of defatted persimmon powder to NADES is 1 g: 25 mL.

[0070] The yield of the persimmon tannin-pectin complex obtained in this example is 191.2 mg / g of defatted persimmon powder.

[0071] Example 10

[0072] The steps of this example are basically the same as those of Example 2. The difference is that in the synchronous extraction of persimmon tannin and pectin in step (3), the solid-liquid ratio of defatted persimmon powder to NADES is 1 g: 30 mL.

[0073] The yield of the persimmon tannin-pectin complex obtained in this example is 203.0 mg / g of defatted persimmon powder.

[0074] Example 11

[0075] The steps of this example are basically the same as those of Example 1, except that in the synchronous extraction of persimmon tannin and pectin in step (3), the extraction time is 20 min.

[0076] The yield of the persimmon tannin-pectin complex obtained in this example is 139.5 mg / g of defatted persimmon powder.

[0077] Example 12

[0078] The steps of this example are basically the same as those of Example 1, except that in the synchronous extraction of persimmon tannin and pectin in step (3), the extraction time is 25 min.

[0079] The yield of the persimmon tannin-pectin complex obtained in this example is 187.0 mg / g of defatted persimmon powder.

[0080] Example 13

[0081] The steps of this example are basically the same as those of Example 1, except that in the synchronous extraction of persimmon tannin and pectin in step (3), the extraction time is 35 min.

[0082] The yield of the persimmon tannin-pectin complex obtained in this example is 255.5 mg / g of defatted persimmon powder.

[0083] Example 14

[0084] The steps of this example are basically the same as those of Example 1, except that in the synchronous extraction of persimmon tannin and pectin in step (3), the extraction time is 40 min.

[0085] The yield of the persimmon tannin-pectin complex obtained in this example is 253.5 mg / g of defatted persimmon powder.

[0086] Example 15

[0087] The steps of this example are basically the same as those of Example 1, except that in the synchronous extraction of persimmon tannin and pectin in step (3), the extraction time is 45 min.

[0088] The yield of the persimmon tannin-pectin complex obtained in this example is 254.5 mg / g of defatted persimmon powder.

[0089] Example 16

[0090] The steps of this example are basically the same as those of Example 6, except that in the synthesis of NADES in step (2), L-proline is selected as the hydrogen bond acceptor and urea is used as the hydrogen bond donor.

[0091] The yield of the persimmon tannin-pectin complex obtained in this example is 218.7 mg / g of defatted persimmon powder.

[0092] Example 17

[0093] The steps of this example are basically the same as those of Example 2, except that in the synthesis of NADES in step (2), betaine is selected as the hydrogen bond acceptor and urea is used as the hydrogen bond donor, and the molar ratio of betaine, urea and water is 2:1:15; in the synchronous extraction of persimmon tannin and pectin in step (3), the solid-liquid ratio of defatted persimmon powder to NADES is 1 g:30 mL.

[0094] The yield of the persimmon tannin-pectin complex obtained in this example is 172.3 mg / g of defatted persimmon powder.

[0095] Example 18

[0096] The steps of this example are basically the same as those of Example 17, except that in the synthesis of NADES in step (2), choline chloride is selected as the hydrogen bond acceptor and citric acid is used as the hydrogen bond donor, and the molar ratio of choline chloride, citric acid and water is 5:2:18.

[0097] The yield of the persimmon tannin-pectin complex obtained in this example is 145.8 mg / g of defatted persimmon powder.

[0098] Example 19

[0099] The steps of this example are basically the same as those of Example 17, except that in the synthesis of NADES in step (2), betaine is selected as the hydrogen bond acceptor and malic acid is used as the hydrogen bond donor, and the molar ratio of betaine, malic acid and water is 2:1:9.

[0100] The yield of the persimmon tannin-pectin complex obtained in this example is 158.1 mg / g of defatted persimmon powder.

[0101] Example 20

[0102] The steps of this example are basically the same as those of Example 17, except that in the synthesis of NADES in step (2), L-proline is selected as the hydrogen bond acceptor and 1,3-butanediol is used as the hydrogen bond donor, and the molar ratio of L-proline, 1,3-butanediol and water is 1:3:15.

[0103] The yield of the persimmon tannin-pectin complex obtained in this example is 135.8 mg / g of defatted persimmon powder.

[0104] Performance Characterization

[0105] (1) Identification by high performance liquid chromatography: The extract was filtered through a 0.22 μm filter membrane and then measured using an Agilent 1200 high performance liquid chromatography system. The chromatographic column selected was ZORBAX SB-Aq (4.6×250 mm, 5 μm), the mobile phase was (A) 0.13% trifluoroacetic acid / water and (B) 0.1% trifluoroacetic acid / acetonitrile, and the binary gradient elution program (43 min) was: 0-21 min, 0-60% B; 21-29 min, 60-100% B; 29-33 min, 100% B; 33-43 min, 100-0% B. The detection temperature was 20-25°C; the injection volume was 10 μL; the flow rate was 1 mL / min; and the PDA detection wavelength was 280 nm. Results are shown in Table 1. Figure 1 .

[0106] Depend on Figure 1 The results show that, in addition to a small amount of free gallic acid (peak at 7.5 minutes), the main components of the extract are high molecular weight tannin and pectin complexes (peak at 10-20 minutes), and an obvious peak that cannot be effectively separated is presented in the liquid phase spectrum.

[0107] (2) Determination of UV-visible absorption spectrum of the product: Take 200 μL of the product aqueous solution (1 mg / mL) and use an ELISA reader to measure the UV-visible absorption spectrum at 200-600 nm. Use water as a blank control. The results are shown in Figure 2 .

[0108] Depend on Figure 2 The results show that from the UV-visible absorption spectrum of the product, it can be seen that the product has multiple irregular absorption peaks in the UV absorption range of 200-400nm, indicating that the product contains many types of groups and the chemical environment is relatively complex, and is essentially a complex.

[0109] (3) Infrared spectroscopic determination of persimmon tannin, persimmon pectin and products:

[0110] 10 mg of persimmon tannin, persimmon pectin or the product was fully mixed and ground with potassium bromide powder at a mass ratio of 1 mg:100 mg. The mixed powder was then prepared into a transparent sheet with a thickness of 1 mm using an air compressor. Nicoleti S50 Fourier transform infrared spectrometer was used at 4000-400 cm -1 Scanning is performed within the range with a scanning resolution of 4cm -1 , potassium bromide was used as blank control. Persimmon tannin and persimmon pectin were used as control examples. The results are shown in Figure 3 .

[0111] Depend on Figure 3(a) From the Fourier transform infrared spectroscopy results of persimmon tannin, it can be seen that there is an -OH stretching vibration signal at 3150 cm -1 wavelength, a methyl CH stretching vibration signal at 2930 cm -1 wavelength, a CH stretching vibration signal in the benzene ring at 2680 cm -1 wavelength, a C=O stretching vibration signal in -COOR at 1704 cm -1 wavelength, a C=C stretching vibration signal in the benzene ring at 1620 cm -1 wavelength, a polyphenol B-ring stretching vibration signal at 1527 cm -1 and an out-of-plane vibration signal of unsaturated CH in the aromatic ring in the wavelength range of 760 cm -1 wavelength.

[0112] From Figure 3 (b) From the Fourier transform infrared spectroscopy results of persimmon pectin, it can be seen that there is an -OH stretching vibration signal at 3405 cm -1 wavelength, a methyl CH stretching vibration signal at 2940 cm -1 wavelength, a C=O stretching vibration signal in -COOR at 1750 cm -1 , a C=C stretching vibration signal at 1610 cm -1 wavelength, and a pyranose ring signal in the wavelength range of 1100 - 1000 cm -1 wavelength.

[0113] From Figure 3 (c) From the Fourier transform infrared spectroscopy results of the product, it can be seen that there is an -OH stretching vibration signal at 3350 cm -1 wavelength, a methyl CH stretching vibration signal at 2965 cm -1 wavelength, and a CH stretching vibration signal in the benzene ring at 2700 cm -1 wavelength, indicating that the characteristic groups of both persimmon pectin and persimmon tannin are present in the product. At the same time, there is a polyphenol B-ring stretching vibration signal at 1530 cm -1 , a pyranose ring signal in the wavelength range of 1100 - 1000 cm -1 wavelength, and an out-of-plane vibration signal of unsaturated CH in the aromatic ring in the wavelength range of 780 - 730 cm -1 wavelength, further confirming that the product contains both persimmon tannin and persimmon pectin.

[0114] Combining the above Figure 3 (a)- Figure 3 (c) infrared spectroscopy results of persimmon tannin, persimmon pectin and the product, it can be seen that only a signal at 1620 cm is observed in the infrared spectrum of the product in the wavelength range of 1750 - 1600 cm -1 wavelength range.-1 At the wavelength, there are resonance signals of C=O stretching vibration in -COOR and C=C stretching vibration in the benzene ring, indicating that there may be a strong conjugation effect between the benzene ring and the carboxyl group in the product. Combining the above results, it shows that the persimmon tannin-pectin complex was successfully prepared in this invention.

[0115] 2. Detect the yields of the persimmon tannin-pectin complexes prepared in Examples 1-15, and the results are shown in Figures 4 - 6 .

[0116] From Figure 4 the results, it can be seen that under the conditions of the molar ratio of betaine, urea and water being 1:2:12, the solid-liquid ratio being 1 g:35 mL, and the extraction time being 40 min, the yields of the extracted persimmon tannin-pectin complexes were investigated at different extraction temperatures (60-100 °C), and it was obtained that: when the extraction temperature was 60 °C, the yield of the extracted persimmon tannin-pectin complex was 204.4 mg / g of defatted persimmon powder; when the extraction temperature was 80 °C, the yield of the extracted product reached 255.4 mg / g of defatted persimmon powder; when the extraction temperature was 90 °C, there was still a slight increase in the product yield (257.6 mg / g of defatted persimmon powder), but this yield value had no significant difference compared with the yield at 80 °C.

[0117] From Figure 5 the results, it can be seen that under the conditions of the molar ratio of betaine, urea and water being 1:2:12, the solid-liquid ratio being 1 g:35 mL, and the extraction temperature being 80 °C, the influence of different extraction times (20-45 min) on the product yield was investigated. The results showed that the product yield reached a relatively large value of 253.5 mg / g of defatted persimmon powder at 30 min, but there was no significant difference in the increase of the product yield as the time was further extended.

[0118] From Figure 6 the results, it can be seen that under the conditions of the molar ratio of betaine, urea and water being 1:2:12, the extraction temperature being 60 °C, and the extraction time being 40 min, the influence of different solid-liquid ratios (1 g:20-45 mL) on the product yield was investigated. The results showed that the product yield was the highest (209.6 mg / g of defatted persimmon powder) when the solid-liquid ratio was 1 g:35 mL.

[0119] 3. Detect the emulsifying activity of persimmon pectin and the persimmon tannin-pectin complex prepared in Example 1 at different oil phase volume fractions: Mix the aqueous solution of persimmon pectin or the aqueous solution of persimmon tannin-pectin complex with medium-chain triglycerides at different volume ratios so that the oil phase volume fraction is 20-80%, while ensuring that the final concentration of the product is 0.5% (m / v). Subsequently, perform high-speed shearing at a rate of 12,000 rpm for 2 min. After shearing, take 4 mL of the emulsion in a graduated centrifuge tube and centrifuge at 3000×g, 20-25 °C for 15 min. Finally, calculate the emulsifying activity = (height of the emulsified layer / total height) × 100. The results are shown in Figure 7 。

[0120] From Figure 7 (a) The results show that as the oil phase volume fraction increases from 20% to 75%, the emulsifying activity of persimmon pectin gradually increases from 17.7% to 73.5%.

[0121] From Figure 7 (b) The results show that as the oil phase volume fraction increases from 20% to 75%, the emulsifying activity of the product persimmon tannin-pectin complex can reach up to 87%. That is to say, under the same conditions, the product persimmon tannin-pectin complex has better emulsifying activity than single persimmon pectin.

[0122] It is particularly noteworthy that single persimmon pectin cannot effectively stabilize the oil-in-water emulsion system with an oil phase volume fraction as high as 80%, while the emulsifying activity of the product can still be maintained at around 80% under this condition, which means that the product has better potential for stabilizing high internal phase emulsion systems (oil phase volume fraction > 75%) than single persimmon pectin.

[0123] The present invention is not limited to the above specific embodiments. Those of ordinary skill in the art starting from the above concepts and making various transformations without creative labor fall within the protection scope of the present invention.

Claims

1. A method for preparing a persimmon tannin-pectin complex based on a natural deep eutectic solvent, characterized in that: The following steps are involved: S1, desugaring persimmons to obtain desugared persimmon powder; S2, mixing the desugared persimmon powder with NADES, extracting, centrifuging the obtained extract after the extraction is completed, and collecting the supernatant; S3. Mix the obtained supernatant with anhydrous ethanol, let it stand for precipitation, collect the precipitate by centrifugation, and freeze-dry it in vacuum to obtain a persimmon tannin-pectin complex.

2. The method for preparing a persimmon tannin-pectin complex based on a natural deep eutectic solvent according to claim 1, characterized in that: The desugaring treatment of persimmons comprises the following steps: The fresh persimmon fruit is dehydrated and powdered to obtain persimmon powder; the persimmon powder is then washed in 10% ethanol, and then the precipitate is collected by centrifugation, vacuum freeze-dried, and the freeze-dried powder is crushed and sieved to obtain the desugared persimmon powder.

3. The method for preparing a persimmon tannin-pectin complex based on a natural deep eutectic solvent according to claim 1, characterized in that: In step S2, the mass volume ratio of the desugared persimmon powder to NADES is 1 g: 20-45 mL.

4. The method for preparing a persimmon tannin-pectin complex based on a natural deep eutectic solvent according to claim 1, characterized in that: In step S2, the extraction temperature is 60-100° C., and the extraction time is 20-45 minutes.

5. The method for preparing a persimmon tannin-pectin complex based on a natural deep eutectic solvent according to claim 1, characterized in that: The synthesis of the NADES comprises the following steps: A hydrogen bond acceptor and a hydrogen bond donor are added into water, and the reaction is stirred at 60 to 90° C. for 3 to 9 hours until a clear and uniform transparent liquid is formed to obtain NADES; wherein the molar ratio of the hydrogen bond acceptor to the hydrogen bond donor is 5:2 to 1:3; the hydrogen bond acceptor is selected from any one of choline chloride, betaine and L-proline, and the hydrogen bond donor is selected from carboxylic acid, diol, polyol, urea or glucose.

6. The method for preparing a persimmon tannin-pectin complex based on a natural deep eutectic solvent according to claim 5, characterized in that: The carboxylic acid is selected from any one of lactic acid, malonic acid, malic acid, tartaric acid and citric acid, the diol is selected from any one of ethylene glycol, 1,2-propylene glycol, 1,3-propylene glycol and 1,3-butylene glycol, the polyol is selected from any one of glycerol, xylitol and sorbitol, and L-proline and glucose cannot be used at the same time.

7. The method for preparing a persimmon tannin-pectin complex based on a natural deep eutectic solvent according to claim 1, characterized in that: In step S2, the centrifugal force during the centrifugation is 6000-10000×g, and the centrifugation time is 10-25 min.

8. The method for preparing a persimmon tannin-pectin complex based on a natural deep eutectic solvent according to claim 1, characterized in that: In step S3, the volume ratio of the supernatant to anhydrous ethanol is 1:2-6; the standing time is 8-24 hours, the cooling temperature is 0-4°C; the vacuum freeze-drying temperature is -50--60°C, and the time is 24-48 hours.

9. The method for preparing a persimmon tannin-pectin complex based on a natural deep eutectic solvent according to claim 1, characterized in that: Also includes: S4. Recycling and reuse of NADES: The supernatant obtained after centrifugation and collection of the precipitate in step S3 is subjected to rotary evaporation under negative pressure to remove anhydrous ethanol and recover NADES, wherein the negative pressure is -0.08 to -0.1 MPa, the rotary evaporation temperature is 35 to 60° C., and the time is 2 to 6 hours.

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