Green and environment-friendly method for extracting apple polyphenol from apples

Abstract

The invention relates to the technical field of polyphenol extraction, and provides a green and environment-friendly method for extracting apple polyphenol from apples, which comprises the following steps: mixing choline chloride and L-lactic acid, adding water, and stirring at 55-65 DEG C to form a uniform eutectic solvent extracting agent; the method comprises the following steps: mixing apple powder with a deep-eutectic solvent extracting agent, and carrying out normal-pressure stirring extraction at 65-75 DEG C; diluting the extracting solution, adjusting the pH value, loading a sample to a macroporous adsorption resin column, eluting with water and an ethanol water solution in sequence, and collecting an ethanol eluent rich in apple polyphenol; concentrating and drying the ethanol eluent to obtain an apple polyphenol product; and meanwhile, combining the effluent of the resin column with the washing liquid, dehydrating and concentrating, and recycling the regenerated extracting agent. The extraction efficiency and purity of apple polyphenol are improved, the loss of active ingredients due to high temperature, oxidation and the like is avoided, and the color and the activity of the product are ensured; the efficient regeneration cycle of the extracting agent is also realized, and the production cost is reduced.

Description

Technical Field

[0001] This invention relates to the field of polyphenol extraction technology, specifically to a green and environmentally friendly method for extracting apple polyphenols from apples. Background Technology

[0002] Apple polyphenols are a collective term for various phenolic compounds found in apples, mainly including flavonoids, phenolic acids, and anthocyanins. These compounds possess significant biological activity. In terms of antioxidation, they can scavenge free radicals in the body, slow down cellular oxidative damage, and prevent the occurrence of various chronic diseases. In the food industry, apple polyphenols can serve as natural antioxidants and preservatives, extending the shelf life of food. In the pharmaceutical field, they can be used to develop drugs for treating cardiovascular diseases, cancer, and other ailments. In the cosmetics industry, they can be used to prepare skincare products with whitening and anti-aging effects.

[0003] Currently, several green and environmentally friendly methods for extracting apple polyphenols from apples have been reported. Some of these methods use natural, low-toxicity solvents, such as water and ethanol, to reduce environmental pollution. For example, some studies have used water extraction, employing water as a solvent to extract polyphenols from apple raw materials under specific temperature and time conditions. While existing green and environmentally friendly methods reduce environmental pollution to some extent, they still have shortcomings in terms of extraction efficiency and product purity. Taking water extraction as an example, due to the strong polarity of water, it is not effective in extracting some less polar polyphenols from apples, resulting in low extraction efficiency. Furthermore, the extract obtained by water extraction has a high impurity content, making subsequent purification steps complex and increasing production costs.

[0004] Furthermore, during the extraction process, active ingredients such as apple polyphenols are easily lost due to high temperatures and oxidation. Some existing extraction methods, in pursuit of higher extraction efficiency, often employ high extraction temperatures, which leads to oxidative degradation of apple polyphenols, reducing the product's activity and color. For methods using organic solvents as extraction agents, the recovery and recycling of these agents is a crucial issue. If the extractant cannot be effectively recovered and recycled, it will not only increase production costs but also pollute the environment. Existing extractant recovery methods, such as distillation and extraction, suffer from high energy consumption and complex operations, and the purity of the recovered extractant may be affected, resulting in reduced extraction efficiency when reused. Therefore, this invention proposes a green and environmentally friendly method for extracting apple polyphenols from apples. Summary of the Invention

[0005] This invention proposes a green and environmentally friendly method for extracting apple polyphenols from apples, which improves the extraction efficiency and purity of apple polyphenols, avoids the loss of active ingredients due to high temperature and oxidation, and ensures the color and activity of the product; it also realizes efficient regeneration and recycling of the extractant, reducing production costs.

[0006] The technical solution of the present invention is as follows: Firstly, this invention proposes a green and environmentally friendly method for extracting apple polyphenols from apples, comprising the following steps: (1) Raw material pretreatment: The apple pomace is dried and ultra-finely pulverized to obtain apple powder; (2) Preparation of extractant: Mix choline chloride and L-lactic acid at a molar ratio of 1:1.5-2.5, add water, and stir at 55-65℃ to form a homogeneous eutectic solvent extractant; (3) Extraction: The apple powder is mixed with the eutectic solvent extractant and extracted under normal pressure at 65-75℃; (4) Purification: Solid-liquid separation was then performed to obtain the extract; the extract was diluted and the pH was adjusted, and then loaded onto a macroporous adsorption resin column. The column was eluted with water and ethanol aqueous solution in sequence, and the ethanol eluent rich in apple polyphenols was collected. (5) Post-processing: The ethanol eluent is concentrated and dried to obtain apple polyphenol product; at the same time, the effluent from the resin column and the washing liquid are combined, dehydrated and concentrated, and the regeneration extractant is recovered.

[0007] This invention introduces an appropriate amount of water into the extractant. While a completely anhydrous extractant can still be formed, its excessively high viscosity limits its actual extraction efficiency. Water significantly reduces the viscosity and surface tension of the extractant, improving its flowability and wetting and penetrating ability to plant cell walls. When the extractant comes into contact with apple powder, its excellent wetting and penetrating ability allows it to enter the apple cells more quickly and fully, contacting and dissolving the apple polyphenols. This greatly improves the mass transfer process, achieving a synergistic effect of extractant performance optimization and efficient extraction.

[0008] As a further technical solution, in step (1), the drying is to dry the apple pomace at 45-55℃ until the moisture content is ≤7.5%; the ultrafine grinding is to grind the dried apple pomace at -20±2℃ and pass it through a 100-mesh sieve.

[0009] In this invention, low-temperature drying effectively prevents the loss of active ingredients in apple pomace due to high temperatures, ensuring the stability of components such as apple polyphenols. Ultrafine pulverization is carried out at a low temperature, which on the one hand prevents polyphenol oxidation caused by temperature rise during pulverization, and on the other hand, pulverizing the apple pomace to a suitable particle size and sieving it significantly increases the specific surface area of ​​the raw material. This increases the contact area between the extractant and the raw material during subsequent extraction, facilitating the full penetration of the extractant into the raw material and improving the dissolution efficiency of polyphenols.

[0010] As a further technical solution, in step (2), the amount of water added is 10%-20% of the total weight of choline chloride and L-lactic acid.

[0011] As a further technical solution, in step (3), the liquid-solid ratio of the apple powder to the eutectic solvent extractant is (10-20): 1 mL / g; the extraction time is 30-60 min.

[0012] As a further technical solution, in step (3), before the extraction at 65-75℃ and normal pressure, the mixture is pre-mixed and moistened at 35-40℃ for 8-12 minutes; after the extraction is completed, the extracted mixture is cooled to below 50℃ before solid-liquid separation.

[0013] The extraction process of this invention includes premixing and wetting, staged temperature-controlled extraction, and post-extraction cooling. Before extraction at 65-75℃ under normal pressure with stirring, the mixture is premixed and wetted at 35-40℃ for 8-12 minutes. Premixing and gradient temperature increase effectively promote raw material wetting and reduce thermal shock. Under the relatively mild conditions of 35-40℃, the extractant gradually penetrates into the raw material cells, initiating the polyphenol dissolution process, allowing polyphenol molecules to gradually diffuse from the cells into the extractant. Subsequently, the temperature is increased to 65-75℃. At this temperature, molecular motion intensifies, accelerating the dissolution and diffusion of polyphenols in the extractant, further improving extraction efficiency. Simultaneously, staged temperature control initiates polyphenol dissolution under relatively mild conditions, reducing thermal oxidation in the subsequent high-temperature extraction stage and preventing polyphenol loss due to excessive oxidation, thus ensuring the color and activity of the product. After extraction, the extracted mixture is cooled to below 50℃ before solid-liquid separation to prevent further oxidation of polyphenols at high temperatures and to prevent changes in the solubility of impurities at high temperatures from affecting the separation effect, ensuring the purity and activity of polyphenols in the extract.

[0014] As a further technical solution, in step (4), the dilution is to add an equal volume of deionized water to the extract; the pH adjustment is to adjust the pH value of the diluted solution to 4.0-5.0.

[0015] As a further technical solution, in step (4), the macroporous adsorption resin is AB-8 type resin, and the resin column has been equilibrated with a solution of pH 4.5 before loading the sample; the elution is to first rinse with 2-3 column volumes of water, and then elute with 3-4 column volumes of 70% (v / v) ethanol aqueous solution.

[0016] As a further technical solution, in step (4), after the solid-liquid separation, the filter residue is washed with a 20% (v / v) ethanol aqueous solution at 50°C, and the washing liquid is incorporated into the extract.

[0017] As a further technical solution, in step (5), the concentration is carried out under the conditions of temperature ≤60℃ and vacuum degree -0.08 MPa; the drying is spray drying, with an air inlet temperature of 175-185℃ and an air outlet temperature of 80-90℃.

[0018] As a further technical solution, in step (5), the dehydration and concentration are carried out at 60-70°C and a vacuum degree of not less than -0.09 MPa.

[0019] The working principle and beneficial effects of this invention are as follows: This invention utilizes choline chloride and L-lactic acid as extraction agents, with the addition of water. Choline chloride and L-lactic acid are mixed in a specific molar ratio, and at a suitable temperature, they form a stable eutectic solvent system through interactions such as hydrogen bonding. The introduction of an appropriate amount of water significantly reduces the viscosity and surface tension of the extractant, improving its flowability and wetting and penetration ability to plant cell walls. This unique hydrogen-bonded network structure gives the extractant excellent solubility and selectivity for apple polyphenols, offering superior extraction performance compared to traditional organic solvents, and is also safe and biodegradable.

[0020] By comparing with several comparative examples, such as extractants prepared using glucose as a hydrogen bond donor and extractants using citric acid as an acceptor, it was found that the composition of the extractant has a decisive influence on its extraction performance. Compared with L-lactic acid, glucose has different hydrogen bond donation / acceptance capabilities, resulting in extractants with weaker viscosity, polarity, hydrogen bond network structure, and interaction with the target polyphenols, leading to reduced solubility and mass transfer efficiency for apple polyphenols. Citric acid is highly acidic and has a complex molecular structure; extractants formed with L-lactic acid may have excessively high viscosity, or relatively poor chemical stability during extraction, concentration, and regeneration (possibly leading to partial esterification or decomposition), affecting their extraction efficiency for polyphenols and their recyclability. The ChCl-LA system formed by choline chloride and L-lactic acid achieves a better balance between efficiency, stability, and recyclability, demonstrating that selecting a suitable extractant composition is the core of optimizing the extraction process. By precisely controlling the extractant composition, efficient and green extraction of apple polyphenols can be achieved. Detailed Implementation

[0021] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0022] Example 1 This embodiment provides a green and environmentally friendly method for extracting apple polyphenols from apples, the steps of which include: (1) Take fresh apple pomace produced by the juice factory, spread it evenly on a tray, and dry it in a 50℃ hot air circulating drying oven for 8 hours to reduce its moisture content to 7.5%; put the dried apple pomace into a vibrating ultra-micro pulverizer that has been pre-cooled to -20℃ by liquid nitrogen, pulverize it for 2 minutes, pass it through a 100-mesh standard sieve, and put it in a nitrogen-filled sealed bag for later use. (2) Weigh food-grade choline chloride (ChCl, hydrogen bond acceptor) and L-lactic acid (LA, hydrogen bond donor) in a molar ratio of 1:2; start stirring and heat to 60°C, slowly add deionized water accounting for 15% of the total weight of ChCl and LA; continue stirring at 200 rpm for about 90 min at this temperature until a homogeneous, transparent, viscous liquid without any crystals is formed, thus obtaining the ChCl-LA extractant; cool to room temperature. (3) Weigh 100.0g of apple powder and add 1.5 liters of the ChCl-LA extractant prepared above (liquid-solid ratio 15:1 mL / g). Turn on the stirrer at 150 rpm. First, premix the mixture under stirring and heat it to 35-40℃ through the jacket circulating water, and keep it for 10 min to fully wet and disperse the raw materials. Then, set the jacket temperature to 70℃, heat the mixture and keep it at 70℃. Under these conditions, stir and extract under normal pressure for 40 min to complete the initial wetting and dissolution (first stage extraction). Then, turn off the heating and cool the extracted mixture to below 50℃ under stirring. The material temperature is precisely controlled by the jacket throughout the process. (4) After extraction, turn off the vacuum and restore normal pressure; perform solid-liquid separation on the extraction mixture to obtain clear extract A and filter residue. Wash the filter residue with 20% (v / v) ethanol aqueous solution at 50℃, and add the washing solution to extract A. Add an equal volume of deionized water to extract A for dilution, and adjust the pH of the diluted extract to 4.5. Load the diluted solution at a flow rate of 2 BV / h. Before loading, the AB-8 macroporous adsorption resin column has been rinsed with 4 BV of 95% ethanol and deionized water until there is no alcohol odor, and balanced with a pH 4.5 buffer solution until the pH of the effluent is 4.5. Control the column volume: 1L, and the average particle size of the resin is 0.5mm. Polyphenols are effectively adsorbed by the resin, while the liquid containing extractant, sugars, and some organic acids is discharged as eluent B. After loading, the resin column is rinsed with two column volumes of deionized water at the same flow rate, and the wash solution C is combined with the eluent B. Subsequently, the resin column is eluted with three column volumes of 70% (v / v) ethanol aqueous solution at a flow rate of 1.5 BV / h. The eluent D is collected, which is a solution rich in high-purity apple polyphenols. (5) Transfer the eluent D into a vacuum concentration tank and recover ethanol at a temperature of 60℃ and -0.08MPa (the recovered ethanol can be purified and reused) to obtain concentrated apple polyphenol extract; spray dry the extract, control the inlet air temperature to 180℃ and the outlet air temperature to 85℃ to obtain powdered apple polyphenol product E, and immediately fill it with nitrogen for packaging. Meanwhile, the combined effluent, along with washing solutions B and C, is transferred to another vacuum concentration tank for dehydration and concentration at 65°C and -0.09 MPa; the distilled water is condensed and recovered to obtain the regenerated extractant.

[0023] Example 2 This embodiment provides a green and environmentally friendly method for extracting apple polyphenols from apples, the steps of which include: (1) Take fresh apple pomace produced by the juice factory, spread it evenly on a tray, and dry it in a 55℃ hot air circulating drying oven for 8 hours to reduce its moisture content to 7.5%; put the dried apple pomace into a vibrating ultra-micro pulverizer that has been pre-cooled to -18℃ by liquid nitrogen, pulverize it for 2 minutes, pass it through a 100-mesh standard sieve, and put it in a nitrogen-filled sealed bag for later use. (2) Weigh food-grade choline chloride (ChCl, hydrogen bond acceptor) and L-lactic acid (LA, hydrogen bond donor) at a molar ratio of 1:2.5; start stirring and heat to 65°C, slowly add 20% of the total weight of ChCl and LA of deionized water; continue stirring at 200 rpm for about 90 min at this temperature until a homogeneous, transparent, viscous liquid without any crystals is formed, thus obtaining the ChCl-LA extractant; cool to room temperature. (3) Weigh 100.0g of apple powder and add 2.0L of the ChCl-LA extractant prepared above (liquid-solid ratio 20:1 mL / g). Turn on the stirrer at 150 rpm. First, premix the mixture under stirring and heat it to 40℃ through the jacket circulating water, and keep it for 12min to fully wet and disperse the raw materials. Then, set the jacket temperature to 75℃, heat the mixture and keep it at 75℃. Under these conditions, stir and extract under normal pressure for 60min. Then, turn off the heating and cool the extracted mixture to below 50℃ under stirring. The material temperature is precisely controlled by the jacket throughout the process. (4) After extraction, the vacuum was turned off and the atmospheric pressure was restored. The extraction mixture was subjected to solid-liquid separation to obtain a clear extract A and a filter residue. The filter residue was washed with a 20% (v / v) ethanol aqueous solution at 50℃, and the washing solution was added to extract A. Extract A was diluted with an equal volume of deionized water, and the pH of the diluted extract was adjusted to 5.0. The diluted solution was loaded at a flow rate of 2 BV / h. Before loading, the AB-8 macroporous adsorption resin column was rinsed sequentially with 4 BV of 95% ethanol and deionized water until there was no alcohol odor, and equilibrated with a pH 4.5 buffer solution until the pH of the effluent was 4.5. The column volume was controlled at 1L and the average resin particle size was 0.5mm. Polyphenols are effectively adsorbed by the resin, while the liquid containing extractant, sugars, and some organic acids is discharged as eluent B. After loading, the resin column is rinsed with 3 column volumes of deionized water at the same flow rate, and the wash solution C is combined with the eluent B. Subsequently, the resin column is eluted with 4 column volumes of 70% (v / v) ethanol aqueous solution at a flow rate of 1.5 BV / h. The eluent D is collected, which is a solution rich in high-purity apple polyphenols. (5) Transfer the eluent D into a vacuum concentration tank and recover ethanol at a temperature of 60℃ and a pressure of -0.08MPa to obtain concentrated apple polyphenol extract; spray dry the extract, control the inlet air temperature to 185℃ and the outlet air temperature to 90℃ to obtain powdered apple polyphenol product E, and immediately fill it with nitrogen for packaging. Meanwhile, the combined effluent, along with washing solutions B and C, is transferred to another vacuum concentration tank for dehydration and concentration at 70°C and -0.09 MPa. The distilled water is condensed and recovered to obtain the regenerated extractant.

[0024] Example 3 This embodiment provides a green and environmentally friendly method for extracting apple polyphenols from apples, the steps of which include: (1) Take fresh apple pomace produced by the juice factory, spread it evenly on a tray, and dry it in a 45℃ hot air circulating drying oven for 8 hours to reduce its moisture content to 7.5%; put the dried apple pomace into a vibrating ultra-micro pulverizer that has been pre-cooled to -22℃ by liquid nitrogen, pulverize it for 2 minutes, pass it through a 100-mesh standard sieve, and put it in a nitrogen-filled sealed bag for later use. (2) Weigh food-grade choline chloride (ChCl, hydrogen bond acceptor) and L-lactic acid (LA, hydrogen bond donor) at a molar ratio of 1:1.5; start stirring and heat to 55°C, slowly add deionized water accounting for 10% of the total weight of ChCl and LA; continue stirring at 200 rpm for about 90 min at this temperature until a homogeneous, transparent, viscous liquid without any crystals is formed, thus obtaining the ChCl-LA extractant; cool to room temperature. (3) Weigh 100.0g of apple powder and add 1.0L of the ChCl-LA extractant prepared above (liquid-solid ratio 10:1 mL / g). Turn on the stirrer at 150 rpm. First, premix the mixture under stirring and heat it to 35℃ through the jacket circulating water, and keep it for 8 minutes to fully wet and disperse the raw materials. Then, set the jacket temperature to 65℃, heat the mixture and keep it at 65℃. Under these conditions, stir and extract under normal pressure for 30 minutes. Then, turn off the heating and cool the extracted mixture to below 50℃ under stirring. The material temperature is precisely controlled by the jacket throughout the process. (4) After extraction, the vacuum was turned off and the atmospheric pressure was restored. The extraction mixture was subjected to solid-liquid separation to obtain a clear extract A and a filter residue. The filter residue was washed with a small amount of 20% (v / v) ethanol aqueous solution at 50℃, and the washing solution was added to extract A. Extract A was diluted with an equal volume of deionized water, and the pH of the diluted extract was adjusted to 4.0. The diluted solution was loaded at a flow rate of 2 BV / h. Before loading, the AB-8 macroporous adsorption resin column was rinsed with 4 BV of 95% ethanol and deionized water until there was no alcohol odor, and equilibrated with a pH 4.5 buffer solution until the pH of the effluent was 4.5. The column volume was controlled at 1L and the average resin particle size was 0.5mm. Polyphenols are effectively adsorbed by the resin, while the liquid containing extractant, sugars, and some organic acids is discharged as eluent B. After sample loading, the resin column is rinsed with two column volumes of deionized water at the same flow rate, and the wash solution C is combined with the eluent B. Subsequently, the resin column is eluted with three column volumes of 70% (v / v) ethanol aqueous solution at a flow rate of 1.5 BV / h. The eluent D is collected, which is a solution rich in high-purity apple polyphenols. (5) Transfer the eluent D into a vacuum concentration tank and recover ethanol at a temperature ≤60℃ and -0.08MPa to obtain concentrated apple polyphenol extract; spray dry the extract, control the inlet air temperature to 175℃ and the outlet air temperature to 80℃ to obtain powdered apple polyphenol product E, and immediately fill it with nitrogen for packaging. Meanwhile, the combined effluent, along with washing solutions B and C, is transferred to another vacuum concentration tank for dehydration and concentration at 60°C and -0.09 MPa; the distilled water is condensed and recovered to obtain the regenerated extractant.

[0025] Comparative Example 1 The difference between this comparative example and Example 1 is that the extraction process did not use segmented temperature control and precise temperature program control. Specifically, apple powder was prepared according to step (1) of Example 1, and the same ChCl-LA extractant was prepared according to step (2). After weighing 100.0g of apple powder and adding 1.5L of extractant (liquid-solid ratio 15:1 mL / g), the premixing, segmented heating and constant temperature program in step (3) were not performed; instead, after turning on the stirrer (150 rpm), the mixture was directly heated to 70℃ and extracted at this temperature for 40min. After the extraction was completed, solid-liquid separation, dilution and purification were performed as in step (4) of Example 1, and concentration, drying and solvent recovery were performed according to step (5).

[0026] Comparative Example 2 This comparative example uses the traditional organic solvent acetone aqueous solution for extraction. Specifically, steps (2) and (3) of Example 1 are not performed. The extraction steps are as follows: 100.0g of apple powder prepared in step (1) of Example 1 is weighed and 1.5L of 50% (v / v) acetone aqueous solution is added. The mixture is placed in an ultrasonic extractor and extracted for 30min at 50℃ and ultrasonic power of 300W. After extraction, the mixture is filtered and the residue is washed with a small amount of acetone aqueous solution of the same concentration. The filtrate and washings are combined and the acetone is recovered by vacuum distillation at 45℃ and -0.08 MPa. The subsequent purification, concentration and drying steps are the same as steps (4)-(5) of Example 1, but the extractant is not regenerated.

[0027] Comparative Example 3 This comparative example uses pure water as the extraction solvent. Specifically, steps (2) and (3) of Example 1 are not performed. The extraction steps are as follows: Weigh 100.0g of apple powder prepared in step (1) of Example 1 and add 1.5L of deionized water; place the mixture in a reflux device and heat it at 90℃ for reflux extraction for 1.5h; after extraction, filter it while it is hot and wash the residue with hot water; combine the filtrate and the washing liquid, and the subsequent purification, concentration and drying steps are the same as steps (4)-(5) of Example 1.

[0028] Comparative Example 4 The difference between this comparative example and Example 1 is that steps (2) and (3) of Example 1 are not performed; the extraction steps are as follows: weigh 100.0g of apple powder prepared in step (1) of Example 1, add 1.5 liters of sodium hydroxide aqueous solution with pH 9.0; stir the mixture at 60°C for 1 h; after extraction, immediately adjust the pH of the extract to near neutral with dilute hydrochloric acid, and then filter; the subsequent purification, concentration and drying steps are the same as steps (4)-(5) of Example 1.

[0029] Comparative Example 5 The difference between this comparative example and Example 1 is that steps (2) and (3) of Example 1 are not performed; the extraction steps are as follows: weigh 100.0g of apple powder prepared in step (1) of Example 1, add 1.5L of 95% (v / v) ethanol aqueous solution; place the mixture in a reflux device and heat and reflux at 78℃ (near the boiling point of ethanol) for 2h; after extraction, filter while hot, and wash the filter residue with hot ethanol; combine the filtrate and the washing liquid, and the subsequent purification, concentration and drying steps are the same as steps (4)-(5) of Example 1, but the extractant is not regenerated.

[0030] Comparative Example 6 The difference between this comparative example and Example 1 is that step (2) of Example 1 is not followed; instead, food-grade choline chloride (hydrogen bond acceptor) and D-glucose (hydrogen bond donor) are weighed at a molar ratio of 1:1; after mixing the two, 20% of the total weight of deionized water is slowly added while stirring at 60°C and 200 rpm, and stirring is continued for about 120 min until a uniform, transparent viscous liquid is formed, thus obtaining the choline chloride-glucose extract. The extract is then cooled to room temperature; all subsequent steps such as extraction, purification, and solvent recovery are exactly the same as steps (3)-(5) of Example 1.

[0031] Comparative Example 7 The difference between this comparative example and Example 1 is that step (2) of Example 1 is not followed; instead, food-grade citric acid (hydrogen bond acceptor) and L-lactic acid (LA) (hydrogen bond donor) are weighed at a molar ratio of 1:1; after mixing the two, 20% of the total weight of deionized water is slowly added while stirring at 60°C and 200 rpm, and stirring is continued for about 120 min until a uniform, transparent viscous liquid is formed, thus obtaining the citric acid-lactic acid extractant. The extractant is then cooled to room temperature; all subsequent steps such as extraction, purification, and solvent recovery are exactly the same as steps (3)-(5) of Example 1.

[0032] Comparative Example 8 The difference between this comparative example and Example 1 is that food-grade choline chloride (ChCl) and L-lactic acid (LA) were weighed in a molar ratio of 1:2, mixed, and stirred continuously at 60°C and 200 rpm for about 120 minutes until a homogeneous, transparent, anhydrous viscous liquid was formed, thus obtaining the anhydrous ChCl-LA extractant. The remaining steps are exactly the same as in Example 1.

[0033] Experimental Example 1: The apple polyphenols prepared in Examples 1-3 and Comparative Examples 1-8 were tested as follows: Total phenol content determination: Refer to the spectrophotometric principle in GB / T 31740.2-2015 "Tea Products Part 2: Tea Polyphenols"; Accurately weigh 10.0 mg of gallic acid standard dried to constant weight, dissolve it in 60% ethanol and dilute to 100 mL to obtain a 100 μg / mL gallic acid standard stock solution; accurately pipette 0, 0.2, 0.4, 0.6, 0.8 and 1.0 mL of the standard stock solution into 10 mL stoppered colorimetric tubes, and add 60% ethanol to make up to 1.0 mL. At this point, the gallic acid concentrations were 0, 20, 40, 60, 80, and 100 μg / mL, respectively. 0.5 mL of Folin-Ciocalteu reagent (pre-diluted with distilled water) was added to each tube, vortexed, and allowed to stand at room temperature in the dark for 5 min. 2.0 mL of 10% (w / v) sodium carbonate solution was added, and the volume was adjusted to 10 mL with 60% ethanol, and thoroughly mixed. After standing at room temperature in the dark for 60 min, the absorbance (A) of each tube was measured at 760 nm using a 1 cm cuvette, with tube "0" as the reference. A standard curve was plotted with gallic acid concentration (μg / mL) as the x-axis (X) and absorbance (A) as the y-axis (Y), yielding the linear regression equation Y = aX + b. Accurately weigh 0.1 g of dried apple polyphenol product E, dissolve it in 60% ethanol, transfer and dilute to a 100 mL volumetric flask, shake well, and use as the sample stock solution; accurately pipette 0.5 mL of the sample stock solution into a 10 mL colorimetric tube, and add 60% ethanol to a final volume of 1.0 mL. Total phenol content (mg GAE / g): Substitute the measured absorbance of the sample into the regression equation of the standard curve to obtain the gallic acid equivalent concentration (C, μg / mL) in the test solution; calculate according to the following formula: Total phenol content = (C×V×D) / (m×1000); where, C: concentration of the test solution obtained from the standard curve (μg / mL); V: sample volume (mL, here 10mL); D: dilution factor (if the sample stock solution is diluted after absorption, then D = total volume of stock solution / sample volume; if there is no secondary dilution, then D = 1); m: mass of the sample (g); 1000: unit conversion factor (μg to mg). Total phenol extraction rate (%): Extraction rate = (Mp×Pp) / (Mr×Pr)×100%; where, Mp: mass of the final apple polyphenol product E (g); Pp: total phenol content of product E (mg GAE / g); Mr: mass of the raw apple powder used for extraction (g); Pr: total phenol content of the raw apple powder (mg GAE / g); Polyphenol yield (mass yield): The final apple polyphenol product E obtained in step (5) is accurately weighed, and the yield is calculated as follows: Yield (%) = (mass of polyphenol product E / mass of raw apple powder) × 100%; Color: The lightness (L) value of powder product E is measured using a colorimeter. A lighter color (higher L value) usually indicates a lower degree of oxidation and better quality.

[0034] Extractant recovery rate: The combined effluent and washing liquid (B+C) were transferred to a vacuum concentration unit of known weight (W1); dehydration and concentration were carried out at 65℃ and -0.09MPa until the distillate was minimal and the material was viscous; the concentrated regenerated extractant was transferred to a dry container of known weight (W2), cooled to room temperature, and the total weight (W3) was accurately weighed; Total mass recovery rate (%) = [(W3-W2) / total mass of initial extractant input] × 100%; The results are shown in Table 1 below: Table 1

[0035] Based on the foregoing, the ChCl-LA extractant segmented temperature-controlled extraction method represented by Examples 1-3 achieves the best balance in three dimensions: extraction efficiency (high extraction rate and yield), product quality (high purity, high activity, and good color), and process sustainability (efficient recycling of extractant).

[0036] Compared to Example 1, Comparative Example 1 showed a significant decrease in both extraction efficiency and product quality. This directly demonstrates the crucial role of the segmented temperature control procedure in this method. Premixing and gradient heating (holding at 35-40℃ and then increasing to 70℃) effectively promote raw material wetting, reduce thermal shock, and initiate polyphenol dissolution under relatively mild conditions. This reduces thermal oxidation in the subsequent high-temperature extraction stage, ultimately resulting in higher extraction efficiency and better product color. Simple direct heating extraction, on the other hand, leads to higher oxidation losses.

[0037] Comparative Example 2 used the traditional organic solvent acetone for extraction, and its extraction efficiency and product purity were close to or even slightly lower than those of Example 1, and it lacked solvent recycling capability. Although acetone is an effective solvent for polyphenol extraction, this comparison shows that the ChCl-LA extractant can achieve or even surpass the extraction performance of traditional organic solvents. More importantly, the methods in the examples have significant advantages in terms of greenness and circular economy: acetone is flammable and toxic, requiring strict protection and energy-intensive distillation recovery, and there is a risk of residue; while the extractant is safe, biodegradable, and can be efficiently regenerated and recycled through simple dehydration.

[0038] Comparative Example 3 showed the lowest performance across all indicators for the pure water extraction method, with efficiency and quality far inferior to the extractant method. Water exhibits poor solubility and selectivity for polyphenols (especially low- to medium-polarity polyphenols), and prolonged high-temperature reflux exacerbates the dissolution of impurities such as polysaccharides and proteins, and may promote polyphenol oxidation or hydrolysis, resulting in low extraction rates, poor product purity, and dark color. This contrasts sharply with the superior solubility and selectivity of extractants for polyphenols through their unique hydrogen-bonded network.

[0039] Comparative Example 4: Alkaline extraction resulted in severe deterioration of product quality. Although the extraction rate was acceptable, the total phenol content and color of the product were extremely poor. While alkaline conditions can increase the dissolution rate of polyphenols (ionization of phenolic hydroxyl groups), they also drastically damage the chemical structure of polyphenols, particularly causing ester bond hydrolysis (such as the decomposition of chlorogenic acid), isomerization and oxidative polymerization of flavanols such as catechins, leading to loss of biological activity and severe browning of the product. This demonstrates the significant advantage of extraction solvents in terms of gentle, non-destructive extraction.

[0040] Comparative Example 5: The traditional ethanol extraction method is roughly equivalent to or slightly inferior to the extractant method in terms of efficiency and product quality, but it also lacks recyclability. Ethanol is a commonly used polyphenol extractant in the food industry with excellent performance. This comparison once again highlights the comprehensive competitiveness of the extractant method. While achieving the same technical level, extractants (especially the ChCl-LA system) have advantages in operational safety, energy consumption, and long-term production costs due to their low volatility, non-flammability, and closed-loop recovery characteristics.

[0041] Comparative Example 6, using glucose as a hydrogen bond donor, showed a significantly lower extraction efficiency than the ChCl-LA system. This demonstrates that the composition of the extractant has a decisive influence on its extraction performance. Compared to L-lactic acid, glucose has different hydrogen bond donation / acceptance capabilities, resulting in a weaker interaction between the extracted agent's viscosity, polarity, hydrogen bond network structure, and the target polyphenols, leading to reduced solubility and mass transfer efficiency for apple polyphenols. Therefore, the screening and design of extractants are crucial for optimizing the extraction process.

[0042] Comparative Example 7, using citric acid as the acceptor, exhibited lower extraction efficiency and product quality compared to the ChCl-LA system, with a slightly lower recovery rate. Citric acid's strong acidity and complex molecular structure may result in extractants with LA that have excessively high viscosity, or relatively poor chemical stability during extraction, concentration, and regeneration (potentially leading to partial esterification or decomposition), affecting their polyphenol extraction efficiency and recyclability. In contrast, the ChCl-LA system achieved a better balance between efficiency, stability, and recyclability.

[0043] Compared to the completely anhydrous extractant system in Example 8, the extraction efficiency was significantly lower than that of the aqueous system. This demonstrates that introducing an appropriate amount of water into the extractant is a necessary optimization method. Water can significantly reduce the viscosity and surface tension of the extractant, improve its flowability and wetting and penetration ability to plant cell walls, thereby greatly improving the mass transfer process and increasing the extraction kinetic efficiency. Although a completely anhydrous extractant can still be formed, its excessively high viscosity limits its actual extraction effect.

[0044] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A green and environmentally friendly method for extracting apple polyphenols from apples, characterized by the following steps: include: (1) Raw material pretreatment: The apple pomace is dried and ultra-finely pulverized to obtain apple powder; (2) Preparation of extractant: Mix choline chloride and L-lactic acid at a molar ratio of 1:1.5-2.5, add water, and stir at 55-65℃ to form a homogeneous eutectic solvent extractant; (3) Extraction: The apple powder is mixed with the eutectic solvent extractant and extracted under normal pressure at 65-75℃; (4) Purification: Solid-liquid separation was then performed to obtain the extract; After diluting and adjusting the pH of the extract, it was loaded onto a macroporous adsorption resin column and eluted sequentially with water and ethanol aqueous solution. The ethanol eluent rich in apple polyphenols was collected. (5) Post-processing: The ethanol eluent is concentrated and dried to obtain apple polyphenol product; at the same time, the effluent from the resin column and the washing liquid are combined, dehydrated and concentrated, and the regeneration extractant is recovered.

2. The green and environmentally friendly method for extracting apple polyphenols from apples according to claim 1, characterized in that, In step (1), the drying process involves drying the apple pomace at 45-55℃ until the moisture content is ≤7.5%; the ultrafine grinding process involves grinding the dried apple pomace at -20±2℃ and passing it through a 100-mesh sieve.

3. The green and environmentally friendly method for extracting apple polyphenols from apples according to claim 1, characterized in that, In step (2), the amount of water added is 10%-20% of the total weight of choline chloride and L-lactic acid.

4. The green and environmentally friendly method for extracting apple polyphenols from apples according to claim 1, characterized in that, In step (3), the liquid-to-solid ratio of the apple powder to the eutectic solvent extractant is (10-20): 1 mL / g; the extraction time is 30-60 min.

5. A green and environmentally friendly method for extracting apple polyphenols from apples according to claim 1, characterized in that, In step (3), before the extraction at 65-75℃ under normal pressure, the mixture is pre-mixed and moistened at 35-40℃ for 8-12 minutes; after the extraction is completed, the extracted mixture is cooled to below 50℃ before solid-liquid separation.

6. The green and environmentally friendly method for extracting apple polyphenols from apples according to claim 1, characterized in that, In step (4), the dilution is to add an equal volume of deionized water to the extract; the pH adjustment is to adjust the pH value of the diluted solution to 4.0-5.

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7. The green and environmentally friendly method for extracting apple polyphenols from apples according to claim 1, characterized in that, In step (4), the macroporous adsorption resin is AB-8 type resin, and the resin column has been equilibrated with a solution of pH 4.5 before loading the sample; the elution is to first rinse with 2-3 column volumes of water, and then elute with 3-4 column volumes of 70% (v / v) ethanol aqueous solution.

8. A green and environmentally friendly method for extracting apple polyphenols from apples according to claim 1, characterized in that, In step (4), after the solid-liquid separation, the filter residue is washed with a 20% (v / v) ethanol aqueous solution at 50°C, and the washing liquid is incorporated into the extract.

9. A green and environmentally friendly method for extracting apple polyphenols from apples according to claim 1, characterized in that, In step (5), the concentration is carried out at a temperature ≤60℃ and a vacuum degree of -0.08 MPa; the drying is spray drying with an inlet air temperature of 175-185℃ and an outlet air temperature of 80-90℃.

10. A green and environmentally friendly method for extracting apple polyphenols from apples according to claim 1, characterized in that, In step (5), the dehydration and concentration are carried out at 60-70°C and a vacuum degree of not less than -0.09 MPa.

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