A chitosan-coffee grounds nanoparticle composite and its preparation and application

Abstract

This invention relates to fruit juice flocculants, a chitosan-coffee grounds nanoparticle composite, its preparation and application, comprising the following steps: 1) Obtaining coffee grounds powder: drying and sieving coffee grounds to obtain the desired coffee grounds powder; 2) Dissolving the coffee grounds powder in water, heating, filtering, collecting the filtrate, passing it through a D101 macroporous resin column, eluting with water, dialyzing and drying the eluent to obtain coffee grounds nanoparticles; 3) Mixing a chitosan aqueous solution (chitosan:water) at a mass ratio of 1:100-400 with the coffee grounds nanoparticles and adding it to a reaction vessel for hydrothermal reaction; dialyzing and drying the resulting solution to obtain the chitosan-coffee grounds nanoparticle composite. This invention aims to use nanoparticles with good biocompatibility, low dosage, significant flocculation effect, good antioxidant properties, and visibility to modify chitosan, synthesizing a novel flocculant and providing a new approach for fruit juice clarification.

Description

Technical Field

[0001] This invention belongs to the field of natural products and nanoparticle technology, specifically relating to fruit juice flocculants, specifically a chitosan-coffee grounds nanoparticle composite, its preparation method, and its application. Background Technology

[0002] In recent years, with the improvement of people's living standards and the enhancement of health awareness, the market demand for fruit juice has been increasing, and sales have been rising year by year. Substances such as protein, pectin, and polyphenols in fruit juice can cause turbidity, affecting its taste and color. This quality problem greatly restricts the development of the fruit juice industry and is currently a major issue facing the industry.

[0003] Flocculants, as convenient and effective fruit juice clarification materials, can clarify fruit juice while preserving its quality as much as possible, making this method of fruit juice clarification widely used. Compared with flocculants such as bentonite and gelatin, chitosan is considered an ideal material for fruit juice flocculants due to its high cationic charge density, long polymer chains, and safety and non-toxicity. However, when chitosan is used as a fruit juice flocculant, it suffers from poor bridging ability and weak antioxidant capacity, which greatly limits its application in fruit juice clarification.

[0004] Nanoparticles refer to particles with a size between 1 and 100 nm, also known as ultrafine particles. Due to their high surface area, nanoscale materials often exhibit unique physical, chemical, biological, and optical properties compared to traditional materials due to surface effects. Furthermore, nanoparticles possess spatial effects; under the influence of quantum size effects, their photoelectric, thermal, and mechanical properties can all change, making them a novel type of material with excellent performance, diverse functions, and wide applications. Food-derived nanoparticles have significant advantages, such as wide availability, low cost, and good biocompatibility. Therefore, research on the modification of chitosan using food-derived nanoparticles has attracted considerable interest.

[0005] The waste generated throughout the entire process of fresh coffee cherries—from picking to roasting into coffee beans (Illycaffè, Itally), and then grinding (e.g., using a coffee machine) to brew (or extract with water) into coffee or to making other products—is called coffee grounds.

[0006] This invention aims to modify chitosan with nanoparticles that have good biocompatibility, low dosage, significant flocculation effect, good antioxidant properties, and visibility, thereby synthesizing a novel flocculant and providing a new approach for fruit juice clarification. Summary of the Invention

[0007] The purpose of this invention is to overcome the defects of the prior art and provide a chitosan-coffee grounds nanoparticle composite, which uses hydrothermal extraction to extract nanoparticles from coffee grounds and then combines them with chitosan to form water-soluble chitosan-coffee grounds nanoparticles, which can be used to flocculate turbid substances in apple juice.

[0008] This invention also provides the preparation of chitosan-coffee grounds nanoparticle composites by the above method and their applications.

[0009] To achieve the above objectives, the present invention adopts the following technical solution:

[0010] 1) Obtaining coffee grounds: After coffee beans (Illycaffè, Itally) are ground and extracted by a coffee machine, the unextracted portion is dried and sieved (30 mesh) to obtain coffee grounds powder.

[0011] 2) Preparation of coffee grounds-derived nanoparticles: coffee grounds powder is dissolved in deionized water, heated for 3-5 hours, filtered through filter paper, the filtrate is collected, passed through a D101 macroporous resin column, impurities are removed by elution with deionized water, the eluent is collected, the eluent is concentrated by rotary evaporation to obtain a coffee grounds nanoparticle solution, which is then dialyzed (withholding solution) and freeze-dried to obtain nanoparticles.

[0012] 3) Preparation of chitosan-coffee grounds nanoparticle composite: A chitosan solution with a mass ratio (chitosan:water) of 1:200-400 was mixed with the coffee grounds nanoparticles prepared in step 1) and added to a reaction vessel for hydrothermal reaction for 1-4 hours. The resulting solution was then dialyzed (with the retentate) and freeze-dried to obtain the chitosan-coffee grounds nanoparticle composite.

[0013] Specifically, in step 1), 4-8g of coffee grounds are dissolved in 20-30 times the amount of deionized water.

[0014] Specifically, in step 1), the heating temperature is 50-90℃ and the time is 3-5 hours.

[0015] Specifically, in step 1), the product is eluted with deionized water, and the volume of the eluent is 2-6L.

[0016] Specifically, in step 2), the hydrothermal temperature is 160-200℃.

[0017] Specifically, in steps 1) and 2), the molecular weight cutoff of the dialysis bag used for dialysis is 1000-3000 kDa.

[0018] This invention provides a method for preparing coffee grounds nanoparticles using the above-described method.

[0019] This invention provides a method for preparing chitosan-coffee grounds nanoparticle composites using the above-described method.

[0020] The present invention also provides the application of the above-mentioned chitosan-coffee grounds nanoparticle composite in apple juice flocculation.

[0021] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0022] 1) The nanoparticles in this invention are extracted from waste coffee grounds, making full use of resources and being green and environmentally friendly.

[0023] 2) Chitosan has the problem of poor solubility. This invention combines it with coffee grounds nanoparticles to improve its solubility and expand its application range.

[0024] 3) The chitosan-coffee ground nanoparticle composite prepared by the present invention can improve the problem of poor flocculation effect of chitosan in apple juice and has better flocculation performance for apple juice. Attached Figure Description

[0025] Figure 1 The particle size distribution of coffee grounds nanoparticles was obtained in Example 1;

[0026] Figure 2 Scanning electron microscope images of chitosan-coffee ground nanoparticle composites synthesized at different times; (a) CS, (b) chitosan-coffee ground nanoparticle composite synthesized at 1 h (Example 1), (c) chitosan-coffee ground nanoparticle composite synthesized at 3 h (Example 2);

[0027] Figure 3 Infrared spectra of chitosan-coffee ground nanoparticle composites at different synthesis times; CS, 1h (Example 1), 3h (Example 2);

[0028] Figure 4 The effects of chitosan-coffee ground nanoparticle composites on apple juice flocculation at different synthesis times are shown in the figures: (a) 20℃, (b) 30℃, (c) 40℃, and (d) 50℃.

[0029] Figure 5 Figure showing the protein content of the supernatant after apple juice flocculation by chitosan-coffee grounds nanoparticle complexes synthesized at different times;

[0030] Figure 6 Figure 1. Effect of chitosan-coffee ground nanoparticle composites at different synthesis times on the total phenol content of the supernatant after apple juice flocculation.

[0031] Figure 7 Protein content standard curve;

[0032] Figure 8 Standard curve for total phenol content. Detailed Implementation

[0033] The technical solution of the present invention will be further described in detail below with reference to the embodiments, but the scope of protection of the present invention is not limited thereto.

[0034] Example 1

[0035] A method for preparing a chitosan-coffee grounds nanoparticle composite includes the following steps:

[0036] 1) Obtaining coffee grounds: Coffee beans (Illycaffè, Itally) are ground in a coffee machine and extracted with water (to obtain drinking coffee). The portion that is not extracted by water is dried and sieved (30 mesh) to obtain the powder that passes through the sieve, which is coffee grounds.

[0037] 2) Preparation of coffee grounds nanoparticles: 5g of coffee grounds powder was dissolved in 100mL of deionized water and heated in an 80℃ constant temperature water bath for 3h. The solution was filtered through filter paper (Xinxing quantitative filter paper, Φ=11cm, pore size 30-50μm), and the filtrate was collected. The solution was passed through a D101 macroporous resin column (macroporous resin: Donghong Chemical Co., Ltd., column length: 15cm, inner diameter: 1.2cm) and eluted with deionized water to remove impurities (eluted until no fluorescence was observed). The eluent was collected in a total of 3L. The eluent was concentrated to 0.6L by rotary evaporation to obtain a coffee grounds nanoparticle solution. The solution was dialyzed through a 2500kDa dialysis bag for 24h, with the water changed every 6h. The retentate solution was freeze-dried to obtain coffee grounds nanoparticles (1.015g) (NPs, particle size <100nm).

[0038] 3) Preparation of chitosan-coffee grounds nanoparticle composite: 30 mL of chitosan solution (chitosan:water) at a mass ratio of 1:300 was mixed with the coffee grounds nanoparticles prepared in step 2) and added to a hydrothermal reactor. The mixture was reacted at 180℃ in an electric thermostatic drying oven for 1 h. The reacted solution was dialyzed through a 2500 kDa dialysis bag for 24 h, with water changed every 6 h. The dialyzed solution (retentate) was freeze-dried to obtain 2.424 g of chitosan-coffee grounds nanoparticle composite powder (1 h).

[0039] Example 2

[0040] 1) Obtaining coffee grounds: Coffee grounds are obtained by drying the unextracted portion of coffee beans (Illycaffè, Itally) after they have been ground and extracted by a coffee machine and then sieved (30 mesh).

[0041] 2) Preparation of coffee grounds nanoparticles: 5g of coffee grounds powder was dissolved in 100mL of deionized water and heated in an 80℃ constant temperature water bath for 3h. The solution was filtered through filter paper (Xinxing quantitative filter paper, Φ=11cm), and the filtrate was collected. The solution was passed through a D101 macroporous resin column (column length: 15cm, inner diameter: 1.2cm) and eluted with deionized water to remove impurities (eluted until no fluorescence was observed). The eluent was collected in a total of 3L. The eluent was concentrated to 0.5L by rotary evaporation to obtain a coffee grounds nanoparticle solution. The solution was dialyzed through a 2500kDa dialysis bag for 24h, with the water changed every 6h. The retentate solution was freeze-dried to obtain coffee grounds nanoparticles (1.015g) (NPs, particle size <100nm).

[0042] 3) Preparation of chitosan-coffee grounds nanoparticle composite: 30 mL of chitosan solution with a mass ratio (chitosan:water) of 1:300 was mixed with the coffee grounds nanoparticles prepared in step 1) and added to a hydrothermal reactor. The mixture was reacted at 180℃ in an electric thermostatic drying oven for 3 h. The reacted solution was dialyzed through a 2500 kDa dialysis bag for 24 h, with the water changed every 6 h. The dialyzed solution (retentate) was freeze-dried to obtain 2.045g (3h) of chitosan-coffee grounds nanoparticle composite powder.

[0043] The following experiments were conducted using the chitosan-coffee ground nanoparticle composites prepared in Example 1 (1h) and Example 2 (3h) as examples, and chitosan that was not synthesized with coffee ground nanoparticles was used as a comparison.

[0044] Depend on Figure 1 It can be seen that the product obtained from coffee grounds in Examples 1 and 2 (coffee ground nanoparticles (NPs)) has a particle size of 25.42 nm ± 6.31 nm, proving that nanoparticles (nanoparticle size of 1-100 nm) were successfully prepared.

[0045] Depend on Figure 2 It is known that chitosan has a spherical structure, while the chitosan-coffee ground nanoparticle composite synthesized in Examples 1 and 2 has a network structure. Due to the difference in structure, the chitosan-coffee ground nanoparticle composite is more likely to play a network trapping role, thus giving it a better flocculation effect in apple juice flocculation.

[0046] Depend on Figure 3 It can be seen that the chitosan-coffee ground nanoparticle composites of Examples 1 and 2 exhibit good infrared performance at 3500 cm⁻¹. -1 and 1650cm- 1 The strong absorption peaks at the points are attributed to the two hydrophilic groups, hydroxyl and carboxyl, respectively, thus proving that the chitosan-coffee ground nanoparticle composite has good water solubility.

[0047] Application Experiment 1: The flocculation effect of different concentrations and temperatures on apple juice

[0048] 1) Preparation of apple juice: Juice apples with peel and deionized water at a mass ratio of 1:2. Filter the obtained juice through two layers of gauze (Hua Lu degreased gauze, 40 mesh) to separate apple residue and apple juice.

[0049] 2) Chitosan (CS), coffee grounds nanoparticles (NPs), or chitosan-coffee grounds nanoparticles (Example 1 (1h), Example 2 (3h)) were added to apple juice at concentrations of 0, 0.05, 0.1, 0.2, 0.3, 0.4, 0.5, and 0.6 (g / L, final concentration), respectively. The original apple juice without added chitosan, coffee grounds nanoparticles (NPs), or chitosan-coffee grounds nanoparticle complex served as the control group (0 added). The reactions were carried out at 20℃, 30℃, 40℃, and 50℃ for 80 min, followed by a 10 min ice bath to stop the reaction. The mixture was then centrifuged at 3000 rpm for 10 min. The absorbance of the supernatant was measured at a wavelength of 595 nm. The transmittance was calculated as follows:

[0050] T=10 -A

[0051] In the formula: T─── transmittance, %

[0052] A───Absorbance value at 595nm

[0053] Depend on Figure 4 It was found that when the flocculation time was fixed at 80 min, the optimal flocculation conditions for chitosan were 0.4 g / L, with a transmittance of 39%, and the optimal clarification conditions for coffee grounds nanoparticles were 0.4 g / L, with a transmittance of 29%. For chitosan-nanoparticle composites synthesized at 1 h and 3 h, both showed clarification effects on apple juice within the experimental range of 0.05-0.5 g / L, with the optimal flocculation concentration being 0.05 g / L, and the maximum transmittances being 40% and 42%, respectively. The transmittance of the flocculated apple juice initially increased and then decreased with increasing chitosan and its composite concentration. This is because before reaching the optimal concentration, the added flocculant concentration was insufficient to flocculate all the turbidity-causing substances in the juice, so the transmittance gradually increased with increasing flocculant concentration. However, after reaching the optimal concentration, further increasing the concentration of chitosan or the chitosan-nanoparticle composite would act as a stabilizer, thus affecting the flocculation effect and causing a decrease in transmittance. The optimal clarification temperature for chitosan (CS), coffee grounds nanoparticles (NPs), and chitosan-coffee grounds nanoparticle complexes (1h and 3h) was 30℃. As the temperature increased, the transmittance of the clarified juice also showed a trend of first increasing and then decreasing. This is because as the temperature rises, the juice gradually oxidizes, thus decreasing the transmittance. Conversely, at excessively low temperatures, chitosan or the chitosan-nanoparticle complex cannot dissolve well, thus affecting the clarification effect.

[0054] At a temperature of 20℃ and an addition concentration of 0.05-0.1 g / L, the chitosan-coffee ground nanoparticle complex (Examples 1 and 2) showed significantly better flocculation effects than chitosan (CS) and coffee ground nanoparticles (NPs). At temperatures of 30℃ and 40℃ and an addition concentration of 0.05-0.3 g / L, the chitosan-coffee ground nanoparticle complex (Examples 1 and 2) showed significantly better flocculation effects than chitosan (CS) and coffee ground nanoparticles (NPs). However, the effect was unstable when the temperature reached 50℃.

[0055] Application Experiment 2 and Application Experiment 3 were conducted under the following conditions for obtaining the supernatant of apple juice after flocculation: The process and conditions were the same as in Application Experiment 1, except that the amount of chitosan (CS), coffee ground nanoparticles (NPs) and chitosan-nanoparticle complexes with different synthesis times (Example 1 (1h) and Example 2 (3h)) added was fixed at 0.05 g / L. The original fruit juice without added chitosan (CS), coffee ground nanoparticles (NPs) or chitosan-coffee ground nanoparticle complex was used as the control group (CON). The reaction time was 80 min in a water bath at 30°C, the reaction was stopped after 10 min in an ice bath, and the supernatant was collected after centrifugation at 3000 rpm for 10 min.

[0056] Application Experiment 2: Detection of Protein Content in Apple Juice Supernatant after Flocculation

[0057] 1) Reagents

[0058] ① Protein working stock solution: 100 mL of 95% ethanol (v / v), 350 mg of Coomassie Brilliant Blue G-250, and 200 mL of 88% phosphate solution (w / w).

[0059] ② Protein working solution: 425 mL ddH2O, 15 mL 95% ethanol (v / v), 30 mL 88% phosphate (w / w), and 30 mL protein working stock solution.

[0060] ③ Bovine serum albumin solution (BSA): 1 mg / mL

[0061] 2) Determination of standard curve

[0062]

[0063]

[0064] After preparing the standard according to the above formula, the corresponding concentration was obtained.

[0065] 3) When preparing the standard curve, protein concentration is used as the x-axis, and OD... 595 Plot a standard curve for the ordinate (see attached diagram) Figure 7 ).

[0066] 4) Protein content determination of samples

[0067] Add 20 μL of centrifuged apple juice supernatant to a test tube, then add 1 mL of protein working solution and shake well. After standing for 5 minutes, measure the protein content in the sample using a UV spectrophotometer at a wavelength of 595 nm and record the value. Substitute the measured value into the standard curve to determine the protein content in the sample.

[0068] Depend on Figure 5 It was found that, compared with the control group, the protein content in the fruit juice supernatant clarified by chitosan and chitosan-nanoparticle complex was significantly reduced, with the protein content after clarification by chitosan-nanoparticle complex being even lower than that after chitosan alone. The experimental results demonstrate that the chitosan-nanoparticle complex has a more efficient ability to flocculate proteins compared to chitosan.

[0069] Application Experiment 3: Detection of Total Phenolic Content in Apple Juice Supernatant after Flocculation

[0070] 1) Reagent: Gallic acid reference stock solution (0.1 mg / mL): Accurately weigh 10 mg (accurate to 0.1 mg) of gallic acid standard, dissolve it in a small amount of water, transfer it to a 100 mL brown volumetric flask, add water to make up to the mark, shake well, and store at 4°C protected from light.

[0071] Gallic acid standard series solutions: Accurately measure 0.0 mL, 0.25 mL, 0.50 mL, 0.75 mL, 1.00 mL, 1.25 mL, and 1.5 mL of gallic acid reference stock solution into 25 mL amber volumetric flasks, dilute to the mark with water, shake well, and store at 4℃. The gallic acid standard series concentrations are 0 μg / mL, 1.0 μg / mL, 2.0 μg / mL, 3.0 μg / mL, 4.0 μg / mL, 5.0 μg / mL, and 6.0 μg / mL. Prepare fresh before use.

[0072] 12% sodium carbonate solution: Weigh 12g of anhydrous sodium carbonate (accurate to 0.01g), dissolve in an appropriate amount of water, transfer to a 100mL volumetric flask, add water to the mark, and shake well.

[0073] 80% ethanol extractant: Measure 80 mL of anhydrous ethanol, place it in a 100 mL volumetric flask, and add water to bring the volume to the mark.

[0074] 2) Sample preparation: Accurately measure 2 mL of the supernatant of the flocculated apple juice and place it in a 50 mL centrifuge tube. Add 30 mL of 80% ethanol extractant and sonicate for 40 min. After sonication, centrifuge at 8000 rpm at 4℃ for 5 min, and filter through a 0.22 μm filter membrane to obtain the filtrate.

[0075] 3) Standard Curve: Accurately measure 1.0 mL of each gallic acid standard solution at various concentrations into a 25 mL graduated test tube. Add 1.0 mL of 1.0 mol / L Folin-Phenol reagent, shake well, and let stand for 5 minutes. Then add 2.0 mL of 12% sodium carbonate solution, and dilute to the mark with water. Let stand at room temperature in the dark for 1.5 hours, and measure the absorbance at 760 nm. Plot the standard curve with the mass of gallic acid (mg) in 25 mL of solution on the x-axis and the absorbance on the y-axis (see attached diagram). Figure 8 ).

[0076] 4) Determination of total phenol content in the sample: Accurately measure 1 mL of the filtrate obtained in 2), place it in a 25 mL graduated test tube, add 1.0 mL of 1.0 mol / L Folin-Phenol reagent, shake well and let stand for 5 min, then add 2.0 mL of 12% sodium carbonate solution, shake well, add water to make up to the mark, let stand at room temperature in the dark for 1.5 h, and measure the absorbance at 760 nm.

[0077] The total phenol content (calculated as gallic acid) in the sample is expressed as a percentage (%) and calculated using the formula:

[0078]

[0079] In the formula: X─── total phenol content in the sample (calculated as gallic acid)

[0080] m — Mass of gallic acid in the sample (mg) determined by the standard curve.

[0081] v───Sample volume (mL)

[0082] d───Sample dilution factor

[0083] Depend on Figure 6 It was found that the total phenol content of apple juice gradually decreased after clarification with chitosan and chitosan-nanoparticle complex. This is because chitosan and chitosan-nanoparticle complex flocculate certain phenolic substances, such as tannins and pigments, that cause turbidity in the juice during the clarification process. Therefore, compared with the control group, the total phenol content of the supernatant after clarification with chitosan and chitosan-nanoparticle complex decreased overall. Compared with chitosan, the chitosan-coffee grounds nanoparticle complex showed a greater decrease in total phenol content, indicating a more significant flocculation effect on phenolic substances.

[0084] Depend on Figure 1 , Figure 2 , Figure 3 , Figure 4 , Figure 5 and Figure 6It is evident that the chitosan-coffee grounds nanoparticle complexes prepared in Examples 1 and 2 of this invention, compared to chitosan, exhibit better flocculation effects on apple juice while requiring a smaller dosage, effectively flocculating proteins and phenolic substances that cause turbidity. Structurally, the chitosan-coffee grounds nanoparticle complex has a network structure, which enhances its flocculation effect. Furthermore, the chitosan-coffee grounds nanoparticle complex possesses abundant hydrophilic groups such as hydroxyl and carboxyl groups, resulting in excellent water solubility.

[0085] This invention uses coffee grounds nanoparticles to modify chitosan, and its flocculation effect on apple juice is significantly better than using chitosan or coffee grounds nanoparticles (NPs) alone (application experiments 1, 2, 3).

[0086] Compared with existing technologies, this invention uses inexpensive and readily available coffee grounds. The coffee grounds aqueous solution is heated, and the resulting coffee grounds nanoparticles react with chitosan to obtain a chitosan-coffee grounds nanoparticle complex. This complex has a better flocculation effect, and since coffee grounds are waste generated during coffee preparation, it is a form of waste utilization and is more green and environmentally friendly.

[0087] This invention yields a novel chitosan-modified product that not only satisfies the pursuit of apple juice quality but also provides a new way to reuse coffee grounds. The composite also exhibits excellent flocculation properties.

[0088] The above description is only a preferred embodiment of the present invention and is 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 method for preparing a chitosan-coffee grounds nanoparticle composite, characterized in that, It includes the following steps: 1) Obtaining coffee grounds: Dry the coffee grounds and sieve them through a 20-50 mesh. The grounds that pass through the sieve are the desired coffee grounds. 2) Preparation of coffee grounds-derived nanoparticles: Dissolve 4-8 g of coffee grounds powder in water, heat for 1-6 h, filter, collect the filtrate, pass it through a D101 macroporous resin column, elute with water, collect an eluent volume of 2-6 L, dialyze to obtain the cutoff liquid, and dry to obtain coffee grounds nanoparticles; heating temperature is 50-90℃, time is 1-6 h; filter paper is used, quantitative filter paper, Φ=10-15cm, pore size 30-50 μm; the dialysis bag used for dialysis has a molecular weight cutoff of 1000-3000 kDa; 3) Preparation of chitosan-coffee ground nanoparticle complex: 20-50 mL of chitosan aqueous solution with a chitosan:water mass ratio of 1:100-400 was mixed with the coffee ground nanoparticles prepared in step 2) and added to a reaction vessel for hydrothermal reaction for 1-6 h; the solution after reaction was dialyzed and dried to obtain chitosan-coffee ground nanoparticle complex. The molecular weight cutoff of the dialysis bag used for dialysis was 1000-3000 kDa.

2. The method for preparing the chitosan-coffee grounds nanoparticle composite as described in claim 1, characterized in that, In step 2), 4-8 g of coffee grounds are dissolved in 10-50 times their weight of water.

3. The method for preparing the chitosan-coffee grounds nanoparticle composite as described in claim 1, characterized in that, In step 2), the heating temperature is 80-90℃ and the time is 1-3h.

4. The method for preparing the chitosan-coffee grounds nanoparticle composite as described in claim 1 or 2, characterized in that, In step 2), the D101 macroporous resin column has the following specifications: column length: 15-20 cm, inner diameter: 1.0-1.5 cm. Impurities are removed by elution with deionized water, and the eluent is collected. The eluent is concentrated by rotary evaporation to obtain a coffee grounds nanoparticle solution. After dialysis and drying, coffee grounds nanoparticles are obtained.

5. The method for preparing the chitosan-coffee grounds nanoparticle composite as described in claim 1, characterized in that, In step 3), the hydrothermal reaction temperature is 160-200℃.

6. The method for preparing the chitosan-coffee grounds nanoparticle composite as described in claim 1, characterized in that, In steps 2) and 3), the molecular weight cutoff of the dialysis bag used for dialysis is 1000-2500 kDa.

7. The method for preparing the chitosan-coffee grounds nanoparticle composite as described in claim 1, characterized in that, Step 1) Obtaining coffee grounds: After coffee beans are ground in a coffee machine, extracted with water, or brewed, the portion that is not extracted by water is dried and then sieved through a 20-50 mesh to obtain coffee grounds.

8. Chitosan-coffee grounds nanoparticle composites prepared by any one of the preparation methods described in claims 1 to 7.

9. The application of the chitosan-coffee grounds nanoparticle composite of claim 8 as a fruit juice flocculant.

10. The application as described in claim 9, characterized in that, The application of the chitosan-coffee grounds nanoparticle composite of claim 8 as a flocculant in apple juice flocculation; At a temperature of 15-25℃, the chitosan-coffee ground nanoparticle composite was added to apple juice at a concentration of 0.05-0.1 g / L. At temperatures above 25 to 40°C, the chitosan-coffee grounds nanoparticle complex was added to apple juice at a concentration of 0.05-0.3 g / L.

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