Method for extracting micro-plastics in solid beverage granules

Abstract

The invention discloses a method for extracting micro-plastics in solid beverage granules, which comprises the following steps: S1, adding an alkaline solution into the solid beverage granules containing the micro-plastics, uniformly shaking, then heating in a water bath, intermittently adding a hydrogen peroxide solution at the adding frequency of 0.5 mL / 10min during the heating in the water bath; and S2, after the water bath heating is completed, reducing the water bath temperature for reaction, after the reaction is completed, carrying out suction filtration while the reaction is hot, washing with a surfactant, and carrying out suction filtration to obtain the micro-plastics, thereby completing the extraction. According to the method, animal and plant fat, protein and cellulose in the components of the solid beverage granules can be digested, so that the problems of more steps, long time consumption, low digestion efficiency of the solid beverage granules and easiness in causing micro-plastic loss in the prior art are solved, and the micro-plastic extraction accuracy is improved; the micro-plastic in the solid beverage granules can be quantitatively detected and researched.

Description

Technical Field

[0001] The present invention relates to the technical field of microplastic extraction from solid beverage granules, and specifically relates to a method for extracting microplastics from solid beverage granules. Background Art

[0002] Microplastics (plastics with a diameter less than 5 mm) have complex and diverse shapes, are widely present in the environment, and have certain environmental risks due to characteristics such as small size, large specific surface area, and stable chemical properties. Existing research has found that a large amount of microplastics exist in air, soil, and water bodies. It has been reported that a large amount of microplastics have been detected in animals, humans, and their excreta. More research has found that a large amount of microplastics have been detected in tea bags, drinking water, and foods in plastic packaging. As one of the main sources of modern people's tea drinks, solid beverage granules such as coffee and milk powder are inseparable from plastic products in their production processes and packaging, so the possibility of microplastics existing is extremely high. However, there has not yet been the development of a pretreatment method for the extraction of microplastics from such solid beverage granules. For the pretreatment of environmental media (such as soil, sediment, and water), oxidative digestion is used for pretreatment to remove the interference of organic matter and then microplastics are collected by flotation. However, solid beverage granules such as coffee and milk powder contain a large amount of interfering substances such as fat, soybean meal, starch, and crude fiber that are difficult to remove by mild digestion methods. A large amount of interfering substances have similar density and surface hydrophilicity and hydrophobicity to microplastics, and it is difficult to separate them by flotation. Therefore, it is necessary to exclude the interference of such substances in the digestion step.

[0003] Some organic components in solid beverage granules, such as tannins, acids, and other antioxidants, may react with chemical digestion agents, resulting in a decrease in the effectiveness of the digestion agents; during the digestion process, some organic components may form coatings or aggregates with microplastics, and may also form viscous substances, making it difficult to completely digest. The strong acids and strong bases used for total digestion will cause serious damage to microplastics while removing impurity interference.

[0004] Due to the fact that the components of solid beverage granules contain a large amount of animal and plant fats, proteins, and cellulose, it is impossible to completely remove the interfering components only by using existing related methods for solid beverage granules, resulting in residual solid substances after digestion, multiple steps, long time consumption, low removal efficiency, easy loss of microplastics, inaccurate extraction of microplastics, and thus it is difficult to accurately detect the content of microplastics in solid beverage granules and difficult to conduct quantitative detection and research on microplastics in solid beverage granules. Summary of the Invention

[0005] In order to solve the above problems, the present invention provides a method for extracting microplastics from solid beverage granules.

[0006] A method for extracting microplastics from solid beverage granules includes the following steps:

[0007] S1. Add an alkaline solution with a mass concentration of 2 - 8% to the solid beverage granules containing microplastics at a ratio of 1 g: 5 - 10 mL, shake well, and then heat in a water bath at 65 - 75 °C for 3 - 6 h. During the water bath heating, intermittently add a hydrogen peroxide solution with a mass concentration of 10 - 30%. The addition frequency of the hydrogen peroxide solution is 0.5 mL / 10 min;

[0008] S2. After the water bath heating is completed, lower the water bath temperature to 40 - 60 °C and react for 6 - 12 h. After the reaction is completed, filter while it is hot and rinse with a surfactant. Filter to obtain microplastics, and the extraction is completed.

[0009] Note: Through the above method, it is possible to avoid the problem in the prior art that after mixing hydrogen peroxide and an alkaline solution, a violent reaction occurs, resulting in the inability to exert their respective effects. At the same time, using hydrogen peroxide and an alkaline solution for the reaction can remove substances such as fat and protein while relatively completely retaining the microplastics for subsequent extraction and analysis.

[0010] Further, the solid beverage granules include two - in - one coffee, three - in - one coffee, milk powder, and soy powder.

[0011] Note: The above - mentioned solid beverage granules usually contain various components, such as coffee powder, milk powder, sugar, non - dairy creamer, flavor, stabilizer, and preservative. During the digestion process, they may affect the extraction and detection of microplastics. At the same time, some of these components may be heat - sensitive and react with microplastics during the digestion process. Therefore, certain experimental conditions should be set to avoid the reaction between the component substances in the solid beverage granules and microplastics.

[0012] Further, the microplastics include one or more of MPs such as PE or PS or PVC or PET.

[0013] Note: The above - mentioned plastics are all common microplastics in the production, packaging, etc. of solid beverage granules.

[0014] Further, the alkaline solution is a KOH solution, and the surfactant is Tween20 with a mass concentration of 5 - 15%.

[0015] Note: The selection of the above - mentioned solutions is more suitable for the treatment process of solid beverage granules.

[0016] Further, during the reaction process in S2, ultrasonic assistance with 200 - 300 W is used.

[0017] Description: Through the above ultrasonic-assisted reaction, the process of using KOH and hydrogen peroxide to treat fats, proteins, etc. in solid beverage granules can be accelerated, and by setting the above parameters, the damage of KOH and hydrogen peroxide to microplastics can be avoided. Thus, while improving the digestion speed, the extraction accuracy of microplastics can be enhanced.

[0018] The beneficial effects of the present invention are as follows:

[0019] The present invention can digest animal and plant fats, proteins, and cellulose in solid beverage granule components, solving the problems in the prior art of multiple steps, long time consumption, low digestion efficiency of solid beverage granules, and easy loss of microplastics, improving the extraction accuracy of microplastics to achieve quantitative detection and research on microplastics in solid beverage granules; through comparative analysis experiments on the digestion and separation methods of MPs in solid beverage granules, by purposefully selecting and optimizing factors such as the type of digestion reagent, H 2 O 2 addition frequency, digestion steps, etc., the method of separating MPs based on the influence of digesting organic matter on MPs can more efficiently separate MPs. The experimental results prove that compared with the prior art, the method of the present invention is more conducive to separating MPs from solid coffee beverages; at the same time, the addition of H 2 O 2 frequency will affect the separation effect. The present invention further reveals the preferred separation method for solid coffee beverages with high fat content, providing relevant references and theoretical supports for the control and research of MPs pollution in foods rich in animal and plant fats and proteins. Description of the Drawings

[0020] Figure 1 is the technical flowchart of the method for extracting microplastics from solid beverage granules in an embodiment of the present invention;

[0021] Figure 2 is the state of the beaker after digestion of the three-in-one coffee in an embodiment of the present invention by Fenton's and KOH + H 2 O 2 respectively;

[0022] Figure 3 is the photo of the filter membrane in an embodiment of the present invention. Among them, a is the digestion removal rate of BDC-1 after digestion by Fenton's and KOH + H 2 O 2 respectively and the photo of the filter membrane after filtration to the PTFE filter membrane after digestion; Figure 3 b is the digestion removal rate of different coffees by KOH + H 2 O 2 respectively and the photo of the filter membrane after filtration to the PTFE filter membrane after digestion;

[0023] Figure 4These are the photos taken in the embodiments of the present invention. Among them, a is a PE standard product with a size of 75 - 90 μm; Figure 4 b is the photo taken before adding the PE standard product (for manual counting); Figure 4 c is the photo taken on the black grid filter membrane after the PE standard product is recovered (for manual counting);

[0024] Figure 5 These are the filter membrane photos in the embodiments of the present invention. Among them, a is the filter membrane photo of the PE recovery rate after two digestion treatments of BDC - 1 and the filter membrane after digestion and filtration onto the black grid filter membrane; Figure 5 b is the filter membrane photo of the PE recovery rate after digestion treatment of different coffees with KOH + H 2 O 2 and the filter membrane after digestion and filtration onto the black grid filter membrane;

[0025] Figure 6 These are the micrographs of the original samples of 12 MPs (ABS, HDPE, LDPE, PA66, PBS, PET, PHA, PLA, POM, PP, PS, PVC) in Example 1 of the present invention and after digestion with KOH + H 2 O 2 at 70 °C for 5 hours and then incubated at 50 °C for 10 hours.

[0026] Figure 7 This is a diagram of the experimental process in which a large number of bubbles are generated after pouring 1 - 2 ml of 30% hydrogen peroxide solution into 15 ml of 5% alkaline solution at room temperature.

[0027] Figure 8 These are the diagrams of the number of microplastics ≥ 20 μm in CK, BC - 1, BDC - 1, BDC - 2, and BDC - 3 in the embodiments of the present invention (CK: control group, BC - 1: black coffee, BDC - 1: three - in - one coffee No. 1, BDC - 2: three - in - one coffee No. 2, BDC - 3: two - in - one coffee, BDC - 4: three - in - one coffee No. 3

[0028] Figure 9 These are the different - sized microplastics detected in BDC - 1 and their quantities.

[0029] Figure 10 These are the diagrams of the proportion data of various microplastics in different coffee samples. Detailed implementation manners

[0030] To further elaborate on the methods adopted and the effects achieved by the present invention, the technical solutions of the present invention will be clearly and completely described below in combination with experiments.

[0031] The solutions of the present invention will be explained below in conjunction with embodiments. Those skilled in the art will understand that these embodiments can be subject to various changes, modifications, substitutions, and variations without departing from the principles and purposes of the method of the present invention. The scope of the method of the present invention is defined by the claims and their equivalents. For those technical or conditions not specified in the embodiments, they are carried out according to the techniques or conditions described in the literature in this field. The materials, reagents, and instruments are all conventional products that can be obtained through commercial channels.

[0032] The components of solid beverage granules generally include fat, protein, and cellulose. These components may affect the extraction and detection of microplastics during the digestion process by reagents. At the same time, some of these components may react with microplastics during the digestion process, and some components may not be completely removed, or even adhere to and wrap microplastics, resulting in greater difficulty in digesting solid beverage granules. There is relatively little relevant research in the prior art.

[0033] In addition, as can be seen from the problems in the foregoing background art, the digestion methods in the prior art cannot effectively digest the animal and plant fats, proteins, and cellulose in solid beverage granules. And if strong digestion means (such as in combination with strong acids, etc.) are used, it may react with microplastics and fail to achieve the effect of extracting microplastics.

[0034] Specifically, using H 2 O 2 、Fenton’s and KOH for treatment can have a partial digestion effect on solid beverage granules. This is because H 2 O 2 and Fenton’s release strong oxidizing substances such as singlet oxygen and hydroxyl radicals, which have good digestion effects on complex organic matter in environmental media, such as fulvic acid, humic acid, protein, and polysaccharide, and are widely used in the extraction of microplastics in various environmental media. KOH, due to its strong alkalinity and corrosiveness, has a good digestion effect on animal fats and proteins and is widely used in the digestion of various biological samples and the extraction and detection of microplastics.

[0035] However, when using KOH or H 2 O 2 、Fenton’s alone to digest the fat, protein, and cellulose in solid beverage granules, the fat, protein, and cellulose in solid beverage granules cannot be completely digested, and there are situations where the digestion efficiency of microplastics is low and the reaction rate is slow. If KOH and H 2 O 2 are used simultaneously, there is a problem that the experiment cannot be carried out (because a large amount of bubbles will be generated when the two are mixed, carrying microplastics and overflowing, and the experiment cannot continue; for example, as Figure 7As shown in FIG. 1 , when 1-2 ml of a 30% hydrogen peroxide solution is added to 15 ml of a 5% alkaline solution at room temperature, bubbles are generated immediately and the operation cannot be continued. If the concentrations of the two are reduced, the digestion process cannot be achieved. Therefore, in the prior art, KOH and H are usually not used simultaneously. 2 O 2 These two compounds are used to extract microplastics;

[0036] The present invention has been found through research that KOH and H 2 O 2 When combined, a strong oxidizing environment is formed in which H 2 O 2 It can be decomposed into water and oxygen under the catalysis of KOH, and release a large number of free radicals such as (·OH). These free radicals have extremely high oxidizing ability and can oxidize organic matter. However, it is necessary to avoid the generation and overflow of the above-mentioned bubbles, and avoid the reaction of KOH and H 2 O 2 Long-term use alone will cause degradation of microplastics. To this end, the solution proposed by the embodiment of the present invention is as follows:

[0037] Example 1: A method for extracting microplastics from a solid beverage granule, comprising the following steps:

[0038] S1. Add 15 ml of 5% alkaline solution to 2 g of solid beverage powder containing microplastics, shake well, and then heat in a water bath at 70°C for 5 h. During the water bath heating, add hydrogen peroxide solution with a mass concentration of 30% intermittently, and the intermittent addition frequency of the hydrogen peroxide solution is 0.5 mL / 10 min. The solid beverage powder includes two-in-one coffee, three-in-one coffee, milk powder and soybean powder; for example, black coffee BC-1 is selected in this embodiment;

[0039] S2. After the water bath heating is completed, the water bath temperature is lowered to 50°C and the reaction is carried out for 10 hours. During the reaction, 250W ultrasonic wave is used to assist. After the reaction is completed, the microplastics are obtained by filtration while hot and rinsed with a surfactant. The extraction is completed.

[0040] The alkaline solution is a KOH solution, and the surfactant is Tween20 with a mass concentration of 10%; the microplastics include one or more MPs such as PE, PS, PVC, or PET.

[0041] Implementation results: After the above operation method, BC-1 was extracted as above, and the above test found that microplastics existed in the solid beverage granules. The content of microplastics is as follows Figure 8 shown.

[0042] Relevant principle: In Example 1 of the present invention, through the above-mentioned implementation method, the generation of bubbles during the reaction between potassium hydroxide and hydrogen peroxide can be avoided. By setting the temperature-time parameters and the addition method, the reaction efficiency can be improved, and at the same time, the generation and overflow of bubbles during the mixing of KOH and H 2 O 2 can be avoided. Specifically, in the strongly alkaline and strongly oxidizing environment formed by the combination of potassium hydroxide and hydrogen peroxide, the organic substances such as fat, protein, and cellulose in the solid beverage granule of the present invention undergo the following reaction mechanisms:

[0043] ① Saponification of fat: Under strongly alkaline conditions, fats and oils will undergo saponification reactions, that is, glycerides of fatty acids react with alkalis to form fatty acid salts (soaps) and glycerol. This process can be expressed as: RCOOCH 2 CH(OH)CH 2 OR'+3KOH→3RCOOK+CH 2 OHCHOHCH 2 OH; where R and R' represent fatty acid chains. ② Under alkaline and strongly oxidizing conditions, the peptide bonds of proteins can be hydrolyzed, resulting in the degradation of proteins into smaller peptide chains or even amino acids. Strong oxidizing properties can significantly accelerate this process, generating hydroxyl radicals, which can attack peptide bonds, R-NH-CO-R'+H 2 O→R-NH 2 +R'-COOH; where R and R' represent amino acid residues. Although KOH alone can promote the hydrolysis of proteins, the addition of H 2 O 2 may accelerate this process because it can generate hydroxyl radicals, which can attack peptide bonds, thereby accelerating the degradation of proteins and improving the digestion efficiency. ③ The hydrogen bonds and van der Waals forces between cellulose molecular chains make its structure stable and difficult to be destroyed by simple chemical reactions. By using the combination of KOH and H 2 O 2 , KOH provides OH - ions, which can react with the hydroxyl groups (-OH) in cellulose molecules to break the β-1,4-glycosidic bonds in cellulose molecular chains. At the same time, H 2 O 2 can decompose to generate hydroxyl radicals (·OH) under alkaline conditions. These radicals have extremely high oxidation ability and can further attack cellulose molecular chains to accelerate their breakage. The combination of KOH and H 2 O 2 in the present invention can avoid side reactions that may occur during the degradation of cellulose and at the same time destroy the stability of vitamins, thereby accelerating the oxidation process. Therefore, the above combination of KOH and H 2 O 2The special reaction mechanisms that can be achieved in combination are mainly the acceleration of protein hydrolysis and the acceleration of cellulose oxidation, which cannot be achieved by using KOH or H 2 O 2 alone.

[0044] In summary, the method of the present invention, firstly, can overcome the problem of gas generation during the digestion process of the solid beverage granule by the mixture of KOH and H 2 O 2 , which was not considered / there was no relevant method to solve in the prior art; secondly, it can accelerate the digestion reaction and improve the digestion efficiency, and this beneficial effect cannot be achieved by the prior art either (for specific effect comparison, see Comparative Examples 1-7 below).

[0045] Example 2: This example is substantially the same as Example 1, except that the KOH concentration is different. In S1, a 2% KOH solution is added to the solid beverage granule containing microplastics at a ratio of 1 g: 7.5 mL.

[0046] Example 3: This example is substantially the same as Example 1, except that the KOH concentration is different. In S1, an 8% KOH solution is added to the solid beverage granule containing microplastics at a ratio of 1 g: 7.5 mL.

[0047] Example 4: This example is substantially the same as Example 1, except that the temperature parameter is different. In S1, it is heated in a water bath at 75 °C for 5 h.

[0048] Example 5: This example is substantially the same as Example 1, except that the temperature parameter is different. In S1, it is heated in a water bath at 65 °C for 5 h.

[0049] Example 6: This example is substantially the same as Example 1, except that the incubation time is different. In S2, the reaction is carried out for 6 h.

[0050] Example 7: This example is substantially the same as Example 1, except that the incubation time is different. In S2, the reaction is carried out for 12 h.

[0051] Example 8: This example is substantially the same as Example 1, except that the concentration of the hydrogen peroxide solution is different. In S1, a 10% hydrogen peroxide solution is added intermittently.

[0052] Example 9: This example is substantially the same as Example 1, except that the concentration of the hydrogen peroxide solution is different. In S1, a 20% hydrogen peroxide solution is added intermittently.

[0053] Example 10: This example is substantially the same as Example 1, except that the ultrasonic parameter is different. In S2, 200 W ultrasonic assistance is used.

[0054] Example 11: This example is substantially the same as Example 1, except that the ultrasonic parameters are different, and 300 W ultrasonic waves are used for assistance in S2.

[0055] Example 12: This example is substantially the same as Example 1, except that the raw material ratio is different. In S1, an alkaline solution is added to the solid beverage granule containing microplastics at a ratio of 1 g:5 mL.

[0056] Example 13: This example is substantially the same as Example 1, except that the raw material ratio is different. In S1, an alkaline solution is added to the solid beverage granule containing microplastics at a ratio of 1 g:10 mL.

[0057] Example 14: This example is substantially the same as Example 1, except that in S2, the water bath temperature is reduced to 40 °C.

[0058] Example 15: This example is substantially the same as Example 1, except that in S2, the water bath temperature is reduced to 60 °C.

[0059] Example 16: This example is substantially the same as Example 1, except that in S1, the water bath heating is carried out for 6 h.

[0060] Example 17: This example is substantially the same as Example 1, except that in S1, the water bath heating is carried out for 3 h.

[0061] Experimental Example 1: This experimental example is a blank group. Add the bagged instant coffee No. 1 solid beverage granule, and directly set up the experiment according to the method of Example 1, that is, add 15 mL of 5% KOH solution, shake and rock the beaker to make the coffee and the solution mix evenly; then add 30% H 2 O 2 , place it in a water bath at 70 °C for digestion for 5 h, then stop adding and reduce the temperature to 50 °C and incubate for 10 h. During the process, 250 W ultrasonic waves are used for assisted digestion. After digestion is completed, through machine calculation, the microplastic content of the instant coffee No. 1 for this experiment itself is obtained.

[0062] In order to reflect the advantages of the solution of the present invention, the following experimental examples and comparative examples are set up. In the following Examples 2-4 and comparative examples, experiments are all carried out with microplastic samples that can be fluorescently stained, so as to prove whether the implementation method has the effect of digesting and harming microplastics and the digestion effect on the solid beverage granule, so as to highlight the effect of the present invention:

[0063] Experimental Example 2: As Figure 1As shown, first, use instant coffee No. 1 as the experimental sample, and set 3 replicate control groups for each experiment. Add 2 g of instant coffee powder of instant coffee No. 1 to a beaker, add the PE (75 - 90 μm) standard, add 15 mL of 5% KOH solution, and shake the beaker to mix the coffee and the solution evenly. Then add 30% H 2 O 2 at a frequency of 0.5 mL / 10 min, place it in a water bath at 70 °C for digestion for 5 h, then stop adding, and reduce the temperature to 50 °C and incubate for 10 h. During the process, use a 250 W ultrasonic wave to assist digestion. After digestion, the condition of the beaker is shown in Figure 2 (the beaker on the right), and the digestion removal rate effect is shown in Figure 3 a. The microscopic photo of the PE standard, the photos of counting before and after recovery by taking pictures are shown in Figure 4 , and the recovery rate of PE after digestion is shown in Figure 5 a. The apparent morphology photos of 12 kinds of MPs (ABS, HDPE, LDPE, PA66, PBS, PET, PHA, PLA, POM, PP, PS, PVC) before and after digestion using the same digestion scheme are shown in Figure 6 . Suction filtration: Use a circulating water suction filtration pump to filter the digestion solution. The filter membrane uses an acetate black grid filter membrane (5 μm, 47 mm). Rinse the beaker and the glassware for vacuum suction filtration with a Tween20 solution diluted with ultrapure water to prevent the loss of MPs adhering to the wall due to experimental operations. The photo of the black grid filter membrane after suction filtration is shown in Figure 4 c. Photographing and counting: After the black grid filter membrane after suction filtration is photographed with a low-power microscope or a close-focus camera, manual counting is performed using image J based on the photo, and the PE recovery rate is calculated (PE recovery rate = microplastics obtained by photographing and counting after digestion / microplastics obtained by photographing and counting before digestion and before adding).

[0064] Experimental example 3: First, use three kinds of multi-in-one coffee, namely instant coffee No. 2 in bags, instant coffee No. 3, and two-in-one coffee, as the experimental samples, and set 3 replicate control groups for each experiment. Add 2 g of multi-in-one coffee powder to a beaker, add the PE (75 - 90 μm) standard, add 15 mL of 5% KOH solution, and shake the beaker to mix the coffee and the solution evenly. Add 30% H 2 O 2 at a frequency of 0.5 mL / 10 min, place it in a water bath at 70 °C for digestion for 5 h, then stop adding and reduce the temperature to 50 °C and incubate for 10 h. During the process, use a 250 W ultrasonic wave to assist digestion. After digestion, the condition of the beaker is shown in Figure 2 (the beaker on the right), and the digestion removal rate effect is shown in Figure 3 b. The microscopic photo of the PE standard, the photos of counting before and after recovery by taking pictures are shown in Figure 4 , and the recovery rate of PE after digestion is shown inFigure 5 b. Apparent morphology photos of 12 kinds of MPs (ABS, HDPE, LDPE, PA66, PBS, PET, PHA, PLA, POM, PP, PS, PVC) before and after digestion using the same digestion scheme are shown in Figure 6 . Filtration by suction: Filter the digestion solution using a circulating water suction pump. Use an acetate black grid filter membrane (5 μm, 47 mm) for the filter membrane. Rinse the beaker and glassware for vacuum suction filtration with a Tween20 solution diluted with ultrapure water to prevent MPs from adhering to the wall and being lost during the experimental operation. The figure of the black grid filter membrane after filtration is shown in Figure 4 c. Photographing and counting: After photographing the black grid filter membrane after filtration using a low-power microscope or a close-focus camera, perform manual counting using Image J based on the photos to calculate the PE recovery rate.

[0065] Experimental Example 4: Without adding experimental samples, set 3 replicate control groups for each experiment. Add a PE (75 - 90 μm) standard product, add 15 mL of 5% KOH solution, shake and rock the beaker to mix the coffee and the solution evenly. Add 30% H 2 O 2 at a frequency of 0.5 mL / 10 min, place it in a water bath at 70 °C for digestion for 5 h, then stop adding and reduce the temperature to 50 °C and incubate for 10 h. Use 250 W ultrasonic waves to assist in digestion during the process. After digestion is completed, calculate the PE recovery rate.

[0066] Based on the settings of the above experimental examples, since microplastics are contained in coffee itself (microplastics will be generated during current raw materials, food processing, and packaging processes), therefore, first calculate the microplastic content in the coffee used in this example and the experimental examples by the method of Experimental Example 1 (CK) (such as the proportion of different types of microplastics in the coffee sample described Figure 10 above). In subsequent Experimental Example 2, Experimental Example 3, Experimental Example 4, and all examples including Example 1 (BC-1), the microplastic content in the coffee itself has been removed from the calculated microplastic recovery rate. The results are shown in Figure 8 、 Figure 9 .

[0067] After conducting tests through the above Experimental Example 1, Experimental Example 2, and Experimental Example 3, the obtained recovery rates are as shown in Table 1 below:

[0068] Table 1 Microplastic recovery rate table

[0069]

[0070] As can be seen from Table 1 above, in Experimental Example 4, the microplastic recovery rate reached 99%, proving that the reagents and operation methods used in the method of the present invention can achieve good treatment effects. Moreover, after adding different solid beverage granules for treatment in Experimental Example 2 and Example 3 respectively, after the digestion of the solid beverage granules was completed, the microplastic recovery rate therein reached more than 89%, proving that the microplastics after the digestion treatment of the solid beverage granules in the present invention were less affected and lost, indicating that the method of the present invention can be used to extract microplastics from solid beverage granules.

[0071] Comparative Example 1: First, use bagged BDC-1 three-in-one coffee as the experimental sample, and set 3 replicate control groups for each experiment. Add 2 g of BDC-1 coffee powder to a beaker, add a PE (75-90 μm) standard, and add 15 mL of 0.05 M Fe 2+ (7.5 g FeSO 4 ^7H 2 O + 500 mL H 2 O) solution, shake and swirl the beaker to mix the coffee and the solution evenly. Add 30% H 2 O 2 at a frequency of 1 mL / 10 min, place it in a 70 °C water bath for digestion for 6 h, and use 250 W ultrasonic wave to assist digestion during the process. The condition of the beaker after digestion is shown in Figure 2 (the beaker on the left), and the digestion removal rate effect is shown in Figure 3 a. The microscopic photos of the PE standard, the photos of the counting before and after addition are shown in Figure 4 , and the PE recovery rate after digestion is shown in Figure 5 a. Filtration: Use a circulating water suction pump to filter the digestion solution. The filter membrane uses an acetate black grid filter membrane (5 μm, 47 mm). Rinse the beaker and the glassware for vacuum filtration with a Tween20 solution diluted with ultrapure water to prevent the loss of MPs sticking to the wall due to experimental operations. The figure of the black grid filter membrane after filtration is shown in Figure 4 c. Photographing and counting: After the black grid filter membrane after filtration is photographed with a low-power microscope or a close-focus camera, artificial counting is performed using image J based on the photos to calculate the PE recovery rate.

[0072] Comparative Example 2: Use bagged BDC-1 three-in-one coffee as the experimental sample, and set 3 replicate control groups for each experiment. Add 2 g of BDC-1 coffee powder to a beaker, add a PE (75-90 μm) standard, and add 30 mL of 30% H 2 O 2, Shake the beaker to mix the coffee and the solution evenly. Digest it in a water bath at 70 °C for 5 h, and use a 250 W ultrasonic wave to assist digestion during the process. Filtration by suction: Filter the digested solution with a circulating water suction pump, and use a PTFE-PP (10 μm, 47 mm) filter membrane for suction filtration. Because of incomplete digestion, some organic components in the coffee flocculate and agglomerate with each other to form flocs, and a large amount of caking occurs, which leads to the blockage of the filter membrane and makes filtration impossible. Therefore, Comparative Example 2 cannot effectively digest the multi-in-one coffee.

[0073] After conducting experiments on the above Comparative Example 1 and Comparative Example 2, the recovery rates obtained are as shown in Table 2 below:

[0074] Table 2 Microplastic recovery rate table

[0075] Parameter Microplastic recovery rate Comparative example 1 70％ Comparative example 2 31％

[0076] As can be seen from Table 2 above, when extracting microplastics by the method related to the prior art of Comparative Example 1, the recovery rate of microplastics is relatively low, 70% and below, indicating that changing the steps or using other methods for experiments will affect the microplastics and make it impossible to extract them accurately. In contrast, the recovery rates of microplastics in Experimental Example 2 and Experimental Example 3 are relatively high. Therefore, the method in the embodiment of the present invention is more preferable.

[0077] Moreover, the experimental results show that after digestion in Comparative Example 2, the solution was observed to be relatively turbid, and obvious fat caking could be seen after cooling. This is because H 2 O 2 does not have the function of removing fat. Therefore, the microplastics in Comparative Example 2 may be largely contained in substances such as fat and are difficult to extract.

[0078] Comparative Example 4: It was found that when using the enzyme digestion technology to extract microplastics in the three-in-one coffee, however, it takes one week to several months for enzyme digestion to achieve partial digestion of the three-in-one coffee. Therefore, Comparative Example 4 cannot be compared with the extraction efficiency in the embodiment of the present invention.

[0079] Comparative Example 5: As Figure 2 shown, it was found that when using Fenton's technology to extract microplastics in the three-in-one coffee in Comparative Example 1, a lot of bubbles were generated to stick the MPs to the beaker wall, and the recovery rate of the finally obtained MPs was at least 20% lower than that of Comparative Example 2. Therefore, in this Comparative Example 5, its treatment process will affect the recovery of microplastics in the solid beverage granules, resulting in the inapplicability of this method to the extraction process of microplastics in the solid beverage granules.

[0080] Comparative Example 6: Slowly mix 15 ml of alkaline solution KOH with a mass concentration of 1% and 15 ml of hydrogen peroxide solution with a mass concentration of 10%. Before complete addition, a large amount of bubbles were generated, resulting in the inability to proceed with the reaction.

[0081] Comparative Example 7: The difference from Experimental Example 1 is that the mass concentration of the alkaline solution KOH is 1%, and the mass concentration of the hydrogen peroxide solution is 10%. Through experiments, it is found that the recovery rate of microplastics in Comparative Example 6 is less than 80%. Therefore, the parameters in Experimental Example 1, that is, Embodiment 1 of the present invention, are more preferable.

Claims

1. A method for extracting microplastics from solid beverage granules, characterized in that: The following steps are involved: S1. Add 2-8% alkaline solution to the solid beverage containing microplastics at a ratio of 1g:5-10mL, shake well, and then heat in a water bath at 65-75°C for 3-6h. During the water bath heating, add 10-30% hydrogen peroxide solution intermittently. The frequency of intermittent addition of hydrogen peroxide solution is 0.5mL / 10min. S2. After the water bath heating is completed, lower the water bath temperature to 40-60°C and react for 6-12 hours. After the reaction is completed, filter while hot and rinse with a surfactant. Filter to obtain microplastics and the extraction is completed.

2. The method for extracting microplastics from a solid beverage granule according to claim 1, characterized in that: The solid beverage powder includes two-in-one coffee, three-in-one coffee, yeast melanin coffee, milk powder and bean powder.

3. The method for extracting microplastics from a solid beverage granule according to claim 1, characterized in that: The microplastics include one or more MPs such as PE, PS, PVC or PET.

4. The method for extracting microplastics from a solid beverage granule according to claim 1, characterized in that: The alkaline solution is a KOH solution, and the surfactant is Tween20 with a mass concentration of 5-15%.

5. The method for extracting microplastics from a solid beverage granule according to claim 1, characterized in that: During the reaction process described in S2, 200-300W ultrasonic wave is used for assistance.

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