Method for removing pesticide residues in instant tea powder

Abstract

The invention relates to the technical field of food processing, and particularly discloses a method for removing pesticide residues in instant tea powder. The method comprises the following steps: preparing instant tea powder containing pesticide residues into a solution, and adding a compound pretreatment agent; pretreatment is performed through a two-stage nanofiltration membrane series system with different molecular weight cut-off; after the trapped fluid is concentrated, a compound resin column is selected for adsorption according to the pesticide residue screening result; online ultraviolet spectrum monitoring is adopted, high-purity ethanol elution fractions are collected section by section, and residual liquid is refluxed and reused; and finally, carrying out vacuum concentration and temperature-controlled spray drying to obtain a zero-pesticide-residue product. Through cooperation of multiple technologies of function protection, multi-stage separation, precise adsorption and intelligent control, the problems of low removal rate of pesticide residues, large loss of active ingredients, deterioration of flavor and the like in a traditional method are effectively solved, the active ingredients and the flavor of the product are reserved while organic phosphorus and pyrethroid pesticide residues are efficiently removed, and the product quality is improved. The international standard is met.

Description

Technical Field

[0001] This application relates to the field of food processing technology, specifically a method for removing pesticide residues from instant tea powder. Background Technology

[0002] Instant tea powder is widely used in the beverage, food, and health product industries due to its rapid dissolution, portability, and ease of use. However, in the large-scale cultivation of tea, the application of chemical pesticides to control pests and diseases is difficult to completely avoid, resulting in pesticide residues often remaining in the fresh tea leaves. During the processing of instant tea powder, these pesticide residues are further transferred and accumulated through extraction and concentration processes, making pesticide residue problems particularly prominent in the final product.

[0003] Excessive pesticide residues not only pose various potential risks to consumer health, including neurotoxicity, endocrine disruption, and carcinogenicity, but also constitute a major technical barrier in the international trade of instant tea powder. In particular, markets such as the EU and Japan have established extremely strict standards for pesticide residue limits; products exceeding these limits are easily rejected, severely restricting the export competitiveness and development potential of my country's instant tea industry.

[0004] Among existing pesticide residue removal technologies, activated carbon adsorption and macroporous adsorption resin purification are currently widely used methods. However, their direct application to instant tea powder systems still has significant limitations: instant tea powder has a complex composition, containing not only the target pesticide residues but also a large amount of sugars, natural pigments, organic acids, and other components. These substances compete with pesticide molecules for adsorption sites on the resin surface, leading to a significant decrease in the actual adsorption capacity of the resin for pesticide residues, resulting in reduced production efficiency and increased costs. On the other hand, increasing the amount of resin or extending the contact time to improve the pesticide residue removal rate will exacerbate the non-specific adsorption of high-value functional active ingredients such as tea polyphenols, catechins, and caffeine, causing a decrease in product yield and quality, creating a contradiction between "residue removal" and "component preservation." Based on the above, this application provides a method for removing pesticide residues from instant tea powder. Summary of the Invention

[0005] To address the problems of low pesticide residue removal rate, low processing efficiency, low retention rate of natural active ingredients, and easy damage to flavor and quality in existing instant tea powder, this application provides a method for removing pesticide residues from instant tea powder.

[0006] In the first aspect, this application provides a method for removing pesticide residues from instant tea powder, employing the following technical solution: A method for removing pesticide residues from instant tea powder includes the following steps: S1. Raw material preparation: Add deionized water to the instant tea powder containing pesticide residues to prepare an instant tea powder solution with a mass fraction of 2-10%, and then add a compound pretreatment agent to obtain a treatment solution; S2. Nanofiltration membrane treatment: The treatment solution is passed through a series system of nanofiltration membranes with different molecular weight cutoffs. It passes through the first-stage nanofiltration membrane at the first operating pressure and then through the second-stage nanofiltration membrane at the second operating pressure. The retentate is collected. S3. Resin adsorption to remove pesticide residues: The retentate is concentrated to obtain a concentrate. Based on the pesticide residue screening results of the raw materials, macroporous adsorption resin and anion exchange resin are selected for compounding and column packing. The concentrate is then loaded onto the compound resin column. S4. Collect the eluent after removing impurities: After the sample is loaded, wash with deionized water and then elute with ethanol. At the same time, use a UV spectrometer to monitor the absorbance of the eluent at 280 nm. Collect the main peak fraction with absorbance > 70% of the maximum absorbance value according to the monitoring curve and combine them into the eluent. S5. Concentration and Drying: After the eluent is concentrated under reduced pressure, it is spray-dried. When the product moisture content is ≤7%, instant tea powder with zero pesticide residue is obtained.

[0007] Preferably, the total amount of the compound pretreatment agent added in step S1 is 0.5-0.8% of the mass of the instant tea powder solution, including tea polyphenol modified activated carbon, EDTA-2Na and one or more natural antioxidants selected from ferulic acid, gallic acid, chlorogenic acid, ascorbic acid and their salts, with a mass ratio of 12-14:0.6-1:1.

[0008] Preferably, the preparation method of the tea polyphenol modified activated carbon is as follows: tea residue generated during tea processing is crushed and passed through a 40-80 mesh sieve, and carbonized at a temperature of 300-600℃ for 1-3 hours to obtain tea residue-based activated carbon; the obtained tea residue-based activated carbon is mixed with a tea polyphenol solution with a mass fraction of 1-5% at a mass ratio of 1:3-10, stirred at 25-60℃ for 2-4 hours, and then subjected to solid-liquid separation. The obtained solid is washed with deionized water at 60-80℃ until the washing liquid is colorless and no tea polyphenol residue is detected by Folin-Ciocalteu reagent. Subsequently, it is dried at 60-100℃ for 12-24 hours to obtain tea polyphenol modified activated carbon.

[0009] Preferably, in step S2, the first operating pressure is 0.2-0.4 MPa, the molecular weight cutoff of the first-stage nanofiltration membrane is 600-800 Da, the second operating pressure is 0.4-0.6 MPa, the molecular weight cutoff of the second-stage nanofiltration membrane is 300-500 Da, and the flow rate through the nanofiltration membrane is 10-20 L / min.

[0010] Preferably, in step S3, the volume is concentrated to 20-35% of the original volume, and the loading flow rate is 1-4 BV / h.

[0011] Preferably, the compounded resin in step S3 is composed of a macroporous adsorption resin and anion exchange resin; wherein the macroporous adsorption resin is selected from at least one of D101, HPD-100, X-5, XAD-2, H103, and HPD-400; and the anion exchange resin is selected from at least one of D201, D301, D311, IRA-67, and IRA-96.

[0012] Preferably, in step S3, the D101 macroporous adsorption resin and the D201 anion exchange resin are compounded and packed into a column at a volume ratio of 2-4:1.

[0013] Preferably, in step S4, the amount of deionized water used is 2-4 BV, the washing speed is 2-4 BV / h, the ethanol mass fraction is 40-80%, the amount of ethanol used is 3-8 BV, and the elution speed is 1-2 BV / h.

[0014] Preferably, in step S4, the fraction with absorbance value ≤ 70% of the maximum absorbance value is collected and refluxed into the treatment solution in S2 for repeated treatment.

[0015] Preferably, in step S5, the reduced pressure concentration temperature is 50-65℃, the concentration is made to a solid content of 20-40%, the inlet air temperature of the spray drying is 160-180℃, and the outlet air temperature is 80-90℃.

[0016] Secondly, this application provides a method for removing pesticide residues from instant tea powder to prepare zero-pesticide-residue instant tea powder. The pesticide residue content of the instant tea powder meets EU and other international standards, and the retention rates of tea polyphenols, catechins, and caffeine are all higher than 90%.

[0017] In summary, this application has the following beneficial effects: (1) Achieving a balance between deep removal of pesticide residues and efficient retention of active ingredients: By innovatively adopting a multi-technology synergistic process of "pretreatment with compound pretreatment agent - multi-stage nanofiltration precision separation - resin compound directional adsorption - online monitoring and intelligent control", the contradiction between residue removal and quality preservation is systematically resolved. The multi-stage nanofiltration membrane series system achieves preliminary graded removal of small molecule pesticides and pre-enrichment of tea active ingredients through the synergistic effect of different molecular weight cutoff ranges, greatly reducing the treatment load of subsequent resins. The resin compounding strategy based on pesticide residue screening results achieves directional and efficient adsorption of pesticides of different properties such as organophosphates and pyrethroids, thereby significantly improving the pesticide residue removal rate, ensuring that the product meets the most stringent international standards such as the EU, and at the same time improving the retention rate of key active ingredients such as tea polyphenols, catechins, and caffeine.

[0018] (2) Significantly improved flavor quality and product stability: This application innovatively employs a compound pretreatment agent (tea polyphenol-modified activated carbon, EDTA-2Na, and ferulic acid) to synergistically enhance the initial removal efficiency of pesticide residues. The tea polyphenol-modified activated carbon utilizes the specific binding interaction (such as hydrogen bonds and π-π interactions) between its surface-modified tea polyphenols and pesticide molecules to achieve highly efficient targeted adsorption of pesticide residues. At the same time, because it is homologous to tea components, it effectively reduces the adsorption loss of natural active ingredients such as tea polyphenols and caffeine. EDTA-2Na reduces nanofiltration membrane fouling and stabilizes the system by chelating metal ions; ferulic acid utilizes its antioxidant properties to protect heat-sensitive flavor substances from oxidative degradation, thereby preserving the original flavor and quality of instant tea powder to the greatest extent while removing pesticide residues.

[0019] (3) The process is intelligent and green, with outstanding economic benefits: The application of online ultraviolet spectroscopy real-time monitoring and segmented collection technology has enabled precise control of the elution process, ensuring the collection of high-purity product fractions. At the same time, fractions containing residual components are recycled back to the previous process for recycling. This not only significantly improves the effective utilization rate of raw materials and reduces ethanol solvent consumption, but also reduces the emission of waste gas, wastewater, and solid waste, reflecting the concept of green manufacturing. Nanofiltration membrane pretreatment effectively delays resin contamination and failure. Combined with the compounding strategy, it improves the resin adsorption capacity and selectivity, and reduces the overall production cost. The entire process parameters are precisely designed, highly automated, easy to scale up, and have good stability and repeatability. Detailed Implementation

[0020] The present application will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are only for explaining the present application and are not intended to limit the scope of the present application.

[0021] Where specific techniques or conditions are not specified in the examples, they shall be performed in accordance with the techniques or conditions described in the literature in this field, or in accordance with the product instructions. Reagents or instruments whose manufacturers are not specified are all conventional products that can be purchased through legitimate channels.

[0022] Unless otherwise specified, the experimental methods used in the following embodiments are conventional methods. Unless otherwise specified, the experimental materials used in the following embodiments are commercially available products.

[0023] Example 1 A method for removing pesticide residues from instant tea powder includes the following steps: S1. Raw material preparation: Instant tea powder with residual amounts of 0.04 mg / kg of both fipronil and bifenthrin was mixed with deionized water to prepare a 2% (w / w) instant tea powder solution. Then, 0.5% (w / w) of a compound pretreatment agent (tea polyphenol-modified activated carbon, EDTA-2Na, and ferulic acid in a mass ratio of 12:0.6:1) was added to the instant tea powder solution to obtain a treatment solution. The preparation method of tea polyphenol-modified activated carbon is as follows: tea residue generated during tea processing was crushed and passed through a 40-mesh sieve and carbonized at 300℃ for 1 hour to obtain tea residue-based activated carbon. The obtained tea residue-based activated carbon was mixed with a 1% (w / w) tea polyphenol solution at a mass ratio of 1:3 and stirred at 25℃ for 2 hours. Then, solid-liquid separation was performed. The obtained solid was washed with deionized water at 60℃ until the washing liquid was colorless and no tea polyphenol residue was detected by Folin-Ciocalteu reagent. Then, it was dried at 60℃ for 12 hours to obtain tea polyphenol-modified activated carbon. S2. Nanofiltration membrane treatment: The treatment solution is passed through a series system of nanofiltration membranes with different molecular weight cutoffs at a flow rate of 10 L / min. It passes through a first-stage nanofiltration membrane with a molecular weight cutoff of 600 Da at a first operating pressure of 0.2 MPa, and then through a second-stage nanofiltration membrane with a molecular weight cutoff of 300 Da at a second operating pressure of 0.4 MPa. The retentate is collected. S3. Resin adsorption to remove pesticide residues: The retentate is concentrated to 20% of its original volume to obtain a concentrate. Based on the pesticide residue screening results of the raw materials, D101 macroporous adsorption resin and D201 anion exchange resin are selected and compounded in a volume ratio of 2:1 and packed into a column. The concentrate is loaded into the compounded resin column at a flow rate of 1 BV / h. S4. Collect the eluent after impurity removal: After the sample loading is completed, wash with 2 BV of deionized water at a rate of 2 BV / h, and then elute with 3 BV of 40% ethanol at a rate of 1 BV / h. At the same time, use an online ultraviolet spectrometer to monitor the absorbance value of the eluent at a wavelength of 280 nm in real time. According to the monitoring curve, collect the main peak fraction with absorbance value >70% of the maximum absorbance value in segments, combine them as the eluent, and reflux the remaining fractions into the next batch of S2 treatment solution. S5. Concentration and Drying: The eluent is concentrated under reduced pressure at 50°C to a solid content of 20%. Spray drying is performed with an inlet air temperature of 160°C and an outlet air temperature of 80°C. When the product moisture content is ≤7%, instant tea powder with zero pesticide residue is obtained.

[0024] Example 2 S1. Raw material preparation: Instant tea powder with residual amounts of 0.04 mg / kg of both fipronil and bifenthrin was mixed with deionized water to prepare a 6% (w / w) instant tea powder solution. Then, 0.6% (w / w) of a compound pretreatment agent (tea polyphenol-modified activated carbon, EDTA-2Na, and ferulic acid in a mass ratio of 13:0.8:1) was added to the instant tea powder solution to obtain a treatment solution. The preparation method of tea polyphenol-modified activated carbon is as follows: tea residue generated during tea processing was crushed and passed through a 60-mesh sieve, and carbonized at 450℃ for 2 hours to obtain tea residue-based activated carbon. The obtained tea residue-based activated carbon was mixed with a 3% (w / w) tea polyphenol solution at a mass ratio of 1:6, stirred at 40℃ for 3 hours, and then subjected to solid-liquid separation. The obtained solid was washed with deionized water at 70℃ until the washing liquid was colorless and no tea polyphenol residue was detected by Folin-Ciocalteu reagent. Then, it was dried at 80℃ for 18 hours to obtain tea polyphenol-modified activated carbon. S2. Nanofiltration membrane treatment: The treatment solution is passed through a series system of nanofiltration membranes with different molecular weight cutoffs at a flow rate of 15 L / min. It passes through a first-stage nanofiltration membrane with a molecular weight cutoff of 700 Da at a first operating pressure of 0.3 MPa, and then through a second-stage nanofiltration membrane with a molecular weight cutoff of 400 Da at a second operating pressure of 0.5 MPa. The retentate is collected. S3. Resin adsorption to remove pesticide residues: The retentate is concentrated to 25% of its original volume to obtain a concentrated solution. Based on the pesticide residue screening results of the raw materials, D101 macroporous adsorption resin and D201 anion exchange resin are selected and compounded in a volume ratio of 3:1 and packed into a column. The concentrated solution is loaded into the compound resin column at a flow rate of 2.5 BV / h. S4. Collect the eluent after impurity removal: After sample loading, wash with 3 BV of deionized water at a rate of 3 BV / h, and then elute with 6 BV of 60% ethanol at a rate of 1.5 BV / h. At the same time, use an online ultraviolet spectrometer to monitor the absorbance value of the eluent at a wavelength of 280 nm in real time. According to the monitoring curve, collect the main peak fraction with absorbance value >70% of the maximum absorbance value in segments, combine them as the eluent, and reflux the remaining fractions into the next batch of S2 treatment solution. S5. Concentration and Drying: The eluent is concentrated under reduced pressure at 60°C to a solid content of 30%. Spray drying is performed with an inlet air temperature of 170°C and an outlet air temperature of 85°C. When the product moisture content is ≤7%, instant tea powder with zero pesticide residue is obtained.

[0025] Example 3 S1. Raw material preparation: Instant tea powder with residual amounts of 0.04 mg / kg of both fipronil and bifenthrin was mixed with deionized water to prepare a 10% (w / w) instant tea powder solution. Then, 0.8% (w / w) of a compound pretreatment agent (tea polyphenol-modified activated carbon, EDTA-2Na, and ferulic acid in a mass ratio of 14:1:1) was added to the instant tea powder solution to obtain a treatment solution. The preparation method of tea polyphenol-modified activated carbon is as follows: tea residue generated during tea processing was crushed and passed through an 80-mesh sieve, and carbonized at 600℃ for 3 hours to obtain tea residue-based activated carbon. The obtained tea residue-based activated carbon was mixed with a 5% (w / w) tea polyphenol solution at a mass ratio of 1:10, stirred at 60℃ for 4 hours, and then subjected to solid-liquid separation. The obtained solid was washed with deionized water at 80℃ until the washing liquid was colorless and no tea polyphenol residue was detected by Folin-Ciocalteu reagent. Then, it was dried at 100℃ for 24 hours to obtain tea polyphenol-modified activated carbon. S2. Nanofiltration membrane treatment: The treatment solution is passed through a series system of nanofiltration membranes with different molecular weight cutoffs at a flow rate of 20 L / min. It passes through a first-stage nanofiltration membrane with a molecular weight cutoff of 800 Da at a first operating pressure of 0.4 MPa, and then through a second-stage nanofiltration membrane with a molecular weight cutoff of 500 Da at a second operating pressure of 0.6 MPa. The retentate is collected. S3. Resin adsorption to remove pesticide residues: The retentate is concentrated to 35% of its original volume to obtain a concentrate. Based on the pesticide residue screening results of the raw materials, D101 macroporous adsorption resin and D201 anion exchange resin are selected and compounded in a volume ratio of 4:1 and packed into a column. The concentrate is loaded into the compounded resin column at a flow rate of 4 BV / h. S4. Collect the eluent after impurity removal: After the sample loading is completed, wash with 4 BV of deionized water at a rate of 4 BV / h, and then elute with 8 BV of 80% ethanol at a rate of 2 BV / h. At the same time, use an online ultraviolet spectrometer to monitor the absorbance value of the eluent at a wavelength of 280 nm in real time. According to the monitoring curve, collect the main peak fraction with absorbance value >70% of the maximum absorbance value in segments, combine them as the eluent, and reflux the remaining fractions into the next batch of S2 treatment solution. S5. Concentration and Drying: The eluent is concentrated under reduced pressure at 65°C to a solid content of 40%. Spray drying is performed with an inlet air temperature of 180°C and an outlet air temperature of 90°C. When the product moisture content is ≤7%, instant tea powder with zero pesticide residue is obtained.

[0026] Comparative Example 1 A method for removing pesticide residues from instant tea powder includes the following steps: S1. Raw material preparation: Add deionized water to instant tea powder with a residue of 0.04 mg / kg of both fipronil and bifenthrin to prepare an instant tea powder solution with a mass fraction of 2%. S2. Nanofiltration membrane treatment: The instant tea powder solution is passed through a series system of nanofiltration membranes with different molecular weight cutoffs at a flow rate of 10 L / min. It is passed through a first-stage nanofiltration membrane with a molecular weight cutoff of 600 Da at a first operating pressure of 0.2 MPa, and then through a second-stage nanofiltration membrane with a molecular weight cutoff of 300 Da at a second operating pressure of 0.4 MPa. The retentate is collected. S3. Resin adsorption to remove pesticide residues: The retentate is concentrated to 20% of its original volume to obtain a concentrate. Based on the pesticide residue screening results of the raw materials, D101 macroporous adsorption resin and D201 anion exchange resin are selected and compounded in a volume ratio of 2:1 and packed into a column. The concentrate is loaded into the compounded resin column at a flow rate of 1 BV / h. S4. Collect the eluent after impurity removal: After the sample loading is completed, wash with 2 BV of deionized water at a rate of 2 BV / h, and then elute with 3 BV of 40% ethanol at a rate of 1 BV / h. At the same time, use an online ultraviolet spectrometer to monitor the absorbance value of the eluent at a wavelength of 280 nm in real time. According to the monitoring curve, collect the main peak fraction with absorbance value >70% of the maximum absorbance value in segments, combine them as the eluent, and reflux the remaining fractions into the next batch of S2 treatment solution. S5. Concentration and Drying: The eluent is concentrated under reduced pressure at 50°C to a solid content of 20%. Spray drying is performed with an inlet air temperature of 160°C and an outlet air temperature of 80°C. When the product moisture content is ≤7%, instant tea powder with zero pesticide residue is obtained.

[0027] Comparative Example 2 A method for removing pesticide residues from instant tea powder includes the following steps: S1. Raw material preparation: Instant tea powder with a residue of 0.04 mg / kg of both fipronil and bifenthrin was mixed with deionized water to prepare an instant tea powder solution with a mass fraction of 2%. Then, 0.5% of the mass of the instant tea powder solution was added with a compound pretreatment agent (the mass ratio of EDTA-2Na and ferulic acid was 0.6:1) to obtain the treatment solution. S2. Nanofiltration membrane treatment: The treatment solution is passed through a series system of nanofiltration membranes with different molecular weight cutoffs at a flow rate of 10 L / min. It passes through a first-stage nanofiltration membrane with a molecular weight cutoff of 600 Da at a first operating pressure of 0.2 MPa, and then through a second-stage nanofiltration membrane with a molecular weight cutoff of 300 Da at a second operating pressure of 0.4 MPa. The retentate is collected. S3. Resin adsorption to remove pesticide residues: The retentate is concentrated to 20% of its original volume to obtain a concentrate. Based on the pesticide residue screening results of the raw materials, D101 macroporous adsorption resin and D201 anion exchange resin are selected and compounded in a volume ratio of 2:1 and packed into a column. The concentrate is loaded into the compounded resin column at a flow rate of 1 BV / h. S4. Collect the eluent after impurity removal: After the sample loading is completed, wash with 2 BV of deionized water at a rate of 2 BV / h, and then elute with 3 BV of 40% ethanol at a rate of 1 BV / h. At the same time, use an online ultraviolet spectrometer to monitor the absorbance value of the eluent at a wavelength of 280 nm in real time. According to the monitoring curve, collect the main peak fraction with absorbance value >70% of the maximum absorbance value in segments, combine them as the eluent, and reflux the remaining fractions into the next batch of S2 treatment solution. S5. Concentration and Drying: The eluent is concentrated under reduced pressure at 50°C to a solid content of 20%. Spray drying is performed with an inlet air temperature of 160°C and an outlet air temperature of 80°C. When the product moisture content is ≤7%, instant tea powder with zero pesticide residue is obtained.

[0028] Comparative Example 3 A method for removing pesticide residues from instant tea powder includes the following steps: S1. Raw material preparation: Instant tea powder with residual amounts of 0.04 mg / kg of both fipronil and bifenthrin was mixed with deionized water to prepare a 2% (w / w) instant tea powder solution. Then, 0.5% (w / w) of a compound pretreatment agent (the mass ratio of tea polyphenol-modified activated carbon and ferulic acid was 12:1) was added to the instant tea powder solution to obtain a treatment solution. The preparation method of tea polyphenol-modified activated carbon was as follows: tea residue generated during tea processing was crushed and passed through a 40-mesh sieve, and carbonized at 300℃ for 1 hour to obtain tea residue-based activated carbon. The obtained tea residue-based activated carbon was mixed with a 1% (w / w) tea polyphenol solution at a mass ratio of 1:3, stirred at 25℃ for 2 hours, and then subjected to solid-liquid separation. The obtained solid was washed with deionized water at 60℃ until the washing liquid was colorless and no tea polyphenol residue was detected by Folin-Ciocalteu reagent. Then, it was dried at 60℃ for 12 hours to obtain tea polyphenol-modified activated carbon. S2. Nanofiltration membrane treatment: The treatment solution is passed through a series system of nanofiltration membranes with different molecular weight cutoffs at a flow rate of 10 L / min. It passes through a first-stage nanofiltration membrane with a molecular weight cutoff of 600 Da at a first operating pressure of 0.2 MPa, and then through a second-stage nanofiltration membrane with a molecular weight cutoff of 300 Da at a second operating pressure of 0.4 MPa. The retentate is collected. S3. Resin adsorption to remove pesticide residues: The retentate is concentrated to 20% of its original volume to obtain a concentrate. Based on the pesticide residue screening results of the raw materials, D101 macroporous adsorption resin and D201 anion exchange resin are selected and compounded in a volume ratio of 2:1 and packed into a column. The concentrate is loaded into the compounded resin column at a flow rate of 1 BV / h. S4. Collect the eluent after impurity removal: After the sample loading is completed, wash with 2 BV of deionized water at a rate of 2 BV / h, and then elute with 3 BV of 40% ethanol at a rate of 1 BV / h. At the same time, use an online ultraviolet spectrometer to monitor the absorbance value of the eluent at a wavelength of 280 nm in real time. According to the monitoring curve, collect the main peak fraction with absorbance value >70% of the maximum absorbance value in segments, combine them as the eluent, and reflux the remaining fractions into the next batch of S2 treatment solution. S5. Concentration and Drying: The eluent is concentrated under reduced pressure at 50°C to a solid content of 20%. Spray drying is performed with an inlet air temperature of 160°C and an outlet air temperature of 80°C. When the product moisture content is ≤7%, instant tea powder with zero pesticide residue is obtained.

[0029] Comparative Example 4 A method for removing pesticide residues from instant tea powder includes the following steps: S1. Raw material preparation: Instant tea powder with residual amounts of 0.04 mg / kg of both fipronil and bifenthrin was mixed with deionized water to prepare a 2% (w / w) instant tea powder solution. Then, 0.5% (w / w) of a compound pretreatment agent (the mass ratio of tea polyphenol-modified activated carbon and EDTA-2Na was 12:0.6) was added to the instant tea powder solution to obtain a treatment solution. The preparation method of tea polyphenol-modified activated carbon was as follows: tea residue generated during tea processing was crushed and passed through a 40-mesh sieve, and carbonized at 300℃ for 1 hour to obtain tea residue-based activated carbon. The obtained tea residue-based activated carbon was mixed with a 1% (w / w) tea polyphenol solution at a mass ratio of 1:3, stirred at 25℃ for 2 hours, and then subjected to solid-liquid separation. The obtained solid was washed with deionized water at 60℃ until the washing liquid was colorless and no tea polyphenol residue was detected by Folin-Ciocalteu reagent. Then, it was dried at 60℃ for 12 hours to obtain tea polyphenol-modified activated carbon. S2. Nanofiltration membrane treatment: The treatment solution is passed through a series system of nanofiltration membranes with different molecular weight cutoffs at a flow rate of 10 L / min. It passes through a first-stage nanofiltration membrane with a molecular weight cutoff of 600 Da at a first operating pressure of 0.2 MPa, and then through a second-stage nanofiltration membrane with a molecular weight cutoff of 300 Da at a second operating pressure of 0.4 MPa. The retentate is collected. S3. Resin adsorption to remove pesticide residues: The retentate is concentrated to 20% of its original volume to obtain a concentrate. Based on the pesticide residue screening results of the raw materials, D101 macroporous adsorption resin and D201 anion exchange resin are selected and compounded in a volume ratio of 2:1 and packed into a column. The concentrate is loaded into the compounded resin column at a flow rate of 1 BV / h. S4. Collect the eluent after impurity removal: After the sample loading is completed, wash with 2 BV of deionized water at a rate of 2 BV / h, and then elute with 3 BV of 40% ethanol at a rate of 1 BV / h. At the same time, use an online ultraviolet spectrometer to monitor the absorbance value of the eluent at a wavelength of 280 nm in real time. According to the monitoring curve, collect the main peak fraction with absorbance value >70% of the maximum absorbance value in segments, combine them as the eluent, and reflux the remaining fractions into the next batch of S2 treatment solution. S5. Concentration and Drying: The eluent is concentrated under reduced pressure at 50°C to a solid content of 20%. Spray drying is performed with an inlet air temperature of 160°C and an outlet air temperature of 80°C. When the product moisture content is ≤7%, instant tea powder with zero pesticide residue is obtained.

[0030] Comparative Example 5 A method for removing pesticide residues from instant tea powder includes the following steps: S1. Raw material preparation: Instant tea powder with a residue of 0.04 mg / kg of both fipronil and bifenthrin was mixed with deionized water to prepare an instant tea powder solution with a mass fraction of 2%. Then, 0.5% of the mass of the instant tea powder solution was added to the compound pretreatment agent (the mass ratio of tea residue-based activated carbon, EDTA-2Na and ferulic acid was 12:0.6:1) to obtain the treatment solution. The preparation method of tea residue-based activated carbon is as follows: the tea residue generated during the tea processing was crushed and passed through a 40-mesh sieve, and carbonized at 300℃ for 1 hour to obtain tea residue-based activated carbon. S2. Nanofiltration membrane treatment: The treatment solution is passed through a series system of nanofiltration membranes with different molecular weight cutoffs at a flow rate of 10 L / min. It passes through a first-stage nanofiltration membrane with a molecular weight cutoff of 600 Da at a first operating pressure of 0.2 MPa, and then through a second-stage nanofiltration membrane with a molecular weight cutoff of 300 Da at a second operating pressure of 0.4 MPa. The retentate is collected. S3. Resin adsorption to remove pesticide residues: The retentate is concentrated to 20% of its original volume to obtain a concentrate. Based on the pesticide residue screening results of the raw materials, D101 macroporous adsorption resin and D201 anion exchange resin are selected and compounded in a volume ratio of 2:1 and packed into a column. The concentrate is loaded into the compounded resin column at a flow rate of 1 BV / h. S4. Collect the eluent after impurity removal: After the sample loading is completed, wash with 2 BV of deionized water at a rate of 2 BV / h, and then elute with 3 BV of 40% ethanol at a rate of 1 BV / h. At the same time, use an online ultraviolet spectrometer to monitor the absorbance value of the eluent at a wavelength of 280 nm in real time. According to the monitoring curve, collect the main peak fraction with absorbance value >70% of the maximum absorbance value in segments, combine them as the eluent, and reflux the remaining fractions into the next batch of S2 treatment solution. S5. Concentration and Drying: The eluent is concentrated under reduced pressure at 50°C to a solid content of 20%. Spray drying is performed with an inlet air temperature of 160°C and an outlet air temperature of 80°C. When the product moisture content is ≤7%, instant tea powder with zero pesticide residue is obtained.

[0031] Comparative Example 6 A method for removing pesticide residues from instant tea powder includes the following steps: S1. Raw material preparation: Instant tea powder with residual amounts of 0.04 mg / kg of both fipronil and bifenthrin was mixed with deionized water to prepare an instant tea powder solution with a mass fraction of 2%. Then, 0.5% of the mass of the instant tea powder solution was added to a compound pretreatment agent (coconut shell activated carbon, EDTA-2Na and ferulic acid in a mass ratio of 12:0.6:1) to obtain the treatment solution. S2. Nanofiltration membrane treatment: The treatment solution is passed through a series system of nanofiltration membranes with different molecular weight cutoffs at a flow rate of 10 L / min. It passes through a first-stage nanofiltration membrane with a molecular weight cutoff of 600 Da at a first operating pressure of 0.2 MPa, and then through a second-stage nanofiltration membrane with a molecular weight cutoff of 300 Da at a second operating pressure of 0.4 MPa. The retentate is collected. S3. Resin adsorption to remove pesticide residues: The retentate is concentrated to 20% of its original volume to obtain a concentrate. Based on the pesticide residue screening results of the raw materials, D101 macroporous adsorption resin and D201 anion exchange resin are selected and compounded in a volume ratio of 2:1 and packed into a column. The concentrate is loaded into the compounded resin column at a flow rate of 1 BV / h. S4. Collect the eluent after impurity removal: After the sample loading is completed, wash with 2 BV of deionized water at a rate of 2 BV / h, and then elute with 3 BV of 40% ethanol at a rate of 1 BV / h. At the same time, use an online ultraviolet spectrometer to monitor the absorbance value of the eluent at a wavelength of 280 nm in real time. According to the monitoring curve, collect the main peak fraction with absorbance value >70% of the maximum absorbance value in segments, combine them as the eluent, and reflux the remaining fractions into the next batch of S2 treatment solution. S5. Concentration and Drying: The eluent is concentrated under reduced pressure at 50°C to a solid content of 20%. Spray drying is performed with an inlet air temperature of 160°C and an outlet air temperature of 80°C. When the product moisture content is ≤7%, instant tea powder with zero pesticide residue is obtained.

[0032] Comparative Example 7 A method for removing pesticide residues from instant tea powder includes the following steps: S1. Raw material preparation: Instant tea powder with residual amounts of 0.04 mg / kg of both fipronil and bifenthrin was mixed with deionized water to prepare a 2% (w / w) instant tea powder solution. Then, 0.5% (w / w) of a compound pretreatment agent (tea polyphenol-modified activated carbon, EDTA-2Na, and ferulic acid in a mass ratio of 12:0.6:1) was added to the instant tea powder solution to obtain a treatment solution. The preparation method of tea polyphenol-modified activated carbon is as follows: tea residue generated during tea processing was crushed and passed through a 40-mesh sieve and carbonized at 300℃ for 1 hour to obtain tea residue-based activated carbon. The obtained tea residue-based activated carbon was mixed with a 1% (w / w) tea polyphenol solution at a mass ratio of 1:3 and stirred at 25℃ for 2 hours. Then, solid-liquid separation was performed. The obtained solid was washed with deionized water at 60℃ until the washing liquid was colorless and no tea polyphenol residue was detected by Folin-Ciocalteu reagent. Then, it was dried at 60℃ for 12 hours to obtain tea polyphenol-modified activated carbon. S2. Nanofiltration membrane treatment: The treatment solution is passed through a series system of nanofiltration membranes with different molecular weight cutoffs at a flow rate of 10 L / min. It passes through a first-stage nanofiltration membrane with a molecular weight cutoff of 600 Da at a first operating pressure of 0.2 MPa, and then through a second-stage nanofiltration membrane with a molecular weight cutoff of 300 Da at a second operating pressure of 0.4 MPa. The retentate is collected. S3. Resin adsorption to remove pesticide residues: The retentate is concentrated to 20% of its original volume to obtain a concentrated solution. Based on the pesticide residue screening results of the raw materials, D101 macroporous adsorption resin is selected for column packing. The concentrated solution is loaded onto the resin column at a flow rate of 1 BV / h. S4. Collect the eluent after impurity removal: After the sample loading is completed, wash with 2 BV of deionized water at a rate of 2 BV / h, and then elute with 3 BV of 40% ethanol at a rate of 1 BV / h. At the same time, use an online ultraviolet spectrometer to monitor the absorbance value of the eluent at a wavelength of 280 nm in real time. According to the monitoring curve, collect the main peak fraction with absorbance value >70% of the maximum absorbance value in segments, combine them as the eluent, and reflux the remaining fractions into the next batch of S2 treatment solution. S5. Concentration and Drying: The eluent is concentrated under reduced pressure at 50°C to a solid content of 20%. Spray drying is performed with an inlet air temperature of 160°C and an outlet air temperature of 80°C. When the product moisture content is ≤7%, instant tea powder with zero pesticide residue is obtained.

[0033] Comparative Example 8 A method for removing pesticide residues from instant tea powder includes the following steps: S1. Raw material preparation: Instant tea powder with residual amounts of 0.04 mg / kg of both fipronil and bifenthrin was mixed with deionized water to prepare a 2% (w / w) instant tea powder solution. Then, 0.5% (w / w) of a compound pretreatment agent (tea polyphenol-modified activated carbon, EDTA-2Na, and ferulic acid in a mass ratio of 12:0.6:1) was added to the instant tea powder solution to obtain a treatment solution. The preparation method of tea polyphenol-modified activated carbon is as follows: tea residue generated during tea processing was crushed and passed through a 40-mesh sieve and carbonized at 300℃ for 1 hour to obtain tea residue-based activated carbon. The obtained tea residue-based activated carbon was mixed with a 1% (w / w) tea polyphenol solution at a mass ratio of 1:3 and stirred at 25℃ for 2 hours. Then, solid-liquid separation was performed. The obtained solid was washed with deionized water at 60℃ until the washing liquid was colorless and no tea polyphenol residue was detected by Folin-Ciocalteu reagent. Then, it was dried at 60℃ for 12 hours to obtain tea polyphenol-modified activated carbon. S2. Nanofiltration membrane treatment: The treatment solution is passed through a series system of nanofiltration membranes with different molecular weight cutoffs at a flow rate of 10 L / min. It passes through a first-stage nanofiltration membrane with a molecular weight cutoff of 600 Da at a first operating pressure of 0.2 MPa, and then through a second-stage nanofiltration membrane with a molecular weight cutoff of 300 Da at a second operating pressure of 0.4 MPa. The retentate is collected. S3. Resin adsorption to remove pesticide residues: The retentate is concentrated to 20% of its original volume to obtain a concentrated solution. Based on the pesticide residue screening results of the raw materials, D201 type anion exchange resin is selected for column packing. The concentrated solution is loaded onto the resin column at a flow rate of 1 BV / h. S4. Collect the eluent after impurity removal: After the sample loading is completed, wash with 2 BV of deionized water at a rate of 2 BV / h, and then elute with 3 BV of 40% ethanol at a rate of 1 BV / h. At the same time, use an online ultraviolet spectrometer to monitor the absorbance value of the eluent at a wavelength of 280 nm in real time. According to the monitoring curve, collect the main peak fraction with absorbance value >70% of the maximum absorbance value in segments, combine them as the eluent, and reflux the remaining fractions into the next batch of S2 treatment solution. S5. Concentration and Drying: The eluent is concentrated under reduced pressure at 50°C to a solid content of 20%. Spray drying is performed with an inlet air temperature of 160°C and an outlet air temperature of 80°C. When the product moisture content is ≤7%, instant tea powder with zero pesticide residue is obtained.

[0034] Various indicator testing experiments This application verifies the technical effects of Examples 1-3 and Comparative Examples 1-7 through the following experiments. All experiments follow the principle of controlling variables and use the same batch of green tea instant tea powder with excessive pesticide residues as raw materials.

[0035] The experiment consisted of 10 groups, including Examples 1-3 and Comparative Examples 1-7. Each experiment was repeated 3 times, and the average value of the results was taken.

[0036] Detection methods: ① Pesticide residue detection: HPLC-MS / MS method was used according to GB 23200.113-2018; ② Active ingredient detection: Tea polyphenols were detected according to GB / T 31740.2-2015, and EGCG, caffeine, etc., were detected using HPLC; ③ Flavor component detection: Headspace solid-phase microextraction-gas chromatography-mass spectrometry was used. The detection results are shown in Table 1.

[0037] Table 1 Comparison of various indicators between the examples and the comparative examples

[0038] Based on the test results in Table 1, it can be seen that Examples 1-3 of this application comprehensively outperform all comparative examples in terms of pesticide residue removal rate, active ingredient retention rate, and flavor component retention rate, fully demonstrating the overall and synergistic advantages of the technical solution provided in this application. Specifically, the removal rates of two typical pesticides (dinotefuran and bifenthrin) in the three examples are consistently above 97.8%, reaching a maximum of 99.2%, ensuring that the final product meets the requirement of "zero pesticide residue." At the same time, the retention rates of core functional components such as tea polyphenols, EGCG, and caffeine are all above 95%, and the retention rates of key flavor substances linalool and geraniol are also above 90%, successfully achieving the dual goals of "deep residue removal" and "ultimate freshness preservation."

[0039] Comparison of the comparative examples shows that Comparative Example 1 (without any pretreatment agent) had the lowest scores in all indicators, confirming that the compound pretreatment agent is the fundamental prerequisite for the efficient operation of the entire process. Its absence will lead to excessive load and low efficiency in subsequent nanofiltration and resin treatment. Comparative Examples 2-4 (each lacking one of the following: tea polyphenol-modified activated carbon, ferulic acid, or EDTA-2Na) were better than Comparative Example 1, but significantly inferior to the complete example, especially in flavor retention. This strongly demonstrates the indispensable synergistic effect among tea polyphenol-modified activated carbon (targeted adsorption), ferulic acid (antioxidant and flavor protector), and EDTA-2Na (chelation and scale reduction). The absence of any single component will lead to a decline in overall performance. Comparative Example 5 (using tea residue-based activated carbon) had a acceptable pesticide residue removal rate, but the retention rates of active and flavor components decreased significantly, highlighting the key value of the "tea polyphenol modification" process in improving adsorption selectivity. The non-specific adsorption of tea residue-based activated carbon results in the loss of a large amount of beneficial components. The data for Comparative Example 6 (using coconut shell activated carbon) were lower than those using tea residue-based activated carbon, indicating that unmodified tea residue-based activated carbon still performs better than other activated carbons in terms of pesticide residue removal and active ingredient retention in instant tea powder. The experimental results of Comparative Examples 7 and 8 (using only a single type of resin) further demonstrate that, for complex and diverse pesticide residues, the strategy of using a combination of D101 and D201 resins, compared to using a single resin, can more comprehensively cover pesticide molecules with different properties, thus achieving a higher and more stable pesticide residue removal rate, proving the scientific validity and necessity of the compound resin strategy.

[0040] In summary, this application systematically solves the industry problem of deep removal and high-quality retention of pesticide residues in instant tea powder by ingeniously coupling and synergistically using multiple technologies such as compound pretreatment agents, multi-stage nanofiltration, compound resin adsorption, and online monitoring reflux. The various technical features support each other and are indispensable, together forming a complete technical solution that is efficient, stable, and economical.

[0041] The above specific embodiments are merely explanations of this application and are not intended to limit this application. After reading this specification, those skilled in the art can make modifications to these embodiments without contributing any inventive step, but such modifications are protected by patent law as long as they fall within the scope of the claims of this application.

Claims

1. A method for removing pesticide residues from instant tea powder, characterized in that, Includes the following steps: S1. Raw material preparation: Add deionized water to the instant tea powder containing pesticide residues to prepare an instant tea powder solution with a mass fraction of 2-10%, and then add a compound pretreatment agent to obtain a treatment solution; S2. Nanofiltration membrane treatment: The treatment solution is passed through a series system of nanofiltration membranes with different molecular weight cutoffs. It passes through the first-stage nanofiltration membrane at the first operating pressure and then through the second-stage nanofiltration membrane at the second operating pressure. The retentate is collected. S3. Resin adsorption to remove pesticide residues: The retentate is concentrated to obtain a concentrate. Based on the pesticide residue screening results of the raw materials, macroporous adsorption resin and anion exchange resin are selected for compounding and column packing. The concentrate is then loaded onto the compound resin column. S4. Collect the eluent after removing impurities: After the sample is loaded, wash with deionized water and then elute with ethanol. At the same time, use a UV spectrometer to monitor the absorbance of the eluent at 280 nm. Collect the main peak fraction with absorbance > 70% of the maximum absorbance value according to the monitoring curve and combine them into the eluent. S5. Concentration and Drying: After the eluent is concentrated under reduced pressure, it is spray-dried. When the product moisture content is ≤7%, instant tea powder with zero pesticide residue is obtained.

2. The method for removing pesticide residues from instant tea powder according to claim 1, characterized in that, The total amount of the compound pretreatment agent added in step S1 is 0.5-0.8% of the mass of the instant tea powder solution. It includes tea polyphenol modified activated carbon, EDTA-2Na and one or more natural antioxidants selected from ferulic acid, gallic acid, chlorogenic acid, ascorbic acid and their salts, with a mass ratio of 12-14:0.6-1:

1.

3. The method for removing pesticide residues from instant tea powder according to claim 2, characterized in that, The preparation method of the tea polyphenol modified activated carbon is as follows: tea residue generated during tea processing is crushed and passed through a 40-80 mesh sieve, and carbonized at 300-600℃ for 1-3 hours to obtain tea residue-based activated carbon; the obtained tea residue-based activated carbon is mixed with a tea polyphenol solution of 1-5% by mass at a mass ratio of 1:3-10, stirred at 25-60℃ for 2-4 hours, and then subjected to solid-liquid separation. The obtained solid is washed with deionized water at 60-80℃ until the washing liquid is colorless and no tea polyphenol residue is detected by Folin-Ciocalteu reagent. Then it is dried at 60-100℃ for 12-24 hours to obtain tea polyphenol modified activated carbon.

4. The method for removing pesticide residues from instant tea powder according to claim 1, characterized in that, In step S2, the first operating pressure is 0.2-0.4 MPa, the molecular weight cutoff of the first-stage nanofiltration membrane is 600-800 Da, the second operating pressure is 0.4-0.6 MPa, the molecular weight cutoff of the second-stage nanofiltration membrane is 300-500 Da, and the flow rate through the nanofiltration membrane is 10-20 L / min.

5. The method for removing pesticide residues from instant tea powder according to claim 1, characterized in that, In step S3, the volume is concentrated to 20-35% of the original volume, and the loading flow rate is 1-4 BV / h.

6. The method for removing pesticide residues from instant tea powder according to claim 1, characterized in that, In step S3, the compounded resin is composed of macroporous adsorption resin and anion exchange resin; wherein the macroporous adsorption resin is selected from at least one of D101, HPD-100, X-5, XAD-2, H103, and HPD-400; and the anion exchange resin is selected from at least one of D201, D301, D311, IRA-67, and IRA-96.

7. The method for removing pesticide residues from instant tea powder according to claim 6, characterized in that, In step S3, the D101 macroporous adsorption resin and the D201 anion exchange resin are compounded and packed into a column at a volume ratio of 2-4:

1.

8. The method for removing pesticide residues from instant tea powder according to claim 1, characterized in that, In step S4, the amount of deionized water used is 2-4 BV, the washing speed is 2-4 BV / h, the ethanol mass fraction is 40-80%, the amount of ethanol used is 3-8 BV, and the elution speed is 1-2 BV / h.

9. The method for removing pesticide residues from instant tea powder according to claim 1, characterized in that, In step S5, the reduced pressure concentration temperature is 50-65℃, and the concentration is carried out until the solid content is 20-40%. The inlet air temperature for spray drying is 160-180℃, and the outlet air temperature is 80-90℃.

10. A pesticide-residue-free instant tea powder prepared by the method for removing pesticide residues from instant tea powder according to any one of claims 1-9, characterized in that, The pesticide residue levels of the instant tea powder meet EU and other international standards, and the retention rates of tea polyphenols, catechins, and caffeine are all higher than 90%.

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