Preparation and application of polylysine grafted hydroformylated starch fruit and vegetable cleaning agent

Abstract

The invention discloses preparation and application of a polylysine grafted hydroformylated starch fruit and vegetable cleaning agent, and belongs to the field of detergents. According to the starch-based derivative provided by the invention, natural macromolecular starch is oxidized by sodium periodate, so that the starch is subjected to ring opening hydroformylation, then amino groups of polylysine and aldehyde groups of the hydroformylated starch are subjected to a Schiff base reaction, sodium cyanoborohydride is added to reduce Schiff base bonds into more stable C-N single bonds, and thus the polylysine is grafted to the starch. The starch-based derivative disclosed by the invention is wide in raw material source, high in yield and low in price, has the characteristics of a surfactant, is biodegradable, safe and mild, and has no chemical reagent residue; and the product disclosed by the invention has relatively good bacterium (food-borne pathogenic bacteria) removal capability and pesticide residue removal capability in fruit cleaning.

Description

Technical Field

[0001] The invention relates to the preparation and application of a polylysine grafted hydroformylated starch fruit and vegetable cleaning agent, belonging to the field of detergents. Background Art

[0002] Fruits and vegetables are rich in nutrients and are an important part of our daily diet. Pesticides are the most effective weapon for preventing and controlling pests and weeds, and have important economic value in promoting the quality and yield of fruits and vegetables. The misuse of pesticides can lead to serious pesticide residues on the surface of fruits, posing a serious threat to human health. Short-term effects include headaches and nausea, and long-term effects include cancer, reproductive problems, and endocrine disorders.

[0003] At present, the common fruit cleaning methods used by people at home include water washing, NaCl cleaning, baking soda cleaning, commercial fruit detergent cleaning, ultrasonic cleaning, etc. At the same time, many technologies have developed green and efficient cleaning agents for cleaning pesticides on the surface of fruits and vegetables. Patent CN118995339A discloses the use of coconut oil dimethyl amine oxide, fatty alcohol polyoxyethylene ether sodium sulfate, sodium olefin sulfonate, diaminopropyl dodecylamine, compound bacterial fermentation products and water to prepare a cleaning agent, which has the effect of efficiently removing oil and agricultural residues; Patent CN117903886A discloses the use of eggshell powder, starch, calcined calcium hydroxide and montmorillonite and other raw materials to prepare a cleaning agent, which can highly absorb wax, agricultural residues and other substances from fruits and vegetables, and has a good antibacterial effect; Patent CN114456883A discloses the use of modified clay, cyclodextrin, starch, etc. to prepare fruit and vegetable cleaning powder, which can remove pesticide residues and has an antibacterial effect. The above technologies have problems such as poor pesticide removal and sterilization effects, hydrolysis of more toxic products during the cleaning process, promotion of penetration and residue of pesticides and surfactants, high equipment costs, and possible damage to fruits and affecting taste.

[0004] Therefore, there is an urgent need to develop a green, safe and efficient fruit cleaning agent that can effectively remove pesticide residues and foodborne pathogens when cleaning fruits and vegetables, and further prevent pesticide penetration, which has extremely high practical and economic value. Summary of the invention

[0005] In order to solve the above problems, the present invention provides a starch-based derivative, wherein natural macromolecular starch is oxidized with sodium periodate to open the starch ring for hydroformylation, and then the amino group of polylysine is used to react with the aldehyde group of hydroformylation starch for Schiff base reaction, and sodium cyanoborohydride is added to reduce the Schiff base bond to a more stable CN single bond, thereby grafting polylysine onto starch. The raw material source of this starch-based derivative is wide, the yield is large and cheap, it has surfactant properties, is biodegradable, safe and mild, and has no chemical reagent residues. In addition, the product of the present invention has excellent sterilization (foodborne pathogenic bacteria) and pesticide residue removal capabilities in fruit washing.

[0006] The first object of the present invention is to provide a method for improving the removal rate of pesticides on the surface of washed fruits and vegetables based on polylysine grafted hydroformyl starch, using a polylysine grafted hydroformyl starch aqueous solution to wash fruits and vegetables; The preparation method of polylysine grafted hydroformyl starch comprises: (1) Dissolve sodium periodate and starch in water at a molar ratio of 0.8-1.2:1, adjust the pH to 2-5, and react for 2-6 hours; centrifuge, wash, and dry to obtain aldehyde starch; (2) Dissolve the formaldehyde starch and polylysine in water at a molar ratio of 1:0.02-0.20, adjust the pH to 6.0-7.0, and react for 0.5-1.5 h; add sodium cyanoborohydride, adjust the pH to 6.0-8.0, and react for 3-8 h; centrifuge, wash, and dry to obtain the polylysine-grafted formaldehyde starch.

[0007] In one embodiment, the molar ratio in step (1) is the molar ratio of the starch structural unit to sodium periodate; and the molar ratio of the hydroformylation starch to polylysine in step (2) is the molar ratio of the aldehyde group in the hydroformylation starch to the lysine monomer.

[0008] Optionally, in step (2), the molar ratio of aldehyde starch to polylysine is 1:0.06-0.20; preferably, the molar ratio is 1:0.08-0.16.

[0009] In one embodiment, the starch in step (1) includes one or more of corn starch, potato starch, and porous starch.

[0010] In one embodiment, the porous starch is porous corn starch.

[0011] In one embodiment, the ratio of starch to water in step (1) is 3.0-5.0 g: 30-50 mL; and the ratio of aldehyde starch to water in step (2) is 1.0-5.0 g: 60-300 mL.

[0012] In one embodiment, the centrifugation in steps (1) and (2) is performed at 3500-8000 rpm for 3-15 min.

[0013] In one embodiment, drying comprises freeze drying, vacuum drying, hot air drying, microwave drying.

[0014] In one embodiment, the concentration of the polylysine grafted hydroformyl starch aqueous solution is 0.25-1.25%; the cleaning temperature is 25-40° C.; and the cleaning time is 15-25 min.

[0015] The second object of the present invention is to provide a polylysine grafted hydroformylation starch, the preparation method of the polylysine grafted hydroformylation starch comprising: (1) Dissolve sodium periodate and starch in water at a molar ratio of 0.2-1.8:1, adjust the pH to 2-5, and react for 2-8 hours; centrifuge, wash, and dry to obtain aldehyde starch; (2) Dissolve the formaldehyde starch and polylysine in water at a molar ratio of 1:0.01-0.50, adjust the pH to 6.0-7.0, and react for 0.5-1.5 h; add sodium cyanoborohydride, adjust the pH to 6.0-8.0, and react for 3-8 h; centrifuge, wash, and dry to obtain the polylysine-grafted formaldehyde starch.

[0016] In one embodiment, the molar ratio in step (1) is the molar ratio of the starch structural unit to sodium periodate; and the molar ratio of the hydroformylation starch to polylysine in step (2) is the molar ratio of the aldehyde group in the hydroformylation starch to the lysine monomer.

[0017] In one embodiment, in step (1), sodium periodate and starch are reacted for 2 to 6 hours in a molar ratio of 0.8 to 1.2:1; and in step (2), the molar ratio of aldehyde starch to polylysine is 1:0.02 to 0.20.

[0018] Optionally, in step (2), the molar ratio of aldehyde starch to polylysine is 1:0.06-0.20; preferably, the molar ratio is 1:0.08-0.16.

[0019] In one embodiment, the starch in step (1) comprises: one or more of corn starch, potato starch, and porous starch; The ratio of starch to water in step (1) is 3.0-5.0 g: 30-50 mL; In step (2), the ratio of aldehyde starch to water is 1.0-5.0 g: 60-300 mL; In steps (1) and (2), centrifugation is performed at 3500-8000 rpm for 3-15 min.

[0020] The third object of the present invention is to provide the use of any of the polylysine grafted hydroformylated starches in the preparation of cleaning agents.

[0021] In one embodiment, the starch in step (1) includes one or more of corn starch, potato starch, and porous starch.

[0022] In one embodiment, the ratio of starch to water in step (1) is 3.0-5.0 g: 30-50 mL; and the ratio of aldehyde starch to water in step (2) is 1.0-5.0 g: 60-300 mL.

[0023] In one embodiment, the centrifugation in steps (1) and (2) is performed at 3500-8000 rpm for 3-15 min.

[0024] In one embodiment, drying comprises freeze drying, vacuum drying, hot air drying, microwave drying.

[0025] In one embodiment, the concentration of the polylysine grafted aldehyde starch aqueous solution is 0.25-1.25%; the cleaning temperature is 25-40° C.; and the cleaning time is 15-25 min.

[0026] The fourth object of the present invention is to provide a pesticide cleaning agent containing any of the above-mentioned polylysine-grafted aldehyded starches.

[0027] Beneficial Effects of the Invention The present invention provides a starch-based derivative, wherein natural macromolecular starch is oxidized with sodium periodate to open the starch ring for hydroformylation, then the amino group of polylysine is used to react with the aldehyde group of hydroformylation starch for Schiff base reaction, and sodium cyanoborohydride is added to reduce the Schiff base bond to a more stable CN single bond, thereby grafting polylysine onto the starch. The raw material source of this starch-based derivative is wide, the yield is large and cheap, it has surfactant properties, is biodegradable, safe and mild, and has no chemical reagent residues. In addition, the product of the present invention has good sterilization (foodborne pathogenic bacteria) ability and pesticide residue removal ability in fruit washing.

[0028] Specifically: (1) The grafted poly-lysine starch prepared by the present invention was used to wash different fruits and vegetables at a concentration of 1% (g / 100 mL), and the sterilization rate for Escherichia coli reached more than 97.24%, and the sterilization rate for Staphylococcus aureus reached more than 94.13%; (2) The grafted poly-lysine starch prepared by the present invention can remove pesticides from different fruits and vegetables at a concentration of 1% (g / 100 mL), with a removal rate of more than 82.58%, and up to 96.62%, and can prevent the secondary migration of pesticides. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 The scanning electron microscope images are of corn starch raw material, hydroformylation corn starch intermediate, and polylysine grafted hydroformylation corn starch final product; Figure 2 The scanning electron microscope images are of potato starch raw material, hydroformylation potato starch intermediate, and polylysine grafted hydroformylation potato starch final product; Figure 3 The scanning electron microscope images are of porous starch raw material, hydroformylation porous starch intermediate, and polylysine grafted hydroformylation porous starch final product; Figure 4 This is the surface Raman imaging of chlorothalonil on unwashed apples; Figure 5 This is the deep Raman imaging of chlorothalonil on unwashed apples; Figure 6 This is the surface Raman imaging of chlorothalonil after washing apples with poly-lysine grafted aldehyded corn starch; Figure 7 This is the deep Raman imaging of thiophanate-methyl after washing apples with poly-lysine grafted aldehyded corn starch; Figure 8 This is the surface Raman imaging of thiophanate-methyl after washing apples with corn starch (Comparative Example 1); Fig. 9 This is the surface Raman imaging of chlorothalonil after washing apples with aldehyde-modified corn starch (Comparative Example 2); Fig.10 This is the surface Raman imaging image of thiophanate-methyl after washing apples with tap water (Comparative Example 3); Fig.11 This is the surface Raman imaging image of thiophanate-methyl after washing apples with sodium chloride (Comparative Example 4); Fig.12 This is the surface Raman imaging of thiophanate-methyl after washing apples with baking soda (Comparative Example 5); Fig.13 This is the surface Raman imaging image of thiophanate-methyl after washing apples with detergent (Comparative Example 6); Fig.14 This is the deep Raman imaging of thiophanate-methyl after washing apples with detergent (Comparative Example 6). DETAILED DESCRIPTION

[0030] The preferred embodiments of the present invention are described below. It should be understood that the embodiments are for better explaining the present invention and are not used to limit the present invention.

[0031] Test method: 1. The calculation formula of the yield (PY) of aldehyde starch is as follows:

[0032] In formula (1), m 1 is the mass of native starch, g; m 2 is the mass of aldehyde starch, g.

[0033] 2. Detection of aldehyde content of aldehyde-modified starch The semi-micro hydroxylamine hydrochloride method is used for determination, and the specific operation process is as follows: Weigh 0.1 g of aldehyde starch and dissolve it in 25 mL of deionized water, then add 20 mL of hydroxylamine hydrochloride (0.05 g / mL, adjust the pH to 5.0 with 0.1 mol / L NaOH). The mixture was reacted in a 50°C water bath for 4 h under magnetic stirring. After the reaction, the hydrochloric acid generated in the reaction system was titrated with 0.1 mol / L NaOH to make the pH value of the total system reach 5.0, and the consumption of NaOH was recorded. Repeat the measurement 3 times and calculate the average value. The aldehyde content (AC, %) was calculated according to formula (2):

[0034] In formula (2): C NaOH , the mass concentration of NaOH used for titration reaction, i.e. 0.1 mol / L; m , mass of aldehyde-formylated starch, g; V 1, the amount of NaOH consumed in titrating hydroformylation starch, L; V 2, the amount of NaOH consumed when titrating the same mass of starch, L; 160, the molecular weight of the repeating unit in the hydroformylation starch.

[0035] 3. Kjeldahl method to detect lysine content Accurately weigh 0.5 g of sample and add it to the digestion tube, then add 3 g of K2SO4 and 0.2 g of CuSO4 to each digestion tube, and finally add 10 mL of concentrated sulfuric acid and gently shake it to soak the sample. At the same time, treat a blank containing all these reagents. The blank control is aldehyde starch. Use a graphite digestion instrument to digest, digest at 100℃ for 20 min, 200℃ for 20 min, 300℃ for 20 min, and 420℃ for 90 min, until the sample in the tube becomes a blue-green transparent clear liquid. Use an automatic distillation device to titrate the sample collected by distillation with hydrochloric acid. Use bromocresol green methyl red indicator (5:1) for endpoint indication: the solution color changes from blue to pink. The total nitrogen content of each sample is calculated according to formula (3), and the lysine content in the sample can be obtained according to formula (4) based on the nitrogen content in the sample.

[0036]

[0037]

[0038] In formula (3), TN is the total nitrogen content of the sample, mol N / g; V 1 is the volume of hydrochloric acid consumed by the blank, mL, V 2 is the volume of hydrochloric acid consumed by the sample, mL; C The concentration of hydrochloric acid is 0.236 mol / L; mis the mass of hydroformylation starch, g; 146.19 is the relative molecular mass of polylysine (ε-PL) monomer.

[0039] 4. Detection of the removal effect of Chlorothalonil Sample processing: The pre-treatment method in GB23200.113-2018 was adopted.

[0040] Detection method and result calculation: The HPLC method was used to determine the content of thiophanate-methyl in the sample. The liquid phase detection conditions were as follows: the liquid chromatography instrument model was Agilent 1260 Infinity II HPLC, the chromatographic column was Waters Sunfire C18 (250×4.6 mm, 5 μm), the injection volume was 20 μL, the mobile phase was acetonitrile-water (80:20, V / V), the flow rate was 1 mL / min, the column temperature was 25°C, the detection wavelength of the UV detector was 240 nm, and the retention time was 4.4 min. The peak area and concentration of thiophanate-methyl showed good linearity in the range of 0.01 mg / L~20 mg / L: y=123.1546x+1.8937, R 2 =0.9973 (y represents the peak area, x represents the concentration of chlorothalonil, mg / L). The chlorothalonil removal rate under the current cleaning conditions was calculated according to formula (5).

[0041]

[0042] In formula (5) C 0 is the concentration of thiophanate-methyl in positive samples, C 1 is the residual thiophanate-methyl concentration in the sample after cleaning.

[0043] The raw materials used in the examples are: Poly-lysine was purchased from Zhangshu Lion Biotechnology Co., Ltd.; Corn starch was purchased from Shanghai Yuanye Biological Co., Ltd.; (Corn) porous starch was purchased from Jiangsu Baobao Suqian National Biotechnology Co., Ltd.; Potato starch, sodium cyanoborohydride, and sodium periodate were purchased from Shanghai Aladdin Biochemical Technology Co., Ltd.

[0044] Example 1: Preparation of polylysine grafted hydroformyl starch The steps for preparing polylysine grafted hydroformyl starch are as follows: (1) Accurately weigh 5.95 g of sodium periodate and completely dissolve it in 45 mL of water, add 4.5 g of corn starch (the molar ratio of starch structural unit to sodium periodate is 1:1), adjust the pH of the solution to 3.0, and stir the reaction in a 35°C water bath in the dark for 4 h (400 r / min). After the reaction, centrifuge (5000 r / min, 5 min) to separate the solid product, wash it with water until it is neutral, and freeze-dry it to obtain the hydroformylated corn starch (store it in a dry and dark place). (2) Polylysine grafted aldehyde starch was prepared by chemical grafting method. 3 g of aldehyde starch was dissolved in 180 mL of water. Different masses (i.e., 0.1063 g, 0.2126 g, and 0.0425 g) of ε-PL were weighed and added to the above solution according to the reaction molar ratio of aldehyde group in aldehyde starch to lysine monomer (molecular weight 146.19) of 1:0.04, 1:0.08, and 1:0.16. The pH value of the suspension was adjusted to 6.5 with 0.1 mol / L hydrochloric acid / 0.1 mol / L sodium hydroxide and stirred at room temperature for 1 h. Sodium cyanoborohydride was added in an amount equal to that of ε-PL to adjust the pH value to 7.0 (adjusted every 15 min with 0.1 mol / L HCl) and the reaction was carried out for 5 h. The precipitate was obtained by centrifugation (5000 r / min, 5 min), washed with water until neutral, and freeze-dried in vacuum for 30 min. h, and poly-lysine grafted hydroformylated corn starch with different grafting rates were obtained, which were named corn hydroformylation-0.04-ε-PL, corn hydroformylation-0.08-ε-PL, and corn hydroformylation-0.16-ε-PL according to the amount of ε-PL used.

[0045] Example 2: Starch property detection On the basis of Example 1, the corn starch in step (1) is replaced by potato starch or porous (corn) starch, and the remaining steps are consistent with Example 1, to prepare hydroformylation potato starch, hydroformylation porous starch, polylysine grafted hydroformylation potato starch and polylysine grafted hydroformylation porous starch with different polylysine grafting degrees, respectively.

[0046] The hydroformylated corn starch, polylysine grafted hydroformylated corn starch, hydroformylated potato starch, polylysine grafted hydroformylated potato starch, hydroformylated porous starch and polylysine grafted hydroformylated porous starch prepared in Examples 1 and 2 were characterized, and the results are as follows: 1. Take different hydroformylation starches and detect their aldehyde content, hydroformylation degree and product yield. The results are shown in Table 1.

[0047] Table 1 Aldehyde content, degree of hydroformylation and yield of hydroformyl starch

[0048] The results show that the aldehyde content of corn starch, potato starch, and porous starch decreases in turn after oxidation (the degree of hydroformylation decreases in turn), but the product yield increases in turn. This is because the aldehyde content is related to the linearity of starch, and a high linearity is conducive to the oxidation reaction. As the degree of oxidation increases, the original starch molecular structure is destroyed, the chain length decreases, and the molecular chain breaks, resulting in a decrease in yield.

[0049] 2. Take different polylysine-grafted aldehyde starches and test the N content, lysine content and yield. The results are shown in Table 2.

[0050] Table 2 Nitrogen content, lysine content and yield of polylysine grafted hydroformylation starch

[0051] The results show that when dialdehyde starch reacts with ε-PL at different molar ratios, the nitrogen content, lysine content and yield of the obtained products are different. As the molar ratio of dialdehyde starch aldehyde group to lysine monomer increases, the lysine content in the product also increases, and the two are positively correlated, which indicates that dialdehyde starch and ε-PL use Schiff base reaction to form a new cross-linked product through the combination of the active aldehyde group on dialdehyde starch and the amino group on ε-PL; In addition, as the molar ratio of dialdehyde starch aldehyde group to lysine monomer increases, the yield of the product gradually decreases, because the molecular chain breaks with the oxidation reaction, resulting in a decrease in yield.

[0052] 3. Morphology characterization Scanning electron microscopy (SEM) was used to observe the microstructure of untreated starch, aldehyde-modified starch, and poly-lysine-grafted aldehyde-modified starch. Figure 1 , Figure 2 and Figure 3 As shown in the figure, compared with native starch, the surface of aldehyde-modified starch becomes rough, damaged and concave. This may be due to the partial breakage of the α-1,4-glycosidic bond of the starch molecule, which leads to the shortening of the polysaccharide chain, the change of the molecular structure, the destruction of the crystal structure, and the appearance of surface damage and concave.

[0053] In addition, the breaking of α-1,4-glycosidic bonds not only affects the length of starch molecules, but may also reduce their overall stability. The hydroxyl group (-OH) of the starch molecule is oxidized to an aldehyde group (-CHO). The introduction of the aldehyde group may change the hydrophobicity of the starch, making its surface rougher and increasing its interaction area with other substances; after grafting ε-PL, new wrinkles and unevenness appear on the surface of the aldehyde-starch-ε-PL. These protrusions or depressions may be related to the grafting position of the ε-PL molecular chain on the starch surface. The higher the grafting rate, the more ε-PL molecules are connected to the starch molecules, so the wrinkles and unevenness of the surface are more obvious.

[0054] Example 3: Application of polylysine grafted hydroformylation corn / potato / porous starch in fruit and vegetable cleaning The polylysine-grafted hydroformylated corn starch prepared in Examples 1 and 2 was used to test its effect in washing fruits and vegetables.

[0055] 1. Sterilization effect detection (1) Detection of the antibacterial effect of polylysine-grafted aldehyde-modified corn starch Preparation of positive samples: Select apples of uniform size, ripe, undamaged and disease-free, and disinfect them with 1.2% (W / V) sodium hypochlorite solution for 8 minutes. After that, rinse them three times with sterile water and air-dry them in a sterile operating table as negative controls.

[0056] The bacteria (Escherichia coli (ATCC 8099) and Staphylococcus aureus (ATCC6538) were used as model pathogens) cultured to the logarithmic growth phase were diluted to 10 8 CFU / mL, sterile apples were immersed in the above bacterial suspension for 15 min, air-dried in a clean bench for 20-30 min, and apples infected with bacteria were obtained as positive samples to be cleaned.

[0057] Prepare a 1% (g / 100 mL) corn aldehyde-0.16-ε-PL starch solution at a water temperature of 30°C. Place the positive samples in the solution and soak and wash for 20 min (stir every 5 min). Wash the samples infected with bacteria and then rinse with sterile water as the test group.

[0058] Colony count: Chop unwashed / washed apples, take 25 g of sample and mix with 225 mL of sterile saline solution in a sterile bag, and homogenize with a slapping homogenizer for 5 min; dilute the homogenate 10 times with sterile saline, take 100 µL of the appropriate dilution and apply it on the surface of LB agar medium (repeat six parallels), and incubate at 37°C for 24 h. Count the colonies, and the results are expressed as CFU / g. The sterilization rate is calculated according to formula (6).

[0059]

[0060] In formula (6) N 0 is the total number of colonies on the unwashed sample (CFU / g); N 1 is the total number of colonies on the sample after cleaning (CFU / g).

[0061] (2) Detection of the antibacterial effect of polylysine-grafted aldehyde-formylated potato starch On the basis of step (1), the polylysine grafted hydroformylation corn starch is replaced by polylysine grafted hydroformylation potato starch, and the apple is replaced by sweet potato, and the cleaning effect of the polylysine grafted hydroformylation potato starch on the sweet potato is tested.

[0062] (3) Detection of the antibacterial effect of polylysine-grafted porous starch On the basis of step (1), the polylysine grafted hydroformylation corn starch was replaced by polylysine grafted hydroformylation porous starch, and the apple was replaced by cabbage, and the cleaning effect of the polylysine grafted hydroformylation porous starch on the cabbage was tested.

[0063] The test results showed that the sterilization rate of apples washed with 1% corn hydroformylation-0.16-ε-PL starch was 97.15% for Staphylococcus aureus and 99.14% for Escherichia coli; the sterilization rate of sweet potatoes washed with 1% potato hydroformylation-0.16-ε-PL starch was 98.32% for Staphylococcus aureus and 99.34% for Escherichia coli; the sterilization rate of cabbage washed with 1% porous hydroformylation-0.16-ε-PL starch was 97.27% for Staphylococcus aureus and 99.07% for Escherichia coli; while the sterilization rate of Escherichia coli washed with sterile water was only 16.87%~19.24% and 18.34%~20.37% for Staphylococcus aureus. It can be seen that washing with hydroformylation starch can significantly reduce the risk of foodborne pathogens on the surface of fruits and vegetables.

[0064] 2. Overall removal effect of pesticides (1) The pesticide removal effect of polylysine grafted aldehyde-modified corn starch was tested in the following steps: Positive sample preparation: Prepare a 15 mg / L chlorothalonil aqueous solution, select apples of uniform size, ripe, undamaged, and disease-free, soak them in the aqueous solution for 4 h, and air-dry for 1 hour; Cleaning: Prepare a 1% (g / 100 mL) concentration of polylysine grafted hydroformylated corn starch (corn hydroformylation-0.04-ε-P, corn hydroformylation-0.08-ε-PL, corn hydroformylation-0.16-ε-PL) cleaning solution with different grafting rates. The water temperature is 30°C. Place the positive sample in the solution and clean for 20 min. Detection: The pretreatment method in GB23200.113-2018 was combined with HPLC to evaluate the pesticide removal rate. The Agilent 1260 Infinity II HPLC system (Beijing, China) equipped with a UV detector and a Waters Sunfire C18 column (250 × 4.6 mm, 5 μm) was used to analyze the content of chlorothalonil in fruit and vegetable samples. The mobile phase was a mixture of acetonitrile and water (80:20, V / V), the flow rate was 1 mL / min, the injection volume was 20 μL, and the column temperature was maintained at 25 °C. The detection wavelength was 240 nm, and the retention time was 4.4 min.

[0065] (2) Detection of the pesticide removal effect of polylysine grafted hydroformylation potato starch Based on step (1), apples were replaced with sweet potatoes for 1 h. The remaining steps were the same as step (1). The pesticide removal effects of polylysine grafted hydroformylation potato starch with different grafting rates (potato hydroformylation-0.04-ε-P, potato hydroformylation-0.08-ε-PL, potato hydroformylation-0.16-ε-PL) were detected.

[0066] (3) Testing the pesticide removal effect of polylysine-grafted aldehyde-formylated porous starch On the basis of step (1), apples were replaced by cabbages and soaked for 20 min. The remaining steps were the same as step (1). The pesticide removal effects of polylysine grafted hydroformylation porous starch with different grafting rates (porous hydroformylation-0.04-ε-P, porous hydroformylation-0.08-ε-PL, porous hydroformylation-0.16-ε-PL) were detected.

[0067] The test results showed that the removal rates of corn hydroformyl-0.04-ε-PL on apples were 82.58%, corn hydroformyl-0.08-ε-PL on apples were 95.01%, and corn hydroformyl-0.16-ε-PL on apples were 96.62%; the removal rates of potato hydroformyl-0.04-ε-PL on sweet potatoes were 81.48%, and potato hydroformyl-0.08-ε-PL on sweet potatoes were 96.62%. The removal rate of PL on chlorothalonil on sweet potato was 96.81%, and the removal rate of potato hydroformyl-0.16-ε-PL on sweet potato was 95.26%; the removal rate of porous hydroformyl-0.04-ε-PL on chlorothalonil on cabbage was 89.65%, the removal rate of porous hydroformyl-0.08-ε-PL on cabbage was 91.99%, and the removal rate of porous hydroformyl-0.16-ε-PL on cabbage was 90.02%. The above-mentioned different types and different grafting ratios of polylysine grafted hydroformyl starch have good removal efficiency for chlorothalonil on fruits and vegetables.

[0068] 3. Pesticide surface removal effect and secondary migration detection For most fresh fruits and vegetables, it is necessary to evaluate whether the pesticides will remain on the surface of the fruit after washing and whether they will migrate into the fruit. Taking the apple in 2 as an example, Raman imaging is used to detect the pesticide surface removal effect and whether there is secondary migration. The steps are as follows: Raman spectra were collected using a DXR2xi Raman imaging microscope spectrometer (Thermo Fisher Scientific, Madison, WI, USA). The scanning wavelength was 400-2000 cm⁻¹, the excitation wavelength was 785 nm, the laser power was 3.0 mW, the exposure time was 0.5 s, and the scan was repeated twice. Surface imaging used a ⅹ10 objective lens, a 50 μm pinhole, the length and width of the scanning area were both 100 μm, and the step length was 10 μm. Depth imaging used a ⅹ50 telephoto objective lens, a 50 μm confocal pinhole, a scanning area width of 30 μm, a depth of 250 μm, and a step length of 5 μm. Surface and depth imaging was performed at randomly selected locations on the apple surface, and each sample was repeated three times. The Raman spectrum of thiocarbamide was measured, and 2242 cm -1 As its characteristic peak, OMNIC TM The software generates an imaging spectrum at a given wave number.

[0069] Surface imaging and depth imaging of samples with positive thiophanate-methyl residues Figure 4 and Figure 5 As shown; after cleaning with 1% corn aldehyde-0.16-ε-PL, the surface imaging and depth imaging are shown in Figure 6 , Figure 7 As shown, the results showed that 1% cornformyl-0.16-ε-PL could effectively remove the residual thiophanate-methyl on the surface of apples without causing the migration of thiophanate-methyl into the interior of the fruit.

[0070] Comparative Example 1: Removal of chlorothalonil from fruits and vegetables by washing with native starch On the basis of Example 3, the cleaning solution of polylysine grafted formaldehyde starch was replaced with unmodified starch solution (1%), and the sterilization effect, overall pesticide removal effect, pesticide surface removal effect and secondary migration test were tested. The steps were consistent with Example 3.

[0071] Comparative Example 2: Removal of chlorothalonil from fruits and vegetables by washing with hydroformyl starch On the basis of Example 3, the polylysine grafted formaldehyde starch cleaning solution was replaced with formaldehyde starch solution (1%), and the sterilization effect, overall pesticide removal effect, pesticide surface removal effect and secondary migration test were tested. The steps were consistent with Example 3.

[0072] Comparative Example 3: Removal of chlorothalonil from fruits and vegetables by tap water On the basis of Example 3, the cleaning solution of polylysine grafted formaldehyde starch was replaced with tap water, and the sterilization effect, overall pesticide removal effect, pesticide surface removal effect and secondary migration test were tested. The steps were consistent with Example 3.

[0073] Comparative Example 4: Cleaning and removing chlorothalonil from fruits and vegetables with sodium chloride solution On the basis of Example 3, the cleaning solution of polylysine grafted formaldehyde starch was replaced with sodium chloride solution (1%), and the sterilization effect, overall pesticide removal effect, pesticide surface removal effect and secondary migration test were tested. The steps were consistent with Example 3.

[0074] Comparative Example 5: Using baking soda solution to remove chlorothalonil from fruits and vegetables On the basis of Example 3, the cleaning solution of polylysine grafted formaldehyde starch was replaced with baking soda solution (1%), and the sterilization effect, overall pesticide removal effect, pesticide surface removal effect and secondary migration test were tested. The steps were consistent with Example 3.

[0075] Comparative Example 6: Removal of Chlorothalonil from Fruits and Vegetables by Using Detergent On the basis of Example 3, the poly-lysine grafted formaldehyde starch cleaning solution was replaced with a certain brand of dishwashing liquid (1%), and the sterilization effect, overall pesticide removal effect, pesticide surface removal effect and secondary migration test were tested. The steps were consistent with Example 3.

[0076] Comparative Example 7: Electrostatic Grafting of Polylysine On the basis of Example 1, the grafting method of polylysine was changed to electrostatic grafting method to prepare corn aldehyde-0.16-ε-PL starch, and the specific steps were as follows: 3 g of aldehyded starch and 0.2126 g of ε-PL were weighed and dissolved in 180 mL of water. The pH value of the suspension was adjusted to 6.5 with 0.1 mol / L hydrochloric acid or 0.1 mol / L sodium hydroxide. The mixture was stirred at room temperature for 6 h, centrifuged (5000 r / min, 5 min) to obtain a precipitate, washed with water until neutral, and vacuum freeze-dried for 30 h. The sterilization effect and overall pesticide removal effect of the polylysine aldehyded starch prepared by the electrostatic method were detected, and the steps were consistent with Example 3.

[0077] The corn hydroformylation-0.16-ε-PL starch, potato hydroformylation-0.16-ε-PL and porous hydroformylation-0.16-ε-PL prepared in Examples 1 and 2 were used to test the removal rate of harmful bacteria and pesticides at a concentration of 1% for the cleaning agents of Comparative Examples 1 to 7. The experimental results are shown in Tables 3 to 5 and Figure 8~Figure 14 shown.

[0078] Table 3 Cleaning effect of different cleaning agents on apples

[0079] Table 4 Cleaning effect of different cleaning agents on sweet potatoes

[0080] Table 5 The cleaning effect of different cleaning agents on cabbage

[0081] On this basis, the secondary migration depth of pesticides after washing apples with detergent and corn aldehyde-0.16-ε-PL starch at a concentration of 1% was tested. The results showed that washing with detergent would cause the pesticides to migrate 200 μm into the fruit. Fig.14 ).

[0082] The results show that the starch-based derivatives prepared in Examples 1 and 2 have excellent bactericidal and removal effects on foodborne pathogens, have a good removal rate for non-systemic bacteria and will not migrate secondary to the inside of the fruit pulp, and are a type of safe and efficient fruit and vegetable cleaning agent.

[0083] Example 4: Application of polylysine-grafted hydroformylated corn starch in washing fruits The polylysine-grafted hydroformylated corn starch prepared in Example 1 was used to optimize the cleaning conditions, as follows: 1. Concentration optimization (1) Preparation of positive samples: Prepare a 15 mg / L chlorothalonil aqueous solution. Select apples of uniform size, ripe, undamaged, and disease-free, soak them in the aqueous solution for 4 h, and air-dry them for 1 hour.

[0084] (2) Cleaning: Corn aldehyde-0.16-ε-PL cleaning solution of different concentrations (0.1%, 0.25%, 0.5%, 0.75%, 1%, 1.25%) was prepared, the water temperature was 30℃, the positive samples were placed in it and washed for 20 minutes, and the removal rate of thiophanate-methyl was tested.

[0085] The results showed that the removal rates of thiophanate-methyl at concentrations of 0.1%, 0.25%, 0.5%, 0.75%, 1% and 1.25% were 68.99%, 87.88%, 91.23%, 91.53%, 96.62% and 95.64%, respectively; it can be seen that with the increase of concentration (0.1%~1%), the removal rate gradually increased. When the concentration was greater than 1%, the removal rate did not change significantly. The optimal concentration of corn hydroformyl-0.16-ε-PL starch was 1%, because the critical micelle concentration was reached at 1%.

[0086] 2. Cleaning temperature A cleaning solution with a mass concentration of 1% corn aldehyde-0.16-ε-PL was prepared, and the positive samples were placed in the solution and cleaned for 20 min at water temperatures of 20℃, 25℃, 30℃, 35℃, and 40℃, and the removal rate of thiophanate-methyl was tested.

[0087] The results showed that the removal rates of thiophanate-methyl at 20℃, 25℃, 30℃, 35℃ and 40℃ were 82.75%, 84.16%, 92.88%, 91.81% and 92.96% respectively; it can be seen that with the increase of water temperature (20~30℃), the removal effect of thiophanate-methyl gradually increased, and the removal rate no longer increased significantly when the temperature continued to rise (20~30℃). Therefore, the optimal water temperature is 30℃.

[0088] 3. Cleaning time A 1% cornformaldehyde-0.16-ε-PL cleaning solution was prepared with a water temperature of 30°C. The positive samples were cleaned for 5 min, 10 min, 15 min, 20 min, and 25 min respectively, and the removal rate of chlorothalonil was tested.

[0089] The results showed that the removal rates of chlorothalonil were 70.86%, 83.23%, 91.89%, 94.91% and 95.08% at 5 min, 10 min, 15 min, 20 min and 25 min, respectively; it can be seen that with the increase of cleaning time, the removal rate of chlorothalonil continued to increase, and the optimal cleaning time was 20 min.

[0090] The above results show that the optimal cleaning condition is 1% (w / v) corn aldehyde-0.16-ε-PL cleaning solution, 30℃ for 20min.

[0091] Example 5: Removal of other pesticides by polylysine grafted hydroformylation of corn starch On the basis of Example 3, apples were used as actual samples, thiram and chlorpyrifos were substituted for thiram and chlorpyrifos at equal concentrations, a 1% concentration of cornformyl-0.16-ε-PL cleaning solution was prepared, the water temperature was 30°C, the positive samples were placed in the solution and cleaned for 20 min, the pesticide removal rate was calculated, and the removal rate of non-systemic pesticides by the starch-based derivatives prepared by the present invention was evaluated.

[0092] The results show that the removal rates of thiram and chlorpyrifos on apples by polylysine grafted hydroformylation corn starch are 90.51%, and 97.36%, respectively. In conclusion, the polylysine grafted hydroformylation starch prepared by the present invention has a good removal effect on non-systemic pesticides.

[0093] Although the present invention has been disclosed as above in the form of a preferred embodiment, it is not intended to limit the present invention. Anyone familiar with this technology can make various changes and modifications without departing from the spirit and scope of the present invention. Therefore, the scope of protection of the present invention should be based on the definition of the claims.

Claims

1. A method for improving the removal rate of pesticides on the surface of fruits and vegetables based on polylysine grafted hydroformyl starch, characterized in that: Wash fruits and vegetables with polylysine-grafted hydroformyl starch aqueous solution; The preparation method of polylysine grafted hydroformyl starch comprises: (1) Dissolve sodium periodate and starch in water at a molar ratio of 0.8-1.2:1, adjust the pH to 2-5, and react for 2-6 hours; centrifuge, wash, and dry to obtain aldehyde starch; (2) Dissolve the formaldehyde starch and polylysine in water at a molar ratio of 1:0.02-0.20, adjust the pH to 6.0-7.0, and react for 0.5-1.5 h; add sodium cyanoborohydride, adjust the pH to 6.0-8.0, and react for 3-8 h; centrifuge, wash, and dry to obtain the polylysine-grafted formaldehyde starch.

2. The method according to claim 1, characterized in that The starch in step (1) includes one or more of corn starch, potato starch, and porous starch.

3. The method according to claim 1, characterized in that The ratio of starch to water in step (1) is 3.0-5.0 g: 30-50 mL; the ratio of aldehyde starch to water in step (2) is 1.0-5.0 g: 60-300 mL.

4. The method according to claim 1, characterized in that In steps (1) and (2), centrifugation is performed at 3500-8000 rpm for 3-15 min.

5. The method according to claim 1, characterized in that Drying includes freeze drying, vacuum drying, hot air drying and microwave drying.

6. The method according to claim 1, characterized in that The concentration of the polylysine grafted aldehyde starch aqueous solution is 0.25~1.25%; the cleaning temperature is 25~40 ℃; and the cleaning time is 15~25 min.

7. A polylysine-grafted hydroformyl starch, characterized in that: The preparation method of the polylysine grafted hydroformyl starch comprises: (1) Dissolve sodium periodate and starch in water at a molar ratio of 0.2-1.8:1, adjust the pH to 2-5, and react for 2-8 hours; centrifuge, wash, and dry to obtain aldehyde starch; (2) Dissolve the formaldehyde starch and polylysine in water at a molar ratio of 1:0.01-0.50, adjust the pH to 6.0-7.0, and react for 0.5-1.5 h; add sodium cyanoborohydride, adjust the pH to 6.0-8.0, and react for 3-8 h; centrifuge, wash, and dry to obtain the polylysine-grafted formaldehyde starch.

8. The polylysine grafted hydroformyl starch according to claim 7, characterized in that: The starch in step (1) includes one or more of corn starch, potato starch, and porous starch; The ratio of starch to water in step (1) is 3.0-5.0 g: 30-50 mL; In step (2), the ratio of aldehyde starch to water is 1.0-5.0 g: 60-300 mL; In steps (1) and (2), centrifugation is performed at 3500-8000 rpm for 3-15 min.

9. Use of the polylysine grafted aldehyde starch according to any one of claims 7 to 8 in the preparation of a cleaning agent.

10. A pesticide cleaning agent, characterized in that: Contains the polylysine grafted hydroformylated starch according to any one of claims 7 to 8.

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