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

Abstract

The application discloses preparation and application of polylysine grafted aldehyde starch fruit and vegetable cleaning agent and belongs to the field of detergents. The application provides a kind of starch-based derivative, natural macromolecular starch is oxidized by sodium periodate, the ring-opening aldehyde of starch is made, then the amino group of polylysine is reacted with the aldehyde group of aldehyde starch to form Schiff base, sodium cyanoborohydride is added to reduce the Schiff base bond into a more stable C-N single bond, so that the polylysine is grafted onto the starch. The raw material of the starch-based derivative of the application is widely available, has large output and is cheap, has surfactant characteristics, is biodegradable, safe and mild, has no chemical reagent residue, and the product of the application has good bacteria removal (foodborne pathogenic bacteria) ability and pesticide residue removal ability in fruit cleaning.

Description

TECHNICAL FIELD

[0001] The present application relates to the preparation and application of polylysine grafted aldehyde starch fruit and vegetable cleaning agent, and belongs to the field of detergents. BACKGROUND

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

[0003] Current fruit cleaning methods commonly used by people at home include water flushing, NaCl cleaning, baking soda washing, commercial fruit detergent cleaning, and ultrasonic cleaning. At the same time, many technologies develop green and efficient cleaning agents for cleaning pesticide residues on the surface of fruits and vegetables. Patent CN118995339A discloses a cleaning agent prepared using cocodimethyl amine oxide, fatty alcohol polyoxyethylene ether sodium sulfate, sodium alkenyl sulfonate, diamino propyl dodecyl amine, and a compound bacterial fermentation product and water, which has high efficiency in removing oil stains and pesticide residues; patent CN117903886A discloses a cleaning agent prepared using eggshell powder, starch, calcined calcium hydroxide, and montmorillonite, which can absorb and remove the wax and pesticide residues on fruits and vegetables, and has good antibacterial effect; patent CN114456883A discloses a fruit and vegetable cleaning powder prepared using modified clay, cyclodextrin, and starch, which can remove pesticide residues and has antibacterial effect. The above-mentioned technologies have the problems of poor pesticide removal and antibacterial effect, hydrolysis of toxic products during the cleaning process, promotion of pesticide and surfactant penetration and residue, high equipment cost, and possible damage to fruits and impact on taste.

[0004] Therefore, there is an urgent need to develop a green, safe, and efficient fruit cleaning agent that can efficiently remove pesticide residues and foodborne pathogenic bacteria, and further prevent pesticide penetration, which has high practical and economic value. SUMMARY

[0005] To solve the above problems, the present application provides a starch-based derivative. The natural macromolecular starch is oxidized with sodium periodate to open the ring and aldehyde, then the amino group of polylysine reacts with the aldehyde group of aldehyde starch to form a Schiff base, and sodium cyanoborohydride is added to reduce the Schiff base bond to a more stable C-N single bond, thereby grafting polylysine onto starch. The raw material of this starch-based derivative is widely available, has large output and is inexpensive, has surfactant properties, is biodegradable, safe and mild, has no chemical reagent residues, and the product of the present application has excellent antibacterial (foodborne pathogenic bacteria) and pesticide removal capabilities in fruit cleaning.

[0006] The first object of the present application is to provide a method for improving the pesticide removal rate on the surface of fruits and vegetables by using polylysine grafted aldehyde starch, which uses polylysine grafted aldehyde starch aqueous solution to clean fruits and vegetables.

[0007] The preparation method of the polylysine grafted aldehyde starch comprises:

[0008] (1) Dissolve sodium periodate and starch in water according to 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;

[0009] (2) Dissolve the aldehyde starch and polylysine in water according to a molar ratio of 1:0.02-0.20, adjust the pH to 6.0-7.0, and react for 0.5-1.5 hours; add sodium cyanoborohydride, adjust the pH to 6.0-8.0, and react for 3-8 hours; centrifuge, wash, and dry to obtain polylysine grafted aldehyde starch.

[0010] In an embodiment, the molar ratio in step (1) is the molar ratio of starch structural units reacting with sodium periodate; and in step (2), the molar ratio of aldehyde starch and polylysine is the molar ratio of aldehyde groups in the aldehyde starch to lysine monomers.

[0011] Optionally, in step (2), the molar ratio of aldehyde starch and polylysine is 1:0.06-0.20; preferably, the molar ratio is 1:0.08-0.16.

[0012] In an embodiment, the starch in step (1) comprises one or more of corn starch, potato starch, and porous starch.

[0013] In an embodiment, the porous starch is porous corn starch.

[0014] In an embodiment, the amount ratio of starch to water in step (1) is 3.0-5.0 g:30-50 mL; and the amount ratio of aldehyde starch to water in step (2) is 1.0-5.0 g:60-300 mL.

[0015] In an embodiment, the centrifugation in steps (1) and (2) is 3500-8000 rpm for 3-15 minutes.

[0016] In an embodiment, the drying comprises freeze-drying, vacuum drying, hot air drying, and microwave drying.

[0017] In an 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 minutes.

[0018] A second object of the present application is to provide a polylysine grafted aldehyde starch, and a preparation method thereof, comprising:

[0019] (1) dissolving sodium periodate and starch in water according to a molar ratio of 0.2-1.8:1, adjusting pH to 2-5, and reacting for 2-8 hours; centrifuging, washing, and drying to obtain aldehyde starch;

[0020] (2) dissolving the aldehyde starch and polylysine in water according to a molar ratio of 1:0.01-0.50, adjusting pH to 6.0-7.0, and reacting for 0.5-1.5 hours; adding sodium cyanoborohydride, adjusting pH to 6.0-8.0, and reacting for 3-8 hours; centrifuging, washing, and drying to obtain the polylysine grafted aldehyde starch.

[0021] In an embodiment, the molar ratio in step (1) is the molar ratio of starch structural units reacting with sodium periodate; and the molar ratio of aldehyde starch and polylysine in step (2) is the molar ratio of aldehyde groups in the aldehyde starch to lysine monomers.

[0022] In an embodiment, the molar ratio of sodium periodate and starch in step (1) is 0.8-1.2:1, and the reaction time is 2-6 hours; and the molar ratio of aldehyde starch and polylysine in step (2) is 1:0.02-0.20.

[0023] Alternatively, the molar ratio of aldehyde starch and polylysine in step (2) is 1:0.06-0.20; and preferably, the molar ratio is 1:0.08-0.16.

[0024] In an embodiment, the starch in step (1) comprises one or more of corn starch, potato starch, and porous starch.

[0025] The amount ratio of starch and water in step (1) is 3.0-5.0 g:30-50 mL.

[0026] The amount ratio of aldehyde starch and water in step (2) is 1.0-5.0 g:60-300 mL.

[0027] The centrifugation in steps (1) and (2) is 3500-8000 rpm for 3-15 minutes.

[0028] A third object of the present application is to provide the use of any of the polylysine grafted aldehyde starchs in the preparation of cleaning agents.

[0029] In an embodiment, the starch in step (1) comprises one or more of corn starch, potato starch, and porous starch.

[0030] In an embodiment, the starch and water in step (1) are used in a ratio of 3.0-5.0 g:30-50 mL; and the aldehyde starch and water in step (2) are used in a ratio of 1.0-5.0 g:60-300 mL.

[0031] In an embodiment, the centrifugation in steps (1) and (2) is 3500-8000 rpm for 3-15 min.

[0032] In an embodiment, the drying includes freeze drying, vacuum drying, hot air drying, and microwave drying.

[0033] In an embodiment, the concentration of the polylysine-grafted aldehyde starch aqueous solution is 0.25-1.25%; the washing temperature is 25-40 ℃; and the washing time is 15-25 min.

[0034] A fourth object of the present application is to provide a pesticide cleaning agent containing any of the above polylysine-grafted aldehyde starches.

[0035] Advantages of the present application

[0036] The present application provides a starch-based derivative, in which natural macromolecular starch is oxidized with sodium periodate, ring-opening aldehyde is formed, then Schiff base reaction is performed between the amino group of polylysine and the aldehyde group of the aldehyde starch, sodium cyanoborohydride is added to reduce the Schiff base bond into a more stable C-N single bond, and thus polylysine is grafted onto the starch. The starch-based derivative has a wide source of raw materials, large output and low cost, has surfactant properties, is biodegradable, safe and mild, has no chemical reagent residues, and has good bacteria (foodborne pathogenic bacteria) removal ability and pesticide removal ability in fruit cleaning.

[0037] Specifically:

[0038] (1) The grafted polylysine starch prepared by the present application has a bacteria removal rate of 97.24% or more for E. coli and 94.13% or more for S. aureus when cleaning different fruits and vegetables at a concentration of 1% (g / 100 mL).

[0039] (2) The grafted polylysine starch prepared by the present application has a pesticide removal rate of 82.58% or more, and the highest can reach 96.62%, and can prevent the secondary migration of pesticides when cleaning different fruits and vegetables at a concentration of 1% (g / 100 mL). BRIEF DESCRIPTION OF DRAWINGS

[0040] Figure 1 Scanning electron microscope images of the corn starch raw material, the aldehyde corn starch intermediate, and the polylysine-grafted aldehyde corn starch final product;

[0041] Figure 2Scanning electron micrographs of potato starch raw material, aldehyde potato starch intermediate, and polylysine grafted aldehyde potato starch final product;

[0042] Figure 3 Scanning electron micrographs of porous starch raw material, aldehyde porous starch intermediate, and polylysine grafted aldehyde porous starch final product;

[0043] Figure 4 Surface Raman imaging of captan on unwashed apples;

[0044] Figure 5 Depth Raman imaging of captan on unwashed apples;

[0045] Figure 6 Surface Raman imaging of captan on washed apples with polylysine grafted aldehyde corn starch;

[0046] Figure 7 Depth Raman imaging of captan on washed apples with polylysine grafted aldehyde corn starch;

[0047] Figure 8 Surface Raman imaging of captan on washed apples with corn starch (Comparative Example 1);

[0048] Figure 9 Surface Raman imaging of captan on washed apples with aldehyde corn starch (Comparative Example 2);

[0049] Figure 10 Surface Raman imaging of captan on washed apples with tap water (Comparative Example 3);

[0050] Figure 11 Surface Raman imaging of captan on washed apples with sodium chloride (Comparative Example 4);

[0051] Figure 12 Surface Raman imaging of captan on washed apples with baking soda (Comparative Example 5);

[0052] Figure 13 Surface Raman imaging of captan on washed apples with dishwashing liquid (Comparative Example 6);

[0053] Figure 14 Depth Raman imaging of captan on washed apples with dishwashing liquid (Comparative Example 6). DETAILED DESCRIPTION

[0054] The following describes preferred embodiments of the present application, and it should be understood that the embodiments are for better explaining the present application, and are not used to limit the present application.

[0055] Test Method:

[0056] 1. Product yield (PY) of the aldehyde starch was calculated according to the following formula:

[0057]

[0058] In formula (1), 1 is the mass of the original starch, g; and 2 is the mass of the aldehyde starch, g. m 1 is the mass of the original starch, g; and 2 is the mass of the aldehyde starch, g. m 1 is the mass of the original starch, g; and 2 is the mass of the aldehyde starch, g.

[0059] 2. Aldehyde group content of the aldehyde starch

[0060] The aldehyde group content was determined by a semi-micro hydroxylamine hydrochloride method, and the specific operation process was as follows:

[0061] 0.1 g of the aldehyde starch was dissolved in 25 mL of deionized water, and then 20 mL of hydroxylamine hydrochloride (0.05 g / mL, and the pH was adjusted to 5.0 by 0.1 mol / L NaOH) was added. The mixture was reacted at 50°C in a water bath under magnetic stirring for 4 h. After the reaction, the generated hydrochloric acid in the reaction system was titrated with 0.1 mol / L NaOH until the pH value of the total system reached 5.0, and the consumption of NaOH was recorded. The average value was calculated after repeating the determination for three times. The aldehyde group content (AC, %) was calculated according to formula (2):

[0062]

[0063] In formula (2), 1 is the mass of the aldehyde starch, g; 2 is the consumption of NaOH for titration, L; 3 is the consumption of NaOH for titration of the same mass of starch, L; and 160 is the molecular mass of the repeating unit in the aldehyde starch. C NaOH 0.1 mol / L, which is the mass concentration of NaOH used for titration reaction; m 1 is the mass of the aldehyde starch, g; 2 is the consumption of NaOH for titration, L; 3 is the consumption of NaOH for titration of the same mass of starch, L; and 160 is the molecular mass of the repeating unit in the aldehyde starch. V 1 is the mass of the aldehyde starch, g; 2 is the consumption of NaOH for titration, L; 3 is the consumption of NaOH for titration of the same mass of starch, L; and 160 is the molecular mass of the repeating unit in the aldehyde starch. V 1 is the mass of the aldehyde starch, g; 2 is the consumption of NaOH for titration, L; 3 is the consumption of NaOH for titration of the same mass of starch, L; and 160 is the molecular mass of the repeating unit in the aldehyde starch.

[0064] 3. Lysine content determined by Kjeldahl method

[0065] Accurately weigh 0.5 g of sample into a digestion tube, then add 3 g of K2SO4 and 0.2 g of CuSO4 into each digestion tube, and finally add 10 mL of concentrated sulfuric acid to soak the sample, while treating the blank containing all these reagents. The blank control is aldehyde starch. Use a graphite digestion instrument for digestion, 100°C for 20 min, 200°C for 20 min, 300°C for 20 min, and 420°C for 90 min, until the sample in the tube turns into a blue-green transparent clear liquid. Use an automatic distillation device to collect the sample for titration with hydrochloric acid. Use bromocresol green methyl red indicator (5:1) for end point indication: the solution color changes from blue to pink. Calculate the total nitrogen content of each sample 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.

[0066]

[0067]

[0068] 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 is the concentration of hydrochloric acid 0.236 mol / L; m is the mass of aldehyde starch, g; 146.19 is the relative molecular mass of polylysine (ε-PL) monomer.

[0069] 4. Detection of the removal effect of chlorothalonil

[0070] Sample treatment: use the pretreatment method in GB23200.113-2018.

[0071] Detection method and result calculation: use HPLC method to determine the content of chlorothalonil in the sample, and the liquid phase detection conditions are as follows: the liquid chromatograph instrument model is Agilent 1260 Infinity II HPLC, the chromatographic column is Waters Sunfire C18 (250×4.6 mm, 5 μm), the sample size is 20 μL, the mobile phase is acetonitrile-water (80:20, V / V), the flow rate is 1 mL / min, the column temperature is 25°C, the ultraviolet detector detection wavelength is 240 nm, and the retention time is 4.4 min. The peak area and concentration of chlorothalonil in the range of 0.01 mg / L~20 mg / L show good linearity: y=123.1546x+1.8937, R 2= 0.9973 (y represents the peak area, x indicates the concentration of chlorothalonil, mg / L). The removal rate of chlorothalonil under the current cleaning condition was calculated according to formula (5).

[0072]

[0073] In formula (5) C 0 is the concentration of chlorothalonil in the positive sample, C 1 is the concentration of chlorothalonil remaining in the sample after cleaning.

[0074] Raw materials used in the examples:

[0075] Polylysine was purchased from Shanshushi Lion King Biological Technology Co., Ltd.;

[0076] Corn starch was purchased from Shanghai Yuan Ye Biological Co., Ltd.;

[0077] (Pearl) porous starch was purchased from Jiangsu Baobao Suzhou Guomin Biological Technology Co., Ltd.;

[0078] Potato starch, sodium cyanoborohydride, and sodium periodate were purchased from Shanghai Aladdin Biochemical Technology Co., Ltd.

[0079] Example 1: Preparation of polylysine grafted aldehyde starch

[0080] The polylysine grafted aldehyde starch was prepared as follows:

[0081] (1) Accurately weigh 5.95 g of sodium periodate in 45 mL of water and completely dissolve, add 4.5 g of corn starch (according to the molar ratio of starch structural unit to sodium periodate reaction is 1:1), adjust the solution pH to 3.0, and stir under 35°C water bath in the dark for 4 h (400 r / min); After the reaction is completed, centrifuge (5000 r / min, 5 min) to separate the solid product, wash with water until neutral, freeze-dry, and obtain aldehyde corn starch (store in a dry and dark place);

[0082] (2) Preparation of polylysine grafted aldehyde starch by chemical grafting method, 3 g of aldehyde starch was dissolved in 180 mL of water, and different amounts of ε-PL (i.e. 0.1063 g, 0.2126 g, 0.0425 g) were added to the solution according to the molar ratio of aldehyde groups in aldehyde starch to lysine monomer (molecular weight 146.19) of 1:0.04, 1:0.08, 1:0.16, respectively. 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. An equal amount of sodium cyanoborohydride as ε-PL was added, and the pH value was adjusted to 7.0 (with 0.1 mol / L HCl, adjusted every 15 min). 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 vacuum freeze-dried for 30 h to obtain polylysine grafted aldehyde corn starch with different grafting rates. According to the amount of ε-PL, they were named corn aldehyde-0.04-ε-PL, corn aldehyde-0.08-ε-PL, and corn aldehyde-0.16-ε-PL, respectively.

[0083] Example 2: Detection of starch properties

[0084] On the basis of Example 1, the corn starch in step (1) was replaced by potato starch and porous (corn) starch, and the remaining steps were the same as those in Example 1 to prepare aldehyde potato starch, aldehyde porous starch, and polylysine grafted aldehyde potato starch and polylysine grafted aldehyde porous starch with different grafting degrees.

[0085] The aldehyde corn starch, polylysine grafted aldehyde corn starch, aldehyde potato starch, polylysine grafted aldehyde potato starch, aldehyde porous starch, and polylysine grafted aldehyde porous starch prepared in Examples 1 and 2 were subjected to product characterization, and the results are as follows:

[0086] 1. Different aldehyde starches were taken to detect the aldehyde group content, aldehyde degree, and product yield, and the results are shown in Table 1.

[0087] Table 1 Aldehyde group content, aldehyde degree, and yield of aldehyde starch

[0088]

[0089] The results show that the aldehyde group content of corn starch, potato starch, and porous starch decreases in turn (the aldehyde degree decreases in turn) after oxidation, but the product yield increases in turn. This is because the aldehyde group content is related to the amylose content of starch, and high amylose content is beneficial to the oxidation reaction. With the increase of oxidation degree, the original starch molecular structure is destroyed, the chain length is reduced, and the molecular chain is broken, resulting in a decrease in yield.

[0090] 2. The nitrogen content, lysine content and yield of different polylysine grafted aldehyde starch were detected, and the results are shown in Table 2.

[0091] Table 2 Nitrogen content, lysine content and yield of polylysine grafted aldehyde starch

[0092]

[0093] 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 product are different. With the increase of the molar ratio of aldehyde group of dialdehyde starch to lysine monomer, the lysine content in the product also increases, which shows a positive correlation, indicating that dialdehyde starch and ε-PL use Schiff base reaction, and a new cross-linked product is generated by combining the active aldehyde group on dialdehyde starch with the amino group on ε-PL. In addition, with the increase of the molar ratio of aldehyde group of dialdehyde starch to lysine monomer, the yield of the product gradually decreases, because with the progress of oxidation reaction, the molecular chain is broken, resulting in a decrease in yield.

[0094] 3. Morphology characterization

[0095] The micro-morphology of untreated starch, aldehyde starch and polylysine grafted aldehyde starch was observed by scanning electron microscope (SEM), and the results are shown in Figure 1 , Figure 2 and Figure 3 Compared with the original starch, the surface of aldehyde starch becomes rough, with damage and concave. This may be due to the partial breakage of α-1,4-glucosidic bonds in starch molecules, resulting in shortening of polysaccharide chains, change of molecular structure, destruction of crystalline structure, and thus presenting the morphology of surface damage and concave.

[0096] In addition, the breakage of α-1,4-glucosidic bonds not only affects the length of starch molecules, but also may reduce the overall stability of starch molecules. The hydroxyl group (-OH) of starch molecules is oxidized to aldehyde group (-CHO), and the introduction of aldehyde group may change the hydrophobicity of starch, making its surface more rough and increasing its interaction area with other substances; after grafting ε-PL, new wrinkles appear on the surface of aldehyde starch-ε-PL, which is uneven. These protrusions or concavities may be related to the grafting position of ε-PL molecular chain on the surface of starch. 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.

[0097] Example 3: Application of polylysine grafted aldehyde corn / potato / porous starch in fruit and vegetable cleaning

[0098] The polylysine grafted aldehyde corn starch prepared in Examples 1 and 2 was taken to detect its effect in fruit and vegetable cleaning.

[0099] 1. Bactericidal effect detection

[0100] (1) Detection of antibacterial effect of polylysine grafted aldehyde corn starch

[0101] Preparation of positive samples: Select uniform size, mature, undamaged, and disease-free apples, and use 1.2% (W / V) sodium hypochlorite solution for surface disinfection for 8 min. Then, rinse with sterile water three times and air dry in a sterile operation table as a negative control.

[0102] Dilute the bacteria (using Escherichia coli (ATCC 8099) and Staphylococcus aureus (ATCC 6538) as model pathogenic bacteria) cultured to the logarithmic growth phase to 10 8 CFU / mL, and immerse the bacteria-infected apples in the above bacterial suspension for 15 min, and then air dry in a clean bench for 20-30 min to obtain bacteria-infected apples as positive samples to be washed.

[0103] Prepare a 1% (g / 100 mL) corn aldehyde-0.16-ε-PL starch solution, and the water temperature of the above solution is 30°C. Place the positive samples in the solution and soak for 20 min (stir every 5 min), then wash the bacteria-infected samples, and then rinse with sterile water as the test group.

[0104] Colony counting: Cut the apples into pieces, mix 25 g of the sample with 225 mL of sterile saline solution in a sterile bag, and use a beating homogenizer to homogenize for 5 min; dilute the homogenate with sterile saline solution by 10 times, and take 100 μL of the appropriate dilution and spread on the surface of LB agar medium (repeat six times in parallel), and incubate at 37°C for 24 h. Count the colonies, and the result is expressed as CFU / g. The bacteria removal rate is calculated according to formula (6).

[0105]

[0106] 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 washed sample (CFU / g).

[0107] (2) Detection of antibacterial effect of polylysine grafted aldehyde potato starch

[0108] On the basis of step (1), replace the polylysine grafted aldehyde corn starch with polylysine grafted aldehyde potato starch, and replace the apples with sweet potatoes to detect the washing effect of polylysine grafted aldehyde potato starch on sweet potatoes.

[0109] (3) Detection of antibacterial effect of polylysine grafted aldehyde porous starch

[0110] On the basis of step (1), replace polylysine grafted aldehyde corn starch with polylysine grafted aldehyde porous starch, and replace apples with Chinese cabbage to detect the cleaning effect of polylysine grafted aldehyde porous starch on Chinese cabbage.

[0111] The detection results show that the sterilization rate of Staphylococcus aureus on apples washed with 1% corn aldehyde-0.16-ε-PL starch is 97.15%, and the sterilization rate of Escherichia coli is 99.14%; the sterilization rate of Staphylococcus aureus on sweet potatoes washed with 1% potato aldehyde-0.16-ε-PL starch is 98.32%, and the sterilization rate of Escherichia coli is 99.34%; the sterilization rate of Staphylococcus aureus on Chinese cabbage washed with 1% porous aldehyde-0.16-ε-PL starch is 97.27%, and the sterilization rate of Escherichia coli is 99.07%; while the sterilization rate of Escherichia coli by sterile water is only 16.87%~19.24%, and the sterilization rate of Staphylococcus aureus is only 18.34%~20.37%. It can be seen that washing with aldehyde starch can significantly reduce the risk of foodborne pathogens on the surface of fruits and vegetables.

[0112] 2. Overall pesticide removal effect

[0113] (1) The pesticide removal effect of polylysine grafted aldehyde corn starch was detected, and the steps were as follows:

[0114] Preparation of positive samples: prepare a 15 mg / L chlorothalonil aqueous solution, select apples that are uniform in size, mature, undamaged, and free of disease, soak them in the aqueous solution for 4 h, and air dry for 1 h;

[0115] Washing: prepare 1% (g / 100 mL) polylysine grafted aldehyde corn starch (corn aldehyde-0.04-ε-P, corn aldehyde-0.08-ε-PL, corn aldehyde-0.16-ε-PL) cleaning solution with different grafting rates, and the water temperature is 30°C. Put the positive samples into the water for 20 min;

[0116] Detection: use the pretreatment method in GB23200.113-2018 combined with HPLC to evaluate the pesticide removal rate. Use Agilent 1260 Infinity II high performance liquid chromatography system (Beijing, China) equipped with ultraviolet detector and Waters Sunfire C18 chromatographic column (250 × 4.6 mm, 5 μm) to analyze the content of chlorothalonil in fruit and vegetable samples. The mobile phase is a mixture of acetonitrile and water (80:20, V / V) with a flow rate of 1 mL / min, the injection volume is 20 μL, and the column temperature is maintained at 25°C. The detection wavelength is 240 nm, and the retention time is 4.4 min.

[0117] (2) Detection of pesticide removal effect of polylysine grafted aldehyde potato starch On the basis of step (1), replace apples with sweet potatoes for 1 h, and the rest of the steps are consistent with step (1). The pesticide removal effect of polylysine grafted aldehyde potato starch (potato aldehyde-0.04-ε-P, potato aldehyde-0.08-ε-PL, potato aldehyde-0.16-ε-PL) with different grafting rates is detected.

[0118] (3) Detection of pesticide removal effect of polylysine grafted aldehyde porous starch

[0119] On the basis of step (1), replace apples with cabbage for 20 min, and the rest of the steps are consistent with step (1). The pesticide removal effect of polylysine grafted aldehyde porous starch (porous aldehyde-0.04-ε-P, porous aldehyde-0.08-ε-PL, porous aldehyde-0.16-ε-PL) with different grafting rates is detected.

[0120] The test results show that the removal rate of chlorothalonil on apples by corn aldehyde-0.04-ε-PL is 82.58%, the removal rate of chlorothalonil on apples by corn aldehyde-0.08-ε-PL is 95.01%, and the removal rate of chlorothalonil on apples by corn aldehyde-0.16-ε-PL is 96.62%; the removal rate of chlorothalonil on sweet potatoes by potato aldehyde-0.04-ε-PL is 81.48%, the removal rate of chlorothalonil on sweet potatoes by potato aldehyde-0.08-ε-PL is 96.81%, and the removal rate of chlorothalonil on sweet potatoes by potato aldehyde-0.16-ε-PL is 95.26%; the removal rate of chlorothalonil on cabbage by porous aldehyde-0.04-ε-PL is 89.65%, the removal rate of chlorothalonil on cabbage by porous aldehyde-0.08-ε-PL is 91.99%, and the removal rate of chlorothalonil on cabbage by porous aldehyde-0.16-ε-PL is 90.02%. The above-mentioned polylysine grafted aldehyde starch of different types and different grafting proportions has good removal efficiency for chlorothalonil on fruits and vegetables.

[0121] 3. Pesticide surface removal effect and secondary migration detection

[0122] For most fresh fruits and vegetables, it is necessary to evaluate whether pesticides will still remain on the surface of fruits after washing and whether they will migrate to the inside of the fruits. Taking the apples in item 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:

[0123] Raman spectra were collected using a DXR2xi Raman imaging microscope spectrometer (Thermo Fisher Scientific, Madison, WI, USA). The scan 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 seconds, and the scan was 2 times. Surface imaging used a x10 objective, a 50 μm pinhole, the length and width of the scan area were both 100 μm, and the step was 10 μm. Depth imaging used a x50 long working distance objective, a 50 μm confocal pinhole, the width of the scan area was 30 μm, the depth was 250 μm, and the step was 5 μm. Surface and depth imaging were randomly selected on the surface of the apple, and each sample was repeated three times. The Raman spectrum of the chlorothalonil was measured, and the 2242 cm -1 As its characteristic peak, the imaging spectrum at the wave number was obtained by using OMNIC TM software.

[0124] The surface imaging and depth imaging of the chlorothalonil residue positive sample are as shown in Figure 4 and Figure 5 The surface imaging and depth imaging after 1% corn aldehyde-0.16-ε-PL cleaning are as shown in Figure 6 , Figure 7 The results show that 1% corn aldehyde-0.16-ε-PL can effectively remove the chlorothalonil residue on the surface of the apple, and does not cause the migration of chlorothalonil into the inside of the fruit.

[0125] Comparative Example 1: Original starch cleaning removes chlorothalonil on fruits and vegetables

[0126] On the basis of Example 3, the polylysine grafted aldehyde starch cleaning solution was replaced by an unmodified starch solution (1%), and the bactericidal effect, the overall pesticide removal effect, the pesticide surface removal effect, and the secondary migration detection were detected, and the steps were consistent with those of Example 3.

[0127] Comparative Example 2: Aldehyde starch cleaning removes chlorothalonil on fruits and vegetables

[0128] On the basis of Example 3, the polylysine grafted aldehyde starch cleaning solution was replaced by an aldehyde starch solution (1%), and the bactericidal effect, the overall pesticide removal effect, the pesticide surface removal effect, and the secondary migration detection were detected, and the steps were consistent with those of Example 3.

[0129] Comparative Example 3: Tap water cleaning removes chlorothalonil on fruits and vegetables

[0130] On the basis of Example 3, the polylysine grafted aldehyde starch cleaning solution was replaced by tap water, and the bactericidal effect, the overall pesticide removal effect, the pesticide surface removal effect, and the secondary migration detection were detected, and the steps were consistent with those of Example 3.

[0131] Comparative Example 4: Sodium chloride solution for cleaning to remove chlorothalonil on fruits and vegetables

[0132] On the basis of Example 3, the polylysine grafted aldehyde starch cleaning solution was replaced by a sodium chloride solution (1%), and the sterilization effect, pesticide overall removal effect, pesticide surface removal effect, and secondary migration were detected, with the steps being consistent with those of Example 3.

[0133] Comparative Example 5: Baking soda solution for cleaning to remove chlorothalonil on fruits and vegetables

[0134] On the basis of Example 3, the polylysine grafted aldehyde starch cleaning solution was replaced by a baking soda solution (1%), and the sterilization effect, pesticide overall removal effect, pesticide surface removal effect, and secondary migration were detected, with the steps being consistent with those of Example 3.

[0135] Comparative Example 6: Dishwashing liquid for cleaning to remove chlorothalonil on fruits and vegetables

[0136] On the basis of Example 3, the polylysine grafted aldehyde starch cleaning solution was replaced by a certain brand of dishwashing liquid (1%), and the sterilization effect, pesticide overall removal effect, pesticide surface removal effect, and secondary migration were detected, with the steps being consistent with those of Example 3.

[0137] Comparative Example 7: Static grafting of polylysine

[0138] On the basis of Example 1, the grafting method of polylysine was changed to static grafting, and corn aldehyde-0.16-ε-PL starch was prepared, with the specific steps being as follows:

[0139] 3 g of aldehyde starch and 0.2126 g of ε-PL were weighed and dissolved in 180 mL of water, and 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, and stirred at room temperature for 6 h. Centrifugation (5000 r / min, 5 min) was performed to obtain a precipitate, which was washed to neutral with water, and vacuum freeze-dried for 30 h. The sterilization effect and pesticide overall removal effect of the polylysine aldehyde starch prepared by static grafting were detected, with the steps being consistent with those of Example 3.

[0140] The corn aldehyde-0.16-ε-PL starch, potato aldehyde-0.16-ε-PL, and porous aldehyde-0.16-ε-PL prepared in Examples 1 and 2, and the cleaning agents of Comparative Examples 1 to 7 were used to detect the removal rates of harmful bacteria and pesticides at a concentration of 1%, and the experimental results are shown in Tables 3 to 5 and Figures 8-14

[0141] Table 3 Cleaning effect of different cleaning agents on apples

[0142]

[0143] ​Table 4 Cleaning effect of different cleaning agents on sweet potatoes

[0144]

[0145] Table 5 Cleaning effect of different cleaning agents on Chinese cabbage

[0146]

[0147] On this basis, the secondary migration depth of pesticides after cleaning apples with dishwashing liquid and corn aldehyde-0.16-ε-PL starch at a concentration of 1% was detected, and the results showed that cleaning with dishwashing liquid would cause the secondary migration of pesticides into the fruit by 200 μm Figure 14 ).

[0148] The results showed that the starch-based derivatives prepared in Examples 1 and 2 had excellent bactericidal removal effect on food-borne pathogenic bacteria, good removal rate for non-systemic fungicides, and no secondary migration into the flesh, and were a class of safe and efficient fruit and vegetable cleaning agents.

[0149] Example 4: Application of polylysine grafted aldehyde corn starch in cleaning fruits

[0150] The polylysine grafted aldehyde corn starch prepared in Example 1 was taken to optimize the cleaning conditions, as follows:

[0151] 1. Concentration optimization

[0152] (1) Preparation of positive samples:

[0153] A 15 mg / L aqueous solution of chlorothalonil was prepared. Uniform, mature, undamaged, and disease-free apples were selected and soaked in the aqueous solution for 4 h, and then air-dried for 1 h.

[0154] (2) Cleaning:

[0155] Different concentrations (0.1%, 0.25%, 0.5%, 0.75%, 1%, 1.25%) of corn aldehyde-0.16-ε-PL cleaning solution were prepared, and the water temperature was 30°C. The positive samples were placed in the cleaning solution for 20 min, and the removal rate of chlorothalonil was detected.

[0156] The results showed that the removal rates of chlorothalonil 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 as the concentration increased (0.1%~1%), the removal rate gradually increased, and when the concentration was greater than 1%, the removal rate did not change significantly. The best concentration of corn aldehyde-0.16-ε-PL starch was 1%, because it reached the critical micelle concentration at 1%.

[0157] 2. Washing temperature

[0158] The corn aldehyde-0.16-ε-PL cleaning solution with a mass concentration of 1% was configured, and the positive samples were placed in the cleaning solution at water temperatures of 20°C, 25°C, 30°C, 35°C and 40°C respectively for 20 min, and the removal rate of chlorothalonil was detected.

[0159] The results show that the removal rates of chlorothalonil at 20°C, 25°C, 30°C, 35°C and 40°C are 82.75%, 84.16%, 92.88%, 91.81% and 92.96% respectively. It can be seen that the removal effect of chlorothalonil gradually increases as the water temperature rises (20-30°C), and the removal rate no longer increases significantly as the temperature continues to rise (20-30°C). Therefore, the optimal water temperature is 30°C.

[0160] 3. Washing time

[0161] The corn aldehyde-0.16-ε-PL cleaning solution with a concentration of 1% was configured, and the positive samples were cleaned at 30°C for 5 min, 10 min, 15 min, 20 min and 25 min respectively, and the removal rate of chlorothalonil was detected.

[0162] The results show that the removal rates of chlorothalonil at 5 min, 10 min, 15 min, 20 min and 25 min are 70.86%, 83.23%, 91.89%, 94.91% and 95.08% respectively. It can be seen that the removal rate of chlorothalonil increases as the cleaning time increases, and the optimal cleaning time is 20 min.

[0163] The results show that the optimal cleaning conditions are 1% (w / v) corn aldehyde-0.16-ε-PL cleaning solution, 30°C and 20 min.

[0164] Example 5: Removal of other pesticides by polylysine grafted aldehyde corn starch

[0165] Based on Example 3, apples were used as actual samples, and chlorothalonil was replaced by equal-concentration thiram and chlorpyrifos. The corn aldehyde-0.16-ε-PL cleaning solution with a concentration of 1% was configured, and the positive samples were placed in the cleaning solution at a water temperature of 30°C for 20 min. The removal rate of pesticides was calculated, and the removal rate of the starch-based derivative prepared in the application on non-systemic pesticides was evaluated.

[0166] The results show that the removal rate of polylysine grafted aldehyde corn starch on thiram on apples is 90.51%, and the removal rate of chlorpyrifos is 97.36%. In summary, the polylysine grafted aldehyde starch prepared in the application has good removal effect on non-systemic pesticides.

[0167] Although the present application has been disclosed in its preferred embodiments with reference to the accompanying drawings, it is not intended to limit the present application thereto, and various modifications and alterations can be made thereto by those skilled in the art without departing from the spirit and scope of the present application, and the scope of protection of the present application should be defined by the appended claims.

Claims

1. A method for increasing the removal rate of pesticides from the surface of fruits and vegetables by grafting aldehyde-modified starch with polylysine, characterized by, The polylysine grafted aldehyde starch aqueous solution is used for cleaning fruits and vegetables; The preparation method of the polylysine grafted aldehyde starch comprises: (1) dissolving sodium periodate and starch in water according to a molar ratio of 0.8-1.2:1, adjusting pH to 2-5, and reacting for 2-6 hours; centrifuging, washing, and drying to obtain aldehyde starch; (2) dissolving the aldehyde starch and polylysine in water according to a molar ratio of 1:0.02-0.20, adjusting pH to 6.0-7.0, and reacting for 0.5-1.5 hours; adding sodium cyanoborohydride, adjusting pH to 6.0-8.0, and reacting for 3-8 hours; centrifuging, washing, and drying to obtain the polylysine grafted aldehyde starch.

2. The method of claim 1, wherein, The starch in step (1) comprises one or more of corn starch, potato starch, and porous starch.

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

4. The method of claim 1, wherein, The centrifugation in steps (1) and (2) is 3500-8000 rpm for 3-15 minutes.

5. The method of claim 1, wherein, The drying comprises freeze drying, vacuum drying, hot air drying, and microwave drying.

6. The method of claim 1, wherein, The concentration of the polylysine grafted aldehyde starch aqueous solution is 0.25-1.25%, the cleaning temperature is 25-40 DEG C, and the cleaning time is 15-25 minutes.

7. A polylysine grafted aldehyde starch, characterized in that, The preparation method of the polylysine grafted aldehyde starch comprises: (1) dissolving sodium periodate and starch in water according to a molar ratio of 0.2-1.8:1, adjusting pH to 2-5, and reacting for 2-8 hours; centrifuging, washing, and drying to obtain aldehyde starch; (2) dissolving the aldehyde starch and polylysine in water according to a molar ratio of 1:0.01-0.50, adjusting pH to 6.0-7.0, and reacting for 0.5-1.5 hours; adding sodium cyanoborohydride, adjusting pH to 6.0-8.0, and reacting for 3-8 hours; centrifuging, washing, and drying to obtain the polylysine grafted aldehyde starch.

8. The polylysine grafted aldehyde starch of claim 7, wherein, The starch in step (1) comprises one or more of corn starch, potato starch, and porous starch; The amount ratio of the starch to water in step (1) is 3.0-5.0 g:30-50 mL; The amount ratio of the aldehyde starch to water in step (2) is 1.0-5.0 g:60-300 mL; The centrifugation in steps (1) and (2) is 3500-8000 rpm for 3-15 minutes.

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

10. A pesticide cleaning agent, characterized by, The polylysine grafted aldehyde starch according to any one of claims 7-8 is contained.

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