Method for detecting content of anionic detergent in rice and flour product based on ultraviolet spectrophotometer

Abstract

The invention discloses a method for detecting the content of an anionic detergent in a rice and flour product based on an ultraviolet spectrophotometer, which comprises the following steps: adding water into the rice and flour product to be detected for soaking, and crushing to obtain rice and flour paste; mixing the rice and flour paste with water, and adding a potassium ferrocyanide solution and a zinc acetate solution for reaction to obtain an extracting solution of the rice and flour product to be detected; transferring part of the extracting solution of the to-be-detected rice and flour product to be mixed with a color developing auxiliary agent, adding an organic solvent to extract a compound formed by the color developing auxiliary agent and an anionic detergent in the extracting solution of the to-be-detected rice and flour product, and performing liquid separation to obtain an organic phase; testing the absorbance of the organic phase by using an ultraviolet spectrophotometer to obtain the absorbance of the organic phase; preparing sodium dodecyl benzene sulfonate standard solutions with different concentrations, and drawing a standard curve; and calculating the content of the anionic detergent in the to-be-detected rice and flour product based on the standard curve. The method is high in accuracy, low in detection limit concentration and low in cost.

Description

Technical Field

[0001] The present application relates to the field of detecting the content of anionic detergents, and in particular to a method for detecting the content of anionic detergents in rice and flour products based on an ultraviolet spectrophotometer. Background Art

[0002] During the industrial processing of rice and flour products (such as rice vermicelli, noodles, and vermicelli), some manufacturers add anionic detergents to reduce the adhesion of starchy raw materials and improve the dispersion of the finished product. Anionic detergents are industrial cleaning agents with a primarily surfactant function, and common types include sodium dodecylbenzenesulfonate (SDBS) and sodium dodecyl sulfate (SDS). Long-term consumption of anionic detergents can damage the gastrointestinal mucosal barrier, induce chronic inflammation (such as gastritis and enteritis), and increase health risks.

[0003] The current testing standards for anionic detergents, such as GB / T 5750.4-2023, are mainly applicable to water samples. No national standards, industry standards, or local standards have been issued for testing anionic detergents in rice and flour products. Summary of the Invention

[0004] This application proposes a method for detecting the content of anionic detergents in rice and flour products based on ultraviolet spectrophotometry, which can improve the accuracy of detecting the content of anionic detergents in rice and flour products, reduce the detection limit concentration, and has low cost and a wide range of applications.

[0005] A method for detecting the content of anionic detergent in rice and flour products based on ultraviolet spectrophotometry, comprising:

[0006] Soak the rice and flour product to be tested in water, and grind it to obtain rice and flour paste;

[0007] Mixing rice flour paste with water, adding potassium ferrocyanide solution and zinc acetate solution to react, and separating the solid and liquid to obtain an extract of the rice flour product to be tested;

[0008] A portion of the extract of the rice and flour product to be tested is pipetted and mixed with a color developing agent, an organic solvent is added to extract a complex formed by the color developing agent and the anionic detergent in the extract of the rice and flour product to be tested, and the organic phase is separated to obtain an organic phase; and the absorbance of the organic phase is measured using an ultraviolet spectrophotometer;

[0009] Prepare sodium dodecylbenzenesulfonate standard solutions of different concentrations, test the absorbance of the sodium dodecylbenzenesulfonate standard solutions of different concentrations using an ultraviolet spectrophotometer, and draw a standard curve of sodium dodecylbenzenesulfonate mass-absorbance;

[0010] Based on the standard curve, the absorbance of the organic phase was substituted to calculate the content of anionic detergent in the rice and flour product to be tested.

[0011] The present application first soaks the rice flour product to be tested in water to reduce the toughness of the rice flour product, and crushes it after soaking for a period of time to better reduce the particle size of the rice flour paste. The small-particle rice flour paste is then mixed with water to increase the water content in the rice flour paste, which helps to improve the solubility of the double precipitant of potassium ferrocyanide and zinc acetate in the system, improves the ability of precipitating protein and starch in the rice flour product, reduces the impurity content of the extract of the rice flour product to be tested, then pipettes a portion of the extract of the rice flour product to be tested and mixes it with a color-developing auxiliary agent, extracts and enriches the color-developable complex with an organic solvent, detects its absorbance with an ultraviolet spectrophotometer, calculates the content of anionic detergent in the rice flour product to be tested, improves the accuracy of using an ultraviolet spectrophotometer to detect the content of anionic detergent in the rice flour product, and reduces the detection limit concentration. At the same time, the equipment technology of the ultraviolet spectrophotometer is mature and the price is low. For example, compared with a continuous flow analyzer, the detection cost is lower and the universality is stronger.

[0012] In some embodiments, the ratio of the rice and flour product to be tested to water is 1: (1-3) g / mL.

[0013] In some embodiments, the soaking time is 0.5 h to 2 h.

[0014] In some embodiments, the color development aid includes one or more of phenanthroline and methylene blue.

[0015] In some embodiments, the color development aid includes phenanthroline, ferrous ammonium sulfate, and a pH buffer.

[0016] In some embodiments, 10 mL to 50 mL of the extract of the rice and flour product to be tested is taken, 2 mL to 5 mL of phenanthroline, 10 mL to 15 mL of pH buffer, 1 mL to 2 mL of hydroxylamine hydrochloride-ammonium ferrous sulfate solution are added, and an organic solvent is added for extraction, and the liquid is separated to obtain a solution rich in Fe. 2+ -The organic phase of the ion-pair complex of diazophenanthroline complex and sulfonic acid group.

[0017] In some embodiments, the organic solvent includes one or more of chloroform, dichloromethane, and tetrachloromethane.

[0018] In some embodiments, the step of testing the absorbance of sodium dodecylbenzenesulfonate standard solutions of different concentrations using an ultraviolet spectrophotometer includes: preparing sodium dodecylbenzenesulfonate standard solutions of different concentrations, adding water to each solution to make the volume consistent with the volume of the extract of a portion of the rice and flour product to be tested, adding a color development aid to the fixed volume of the sodium dodecylbenzenesulfonate standard solutions of different concentrations, adding an organic solvent to extract the complex formed by the color development aid and the sodium dodecylbenzenesulfonate, respectively obtaining the organic phase of the standard solution, and testing the absorbance of the organic phase of the standard solution using an ultraviolet spectrophotometer.

[0019] In some embodiments, the step of testing the absorbance of sodium dodecylbenzenesulfonate standard solutions of different concentrations using an ultraviolet spectrophotometer comprises: preparing 0 mL 10 mg / L, 0.25 mL 10 mg / L, 0.5 mL 10 mg / L, 1 mL 10 mg / L, 2 mL 10 mg / L, 3 mL 10 mg / L, 4 mL 10 mg / L, and 5 mL 10 mg / L sodium dodecylbenzenesulfonate standard solutions, respectively, adding water to 50 mL, adding 2 mL to 5 mL of diazine, 10 mL to 15 mL of pH buffer, and 1 mL to 2 mL of hydroxylamine hydrochloride-ammonium ferrous sulfate solution, adding chloroform for extraction to obtain organic phases of standard solutions of different concentrations, respectively testing the absorbance of the organic phases of the standard solutions using an ultraviolet spectrophotometer, and drawing a standard curve.

[0020] In some embodiments, the wavelength of the UV spectrophotometer test is 500 nm to 530 nm.

[0021] In some embodiments, the wavelength tested by the ultraviolet spectrophotometer is 640 nm to 670 nm.

[0022] In some embodiments, in the step of calculating the mass of the anionic detergent in the rice and flour product to be tested by substituting the absorbance of the organic phase based on the standard curve, the calculation formula is:

[0023] X=(m1×V1) / (M×V2),

[0024] Wherein, X is the content of anionic detergent in the rice and flour product to be tested during the step of soaking the rice and flour product to be tested in water, and the unit is mg / kg;

[0025] m1 is the mass of the anionic detergent in the organic phase in the step of pipetting a portion of the extract of the rice and flour product to be tested and mixing it with the color-developing aid, adding an organic solvent to extract the complex formed by the color-developing aid and the anionic detergent in the extract of the rice and flour product to be tested, and separating the liquid to obtain the organic phase, in μg;

[0026] M is the mass of the dry rice flour sample in the step of mixing rice flour with water, adding potassium ferrocyanide solution and zinc acetate solution to react, and separating the solid and liquid to obtain the extract of the rice flour product to be tested, in g;

[0027] V1 is the volume of the extract of the rice and flour product to be tested in the step of mixing rice flour paste with water, adding potassium ferrocyanide solution and zinc acetate solution to react, and separating the solid and liquid to obtain the extract of the rice and flour product to be tested, in mL;

[0028] V2 is the volume of the extract of the rice and flour product to be tested, which is obtained by pipetting a portion of the extract of the rice and flour product to be tested and mixing it with the color development auxiliary agent, and the unit is mL. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the following is a brief introduction to the drawings required for use in the embodiments of the present application. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on the drawings without any creative work.

[0030] Figure 1 This is a comminution diagram of the rice and flour products to be tested in Preparation Examples 1 to 4 of this application;

[0031] Figure 2 This is a picture of the extract of the rice and flour products to be tested in Preparation Examples 5 to 7 of this application;

[0032] Figure 3 This is the test record of the methylene blue method in the examples of this application;

[0033] Figure 4 This is the test record of the diazine method in the examples of this application. DETAILED DESCRIPTION

[0034] " scope " disclosed in the application is limited in the form of lower limit and upper limit, and given range is limited by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundary of special range. The scope limited in this way can be to include end value or not include end value, and can be arbitrarily combined, that is, any lower limit can form a scope with any upper limit combination. For example, if the scope of 60-120 and 80-110 is listed for specific parameters, it is understood that the scope of 60-110 and 80-120 is also expected. In addition, if the minimum range value 1 and 2 listed, and if the maximum range value 3,4 and 5 are listed, then the following scope can all be expected: 1-3, 1-4, 1-5, 2-3, 2-4 and 2-5. In this application, unless otherwise specified, the numerical range " ab " represents the abbreviation of any real number combination between a and b, wherein a and b are all real numbers. For example, a numerical range of "0-5" indicates that all real numbers between "0-5" are listed herein, and "0-5" is simply an abbreviation for these numerical combinations. Furthermore, when a parameter is expressed as an integer ≥ 2, this is equivalent to disclosing that the parameter is, for example, an integer of 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0035] Unless otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution.

[0036] Unless otherwise specified, all technical features and optional technical features of this application can be combined with each other to form a new technical solution.

[0037] Unless otherwise specified, all steps of the present application may be performed sequentially or randomly, preferably sequentially. For example, a method includes steps (a) and (b), which indicates that the method may include steps (a) and (b) performed sequentially, or may include steps (b) and (a) performed sequentially. For example, a method may further include step (c), which indicates that step (c) may be added to the method in any order, for example, the method may include steps (a), (b), and (c), or may include steps (a), (c), and (b), or may include steps (c), (a), and (b), etc.

[0038] Unless otherwise specified, in this application, the terms "first", "second", etc. are used to distinguish different objects rather than to describe a specific order or a primary-secondary relationship.

[0039] In this application, the terms "plurality" and "multiple" refer to two or more.

[0040] Current testing standards for anionic detergents, such as GB / T 5750.4-2023, are applicable only to water samples, and their core methods rely on the low-interference properties of the water matrix. However, rice and flour products are complex, containing various substances such as starch, protein, and fat. Starch easily forms colloids with anionic detergents, hindering the color development reaction. Proteins can adsorb anionic detergents through hydrophobic interactions, reducing extraction efficiency. Lipids can interfere with the separation and purification of organic solvents such as chloroform, thus interfering with the detection of anionic detergents in rice and flour products and affecting their accuracy.

[0041] Compared with the detection automation, anti-interference ability and strict process control of continuous flow analyzers, ultraviolet-visible spectrophotometers (also referred to as UV spectrophotometers) are low-cost, but the detection accuracy and detection limit concentration for complex samples still need to be optimized.

[0042] In view of this, the present application proposes a method for detecting the content of anionic detergents in rice and flour products based on ultraviolet spectrophotometry, which can improve the accuracy of detecting the content of anionic detergents in rice and flour products, reduce the detection limit concentration, and has low cost and a wide range of applications.

[0043] A method for detecting the content of anionic detergent in rice and flour products based on ultraviolet spectrophotometry, comprising:

[0044] Soak the rice and flour product to be tested in water, and grind it to obtain rice and flour paste;

[0045] Mixing rice flour paste with water, adding potassium ferrocyanide solution and zinc acetate solution to react, and performing solid-liquid separation to obtain an extract of the rice flour product to be tested; or, obtaining a liquid (supernatant) after solid-liquid separation; and constant-volume the liquid (supernatant) to obtain an extract of the rice flour product to be tested;

[0046] A portion of the extract of the rice and flour product to be tested is pipetted and mixed with a color developing agent, an organic solvent is added to extract a complex formed by the color developing agent and the anionic detergent in the extract of the rice and flour product to be tested, and the organic phase is separated to obtain an organic phase; and the absorbance of the organic phase is measured using an ultraviolet spectrophotometer;

[0047] Prepare sodium dodecylbenzenesulfonate standard solutions of different concentrations, test the absorbance of the sodium dodecylbenzenesulfonate standard solutions of different concentrations using an ultraviolet spectrophotometer, and draw a standard curve of sodium dodecylbenzenesulfonate mass-absorbance;

[0048] Based on the standard curve, the absorbance of the organic phase was substituted to calculate the content of anionic detergent in the rice and flour product to be tested.

[0049] The present application first soaks the dried rice and flour product to be tested in water to reduce the toughness of the dried rice and flour product, and crushes it after soaking for a period of time to better reduce the particle size of the rice and flour paste. The small-particle rice and flour paste is then mixed with water to increase the water content in the rice and flour paste, helping to improve the solubility of the double precipitant of potassium ferrocyanide and zinc acetate in the system, improving the ability to precipitate protein and starch in the rice and flour product, reducing the impurity content of the extract of the rice and flour product to be tested, then pipetting a portion of the extract of the rice and flour product to be tested and mixing it with a color-developing auxiliary agent, extracting and enriching the color-developable complex with an organic solvent, detecting its absorbance with an ultraviolet spectrophotometer, calculating the content of anionic detergent in the rice and flour product to be tested, improving the accuracy of detecting the content of anionic detergent in the rice and flour product using an ultraviolet spectrophotometer, and reducing the detection limit concentration. At the same time, the equipment technology of the ultraviolet spectrophotometer is mature and the price is low. For example, compared with a continuous flow analyzer, the detection cost is lower and the universality is stronger.

[0050] Among them, potassium ferrocyanide and zinc acetate are ionic double precipitants. The ions dissociated from potassium ferrocyanide interact with the surface charges of substances such as proteins, changing the charge distribution on the surface of substances such as proteins. The components produced by the hydrolysis of zinc acetate can destroy the hydration layer of substances such as proteins, making them more prone to aggregation. The synergistic mechanism can change the physical properties of substances such as proteins in rice and flour products, condense them into tiny particles, and gradually aggregate and grow larger to form precipitates. This can not only improve the efficiency of solid-liquid separation, but also reduce the amount of macromolecular substances such as proteins in the extract of rice and flour products, thereby improving the accuracy of detection. For example, single precipitants such as trichloroacetic acid and lead acetate have poor precipitation effects on rice and flour products. Figure 2 shown.

[0051] In some embodiments, in the step of soaking the rice and flour product to be tested in water and crushing it to obtain a rice and flour paste, the ratio of the rice and flour product to be tested to water is 1: (1-3) g / mL.

[0052] Exemplarily, the ratio of the rice and flour product to be tested to water can be 1:1 g / mL, 1:1.1 g / mL, 1:1.2 g / mL, 1:1.3 g / mL, 1:1.4 g / mL, 1:1.5 g / mL, 1:1.6 g / mL, 1:1.7 g / mL, 1:1.8 g / mL, 1:1.9 g / mL, 1:2.0 g / mL, 1:2.1 g / mL, 1:2.2 g / mL, 1:2.3 g / mL, 1:2.4 g / mL, 1:2.5 g / mL, 1:2.6 g / mL, 1:2.7 g / mL, 1:2.8 g / mL, 1:2.9 g / mL, 1:3.0 g / mL, or 1:(1-3) g / mL, or any value or interval consisting of any values.

[0053] Dried rice and flour products are highly ductile and easily absorb water, making it difficult for conventional grinders to completely crush the sample. Initial crushing followed by soaking in water reduces the toughness of the dried rice and flour product before further crushing. Controlling the ratio of the tested dried rice and flour product to water within the aforementioned range allows the dried rice and flour product to fully absorb water and swell, reducing its toughness and facilitating subsequent crushing to form a rice paste with a smaller particle size. This also promotes the subsequent dissolution and dissociation of potassium ferrocyanide and zinc acetate in the rice paste, enhancing its ability to precipitate protein and starch. Combined with the subsequent solid-liquid separation step, this can further improve the efficiency of solid-liquid separation, reduce supernatant turbidity, and enhance detection accuracy.

[0054] In some embodiments, the soaking time is 0.5 h to 2 h.

[0055] Exemplarily, the soaking time can be 0.5 h, 0.6 h, 0.7 h, 0.8 h, 0.9 h, 1.0 h, 1.1 h, 1.2 h, 1.3 h, 1.4 h, 1.5 h, 1.6 h, 1.7 h, 1.8 h, 1.9 h, 2.0 h, or any value between 0.5 h and 2 h or an interval consisting of any values.

[0056] The soaking time is within the above range, and the rice and flour sample to be measured can absorb sufficient moisture, can improve starch granule dispersibility, reduce the probability of forming colloid with anionic detergent, play a good soaking effect, be beneficial to fully extract anionic detergent in rice and flour products, improve accuracy. If the soaking time is greater than 2h, long soaking can cause starch hydrolysis or microbial growth, interfering with the accuracy of detection.

[0057] In some embodiments, during the steps of mixing the rice paste with water, adding the potassium ferrocyanide solution and the zinc acetate solution to react, and separating the solid and liquid to obtain the liquid (supernatant), the ambient temperature is 20° C. to 30° C. If the temperature is too low, the extraction effect is poor, while if the temperature is too high, the sample becomes more viscous and the extraction effect is also poor.

[0058] In some embodiments, in the step of removing a portion of the extract of the rice and flour product to be tested and mixing it with a color development aid, the color development aid includes one or more of diazophenanthroline and methylene blue.

[0059] The above two color-developing auxiliary agents are easy to obtain, do not require complex synthesis, and are compatible with ultraviolet spectrophotometers, which can reduce detection costs.

[0060] In some embodiments, in the step of removing a portion of the extract of the rice and flour product to be tested and mixing it with a color development aid, the color development aid includes diazine, ammonium ferrous sulfate, and a pH buffer.

[0061] In the method for detecting anionic detergents in rice and flour products to be tested by ultraviolet spectrophotometry, the extract of the rice and flour products to be tested is used in combination with the color development auxiliary system including diazine, ammonium ferrous sulfate, and pH buffer. Ammonium ferrous sulfate provides a stable Fe 2+ source, forming a complex with phenanthroline to reduce Fe 3+ Interference, pH buffer such as ammonium acetate-glacial acetic acid can maintain the pH of the reaction system at about 4, further improve the stability of the complex formed by the color-developing aid and the anionic detergent in the extract of the rice and flour product to be tested, reduce the detection limit concentration based on the ultraviolet spectrophotometer, the detection limit can be less than or equal to 0.5 mg / kg, and can further improve the detection accuracy based on the ultraviolet spectrophotometer, reaching the level of accuracy of continuous flow analyzer detection.

[0062] In some embodiments, the step of removing a portion of the extract of the rice and flour product to be tested and mixing it with a color development aid, adding an organic solvent to extract a complex formed by the color development aid and the anionic detergent in the extract of the rice and flour product to be tested, separating the liquid to obtain an organic phase, and measuring the absorbance of the organic phase with an ultraviolet spectrophotometer to obtain the absorbance of the organic phase comprises:

[0063] Take 10mL~50mL of the extract of the rice and flour product to be tested, add 2mL~5mL of phenanthroline, 10mL~15mL of pH buffer, 1mL~2mL of hydroxylamine hydrochloride-ammonium ferrous sulfate solution, add organic solvent for extraction, separate the liquid to obtain the Fe-rich 2+ -The organic phase of the ion pair complex of diazophenanthroline complex and sulfonic acid group is measured by ultraviolet spectrophotometer to obtain absorbance.

[0064] The water content in the rice batter during the pretreatment step is high, and the high solubility of the double precipitants potassium ferrocyanide and zinc acetate in water can fully dissociate into K + 、[Fe(CN)6] 4- and Zn 2+Through charge neutralization and complexation, it can effectively precipitate macromolecular interferences such as proteins and starch, thereby improving the efficiency of precipitation. On this basis, in the color development step, ferrous ammonium sulfate provides a stable Fe 2+ It forms a stable orange-red complex [Fe(phen)3] with phenanthroline under pH buffer conditions. 2+ The complex is positively charged and preferentially reacts with strongly negatively charged anionic detergents such as SDBS SO3 - Combined with the Fe(phen)3 complex, the charge interference of weak negatively charged interfering substances such as starch hydroxyl groups is reduced, and a strong hydrophobic ion pair complex [SDBS-[Fe(phen)3] + , which helps the subsequent extraction and enrichment of organic solvents. Therefore, through the coordination and systematic optimization of the key steps, the detection method of rice and flour products based on the diazophenanthroline method using the UV spectrophotometer has a lower detection limit concentration and higher accuracy based on the UV spectrophotometer.

[0065] In some embodiments, the organic solvent includes one or more of chloroform, dichloromethane, and tetrachloromethane.

[0066] The above-mentioned organic solvents, especially chloroform, have moderate polarity and can effectively extract hydrophobic ion pair complexes such as SDBS-[Fe(phen)3] 2+ , the liquid separation interface is clear, which reduces the difficulty of liquid separation operation and improves the detection accuracy.

[0067] In some embodiments, the steps of preparing sodium dodecylbenzenesulfonate standard solutions of different concentrations and testing the absorbance of the sodium dodecylbenzenesulfonate standard solutions of different concentrations using an ultraviolet spectrophotometer include: preparing sodium dodecylbenzenesulfonate standard solutions of different concentrations, adding water to each of the solutions to a volume consistent with the volume of an extract of a portion of the rice and flour product to be tested, adding a color-developing aid to the fixed volume of the sodium dodecylbenzenesulfonate standard solutions of different concentrations, adding an organic solvent to extract a complex formed by the color-developing aid and the sodium dodecylbenzenesulfonate, obtaining organic phases of the standard solutions, and testing the absorbance of the organic phases of the standard solutions using an ultraviolet spectrophotometer.

[0068] After preparing the standard, add water to the same volume as the sample extract to improve test accuracy. If the sample volume is inconsistent, the total volume of the sample and standard will differ during liquid-liquid extraction, resulting in different shaking and extraction effects, which will affect the accuracy of the test results.

[0069] In some embodiments, preparing sodium dodecylbenzenesulfonate standard solutions of different concentrations, testing the absorbance of the sodium dodecylbenzenesulfonate standard solutions of different concentrations with an ultraviolet spectrophotometer, and drawing a standard curve of sodium dodecylbenzenesulfonate mass-absorbance, the steps include: preparing 0 mL 10 mg / L, 0.25 mL 10 mg / L, 0.5 mL 10 mg / L, 1 mL 10 mg / L, 2 mL 10 mg / L, 3 mL 10 mg / L, 4 mL 10 mg / L, and 5 mL 10 mg / L sodium dodecylbenzenesulfonate standard solutions, respectively, adding water to 50 mL, adding 2 mL to 5 mL of diazine, 10 mL to 15 mL of pH buffer, and 1 mL to 2 mL of hydroxylamine hydrochloride-ammonium ferrous sulfate solution, adding chloroform for extraction to obtain organic phases of standard solutions of different concentrations, respectively testing the absorbance of the organic phases of the standard solutions with an ultraviolet spectrophotometer, and drawing a standard curve.

[0070] In some embodiments, the wavelength of the UV spectrophotometer test is 500 nm to 530 nm.

[0071] In some embodiments, the wavelength tested by the ultraviolet spectrophotometer is 640 nm to 670 nm.

[0072] In some embodiments, in the step of calculating the mass of the anionic detergent in the rice and flour product to be tested by substituting the absorbance of the organic phase based on the standard curve, the calculation formula is:

[0073] X=(m1×V1) / (M×V2),

[0074] Wherein, X is the content of anionic detergent in the rice and flour product to be tested during the step of soaking the rice and flour product to be tested in water, and the unit is mg / kg;

[0075] m1 is the mass of the anionic detergent in the organic phase in the step of pipetting a portion of the extract of the rice and flour product to be tested and mixing it with the color-developing aid, adding an organic solvent to extract the complex formed by the color-developing aid and the anionic detergent in the extract of the rice and flour product to be tested, and separating the liquid to obtain the organic phase, in μg;

[0076] M is the mass of the dry rice paste sample in the step of mixing rice paste with water, adding potassium ferrocyanide solution and zinc acetate solution to react, and performing solid-liquid separation to obtain an extract of the rice and flour product to be tested; or, obtaining a supernatant after solid-liquid separation; and constanting the supernatant to volume to obtain an extract of the rice and flour product to be tested, in g;

[0077] V1 is the step of mixing rice flour paste with water, adding potassium ferrocyanide solution and zinc acetate solution to react, and performing solid-liquid separation to obtain an extract of the rice flour product to be tested; or, obtaining a supernatant after solid-liquid separation; and constanting the supernatant to obtain an extract of the rice flour product to be tested, in which the volume of the extract of the rice flour product to be tested is expressed in mL;

[0078] V2 is the volume of the extract of the rice and flour product to be tested, which is obtained by pipetting a portion of the extract of the rice and flour product to be tested and mixing it with the color development auxiliary agent, and the unit is mL.

[0079] After the test is complete, the mass content of anionic detergents in the rice and flour products being tested can be calculated using the above formula. In this formula, volume correction (V1 / V2) and sample mass (M) normalization can reduce concentration deviations caused by pipetting or volumetric errors. Converting the instrument-measured mass (m1) to the detergent content (mg / kg) in the sample simplifies the calculation process and improves test efficiency.

[0080] Example

[0081] The following examples describe the disclosure of the present invention in more detail. These examples are intended for illustrative purposes only, as various modifications and variations within the scope of the disclosure of the present invention will be apparent to those skilled in the art. Unless otherwise stated, all parts, percentages, and ratios reported in the following examples are by mass, and all reagents used in the examples are commercially available or synthesized according to conventional methods and can be used directly without further processing, and the instruments used in the examples are commercially available.

[0082] Preparation of Example 1 to 4 Rice Batter

[0083] Preparation Example 1, preparation of rice flour paste, comprising: placing 100 g of the rice flour product to be tested into a homogenizing cup, adding 100 mL of water and soaking for 1 hour, homogenizing and crushing to obtain rice flour paste.

[0084] Preparation Examples 2-3: The preparation of rice flour paste is different from that of Preparation Example 1, except that the volume of water added is different. Preparation Example 2 is soaked in 150 mL of water. Preparation Example 3 is soaked in 200 mL of water.

[0085] Preparation Example 4 is to put 100g of the rice and flour product to be tested into a homogenizing cup and crush it using a homogenizer. The difference from Preparation Example 1 is that no water is added for soaking before homogenizing and crushing.

[0086] from Figure 1 It can be seen that the addition of 200 mL of water in Preparation Example 3 resulted in better soaking and homogenization effects, and a smaller particle size of rice flour paste. Preparation Example 4 was a dry sample directly crushed, resulting in a larger particle size and poor effect.

[0087] Preparation Examples 5-7 Extracts of Rice and Flour Products to be Tested

[0088] Preparation Example 5: 15 g of the rice paste prepared in Preparation Example 3 (equivalent to 5 g of a dry sample of rice paste) was placed in a 50 mL centrifuge tube, 20 mL of water was added, and ultrasonic oscillation was performed at 25°C for 30 min. 1 mL of potassium ferrocyanide solution (92 g / L) and 1 mL of zinc acetate solution (183 g / L) were added successively. After vortexing, the mixture was centrifuged at 4000 rpm for 5 minutes, and the supernatant was transferred to a 50 mL volumetric flask. The residue was added with 20 mL of pure water and the extraction was repeated once. The supernatants were combined in a volumetric flask; the supernatants were brought to volume to obtain the extract of the rice and flour product to be tested.

[0089] Preparation Examples 6 and 7 differ from Preparation Example 5 in the type of precipitant used. In Preparation Example 6, equal amounts of trichloroacetic acid were used as the precipitant, replacing the potassium ferrocyanide solution and the zinc acetate solution. In Preparation Example 7, equal amounts of lead acetate were used as the precipitant, replacing the potassium ferrocyanide solution and the zinc acetate solution.

[0090] from Figure 2 It can be seen that the extract of the rice and flour product to be tested obtained in Preparation Example 5 is clear and transparent, and the precipitation effect is good, indicating that the dual precipitant of potassium ferrocyanide and zinc acetate can have a good precipitation effect on the protein and starch in the rice and flour products. The extract of the rice and flour product obtained by the single precipitant used in Preparation Examples 6 to 7 is turbid, and the precipitation effect is not as good as Preparation Example 5. The accuracy of detecting anionic detergents in rice and flour products is also not as good as Preparation Example 5.

[0091] Examples 1 to 3

[0092] Example 1

[0093] Preparation of rice flour product extracts: Take three negative rice flour products (negative rice flour products refer to samples without anionic detergents), respectively prepare rice flour pastes using the method of Preparation Example 3, add different masses of sodium dodecylbenzenesulfonate as shown in Table 1 below to the rice flour pastes, and respectively prepare rice flour product extracts using the method of Preparation Example 5.

[0094] Measure 50 mL of each of the rice and flour product extracts to be tested and place them into 125 mL separatory funnels to serve as sample solutions. Add 0 mL, 0.5 mL, 1 mL, 2 mL, 3 mL, 4 mL, and 5 mL of a standard working solution of sodium dodecylbenzenesulfonate (10 mg / L) to seven separate 125 mL separatory funnels, respectively. Dilute to 50 mL with pure water to serve as standard solutions.

[0095] Three drops of phenolphthalein solution were added to the sample solution and the standard solution respectively, and sodium hydroxide solution (40 g / L) was added dropwise to make the water sample alkaline. Then, sulfuric acid solution (14 mL / L) was added dropwise to fade the red color. 5 mL of chloroform and 10 mL of methylene blue solution (30 mg of methylene blue was dissolved in 500 mL of pure water, 6.8 mL of sulfuric acid and 50 g of sodium dihydrogen phosphate monohydrate were added and the volume was adjusted to 1 L) were added. The mixture was shaken vigorously for 0.5 min and allowed to stand for stratification. The chloroform phase was separated and placed into a second set of separating funnels. 25 mL of washings (6.8 mL of sulfuric acid and 50 g of sodium dihydrogen phosphate monohydrate were added thereto and the volume was adjusted to 1 L) was added thereto. The mixture was shaken vigorously for 0.5 min and allowed to stand for stratification and retested. Insert a small ball of absorbent cotton into the neck of the separatory funnel, place the chloroform extraction solution into a 25mL dry colorimetric tube, add 5mL of chloroform to each separatory funnel, shake and let it stand to separate the layers, then combine the chloroform phases into a 25mL colorimetric tube, repeat the operation, and finally dilute to the scale with chloroform.

[0096] The organic phases of the chloroform-extracted sample solution and the standard solution were collected separately, and their absorbance was measured at a wavelength of 650 nm using a Puxi TU-1901 dual-beam UV-visible spectrophotometer, with chloroform as the reference and a 3 cm cuvette. A standard curve was automatically drawn using workstation software, with the mass of sodium dodecylbenzenesulfonate in the standard solution as the horizontal axis and the corresponding absorbance as the vertical axis. Based on the standard curve, the absorbance of the organic phase of the rice and flour product sample to be tested, measured by the UV spectrophotometer, was substituted into the equation: X = (m1 × V1) / (M × V2), and the anionic detergent content in the rice and flour product to be tested was calculated.

[0097] Table 1

[0098] Sample name Sample 1 Sample 2 Sample 3 Theoretical addition amount (μg) 5.0 10.0 30.0 Measured value (μg) 4.7158 9.6461 29.4214 Recovery rate (%) 94.3 96.5 98.1

[0099] Minimum detection limit concentration test: Referring to GB / T 5750.4-2023, the lowest non-zero point of the standard curve is used as the detection limit. In aqueous solution, it is 5 μg, which is converted into 1 mg / kg of sample. That is, the minimum detection limit concentration of this example is 1 mg / kg.

[0100] Example 2

[0101] Preparation of rice flour product extracts: Take three negative rice flour products (negative rice flour products refer to samples without anionic detergents), respectively prepare rice flour pastes using the method of Preparation Example 3, add different masses of sodium dodecylbenzenesulfonate as shown in Table 2 below to the rice flour pastes, and respectively prepare rice flour product extracts using the method of Preparation Example 5.

[0102] Measure 50 mL of each of the rice and flour product extracts to be tested and place them into a 125 mL separatory funnel to serve as the sample solution. Add 0 mL, 0.5 mL, 1 mL, 2 mL, 3 mL, 4 mL, and 5 mL of a standard working solution of sodium dodecylbenzenesulfonate (10 mg / L) to seven other 125 mL separatory funnels, respectively. Dilute to 50 mL with pure water to serve as the standard solution.

[0103] Add 2 mL of phenanthroline (2 g / L, 0.2 g of phenanthroline monohydrate dissolved in pure water, 2 drops of hydrochloric acid, and dilute to 100 mL), 10 mL of ammonium acetate solution (250 g of ammonium acetate dissolved in 150 mL of pure water, 700 mL of glacial acetic acid added), 1 mL of hydroxylamine hydrochloride-ferrous solution (10 g of hydroxylamine hydrochloride, 0.211 g of ammonium ferrous sulfate hexahydrate, and dilute to 100 mL) and chloroform to the sample solution and standard solution, respectively. Extract and shake for 2 minutes. Insert a small ball of absorbent cotton into the neck of the separatory funnel, and collect the organic phases of the sample solution and standard solution extracted with chloroform.

[0104] The organic phases of the chloroform-extracted sample solution and the standard solution were collected separately and placed in 10 mL dry colorimetric tubes. The absorbance was measured at a wavelength of 510 nm using a Puxi TU-1901 dual-beam UV-visible spectrophotometer, using chloroform as a reference and a 3 cm cuvette. A standard curve was automatically plotted using workstation software, with the mass of sodium dodecylbenzenesulfonate in the standard solution as the abscissa and the corresponding absorbance as the ordinate.

[0105] Based on the standard curve, the absorbance of the organic phase of the rice and flour product to be tested measured by the ultraviolet spectrophotometer is substituted to calculate the content of the anionic detergent in the rice and flour product to be tested.

[0106] Accuracy test: The above samples were subjected to accuracy test, and the test results are shown in Table 2 below.

[0107] Table 2

[0108] Sample name Sample 1 Sample 2 Sample 3 Theoretical addition amount (μg) 2.5 5.0 30.0 Measured value (μg) 2.4813 4.9921 29.8804 Recovery rate (%) 99.3 99.8 99.6

[0109] Minimum detection limit concentration test: Referring to GB / T 5750.4-2023, the lowest non-zero point of the standard curve was used as the detection limit. In aqueous solution, it was 2.5 μg, which was converted into 0.5 mg / kg for the sample. That is, the minimum detection limit concentration in this example was 0.5 mg / kg.

[0110] From the comparison of the test results of Example 1 and Example 2, it can be seen that based on the measurement of the ultraviolet spectrophotometer, the combined use of the above-mentioned step of extracting the rice and flour products in the present application and the detection method of the diazine method is more accurate and has a lower detection limit concentration than the methylene blue method.

[0111] Example 3

[0112] The difference between this embodiment and embodiment 2 is that the amount of ammonium acetate solution added is different, and the other steps remain unchanged. The absorbance of the negative rice and flour samples was tested, and the results are shown in Table 3 below.

[0113] Table 3

[0114] Amount of ammonium acetate added (mL) 0 2 5 10 (Example 2) 15 Negative sample result (μg) 0 0 0 0 0 Theoretical addition amount (μg) 5 5 5 5 5 absorbance 0.0312 0.0325 0.0349 0.0362 0.360

[0115] Although low-valent iron ions and phenanthroline can both form stable orange complexes at pH levels of 3 to 9, an excess of phenanthroline, when controlling the solution pH to around 4, and adding 10 mL of ammonium acetate solution, can significantly enhance color development and increase absorbance in a shorter period of time. This minimizes the impact of instrument noise on the results, leading to higher accuracy and sensitivity. As the amount of phenanthroline increases, absorbance does not increase further, indicating that a 10 mL ammonium acetate dosage achieves a high level of accuracy and offers greater economic benefits.

[0116] Example 4

[0117] This example is based on a method for detecting the content of anionic detergents in rice and flour products using an ultraviolet spectrophotometer. 20 batches of commercially available rice flour products were tested using the methylene blue method and the phenanthroline method, respectively.

[0118] The preparation methods of the extracts of the rice and flour products to be tested by the methylene blue method and the phenanthroline method are the same, and both are prepared by the method of Preparation Example 5.

[0119] The steps for detecting the anionic detergent content in the extract of the rice and flour product to be tested by the methylene blue method are the same as those in Example 1. The steps for detecting the anionic detergent content in the extract of the rice and flour product to be tested by the phenanthroline method are the same as those in Example 2.

[0120] Among them, 3 batches had positive results, and the test results are shown in Table 4 below.

[0121] Table 4

[0122]

[0123] Comparative Example 1

[0124] Comparative Example 1 is compared with Example 2 in that the preparation method of the negative rice and flour product extract is different, there is no soaking step, and methanol is used instead of water for extraction and precipitation.

[0125] The preparation method of the negative rice and flour product extract of this comparative example is as follows:

[0126] Three 100g portions of negative rice and flour products were placed in a homogenizer and homogenized to obtain rice and flour granules. 15g of these granules were placed in a 50mL centrifuge tube and added with varying amounts of sodium dodecylbenzenesulfonate as shown in Table 5 below. 20mL of methanol was also added and the mixture was extracted with ultrasonic vibration at 25°C for 30 minutes. 1mL of potassium ferrocyanide solution (92g / L) and 1mL of zinc acetate solution (183g / L) were then added. After vortexing, the mixture was centrifuged at 4000 rpm for 5 minutes. The supernatant was transferred to a 50mL volumetric flask. The residue was extracted again with 20mL of methanol, and the supernatants were combined in a volumetric flask. The supernatants were brought to volume to obtain the extract of the negative rice and flour product.

[0127] 50 mL of the extract of the rice and flour product to be tested was measured respectively, and the accuracy test was performed using the diazine method of Example 2. The results are shown in Table 5 below:

[0128] Table 5

[0129] Sample name Sample 1 Sample 2 Sample 3 Result (μg) 0 0 0 Theoretical addition amount (μg) 2.5 5.0 30.0 Measured value (μg) Not detected 4.7122 29.4520 Recovery rate (%) / 94.24 98.17

[0130] Minimum detection limit concentration test: Referring to GB / T 5750.4-2023, the lowest non-zero point of the standard curve was used as the detection limit. In aqueous solution, it was 5.0 μg, which was converted to 1 mg / kg of sample. That is, the minimum detection limit concentration of this example was 1 mg / kg.

[0131] As can be seen from the embodiments and comparative examples, the present application soaks the dried rice and flour products to be tested in water and then crushes them, which can better reduce the particle size of the rice and flour paste. Mixing with water can increase the water content in the rice and flour paste, help improve the solubility of the double precipitants of potassium ferrocyanide and zinc acetate in the system, improve the ability to precipitate protein and starch in the rice and flour products, reduce the impurity content of the extract of the rice and flour products to be tested, and then use an ultraviolet spectrophotometer for detection, thereby improving the accuracy of detecting the anionic detergent content in the rice and flour products using an ultraviolet spectrophotometer and reducing the detection limit concentration.

[0132] Although illustrative embodiments have been shown and described, those skilled in the art should understand that the above embodiments should not be construed as limitations on the present application, and that changes, substitutions, and modifications may be made to the embodiments without departing from the spirit, principles, and scope of the present application.

Claims

1. A method for detecting the content of anionic detergent in rice and flour products based on ultraviolet spectrophotometry, characterized in that: include: Soak the rice and flour product to be tested in water, and grind it to obtain rice and flour paste; The rice flour paste is mixed with water, potassium ferrocyanide solution and zinc acetate solution are added to react, and solid-liquid separation is performed to obtain an extract of the rice flour product to be tested; Pipetting a portion of the extract of the rice and flour product to be tested and mixing it with a color developing agent, adding an organic solvent to extract a complex formed by the color developing agent and the anionic detergent in the extract of the rice and flour product to be tested, separating the liquids to obtain an organic phase; and measuring the absorbance of the organic phase using an ultraviolet spectrophotometer; Prepare sodium dodecylbenzenesulfonate standard solutions of different concentrations, test the absorbance of the sodium dodecylbenzenesulfonate standard solutions of different concentrations with an ultraviolet spectrophotometer, and draw a sodium dodecylbenzenesulfonate-absorbance standard curve; Based on the standard curve, the absorbance of the organic phase is substituted to calculate the content of the anionic detergent in the rice and flour product to be tested.

2. The method for detecting the content of anionic detergent in rice and flour products based on ultraviolet spectrophotometer according to claim 1, wherein In the step of soaking the rice and flour product to be tested in water and crushing it to obtain rice and flour paste, the ratio of the rice and flour product to be tested to water is 1: (1-3) g / mL; and / or, The soaking time is 0.5h to 2h.

3. The method for detecting the content of anionic detergent in rice and flour products based on ultraviolet spectrophotometer according to claim 1, wherein In the step of removing part of the extract of the rice and flour product to be tested and mixing it with a color development auxiliary agent, the color development auxiliary agent includes one or more of diazophenanthroline and methylene blue.

4. The method for detecting the content of anionic detergent in rice and flour products based on ultraviolet spectrophotometer according to claim 1, wherein In the step of removing part of the extract of the rice and flour product to be tested and mixing it with a color development aid, the color development aid includes diazine, ammonium ferrous sulfate, and a pH buffer.

5. The method for detecting the content of anionic detergent in rice and flour products based on ultraviolet spectrophotometer according to claim 4, wherein The steps of removing a portion of the extract of the rice and flour product to be tested and mixing it with a color developing auxiliary agent, adding an organic solvent to extract a complex formed by the color developing auxiliary agent and the anionic detergent in the extract of the rice and flour product to be tested, and separating the liquids to obtain an organic phase include: 10 mL to 50 mL of the extract of the rice and flour product to be tested is transferred, 2 mL to 5 mL of phenanthroline, 10 mL to 15 mL of pH buffer, and 1 mL to 2 mL of hydroxylamine hydrochloride-ammonium ferrous sulfate solution are added, and an organic solvent is added for extraction. The liquids are separated to obtain an organic phase rich in an ion pair complex of Fe2+-phenanthroline complex and sulfonic acid group.

6. The method for detecting the content of anionic detergent in rice and flour products based on ultraviolet spectrophotometer according to claim 1, wherein In the step of adding an organic solvent to extract the complex formed by the color-developing aid and the anionic detergent in the extract of the rice and flour product to be tested, and separating the liquids to obtain the organic phase, the organic solvent includes one or more of chloroform, dichloromethane, and tetrachloromethane.

7. The method for detecting the content of anionic detergent in rice and flour products based on ultraviolet spectrophotometer according to claim 1, wherein: The steps of preparing sodium dodecylbenzenesulfonate standard solutions of different concentrations and testing the absorbance of the sodium dodecylbenzenesulfonate standard solutions of different concentrations with an ultraviolet spectrophotometer include: Sodium dodecylbenzenesulfonate standard solutions of different concentrations are prepared, and water is added to the solutions to make the volumes consistent with the volumes of the extracts of the rice and flour products to be tested in the parts, a color developing auxiliary agent is added to the fixed-volume sodium dodecylbenzenesulfonate standard solutions of different concentrations, an organic solvent is added to extract a complex formed by the color developing auxiliary agent and the sodium dodecylbenzenesulfonate, and organic phases of the standard solutions are obtained respectively, and the absorbance of the organic phases of the standard solutions is tested respectively by an ultraviolet spectrophotometer.

8. The method for detecting the content of anionic detergent in rice and flour products based on ultraviolet spectrophotometer according to claim 7, wherein: The steps of preparing sodium dodecylbenzenesulfonate standard solutions of different concentrations, testing the absorbance of the sodium dodecylbenzenesulfonate standard solutions of different concentrations with an ultraviolet spectrophotometer, and drawing a standard curve of sodium dodecylbenzenesulfonate mass-absorbance include: 0 mL 10 mg / L, 0.25 mL 10 mg / L, 0.5 mL 10 mg / L, 1 mL 10 mg / L, 2 mL 10 mg / L, 3 mL 10 mg / L, 4 mL 10 mg / L, and 5 mL 10 mg / L sodium dodecylbenzenesulfonate standard solutions were prepared, and water was added to make the volume 50 mL respectively. 2 mL to 5 mL of phenanthroline, 10 mL to 15 mL of pH buffer, and 1 mL to 2 mL of hydroxylamine hydrochloride-ammonium ferrous sulfate solution were added. The mixture was extracted with chloroform to obtain organic phases of standard solutions of different concentrations. The absorbance of the organic phases of the standard solutions was tested by ultraviolet spectrophotometer to draw standard curves.

9. The method for detecting the content of anionic detergent in rice and flour products based on ultraviolet spectrophotometer according to claim 1, wherein The wavelength tested by the ultraviolet spectrophotometer is 500nm-530nm or 640nm-670nm.

10. The method for detecting the content of anionic detergent in rice and flour products based on ultraviolet spectrophotometry according to any one of claims 1 to 9, characterized in that: In the step of calculating the content of the anionic detergent in the rice and flour product to be tested by substituting the absorbance of the organic phase based on the standard curve, the calculation formula is: X=(m1×V1) / (M×V2), Wherein, X is the content of anionic detergent in the rice and flour product to be tested in the step of soaking the rice and flour product to be tested in water, and the unit is mg / kg; m1 is the mass of the anionic detergent in the organic phase in the step of mixing the extract of the rice and flour product to be tested with the color-developing aid, adding an organic solvent to extract the complex formed by the color-developing aid and the anionic detergent in the extract of the rice and flour product to be tested, and separating the liquid to obtain the organic phase, in μg; M is the mass of the dry rice paste sample in the step of mixing the rice paste with water, adding potassium ferrocyanide solution and zinc acetate solution to react, and separating the solid and liquid to obtain the extract of the rice noodle product to be tested, in g; V1 is the volume of the extract of the rice noodle product to be tested in the step of mixing the rice noodle paste with water, adding potassium ferrocyanide solution and zinc acetate solution to react, and performing solid-liquid separation to obtain the extract of the rice noodle product to be tested, in mL; V2 is the volume of the extract of the rice and flour product to be tested in the step of pipetting a portion of the extract of the rice and flour product to be tested and mixing it with the color development auxiliary agent, and the unit is mL.

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