A method for detecting starch substitution degree based on impedance and conductivity

Abstract

The present invention provides a method for detecting starch substitution degree based on impedance and conductivity, comprising placing a detection cavity containing a modified starch suspension to be tested between two parallel detection electrode plates, the modified starch suspension to be tested is in contact with the detection electrode plates, and placing the detection cavity and the detection electrode plates in a uniform electric field, collecting impedance and conductivity signals between the detection electrode plates under the uniform electric field, and obtaining the modified starch substitution degree to be tested according to the relationship between the degree of substitution of the same modified starch with a known degree of substitution, the concentration of the suspension, impedance and conductivity. The method provided by the present invention can realize simple, rapid and low-cost detection of starch substitution degree based on the impedance and conductivity of the modified starch suspension, solving the problems of the complexity, cumbersomeness and high instrument requirements of the starch substitution degree detection method in the prior art; the detection method provided by the present invention has good accuracy, is applicable to modified starch of any type and different substitution groups, and has good universality.

Description

Technical Field

[0001] The invention belongs to the technical field of starch substitution degree detection, and particularly relates to a method for detecting starch substitution degree based on impedance and conductivity. Background Art

[0002] Starch is a high molecular carbohydrate composed of glucose molecules. The degree of substitution (DS) of starch refers to the average number of hydroxyl groups derived from each D-pyranose glucose unit. Theoretically, there are up to 3 hydroxyl groups that can be substituted on the D-pyranose glucose unit of starch, that is, the maximum degree of substitution of starch is 3, but in actual industrial production, the average degree of substitution of modified starch is less than 3. Starches substituted with different reagents and with different degrees of substitution are used in the chemical, textile and food industries. For example, acetylated starch with a low degree of substitution can be used as a thickener and stabilizer for food and medicine; acetylated starch with a high degree of substitution can be used to make starch-based plastic films; carboxymethyl starch with a high degree of substitution is used in the preparation of building adhesives, etc. It is of great significance to measure the degree of substitution of starch.

[0003] At present, the commonly used methods for determining the degree of substitution of starch are: chromatography, colorimetry, titration, etc. However, these methods all have certain limitations. For example, chromatography requires professional equipment and is costly; the pretreatment process of colorimetry and titration is cumbersome and requires the consumption of a large amount of chemical reagents. In recent years, the detection of the degree of substitution of polysaccharides has developed rapidly. Prior art CN109211957A provides a method for determining the N-substitution degree of hydroxypropyl chitosan, which includes dissolving a dried hydroxypropyl chitosan sample in a deuterated reagent, obtaining a nuclear magnetic resonance spectrum of the sample by a nuclear magnetic resonance instrument, and finally calculating and analyzing. Prior art CN112730322A provides a method for detecting the molar substitution degree of hydroxyethyl cellulose, which includes forming a near-infrared spectrum atlas of the sample, establishing a model, and finally comparing and analyzing the spectra. The above detection methods all require relatively professional instruments and equipment, and the operation process is cumbersome. How to detect the degree of substitution of starch simply, quickly and at low cost has become a problem that needs to be solved urgently in the industry.

[0004] The hydroxyl groups on the glucose units of modified starch are replaced by other groups, which changes the polarity of the starch molecules, reduces the impedance of the starch suspension, and increases the conductivity. Therefore, the different electrical properties of starches with different degrees of substitution can be used to distinguish them. Summary of the invention

[0005] In order to solve all or part of the above technical problems, the present invention provides the following technical solutions:

[0006] The main purpose of the present invention is to provide a method for detecting starch substitution degree based on impedance and conductivity, comprising:

[0007] S1. placing a detection cavity containing a sample to be tested between two parallel detection electrode plates, and making the sample to be tested contact the two detection electrode plates, wherein the sample to be tested is a modified starch suspension; and placing the detection cavity containing the sample to be tested and the two detection electrode plates in a uniform electric field, wherein the uniform electric field is generated by two parallel signal electrode plates;

[0008] S2, applying an excitation voltage signal between the two signal electrode plates, and collecting a detection signal between the two detection electrode plates, thereby obtaining the impedance of the sample to be tested. Z and conductivity G ;

[0009] S3. Calculate the degree of substitution of the modified starch in the sample to be tested according to the following formula (1): Y ,

[0010] Y =(0.5 Z -2 +1.4 G )× c +C (1)

[0011] Among them, the C value range is -0.87~0.20, Z The unit is kΩ, G The unit is mS, c is the concentration of modified starch in the sample to be tested, and c The value range is 0.5~2.0 g / 100mL.

[0012] Modified starch is obtained by replacing the hydroxyl groups in starch molecules with carboxymethyl, acetyl or other substituent groups. The present invention finds that under the action of a uniform electric field, the substituent groups in the modified starch carry heterogeneous charges due to ionization, and thus can move to detection electrode plates of different polarities; therefore, the present invention promotes the interaction between the substituent groups in the modified starch and other molecules or ions by applying a uniform electric field, reduces the activation energy, and changes the selectivity of different groups under the electric field condition, thereby promoting the enhancement of the signal response of a specific frequency, which is beneficial to improving the detection precision of the electrical properties of the modified starch and improving the detection accuracy of the degree of substitution.

[0013] In some embodiments, the signal electrode plate is perpendicular to the detection electrode plate. Applying an excitation voltage signal between the two signal electrode plates and collecting the detection signal between the two detection electrode plates, the detection electrode plate is perpendicular to the signal electrode plate, which can promote the uniform distribution of the sample in the electric field and avoid the detection electrode plate being affected by the electric field and causing signal interference.

[0014] In some embodiments, the detection cavity and the two detection electrode plates are both disposed in a shell, and the signal electrode plates are disposed on two opposite side walls of the shell.

[0015] In some embodiments, the two signal electrode plates are electrically connected to an electrical signal generating device, which is used to apply an excitation voltage signal; the two detection electrode plates are electrically connected to an electrical signal acquisition device, which is used to acquire the detection signal between the two detection electrode plates.

[0016] In some embodiments, the detection cavity is an insulating cavity, and the detection electrode plates are arranged on two opposite inner walls of the detection cavity, so that the sample to be tested can contact the two detection electrode plates when placed in the detection cavity.

[0017] In some embodiments, the excitation voltage is a sine wave with a level of 500-1500 mV peak-to-peak and a frequency of 100-1000 Hz. If the voltage and frequency are too high, a strong electric field energy may be generated, which may damage the chemical bonds between the substituent groups and the main molecules in the modified starch to a certain extent, causing molecular degradation, changing the molecular structure of the substance and affecting the physical properties of the substance, thus affecting the detection accuracy; if the voltage and frequency are too low, the ionization effect is weak, the interaction between the groups is poor, the orientation of the molecular chains and particles is poor, and the signal detection is interfered.

[0018] In some embodiments, the method specifically includes: preparing a series of modified starches with known substitution degrees into modified starch suspensions with known substitution degrees, wherein the concentration of the modified starch suspensions with known substitution degrees is 0.5-2.0 g / 100 mL; testing the modified starch suspensions with known substitution degrees according to steps S1-S2 to obtain the conductivity and impedance of the modified starch suspensions with known substitution degrees; determining the relationship between the degree of substitution, concentration, impedance and conductivity of the modified starch suspensions with known substitution degrees, thereby obtaining formula (1).

[0019] In the method of the present invention, the same solvent is used to prepare the modified starch to be tested into a modified starch suspension and the modified starch with known substitution degree into a modified starch suspension with known substitution degree. Preferably, water is used as the solvent to prepare the suspension.

[0020] In some embodiments, the hydroxyl groups on the glucose units of the modified starch contained in the modified starch suspension with known substitution degree and the sample to be tested are substituted with the same substituents, that is, the modified starch with known substitution degree and the sample to be tested belong to the same modified starch.

[0021] In some embodiments, the concentration of the modified starch suspension with known degree of substitution is the same as the concentration of the modified starch in the sample to be tested.

[0022] The detection method provided by the present invention is applicable to any modified starch, including oxidized starch, cationic starch, carboxymethyl starch, acetate tapioca starch, acetylated starch, hydroxypropyl starch, acetylated distarch phosphate, hydroxypropyl distarch phosphate, etc., but is not limited thereto.

[0023] In some embodiments, the method detects that the degree of substitution of modified starch is in the range of 0.2-1.45.

[0024] In some embodiments, the material of the detection cavity includes one or more of plastic and nylon, but is not limited thereto.

[0025] In some embodiments, the material of the electrode plate of the housing may include copper, zinc, platinum, stainless steel, etc., but is not limited thereto.

[0026] In some typical embodiments, the length, width and height of the shell are, for example, 80 to 150 mm. The detection cavity is, for example, an oblate cylindrical shape, with a bottom diameter of 30 to 75 mm and a height of 8 to 30 mm. The contact surface between the detection electrode plate and the modified starch suspension is, for example, circular, with a diameter of 15 to 45 mm and a thickness of 2 to 10 mm. However, it should be understood that in other embodiments, the specific size and shape of the shell, the detection cavity, and the detection electrode plate can be flexibly adjusted as needed.

[0027] Compared with the prior art, the present invention has at least the following beneficial effects:

[0028] (1) The hydroxyl groups on the glucose units of modified starch are replaced by other groups, and the polarity of the starch molecules changes, which leads to changes in the impedance and conductivity of the starch suspension. The present invention uses the different electrical properties of starches with different degrees of substitution to explore the relationship between the degree of starch substitution and the concentration, impedance and conductivity of the starch suspension, thereby providing a method for detecting the degree of starch substitution based on impedance and conductivity, solving the problem that the method for detecting the degree of starch substitution in the prior art is complex and cumbersome, and has high requirements on instruments;

[0029] (2) The present invention improves the detection accuracy of the electrical properties of modified starch by applying a uniform electric field during the detection process, thereby improving the detection accuracy of the degree of substitution;

[0030] (3) The method provided by the present invention has good accuracy and is applicable to modified starch of any type and with different substitution groups, and has good universality;

[0031] (4) The detection device provided by the present invention can quickly obtain the impedance and conductivity information of the starch suspension sample, and cooperate with the above method to realize the simple, rapid and low-cost detection of starch substitution degree. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0033] Figure 1 is a schematic diagram of the structure of the device for detecting the degree of substitution of starch used in Example 1 of the present invention;

[0034] Explanation of the reference numerals: 101 - signal electrode plate; 102 - detection cavity; 103 - detection electrode plate; 104 - electrical signal acquisition device; 105 - electrical signal generating device. DETAILED DESCRIPTION

[0035] The technical solution of the present invention is described in detail below in conjunction with specific embodiments so that those skilled in the art can better understand and implement the technical solution of the present invention. The specific functional details disclosed herein should not be interpreted as limiting, but only as the basis for the claims and as a representative basis for teaching those skilled in the art to adopt the present invention in different ways in any appropriate detailed embodiment.

[0036] In the following examples, unless otherwise specified, the various raw materials, reagents, reaction equipment, testing equipment and methods used can be obtained through commercial purchase or other channels.

[0037] Example 1

[0038] Example 1 provides a method for detecting the degree of substitution of starch. Figure 1 It is a schematic diagram of the structure of the device used to implement the method, such as Figure 1 As shown, the device includes two parallel signal electrode plates 101, a detection cavity 102, two parallel detection electrode plates 103, an electrical signal acquisition device 104 and an electrical signal generating device 105;

[0039] The detection cavity 102 in this embodiment is a hollow cylindrical structure, and two detection electrode plates 103 are respectively installed on the inner walls of the two bottom surfaces of the hollow cylindrical structure, and the two detection electrode plates 103 are coaxially arranged. During detection, the sample to be tested is placed in the detection cavity 102 and contacts the two detection electrode plates 103;

[0040] The detection cavity 102 is arranged in the shell, so that the detection electrode plates 103 located on the inner walls of the two bottom surfaces of the detection cavity 102 are also located in the shell; the signal electrode plates 101 are two oppositely arranged side walls of the shell, and the two signal electrode plates 101 are perpendicular to the detection electrode plates 103; during detection, the two signal electrode plates 101 form a uniform electric field so that the detection cavity 102 containing the sample to be tested and the detection electrode plates 103 are both located in the uniform electric field; the signal electrode plates 101 are electrically connected to the electric signal generating device 105, and the detection electrode plates 103 are electrically connected to the electric signal collecting device 104;

[0041] In this embodiment, the detection electrode plate 103 and the signal electrode plate 101 are made of copper-zinc alloy, and the detection cavity 102 is food-grade polypropylene plastic; the shell is a cube with a length, width and height of 90 mm; the contact surface between the detection electrode plate 103 and the sample to be tested is circular, the diameter of the detection electrode plate 103 is 20 mm, and the thickness is 3 mm; the bottom diameter of the detection cavity 102 is 35 mm, and the height is 10 mm.

[0042] This embodiment uses the above device to detect the degree of substitution of acetate tapioca starch, which specifically includes the following steps:

[0043] Take commercially available acetate cassava starch with substitution degree of 0.2, 0.4, 0.6, 0.8, 1.0, 1.2, 1.4 as standard starch (determine the acetate amount of acetate cassava starch according to GB29925-2013. Substitution degree (%) = (molar mass of substituent × amount of substituent) / (molar mass of acetate × amount of acetate)), use water as solvent, and prepare it into an acetate cassava starch suspension with a concentration of 1.0 g / 100 mL;

[0044] An acetate cassava starch suspension with a known degree of substitution is injected into the detection cavity so that the acetate cassava starch suspension contacts two detection electrode plates; an electric signal generating device is used to apply an excitation voltage between two parallel signal electrode plates, wherein the excitation voltage is a sine wave, the level peak of the excitation voltage is 1500 mV, and the frequency is 100 Hz; then, the detection signal between the two detection electrode plates is collected by an electric signal collecting device to obtain the impedance (kΩ) and conductivity (mS) values ​​of the acetate cassava starch suspension;

[0045] By collecting the obtained data, the relationship between the degree of substitution, concentration, impedance and conductivity of acetate cassava starch suspension was analyzed and the relationship was obtained: Y =0.5 Z -2 +1.4 G -0.18.

[0046] Using water as solvent, the acetate cassava starch to be tested is prepared into a starch suspension sample with a concentration of 1.0 g / 100 mL, and the starch suspension sample is injected into the detection cavity and both detection electrode plates are in contact with the starch suspension sample; an electric signal generating device is used to apply an excitation voltage between the two signal electrode plates, and the excitation voltage is a sine wave, the level peak of the excitation voltage is 1500 mV, and the frequency is 100 Hz; then the detection signal between the detection electrode plates is collected by the electric signal acquisition device to obtain the impedance of the starch suspension sample to be tested. Z (kΩ) and conductivity G (mS);

[0047] The concentration of the acetate cassava starch suspension to be tested c 1.0 g / 100mL, impedance Z (kΩ) and conductivity G (mS) Substitute into the formula Y =0.5 Z -2 +1.4 G -0.18, and the substitution degree Y of the sample to be tested is calculated. The detection range corresponding to this relationship is 0.5~1.15.

[0048] The method of this embodiment and the GB29925-2013 method were respectively used to test 10 types of acetate cassava starch sold by different manufacturers. The results are shown in Table 1 below.

[0049] Table 1 Determination results of substitution degree of different acetate cassava starches by the method of Example 1

[0050] ;

[0051] The relative deviation of the measurement results of the method of this embodiment and the method of the prior art is within ±2%, and the method of this embodiment 1 has higher accuracy.

[0052] Example 2

[0053] The device used in this embodiment 2 is basically the same as that in embodiment 1, except that the detection electrode plate and the signal electrode plate are made of stainless steel; the detection cavity is made of food-grade PET plastic. The length, width and height of the shell are all 120 mm; the contact surface between the detection electrode plate and the sample is circular, the detection electrode plate has a diameter of 30 mm and a thickness of 6 mm, and the detection cavity has a diameter of 60 mm and a height of 20 mm.

[0054] The detection process of this embodiment is basically the same as that of embodiment 1. The starch samples detected in this embodiment are carboxymethyl starch samples sold by different manufacturers;

[0055] Take commercially available carboxymethyl starch with substitution degree of 0.2, 0.4, 0.6, 0.8, 1.0, 1.2, 1.4, 1.6 as standard starch (determine the amount of carboxymethyl in carboxymethyl starch according to GB / T20375-2006. Substitution degree (%) = (molar mass of substituent × amount of substituent) / (molar mass of carboxymethyl × amount of carboxymethyl)), use water as solvent, and prepare it into a starch suspension with a concentration of 0.8 g / 100 mL;

[0056] A starch suspension with a known degree of substitution is injected into the detection cavity so that the starch suspension contacts two detection electrode plates; an electric signal generator is used to apply an excitation voltage between two parallel signal electrode plates, wherein the excitation voltage is a sine wave, the level peak of the excitation voltage is 1000 mV, and the frequency is 500 Hz; then, the detection signal between the two detection electrode plates is collected by an electric signal acquisition device to obtain the impedance (kΩ) and conductivity (mS) values ​​of the carboxymethyl starch suspension;

[0057] By collecting the acquired data, the relationship between the degree of substitution, concentration, impedance and conductivity of carboxymethyl starch was analyzed and the relationship was obtained: Y =(0.5 Z -2 +1.4 G )×0.8-0.23.

[0058] Using water as solvent, the carboxymethyl starch sample to be tested was prepared to a concentration of c =0.8 g / 100 mL of starch suspension sample, inject the starch suspension into the detection cavity and make two detection electrode plates contact with the starch colloid sample; use an electric signal generating device to apply an excitation voltage between the two parallel signal electrode plates, the excitation voltage is a sine wave, the level peak of the applied excitation voltage is 1000 mV, and the frequency is 500 Hz; then use an electric signal acquisition device to collect the detection signal between the two detection electrode plates to obtain the impedance of the starch suspension sample. Z (kΩ) and conductivity G (mS);

[0059] The concentration of the carboxymethyl starch suspension sample to be tested c 0.8 g / 100mL, impedance Z (kΩ) and conductivity G (mS) Substitute into the formula Y =(0.5 Z -2 +1.4 G )×0.8-0.23, and calculate the substitution degree Y of the sample to be tested. The detection range corresponding to this relationship is 0.4~1.45.

[0060] The method of this example and the GB / T20375-2006 method were used to test 10 kinds of highly substituted carboxymethyl starch sold by different manufacturers. The results are shown in Table 2 below.

[0061] Table 2 Determination results of different carboxymethyl starch substitution degrees by the method of Example 2

[0062] ;

[0063] The relative deviation of the measurement results of the method of this embodiment and the method of the prior art is within ±2%, and the method of this embodiment 2 has higher accuracy.

[0064] Example 3

[0065] The device used in this embodiment is the same as that in embodiment 1.

[0066] The detection process of this embodiment is basically the same as that of embodiment 1. The starch samples detected in this embodiment are acetylated starch samples sold by different manufacturers;

[0067] Take commercially available acetylated starch with substitution degree of 0.2, 0.4, 0.6, 0.8, and 1.0 as standard starch (GB / T 20373-2021 Determination of the amount of acetyl in acetylated starch. Substitution degree (%) = (molar mass of substituent × amount of substituent) / (molar mass of acetyl × amount of acetyl)), use water as solvent, and prepare it into a starch suspension with a concentration of 2 g / 100 mL;

[0068] A starch suspension with a known degree of substitution is injected into the detection cavity so that the starch suspension contacts two detection electrode plates; an electric signal generator is used to apply an excitation voltage between two parallel signal electrode plates, wherein the excitation voltage is a sine wave, the level peak of the excitation voltage is 500 mV, and the frequency is 1000 Hz; then, the detection signal between the two detection electrode plates is collected by an electric signal acquisition device to obtain the impedance (kΩ) and conductivity (mS) values ​​of the acetylated starch suspension;

[0069] By collecting the acquired data, the relationship between the degree of substitution, concentration, impedance and conductivity of the acetylated starch suspension was analyzed and the relationship was obtained: Y =(0.5 Z -2 +1.4 G )×2-0.53.

[0070] Using water as solvent, the acetylated starch sample to be tested was prepared to a concentration of cA starch suspension sample with a concentration of 2 g / 100 mL is injected into the detection chamber and two detection electrode plates are in contact with the starch suspension sample. An electric signal generating device is used to apply an excitation voltage between the two parallel signal electrode plates, and the applied excitation voltage has a peak level of 500 mV and a frequency of 1000 Hz. Then, the detection signal between the parallel detection electrode plates is collected by an electric signal acquisition device to obtain the impedance of the starch suspension sample. Z (kΩ) and conductivity G (mS);

[0071] The concentration of acetylated starch suspension sample c =2 g / 100mL, impedance Z (kΩ) and conductivity G (mS) Substitute into the formula Y =(0.5 Z -2 +1.4 G )×2-0.53, and calculate the substitution degree Y of the sample to be tested. The detection range corresponding to this relationship is 0.3~0.95.

[0072] The method of this embodiment and the GB / T 20373-2021 method were used to test 10 acetylated starch food thickeners sold by different manufacturers. The results are shown in Table 3 below.

[0073] Table 3 Determination results of different acetylated starch substitution degrees by the method of Example 3

[0074] ;

[0075] The relative deviation of the measurement results of the method of this embodiment and the method of the prior art is within ±2%, and the method of this embodiment 3 has higher accuracy.

[0076] Comparative Example 1

[0077] The device used in this comparative example is the same as that in Example 1.

[0078] The detection process of this comparative example is basically the same as that of Example 1. The starch samples detected in this example are acetate tapioca starch samples sold by different manufacturers;

[0079] Take commercially available acetate cassava starch samples with degrees of substitution of 0.2, 0.4, 0.6, 0.8, 1.0, 1.2, and 1.4 as standard starch, use water as solvent, and prepare them into a standard starch suspension with a concentration of 1.0 g / 100 mL;

[0080] The standard starch suspension is injected into the detection cavity so that the standard starch suspension contacts two detection electrode plates; an electric signal generating device is used to apply an excitation voltage between two parallel signal electrode plates, wherein the excitation voltage is a sine wave, the level peak of the excitation voltage is 2000 mV, and the frequency is 1500 Hz; then, the detection signal between the two detection electrode plates is collected by an electric signal collecting device to obtain the impedance (kΩ) and conductivity (mS) values ​​of the acetate cassava starch suspension;

[0081] By collecting the obtained data, the relationship between the degree of substitution, concentration, impedance and conductivity of acetate cassava starch was analyzed and the relationship was obtained: Y =0.4 Z -2 +1.3 G +0.12;

[0082] Using water as solvent, the acetate cassava starch sample to be tested was prepared to a concentration of c A starch suspension sample with a concentration of 1.0 g / 100 mL is injected into the detection chamber and two electrode plates are in contact with the starch suspension sample; an electric signal generating device is used to apply an excitation voltage between the two parallel signal electrode plates, and the applied excitation voltage has a peak level of 2000 mV and a frequency of 1500 Hz; then the detection signal between the detection electrode plates is collected by the electric signal collecting device to obtain the impedance of the starch suspension sample. Z (kΩ) and conductivity G (mS);

[0083] The concentration of starch suspension sample c =1.0 g / 100mL, impedance Z (kΩ) and conductivity G (mS) Substitute into the formula Y =0.4 Z -2 +1.3 G +0.12, and the substitution degree Y of the sample to be tested is calculated. The detection range corresponding to this relationship is 0.2~1.10.

[0084] The method of this comparative example and the GB29925-2013 method were used to test 10 types of acetate cassava starch sold by different manufacturers. The test results are shown in Table 4 below.

[0085] Table 4 Comparative Example 1 method for the determination of different acetate cassava starch substitution degree results

[0086] ;

[0087] The relative deviation of the measurement results between the method of this comparative example and the method of the prior art varies in the range of ± (1%~8%), which is quite different, indicating that the method of comparative example 1 has poor precision, and the excessively high voltage and frequency affect the interaction between the acetate groups and the starch molecules in the acetate cassava starch, resulting in a decrease in the stability of the molecular structure, which affects the detection of the electrical signal, and there is a large deviation from the detection results of the prior art.

[0088] Comparative Example 2

[0089] The device used in this comparative example is the same as that in Example 1.

[0090] The detection process of this comparative example is basically the same as that of Example 1. The starch samples detected in this example are acetate tapioca starch samples sold by different manufacturers;

[0091] Take commercially available acetate cassava starch samples with degrees of substitution of 0.2, 0.4, 0.6, 0.8, 1.0, 1.2, and 1.4 as standard starch, use water as solvent, and prepare them into a standard starch suspension with a concentration of 1.0 g / 100 mL;

[0092] The standard starch suspension is injected into the detection cavity so that the standard starch suspension contacts two detection electrode plates; an electric signal generating device is used to apply an excitation voltage between two parallel signal electrode plates, wherein the excitation voltage is a sine wave, the level peak of the excitation voltage is 200 mV, and the frequency is 50 Hz; then, the detection signal between the two detection electrode plates is collected by an electric signal collecting device to obtain the impedance (kΩ) and conductivity (mS) values ​​of the acetate cassava starch suspension;

[0093] By collecting the obtained data, the relationship between the degree of substitution, concentration, impedance and conductivity of acetate cassava starch was analyzed and the relationship was obtained: Y =1.2 Z -2 +1.2 G -0.14;

[0094] Using water as solvent, the acetate cassava starch sample to be tested was prepared to a concentration of c A starch suspension sample with a concentration of 1.0 g / 100 mL is injected into the detection chamber and two electrode plates are in contact with the starch suspension sample. An electric signal generating device is used to apply an excitation voltage between the two parallel signal electrode plates, and the applied excitation voltage has a peak level of 200 mV and a frequency of 50 Hz. Then, the detection signal between the detection electrode plates is collected by the electric signal collecting device to obtain the impedance of the starch suspension sample. Z (kΩ) and conductivity G (mS);

[0095] The concentration of starch suspension samplec =1.0 g / 100mL, impedance Z (kΩ) and conductivity G (mS) Substitute into the formula Y =1.2 Z -2 +1.2 G -0.14, and the substitution degree Y of the sample to be tested is calculated. The detection range corresponding to this relationship is 0.22~0.86.

[0096] The method of this comparative example and the GB29925-2013 method were used to test 10 types of acetate cassava starch sold by different manufacturers. The test results are shown in Table 5 below.

[0097] Table 5 Determination results of substitution degree of different acetate cassava starch by comparative example 2

[0098] ;

[0099] The relative deviation of the measurement results between the method of this comparative example and the method of the prior art varies in the range of ± (2%~9%), which is quite different. This shows that the precision of the comparative example 2 method is poor, the voltage and frequency are too low, the ionization effect of starch molecules and acetate groups is weak, the interaction between the groups is poor, and the orientation of molecular chains and particles is poor, which affects the detection of electrical signals and has a large deviation from the detection results of the prior art.

[0100] Comparative Example 3

[0101] The device used in this comparative example is the same as that in Example 1, but the electric signal generating device does not operate, that is, no uniform electric field is generated between the signal electrode plates.

[0102] The detection process of this comparative example is basically the same as that of Example 1. The starch samples detected in this example are acetate tapioca starch samples sold by different manufacturers;

[0103] Take commercially available acetate cassava starch samples with degrees of substitution of 0.2, 0.4, 0.6, 0.8, 1.0, 1.2, and 1.4 as standard starch, use water as solvent, and prepare them into a standard starch suspension with a concentration of 1.0 g / 100 mL;

[0104] Injecting a standard starch suspension into the detection cavity so that the standard starch suspension contacts two detection electrode plates; collecting detection signals between the two detection electrode plates by an electrical signal acquisition device to obtain impedance (kΩ) and conductivity (mS) values ​​of the acetate cassava starch suspension;

[0105] By collecting the obtained data, the relationship between the degree of substitution, concentration, impedance and conductivity of acetate cassava starch was analyzed and the relationship was obtained: Y =1.8Z -2 +0.6 G -0.19.

[0106] Using water as solvent, the acetate cassava starch sample to be tested was prepared to a concentration of c A starch suspension sample with a concentration of 1.0 g / 100 mL is injected into the detection chamber and the two electrode plates are in contact with the starch suspension sample; the detection signal between the detection electrode plates is collected by an electrical signal acquisition device to obtain the impedance of the starch suspension sample. Z (kΩ) and conductivity G (mS);

[0107] The concentration of starch suspension sample c =1.0 g / 100mL, impedance Z (kΩ) and conductivity G (mS) Substitute into the formula Y =1.8 Z -2 +0.6 G -0.19, and the substitution degree Y of the sample to be tested is calculated. The detection range corresponding to this relationship is 0.25~0.95.

[0108] The method of this comparative example and the GB29925-2013 method were used to test 10 types of acetate cassava starch sold by different manufacturers. The test results are shown in Table 6 below.

[0109] Table 6 Determination results of substitution degree of different acetate cassava starch by comparative example 3

[0110] ;

[0111] The relative deviation of the measurement results between the method of this comparative example and the method of the prior art varies within the range of ± (5%~10%), which is quite different. This indicates that if a uniform electric field is not applied, the sample stability is poor and the precision of its electrical property detection is poor.

[0112] The various aspects, embodiments, features and examples of the present invention should be considered as illustrative in all aspects and are not intended to limit the present invention, the scope of the present invention is defined only by the claims. Other embodiments, modifications and uses will be apparent to those skilled in the art without departing from the spirit and scope of the claimed invention.

[0113] In addition, the inventors of this case also referred to the aforementioned embodiments and conducted experiments with other raw materials, process operations, and process conditions described in this specification, and obtained relatively ideal results.

[0114] Although the present invention has been described with reference to illustrative embodiments, it will be appreciated by those skilled in the art that various other changes, omissions and / or additions may be made without departing from the spirit and scope of the present invention and that the elements of the embodiments may be replaced by substantial equivalents. In addition, many modifications may be made without departing from the scope of the present invention to adapt specific circumstances or materials to the teachings of the present invention. Therefore, it is not intended herein to limit the present invention to the disclosed specific embodiments for performing the present invention, but it is intended that the present invention will include all embodiments within the scope of the appended claims. In addition, unless specifically stated, any use of the terms first, second, etc. does not indicate any order or importance, but rather uses the terms first, second, etc. to distinguish one element from another element.

Claims

1. A method for detecting starch substitution degree based on impedance and conductivity, characterized in that: include: S1. placing a detection cavity containing a sample to be tested between two parallel detection electrode plates, and making the sample to be tested contact the two detection electrode plates, wherein the sample to be tested is a modified starch suspension; and placing the detection cavity containing the sample to be tested and the two detection electrode plates in a uniform electric field, wherein the uniform electric field is generated by two parallel signal electrode plates; S2, applying an excitation voltage signal between the two signal electrode plates, the applied excitation voltage is a sine wave, the level is 500-1500 mV peak-to-peak, and the frequency is 100-1000 Hz, and collecting the detection signal between the two detection electrode plates, so as to obtain the impedance of the sample to be tested Z and conductivity G ; S3. Calculate the degree of substitution of the modified starch in the sample to be tested according to the following formula (1): Y , Y =（0.5 Z -2 +1.4 G ）× c +C （1） Among them, the C value range is -0.87~0.20, Z The unit is kΩ, G The unit is mS, c is the concentration of modified starch in the sample to be tested, and c The value range is 0.5~2.0 g / 100mL.

2. The method according to claim 1, characterized in that: The signal electrode plate is perpendicular to the detection electrode plate.

3. The method according to claim 1, characterized in that: The detection cavity and the two detection electrode plates are both arranged in a shell, and the signal electrode plates are arranged on two opposite side walls of the shell.

4. The method according to claim 1, characterized in that: The two signal electrode plates are electrically connected to an electric signal generating device, and the electric signal generating device is used to apply an excitation voltage signal; the two detection electrode plates are electrically connected to an electric signal collecting device, and the electric signal collecting device is used to collect the detection signal between the two detection electrode plates.

5. The method according to claim 1, characterized in that Specifically include: A series of modified starches with known substitution degrees are prepared into modified starch suspensions with known substitution degrees, and the concentration of the modified starch suspensions with known substitution degrees is 0.5-2.0 g / 100 mL; the modified starch suspensions with known substitution degrees are tested according to steps S1-S2 to obtain the conductivity and impedance of the modified starch suspensions with known substitution degrees; the relationship among the degree of substitution, concentration, impedance and conductance of the modified starch suspensions with known substitution degrees is determined, thereby obtaining formula (1).

6. The method according to claim 5, characterized in that: The hydroxyl groups on the glucose units of the modified starch contained in the modified starch suspension with known substitution degree and the sample to be tested are substituted with the same substitution groups.

7. The method according to claim 5, characterized in that: The concentration of the modified starch suspension with known substitution degree is the same as the concentration of the modified starch in the sample to be tested.

8. The method according to claim 1, characterized in that: The modified starch applicable to the method includes oxidized starch, cationic starch, carboxymethyl starch, acetate tapioca starch, acetylated starch, hydroxypropyl starch, acetylated distarch phosphate or hydroxypropyl distarch phosphate.

9. The method according to claim 1, characterized in that: The range of the degree of substitution of modified starch detected by the method is 0.2-1.45.

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