CN111579574B - Method for detecting ordered structure of starch by using solid nuclear magnetic resonance technology based on paramagnetic doping - Google Patents
Method for detecting ordered structure of starch by using solid nuclear magnetic resonance technology based on paramagnetic doping Download PDFInfo
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- CN111579574B CN111579574B CN202010632708.4A CN202010632708A CN111579574B CN 111579574 B CN111579574 B CN 111579574B CN 202010632708 A CN202010632708 A CN 202010632708A CN 111579574 B CN111579574 B CN 111579574B
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Abstract
The invention relates to the technical field of starch structure detection, in particular to a method for detecting an ordered structure of starch by using a solid nuclear magnetic resonance technology based on paramagnetic doping. The method of the invention comprises the following steps: mixing a paramagnetic copper salt aqueous solution with starch to be detected to obtain a starch dispersion liquid; carrying out vacuum freeze drying on the starch dispersion liquid to obtain a paramagnetic doped starch sample to be detected; by using 13 C cross-polarized or 13 And C, directly exciting a magic angle rotating solid nuclear magnetic resonance technology to characterize the paramagnetic doped starch sample to be detected, so as to obtain the ordered structure of the starch to be detected. The method can reduce the relaxation time of the starch sample, further greatly shorten the spectrogram acquisition time, and more directly, quickly and quantitatively acquire the ordered structure information of the starch sample.
Description
Technical Field
The invention relates to the technical field of starch structure detection, in particular to a method for detecting an ordered structure of starch by utilizing a solid nuclear magnetic resonance technology based on paramagnetic doping.
Background
An in-depth understanding of the starch ordered structure is very important for the physicochemical properties of starch as well as the processing and digestion characteristics of starch-based foods.
The current characterization methods for starch ordered structure are very limited, and the methods adopted in the past comprise differential thermal analysis and Fourier transform infrared spectroscopy. By adopting differential thermal analysis, the existence of starch melting enthalpy causes that the starch cannot quantitatively obtain the crystallinity information of the sample under the complex process conditions of melting, plasticizing, expanding, dissolving and the like; fourier transform infrared signals are not sensitive to short range order or crystallinity, so X-ray diffraction and 13 c cross polarization magic angle rotating solid nuclear magnetic resonance spectroscopy, two well-known accurate and reliable characterization means are used for distinguishing the structural information of the starch granules. Among them, the solid nuclear magnetic resonance technology for short-range ordered structure research has proved to be the best means for characterizing the molecular ordered structure of starch-based materials. By using 13 C cross-polarization solid nuclear magnetic resonance technology qualitatively and quantitatively researches the ordered structure of the starch helix become a typical method. The method using a shorter relaxation time 1 H, carrying out observation on the mixture by using the probe,by passing 1 H and 13 the cross polarization phenomenon of C realizes the pair 13 Indirect observation of the chemical environment of the C-nucleus. However, when the method is used for quantitatively analyzing the starch ordered structure proportion, the polarization transfer efficiency of the carbon nuclei under 6 different chemical environments is similar, and the real proportion of the 6 carbon nuclei cannot be completely quantitatively represented; if adopted 13 C direct excitation sequence test of starch ordered structure proportion and starch medium 13 The relaxation time of the C nucleus is extremely long, resulting in 13 The acquisition time of the direct excitation spectrogram is too long.
Disclosure of Invention
The invention aims to provide a method for detecting the ordered structure of starch by using a solid nuclear magnetic resonance technology based on paramagnetic doping, which can reduce the relaxation time of a starch sample, further greatly shorten the spectrogram acquisition time and more directly, quickly and quantitatively obtain the ordered structure information of the starch sample.
In order to achieve the above object, the present invention provides the following technical solutions:
the invention provides a method for detecting a starch ordered structure by using a solid nuclear magnetic resonance technology based on paramagnetic doping, which comprises the following steps:
mixing a paramagnetic copper salt aqueous solution with starch to be detected to obtain a starch dispersion liquid;
carrying out vacuum freeze drying on the starch dispersion liquid to obtain a paramagnetic doped starch sample to be detected;
by using 13 C cross-polarized or 13 And C, directly exciting a magic angle rotating solid nuclear magnetic resonance technology to characterize the paramagnetic doped starch sample to be detected, so as to obtain the ordered structure of the starch to be detected.
Preferably, the starch to be detected comprises rice starch, corn starch or potato starch.
Preferably, the paramagnetic copper salt in the aqueous solution of paramagnetic copper salt is copper sulfate or copper chloride.
Preferably, the concentration of copper ions in the paramagnetic copper salt aqueous solution is 10mmol/L; the dosage ratio of the starch to be detected to the paramagnetic copper salt aqueous solution is 1g (10-50) mL.
Preferably, the time for vacuum freeze drying is 24-72 h.
Preferably, before the vacuum freeze-drying, the method further comprises the step of quickly freezing the starch dispersion liquid by using liquid nitrogen.
Preferably, the quick-freezing time is 20 s-2 min.
Preferably, the mixing is carried out in a rotary blending machine, and the mixing time is 2-5 h.
The invention provides a method for detecting a starch ordered structure by using a solid nuclear magnetic resonance technology based on paramagnetic doping, which comprises the following steps: mixing a paramagnetic copper salt aqueous solution with starch to be detected to obtain a starch dispersion liquid; carrying out vacuum freeze drying on the starch dispersion liquid to obtain a paramagnetic doped starch sample to be detected; by using 13 C cross-polarized or 13 And C, directly exciting a magic angle rotating solid nuclear magnetic resonance technology to characterize the paramagnetic doped starch sample to be detected, so as to obtain the ordered structure of the starch to be detected.
The invention achieves the aim of reducing the starch to be detected by doping the paramagnetic copper salt into the starch sample and establishing the spin diffusion between the paramagnetic copper salt and the starch to be detected on the premise of not damaging the starch structure 1 H and 13 the purpose of C nuclear longitudinal relaxation time is further to greatly shorten the sampling time of a solid nuclear magnetic resonance spectrogram and realize the rapid, qualitative, quantitative and nondestructive detection of the ordered structure of the starch to be detected.
The method of the invention can greatly reduce 13 C, directly exciting the spectrum acquisition time of the magic angle rotating solid nuclear magnetic technology, and greatly reducing the test cost of the sample on the premise of solving the approximation problem of the hydrocarbon polarization transfer efficiency; the method of the invention can also be used for 13 The spectrum acquisition time of the C cross polarization magic angle rotating solid nuclear magnetic resonance technology is further shortened, and the spectrum acquisition time is shortened, so that the application of a subsequent complex nuclear magnetic resonance experiment sequence becomes possible.
Drawings
FIG. 1 shows the results of example 1 before and after paramagnetic corn starch doping in a direct excitation mode 13 C solid nuclear magnetic resonanceA vibration spectrum.
Detailed Description
The invention provides a method for detecting a starch ordered structure by using a solid nuclear magnetic resonance technology based on paramagnetic doping, which comprises the following steps:
mixing a paramagnetic copper salt aqueous solution with starch to be detected to obtain a starch dispersion liquid;
carrying out vacuum freeze drying on the starch dispersion liquid to obtain a paramagnetic doped starch sample to be detected;
by using 13 C cross-polarized or 13 And C, directly exciting a magic angle rotating solid nuclear magnetic resonance technology to characterize the paramagnetic doped starch sample to be detected, so as to obtain the ordered structure of the starch to be detected.
The invention mixes paramagnetic copper salt water solution with starch to be measured to obtain starch dispersion liquid.
In the present invention, the aqueous solution of paramagnetic copper salt is preferably obtained by dissolving paramagnetic copper salt in deionized water. In the present invention, the paramagnetic copper salt is preferably copper sulfate or copper chloride, and when the paramagnetic copper salt exists as a crystalline hydrate, the paramagnetic copper salt further includes a corresponding hydrate thereof. In the present invention, the concentration of copper ions in the aqueous solution of paramagnetic copper salt is preferably 10mmol/L.
The invention has no special requirements on the type of the starch to be detected, and the starch can be any starch which is well known in the field. In the present invention, the starch to be tested preferably includes wheat starch, corn starch and potato starch.
In the invention, the dosage ratio of the starch to be detected to the paramagnetic copper salt aqueous solution is preferably 1g (10-50) mL, and more preferably 1g (20-40) mL.
In the present invention, the mixing is preferably carried out in a rotary homogenizer; the mixing time is preferably 2 to 5 hours, and more preferably 2.5 to 4 hours; the rotational speed of the mixing is preferably 50rpm.
After the starch dispersion liquid is obtained, the starch dispersion liquid is subjected to vacuum freeze drying to obtain a paramagnetic doped starch sample to be detected.
Before the vacuum freeze drying, the starch dispersion liquid is preferably quickly frozen by liquid nitrogen. In the present invention, the time for quick-freezing is preferably 20s to 2min, more preferably 30s to 1.5min. After the frozen sample is frozen, the frozen sample is preferably stored in a refrigerator at-20 ℃ for later use.
In the present invention, the vacuum freeze-drying time is preferably 24 to 72 hours, more preferably 30 to 70 hours, and most preferably 40 to 60 hours. The temperature of the vacuum freeze-drying is not particularly required, and the vacuum freeze-drying temperature well known in the art can be adopted. The method removes the moisture in the paramagnetic and doped starch sample to be detected by utilizing vacuum freeze drying without damaging the starch structure, and keeps the starch molecules in the glass state.
After obtaining the paramagnetic doped starch sample to be tested, the invention utilizes 13 C cross-polarized or 13 And C, directly exciting a magic angle rotating solid nuclear magnetic resonance technology to characterize the paramagnetic doped starch sample to be detected, so as to obtain the ordered structure of the starch to be detected.
The invention is right 13 The characterization process of the C cross-polarization magic angle spinning solid NMR technology and the 13C direct excitation magic angle spinning solid NMR technology has no special requirement, and the characterization process and the characterization conditions which are well known in the art can be adopted, and the specific reference can be made (A Method for Estimating the Nature a and related reactants of Amorphous, single, and Double-reliable components in Starch grains by 13 C CP/MAS NMR, tan et al, biomacromolecules les,2007,8, 885-8). In an embodiment of the present invention, the characterizing conditions are specifically: paramagnetic doped starch sample to be tested is processed by K 2 CO 3 After the supersaturated solution is balanced in moisture content, the supersaturated solution is loaded into a zirconium oxide rotor with the thickness of 4 mm, and a sample is measured 1 H and 13 c nuclear longitudinal relaxation time (T1), and use 13 Cross-polarization of C or 13 C directly excites the magic angle rotation sequence to analyze the ordered structure (the rotating speed is 8 kHz). Collecting amorphous patterns after starch gelatinization 13 C spectrogram, adjusting spectrogram proportion by taking C4 peak at 84ppm as reference '0' point, and then obtaining the existence of the sample by performing difference spectrum on the starch to be detected and the amorphous sample thereofAnd (3) a sequence structure spectrum, wherein the C1 region in the sequence spectrum can represent the double helix conformation of the sample. The proportion and the crystallinity between the spiral ordered structures in the sample can be quantitatively obtained by calculating the peak areas of the C1 region in the ordered spectrum and the amorphous spectrum.
According to the invention, paramagnetic copper salt is doped in the starch sample, and the purpose of reducing the longitudinal relaxation time of the starch to be detected is achieved by establishing the spin diffusion between the paramagnetic copper salt and the starch to be detected on the premise of not damaging the starch structure, so that the sampling time of a solid nuclear magnetic resonance spectrogram is greatly shortened, and the rapid, qualitative, quantitative and nondestructive detection of the ordered structure of the starch to be detected is realized.
The method for detecting the ordered structure of starch by using the solid-state nuclear magnetic resonance technology based on paramagnetic doping provided by the present invention is described in detail below with reference to the examples, but they should not be construed as limiting the scope of the present invention.
Example 1
Accurately weighing 0.025g of blue vitriol solid, and fully dissolving in 10mL of deionized water to prepare a blue vitriol aqueous solution (the concentration is 10 mmol/L);
weighing 1.0g of corn starch sample, adding 10mL of copper sulfate aqueous solution, placing in a rotary blending instrument, rotating for 5h (the rotating speed is 50 rpm), quickly freezing for 30s by using liquid nitrogen, then placing in a refrigerator at the temperature of-20 ℃ for freezing for 3h, and carrying out vacuum freeze drying for 37h to obtain a paramagnetic doped starch sample to be detected;
characterizing the paramagnetic doped starch sample to be tested by utilizing a magic angle rotating solid nuclear magnetic resonance technology (the characterization condition is that the sample is subjected to K 2 CO 3 After the supersaturated solution has balanced water content, the solution is loaded into a 4 mm zirconia rotor, and a sample is measured 1 H and 13 c nuclear longitudinal relaxation time (T1), and using 13 Cross polarization of C and 13 c directly excites the magic angle rotation sequence to analyze the ordered structure (the rotating speed is 8 kHz). Collecting amorphous patterns after starch gelatinization 13 C spectrogram, adjusting spectrogram proportion with 84ppm C4 peak as reference "0" point, and performing difference spectrum on starch to be detected and its amorphous sample to obtain sample ordered structure spectrogram (shown in figure 1), wherein C1 region in the ordered spectrogram can represent sampleThe double helical conformation of the article. The proportion and the crystallinity between the spiral ordered structures in the sample can be quantitatively obtained by calculating the peak areas of the C1 regions in the ordered spectrum and the amorphous spectrum), and the ordered structure of the starch to be detected is obtained.
Example 2
Accurately dissolving 0.017g of copper chloride dihydrate solid in 10mL of deionized water to prepare a copper chloride aqueous solution (the concentration is 10 mmol/L);
weighing 1.0g of rice starch sample, adding 20mL of copper chloride aqueous solution, placing in a rotary blending instrument, rotating for 4.5h (the rotating speed is 50 rpm), quickly freezing for 25s by using liquid nitrogen, then placing in a refrigerator at the temperature of-20 ℃ for freezing for 2h, and carrying out vacuum freeze drying for 38h to obtain a paramagnetic doped starch sample to be detected;
and characterizing the paramagnetic doped starch sample to be tested by utilizing a magic angle rotating solid nuclear magnetic resonance technology (the characterization conditions are the same as those in example 1), so as to obtain the ordered structure of the starch to be tested.
Example 3
Accurately weighing 0.025g of blue vitriol solid, and fully dissolving in 10mL of deionized water to prepare a blue vitriol aqueous solution (the concentration is 10 mmol/L);
weighing 1.0g of potato starch sample, adding 50mL of copper sulfate aqueous solution, placing in a rotary blending instrument, rotating for 6h (the rotating speed is 50 rpm), quickly freezing for 20s by using liquid nitrogen, then placing in a refrigerator with the temperature of-20 ℃ for freezing for 2.5h, and carrying out vacuum freeze drying for 40h to obtain a paramagnetic doped starch sample to be detected;
and characterizing the paramagnetic doped starch sample to be detected by utilizing a magic angle rotating solid nuclear magnetic resonance technology (the characterization conditions are the same as those in example 1), so as to obtain the ordered structure of the starch to be detected.
Comparative examples 1 to 3
The method is different from the embodiments 1 to 3 only in that three kinds of starch are not doped, and the specific steps are as follows: directly balancing the moisture of the starch to be measured, loading the starch to be measured into a 4 mm zirconium oxide rotor, and measuring a sample 1 H and 13 c nuclear longitudinal relaxation time (T1), and using 13 Cross polarization of C and 13 c directly excites the magic angle rotation sequence to analyze the ordered structure (the rotating speed is 8 kHz).
The cycle waiting times (about 5T 1) of examples 1 to 3 and comparative examples 1 to 3 are shown in Table 1.
TABLE 1 13 C cross-polarized and 13 c direct excitation mode, circulation waiting time change of starch to be measured before and after paramagnetic doping
| Varieties of starch | Cross polarization of ( 1 H) | After paramagnetic doping | Direct excitation of 13 C) | After paramagnetic doping |
| Corn starch | 5 seconds | 1 second | 50 seconds | 5 seconds |
| Rice starch | 5 seconds | 2 |
80 seconds | 10 seconds |
| Potato starch | 3 seconds | 1 second | 100 seconds | 20 seconds |
According to the embodiment and the comparative example, the invention provides the method for detecting the starch ordered structure by using the solid nuclear magnetic resonance technology based on paramagnetic doping, and the method can reduce the relaxation time of the starch sample, further greatly shorten the spectrogram acquisition time and more directly, quickly and quantitatively obtain the starch sample ordered structure information.
The foregoing is only a preferred embodiment of the present invention, and it should be noted that, for those skilled in the art, various modifications and decorations can be made without departing from the principle of the present invention, and these modifications and decorations should also be regarded as the protection scope of the present invention.
Claims (7)
1. A method for detecting the ordered structure of starch by utilizing a solid nuclear magnetic resonance technology based on paramagnetic doping comprises the following steps:
mixing a paramagnetic copper salt aqueous solution with starch to be detected to obtain a starch dispersion liquid; the paramagnetic copper salt in the paramagnetic copper salt aqueous solution is copper sulfate or copper chloride;
carrying out vacuum freeze drying on the starch dispersion liquid to obtain a paramagnetic doped starch sample to be detected;
by using 13 C cross-polarized or 13 And C, directly exciting a magic angle rotating solid nuclear magnetic resonance technology to characterize the paramagnetic doped starch sample to be detected, so as to obtain the ordered structure of the starch to be detected.
2. The method of claim 1, wherein the starch to be tested comprises rice starch, corn starch, or potato starch.
3. The method according to claim 1, wherein the concentration of copper ions in the aqueous solution of a paramagnetic copper salt is 10mmol/L; the dosage ratio of the starch to be detected to the paramagnetic copper salt aqueous solution is 1g (10-50) mL.
4. The method according to claim 1, wherein the time for vacuum freeze drying is 24 to 72h.
5. The method of claim 1, further comprising, prior to said vacuum freeze-drying, flash freezing said starch dispersion with liquid nitrogen.
6. The method as claimed in claim 5, wherein the time for quick freezing is from about 2s to about 2min.
7. The method according to claim 1, wherein the mixing is carried out in a rotary mixer for 2 to 5 hours.
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| CN108779364A (en) * | 2016-03-30 | 2018-11-09 | 埃卡特有限公司 | The effect pigment coated with organic bond for powder painting and the method for effect pigment and application thereof for producing the coating |
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| CN102077108A (en) * | 2008-04-28 | 2011-05-25 | 康奈尔大学 | Tool for accurate quantification in molecular mri |
| CN108779364A (en) * | 2016-03-30 | 2018-11-09 | 埃卡特有限公司 | The effect pigment coated with organic bond for powder painting and the method for effect pigment and application thereof for producing the coating |
| CN105884913A (en) * | 2016-06-02 | 2016-08-24 | 大连理工大学 | Method for preparing trimethyl silica-based starch ether |
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