阅读说明：本技术 一种基于顺磁掺杂的利用固体核磁共振技术检测淀粉有序结构的方法 (Method for detecting ordered structure of starch by using solid nuclear magnetic resonance technology based on paramagnetic doping ) 是由 吴迪 马红 汤晓智 于 2020-07-02 设计创作，主要内容包括：本发明涉及淀粉结构检测技术领域,尤其涉及一种基于顺磁掺杂的利用固体核磁共振技术检测淀粉有序结构的方法。本发明的方法包括以下步骤：将顺磁性铜盐水溶液与待测淀粉混合,得到淀粉分散液；将所述淀粉分散液进行真空冷冻干燥,得到顺磁掺杂的待测淀粉样品；利用<Sup>13</Sup>C交叉极化或<Sup>13</Sup>C直接激发魔角旋转固体核磁共振技术对所述顺磁掺杂的待测淀粉样品进行表征,得到待测淀粉的有序结构。采用本发明的方法可以降低淀粉样品的弛豫时间,进而大幅缩短谱图采集时间,更加直接、快速、定量地获取淀粉样品有序结构信息。(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.)

1. A method for detecting the ordered structure of starch by using 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;

carrying out vacuum freeze drying on the starch dispersion liquid to obtain a paramagnetic doped starch sample to be detected;

by using¹³C crossingCross-polarized or¹³And 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 of claim 1, wherein the paramagnetic copper salt in the aqueous solution of paramagnetic copper salt is copper sulfate or copper chloride.

4. A process according to claim 1 or 3, characterized in that the concentration of copper ions in the aqueous solution of a paramagnetic copper salt is 10 mmol/L; the dosage ratio of the starch to be detected to the paramagnetic copper salt aqueous solution is 1g (10-50) mL.

5. The method according to claim 1, wherein the vacuum freeze-drying time is 24-72 hours.

6. The method of claim 1, further comprising, prior to said vacuum freeze-drying, flash freezing said starch dispersion with liquid nitrogen.

7. The method as claimed in claim 6, wherein the time for quick freezing is 20 s-2 min.

8. The method according to claim 1, wherein the mixing is performed in a rotary homogenizer for a time of 2-5 hours.

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 using a solid nuclear magnetic resonance technology based on paramagnetic doping.

Background

An in-depth understanding of the ordered structure of starch is important for the physicochemical properties of starch as well as the processing and digestion characteristics of starch-based foods.

The current characterization means for the ordered structure of starch is very limited,methods commonly used in the past include 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; the Fourier transform infrared signal is not sensitive enough to short range order or crystallinity, so X-ray diffraction and diffraction are mainly used at present¹³C 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 ordered structure of starch-based material molecules. By using¹³C 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 time¹H is observed by¹H and¹³c cross polarization phenomenon realizes the pair¹³Indirect observation of the chemical environment of the C-nucleus. However, when the method is used for quantitatively analyzing the starch ordered structure proportion, the approximation of the polarization transfer efficiency of the carbon nuclei under 6 different chemical environments exists, and the real proportion of the 6 carbon nuclei cannot be completely and quantitatively represented; if adopted¹³C direct excitation sequence test of starch ordered structure proportion and starch medium¹³The relaxation time of the C nucleus is extremely long, resulting in¹³The 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 using¹³C cross-polarized or¹³And 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 10 mmol/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 of 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 using¹³C cross-polarized or¹³And 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 structure¹H and¹³the 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 reduce¹³C, 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 for¹³The 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 mode¹³C solid nuclear magnetic resonance 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 using¹³C cross-polarized or¹³And 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 a paramagnetic copper salt is preferably obtained by dissolving a 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 of the present invention further includes a corresponding hydrate thereof. In the present invention, the concentration of copper ions in the aqueous solution of the paramagnetic copper salt is preferably 10 mmol/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 2-5 h, and more preferably 2.5-4 h; the rotational speed of the mixing is preferably 50 rpm.

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 1.5 min. After the frozen sample is frozen, the frozen sample is preferably stored in a refrigerator at-20 ℃ for later use.

In the invention, the vacuum freeze-drying time is preferably 24-72 h, more preferably 30-70 h, and most preferably 40-60 h. The temperature of the vacuum freeze-drying is not particularly required in the invention, and the vacuum freeze-drying temperature well known in the field 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 utilizes¹³C cross-polarized or¹³And 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 right¹³The characterization processes of the C cross polarization magic angle rotating solid nuclear magnetic resonance technology and the 13C direct excitation magic angle rotating solid nuclear magnetic resonance technology have no special requirements, and adoptBy using characterization procedures and characterization conditions well known in the art, reference may be made specifically to (A Method for Estimating the Nature a and Relative properties of Amorphous, Single, and Double-reliable Components in Starch Granules by¹³C CP/MAS NMR, Tan et al, biomacromolecus 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 K₂CO₃After the supersaturated solution has balanced water content, the solution is loaded into a 4 mm zirconia rotor, and a sample is measured¹H and¹³c nuclear longitudinal relaxation time (T1), and use¹³Cross-polarization of C or¹³C directly excites the magic angle rotation sequence to analyze the ordered structure (the rotating speed is 8 kHz). Collecting amorphous patterns after starch gelatinization¹³And C spectrogram proportion is adjusted by taking the C4 peak at 84ppm as a reference point of '0', and then the difference spectrum of the starch to be detected and the amorphous sample is carried out to obtain a sample ordered structure spectrogram, wherein the C1 region in the ordered spectrogram can represent the double helix conformation of the sample. The proportion and the crystallinity between the helical ordered structures in the sample can be obtained quantitatively by calculating the peak area 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.