CN104655666A - Low field nuclear magnetic resonance detection method of edible gelatin quality - Google Patents

Abstract

The invention discloses a low-field nuclear magnetic resonance detection method for the quality of edible gelatin. The method comprises the following steps: a. Dissolving edible gelatin and industrial gelatin in distilled water according to the ratio of the mass volume concentration of water to 25%; Low-field nuclear magnetic resonance detection, thereby obtaining the low-field nuclear magnetic resonance relaxation spectrum information of pure gelatin; preparing a series of edible gelatin adulterated samples mixed with different mass fractions of industrial gelatin, and performing low-field nuclear magnetic resonance detection to obtain each adulterated sample The low-field NMR relaxation spectrum information of the edible gelatin low-field NMR relaxation spectrum information is established; b, the gelatin sample to be tested is subjected to low-field NMR detection, and the obtained relaxation spectrum information is compared with the edible gelatin low-field The relaxation spectrum information in the NMR relaxation spectrum database is analyzed and compared to determine whether the edible gelatin to be tested is mixed with industrial gelatin. The method has the advantages of high measurement accuracy, good repeatability, good stability, short time consumption and the like.

Description

Low-field NMR detection method for the quality of edible gelatin

technical field

The invention relates to a method for detecting food additives, in particular to a method for using low-field nuclear magnetic resonance spectrum information to identify edible gelatin and industrial gelatin, and to detect the adulterated amount of industrial gelatin in edible gelatin.

Background technique

Edible gelatin is a hydrolyzed product of collagen, fat-free and high-protein, and is a legal food additive stipulated by the state. It is widely used in various food industries as gelling agent, stabilizer, thickener, etc. Industrial gelatin is the gelatin extracted from waste leather after tanning in the tanning industry or scraps cut from tanned leather. It is inevitably mixed with impurities such as heavy metals and chemicals, which are potentially harmful to human health.

The exposure of the "poisonous capsule" incident and the "leather shoe yogurt" incident in 2012 shows that industrial gelatin has flowed to the pharmaceutical industry and the food industry. At present, the detection of leather hydrolyzate has been included in the second batch of "List of Non-edible Substances and Food Additives That May Be Illegally Added in Food" by the Ministry of Health, and the detection of whether it contains any of them can be used as a check to determine whether it is mixed with industrial gelatin. basis, but the column for the detection method of industrial gelatin is displayed as "none".

In fact, at present, the quality of edible gelatin is generally judged by detecting the content of heavy metal chromium in gelatin. Common methods include atomic absorption spectroscopy, chemiluminescence, electrochemical methods, chromatography and mass spectrometry. However, there are more or less problems in these methods. For example, the commonly used atomic absorption spectrometry requires the gelatin sample to be pretreated by high temperature ashing or microwave digestion, and the pretreatment time generally needs more than two hours; and the patent No. is CN102841090A The method for detecting the hexavalent chromium content in gelatin proposed in the paper needs to extract the hexavalent chromium in the sample in an acidic environment, then decolorize, and finally detect the hexavalent chromium content by ultraviolet spectrophotometry. These methods need to use a large amount of chemical reagents, and the operation is cumbersome and time-consuming. In addition, it is difficult to identify whether industrial gelatin is added to the capsules only by measuring the chromium content. Therefore, it is particularly important to find a fast and effective detection method for the identification of edible/industrial gelatin for the quality control of gelatin.

Low-field nuclear magnetic resonance (LF-NMR) is a new type of nondestructive testing technology, mainly through the longitudinal relaxation time (T ₁ ), transverse relaxation time (T ₂ ), diffusion coefficient and CPMG (Carr-Purce1l -Meiboom-Gill) echo data analysis, qualitative and quantitative analysis of substances, with fast, accurate, non-destructive characteristics, has played a role in the analysis and research of many fields in the food industry, but there is no application of low-field nuclear magnetic resonance technology for gelatin Quality identification reports.

In summary, it is of great significance to explore low-field NMR technology in the research of gelatin quality identification.

Contents of the invention

The object of the present invention is to provide a detection method for identifying the quality of edible gelatin by utilizing the information of the relaxation spectra of low-field nuclear magnetic resonance.

In order to achieve the above object, the present invention adopts the following technical solutions: a low-field nuclear magnetic resonance detection method of edible gelatin quality, mainly comprising the following steps:

(1) Establishment of information database of low-field NMR relaxation spectrum of edible gelatin

The pure edible gelatin and the pure industrial gelatin are respectively dissolved in water, prepared into a solution with a mass volume concentration of 25%, and the low-field nuclear magnetic resonance relaxation spectrum information of the pure edible gelatin and the pure industrial gelatin is obtained through low-field nuclear magnetic resonance detection; Industrial gelatin is mixed with edible gelatin, prepared into a series of standard adulterated gelatin samples mixed with industrial gelatin with different mass percentages, the standard adulterated gelatin samples were dissolved in water respectively, and prepared into a solution with a mass volume concentration of 25%, respectively. Field nuclear magnetic resonance detection, obtain the low-field nuclear magnetic resonance relaxation spectrum information of each standard adulterated gelatin sample, and establish a low-field nuclear magnetic resonance relaxation spectrum information database of edible gelatin quality;

(2) Detection of edible gelatin samples to be tested

The edible gelatin sample to be tested is dissolved in water, and the gelatin solution with a mass volume concentration of 25% is prepared, and the low-field nuclear magnetic resonance relaxation spectrum information of the edible gelatin to be tested is obtained through low-field nuclear magnetic resonance detection; it is compared with the quality of the edible gelatin Analyze and compare the spectral information in the low-field nuclear magnetic resonance relaxation spectral information database to determine whether the edible gelatin to be tested is adulterated gelatin, and if it is adulterated gelatin, further determine the adulterated mass percentage of the adulterated gelatin.

In the series of standard adulterated gelatin samples mixed with different mass percentages of industrial gelatin, the mass percentages of adulterated industrial gelatin are 1-9% and 10-90%, within the range of 1-9%, the percentage content gradient It is 1%, and in the range of 10-90%, the percentage content gradient is 10%.

The low-field NMR relaxation spectrum information includes the start time T ₂₁ of the first peak, the start time T ₂₂ of the second peak, the start time T ₂₃ of the third peak, and the peak area percentage S ₂₁ of the first peak , the peak area percentage S ₂₂ of the second peak, the peak area percentage S ₂₃ of the third peak, and the single-component relaxation time T _2W .

The low-field nuclear magnetic resonance detection method of edible gelatin quality of the present invention has following advantages and characteristics:

1. The identification speed is fast and the identification result is accurate;

2. Good repeatability and stability;

3. The minimum detection limit of the method for industrial gelatin adulteration in edible gelatin is 1%.

Description of drawings

Fig. 1 is the multi-component relaxation spectrum of edible gelatin, industrial gelatin, gelatin to be measured;

Fig. 2 is the multicomponent relaxation spectrum of adulterated known industrial gelatin (0%-100%);

Fig. 3 is the T of adulteration known industrial gelatin (0%-100%) sample The change situation of _{the peak} start time along with adulterant amount;

Fig. 4 is the S ₂₂ ratio of adulteration known industrial gelatin (0%-100%) sample with the variation situation of adulteration amount;

Fig. 5 is the T of adulteration known industrial gelatin (0%-100%) sample The change situation of _peak start time along with adulterant amount;

Fig. 6 is the S ₂₃ ratio of the adulterated known industrial gelatin (0%-100%) sample with the variation of adulterated amount;

Fig. 7 is the multicomponent relaxation spectrum of adulterated industrial gelatin (0%-9%) sample;

The single-component relaxation spectrum of Fig. 8 adulterated industrial gelatin (0%-100%) sample;

Fig. 9 is the variation situation of the T _2W of adulterated industrial gelatin (0%-100%) sample with the amount of adulterant;

Fig. 10 is the one-component relaxation spectrum of adulterated industrial gelatin (0%-9%) sample;

Detailed ways

(1) Preparation of gelatin solution

Weigh a certain quality of pure edible gelatin in a beaker, add a certain volume of distilled water, wherein the mass volume concentration of edible gelatin and distilled water is 25%, and make the edible gelatin swell in distilled water for 2 hours. Place the beaker in a constant temperature water bath at 65°C for 15 minutes, and stir during the water bath to ensure that the gelatin is completely dissolved. The preparation method of other gelatin solutions is the same as the preparation method of this edible gelatin solution. According to 1%-9% and 10%-90% adulterated mass fractions, the industrial gelatin is mixed into various edible gelatins respectively, and the preparation method of the adulterated sample solution is the same as that of the pure edible gelatin solution.

(2) Establishment of a database for the relaxation information of edible gelatin in low-field NMR

Take 3ml of the gelatin solution prepared in (1) and transfer it into the nuclear magnetic resonance test tube. First, keep the temperature in a constant temperature water bath at 32°C for 10 minutes, then place it in the nuclear magnetic probe to stabilize for 1 minute, and then take samples. After sampling, place the sample again at 32°C for 5 minutes. , for the next sampling, each sample was measured three times. The measured spectrum information includes the start time T ₂₁ of the first peak, the start time T ₂₂ of the second peak, the start time T ₂₃ of the third peak, the peak area percentage S ₂₁ of the first peak, the Peak area percentage S ₂₂ , peak area percentage S ₂₃ of the third peak, and one-component relaxation time T _2W . Correlation was established between these spectral information and the quality of edible gelatin, and a database of low-field NMR relaxation information of edible gelatin was established.

①Multi-component relaxation spectrum (T ₂ , ms)

In the multi-component relaxation spectrum, the peaks were named as T ₂₁ peak, T ₂₂ peak and T ₂₃ peak in order of appearance. Known from Figure 1, the relaxation spectra of edible gelatin and industrial gelatin are significantly different: under the condition that the mass volume concentration is 25%, edible gelatin has three peaks, industrial gelatin has two peaks, and the T ₂₂ peak of industrial gelatin The relaxation times of T _{23 and} T 23 peaks are shorter than those of edible gelatin T ₂₂ and T ₂₃ peaks. This may be because the raw material of industrial gelatin-leather waste contains tanning agents, which are used for tanning raw hides. The tanning effect is cross-linking and suturing, that is, new intermolecular bonds are formed in the collagen structure, making the physical properties of collagen The chemical properties change, and the process of making gelatin is to destroy the covalent crosslinks and non-covalent bonds between and within the stable collagen fibers through appropriate treatment methods, release the original collagen molecules, and then stabilize the collagen helix by heating The hydrogen bonds of the gelatin are also broken to release the gelatin. The tanning agent and other impurities contained in industrial gelatin may cause the protein structure in it to be different from that in edible gelatin, which will cause the chemical environment of the peak in industrial gelatin to change to a certain extent, and finally lead to the peak of industrial gelatin. Different peaks from edible gelatin. The relaxation spectra of the two gelatin samples to be measured are significantly different from those of edible gelatin and industrial gelatin: there is a T ₂₁ peak, and the relaxation time of the T ₂₃ peak is shorter than that of the T ₂₃ peak of edible gelatin. But the relaxation time of T ₂₃ peak is longer than that of industrial gelatin.

The multicomponent relaxation spectrum of industrial gelatin adulterated edible gelatin is shown in Figure 2, and each peak is named as T ₂₁ peak, T ₂₂ peak and T ₂₃ peak respectively according to the order of appearance, and the corresponding peak area percentage (the area of this peak The percentage of the entire map area) is expressed as S ₂₁ percent, S ₂₂ percent and S ₂₃ percent. As can be seen from Figure 2, when the adulterated amount is 40%, the _T21 peak of the sample disappears; with the increase of the adulterated mass fraction, the _T23 peak of the adulterated sample deviates from the _T23 peak of edible gelatin, which is towards industrial The T ₂₃ peaks of gelatin are close together.

In order to further analyze the change law of LF-NMR signals of samples with different amounts of adulteration, the T ₂₂ , T ₂₃ peak onset time, T ₂₂ , T ₂₃ peak area accounted for the percentage of the entire T ₂ spectrum area with the industrial gelatin adulterated quality The changes of scores are listed in Figure 3, Figure 4, Figure 5, and Figure 6, respectively.

Known from Fig. 3 to Fig. 6, T ₂₂ peak starting time has no obvious regular change with the change of adulterated mass fraction, and the peak area percentage S ₂₂ percentage of T ₂₂ peak decreases with the increase of adulterated mass fraction; T The onset time of peak ₂₃ decreases with the increase of adulterated mass fraction, and has a good binomial function relationship (R ² >0.90); the peak area percentage of T ₂₃ peak S ₂₃ percentage increases Large and increasing, and a good linear relationship (R ² >0.90).

The industrial gelatin was mixed with other edible gelatins, and the low-field nuclear magnetic resonance detection also obtained similar results and rules, especially the rule that the onset time of the T ₂₃ peak shortened with the increase of the adulterated mass fraction. Known from Fig. 1, the T ₂₃ peak start time of industrial gelatin is shorter than the T ₂₃ peak start time of edible gelatin, this is because the impurity that does not have in edible gelatin such as chromium in industrial gelatin makes the T ₂₃ peak corresponding in industrial gelatin The binding force of the hydrogen protons in the edible gelatin is greater than that of the hydrogen protons corresponding to the T ₂₃ peak in the edible gelatin. When the industrial gelatin is mixed into the edible gelatin, the chemical environment of the hydrogen protons in the original edible gelatin is changed. As the mass fraction of doping increases, the binding force of hydrogen protons in the sample increases, and then the T ₂₃ peak onset time of the sample decreases with the increase of mass fraction of doping.

Utilize the T ₂₃ peak start time to explore the detection limit of industrial gelatin adulterated edible gelatin, as shown in Figure 7, when the adulterated mass fraction is 1%, the T ₂₃ peak start time of the adulterated sample is different from the T of edible gelatin ₂₃ peak onset times were significantly different, so the lowest detection limit was 1%.

②One-component relaxation spectrum (T _2W , ms)

Taking the gelatin sample as an integral component for inversion, the single-component relaxation spectra of samples with different doping amounts can be obtained, as shown in Figure 8.

It can be seen from Figure 8 that with the increase of adulterated mass fraction, the one-component relaxation time (T _2w ) of gelatin samples gradually decreases, and the relationship between the T _2W value of gelatin samples and the adulterated mass fraction is shown in Figure 9 .

Figure 9 shows that the T _2W value of gelatin samples shortens with the increase of doping mass fraction, and there is a good binomial function relationship between them (R ² >0.90). This is due to the incorporation of industrial gelatin into edible gelatin, which changes the chemical environment of the hydrogen protons in the sample, and increases the binding force of the hydrogen protons, which eventually makes the T _2W detected by LF-NMR reflect the overall characteristics of the sample. The relaxation properties are also changed.

Use the single-component relaxation time (T _2w ) to explore the detection limit of industrial gelatin adulterated edible gelatin, as shown in Figure 10, when the adulterated mass fraction is 1%, the T _2w of the adulterated sample and the T of edible gelatin _2w is significantly different, so the lowest detection limit is 1%.

The research results show that the types of edible gelatin and industrial gelatin can be continuously expanded, the database of low-field NMR relaxation spectra of gelatin can be improved, and the edible gelatin without quality assurance in the market can be identified and tested.

Claims (3)

1. a low-field nuclear magnetic resonance detection method for edible gelatin quality, is characterized in that, mainly comprise the following steps:

(1) foundation of the low-field nuclear magnetic resonance relaxation diagram spectrum information database of edible gelatin quality

Pure edible gelatin and pure industrial gelatine are dissolved in water respectively, are mixed with the solution that mass body volume concentrations is 25%, detect through low-field nuclear magnetic resonance, obtain the low-field nuclear magnetic resonance relaxation diagram spectrum information of pure edible gelatin and pure industrial gelatine; Industrial gelatine is mixed edible gelatin, be mixed with a series of standard being mixed with the industrial gelatine of different quality percentage and mix pseudo-gelatin sample, standard is mixed pseudo-gelatin sample and be dissolved in water respectively, be mixed with the solution that mass body volume concentrations is 25%, carry out low-field nuclear magnetic resonance detection respectively, obtain the low-field nuclear magnetic resonance relaxation diagram spectrum information that each standard mixes pseudo-gelatin sample, set up the low-field nuclear magnetic resonance relaxation diagram spectrum information database of edible gelatin quality;

(2) detection of edible gelatin quality to be measured

By water-soluble for edible gelatin sample to be measured, be mixed with the gelatin solution that mass body volume concentrations is 25%, detect the low-field nuclear magnetic resonance relaxation diagram spectrum information obtaining edible gelatin to be measured through low-field nuclear magnetic resonance; Profile information in the low-field nuclear magnetic resonance relaxation diagram spectrum information database of itself and edible gelatin quality being carried out com-parison and analysis, determining that whether edible gelatin to be measured is for mixing pseudo-gelatin, mixes pseudo-gelatin in this way, then that determines to mix pseudo-gelatin further mixes pseudo-mass percentage.

2. the low-field nuclear magnetic resonance detection method of edible gelatin quality according to claim 1, it is characterized in that: described a series of standard being mixed with the industrial gelatine of different quality percentage is mixed in pseudo-gelatin sample, the mass percent mixing pseudo-industrial gelatine is 1-9% and 10-90%, within the scope of 1-9%, percentage composition gradient is 1%, within the scope of 10-90%, percentage composition gradient is 10%.

3. the low-field nuclear magnetic resonance detection method of edible gelatin quality according to claim 1, is characterized in that: described low-field nuclear magnetic resonance relaxation diagram spectrum information comprises the initial time T of first peak ₂₁, the second peak initial time T ₂₂, the 3rd peak initial time T ₂₃, first peak peak area percent S ₂₁, the second peak peak area percent S ₂₂, the 3rd peak peak area percent S ₂₃and single component relaxation time T _2W.