CN109374667B - Nuclear magnetic resonance spectrum method for identifying ultra-high temperature sterilized milk and reconstituted milk - Google Patents
Nuclear magnetic resonance spectrum method for identifying ultra-high temperature sterilized milk and reconstituted milk Download PDFInfo
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Abstract
The invention provides a nuclear magnetic resonance spectrum method for identifying ultra-high temperature sterilized milk and reconstituted milk, which comprises the following steps: 1) respectively detecting milk samples of reconstituted milk and ultra-high temperature sterilized milk prepared from whole milk powder by a nuclear magnetic resonance spectroscopy method, and integrating peak areas of chemical shift positions; 2) performing principal component analysis on the relative integral result, establishing an analysis model of partial least square variance, and determining a characterization factor capable of completely classifying the two types of milk; 3) and constructing a partial least square variance discriminant analysis model for distinguishing the ultra-high temperature sterilized milk from the reconstituted milk based on the determined characterization factors. The identification method provided by the invention adopts a nuclear magnetic resonance spectrometer for determination, the pretreatment method is simple and easy to operate, the types and the contents of substances in two kinds of milk can be comprehensively analyzed, the online automatic detection of the sample is realized, and the detection efficiency of the sample is greatly improved. The identification model established by the invention has strong feasibility and high accuracy, and provides a convenient and practical technical support for the authenticity identification of dairy products in the future.
Description
Technical Field
The invention belongs to the field of food inspection, and particularly relates to a detection and discrimination method of a dairy product.
Background
The liquid milk is very popular with consumers due to the unique taste and rich nutritive value. With the improvement of consumption level, the demand of liquid milk is continuously increased, so that the supply of milk and goat milk serving as raw materials is insufficient, and in order to reduce cost, many enterprises blend and recover the milk by using milk powder in the production process without marking, so that the nutritional value of the body milk is greatly reduced, and the legal rights and interests of consumers are seriously violated. Common commercial liquid milk mainly comprises ultra-high temperature sterilized milk and pasteurized milk, and the phenomenon that milk powder is mixed in the ultra-high temperature sterilized milk is particularly prominent. The temperature adopted in the processing process of the ultra-high temperature sterilized milk is 138-145 ℃ for 2-5s, and the processing of the milk powder needs ultra-high temperature instant sterilization and spray drying, so the loss of the nutritional value is large. The existing methods for detecting reconstituted milk mainly focus on certain specific target substances, such as furosine, lactulose and heat-denatured protein, and the methods are complex and long in time consumption in pretreatment and are easy to cause false positive. Therefore, the method has great significance for ensuring the rights and health of consumers, eliminating consumption panic, more accurately and efficiently distinguishing reconstituted milk and establishing a detection method for distinguishing ultra-high temperature sterilization and reconstituted milk.
The nuclear magnetic resonance spectrum technology plays an important role in food component safety detection, the pretreatment of the technology is simple, and all metabolites in the liquid milk can be comprehensively and nondestructively analyzed. The method is combined with a chemometrics method, the characterization factors of the ultra-high temperature sterilized milk and the reconstituted milk are found out, and the reconstituted milk and the ultra-high temperature sterilized milk discrimination models with strong feasibility and high accuracy are established, so that a powerful technical support can be provided for the authenticity discrimination of the dairy product in the future.
Disclosure of Invention
Aiming at the problem that reconstituted milk appears in the market as ultra-high temperature sterilized milk, the invention aims to provide a nuclear magnetic resonance spectrum method for identifying the ultra-high temperature sterilized milk and the reconstituted milk, establish a convenient, sensitive and accurate detection method and a discrimination model and realize the rapid automatic determination of the discrimination of the ultra-high temperature sterilized milk and the reconstituted milk.
The technical scheme for realizing the aim of the invention is as follows:
a nuclear magnetic resonance spectrum method for distinguishing ultra-high temperature sterilized milk and reconstituted milk comprises the following steps:
1) respectively detecting milk samples of reconstituted milk and ultra-high temperature sterilized milk prepared from whole milk powder by a nuclear magnetic resonance spectroscopy method, and integrating peak areas of chemical shift positions;
2) performing principal component analysis on the relative integral result, establishing an analysis model of partial least square variance, and determining a characterization factor capable of completely classifying the two types of milk;
3) constructing a partial least square variance discriminant analysis model for distinguishing the ultra-high temperature sterilized milk from the reconstituted milk based on the characterization factors determined in the step 2).
Wherein the reconstituted milk is prepared by dissolving whole milk powder in water according to the concentration of 3.0g/100mL of protein content.
Further, in step 1), the milk sample is pretreated, which comprises: centrifuging the emulsion sample, taking the lower layer liquid, dissolving in acetonitrile, centrifuging to separate the upper layer solution, and dissolving in TSP (3- (trimethylsilyl) sodium deuteropropionate) solution after concentration.
Preferably, the TSP solution is prepared by dissolving TSP in D at a concentration of 1-10 mmol/L2A solution of O.
In the step 1), a nuclear magnetic resonance spectrometer is used for carrying out non-targeted metabonomics analysis on the milk sample, TSP is used as an internal standard substance, and the detection temperature is 290-300K.
In step 1), the peak area at δ of 0.00ppm is defined as a reference (for example, the peak area at that position is defined as 100), and the peak areas at the respective chemical shifts are relatively integrated.
Further, in step 2), the characterization factors that can completely classify two kinds of milk are determined as peaks at chemical shifts δ of 4.30,4.56,2.41,1.93,4.59ppm by the analysis model of partial least squares variance.
The characterization factors were l-carnitine, succinate and acetate and 2 substances at δ ═ 4.30, 4.59, as determined by analysis.
After the characterization factor is determined in the step 2), the significance of the variance of the characterization factor is analyzed by using a one-way ANOVA method.
In step 3), the partial least square variance discriminant analysis model is displayed by a two-dimensional graph, if the relative integral value of the peak area of the milk sample falls within the numerical range of the reconstituted milk, the milk sample is determined as the reconstituted milk, and if the relative integral value of the peak area of the milk sample falls outside the numerical range of the reconstituted milk, the milk sample is determined as the ultra-high temperature sterilized milk.
Further, the method of nuclear magnetic resonance spectroscopy further comprises the operations of: detecting an unknown milk sample by using a nuclear magnetic resonance spectroscopy method, and substituting the relative integral value of the peak area of the unknown milk sample into the partial least square variance discriminant analysis model obtained in the step 3) for identification based on the characterization factor determined in the step 2).
The invention has the beneficial effects that:
the identification method provided by the invention adopts a nuclear magnetic resonance spectrometer for determination, has a simple pretreatment method and is easy to operate, and can comprehensively analyze the types and the contents of substances in two kinds of milk, thereby realizing the online automatic detection of the sample and greatly improving the detection efficiency of the sample.
The identification model established by the invention has strong feasibility and high accuracy, and provides convenient and practical technical support for the authenticity identification of dairy products in the future.
Drawings
FIG. 1 shows the chemical structural formula, wherein (a) is L-carnitine, (b) is succinate, and (c) is acetate.
FIG. 2 is a diagram showing the analysis of the main components of ultra-high temperature sterilized milk and reconstituted milk.
FIG. 3 is a two-dimensional plot of the partial least squares variance discriminant analysis of the ultra-high temperature sterilized milk and the reconstituted milk.
FIG. 4 is a one-dimensional NMR spectrum of UHT milk, with specific difference names indicated in the figure.
FIG. 5 is a one-dimensional NMR spectrum of reconstituted milk.
FIG. 6 is a two-dimensional diagram of principal component analysis of five characterization factors in ultra-high temperature sterilized milk and reconstituted milk.
FIG. 7 is a partial least squares variance discriminant analysis model of five characterization factors in the ultra-high temperature sterilized milk and the reconstituted milk, wherein the hollow dots are the ultra-high temperature sterilized milk and the solid dots are the reconstituted milk.
Detailed Description
The following detailed description of embodiments of the present invention is provided in connection with the accompanying drawings and examples. It will be understood by those skilled in the art that the scope of the present invention is not limited to the specific embodiments, and various modifications and changes may be made without departing from the spirit of the present invention.
The means employed in the detailed description are, unless otherwise specified, all technical means which are conventional in the art.
Example 1 pretreatment of samples
10 brands of ultra-high temperature sterilized milk and 10 brands of whole milk powder (milk powder) were purchased from each supermarket in Beijing.
The preparation method of the reconstituted milk comprises the following steps: adding milk powder into ultrapure water according to the protein content of 3.0g in 100mL of cow milk, then keeping the temperature to 40 ℃ in a water bath kettle, and homogenizing by hand shaking to obtain the milk sample of the reconstituted milk.
Respectively taking 2mL of the milk samples of the ultra-high temperature sterilized milk and the reconstituted milk, and centrifuging at 8000rpm for 30 min; separating the lower layer solution, taking 1mL, adding 2mL acetonitrile, and vortexing for 5 min; centrifuging at 10000rpm for 10min, separating the upper layer solution, and blowing 2mL with nitrogen. With 1mL of D containing 3mmol/L of TSP2And (3) O redissolving, taking 600 mu L of the solution in a nuclear magnetic tube for further detection, and repeating the experiment for 3 times for each sample.
Example 2 integral area analysis of each characterization factor in two milks:
a pair of milk samples prepared in example 1 were taken and examined by nuclear magnetic resonance:
the model of a nuclear magnetic resonance instrument used for the experiment is Bruker Advance III 400MHz, and the detection temperature is 298K. Detecting and analyzing the sample by using a 1H NMR nuclear magnetic resonance technology, wherein the detection parameters are set as follows:
number of data points, 64K; spectral width, 8223.7 Hz; relaxation time, 2 s; number of scans, 8; acquisition time, 4 s. The obtained maps were shown in FIGS. 4 and 5.
Relative integration of peak area for each characterization factor in different types of milk:
phase adjustment and baseline correction of the spectra were performed using nuclear magnetic resonance spectroscopy software version Topspin 2.1. The peak area at δ of 0.00ppm was defined as 100 using 3mM TSP as an internal standard, and the peak areas at each chemical shift in the two milk samples were relatively integrated.
Calculating relative integral of peak areas at each chemical shift position in the images of 4 and 5, and performing principal component analysis on the ultra-high temperature sterilized milk and the reconstituted milk according to the result of the relative integral area, wherein the result shows that after three principal components are extracted, two kinds of milk can be completely separated, and the variance cumulative contribution rate of the three principal components reaches 96% (the principal component analysis is shown in figure 2 and is obtained by using software Simca-P); a relative integral analysis model of the ultra-high temperature sterilized milk and the reconstituted milk is established by a partial least square variance discrimination method, and the obtained two-dimensional model is shown in figure 3. By this model, peaks at δ of 4.30,4.56,2.41,1.93,4.59ppm were determined as characterizing factors for distinguishing two milks, and the significance of variance of each characterizing factor was analyzed by the one-way anova method, and the results are shown in table 1.
TABLE 1 One-way ANOVA analysis results
***Represents P<0.001; the b P value was calculated by the software SPSS version 21.0; UM stands for ultra-high temperature sterilized milk; RM stands for reconstituted milk.
The peaks at the five chemical shifts were qualitatively analyzed in combination with the reference and nuclear magnetic database, and the qualitative results are shown in table 2. The structural formulas of three substances are shown in figure 1.
TABLE 2 qualitative analysis results of characterization factors
Establishing a discrimination model:
principal component analysis of the other samples was performed based on the relative integral data for each characterization factor in the two types of milk samples, see fig. 6. The variance cumulative contribution rate of the first three main components reaches 96%, and the ultra-high temperature sterilized milk and the reconstituted milk can be separated by the first two main components. Like fig. 2 and 3, the ultra-high temperature sterilized milk and the reconstituted milk can be completely distinguished, and the two-dimensional graph is more visual.
And (3) establishing a discriminant analysis model of the ultra-high temperature sterilized milk and the reconstituted milk by using a partial least square variance discriminant analysis method, and displaying by a two-dimensional graph, wherein if the relative integral value of the peak area of the milk sample falls within the numerical range of the reconstituted milk, the milk sample is judged as the reconstituted milk, and if the relative integral value of the peak area of the milk sample falls outside the numerical range of the reconstituted milk, the milk sample is judged as the ultra-high temperature sterilized milk.
Discrimination is performed using this model, see fig. 7. Falling on the left hollow round point is the ultra-high temperature sterilized milk, and falling on the right solid round point is the reconstituted milk. In the study, 20 kinds of milk in the market were verified with an accuracy of 100%.
Example 3
The unknown milk samples were examined by nmr spectroscopy with the same parameters as in example 2.
The peak areas at δ 4.30,4.56,2.41,1.93,4.59ppm were relatively integrated, and the integrated values were determined using this model. If the relative integral value of the peak area of the unknown milk sample falls within the numerical range of the reconstituted milk, the unknown milk sample is judged as the reconstituted milk, and if the relative integral value of the area falls outside the numerical range of the reconstituted milk, the unknown milk sample is judged as the ultra-high temperature sterilized milk.
The above examples are only for describing the preferred embodiments of the present invention, and are not intended to limit the scope of the present invention, and various modifications and improvements made to the technical solution of the present invention by those skilled in the art without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.
Claims (6)
1. A nuclear magnetic resonance spectrum method for distinguishing ultra-high temperature sterilized milk and reconstituted milk is characterized by comprising the following steps:
1) respectively detecting milk samples of reconstituted milk and ultra-high temperature sterilized milk prepared from whole milk powder by a nuclear magnetic resonance spectroscopy method, and integrating peak areas of chemical shift positions;
2) performing principal component analysis on the relative integral result, establishing an analysis model of partial least square variance, and determining a characterization factor capable of completely classifying the two types of milk;
3) constructing a partial least square variance discriminant analysis model for distinguishing the ultra-high temperature sterilized milk from the reconstituted milk based on the characterization factors determined in the step 2);
4) detecting an unknown milk sample by using a nuclear magnetic resonance spectroscopy method, and substituting the relative integral value of the peak area of the unknown milk sample into the partial least square variance discriminant analysis model obtained in the step 3) for identification based on the characterization factor determined in the step 2);
in step 1), the pretreatment of the milk sample comprises: centrifuging the emulsion sample, taking the lower layer liquid to dissolve in acetonitrile, centrifuging to separate out the upper layer solution, and dissolving in a solution containing TSP (3- (trimethylsilyl) deuterated sodium propionate) after concentration;
in step 2), determining the characterization factors capable of completely classifying the two milks as peaks at chemical shifts δ =4.30, 4.56,2.41,1.93 and 4.59ppm through the analysis model of partial least squares variance;
the reconstituted milk is prepared by dissolving whole milk powder in water according to the concentration of 3.0g/100mL of protein content.
2. The method for nuclear magnetic resonance spectroscopy according to claim 1, wherein the solution of TSP is TSP dissolved in D at a concentration of 1 to 10mmol/L2A solution of O.
3. The nuclear magnetic resonance spectroscopy method according to claim 1, wherein in step 1), the non-targeted metabonomics analysis is performed on the milk sample by using a nuclear magnetic resonance spectrometer, TSP is used as an internal standard, and the detection temperature is 290-300K.
4. The method for nuclear magnetic resonance spectroscopy according to claim 1, wherein in step 1), the peak area at δ =0.00 ppm is defined as a reference, and the peak areas at the respective chemical shifts are relatively integrated.
5. The method for nuclear magnetic resonance spectroscopy according to claim 1, wherein in step 2), after the characterization factor is determined, the significance of the variance of the characterization factor is analyzed by a one-way ANOVA method.
6. The nuclear magnetic resonance spectroscopy method according to any one of claims 1 to 5, wherein in step 3), the partial least squares variance analysis model is displayed as a two-dimensional graph, and the milk sample is determined as the reconstituted milk if the relative integral value of the peak area of the milk sample falls within the numerical range of the reconstituted milk, and is determined as the ultra-high temperature sterilized milk if the relative integral value of the peak area of the milk sample falls outside the numerical range of the reconstituted milk.
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| CN105334272A (en) * | 2015-11-17 | 2016-02-17 | 中国农业科学院北京畜牧兽医研究所 | Method for identifying reconstituted milk in UHT (Ultra High Temperature) sterilized milk |
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| CN105334272A (en) * | 2015-11-17 | 2016-02-17 | 中国农业科学院北京畜牧兽医研究所 | Method for identifying reconstituted milk in UHT (Ultra High Temperature) sterilized milk |
| CN107703173A (en) * | 2017-06-23 | 2018-02-16 | 孟扬 | A kind of identification apparatus and method of the rare species timber based on 1H NMR datas storehouse |
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