Method for identifying exothermic wheat based on gas phase ion mobility spectrometry

Abstract

The invention relates to the technical field of analysis and detection, in particular to a method for identifying exothermic wheat based on gas phase ion mobility spectrometry. The method comprises the following steps: obtaining volatile flavor substances of wheat which is not heated and dried after heating through a gas phase ion mobility spectrometry, determining the difference of the volatile flavor substances and key characteristic volatile flavor substances, and judging the difference between samples by combining a chemometrics method; identifying unheated wheat and heated dried wheat; the key characteristic volatile flavor substances of the non-fever wheat are n-propyl alcohol (M, D), nonanal, dipentene (M) and n-butyl alcohol (D); the key characteristic volatile flavor substances of the heated and dried wheat are 3-hydroxy-2-butanone (M), n-butyraldehyde (D), isoamyl alcohol (M, D) and isobutanol (M). The sample detected by the method does not need to be pretreated, so that interference of external solvents is avoided; compared with a traditional flavor detection method, the method has the advantages of high detection accuracy and lower cost.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of analytical detection technology, and particularly relates to a method for identifying heated wheat based on gas phase ion mobility spectrometry. BACKGROUND

[0002] During conventional storage, wheat is susceptible to the influence of moisture, temperature, environment and other comprehensive factors, and is prone to condensation, heating and even mold, which leads to changes in the quality or flavor of the wheat, reduces the utilization rate of the wheat, and causes storage losses. Wheat has a thin cortex and strong hygroscopicity. When the humidity in the environment increases, the wheat will use water for respiration and heating, and the wheat will sweat, which further promotes the growth and reproduction of microorganisms on the surface of the wheat. Some scholars have pointed out that microbial metabolic activity is the main cause of wheat heating, and the respiration intensity of microorganisms is much higher than that of wheat itself, which can use the nutrients in the wheat to grow and reproduce rapidly to produce more heat. The heating of wheat during storage will lead to a decrease in the content of soluble protein, thereby reducing the quality.

[0003] During storage, the most commonly used measure to prevent the continuous heating of wheat and ultimately lead to mold and waste is drying, which reduces the moisture content of the wheat and inhibits the respiration of the wheat itself and the growth of microorganisms. The appearance of the heated and dried wheat shows no signs of mold, but it is unknown whether the quality and flavor of the wheat are affected. Some studies have found that wheat heating and mold produce volatile substances such as hydrocarbons, aldehydes, alcohols, acids and esters, but there is little research on the volatile components of heated and dried wheat. For wine, the quality of the raw material determines the quality and flavor of the wine, and heating can lead to the consumption of nutrients for fermentation, which may not achieve the desired fermentation effect. Therefore, if a rapid and efficient method for distinguishing between unheated wheat and heated and dried wheat can be found, the quality of the wine can be improved, the efficiency of the wine-making process can be improved, and waste and losses can be reduced.

[0004] Currently, research on heated wheat mainly focuses on the changes in the microstructure and quality of wheat before and after heating, including changes in physical and chemical indicators, changes in germination rate and research on microbial communities. There is relatively little research on the identification technology of unheated wheat and heated and dried wheat based on volatile flavor substances. SUMMARY

[0005] In view of the above problems in the prior art, the present application aims to provide a method for identifying heated wheat based on gas chromatography-ion mobility spectrometry (GC-IMS). The volatile flavor substances of unheated and heated and dried wheat are obtained by GC-IMS, the differences and characteristic volatile flavor substances are determined, and the differences between samples are judged by combining chemometrics methods, so as to solve the problem of the research gap of heated wheat in the above background art, and provide a theoretical basis for identifying unheated and heated and dried wheat from the perspective of volatile flavor.

[0006] In order to achieve the above application purposes, the technical scheme adopted by the present application is as follows:

[0007] The present application provides a method for identifying heated wheat based on gas chromatography-ion mobility spectrometry, which comprises the following steps:

[0008] The volatile flavor substances of unheated and heated and dried wheat are obtained by gas chromatography-ion mobility spectrometry, the differences and characteristic volatile flavor substances are determined, and the differences between samples are judged by combining chemometrics methods, so as to identify unheated and heated and dried wheat.

[0009] The characteristic volatile flavor substances of unheated wheat are n-propanol (M, D), nonanal, dipentene (M), and n-butanol (D); and the characteristic volatile flavor substances of heated and dried wheat are 3-hydroxy-2-butanone (M), n-butyraldehyde (D), isoamyl alcohol (M, D), and isobutyl alcohol (M).

[0010] Further, the gas chromatography parameters of the gas chromatography-ion mobility spectrometry are as follows: a WAX capillary column, 30 m*0.53 mm*1 um; an analysis time of 30 min, a column temperature of 60 DEG C, a carrier gas N2, and a carrier gas flow rate of 2 mL / min initially and 10 mL / min at 10 min, and a flow rate of 100 mL / min for 10 min.

[0011] Further, the ion mobility conditions of the gas chromatography-ion mobility spectrometry are as follows: N2 is used as the drift gas of IMS, the drift gas flow rate is 150 mL / min, the drift tube temperature is 45 DEG C; the automatic headspace sampling mode is used for sampling, the sampling volume is 500 mu L, the incubation time is 15 min, the incubation temperature is 60 DEG C, the sampling needle temperature is 85 DEG C, and the incubation rotation speed is 500 rpm.

[0012] Further, the characteristic volatile compounds of the samples are qualitatively and / or relatively quantitatively detected by the gas chromatography-ion mobility spectrometry, and the detection results are subjected to principal component analysis.

[0013] When the detection result shows that the to-be-detected wheat sample can be significantly distinguished from the known non-heated wheat sample, the to-be-detected wheat sample is heated and dried wheat; when the detection result shows that the to-be-detected wheat sample cannot be significantly distinguished from the known non-heated wheat sample, the to-be-detected wheat sample is non-heated wheat.

[0014] Further, sample qualitative analysis and relative quantification are performed by using VOCal analysis software matched with the instrument for collection and identification, and NIST database and IMS database built in the VOCal software are used for qualitative analysis of the substances according to gas phase retention time and ion migration time;

[0015] Relative quantification and selection of characteristic substances are performed by using Gallery Plot plug-in in VOCal, so as to obtain a sample volatile flavor substance fingerprint spectrum, and the characteristic substances of wheat in different heating conditions are extracted through obvious color contrast of the spectrum, so as to obtain characteristic volatile flavor substances for identifying whether the wheat is heated, and the volatile organic substances are compared between the heated and dried wheat and the non-heated wheat in an intuitive and relative quantitative manner, so as to preliminarily identify the heating condition of the wheat.

[0016] Through qualitative analysis and relative quantification, the plug-in Dynamic is used for principal component analysis of the sample, and the volatile component peak intensity data in a typical characteristic region are analyzed, so as to realize the discrimination of whether the wheat is heated.

[0017] The present application has the following beneficial effects:

[0018] (1) The wheat sample is analyzed by using the rapid, accurate and high-sensitivity GC-IMS technology combined with chemical analysis, the substance information is determined through the migration time and the retention time in the spectrum under the condition that the volatile substances of the sample are not known, the difference of the sample is intuitively understood, and whether the sample is heated is identified by difference analysis of the characteristic substances selected in the fingerprint spectrum combined with chemometrics and other methods.

[0019] (2) The sample detected by GC-IMS does not need to be pretreated, so as to avoid the interference of external solvents; the operation process is simple, the detection accuracy is high, and the cost is lower compared with the traditional flavor detection method.

[0020] (3) The detected sample is rich, including different types of wheat samples, the heating condition of the wheat can provide a theoretical reference for raw material research of liquor and wheat heating research based on volatile flavor, can reduce factors affecting the quality of liquor at the source, reduce waste, can also provide a new idea for mold research, and has strong applicability. BRIEF DESCRIPTION OF DRAWINGS

[0021] Figure 1 It is a gas phase ion mobility spectrum of the wheat sample;

[0022] Figure 2 Differential plot of gas chromatography-ion mobility spectrometry for wheat samples;

[0023] Figure 3 Fingerprint plot of wheat samples;

[0024] Figure 4a Qualitative result plot of gas chromatography-ion mobility spectrometry for wheat samples;

[0025] Figure 4b Zoom-in plot of qualitative result of gas chromatography-ion mobility spectrometry for wheat samples;

[0026] Figure 5 Principal component analysis result plot of wheat samples;

[0027] Figure 6 Permutation test plot of partial least squares discriminant analysis;

[0028] Figure 7 Score plot of partial least squares discriminant analysis;

[0029] Figure 8 VIP score plot of partial least squares discriminant analysis. DETAILED DESCRIPTION

[0030] The specific embodiments of the present application are described below to facilitate the understanding of the present application for those skilled in the art, but it should be clear that the present application is not limited to the scope of the specific embodiments, and for those skilled in the art, it is obvious that various changes are within the spirit and scope of the present application defined and determined by the appended claims, and all the inventions utilizing the concept of the present application are within the scope of protection.

[0031] EMBODIMENT

[0032] The present application is suitable for identifying non-heated wheat and heated wheat after drying using GC-IMS. The following embodiment studies the difference in volatile flavor substances of two batches of wheat samples by GC-IMS technology, and at the same time, combines chemometrics methods to achieve the identification of the heating condition of the wheat samples.

[0033] In the embodiment of the present application, the samples to be tested are different batches of non-heated wheat and heated and dried wheat provided by a certain company in Anhui.

[0034] FlavourSpec food flavor analyzer: equipped with an automatic headspace sampler, VOCal analysis software, Reporter plug-in, Gallery Plot plug-in and Dynamic PCA plug-in, G.A.S Company, Germany.

[0035] The method for identifying non-heated wheat and heated and dried wheat based on GC-IMS comprises the following specific steps:

[0036] S1, wheat sample preparation:

[0037] Different batches of heated and dried wheat and non-heated wheat are selected, the number of batches is N, N is greater than or equal to 2, the same batch contains D non-heated and D heated and dried wheat samples, D is greater than or equal to 2, the total number of samples is N*2D, and 2g of each is placed in a headspace sampling bottle for detection;

[0038] S2, gas phase ion mobility spectrometry detection

[0039] Parameter setting:

[0040] The chromatographic column parameters are set as:

[0041] WAX capillary column (30m*0.53mm*1um), analysis time 30min, chromatographic column temperature 60℃, carrier gas N2, carrier gas flow rate: initial carrier gas flow rate 2mL / min, flow rate 10mL / min at 10min, and flow rate is increased to 100mL / min and kept for 10min.

[0042] The ion mobility spectrometry parameters are set as:

[0043] N2 is used as the drift gas of IMS, the drift gas flow rate is 150mL / min, and the drift tube temperature is 45℃. Automatic headspace sampling is used, the sampling volume is 500μL, the incubation time is 15min, the incubation temperature is 60℃, the sampling needle temperature is 85℃, and the incubation rotation speed is 500rmp.

[0044] Sample testing:

[0045] After the GC-IMS sample is loaded, the sample is automatically headspace sampled after a period of incubation, the sample enters the instrument with the carrier gas, is first subjected to primary separation by gas chromatography, and then enters the ion mobility tube, the molecules to be detected are ionized in the ionization zone, and are migrated under the action of an electric field and reverse drift, secondary separation is realized, and the information of volatile substances of the sample is obtained; GC-IMS combines the high separation degree of gas chromatography and the high sensitivity of ion mobility spectrometry, and can quickly detect volatile organic compounds in the sample without any special sample pretreatment.

[0046] Data processing:

[0047] (1) The GC-IMS spectrum of the detection sample and the comparative difference spectrum are obtained by the Reporter plug-in matched with the instrument, such as Figure 1 and Figure 2Preliminary analysis and comparison of samples, and the same batch of non- fever and fever after drying samples, whether there is a significant difference in volatile organic compounds can be observed directly the size of the difference between samples, easy to further analysis; Results show that: the volatile organic compounds in the sample is concentrated in the 200-1000s area, non- fever and fever after drying wheat volatile matter content exists certain difference, non- fever wheat volatile matter content is significantly higher than the majority of post- fever drying wheat.

[0048] (2) using VOCal analysis software instrument supporting collection and identification, application VOCal software built-in NIST database and IMS database through gas phase retention time and ion mobility time of the material for qualitative analysis, such as Figure 4a , Figure 4b and Table 1, the vertical coordinate is the gas phase retention time, the horizontal coordinate is the ion mobility time, the entire background color is blue, the color represents the concentration of the substance, the lighter color represents the lower concentration of the substance, the darker color represents the higher concentration of the substance. Table 1 shows that there are 23 kinds of volatile flavor substances in wheat samples, including 7 kinds of alcohols, 4 kinds of esters, 6 kinds of aldehydes, 2 kinds of ketones, 1 kind of terpene, 1 kind of sulfur, 1 kind of pyrazine and 1 kind of acid.

[0049] Table 1 two-dimensional chromatogram of wheat flavor substances qualitative results

[0050]

[0051]

[0052]

[0053] (4) Gallery Plot plug-in in VOCal analysis software is used for GC-IMS fingerprint analysis. In the fingerprint, each row represents the signal peak of all volatile substances selected from a sample, and each column represents the relative content of a volatile substance in different samples. The redder and darker the color of the point, the higher the concentration of the substance. The whiter and lighter the color, the lower the concentration of the substance. The fingerprint of the wheat sample is as follows Figure 3As shown in the fingerprint map, the characteristic volatile substances of wheat with different heating conditions were selected by the contrast of the map color. The results showed that the contents of n-propanol (M, D), nonanal, (E)-2-hexenal, ethyl n-hexanoate, n-heptanal, dipentene (M, D), n-hexanol (M, D), n-pentanal (D), hexanal (M, D), ethyl acetate (M, D), 2,6-dimethylpyrazine, n-pentanol (M, D), dipropyl disulfide, methyl 2-methylbutanoate, ethyl propanoate, n-butanol (M, D) and the like in the non-heating wheat were obviously higher than those in the wheat after heating and drying; the contents of 2-propanol (M, D), 2-butanone (M, D), 3-hydroxy-2-butanone (M, D), n-butyraldehyde (M, D), n-pentanal (M), isoamyl alcohol (M, D), isobutyl alcohol (M) and the like in the wheat after heating and drying were higher than those in the non-heating wheat.

[0054] The above substances are characteristic volatile flavor substances screened by GC-IMS fingerprint, and subsequent further screening is performed by partial least squares discriminant analysis (PLS-DA) method.

[0055] (5) A clustering analysis discriminant model is established in combination with chemometrics and the like, and the volatile component data in the typical characteristic region is extracted and analyzed by modeling, and the results are as shown in Figure 5 As can be obviously seen from the model effect diagram, the wheat after heating and drying and the non-heating wheat can be obviously distinguished, and whether the wheat is heated can be further efficiently and accurately discriminated by the model.

[0056] PLS-DA is a statistical analysis method with a supervised mode, which mainly realizes analysis and discrimination and prediction of complex data by data dimension reduction. Taking the volatile flavor substances as the independent variable and the wheat sample as the dependent variable, PLS-DA analysis is performed. The performance of the model is evaluated by cross-validation and replacement test, as shown in Figure 6 After PLS-DA analysis of the data, R 2 X=0.967, R 2 Y=0.991, Q 2 =0.967, and the above values are all greater than 0.5, indicating that the model is reliable and has good stability. Through 200 times of replacement test, R 2 =0.199, Q 2 =-0.565, and Q 2 is less than 0, indicating that the model does not have overfitting phenomenon, and the model verification is effective.

[0057] Figure 7The PLS-DA score plot is shown in Figure 1, wherein GM11A, GM11B, GM21A and GM21B represent non-heated wheat samples, and GM12A, GM12B, GM22A and GM22B represent wheat samples dried after heating. In the two types of wheat samples, the non-heated wheat samples are located in the positive half-axis region of the X axis, and the wheat samples dried after heating are located in the negative half-axis region of the X axis, indicating that there are significant differences in volatile components between the non-heated and heated wheat samples.

[0058] VIP represents the contribution of volatile compounds to sample classification. VIP>1 indicates that the variable has an important role, and the larger the VIP value, the more significant the difference between samples. The variable importance projection value describes the contribution of each flavor component according to the signal intensity, and the results are shown in Table 2. Figure 8 As shown in Table 2, eight volatile compounds (including monomers and dimers) with a VIP score greater than 1.0 were obtained by screening, which are n-propanol (M, D), nonanal, isobutanol (M, D), n-butanol (D), isoamyl alcohol (M, D), n-butyraldehyde (D), dipentene (M), and 3-hydroxy-2-butanone (M).

[0059] In summary, the characteristic volatile substances n-propanol (M, D), nonanal, dipentene (M), n-butanol (D), 3-hydroxy-2-butanone (M), n-butyraldehyde (D), isoamyl alcohol (M, D), and isobutanol (M, D) can be used to distinguish non-heated wheat and wheat dried after heating. The key characteristic volatile flavor substances of non-heated wheat are n-propanol (M, D), nonanal, dipentene (M), and n-butanol (D); and the key characteristic volatile flavor substances of wheat dried after heating are 3-hydroxy-2-butanone (M), n-butyraldehyde (D), isoamyl alcohol (M, D), and isobutanol (M).

[0060] Table 2 PLS-DA factor VIP score table

[0061]

[0062] Through the above examples, the method for identifying non-heated wheat and heated and dried wheat based on GC-IMS is described in detail, and flavor substances such as n-propanol (M, D), nonanal, dipentene (M), n-butanol (D), 3-hydroxy-2-butanone (M), n-butyraldehyde (D), isoamyl alcohol (M, D), and isobutyl alcohol (M, D) can be used as marker substances for the identification of heated wheat. During the heating of wheat, the respiration and growth and reproduction of microorganisms consume the nutrients of wheat, and decomposition, oxidation and other reactions occur, so that the types and concentrations of alcohol substances are reduced, and the types and concentrations of aldehyde and ketone substances are increased. Generally, the heating time of wheat is short, and the wheat does not reach the degree of moldy, so it is difficult to identify and distinguish from the appearance after drying. The GC-IMS instrument used in the present application identifies and distinguishes through the characteristics of the volatile substances of wheat, and is efficient, fast, sensitive and accurate.

[0063] It is apparent to those skilled in the art that the present application is not limited to the details of the foregoing exemplary embodiments, and that the present application can be implemented in other particular forms without departing from the spirit or essential characteristics of the present application. Therefore, the embodiments should be considered in all respects as illustrative and not restrictive, and the scope of the present application is defined by the appended claims rather than the foregoing description, and it is intended to encompass all changes falling within the meaning and range of equivalents of the claims.

[0064] Furthermore, it should be understood that, although the present specification is described in terms of embodiments, not every embodiment contains only one independent technical solution, and the description of the specification is only for the sake of clarity, and those skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can be appropriately combined to form other embodiments that those skilled in the art can understand.

Claims

1. A method for identifying fever wheat based on gas phase ion mobility spectrometry, characterized in that: The following steps are involved: Gas phase ion mobility spectrometry was used to obtain the volatile flavor compounds of unheated and heated wheat, clarifying the differences in volatile flavor compounds and key characteristic volatile flavor compounds. At the same time, chemometric methods were used to judge the differences between samples and identify unheated wheat and heated wheat. The key characteristic volatile flavor substances of unheated wheat are n-propanol M, n-propanol D, nonanal, dipentene M, and n-butanol D; the key characteristic volatile flavor substances of wheat dried after heating are 3-hydroxy-2-butanone M, n-butyraldehyde D, isopentanol M, isopentanol D, and isobutanol M; the suffixes M and D in the names of the substances represent the monomer and dimer of the compound, respectively.

2. The method for identifying fever wheat based on gas phase ion mobility spectrometry according to claim 1, characterized in that: The gas phase parameters of the gas phase ion mobility spectrometry are as follows: chromatographic column: WAX capillary column, 30m*0.53mm*1um; analysis time 30min, chromatographic column temperature 60°C, carrier gas N2, carrier gas flow rate: initial carrier gas flow rate 2mL / min, flow rate 10mL / min at 10 minutes, when increased to 100mL / min and maintained for 10 minutes.

3. The method for identifying fever wheat based on gas phase ion mobility spectrometry according to claim 1, characterized in that: Ion migration conditions for gas phase ion mobility spectrometry: N2 was used as the drift gas of IMS, the drift gas flow rate was 150 mL / min, the drift tube temperature was 45°C; automatic headspace injection was used for sampling, the injection volume was 500 μL, the incubation time was 15 min, the incubation temperature was 60°C, the injection needle temperature was 85°C, and the incubation speed was 500 rpm.

4. The method for identifying fever wheat based on gas phase ion mobility spectrometry according to claim 1, characterized in that: Gas phase ion mobility spectrometry was used to perform qualitative and relative quantitative detection of characteristic volatile compounds in the samples, and principal component analysis was performed on the detection results. If the test results show that the wheat sample to be tested can be significantly distinguished from the known non-heated wheat sample, then the wheat sample to be tested is heat-dried wheat; When the test results show that the wheat sample to be tested cannot be significantly distinguished from a known non-heating wheat sample, the wheat sample to be tested is non-heating wheat.

5. The method for identifying fever wheat based on gas phase ion mobility spectrometry according to claim 4, characterized in that: Sample qualitative and relative quantitative analysis is performed using the VOCal analysis software that comes with the instrument. The NIST database and IMS database built into the VOCal software are used to perform qualitative analysis of substances based on gas phase retention time and ion migration time. Relative quantification and characteristic substance selection were performed using the Gallery Plot plug-in in VOCal, generating fingerprints of the sample's volatile flavor compounds. By contrasting the distinct color patterns in the fingerprints, characteristic compounds were extracted from wheat subjected to different heating conditions, yielding characteristic volatile flavor compounds that could be used to identify whether the wheat had been heated. The differences in volatile organic compounds between heated and unheated wheat were intuitively and relatively quantitatively compared, providing a preliminary identification of the heating condition of the wheat. Through qualitative and relative quantitative analysis, the Dynamic plug-in is used to perform principal component analysis of the sample, and the peak intensity data of volatile components in typical characteristic areas are analyzed to determine whether the wheat has been overheated.

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