Method for judging freshness of early Australian badam

Abstract

The invention belongs to the technical field of food analysis and detection, and relates to a method for judging the freshness of early Australian badam. In the prior art, the detection of almonds is mostly sensory evaluation or physical and chemical index detection, and the freshness of the almonds cannot be quickly, efficiently and accurately judged. The method provided by the invention comprises the following steps: pretreating Australian almonds; detecting by using gas chromatography-mass spectrometry; the original data are retrieved and analyzed through an NIST mass spectrum database to screen out substances with the matching index larger than 75, and after silicon-containing substances are removed, the relative content of coconut aldehyde and nonanal is calculated through a peak area normalization method; and calculating the sum of the relative contents of the coconut aldehyde and the nonanal, and when the sum of the relative contents of the coconut aldehyde and the nonanal is less than or equal to 8.70%, judging that the Australian almonds are fresh. According to the method, the pointer substance influencing the freshness of the badam and the range of the pointer substance are determined, and the rapid, accurate and efficient judgment method for the freshness of the badam is realized.

Description

Technical Field

[0001] The present invention belongs to the technical field of food analysis and detection, and in particular, relates to a method for judging the freshness of early Australian almonds. Background Art

[0002] Nuts are a type of food that is rich in nutrients and has high nutritional value. They contain unsaturated fatty acids required by the human body and play an important role in the health of the human heart, spleen, stomach, and brain. As a nutrient-dense nut, almonds are deeply loved by people for their nutrition and deliciousness. They contain up to 70% unsaturated fatty acids and do not contain cholesterol. They play a unique role in lowering cholesterol levels and maintaining body weight. Almonds have a low water content and a water activity of less than 0.6, which can effectively inhibit the reproduction of harmful bacteria. However, like other nuts, their high fat content makes them prone to oxidation and rancidity in the air. Especially when stored for a long time, oxidation and deterioration will affect the flavor and taste of the product and reduce the product value.

[0003] At present, most of the tests for oily nuts such as almonds at home and abroad are sensory evaluation or physical and chemical index testing. The sensory evaluation method relies on the professionalism and subjectivity of the testers, while the physical and chemical index testing has the disadvantages of cumbersome operation and high testing cost, and cannot quickly, efficiently and accurately obtain the oxidation status of almonds. Especially in the actual application of the factory, testing the freshness of the almond raw materials and judging its oxidation status are of great significance for subsequent processing, storage and sales.

[0004] Gas chromatography-mass spectrometry (GC-MS) has both the separation capability of gas chromatography and the identification capability of mass spectrometry. It has become an important tool for analyzing complex organic compound components in drugs, foods, and environmental samples. It is also widely used in the detection and identification of volatile components in nuts. There are reports in the prior art of using this technology to detect non-nut substances, such as the Chinese invention patent application publication number CN117434177A, the application date is October 25, 2023, and the name is: A method for identifying the storage year of corn. The disclosed method collects corn samples of different storage years; solid phase microextraction-gas chromatography-mass spectrometry is used for detection to obtain volatile component data of corn samples of different storage years; PCA and PLS-DA are combined to analyze the volatile component data and establish a corn storage year identification model; solid phase microextraction-gas chromatography-mass spectrometry is used to detect the corn samples to be tested to obtain the differential compound content in the samples to be tested; based on the corn storage year identification model, the storage year of the corn samples to be tested is obtained. This scheme requires the establishment of models according to different years, which is cumbersome, and nuts, such as almonds, have complex oil components and it is difficult to determine the indicator substances. Jing Wei et al. used gas chromatography-mass spectrometry to analyze the aroma components of macadamia nuts roasting and obtained 37 volatile components, among which pyrazines were considered to be important characteristic substances (Jing Wei, Su Zipeng, Liu Yijun, Lin Lijing. HS-SPME / GC-MS determination of aroma components of macadamia nuts roasting [J]. Food Industry, 2016, 37(09): 241-245.). Zhao Daxuan et al. used this technology to analyze the fatty acids in nuts and found that among the 13 fatty acids, unsaturated fatty acids accounted for a higher proportion, among which the relative content of oleic acid was as high as 49.69% (Zhao Daxuan, Zhao Jing, Qin Binhua, et al. GC-MS analysis of fatty acid components of macadamia nuts [J]. Agricultural Research and Application, 2013(01): 20-22.). Although there have been studies on the aroma components of almonds, the characteristic volatile components related to the oxidation degree of almonds are still unclear. Therefore, in view of the fact that the current methods for detecting the freshness of almond raw materials are cumbersome and highly subjective, there is an urgent need to establish a method based on gas chromatography-mass spectrometry technology to quickly, accurately and efficiently identify the degree of oxidation of oily nuts. Summary of the invention

[0005] 1. Problems to be solved

[0006] In the prior art, the detection of oily nuts such as almonds is mostly sensory evaluation or physical and chemical index detection. The sensory evaluation method depends on the professionalism and subjectivity of the tester; while the physical and chemical index detection operation is cumbersome and the detection cost is high. The above methods cannot quickly, efficiently and accurately judge the freshness of almonds. This application provides a method for judging the freshness of early Australian almonds, determines the indicator substances and ranges that affect the freshness of almonds, and realizes a fast, accurate and efficient method for judging the freshness of almonds.

[0007] 2. Technical solution

[0008] In order to achieve the above purpose, the technical solution provided is:

[0009] The method for judging the freshness of early Australian almonds includes the following steps:

[0010] S1. Pre-treating Australian almonds to obtain a sample to be tested; detecting the sample to be tested by gas chromatography-mass spectrometry to obtain raw data;

[0011] S2. The raw data is retrieved and analyzed by NIST mass spectrum library to screen out substances with a matching index greater than 75, and the relative contents of coconut aldehyde and nonanal are calculated by peak area normalization method after removing silicon-containing substances;

[0012] S3. Calculate the sum of the relative contents of the coconut aldehyde and the nonanal;

[0013] When the sum of the relative contents of the coconut aldehyde and the nonanal is ≤8.70%, the Australian almonds are judged to be fresh.

[0014] Further, the relative contents of pentanol and heptanol are simultaneously calculated using the peak area normalization method;

[0015] The sum of the relative contents of the pentanol and the heptanol is calculated; when the sum of the relative contents of the coconut aldehyde and the nonanal is ≤8.70%, and the sum of the relative contents of the pentanol and the heptanol is ≤20.29%, the Australian almonds are judged to be fresh.

[0016] Furthermore, the substances with a matching index greater than 75 include alcohol substances, aldehyde and ketone substances, alkane substances and other substances.

[0017] Further, the alcohol substances include ethanol, n-butanol, n-pentanol, n-hexanol, n-heptanol, phenylethanol, n-octanol, n-nonanol, 1-octen-3-ol, and linalool;

[0018] The aldehyde and ketone substances include coconut aldehyde, nonanal, and 3-octen-2-one;

[0019] The alkane substances include n-heptane, 1-ethyl-1-methylcyclopentane, octane, decane, undecane, dodecane, and tetradecane;

[0020] The other substances include methyl isocyanate, butene dinitrile, ethyl diether, ethylbenzene, 2-n-butyl furan, propyl octanolactone, 2-pentyl furan, and limonene.

[0021] Furthermore, the pretreatment is to crush the Australian almonds and then perform headspace-solid phase microextraction.

[0022] Furthermore, the microextraction parameters are extraction at 85° C. for 30 min; and the extraction head model of the headspace-solid phase microextraction is 50 / 30 μm DVB / CAR / PDMS.

[0023] Furthermore, after the crushing step, 3 g of the sample to be tested is taken.

[0024] Furthermore, the parameters of the gas chromatography are:

[0025] The carrier gas was high-purity helium with a flow rate of 1.0 mL / min; the injection port temperature was 250°C; the detector temperature was 270°C; the desorption time was 4 min; the heating program was as follows: the initial temperature of the column box was 35°C, maintained for 4 min, then increased to 100°C at 5°C / min, then increased to 220°C at 15°C / min, maintained for 10 min, and the split ratio was 5:1;

[0026] The parameters of the mass spectrometry are:

[0027] Electron ionization source: electron energy 70eV; ion source temperature 230℃; interface temperature 280℃; quadrupole temperature 150℃; full scan mode: scan mass range 10~500u.

[0028] Furthermore, the peak area normalization method calculation formula is:

[0029]

[0030] where x i is the base peak deconvolution area of ​​each substance in the sample to be tested, is the sum of the base peak deconvolution areas of all substances remaining after removing the silicon-containing substances, x i ' is the relative content of each substance;

[0031] Furthermore, the sample to be tested is prepared in triplicate, and the relative contents of pentanol, heptanol, coconut aldehyde and nonanal are measured respectively, and the average value is taken.

[0032] 3. Beneficial effects

[0033] Compared with the existing known technology, the technical solution provided by the present invention has the following beneficial effects:

[0034] 1. The method for judging the freshness of early Australian almonds of the present invention detects the volatile components in the almonds of the Australian production area by gas chromatography-mass spectrometry technology, combines qualitative and quantitative analysis, establishes an analysis model for the freshness of almonds, analyzes the changes in the volatile components of almonds in the Australian region during the accelerated oxidation process, determines the pointer substance and pointer range, selects coconut aldehyde and nonanal as pointer substances, and judges that the sample is fresh when the sum of the relative contents of coconut aldehyde and nonanal is ≤8.70%. This application can be used to judge the freshness of early almonds based on gas chromatography-mass spectrometry and pointer substances, that is, before the acid value or peroxide value and other indicators can be used to detect whether the almonds are fresh, the detection can be completed. This application is helpful for the study of rapid detection of almonds through pointer substances, and provides new ideas for rapid detection of food.

[0035] 2. The method for judging the freshness of early Australian almonds of the present invention detects the volatile components in the almonds of the Australian production area by gas chromatography-mass spectrometry technology, and determines another pair of pointer substances and pointer ranges, amyl alcohol and heptanol, combined with the pointer substances coconut aldehyde and nonanal, when the sum of the relative contents of coconut aldehyde and nonanal is ≤8.70%, and the sum of the relative contents of amyl alcohol and heptanol is ≤20.29%, the sample is judged to be fresh. The combination of two pairs of pointer substances, coconut aldehyde and nonanal, amyl alcohol and heptanol, can more accurately judge the freshness of almonds, and can screen out fresher Australian almonds. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 This is the total ion current chromatogram of almonds produced in Australia in 2022;

[0037] Figure 2 PCA analysis of 10 groups of accelerated oxidation time gradient samples of almonds from Australia in 2022;

[0038] Figure 3 PLSDA analysis of 10 groups of accelerated oxidation time gradient samples of almonds from Australia in 2022;

[0039] Figure 4 Analysis of pentanol and heptanol indicators in almonds from Australia in 2022;

[0040] Figure 5 Analysis of coconut aldehyde and nonanal indicators in almonds from Australia in 2022;

[0041] Figure 6 This is the total ion current chromatogram of almonds produced in Australia in 2023;

[0042] Figure 7Analysis of pentanol and heptanol indicators in almonds from Xinjiang, China in 2022;

[0043] Figure 8 This is an analysis of nonanal indicator substances in almonds produced in Xinjiang, China in 2022. DETAILED DESCRIPTION

[0044] In order to further understand the content of the present invention, the present invention is described in detail in conjunction with embodiments.

[0045] Example 1

[0046] 1. Experimental Materials and Methods

[0047] 1.1. Instruments and samples

[0048] The main instruments used in this example are shown in Table 1.

[0049] Table 1 Instruments

[0050]

[0051] The experimental samples used in this example are:

[0052] The almonds tested were provided by Qia Qia Food Co., Ltd. The samples were from Australia in 2022 and stored in a cold storage at 4°C.

[0053] 1.2 Experimental methods

[0054] 1.2.1. Almond sample pretreatment

[0055] (1) Almond samples from Australia were placed in a constant temperature and humidity chamber at 60°C and 10% humidity for 0, 5, 10, 15, 20, 25, 30, 35, 40, and 50 days for accelerated oxidation treatment.

[0056] (2) Take 30g of almonds and grind them in a food grinder. Weigh 3.0g of sample and place it in a headspace bottle. Repeat three times.

[0057] 1.2.2. Headspace-solid phase microextraction

[0058] The appropriate extraction fiber head and extraction conditions were determined through preliminary experiments, and a 50 / 30μm DVB / CAR / PDMS solid phase microextraction head was selected. The headspace bottle containing the sample was placed in a constant temperature water bath at 85°C, and the extraction head was inserted into the headspace part of the headspace bottle to push out the extraction fiber. After 30 minutes of headspace adsorption, the extraction fiber was withdrawn. After the extraction was completed, the extraction head was directly inserted into the injection port of the gas chromatography-mass spectrometry instrument, and the decomposition temperature was 250°C and the time was 4 minutes.

[0059] 1.2.3. Gas chromatography-mass spectrometry analysis conditions

[0060] Gas chromatography conditions: The chromatographic column was an HP-5ms capillary column, and the temperature program was as follows: the initial temperature of the column box was 35°C, maintained for 4 min, increased to 100°C at 5°C / min, and then increased to 220°C at 15°C / min, maintained for 10 min, and the split ratio was 5:1. The flow rate of the carrier gas (He) was 1.0 mL / min, and the injection port temperature was 250°C.

[0061] Mass spectrometry conditions: electron impact (EI) ion source: ion source temperature 230°C; interface temperature 280°C; quadrupole temperature 150°C; full scan mode: scan mass range 10 to 500u.

[0062] Data processing

[0063] (1) Qualitative analysis: The total ion current chromatogram of the volatile components of almonds obtained by gas chromatography-mass spectrometry is shown in Figure 1 ; After computer data processing, the GC-MS analysis data was searched and analyzed with the NIST standard mass spectrum library to screen out substances with a matching index greater than 75.

[0064] Depend on Figure 1 It can be seen that the types of compounds, chromatographic peak abundance and peak separation obtained by the extraction conditions and gas chromatography-mass spectrometry analysis conditions determined by the preliminary experiment are all good.

[0065] (2) Quantitative analysis: The relative content of the substance components screened in (1) is calculated by the peak area normalization method. The calculation formula is as follows:

[0066]

[0067] where x i is the base peak deconvolution area of ​​each substance in the sample, is the sum of the base peak deconvolution areas of all substances remaining after removing the silicon-containing substances, x i ' is the relative content of each substance.

[0068] The sum of the relative contents of pentanol and heptanol, and the sum of the relative contents of coconut aldehyde and nonanal were calculated.

[0069] The determination of volatile components of almonds was repeated three times in parallel, and the average value of relative content was taken. The results are shown in Table 2.

[0070] Table 2 Quantitative analysis of the main volatile components of Australian almonds

[0071]

[0072]

[0073] 2. Determine the freshness of Batam

[0074] 2.1. Establishing an analytical model for almond freshness

[0075] SIMCA14.1 software was used for principal component analysis (PCA), and Metaboanalyst platform was used for partial least squares discriminant analysis (PLS-DA) to process and fit the data, and an analytical model for almond freshness was established.

[0076] 2.2. Sample principal component analysis results

[0077] The principal component analysis results of almond samples from Australia at 0, 5, 10, 15, 20, 25, 30, 35, 40, and 50 days of oxidation are shown in the figure. Figure 2 As shown in the figure, it can be seen that PCA can be used to analyze and process the temperament data of 10 groups of samples. In addition, it can be seen from the PCA results that the 10 groups of samples from Australia have clustering phenomena, which also reflects to a certain extent the differences in the 10 groups of samples oxidized for different days under accelerated oxidation conditions.

[0078] 2.3. Sample partial least squares discriminant analysis results

[0079] The partial least squares discriminant analysis results of 10 groups of almond samples from Australia under different oxidation days are as follows: Figure 3 As shown in the figure, the variable projection importance analysis (VIP) is calculated by partial least squares method. When the VIP value of the selected index is greater than 1, it means that these indexes play a more important role in the classification or prediction of samples in the model. As can be seen from the figure, alcohol-aldehyde substances are more important. Among the almond samples from Australia, ethanol has the highest VIP value, but ethanol has poor regularity in the actual oxidation process and is not suitable for indicating the oxidation of almonds. After data analysis, the relative contents of coconut aldehyde and nonanal first increase and then decrease, and the sum of the relative contents of coconut aldehyde and nonanal also meets the trend of first increase and then decrease. The sum of the relative contents of coconut aldehyde and nonanal is selected as the indicator substance; the relative contents of amyl alcohol and heptanol also increase first and then decrease, and the sum of the relative contents of amyl alcohol and heptanol also meets the trend of first increase and then decrease. The sum of the relative contents of amyl alcohol and heptanol is selected as another pair of indicator substances; the time corresponding to the maximum value of the relative contents of coconut aldehyde and nonanal is after the time corresponding to the maximum value of the relative contents of amyl alcohol and heptanol.

[0080] 2.4. Indication results of indicator substances

[0081] From Table 3 and Figure 4 It can be seen that in the almond samples from Australia, pentanol and heptanol have strong indicative properties and stability. As the degree of accelerated oxidation of almonds deepens, the relative content shows a trend of first increasing and then decreasing. The sum of the relative contents of pentanol and heptanol also shows this rule. It increases rapidly from the 5th day and decreases after 20 days, indicating that the volatile substances in almonds undergo significant changes during the accelerated oxidation process, which in turn affects the freshness and taste. From Table 4 and Figure 5 It can be seen that coconut aldehyde and nonanal also show a trend of increasing first and then decreasing. On the 40th day of accelerated oxidation, the sum of the relative contents of coconut aldehyde and nonanal was 8.70%. Through sensory evaluation, it was found that almonds had a slight odor. After 40 days, the sum of the relative contents of coconut aldehyde and nonanal began to decrease. On the 50th day, the odor of almonds could be clearly smelled. At this time, there was no need to use pointer substances to judge. Since the sum of the relative contents of coconut aldehyde and nonanal was in an increasing stage before 8.70%, it can be judged separately that when the sum of the relative contents of coconut aldehyde and nonanal is ≤8.70%, the almonds are fresh. In order to more accurately judge the freshness of almonds, coconut aldehyde and nonanal, pentanol and heptanol, two pairs of pointer substances are combined. When the sum of the relative contents of coconut aldehyde and nonanal is ≤8.70%, and the sum of the relative contents of pentanol and heptanol is ≤20.29%, the almonds are fresh.

[0082] Table 3 Relative contents of amyl alcohol and heptanol in 2022 Australian almonds after accelerated oxidation (%)

[0083]

[0084] Table 4 Relative contents of coconut aldehyde and nonanal after accelerated oxidation of 2022 Australian almonds (%)

[0085]

[0086]

[0087] Example 2

[0088] 1. Experimental Materials and Methods

[0089] 1.1. Instruments and samples

[0090] Basically the same as Example 1, except that the sample is fresh almonds from Australia in 2023 and stored in a cold storage at 4°C.

[0091] 1.2 Experimental methods

[0092] Basically the same as Example 1

[0093] 1.3 Data processing

[0094] Basically the same as in Example 1, the total ion current chromatogram of the volatile components of almonds obtained by gas chromatography-mass spectrometry is shown in Figure 6 .

[0095] The determination of volatile components of almonds was repeated three times in parallel, and the average value was taken to calculate the sum of the relative contents of pentanol and heptanol, and the sum of the relative contents of coconut aldehyde and nonanal. The results are shown in Tables 5 and 6.

[0096] Table 5 Relative contents of amyl alcohol and heptanol in 2023 Australian almonds after accelerated oxidation (%)

[0097]

[0098] Table 6 Relative contents of coconut aldehyde and nonanal after accelerated oxidation of 2023 Australian almonds (%)

[0099]

[0100] Combining Tables 5 and 6, it can be seen that the sum of the relative contents of amyl alcohol and heptanol gradually increases with the deepening of the accelerated oxidation of almonds. The maximum value of the sum of the relative contents of coconut aldehyde and nonanal is 2.83%. Through sensory evaluation, the almonds of 50 days have no peculiar smell. Because the overall freshness of the Australian almond samples in 2023 is higher than that of the Australian almond samples in 2022, it can be determined that the Australian almonds in 2023 also meet the following requirements: when judged separately, when the sum of the relative contents of coconut aldehyde and nonanal is ≤8.70%, the almonds are fresh. When the two pairs of indicator substances are combined for judgment, when the sum of the relative contents of coconut aldehyde and nonanal is ≤8.70%, and the sum of the relative contents of amyl alcohol and heptanol is ≤20.29%, the almonds are fresh.

[0101] Example 3

[0102] 1. Experimental Materials and Methods

[0103] 1.1. Instruments and samples

[0104] Basically the same as Example 1, except that the sample is randomly selected Australian almonds.

[0105] 1.2 Experimental methods

[0106] The method is basically the same as Example 1, except that there is no need to accelerate oxidation during the pretreatment of the almond sample.

[0107] Data processing

[0108] Basically the same as Example 1.

[0109] The determination of volatile components of almonds was repeated three times in parallel, and the average value was taken to calculate the sum of the relative contents of pentanol and heptanol, and the sum of the relative contents of coconut aldehyde and nonanal. The results are shown in Table 7.

[0110] Table 7 Relative contents of amyl alcohol, heptanol, coconut aldehyde and nonanal in the volatile components of Australian almonds (%)

[0111]

[0112] According to Table 7, the sum of the relative contents of pentanol and heptanol of samples 1-6 is ≤20.29%, and the sum of the relative contents of coconut aldehyde and nonanal is ≤8.70%, which means that the samples 1-6 are fresh. Sensory evaluation revealed that the samples 1-6 are fresh.

[0113] Comparative Example 1

[0114] 1. Experimental Materials and Methods

[0115] 1.1. Instruments and samples

[0116] Basically the same as Example 1, the difference is that the sample is fresh almonds produced in Xinjiang, China in 2022 and stored in a cold storage at 4°C.

[0117] 1.2 Experimental methods

[0118] The method is basically the same as Example 1, except that during the pretreatment of the almond samples, the almond samples produced in Xinjiang, China are placed in a constant temperature and humidity chamber at a temperature of 60°C and a humidity of 10% for 0, 5, 10, 15, 25, 30, 35, 40, and 45 days for accelerated oxidation treatment.

[0119] 1.3 Data processing

[0120] Basically the same as Example 1

[0121] The determination of volatile components of almonds was repeated three times in parallel, and the average value was taken to calculate the sum of the relative contents of pentanol and heptanol, and the sum of the relative contents of coconut aldehyde and nonanal. The results are shown in Tables 8 and 9.

[0122] Table 8 Relative contents of amyl alcohol and heptanol after accelerated oxidation of almonds from Xinjiang, China, 2022 (%)

[0123]

[0124] Table 9 Relative contents of coconut aldehyde and nonanal after accelerated oxidation of almonds in Xinjiang, China, 2022 (%)

[0125]

[0126] According to Table 8 and Figure 7 It can be seen that the relative contents of pentanol and heptanol in almonds from Xinjiang, China, have no obvious regularity as the degree of accelerated oxidation of almonds deepens, and the sum of the relative contents of pentanol and heptanol also has no obvious regularity; according to Table 9 and Figure 8It can be seen that no coconut aldehyde was detected in almonds produced in Xinjiang, China, and the relative content of nonanal did not show any regularity as the degree of accelerated oxidation of almonds deepened. On the 40th day of accelerated oxidation, the sum of the relative contents of pentanol and heptanol was ≤20.29%, and the sum of the relative contents of coconut aldehyde and nonanal was ≤8.70%, which should be fresh, but a peculiar smell was found through sensory evaluation.

[0127] The above-mentioned embodiments only express the preferred implementation modes of the present invention, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the scope of the present invention. It should be pointed out that, for a person skilled in the art, several modifications, improvements and substitutions can be made without departing from the concept of the present invention, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the present invention patent shall be subject to the attached claims.

Claims

1. A method for judging the freshness of early Australian almonds, characterized in that: The following steps are involved: S1. Pre-treating Australian almonds to obtain a sample to be tested; detecting the sample to be tested by gas chromatography-mass spectrometry to obtain raw data; S2. The raw data is retrieved and analyzed by NIST mass spectrum library to screen out substances with a matching index greater than 75, and the relative contents of coconut aldehyde and nonanal are calculated by peak area normalization method after removing silicon-containing substances; S3. Calculate the sum of the relative contents of the coconut aldehyde and the nonanal; When the sum of the relative contents of the coconut aldehyde and the nonanal is ≤8.70%, the Australian almonds are judged to be fresh.

2. The method for judging the freshness of early Australian almonds according to claim 1, characterized in that: The relative contents of pentanol and heptanol were simultaneously calculated using the peak area normalization method; The sum of the relative contents of the pentanol and the heptanol is calculated; when the sum of the relative contents of the coconut aldehyde and the nonanal is ≤8.70%, and the sum of the relative contents of the pentanol and the heptanol is ≤20.29%, the Australian almonds are judged to be fresh.

3. The method for judging the freshness of early Australian almonds according to claim 1 or 2, characterized in that: The substances with a matching index greater than 75 include alcohols, aldehydes and ketones, alkanes and other substances.

4. The method for judging the freshness of early Australian almonds according to claim 3, characterized in that: The alcohol substances include ethanol, n-butanol, n-pentanol, n-hexanol, n-heptanol, phenylethyl alcohol, n-octanol, n-nonanol, 1-octen-3-ol, and linalool; The aldehyde and ketone substances include coconut aldehyde, nonanal, and 3-octen-2-one; The alkane substances include n-heptane, 1-ethyl-1-methylcyclopentane, octane, decane, undecane, dodecane, and tetradecane; The other substances include methyl isocyanate, butene dinitrile, ethyl diether, ethylbenzene, 2-n-butyl furan, propyl octanolactone, 2-pentyl furan, and limonene.

5. The method for judging the freshness of early Australian almonds according to claim 4, characterized in that: The pretreatment is to crush the Australian almonds and then perform headspace-solid phase microextraction.

6. The method for judging the freshness of early Australian almonds according to claim 5, characterized in that: The microextraction parameters are extraction at 85° C. for 30 min; the head type of the headspace-solid phase microextraction is 50 / 30 μm DVB / CAR / PDMS.

7. The method for judging the freshness of early Australian almonds according to claim 6, characterized in that: After the pulverizing step, 3 g of the sample to be tested was taken.

8. The method for judging the freshness of early Australian almonds according to claim 7, characterized in that: The parameters of the gas chromatography are: The carrier gas was high-purity helium with a flow rate of 1.0 mL / min; the injection port temperature was 250°C; the detector temperature was 270°C; the desorption time was 4 min; the heating program was as follows: the initial temperature of the column box was 35°C, maintained for 4 min, then increased to 100°C at 5°C / min, then increased to 220°C at 15°C / min, maintained for 10 min, and the split ratio was 5:1; The parameters of the mass spectrometry are: Electron ionization source: electron energy 70eV; ion source temperature 230℃; interface temperature 280℃; quadrupole temperature 150℃; full scan mode: scan mass range 10~500u.

9. The method for judging the freshness of early Australian almonds according to claim 8, characterized in that: The peak area normalization calculation formula is: where x i is the base peak deconvolution area of ​​each substance in the sample to be tested, is the sum of the base peak deconvolution areas of all substances remaining after removing the silicon-containing substances, x i ' is the relative content of each substance.

10. The method for judging the freshness of early Australian almonds according to claim 9, characterized in that: The sample to be tested was prepared in triplicate, and the relative contents of amyl alcohol, heptanol, coconut aldehyde and nonanal were measured respectively, and the average value was taken.

Images