Method for extracting and detecting mineral oil in fermented grains or solid grains

Abstract

The application discloses a kind of extraction and detection methods of mineral oil in fermented grains or solid grains, belong to food detection technical field.The present application provides a kind of extraction and detection methods of mineral oil in fermented grains or solid grains for realizing the complete extraction and detection of mineral oil in fermented grains and solid grains, comprising: fermented grains or solid grains are mixed with n-hexane, by first extraction, supernatant and precipitate are obtained;Precipitate is mixed with water, water bath, and the to-be-extracted liquid is obtained;The to-be-extracted liquid is mixed with n-hexane, by second extraction, supernatant is obtained;Supernatant is combined, and the extract containing mineral oil is obtained;It can be detected by injecting two-dimensional gas chromatography hydrogen flame ionization detector again.The present application adopts the mode of surface extraction and water bath extraction, realizes the enrichment of mineral oil in all aspects, and adopts two-dimensional gas chromatography hydrogen flame ionization detector, and saturated hydrocarbon, aromatic hydrocarbon of mineral oil can be more accurately detected in a short time.

Description

Technical Field

[0001] This invention belongs to the field of food testing technology, specifically relating to a method for extracting and detecting mineral oil in fermented mash or solid grains. Background Technology

[0002] Mineral oil is petroleum and synthetic oil and their refined products, containing nC 10 ~nC 50 Hydrocarbons can be broadly classified into two categories: mineral oil saturated hydrocarbons (MOSH) and mineral oil aromatic hydrocarbons (MOAH). The former includes alkanes and cycloalkanes, which have a cumulative effect in the human body, while the latter mainly includes alkyl-substituted polyaromatic hydrocarbons, which have potential teratogenic and carcinogenic properties. Currently, research on mineral oils in food mainly focuses on edible oils, chocolate, milk powder, biscuits, bread, and other similar products. There is currently very little research on methods and standards for detecting mineral oils in alcoholic beverages and many solid grains. High-performance liquid chromatography-tandem mass spectrometry (LC-MS) is widely used in Europe for mineral oil detection, but the problems are: firstly, the equipment is expensive and difficult to popularize; secondly, sample pretreatment is cumbersome, requires strict expertise from laboratory personnel, and is prone to errors and time-consuming.

[0003] GB 2760-2014, the National Food Safety Standard for the Use of Food Additives, stipulates that mineral oil can be used as an antifoaming agent, release agent, anti-sticking agent, and lubricant in fermentation processes and the processing of candies, potato chips, and soy products. Mineral oil can migrate and contaminate food throughout the entire supply chain, from raw materials and production to packaging and transportation. In baijiu (Chinese liquor) production, fermented grains after steaming and cooking are used for distillation, a crucial step in the process. The degree of mineral oil contamination in the fermented grains directly affects the mineral oil content in the liquor. While some research institutes and universities have conducted studies on mineral oil migration contamination in food packaging, research on mineral oil contamination during food processing is almost nonexistent. Therefore, conducting research on the detection of mineral oil in fermented grains and solid grains is essential.

[0004] CN20181100618.0 discloses a method for extracting mineral oil from dairy products, comprising: (1) hydrolyzing the dairy product to be tested with hydrochloric acid solution to obtain a hydrolysate; (2) mixing and centrifuging the hydrolysate, anhydrous ethanol and n-hexane to obtain an upper layer and a lower layer, and collecting the upper layer; (3) adding n-hexane to the lower layer, repeating the mixing and centrifugation, collecting the upper layer, and combining the two upper layers to obtain an extract; and (4) mixing and centrifuging the extract with water, collecting the upper layer, and extracting the mineral oil. CN20191106705.1 discloses a method for extracting mineral oil from a sample, comprising: (1) providing an aqueous solution of a milk powder or solid beverage sample; (2) mixing the aqueous solution of the sample with a mixed solvent, performing a first extraction treatment and a first separation treatment to obtain a first upper layer and a first lower layer; (3) mixing the first lower layer with a mixed solvent, performing a second extraction treatment and a second separation treatment to obtain a second upper layer and a second lower layer; (4) combining the first upper layer and the second upper layer, mixing the resulting mixture with water, and performing a third separation treatment to obtain an extract containing mineral oil; wherein the mixed solvent contains n-hexane and a lower alcohol having 1 to 6 carbon atoms; the first separation treatment, the second separation treatment, and the third separation treatment are centrifuged at 3000 to 5000 r / min for 10 to 20 minutes; the first extraction treatment and the second extraction treatment are shaken at 400 to 800 r / min for 10 to 30 minutes. CN20221045350.2 discloses a qualitative detection method for mineral oil in wine or beverages, comprising: 1) extracting the wine or beverage to be tested with n-hexane, shaking, and allowing it to stand for separation; repeating twice, collecting and combining the upper n-hexane layer in a glass container, and concentrating it to 5 mL under nitrogen to obtain an extract; 2) weighing ethylenediamine-N-propylsilanized silica gel washed with n-hexane, octadecylsilane-bonded silica gel, and 0.3% silver nitrate silica gel particles into a glass test tube, adding the above extract to the glass test tube, shaking, centrifuging, and taking the supernatant to be concentrated under nitrogen. Less than 0.5 mL; after adjusting the volume with n-hexane to 1 mL, a purified solution is obtained; 3) The above purified solution is detected by a two-dimensional gas chromatography-time-of-flight mass spectrometry / flame ionization detector; when the purified solution enters the two-dimensional chromatogram via liquid injection, the mineral oil saturated hydrocarbons and mineral oil aromatic hydrocarbons are separated by different chromatographic columns, and the two-dimensional spectra under two-dimensional gas chromatography-time-of-flight mass spectrometry (GC×GC-TOFMS) and two-dimensional gas chromatography-flame ionization detector (GC×GC-FID) are presented on the spectrum. However, the above method is only applicable to water-soluble foods and not to solid grains.

[0005] CN20221028991.0 discloses a method for detecting mineral oil in food, comprising: (1) weighing samples such as biscuits and instant noodles and grinding them with silica gel to obtain a uniform material system; (2) filling the material system into a mineral oil separation column; wherein the mineral oil separation column comprises a drying layer, a silica gel layer and a bottom filter layer arranged from top to bottom, the mineral oil separation column being selected from glass material; the drying layer being selected from anhydrous sodium sulfate, and the silica gel in the silica gel layer being silica gel activated at 300-500℃ for no less than 16 hours; (3) compacting and covering with an upper filter membrane; (4) adding a mixed internal standard solution to the mineral oil separation column; (5) eluting with a mixed solvent of dichloromethane / n-hexane and collecting the eluent; (6) after the eluent is concentrated by rotary evaporation, it is subjected to epoxidation treatment and then analyzed by LC-GC; the silica gel particle size is activated at 400℃ for at least 16 hours. However, this method uses column chromatography directly, which is not suitable for fermented mash and is too costly. In addition, instant foods such as instant noodles need to be rinsed with hot water, but this method uses column chromatography directly without considering the consumption of the product, making it difficult to guarantee the accuracy of the test results.

[0006] CN20171126958.4 discloses a method for detecting the content of aromatic mineral oil in rice, comprising: (1) extracting 5-10g of rice sample to be tested twice with 10-20mL of n-hexane and combining the extracts; (2) adding magnesium silicate purifying agent to the extract and vortexing it to obtain a vortex liquid; (3) centrifuging the vortex liquid, taking the supernatant, concentrating and adjusting the volume to obtain the test liquid; (4) performing molecular fluorescence detection on the test liquid and determining the content of aromatic mineral oil in the rice sample to be tested based on the detection results. Although this method can detect most of the outer mineral oil of corn, it is difficult to detect the residue inside the corn, which can easily lead to deviations in the detection results; and its fluorescence method uses the fluorescence characteristics of mineral oil at a specific wavelength for detection. If the corn is contaminated with mineral oils such as liquid paraffin that do not have fluorescence characteristics, it will affect the accuracy of the detection results. Summary of the Invention

[0007] This invention aims to achieve complete extraction of mineral oil from fermented grains and solid grains such as rice, sorghum, wheat, and corn that require cooking before consumption, ensuring accurate qualitative detection. The extraction process combines surface extraction and water bath extraction, allowing for the extraction of mineral oil not only from the sample surface but also from the interior of the sample and mineral oil migrating under high temperature and pressure conditions, thus achieving comprehensive enrichment of mineral oil. Furthermore, the separation of fatty acid glycerides from mineral oil in oily solid grains is difficult, suffers from severe matrix interference, and has low detection sensitivity, all of which affect the analysis and detection of mineral oil in the sample. This invention degreases the extract from samples with high oil content, reducing detection errors.

[0008] To achieve the above objectives, the present invention first provides a method for extracting mineral oil from fermented mash or solid grains, which includes the following steps:

[0009] A. Mix the mash or solid grains with n-hexane, shake or vortex for the first extraction, and centrifuge to obtain the supernatant and precipitate;

[0010] B. Mix the precipitate obtained in step A with water, bathe in water, shake or vortex, and then centrifuge to obtain the extract.

[0011] C. Mix the extract obtained in step B with n-hexane, shake or vortex for a second extraction, let stand to separate the layers, and obtain the supernatant.

[0012] D. Combine the supernatant obtained in step A and the supernatant obtained in step B to obtain the extract containing mineral oil.

[0013] In the above extraction method, in step B, the mass-to-volume ratio of the mash or solid grain in step A to the water in step B is 1g:1-3mL.

[0014] In the above extraction method, in step B, the temperature of the water bath is 70℃~90℃.

[0015] In the extraction method described above, step B involves a water bath lasting 1 to 2 hours.

[0016] In the above extraction method, in step A, the solid grain is selected from at least one of corn, sorghum, rice, wheat, barley, highland barley, sweet potato, potato, yam, taro, soybean, peanut, mung bean, broad bean, pea, red bean or cowpea.

[0017] In the above extraction method, in step A, the fermented grains are prepared by the following method: after crushing solid grains, soak the grains in hot water at 75℃~95℃, steam for 25~30 minutes, simmer for 50~60 minutes, and steam again for 35~60 minutes. After removing water from the steamed grains, spread them out to cool, mix them with Daqu (a type of starter culture), put them in a fermentation pit, ferment for no less than 45 days, remove them from the pit, and pile them up to form fermented grains. The amount of Daqu added is 175~225g / kg of solid grains.

[0018] Of course, the raw materials of the extraction method of the present invention are not limited to the above-mentioned fermented mash. Common fermented mash in the art, such as fermented mash of strong aroma baijiu, fermented mash of sauce aroma baijiu, fermented mash of light aroma baijiu, and fermented mash of mixed aroma baijiu, are all applicable to the present invention.

[0019] In the above extraction method, in step A, the mass-to-volume ratio of the mash or solid grain in step A to the n-hexane in step A is 1g:1-3mL.

[0020] In the above extraction method, step A, the oscillation or vortex is oscillation 10 to 15 times or vortex for 3 to 5 minutes.

[0021] In the above extraction method, in step A, the centrifugation is performed at 3000-5000 r / min for 15-25 minutes.

[0022] In the above extraction method, step B, the oscillation or vortex is oscillation 10 to 15 times or vortex for 3 to 5 minutes.

[0023] In the extraction method described above, step B involves centrifugation at 3000–5000 r / min for 15–25 minutes.

[0024] In the above extraction method, in step C, the mass-to-volume ratio of the mash or solid grain in step A to the n-hexane in step C is 1g:1-3mL.

[0025] In the above extraction method, step C, the oscillation or vortex is oscillation 3 to 5 times or vortex for 1 to 3 minutes.

[0026] In the above extraction method, in step C, the static stratification time is 15 to 30 minutes.

[0027] Generally speaking, the fat content in solid grains is shown in Table 1. When the fat content in mash or solid grains is too high, it will affect the accuracy of mineral oil test results.

[0028] Table 1 Fat content in solid grains

[0029]

[0030] Therefore, in the above extraction method, when the fat content in the mash or solid grain exceeds 3%, or when solid grain with a fat content exceeding 3% is used as raw material to prepare the mash, after combining the supernatant obtained in step A and the supernatant obtained in step B, a fat purification operation is also included, specifically:

[0031] D‵. Combine the supernatants obtained in step A and step B, concentrate to 2-3 mL, and then perform silica gel column chromatography using a mixed solvent of dichloromethane and n-hexane in a volume ratio of 3-4:12-16 as the equilibration and eluent. Collect the eluent, which is the extract containing mineral oil.

[0032] As shown in Table 1, when using corn, soybeans, or peanuts alone as extraction raw materials, or when using a mixture of corn, soybeans, and peanuts in pairs or all three as extraction raw materials, fat purification is required. Furthermore, when using mixtures of the grains listed in Table 1 as extraction raw materials, fat purification is also required when the fat content of the mixed grains exceeds 3%. Additionally, when preparing fermented mash using corn, soybeans, or peanuts alone, or using a mixture of corn, soybeans, and peanuts in pairs or all three as raw materials, or when using a mixture of grains with a fat content exceeding 3% as raw materials, fat purification is also required for mineral oil extraction of the fermented mash.

[0033] In the above extraction method, in step D‵, the concentration method is nitrogen blowing concentration or rotary evaporation concentration at 50-60℃.

[0034] In the above extraction method, in step D‵, the silica gel is baked at 390-410℃ for 12-15 hours.

[0035] In the above extraction method, the fat purification operation is more specifically as follows: Combine the supernatant obtained in step A and the supernatant obtained in step B, concentrate with nitrogen blowing or rotary evaporation at 50-60℃ to 2-3 mL, load silica gel activated in a muffle furnace (baked at 390-410℃ for 12-15 h) into a glass syringe or silica gel column with the inner tube and needle discarded, press it firmly, equilibrate the silica gel column with a mixed solvent of dichloromethane and n-hexane at a volume ratio of 3-4:12-16, and when the liquid level is almost exhausted, add the concentrated extract and load the sample, elute with a mixed solvent of dichloromethane and n-hexane at a volume ratio of 3-4:12-16, and collect the eluent, which is the extract containing mineral oil.

[0036] Based on the above extraction method, the present invention also provides a method for detecting mineral oil in mash or solid grains, which includes the following steps:

[0037] a. Concentrate the obtained mineral oil-containing extract to 0.1-0.5 mL, add n-hexane to make up to 1-2 mL, inject into a two-dimensional gas chromatograph with hydrogen flame ionization detector for detection, and obtain a full two-dimensional spectrum;

[0038] b. Analyze the full two-dimensional spectrum. Based on whether a hazy hump appears in the MOSH region, determine whether the mash or solid grain contains mineral oil saturated hydrocarbons. Based on whether a hazy hump appears in the MOAH region, determine whether the mash or solid grain contains mineral oil aromatic hydrocarbons.

[0039] Among the above detection methods, when using a two-dimensional gas chromatography flame ionization detector, the gas chromatography conditions are as follows: one-dimensional column DB-17HT 30m×0.25mm×0.15μm, two-dimensional column DB-1MS. 0.7m×0.25mm×0.1μm; injection temperature 300℃, splitless liquid injection, injection volume 1uL; carrier gas: helium; column flow rate 1.7mL / min; modulation column: initial temperature 50℃, hold for 2-5min, increase to 340℃ at a rate of 10℃ / min, hold for 2-5min; modulator outlet temperature program: initial temperature 50℃, hold for 2-5min, increase to 340℃ at a rate of 10℃ / min, hold for 5-7min; modulator inlet temperature program: 50℃, hold for 6.85-8min, increase to 260℃ at a rate of 13℃ / min, hold for 7-8min; modem conditions: breathing airflow modulator, DV modulation column 1.2m×0.25mm, cycle 4s.

[0040] Among the above detection methods, when using a two-dimensional gas chromatograph with a hydrogen flame ionization detector, the flame ionization detection conditions are as follows: detector temperature is 300℃, air flow rate is 350 mL per minute, hydrogen flow rate is 30 mL per minute, and tail gas nitrogen flow rate is 30 mL per minute.

[0041] The beneficial effects of this invention are:

[0042] 1) Distillation mash contains a large amount of grains, such as sorghum, rice, wheat, corn, and glutinous rice. During the distillation process, mineral oils in the mash decompose under high temperature and pressure, releasing toxic chemicals (such as saturated hydrocarbons and aromatic hydrocarbons). These toxic substances enter the liquor and harm the human body. This invention uses a combination of surface extraction and water bath extraction. It can not only extract mineral oils from the sample surface but also extract mineral oils that migrate from inside the sample under high temperature and pressure through water bath extraction. This allows for comprehensive enrichment of mineral oils, maximizing the extraction of mineral oils produced at room temperature and during high-temperature cooking. This provides a deeper understanding of the migration of mineral oils in the mash and solid grains.

[0043] 2) Due to the complex sample matrix and low mineral oil content, the selectivity and sensitivity of conventional GC-FID cannot meet the analytical requirements. In the high-performance liquid chromatography-gas chromatography (HPLC-GC) method, the HPLC silica gel column can only adsorb 20 mg of oil, and its highly customized nature limits the specifications of the HPLC silica gel column, meaning that the purification capacity of the instrument is limited. The two-dimensional gas chromatography flame ionization detector method proposed in this invention has high resolution, strong selectivity, and large peak capacity, making it more suitable for the analysis of complex samples containing mineral oil. This method has a fast response and can detect mineral oil saturated hydrocarbons and aromatic hydrocarbons more accurately in a short time.

[0044] 3) Mineral oil and fat are miscible. When extracting mineral oil, most of the fat in the sample also dissolves. Similar to corn, soybeans or other grains and nuts, which contain a lot of fat, mineral oil contamination is more serious. The extraction solution purification process of this invention can reduce the influence of fat on mineral oil detection and make the detection results more accurate. Attached Figure Description

[0045] Figure 1 This is a flowchart illustrating the extraction process of mineral oil from fermented mash and solid grains according to the present invention.

[0046] Figure 2 This is a full two-dimensional gas chromatogram of the sorghum mash sample extract under a hydrogen flame ionization detector in Example 1.

[0047] Figure 3 The image shows a full two-dimensional gas chromatogram of the extract from the sorghum mash sample in Comparative Example 1 without water bath, obtained using a flame ionization detector.

[0048] Figure 4 This is a full two-dimensional gas chromatogram of the sorghum mash sample extract after fat purification in Example 2, obtained using a hydrogen flame ionization detector.

[0049] Figure 5 This is a full two-dimensional gas chromatographic spectrum of the sorghum sample extract in Example 3 under a hydrogen flame ionization detector.

[0050] Figure 6 This is a full two-dimensional gas chromatographic spectrum of the corn sample extract in Example 4 under a hydrogen flame ionization detector.

[0051] Figure 7 The image shows a full two-dimensional gas chromatogram of the corn sample extract without fat purification in Comparative Example 2 under a flame ionization detector. Detailed Implementation

[0052] The present invention will be further described in detail below through embodiments, but the scope of protection of the present invention is not limited to the embodiments described herein.

[0053] Example 1

[0054] Preparation of fermented grain samples: 5 catties of sorghum was crushed using a grinder, soaked in 80℃ hot water, steamed for 25 minutes initially, simmered for 50 minutes, and then steamed again for 60 minutes. After steaming, the grain was drained of excess water and spread out to cool. 500g of Daqu (a type of starter culture) was mixed in and placed in a fermentation pit. After 45 days, the grain was removed from the pit and piled up to form fermented grain. 25g of the fermented grain was weighed out for later use.

[0055] I. Extraction of mineral oil from fermented mash samples

[0056] 1) Weigh 25g of fermented mash into a glass container, add 50mL of n-hexane, cover with a glass lid, shake up and down 15 times, and centrifuge at 5000r / min for 20 minutes to obtain the first extract. Take out the fermented mash sample after the first extraction for later use.

[0057] 2) Place the fermented mash sample after the first extraction into a glass container, mix with 50 mL of ultrapure water, and bathe in an 80°C water bath for 1 hour. Remove and let cool, cover with a glass lid, shake up and down 15 times, and centrifuge at 5000 r / min for 20 minutes to obtain 50 mL of the extract.

[0058] 3) Pour 50 mL of the extract to be extracted into a glass container, add 50 mL of n-hexane, cover with a glass lid, shake up and down 3 times, let stand for 15 minutes to separate the layers, and extract the supernatant to obtain the second extract.

[0059] 4) Combine the two extracts, concentrate them to 0.5 mL by nitrogen blowing or by rotary concentration at 50 °C to 0.5 mL, and bring the volume to 1 mL with n-hexane. Inject the solution into a two-dimensional gas chromatograph with flame ionization detector.

[0060] II. Detection of mineral oil in samples

[0061] Gas chromatography conditions: One-dimensional column DB-17HT (30m × 0.25mm × 0.15μm), two-dimensional column DB-1MS (0.7m × 0.25mm × 0.1μm). Injection temperature 300℃, splitless liquid injection, injection volume: 1uL; carrier gas: helium; column flow rate: 1.7mL / min; modulation column: initial temperature 50℃, hold for 2min, ramp to 340℃ at a rate of 10℃ / min, hold for 5min; modulator outlet temperature program: initial temperature 50℃, hold for 2min, ramp to 340℃ at a rate of 10℃ / min, hold for 5min; modulator inlet temperature program: 50℃, hold for 6.85min, ramp to 260℃ at a rate of 13℃ / min, hold for 7min.

[0062] Modem requirements: Breathing airflow modulator, DV modulation column (1.2m×0.25mm), cycle 4s.

[0063] Flame ionization detection conditions: detector temperature 300℃, air flow rate 350 mL / min; hydrogen flow rate 30 mL / min; and purge nitrogen flow rate 30 mL / min.

[0064] III. Results and Analysis

[0065] exist Figure 2In the full two-dimensional gas chromatography-flame ionization detector (GC×GC-FID) spectrum of the mineral oil extracted from the mash sample, a distinct hazy hump appeared in the MOSH region of the mineral oil, indicating that mineral oil saturated hydrocarbons were detected in the extract of the mash sample, but no mineral oil aromatic hydrocarbons were detected.

[0066] Comparative Example 1

[0067] Preparation of fermented grain samples: 5 catties of sorghum was crushed using a grinder, soaked in 80℃ hot water, steamed for 25 minutes initially, simmered for 50 minutes, and then steamed again for 60 minutes. After steaming, the grain was drained of excess water and spread out to cool. 500g of Daqu (a type of starter culture) was mixed in and placed in a fermentation pit. After 45 days, the grain was removed from the pit and piled up to form fermented grain. 25g of the fermented grain was weighed out for later use.

[0068] I. Extraction of mineral oil from fermented mash samples

[0069] 1) Weigh 25g of fermented mash into a glass container, add 50mL of n-hexane, cover with a glass lid, shake up and down 15 times, and centrifuge at 5000r / min for 20 minutes to obtain the first extract. Take out the fermented mash sample after the first extraction for later use.

[0070] 2) Place the fermented mash sample after the first extraction into a glass container, add 50 mL of n-hexane, cover with a glass lid, shake up and down 15 times, and centrifuge at 5000 r / min for 20 minutes to obtain the second extract.

[0071] 3) Combine the two extracts, concentrate them to 0.5 mL by nitrogen blowing or by rotary concentration at 50 °C to 0.5 mL, and bring the volume to 1 mL with n-hexane. Inject the solution into a two-dimensional gas chromatograph with flame ionization detector.

[0072] II. Detection of mineral oil in samples

[0073] The gas chromatography conditions, modem conditions, and flame ionization detection conditions were the same as in Example 1.

[0074] III. Results and Analysis

[0075] exist Figure 3 In the full two-dimensional gas chromatography-flame ionization detector (GC×GC-FID) spectrum (not extracted by water bath during the pretreatment of the fermented mash sample), no obvious hazy humps appeared in the MOSH and MOAH regions of the mineral oil, indicating that no mineral oil saturated hydrocarbons or mineral oil aromatic hydrocarbons were detected in the extract of this fermented mash sample. This suggests that a water bath can increase the extraction yield of mineral oil.

[0076] Example 2

[0077] Preparation of fermented grain samples: 5 catties of sorghum was crushed using a grinder, soaked in 80℃ hot water, steamed for 25 minutes initially, simmered for 50 minutes, and then steamed again for 60 minutes. After steaming, the grain was drained of excess water and spread out to cool. 500g of Daqu (a type of starter culture) was mixed in and placed in a fermentation pit. After 45 days, the grain was removed from the pit and piled up to form fermented grain. 25g of the fermented grain was weighed out for later use.

[0078] I. Extraction of mineral oil from fermented mash samples

[0079] 1) The steps are the same as those in step 1) of Example 1.

[0080] 2) The steps are the same as those in step 2) of Example 1.

[0081] 3) The steps are the same as those in step 3) of Example 1.

[0082] 4) Combine the two extracts and concentrate them to 2 mL by nitrogen blowing.

[0083] 5) Reagent preparation:

[0084] Activated silica gel: Place the silica gel in a muffle furnace and bake at 400℃ for 12 hours. After cooling, remove it and store it in a brown bottle. Store it in a cool, dry place away from light. It is recommended to use it within 2 weeks.

[0085] 20% dichloromethane solution: Mix dichloromethane and n-hexane in a volume ratio of 1:4, mix well and set aside for later use.

[0086] 7g of silica gel activated in a muffle furnace (400℃) was loaded into a glass syringe (with the inner tube and needle removed) and compacted. The silica gel column was equilibrated with 5mL of 20% dichloromethane solution. When the liquid level was nearly exhausted, 2mL of extract was added for loading. The column was then eluted with 30mL of a mixed solvent consisting of 80% n-hexane and 20% dichloromethane. The eluent was collected in a glass dish and concentrated to 0.5mL by nitrogen blowing or by rotary evaporation at 50℃. The volume was then adjusted to 1mL with n-hexane. The solution was injected into a two-dimensional gas chromatograph using a flame ionization detector.

[0087] II. Detection of mineral oil in samples

[0088] The gas chromatography conditions, modem conditions, and flame ionization detection conditions were the same as in Example 1.

[0089] III. Results and Analysis

[0090] exist Figure 4In the full two-dimensional gas chromatography-flame ionization detector (GC×GC-FID) spectrum (GC×GC-FID) of the mineral oil extracted from the mash sample after pretreatment and fat purification, a distinct hazy hump appeared in the MOSH region of the mineral oil, indicating that saturated hydrocarbons of mineral oil were detected in the extract of this mash sample, but no aromatic hydrocarbons of mineral oil were detected. The results are similar to those in Example 1, indicating that for low-fat raw materials, even without purification, the detection results are basically not affected.

[0091] Example 3

[0092] Sample: 100g of commercially available sorghum product. After opening the packaging, weigh out 25g of the sorghum from the inside to avoid introducing additional mineral oil into the sample from the packaging material.

[0093] I. Extraction of mineral oil from product samples

[0094] 1) Weigh 25g of sorghum into a glass container, add 50mL of n-hexane, cover with a glass lid, shake up and down 15 times, and centrifuge at 5000r / min for 20 minutes to obtain the first extract. Take out the sorghum sample after the first extraction for later use.

[0095] 2) Place the sorghum sample after the first extraction into a glass container, mix with 50 mL of ultrapure water, and bathe in an 80°C water bath for 1 hour. Remove and let cool, cover with a glass lid, shake up and down 15 times, and centrifuge at 5000 r / min for 20 minutes to obtain 50 mL of the extract.

[0096] 3) Pour 50 mL of the extract to be extracted into a glass container, add 50 mL of n-hexane, cover with a glass lid, shake up and down 3 times, let stand for 15 minutes to separate the layers, and extract the supernatant to obtain the second extract.

[0097] 4) Combine the two extracts, concentrate them to 0.5 mL by nitrogen blowing or by rotary concentration at 50 °C to 0.5 mL, and bring the volume to 1 mL with n-hexane. Inject the solution into a two-dimensional gas chromatograph with flame ionization detector.

[0098] II. Detection of mineral oil in samples

[0099] Gas chromatography conditions: One-dimensional column DB-17HT (30m × 0.25mm × 0.15μm), two-dimensional column DB-1MS (0.7m × 0.25mm × 0.1μm). Injection temperature 300℃, splitless liquid injection, injection volume: 1uL; carrier gas: helium; column flow rate: 1.7mL / min; modulation column: initial temperature 50℃, hold for 2min, ramp to 340℃ at a rate of 10℃ / min, hold for 5min; modulator outlet temperature program: initial temperature 50℃, hold for 2min, ramp to 340℃ at a rate of 10℃ / min, hold for 5min; modulator inlet temperature program: 50℃, hold for 6.85min, ramp to 260℃ at a rate of 13℃ / min, hold for 7min.

[0100] Modem requirements: Breathing airflow modulator, DV modulation column (1.2m×0.25mm), cycle 4s.

[0101] Flame ionization detection conditions: detector temperature 300℃, air flow rate 350 mL / min; hydrogen flow rate 30 mL / min; and purge nitrogen flow rate 30 mL / min.

[0102] III. Results and Analysis

[0103] exist Figure 5 In the full two-dimensional gas chromatography-flame ionization detector (GC×GC-FID) spectrum of the mineral oil extracted from the sorghum sample, no obvious hazy humps were observed in the MOSH and MOAH regions of the mineral oil, indicating that no mineral oil saturated hydrocarbons or mineral oil aromatic hydrocarbons were detected in the sorghum sample extract, and also indicating that mineral oil contamination is introduced additionally during the processing of the mash.

[0104] Example 4

[0105] Sample: 100g of commercially available corn product. After opening the package, weigh out 25g of the corn from the inside to avoid introducing additional mineral oil into the sample from the packaging material.

[0106] I. Extraction of mineral oil from corn samples

[0107] 1) The steps are the same as those in step 1) of Example 1.

[0108] 2) The steps are the same as those in step 2) of Example 1.

[0109] 3) The steps are the same as those in step 3) of Example 1.

[0110] 4) Combine the two extracts and concentrate them to 2 mL by nitrogen blowing.

[0111] 5) Reagent preparation:

[0112] Activated silica gel: Place the silica gel in a muffle furnace and bake at 400℃ for 12 hours. After cooling, remove it and store it in a brown bottle. Store it in a cool, dry place away from light. It is recommended to use it within 2 weeks.

[0113] 20% dichloromethane solution: Mix dichloromethane and n-hexane in a volume ratio of 1:4, mix well and set aside for later use.

[0114] 7g of silica gel activated in a muffle furnace (400℃) was loaded into a glass syringe (with the inner tube and needle removed) and compacted. The silica gel column was equilibrated with 5mL of 20% dichloromethane solution. When the liquid level was nearly exhausted, 2mL of extract was added for loading. The column was then eluted with 30mL of a mixed solvent consisting of 80% n-hexane and 20% dichloromethane. The eluent was collected in a glass dish and concentrated to 0.5mL by nitrogen blowing or by rotary evaporation at 50℃. The volume was then adjusted to 1mL with n-hexane. The solution was injected into a two-dimensional gas chromatograph using a flame ionization detector.

[0115] II. Detection of mineral oil in samples

[0116] The gas chromatography conditions, modem conditions, and flame ionization detection conditions were the same as in Example 1.

[0117] III. Results and Analysis

[0118] exist Figure 6 In the full two-dimensional gas chromatography-flame ionization detector (GC×GC-FID) spectrum of the mineral oil extracted from the corn sample after pretreatment and fat purification, obvious hazy humps appeared in the MOSH region of the mineral oil, indicating that mineral oil saturated hydrocarbons were detected in the corn sample extract, but no mineral oil aromatic hydrocarbons were detected.

[0119] Comparative Example 2

[0120] Sample: 100g of commercially available corn product. After opening the package, weigh out 25g of the corn from the inside to avoid introducing additional mineral oil into the sample from the packaging material.

[0121] I. Extraction of mineral oil from corn samples

[0122] 1) The steps are the same as those in step 1) of Example 1.

[0123] 2) The steps are the same as those in step 2) of Example 1.

[0124] 3) The steps are the same as those in step 3) of Example 1.

[0125] 4) The steps are the same as those in step 4) of Example 1.

[0126] II. Detection of mineral oil in samples

[0127] The gas chromatography conditions, modem conditions, and flame ionization detection conditions were the same as in Example 1.

[0128] III. Results and Analysis

[0129] exist Figure 7 In the full two-dimensional gas chromatography-flame ionization detector (GC×GC-FID) spectrum of mineral oil extracted from corn samples after pretreatment and without fat purification, a more obvious hazy hump appeared in the MOSH region of the mineral oil, indicating that fat purification can reduce the detection of saturated hydrocarbons in corn mineral oil and make the detection results more accurate.

Claims

1. A method for extracting mineral oil from fermented grains or solid grains, characterized in that: Includes the following steps: A. Mix the mash or solid grains with n-hexane, shake or vortex for the first extraction, and centrifuge to obtain the supernatant and precipitate; B. Mix the precipitate obtained in step A with water, bathe in water, shake or vortex, and then centrifuge to obtain the extract. C. Mix the extract obtained in step B with n-hexane, shake or vortex for a second extraction, let stand to separate the layers, and obtain the supernatant. D. Combine the supernatant obtained in step A and the supernatant obtained in step C to obtain the extract containing mineral oil. In step B, the mass-to-volume ratio of the mash or solid grain in step A to the water in step B is 1g:1~3mL; In step B, the temperature of the water bath is 70℃~90℃; In step C, the mass-to-volume ratio of the mash or solid grain in step A to the n-hexane in step C is 1g:1~3mL; When the fat content in the mash or solid grain exceeds 3%, or when solid grain with a fat content exceeding 3% is used as raw material to prepare the mash, the supernatant obtained in step A and the supernatant obtained in step C are combined, and a fat purification operation is also included, specifically: D‵. Combine the supernatants obtained in step A and step C, concentrate to 2-3 mL, and then perform silica gel column chromatography separation using a mixed solvent of dichloromethane and n-hexane with a volume ratio of 3-4:12-16 as the equilibration and eluent. Collect the eluent, which is the extract containing mineral oil.

2. The extraction method of claim 1, wherein: In step B, the water bath time is 1 to 2 hours.

3. The extraction method of claim 1, wherein: In step A, at least one of the following must be satisfied: The solid grains are selected from at least one of the following: corn, sorghum, rice, wheat, barley, highland barley, sweet potato, potato, yam, taro, soybean, peanut, mung bean, broad bean, pea, red bean, or cowpea; The fermented grains are prepared by the following method: after crushing solid grains, soak the grains in hot water at 75℃~95℃, steam for 25~30 minutes, simmer for 50~60 minutes, and steam again for 35~60 minutes. After removing water from the steamed grains, spread them out to cool, mix them with Daqu (a type of starter culture), put them in a fermentation pit, and ferment for no less than 45 days. After fermentation, the grains are removed from the pit and piled up to form fermented grains. The amount of Daqu added is 175~225g / kg of solid grains. In step A, the mass-to-volume ratio of the mash or solid grain to the n-hexane in step A is 1g:1~3mL; The oscillation or vortex refers to oscillations of 10-15 times or vortices of 3-5 minutes. The centrifugation is performed at 3000~5000 r / min for 15~25 minutes.

4. The extraction method of claim 1, wherein: In step B, at least one of the following must be satisfied: The oscillation or vortex refers to oscillations of 10-15 times or vortices of 3-5 minutes. The centrifugation is performed at 3000~5000 r / min for 15~25 minutes.

5. The extraction method of claim 1, wherein: In step C, at least one of the following must be satisfied: The oscillation or vortex refers to oscillations of 3 to 5 times or vortices of 1 to 3 minutes. The static stratification time is 15-30 minutes.

6. The extraction method of claim 1, wherein: In step D‵, at least one of the following must be satisfied: The concentration method is nitrogen blowing concentration or rotary evaporation concentration at 50~60℃; The silicone is baked at 390~410℃ for 12~15 hours.

7. The method for detecting mineral oil in fermented grains or solid grains, characterized in that: Includes the following steps: a. The mineral oil-containing extract obtained in the method for extracting mineral oil from the fermented grains or solid grains according to any one of claims 1-6 is concentrated to 0.1-0.5 mL, hexane is added to make up to 1-2 mL, and the two-dimensional gas chromatography hydrogen flame ionization detector is injected for detection to obtain a full two-dimensional spectrum; b. The full two-dimensional spectrum is analyzed, whether the MOSH region appears as a misty hump is determined to judge whether the fermented grains or solid grains contain mineral oil saturated hydrocarbons, and whether the MOAH region appears as a misty hump is determined to judge whether the fermented grains or solid grains contain mineral oil aromatic hydrocarbons.

8. The method for detecting mineral oil in distilled liquor or solid grain according to claim 7, characterized in that: When the two-dimensional gas chromatography hydrogen flame ionization detector is detected, the gas chromatography conditions are as follows: one-dimensional chromatographic column DB-17HT 30m x 0.25mm x 0.15μm, two-dimensional chromatographic column DB-1MS 0.7m x 0.25mm x 0.1μm; injection 300°C, no split liquid injection, injection volume 1uL; carrier gas is helium; column flow 1.7mL / min; modulation column: initial temperature 50°C, hold for 2-5min, increase to 340°C at a rate of 10°C / min, hold for 2-5min; modulation outlet temperature program: initial temperature 50°C, hold for 2-5min, increase to 340°C at a rate of 10°C / min, hold for 5-7min; modulation inlet temperature program: 50°C for 6.85-8min, increase to 260°C at a rate of 13°C / min, hold for 7-8min; modulator conditions: breathing air modulator, DV modulation column 1.2m x 0.25mm, cycle 4s.

9. The method for detecting mineral oil in distilled liquor or solid grain according to claim 7, characterized in that: When the two-dimensional gas chromatography hydrogen flame ionization detector is detected, the flame ionization detection conditions are as follows: detector temperature is 300°C, air flow is 350mL per minute; hydrogen flow is 30mL per minute; tail nitrogen flow is 30mL per minute.

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