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

Abstract

The invention discloses a method for extracting and detecting mineral oil in fermented grains or solid grains, and belongs to the technical field of food detection. In order to realize complete extraction and detection of mineral oil in fermented grains and solid grains, the invention provides a method for extracting and detecting mineral oil in fermented grains or solid grains, which comprises the following steps: mixing fermented grains or solid grains with n-hexane, and carrying out first extraction to obtain supernate and precipitate; mixing the precipitate with water, and performing water bath to obtain a to-be-extracted solution; mixing the to-be-extracted liquid with n-hexane, and performing secondary extraction to obtain supernate; combining the supernate to obtain an extract containing mineral oil; and injecting into a two-dimensional gas chromatography hydrogen flame ionization detector for detection. According to the method, a mode of combining surface extraction and water bath extraction is adopted, comprehensive enrichment of the mineral oil is realized, and meanwhile, a two-dimensional gas chromatography flame ionization detector is adopted, so that saturated hydrocarbon and aromatic hydrocarbon of the mineral oil can be more accurately detected in a short time.

Description

Technical Field

[0001] The invention belongs to the technical field of food detection, and in particular relates to a method for extracting and detecting mineral oil in fermented grains or solid grains. Background Art

[0002] Mineral oils are petroleum and synthetic oils and their refined products, including nC 10 ~nC 50 Hydrocarbons can be divided into two categories: mineral oil saturated hydrocarbons (MOSH) and mineral oil aromatic hydrocarbons (MOAH). The former are divided into chain alkanes and cycloalkanes, which have an accumulation effect in the human body, while the latter mainly include alkyl-substituted polyaromatic hydrocarbons, which have potential teratogenicity and carcinogenicity. Nowadays, the research on mineral oil in food is mainly focused on edible oil, chocolate, milk powder, biscuits, bread and other foods. At present, there is little research on the detection methods and standards of mineral oil in alcohol and many solid grains. High-performance liquid chromatography tandem mass spectrometry (LC-MS) is currently widely used in the research of mineral oil detection in Europe, but the problem is: first, the equipment is expensive and difficult to popularize. Secondly, the sample pretreatment work is cumbersome, strict requirements on the experimenters, large errors and time-consuming.

[0003] GB 2760-2014 "National Food Safety Standard for the Use of Food Additives" stipulates that mineral oil can be used as a defoamer, release agent, anti-sticking agent and lubricant in the fermentation process, candy, potato chips and soy product processing. Mineral oil can migrate and contaminate food through the entire industrial chain of raw materials, production, packaging and transportation. In the production of liquor, fermented grains refer to the fermented grains after cooking. Distilling the fermented grains into liquor is a crucial step in the production of liquor. The degree of mineral oil contamination in the fermented grains will directly affect the mineral oil content in the liquor. Some research institutes and universities have conducted research on the migration contamination of mineral oil in food packaging, but there is almost no research on the contamination of mineral oil in food processing. Therefore, it is very important to carry out the detection of mineral oil in fermented grains and the detection of mineral oil in solid grains.

[0004] CN20181100618.0 discloses a method for extracting mineral oil from dairy products, comprising: (1) hydrolyzing the dairy product to be tested with a hydrochloric acid solution to obtain a hydrolyzate; (2) mixing and centrifuging the hydrolyzate, anhydrous ethanol and n-hexane to obtain an upper layer liquid and a lower layer liquid, and collecting the upper layer liquid; (3) adding n-hexane to the lower layer liquid, repeating the mixing and centrifuging, collecting the upper layer liquid, and combining the upper layer liquids obtained twice to obtain an extract; and (4) mixing and centrifuging the extract with water, and collecting the upper layer liquid to extract 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, so as to obtain a first upper layer liquid and a first lower layer liquid; (3) mixing the first lower layer liquid with the mixed solvent, performing a second extraction treatment and a second separation treatment, so as to obtain a second upper layer liquid and a second lower layer liquid; (4) combining the first upper layer liquid and the second upper layer liquid, mixing the obtained mixed liquid with water, and performing a third separation treatment, so as 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 respectively centrifuged at 3000 to 5000 r / min for 10 to 20 minutes; the first extraction treatment and the second extraction treatment are respectively shaken at a speed of 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 letting it stand for stratification; repeating twice, collecting and combining the upper n-hexane in a glass container, and concentrating it to 5 mL with nitrogen blowing to obtain an extract; 2) weighing ethylenediamine-N-propyl silane silica gel and octadecylsilane bonded silica gel washed with n-hexane, and 0.3% silver nitrate silica gel particles in a glass test tube, then adding the above extract to the glass test tube, shaking, centrifuging, and taking the supernatant and blowing it with nitrogen to Less than 0.5mL; after the volume is adjusted to 1ml with n-hexane, a purified liquid is obtained; 3) the purified liquid is detected by a two-dimensional gas chromatography-time-of-flight mass spectrometer / hydrogen flame ionization detector; when the purified liquid enters the comprehensive two-dimensional chromatography through liquid injection, the mineral oil saturated hydrocarbons and mineral oil aromatic hydrocarbons are separated through different chromatographic columns, and the spectrum shows a comprehensive two-dimensional spectrum under the comprehensive two-dimensional gas chromatography time-of-flight mass spectrometer (GC×GC-TOFMS) and a comprehensive two-dimensional spectrum under the comprehensive two-dimensional gas chromatography hydrogen flame ionization detector (GC×GC-FID). However, the above method is only applicable to water-soluble foods, not solid food.

[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, and the mineral oil separation column is made of glass; the drying layer is selected from anhydrous sodium sulfate, and the silica gel in the silica gel layer is silica gel activated at 300-500°C for not 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) continuing to elute with a dichloromethane / n-hexane mixed solvent and collecting the eluate; (6) after the eluate is concentrated by rotary evaporation, it is subjected to epoxidation treatment and then detected and analyzed by LC-GC; the silica gel particle size is activated at 400°C for at least 16 hours. However, this method directly uses column chromatography, which is not suitable for mash and is too expensive. In addition, instant noodles and other fast-acting foods require high-temperature water scalding, but this method directly uses column chromatography and does not take into account the consumption of the product, making it difficult to ensure 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 a rice sample to be tested twice with 10-20mL of n-hexane, and merging to obtain an extract; (2) adding a magnesium silicate purifier to the extract and vortexing it to obtain a vortex liquid; (3) centrifuging the vortex liquid, concentrating the supernatant and fixing the volume to obtain a test liquid; (4) subjecting the test liquid to molecular fluorescence detection, and determining the content of aromatic mineral oil in the rice sample to be tested based on the detection result. 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 test 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 oil without fluorescence characteristics such as liquid paraffin, the accuracy of the test result will be affected. Summary of the invention

[0007] In order to achieve complete extraction of mineral oil from fermented grains and solid grains such as rice, sorghum, wheat, and corn that need to be cooked for consumption, and ensure accurate qualitative detection, the present invention adopts a combination of surface extraction and water bath extraction when extracting mineral oil from fermented grains and solid grains, which can not only extract mineral oil from the surface of the sample, but also extract mineral oil from the inside of the sample and from a high temperature and high pressure environment through a water bath, thereby comprehensively enriching the mineral oil; in addition, fatty acid glycerides in solid grains containing fats and oils are difficult to separate from mineral oils, have serious matrix interference, and have low detection sensitivity, which will affect the analysis and detection of mineral oil in the sample. The present invention performs a degreasing treatment on a sample extract containing high fats and oils, thereby reducing detection errors.

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

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

[0010] B. Mix the precipitate obtained in step A with water, and after water bathing, shake or vortex, and then centrifuge to obtain a liquid to be extracted;

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

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

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

[0014] Wherein, in the above extraction method, in step B, the temperature of the water bath is 70°C to 90°C.

[0015] Wherein, in the above extraction method, in step B, the water bath time is 1 to 2 hours.

[0016] Wherein, in the above extraction method, in step A, the solid food 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] Among them, in the above-mentioned extraction method, in step A, the fermented grain is prepared by the following method: after the solid grain is crushed, it is soaked in hot water at 75℃~95℃, initially steamed for 25~30 minutes, simmered for 50~60 minutes, and re-steamed for 35~60 minutes, the steamed grain is drained and spread out to dry, mixed with Daqu, put into a cellar, fermented for not less than 45 days, taken out of the cellar, and piled up as fermented grain; the amount of Daqu added is 175~225g / kg solid grain.

[0018] Of course, the fermented grains raw materials of the extraction method of the present invention are not limited to the above-mentioned fermented grains. The common fermented grains in the art, such as the fermented grains of strong-flavor liquor, the fermented grains of sauce-flavor liquor, the fermented grains of light-flavor liquor, and the fermented grains of mixed-flavor liquor, are all suitable for the present invention.

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

[0020] Wherein, in the above extraction method, in step A, the shaking or vortexing is shaking 10 to 15 times or vortexing for 3 to 5 minutes.

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

[0022] Wherein, in the above extraction method, in step B, the shaking or vortexing is shaking 10 to 15 times or vortexing for 3 to 5 minutes.

[0023] Wherein, in the above extraction method, in step B, the centrifugation is performed at 3000-5000 r / min for 15-25 minutes.

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

[0025] Wherein, in the above extraction method, in step C, the shaking or vortexing is 3 to 5 times or vortexing for 1 to 3 minutes.

[0026] Wherein, 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 fermented grains or solid grains is too high, it will affect the accuracy of mineral oil detection results.

[0028] Table 1 Fat content in solid food

[0029]

[0030] Therefore, in the above extraction method, when the fat content in the fermented grains or solid grains exceeds 3% by weight, or when solid grains with a fat content of more than 3% by weight are used as raw materials to prepare fermented grains, after combining the supernatant obtained in step A and the supernatant obtained in step B, a fat purification operation is further included, specifically:

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

[0032] Combined with Table 1, it can be seen that when corn, soybeans or peanuts are used as the extraction raw materials alone, or when corn, soybeans and peanuts are mixed in pairs or in a mixture of the three as the extraction raw materials, fat purification is required. In addition, when a mixture of the grains in Table 1 is used as the extraction raw material, when the fat content of the mixed grain exceeds 3%, fat purification is also required. In addition, when mash is prepared using corn, soybeans or peanuts as the raw materials alone, or when mash is prepared using a mixture of corn, soybeans and peanuts in pairs or in a mixture of the three as the raw materials, or when a mixture of grains with a fat content of over 3% is used as the raw material to prepare mash, mineral oil extraction of the mash is also required to be fat purified.

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

[0034] Wherein, in the above extraction method, in step D‵, the silica gel is baked at 390-410°C for 12-15h.

[0035] Among them, in the above extraction method, the fat purification operation is more specifically: combine the supernatant obtained in step A and the supernatant obtained in step B, concentrate by nitrogen blowing or rotary evaporation at 50-60°C to 2-3 mL, put the silica gel activated by muffle furnace (baked at 390-410°C for 12-15h) into a glass syringe or silica gel column with the inner tube and needle discarded, press it tightly, balance the silica gel column with a mixed solvent of dichloromethane and n-hexane in a volume ratio of 3-4:12-16, when the liquid level is close to running out, add the concentrated extract solution, elute with a mixed solvent of dichloromethane and n-hexane in a volume ratio of 3-4:12-16 as eluent, 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 fermented grains or solid grains, which comprises the following steps:

[0037] a. Concentrate the extract containing mineral oil obtained in any one of claims 1 to 7 to 0.1 to 0.5 mL, add n-hexane to make the volume 1 to 2 mL, inject into a two-dimensional gas chromatography hydrogen flame ionization detector for detection, and obtain a full two-dimensional spectrum;

[0038] b. Analyze the full two-dimensional spectrum and judge whether the mash or solid grain contains mineral oil saturated hydrocarbons based on whether a foggy hump appears in the MOSH area. Judge whether the mash or solid grain contains mineral oil aromatic hydrocarbons based on whether a foggy hump appears in the MOAH area.

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

[0040] Among them, in the above detection method, when the two-dimensional gas chromatography hydrogen flame ionization detector is used for detection, the flame ionization detection conditions are: the detector temperature is 300°C, the air flow rate is 350mL per minute; the hydrogen flow rate is 30mL per minute; and the tail blowing nitrogen flow rate is 30mL per minute.

[0041] Beneficial effects of the present invention:

[0042] 1) Fermented grains contain a large amount of grains, such as solid grains such as sorghum, rice, wheat, corn, and glutinous rice. In the process of distilling wine from fermented grains, mineral oil will decompose and release toxic chemicals (saturated hydrocarbons, aromatic hydrocarbons and other toxic substances) under high temperature and high pressure. These toxic substances enter the liquor, thereby harming the human body. The present invention adopts a combination of surface extraction and water bath extraction, which can not only extract mineral oil on the surface of the sample, but also extract mineral oil from the inside of the sample and migrated out under high temperature and high pressure environment through water bath extraction, and comprehensively enrich the mineral oil, so that the maximum amount of mineral oil produced at room temperature and high temperature cooking can be extracted, so as to have a deeper understanding of the migration of mineral oil in fermented grains 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 analysis requirements. In the high performance liquid chromatography-gas chromatography (HPLC-GC) method, the HPLC silica gel column can only adsorb 20 mg of grease, and its highly customized specifications limit the specifications of the HPLC silica gel column, which means that the purification capacity of the instrument is limited. The two-dimensional gas chromatography hydrogen flame ionization detector detection method proposed in the present invention has high resolution, strong selectivity, and large peak capacity. It is more suitable for the analysis of samples containing complex components such as mineral oil. The 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 is also dissolved. For example, corn, soybeans or other grains and nuts contain more fat and are more seriously contaminated by mineral oil. The extraction liquid purification process of the present invention can reduce the influence of fat on mineral oil detection and make the detection result more accurate. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] Figure 1 The present invention is a flow chart for extracting mineral oil from fermented grains and solid grains.

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

[0047] Figure 3 This is a comprehensive two-dimensional spectrum of the sorghum wine mash sample extract that was not water-bathed in Comparative Example 1 under a comprehensive two-dimensional gas chromatography hydrogen flame ionization detector.

[0048] Figure 4 This is a comprehensive two-dimensional spectrum of the sorghum wine mash sample extract after fat purification in Example 2 under a comprehensive two-dimensional gas chromatography hydrogen flame ionization detector.

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

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

[0051] Figure 7 This is a comprehensive two-dimensional spectrum of the corn sample extract without fat purification in Comparative Example 2 under a comprehensive two-dimensional gas chromatography hydrogen flame ionization detector. DETAILED DESCRIPTION

[0052] The present invention is further described in detail below by way of examples, but the protection scope of the present invention is not limited to the scope of the examples.

[0053] Example 1

[0054] Preparation of fermented grain samples: 5 catties of sorghum was crushed with a crusher, soaked in 80℃ hot water, steamed for 25 minutes, simmered for 50 minutes, and steamed for 60 minutes. The steamed grains were dried and spread out to dry, mixed with 500g of Daqu, and stored in a cellar. After 45 days, the grains were taken out of the cellar and piled up as fermented grains. 25g of fermented grains were weighed for later use.

[0055] 1. Extraction of mineral oil from fermented grains samples

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

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

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

[0059] 4) Combine the two extracts, concentrate to 0.5 mL by nitrogen blowing or by rotary concentrating to 0.5 mL at 50°C, make up to 1 mL with n-hexane, and inject into a two-dimensional gas chromatography hydrogen flame ionization detector.

[0060] 2. 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℃, non-split liquid injection, injection volume: 1uL; carrier gas is helium; column flow rate 1.7mL / min; modulation column: initial temperature 50℃, hold for 2min, increase to 340℃ at a rate of 10℃ / min, hold for 5min; temperature increase program at the modulator outlet: initial temperature 50℃, hold for 2min, increase to 340℃ at a rate of 10℃ / min, hold for 5min; temperature increase program at the modulator inlet: 50℃ hold for 6.85min, increase to 260℃ at a rate of 13℃ / min, hold for 7min.

[0062] Modem conditions: using a breathing airflow modulator, a DV modulation column (1.2 m × 0.25 mm), and a period of 4 s.

[0063] Flame ionization detection conditions: detector temperature is 300°C, air flow rate is 350 mL per minute; hydrogen flow rate is 30 mL per minute; tail blowing nitrogen flow rate is 30 mL per minute.

[0064] 3. Results and Analysis

[0065] exist Figure 2In the comprehensive two-dimensional gas chromatography-hydrogen flame ionization detector (GC×GC-FID) spectrum of the mineral oil extracted from the fermented grains sample, an obvious foggy hump appeared in the MOSH region of the mineral oil, indicating that mineral oil saturated hydrocarbons were detected in the extract of the fermented grains 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 with a crusher, soaked in 80℃ hot water, steamed for 25 minutes, simmered for 50 minutes, and steamed for 60 minutes. The steamed grains were dried and spread out to dry, mixed with 500g of Daqu, and stored in a cellar. After 45 days, the grains were taken out of the cellar and piled up as fermented grains. 25g of fermented grains were weighed for later use.

[0068] 1. Extraction of mineral oil from fermented grains samples

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

[0070] 2) Place the fermented grains sample after the first extraction into a glass container, add 50 mL of n-hexane, cover with a glass cover, 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 to 0.5 mL by nitrogen blowing or by rotary concentrating to 0.5 mL at 50°C, make up to 1 mL with n-hexane, and inject into the two-dimensional gas chromatography hydrogen flame ionization detector.

[0072] 2. Detection of mineral oil in samples

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

[0074] 3. Results and Analysis

[0075] exist Figure 3 In the comprehensive two-dimensional gas chromatography hydrogen flame ionization detector (GC×GC-FID) spectrum of mineral oil that was not extracted in the pretreatment process of the fermented grains sample, no obvious foggy hump appeared in the MOSH region and MOAH region of the mineral oil, indicating that no mineral oil saturated hydrocarbons and mineral oil aromatic hydrocarbons were detected in the extract of the fermented grains sample. This shows that the water bath can increase the amount of mineral oil extracted.

[0076] Example 2

[0077] Preparation of fermented grain samples: 5 catties of sorghum was crushed with a crusher, soaked in 80℃ hot water, steamed for 25 minutes, simmered for 50 minutes, and steamed for 60 minutes. The steamed grains were dried and spread out to dry, mixed with 500g of Daqu, and stored in a cellar. After 45 days, the grains were taken out of the cellar and piled up as fermented grains. 25g of fermented grains were weighed for later use.

[0078] 1. Extraction of mineral oil from fermented grains samples

[0079] 1) Step is the same as step 1) in Example 1.

[0080] 2) Step is the same as step 2) in Example 1.

[0081] 3) Step is the same as step 3) in Example 1.

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

[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, take it out and store it in a brown bottle. Keep it away from light and in a dry place. It is recommended to use it up within 2 weeks.

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

[0086] 7g of silica gel activated by muffle furnace (400℃) was loaded into a glass syringe with the inner tube and needle removed. After pressing tightly, 5mL of 20% dichloromethane solution was used to balance the silica gel column. When the liquid level was close to running out, 2mL of extract was added and loaded, and 30mL of mixed solvent consisting of 80% n-hexane + 20% dichloromethane was used for elution. The eluate was collected in a glass container, concentrated to 0.5mL by nitrogen blowing or rotary evaporated to 0.5mL at 50℃, and n-hexane was added to make up to 1mL. Inject into a two-dimensional gas chromatography hydrogen flame ionization detector.

[0087] 2. Detection of mineral oil in samples

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

[0089] 3. Results and Analysis

[0090] exist Figure 4In the comprehensive two-dimensional gas chromatography hydrogen flame ionization detector (GC×GC-FID) spectrum of mineral oil extracted from the fermented grains sample after pretreatment and fat purification, an obvious foggy hump appeared in the MOSH region of the mineral oil, indicating that mineral oil saturated hydrocarbons were detected in the extract of the fermented grains sample, but mineral oil aromatic hydrocarbons were not detected. The results are similar to those in Example 1, indicating that for low-fat raw materials, even if they are not purified, the detection results are basically not affected.

[0091] Example 3

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

[0093] 1. Extraction of mineral oil from product samples

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

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

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

[0097] 4) Combine the two extracts, concentrate to 0.5 mL by nitrogen blowing or by rotary concentrating to 0.5 mL at 50°C, make up to 1 mL with n-hexane, and inject into a two-dimensional gas chromatography hydrogen flame ionization detector.

[0098] 2. 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℃, non-split liquid injection, injection volume: 1uL; carrier gas is helium; column flow rate 1.7mL / min; modulation column: initial temperature 50℃, hold for 2min, increase to 340℃ at a rate of 10℃ / min, hold for 5min; temperature increase program at the modulator outlet: initial temperature 50℃, hold for 2min, increase to 340℃ at a rate of 10℃ / min, hold for 5min; temperature increase program at the modulator inlet: 50℃ hold for 6.85min, increase to 260℃ at a rate of 13℃ / min, hold for 7min.

[0100] Modem conditions: using a breathing airflow modulator, a DV modulation column (1.2 m × 0.25 mm), and a period of 4 s.

[0101] Flame ionization detection conditions: detector temperature is 300°C, air flow rate is 350 mL per minute; hydrogen flow rate is 30 mL per minute; tail blowing nitrogen flow rate is 30 mL per minute.

[0102] 3. Results and Analysis

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

[0104] Example 4

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

[0106] 1. Extraction of mineral oil from corn samples

[0107] 1) Step is the same as step 1) in Example 1.

[0108] 2) Step is the same as step 2) in Example 1.

[0109] 3) Step is the same as step 3) in Example 1.

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

[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, take it out and store it in a brown bottle. Keep it away from light and in a dry place. It is recommended to use it up within 2 weeks.

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

[0114] 7g of silica gel activated by muffle furnace (400℃) was loaded into a glass syringe with the inner tube and needle removed. After pressing tightly, 5mL of 20% dichloromethane solution was used to balance the silica gel column. When the liquid level was close to running out, 2mL of extract was added and loaded, and 30mL of mixed solvent consisting of 80% n-hexane + 20% dichloromethane was used for elution. The eluate was collected in a glass container, concentrated to 0.5mL by nitrogen blowing or rotary evaporated to 0.5mL at 50℃, and n-hexane was added to make up to 1mL. Inject into a two-dimensional gas chromatography hydrogen flame ionization detector.

[0115] 2. Detection of mineral oil in samples

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

[0117] 3. Results and Analysis

[0118] exist Figure 6 In the comprehensive 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, an obvious foggy hump appeared in the MOSH region of the mineral oil, indicating that mineral oil saturated hydrocarbons were detected in the corn sample extract, but mineral oil aromatic hydrocarbons were not detected.

[0119] Comparative Example 2

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

[0121] 1. Extraction of mineral oil from corn samples

[0122] 1) Step is the same as step 1) in Example 1.

[0123] 2) Step is the same as step 2) in Example 1.

[0124] 3) Step is the same as step 3) in Example 1.

[0125] 4) Step is the same as step 4) in Example 1.

[0126] 2. Detection of mineral oil in samples

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

[0128] 3. Results and Analysis

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

Claims

1. A method for extracting mineral oil from fermented grains or solid grains, characterized in that: The following steps are involved: A. Mix the fermented grains or solid grains with n-hexane, shake or vortex for the first extraction, and centrifuge to obtain a supernatant and a precipitate; B. Mix the precipitate obtained in step A with water, and after water bathing, shake or vortex, and then centrifuge to obtain a liquid to be extracted; C. Mix the extract obtained in step B with n-hexane, shake or vortex for a second extraction, and separate the layers to obtain a supernatant; D. Combine the supernatant obtained in step A and the supernatant obtained in step B to obtain an extract containing mineral oil.

2. The extraction method according to claim 1, characterized in that: In step B, at least one of the following is met: The mass volume ratio of the fermented grain or solid grain in step A to the water in step B is 1 g: 1-3 mL; The temperature of the water bath is 70°C to 90°C; The water bath time is 1 to 2 hours.

3. The extraction method according to claim 1, characterized in that: In step A, at least one of the following must be met: The solid food 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; The fermented grain is prepared by the following method: after solid grains are crushed, the grains are soaked in hot water at 75°C to 95°C, the grains are initially steamed for 25 to 30 minutes, the grains are simmered for 50 to 60 minutes, and the grains are re-steamed for 35 to 60 minutes, the steamed grains are dewatered and then spread out to air, mixed with Daqu, put into a cellar, fermented for not less than 45 days, taken out of the cellar, and piled up as fermented grains; the amount of Daqu added is 175 to 225 g / kg of solid grains; The mass volume ratio of the fermented grain or solid grain in step A to the n-hexane in step A is 1 g: 1-3 mL; The shaking or vortexing is performed for 10 to 15 times or vortexing for 3 to 5 minutes; The centrifugation is carried out at 3000-5000 r / min for 15-25 minutes.

4. The extraction method according to claim 1, characterized in that: In step B, at least one of the following is met: The shaking or vortexing is performed for 10 to 15 times or vortexing for 3 to 5 minutes; The centrifugation is carried out at 3000-5000 r / min for 15-25 minutes.

5. The extraction method according to claim 1, characterized in that: In step C, at least one of the following conditions must be met: The mass volume ratio of the fermented grain or solid grain in step A to the n-hexane in step C is 1 g: 1-3 mL; The shaking or vortexing is performed for 3 to 5 times or vortexing for 1 to 3 minutes; The static layering time is 15 to 30 minutes.

6. The extraction method according to any one of claims 1 to 5, characterized in that: When the fat content of the fermented grain or solid grain exceeds 3% by weight, or when the fermented grain is prepared using solid grain with a fat content of more than 3% by weight as a raw material, after combining the supernatant obtained in step A and the supernatant obtained in step B, a fat purification operation is further included, specifically: D‵. Combine the supernatant obtained in step A and the supernatant obtained in step B, concentrate to 2-3 mL, and perform silica gel column chromatography with a mixed solvent of dichloromethane and n-hexane in a volume ratio of 3-4:12-16 as a balance liquid and eluent, and collect the eluent, which is the extract containing mineral oil.

7. The extraction method according to claim 6, characterized in that: In step D‵, at least one of the following conditions must be met: The concentration method is nitrogen blowing concentration, or rotary evaporation concentration at 50-60°C; The silica gel is baked at 390-410° C. for 12-15 hours.

8. A method for detecting mineral oil in fermented grains or solid grains, characterized in that: The steps include: a. Concentrate the extract containing mineral oil obtained in any one of claims 1 to 7 to 0.1 to 0.5 mL, add n-hexane to make the volume 1 to 2 mL, inject into a two-dimensional gas chromatography hydrogen flame ionization detector for detection, and obtain a full two-dimensional spectrum; b. Analyze the full two-dimensional spectrum and judge whether the mash or solid grain contains mineral oil saturated hydrocarbons based on whether a foggy hump appears in the MOSH area. Judge whether the mash or solid grain contains mineral oil aromatic hydrocarbons based on whether a foggy hump appears in the MOAH area.

9. The method for detecting mineral oil in fermented grains or solid grains according to claim 8, characterized in that: When the two-dimensional gas chromatography hydrogen flame ionization detector was used for detection, the gas chromatography conditions were: one-dimensional column DB-17HT 30m×0.25mm×0.15μm, two-dimensional column DB-1MS 0.7m×0.25mm×0.1μm; injection temperature 300℃, non-split liquid injection, injection volume 1uL; carrier gas is helium; column flow rate 1.7mL / min; modulation column: initial temperature 50℃, keep warm for 2~5min, increase to 340℃ at a rate of 10℃ / min, keep warm for 2~5min; temperature rise program at the modulator outlet: initial temperature 50℃, keep warm for 2~5min, increase to 340℃ at a rate of 10℃ / min, keep warm for 5~7min; temperature rise program at the modulator inlet: keep warm at 50℃ for 6.85~8min, increase to 260℃ at a rate of 13℃ / min, keep warm for 7~8min; modem conditions: using a breathing airflow modulator, DV modulation column 1.2m×0.25mm, cycle 4s.

10. The method for detecting mineral oil in fermented grains or solid grains according to claim 8, characterized in that: When the two-dimensional gas chromatography hydrogen flame ionization detector is used for detection, the flame ionization detection conditions are: the detector temperature is 300°C, the air flow rate is 350mL per minute; the hydrogen flow rate is 30mL per minute; and the tail blowing nitrogen flow rate is 30mL per minute.

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