Identification method of kitchen waste grease

Abstract

The invention relates to a method for identifying kitchen waste grease, which comprises the following steps: by taking cis-9-tetradecenoic acid as a detection object, converting triglyceride in the grease into corresponding fatty acid low-carbon alcohol ester through a transesterification method, and detecting and calculating the content of the cis-9-tetradecenoic acid so as to judge whether the kitchen waste grease is contained or not. The identification method provided by the invention is simple in pretreatment operation and high in identification speed; and 2) the target cis-9-tetradecenoic acid in the identification method provided by the invention is a similar compound of a main component in the vegetable oil and is not easy to remove in a refining process, so that the accuracy is high, and a false negative result can be avoided.

Description

Technical Field

[0001] The invention relates to the technical field of grease identification, and in particular to a method for identifying kitchen waste grease. Background Art

[0002] Waste cooking oil refers to the processing oil left over after cooking in the kitchen, the oil produced during the food processing process, and the oil in the leftovers, which is also called "gutter oil". On the one hand, waste cooking oil may contain harmful ingredients to the human body due to repeated heating, which endangers the health of consumers; on the other hand, waste cooking oil has almost no cost, and selling it as normal vegetable oil or mixing it with normal vegetable oil for sale seriously disrupts the market order and infringes on the interests of consumers.

[0003] After processing, the appearance of waste cooking oil is very similar to normal oil and it is difficult to identify by observation.

[0004] Laboratories often use the method of measuring characteristic marker compounds in oils to identify waste cooking oil. For example, during the cooking process, oils may come into contact with peppers, causing capsaicin to be mixed into the waste cooking oil; during the cooking process, oils may come into contact with animal ingredients, causing cholesterol to be mixed into the waste cooking oil. By testing marker compounds such as capsaicin and cholesterol, it is possible to determine whether the oil is waste cooking oil or is mixed with waste cooking oil.

[0005] However, with the improvement of waste cooking oil refining technology, marker compounds such as capsaicin and cholesterol can be removed, making existing identification methods ineffective. Summary of the invention

[0006] In response to the above problems, a method for identifying waste cooking oil is now provided, aiming to quickly and accurately determine whether it contains waste cooking oil, maintain market order, and protect the interests of consumers.

[0007] The specific technical solutions are as follows:

[0008] A method for identifying waste cooking oil takes cis-9-tetradecenoic acid as the detection object, converts triglycerides in the oil into corresponding fatty acid low-carbon alcohol esters through an ester exchange method, detects and calculates the cis-9-tetradecenoic acid content, and determines whether it contains waste cooking oil.

[0009] Cis-9-tetradecenoic acid is a fatty acid specific to animal fats and oils and does not exist in vegetable oils. Therefore, cis-9-tetradecenoic acid will exist in waste cooking oils used for cooking animal food. Based on the above reasons, in the present invention, cis-9-tetradecenoic acid triglycerides in waste cooking oils used for cooking animal food can be converted into low molecular weight fatty acid lower carbon alcohol esters, such as fatty acid methyl esters, which can be used for gastrometry-mass spectrometry detection, and then detected, and the content of cis-9-tetradecenoic acid is converted to determine whether waste cooking oil is contained.

[0010] In the present invention, undecanoic acid triglyceride, which has properties similar to cis-9-tetradecenoic acid triglyceride and does not exist in animal and vegetable oils, is selected as the internal standard of the method.

[0011] Furthermore, the above method comprises:

[0012] Prepare internal standard solution and gradient concentration of cis-9-tetradecenoic acid triglyceride standard working solution;

[0013] Take the gradient standard working solution, add an appropriate amount of internal standard solution and an appropriate amount of organic solvent, mix and shake well, add low-carbon alcohol and alkaline catalyst, remove the alkaline catalyst after the transesterification reaction, centrifuge, take the supernatant and inject it into the GCMS system to draw a concentration-peak area standard working curve;

[0014] Weigh the sample, add appropriate amount of internal standard solution and appropriate amount of organic solvent, mix and shake well, add low-carbon alcohol and alkaline catalyst, remove the alkaline catalyst after the ester exchange reaction, centrifuge, take the supernatant and inject it into the GCMS system, use the ratio of the sample concentration to the internal standard concentration as the horizontal axis, substitute it into the standard working curve, and calculate the cis-9-tetradecenoic acid triglyceride content to determine whether the oil contains waste cooking oil.

[0015] Furthermore, the internal standard solution is an organic solution of triundecanoic acid glycerol.

[0016] Furthermore, the concentrations of the gradient concentration cis-9-tetradecenoic acid triglyceride standard working solutions are 0.10 mg / L, 0.50 mg / L, 2.0 mg / L, 5.0 mg / L, and 10 mg / L, respectively.

[0017] Furthermore, a standard working curve is drawn with the ratio of the concentration of each standard to the concentration of the corresponding internal standard as the abscissa and the ratio of the peak area of ​​each standard to the peak area of ​​the corresponding internal standard as the ordinate.

[0018] Furthermore, the base catalyst is a strong base, and an acid is added after the transesterification reaction to remove the strong base.

[0019] Further, the gas chromatography conditions are: injection port temperature 260-275°C; split injection, split ratio (4-5):1; column temperature is programmed; carrier gas is high purity helium, flow rate 0.9-1.2 mL / min; transfer line temperature 260-275°C 。

[0020] Furthermore, the mass spectrometry conditions were: EI source; ion source temperature 220-235°C; ion monitoring.

[0021] Further, the detection ions of cis-9-tetradecenoic acid methyl ester are m / z 74, 87, 166 and 208, and the detection ions of methyl undecanoate are m / z 74, 87, 200 and 143. 。

[0022] Furthermore, if the content of cis-9-tetradecenoic acid triglyceride is greater than 10 mg / kg, it is determined to contain waste cooking oil.

[0023] The beneficial effects of the above scheme are:

[0024] 1) Compared with the existing method of identifying capsaicin, cholesterol and other labeled compounds, the identification method provided by the present invention has the advantages of simple pre-treatment operation and fast identification speed;

[0025] 2) The target compound cis-9-tetradecenoic acid in the identification method provided by the present invention is a similar compound to the main component of vegetable oil, which is not easily removed during the refining process, so the accuracy is high and the occurrence of false negative results can be avoided;

[0026] 3) cis-9-tetradecenoic acid is a fatty acid specific to animal fats and does not exist in vegetable oils, but cis-9-tetradecenoic acid is present in waste cooking oil from cooking animal food; in the present invention, undecanoic acid triglyceride, which has properties similar to cis-9-tetradecenoic acid triglyceride and does not exist in animal and vegetable oils, is selected as the internal standard for this method. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 This is the selected ion chromatogram of cis-9-tetradecenoic acid methyl ester in normal vegetable oil;

[0028] Figure 2 This is the selected ion chromatogram of cis-9-tetradecenoic acid methyl ester in normal animal fats;

[0029] Figure 3 This is the selected ion chromatogram of cis-9-tetradecenoic acid methyl ester in waste oils and fats used for cooking animal-derived foods;

[0030] Figure 4This is the selected ion chromatogram of cis-9-tetradecenoic acid methyl ester in normal vegetable oil mixed with 10% of waste cooking oil. DETAILED DESCRIPTION

[0031] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0032] It should be noted that, in the absence of conflict, the embodiments of the present invention and the features in the embodiments may be combined with each other.

[0033] The present invention will be further described below in conjunction with the accompanying drawings and specific embodiments, but they are not intended to limit the present invention.

[0034] An embodiment of the present invention provides a method for identifying waste cooking oil, which comprises:

[0035] Weigh cis-9-tetradecenoic acid triglyceride standard and undecanoic acid triglyceride standard, dissolve them in isooctane and make up to volume, to form standard stock solution and internal standard stock solution with concentration of 100 mg / L;

[0036] 10 μL, 50 μL, 200 μL, 500 μL and 1000 μL of 100 mg / L standard stock solution were taken respectively and added to 5 15 mL centrifuge tubes respectively, 100 μL (equivalent to 10 μg) of 100 mg / L triglyceride undecanoate internal standard solution was added respectively, 9.99 mL, 9.95 mL, 9.80 mL, 9.50 mL and 9.00 mL of isooctane were added respectively, mixed and shaken well, 0.5 mL of 2 mol / L potassium hydroxide methanol solution was added, and the lid was closed and shaken vigorously for 30 s; then about 2 g of sodium bisulfate was added, and the lid was closed and shaken vigorously to remove potassium hydroxide; centrifuged at 3000 r / min for 5 min, 1 μL of the supernatant was taken and injected into GC / MS for detection, and the ratio of the concentration of each standard to the concentration of the corresponding internal standard was used as the horizontal coordinate, and the ratio of the peak area of ​​each standard to the peak area of ​​the corresponding internal standard was used as the vertical coordinate to draw the standard working curve;

[0037] Weigh 0.1g of sample (accurate to 0.1mg) into a 15mL centrifuge tube, add 100μL (equivalent to 10μg) of 100mg / L undecanoic acid triglyceride internal standard, add 10mL of isooctane, mix and shake well, add 0.5mL of 2mol / L potassium hydroxide methanol solution, close the lid and shake vigorously for 30s; then add about 2g of sodium bisulfate, close the lid and shake vigorously; centrifuge at 3000r / min for 5min, take 1μL of the upper clear liquid and inject it into GC / MS for detection;

[0038] The gas chromatograph in the above GC / MS detection is as follows: injection port temperature: 270°C; injection mode: split injection, split ratio of 5:1; column temperature is programmed temperature rise; carrier gas: high purity helium, flow rate 1.0 mL / min; transmission line temperature: 270°C. Mass spectrometry conditions are: electron impact ionization source (EI source); ion source temperature: 230°C; detection method: selected ion monitoring (SIM): the detection ions of cis-9-tetradecenoic acid methyl ester are m / z 74, 87, 166 and 208, and the detection ions of methyl undecanoate are m / z 74, 87, 200 and 143.

[0039] The standard curve in the present invention is: y = 0.1778x + 0.00121, and the correlation coefficient (R 2 ) is: 0.9998. It can be seen from the correlation coefficient of the standard working curve that in the present invention, the linear relationship of cis-9-tetradecenoic acid methyl ester is good within the range of 10-1000 mg / kg.

[0040] In the present invention, the quantification limit is calculated based on a 10-fold signal-to-noise ratio of the mass chromatogram, and the results show that the quantification limit of cis-9-tetradecenoic acid is 10 mg / kg.

[0041] In order to verify the reliability of the method, the present invention uses the above identification method to detect the content of cis-9-tetradecenoic acid in 61 batches of normal vegetable oils, 10 batches of animal fats, 10 batches of waste kitchen fats from cooking animal-derived foods, and 21 batches of normal vegetable oils mixed with 10%-50% waste kitchen fats. The results show that the content of cis-9-tetradecenoic acid in 61 batches of normal vegetable oils is less than 10 mg / kg; the content of cis-9-tetradecenoic acid in 10 batches of animal fats is in the range of 126-6302 mg / kg; the content of cis-9-tetradecenoic acid in 10 batches of waste kitchen fats from cooking animal-derived foods is in the range of 105-1258 mg / kg; the content of cis-9-tetradecenoic acid in 21 batches of normal vegetable oils mixed with 10%-50% waste kitchen fats is in the range of 14-309 mg / kg. From the above data, it can be seen that 10 mg / kg can be selected as the threshold value in the present invention. If the cis-9-tetradecenoic acid content in the tested vegetable oil is less than 10 mg / kg, it is judged to be normal vegetable oil; if the cis-9-tetradecenoic acid content in the tested vegetable oil is greater than 10 mg / kg, it is judged to contain waste cooking oil.

[0042] The above description is only a preferred embodiment of the present invention, and does not limit the implementation mode and protection scope of the present invention. For those skilled in the art, it should be aware that all solutions obtained by equivalent substitutions and obvious changes made using the description and illustrations of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for identifying waste cooking oil, characterized in that: Taking cis-9-tetradecenoic acid as the detection object, the triglycerides in the oil are converted into corresponding fatty acid low-carbon alcohol esters through the ester exchange method, and the cis-9-tetradecenoic acid content is detected and calculated to determine whether it contains waste cooking oil.

2. The method for identifying waste cooking oil according to claim 1, characterized in that: include: Prepare internal standard solution and gradient concentration of cis-9-tetradecenoic acid triglyceride standard working solution; Take the gradient standard working solution, add an appropriate amount of internal standard solution, mix and shake well, add low-carbon alcohol and alkaline catalyst, remove the alkaline catalyst after the transesterification reaction, centrifuge, take the supernatant and inject it into the GCMS system to draw a concentration-peak area standard working curve; Weigh the sample, add an appropriate amount of internal standard solution, mix and shake, add low-carbon alcohol and alkaline catalyst, remove the alkaline catalyst after the ester exchange reaction, centrifuge, take the supernatant and inject it into the GCMS system, use the ratio of the sample concentration to the internal standard concentration as the horizontal axis, substitute it into the standard working curve, and calculate the cis-9-tetradecenoic acid content to determine whether it contains waste cooking oil.

3. The method for identifying waste cooking oil according to claim 2, characterized in that: The internal standard solution is an organic solution of triundecanoic acid glycerol.

4. The method for identifying waste cooking oil according to claim 2, characterized in that: The concentrations of the gradient concentration cis-9-tetradecenoic acid triglyceride standard working solutions are 0.10 mg / L, 0.50 mg / L, 2.0 mg / L, 5.0 mg / L, and 10 mg / L, respectively.

5. The method for identifying waste cooking oil according to claim 2, characterized in that: The standard working curve was drawn with the ratio of the concentration of each standard to the corresponding internal standard as the horizontal axis and the ratio of the peak area of ​​each standard to the peak area of ​​the corresponding internal standard as the vertical axis.

6. The method for identifying waste cooking oil according to claim 2, characterized in that: The base catalyst is a strong base, and an acid is added after the transesterification reaction to remove the strong base.

7. The method for identifying waste cooking oil according to claim 2, characterized in that: Gas chromatography conditions were: injection port temperature 260-275°C; split injection, split ratio (4-5):1; column temperature programmed; carrier gas was high purity helium, flow rate 0.9-1.2 mL / min; transfer line temperature 260-275°C 。 8. The method for identifying waste cooking oil according to claim 2, characterized in that: The mass spectrometry conditions were: EI source; ion source temperature 220-235°C; ion monitoring.

9. The method for identifying waste cooking oil according to claim 8, characterized in that: The detection ions of cis-9-tetradecenoic acid methyl ester are m / z 74, 87, 166 and 208, and the detection ions of methyl undecanoate are m / z 74, 87, 200 and 143. 。 10. The method for identifying waste cooking oil according to claim 1 or 2, characterized in that: If the content of cis-9-tetradecenoic acid is greater than 10 mg / kg, it is determined to contain waste cooking oil.

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