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This standard replaces GB/T 22110-2008 Determination of Trans Fatty Acids in Foods — Gas Chromatographic Method, GB/T 22507-2008 Code of Practice for the Prevention and Reduction of Mycotoxin Contamination in Cereals and SN/T 1945-2007 Determination of Trans Fatty Acids in Foods — Capillary Gas Chromatography in whole.
The following changes have been made with respect to the standards replaced.
— the title is revised as "National Food Safety Standard - Determination of Trans Fatty Acid in Foods";
— the scope of application is extended to animal fats and foods containing animal fats;
— the analytes are expanded to 15 fatty acids such as C16:1t~C22:1t.
National Food Safety Standard — Determination of Trans Fatty Acids in Foods
1 Scope
This standard specifies the liquid chromatography method for the determination of trans fatty acids in foods.
This standard is applicable to the determination of trans fatty acids in animal and vegetable oils, hydrogen vegetable oils, refined vegetable oils and frying oils and foods containing animal and vegetable oils, hydrogen vegetable oils, refined vegetable oils and fried oils.
This standard is not applicable to the determination of food sample of free fatty acid content greater than 2%.
2 Theory
The animal or vegetable oil sample or the fats in food sample extracted by the acid hydrolysis method is transesterified with methanol under alkaline conditions to form a fatty acid methyl ester, which is separated on a strongly polar stationary phase capillary column. The fatty acid methyl ester is determined by a gas chromatograph equipped with a hydrogen flame ionization detector and quantified by area normalization method.
3 Reagents and Materials
Unless otherwise specified, reagents used in this method are all analytically pure, and water is the Grade 1 water as specified in GB/T 6682.
3.1 Reagents
3.1.1 Hydrochloric acid (HCl, ρ20=1.19): 36% to 38%.
3.1.2 Ether (C4H10O)
3.1.3 Petroleum ether: boiling range 30°C to 60°C.
3.1.4 Anhydrous ethanol (C2H6O): chromatographically pure.
3.1.5 Anhydrous sodium sulfate: burned at a temperature of 650°C for 4h; store in drying units on standby.
3.1.6 Isooctane (C8H18): chromatographically pure.
3.1.7 Methanol (CH3O): chromatographically pure.
3.1.8 Potassium hydroxide (KOH): 85%.
3.1.9 Sodium hydrogen sulfate (NaHSO4).
3.2 Preparation of reagents
Potassium hydroxide-methanol solution (2 mol/L): weigh 13.2g of potassium hydroxide, dissolve it into 80mL water, dilute to 100mL with water after cooling to room temperature and then mix well.
Petroleum ether and ethyl ether solution (1+1): measure 500mL of petroleum ether and add into 500mL of ethyl ether, mix them uniformly.
3.3 Standards
Fatty acid methyl ester standard: See Table A.1 for the species, and the purity is >99%.
3.4 Preparation of standard solution
3.4.1 Fatty acid methyl ester standard stock solution: accurately weigh 100mg (to the nearest of 0.1mg) of trans fatty acid methyl ester standard in 25mL beaker, dissolve with isooctane and transfer to 10mL volumetric flask. Scale the volume to 10 mL, the concentration of this standard stock solution was 10 mg/mL. Store at (-18 ± 4) °C.
3.4.2 Fatty acid methyl ester mixed standard intermediate solution (0.4mg/mL): Accurately absorb 1mL of standard stock solution and transfer it into a 25mL volumetric flask, and make up to volume with isooctane. The concentration of this mixed standard intermediate solution is 0.4 mg/mL. Store at (-18 ± 4) °C.
3.4.3 Fatty acid methyl ester mixed standard working solution: accurately absorb 5mL of the standard intermediate solution transfer it into a 25mL volumetric flask and use isooctane to fix the volume. The concentration of this standard working solution is 80 g/mL.
4 Apparatuses
4.1 Gas chromatograph: equipped with hydrogen flame ionization detector.
4.2 Constant temperature water bath.
4.3 Vortex oscillator.
4.4 Centrifuge: The speed is between 0 r/min and 4000 r/min.
4.5 Test tube with stopper: 10mL, 50mL.
4.6 Separating funnel: 125mL.
4.7 Round bottom flask: 200 mL, constant weight in an oven at 100 ° C before use.
4.8 Rotary evaporator.
4.9 Balance: with divisions of 0.1g and 0.1mg.
5 Analytical Procedures
5.1 Preparation of specimen
5.1.1 Solid sample
Take a representative sample of 500 g, pulverized and mixed in a pulverizer, and divided into two portions, which are respectively placed in a clean container, sealed and labeled, and stored at 0 °C to 4 °C.
5.1.2 Semi-solid lipid sample
Take a representative sample of 500g, placed in a beaker, melt in a water bath at 60 °C to 70 °C, mix thoroughly, and then divide into two parts after cooling, respectively, into a clean container, sealed and labeled, and stored at 0 °C to 4 °C.
5.1.3 Liquid sample
Take a representative sample of 500g, mix well and divide into two parts, respectively, into a clean container, sealed and labeled, and stored at 0 °C to 4 °C.
5.2 Analytical Procedures
5.2.1 Animal and vegetable oils
Weigh 60 mg of fat and put it into a 10 mL stoppered test tube, add 4 mL of isooctane to dissolve completely, add 0.2 mL of potassium hydroxide-methanol solution, vortex and mix for 1 min, and put it into the test tube to clarify. The excess potassium hydroxide was neutralized by adding 1 g of sodium hydrogen sulfate, vortexed and mixed for 30 s, centrifuged at 4000 r/min for 5 min, and the supernatant is filtered through a 0.45 μm filter, and the filtrate shall be used as a sample to be tested.
5.2.2 Foods containing oils (except for animal and vegetable oils)
5.2.2.1 Determination of fat in foods
Solid and semi-solid lipid samples: weigh 2.0g of uniform sample (to the nearest of 0.01g, can be adjusted for different food samples, ensure that the amount of fat in the food is not less than 0.125g) in 50mL test tube, Add 8 mL of water and mix well, then add 10 mL of hydrochloric acid to mix; liquid sample: weigh 10.00 g of uniform sample into 50 mL test tube, add 10 mL of hydrochloric acid and mix. The test tube is placed in a water bath at 60 ° C to 70 ° C, shaking every 5 min to 10 min, about 40 min to 50 min until the sample is completely hydrolyzed. The tube is taken out, mixed with 10 mL of ethanol, and cooled to room temperature.
The mixture is transferred to a 125 mL separatory funnel, and the tube shall be rinsed twice with 25 mL of diethyl ether. The washings were poured into a separatory funnel. After all the ether is poured, shake it for 1 min, carefully open the plug, let out the gas, and rinse the stopper and the fat attached to the bottle with an appropriate amount of petroleum ether-ether solution (1+1), and let it stand for 10min to 20min until the upper ether liquid is clear. The lower aqueous phase is placed in a 100 mL beaker, the upper organic phase is placed in another clean separatory funnel, and the extracting funnel is washed with a small amount of petroleum ether-diethyl ether solution (1+1), and the organic phase is collected, which is incorporated into the separation funnel. The water phase in the beaker is transferred back into the separatory funnel, and the beaker shall be rinsed twice with 25 mL of diethyl ether. The washing solution is poured into a separatory funnel, and the extraction is repeated twice as described above, and the organic phases are combined in a separatory funnel. The whole organic phase is passed through an appropriate amount of anhydrous sodium sulfate column, and the column is rinsed with a small amount of petroleum ether-ether solution (1+1), and all the effluent is collected in a 100 mL stoppered cylinder, and the volume was adjusted with diethyl ether and mixed.
Accurately transfer 50mL organic phase to the constant weight round bottom flask, rotate the solvent in a 50 °C water bath, set the constant weight at 100 °C ± 5 °C, calculate the fat content in the food; another 50mL organic phase in the 50 °C water bath After the solvent was distilled off by rotation, it was used for the measurement of trans fatty acid methyl ester.
Foreword I
1 Scope
2 Theory
3 Reagents and Materials
4 Apparatuses
5 Analytical Procedures
6 Expression of Analysis Results
7 Precision
8 Others
Annex A Standard Information
Annex B Standard Chromatogram
Annex C Calculation of FID Response Factor and FID Calibration Factor
Annex D FID Response Factor and FID Calibration Factor
