GB 5009.257-2016National food safety standard - Determination of Trans-fatty Acids in Foodstuffs (English PDF)

3.1 Reagents

3.2 Preparation of Reagents

Potassium hydroxide - methanol solution (2 mol/L). weigh-take 13.2 g of potassium

hydroxide; dissolve it in 80 mL of methanol. Cool it down to room temperature. Use

methanol to reach a constant volume of 100 mL.

3.3 Standard Substance

Fatty acid methyl ester standard substance. please refer to Table A.1 for the type of

fatty acid methyl ester standard substance. Purity shall be > 99%.

3.4 Preparation of Standard Solutions

3.4.1 Fatty acid methyl ester standard stock solution. respectively and accurately

weigh-take 100 mg (accurate to 0.1 mg) of trans-fatty acid methyl ester standard

substances; place them in 25 mL beaker. Respectively use isooctane to dissolve them,

then, transfer them into 10 mL volumetric flask. Accurately reach the volume of 10 mL.

The concentration of the standard stock solutions is 10 mg/mL.

4.1 Gas chromatograph. equipped with hydrogen flame ionization detector.

4.2 Constant-temperature water bath kettle.

4.3 Vortex oscillator.

4.7 Round-bottomed flask. 200 mL. Before usage, place it in 100 °C oven to reach a constant weight.

4.8 Rotary evaporator.

4.9 Balance. division value. 0.1 g, 0.1 mg.

5.1 Sample Preparation

5.1.1 Solid sample

Take 500 g of representative test sample. Use a grinder to grind and mix it up. Evenly

divide it into two parts. Respectively load them into clean containers. Seal them up;

5.1.2 Semi-solid lipid sample

Take 500 g of representative sample. Place it in a beaker. At 60 °C ~ 70 °C water bath,

melt it. Thoroughly mix it up. After cooling it down, evenly divide it into two parts.

Respectively load them into clean containers. Seal them up;

5.2 Analytical Procedure

5.2.1 Animal and vegetable fats and oils

Weigh-take 60 mg of fats and oils; place it in a 10 mL test tube with a stopper. Add 2

mL of isooctane to thoroughly dissolve it. Add 0.2 mL of potassium hydroxide-methanol

solution. Conduct vortex mixing for 1 min. Place it till the mixed liquid in the test tube

becomes pellucid.

5.2.2 Foods containing fats and oils (except from animal and vegetable fats and oils)

5.2.2.1 Determination of fats in foods

Solid and semi-solid lipid sample. weigh-take 2.0 g (accurate to 0.01 g; the weighing

amount of different foods may be properly adjusted, so as to guarantee that fat mass

in foods is not less than 0.125 g) of homogeneous sample. Place it in a 50 mL test

tube. Add 8 mL of water to thoroughly mix it up. Then, add 10 mL of hydrochloric acid

to evenly mix it up. Liquid sample. weigh-take 10.00 g of homogeneous sample, then,

place it in a 50 mL test tube. Add 10 mL of hydrochloric acid to evenly mix it up. Place

the above-mentioned test tube into 60 °C ~ 70 °C water bath. In every 5 min ~ 10 min,

oscillate it once. Last for around 40 min ~ 50 min, till the sample is completely

hydrolyzed. Take out the test tube. Add 10 mL of ethanol to thoroughly mix it up, then,

cool it down to room temperature.

5.3 Reference Conditions of Instruments

5.3.1 Capillary gas chromatographic column. SP-2560 polydicyanopropyl siloxane;

column length. 100 m x 0.25 mm. Membrane thickness. 0.2 µm, or others with

equivalent performance.

5.3.2 Detector. hydrogen flame ionization detector.

5.3.3 Carrier gas. high-purity helium 99.999%.

5.3.4 Flow rate of carrier gas. 1.3 mL/min.

5.3.9 Split ratio. 30.1.

5.4 Quantitative Determination

Respectively inject the standard working solution and the sample test solution into the

gas phase chromatograph. In accordance with the chromatographic peak response

area of the standard solution, adopt normalization method for quantitative

determination.

5.6 Blank Test

In blank test, except from the adding of test sample, other test procedures, reagents

and dosage that are completely identical to the sample analysis shall be adopted.

6.1 Calculation of Mass Fraction of Fats in Foods

The mass fraction of fats in foods shall be calculated in accordance with Formula (1).

6.4 Calculation of Trans-fatty Acids Content in Foods

Mass fraction of trans-fatty acids content in foods shall be calculated in accordance

with Formula (4).