GB 5009.227-2023National food safety standard - Determination of peroxide value in foods (English PDF)

3.1 Reagents

3.1.1 Glacial acetic acid (CH3COOH).

3.1.2 Trichloromethane (CHCl3).

3.1.3 Potassium iodide (KI).

3.1.4 Petroleum ether. The boiling range is 30 degrees C~60 degrees C.

Confirmation of petroleum ether. Take 100 mL of petroleum ether in a rotary

evaporation bottle, and evaporate to dryness under reduced pressure by using a rotary

evaporator in a water bath not higher than 40 °C. Wash the rotary evaporation bottle

several times with 30 mL of chloroform-glacial acetic acid solution, and combine the

washing liquid into a 250 mL iodine flask. Accurately add 1.00 mL of saturated

potassium iodide solution, plug the bottle cap tightly, and shake gently for 0.5 min.

Leave it in a dark place for 3 min, add 1.0 mL of starch indicator, and mix well. If no

blue color appears, this petroleum ether can be used for the sample preparation; If a

blue color appears after adding 1.0 mL of starch indicator and mixing, the reagent needs

to be replaced.

3.1.5 Anhydrous sodium sulfate (Na2SO4).

3.1.6 Soluble starch.

3.1.7 Acetone (CH3COCH3).

3.1.8 Amylase (CAS number. 9000-92-4). The enzyme activity is >=2000 U/g.

3.1.9 Papain (CAS number. 9001-73-4). The enzyme activity is >=6000 U/mg.

3.1.10 Sodium thiosulfate (Na2S2O3 - 5H2O).

3.2 Reagent preparation

3.3 Preparation of standard solution

3.3.1 Sodium thiosulfate standard titration solution (0.1 mo1/L). It shall be prepared

and calibrated in accordance with the requirements of GB/T 5009.1; or a standard

titration solution with national certification and a Reference Material Certificate.

3.3.2 Sodium thiosulfate standard titration solution (0.01 mo1/L). It is prepared from

diluting 0.1 mo1/L sodium thiosulfate standard titration solution with newly boiled and

cooled water. Prepare the solution fresh just before use.

3.3.3 Sodium thiosulfate standard titration solution (0.002 mo1/L). It is prepared from

diluting 0.01 mo1/L sodium thiosulfate standard titration solution with newly boiled

and cooled water. Prepare the solution fresh just before use.

4.1 Balance. The sensitivities are 0.01 g, 0.001 g, and 0.0001 g, respectively.

4.2 Electric constant-temperature drying oven.

4.3 Rotary evaporator. It is equipped with a brown rotary evaporation bottle.

4.4 Constant-temperature water bath oscillator.

4.5 High-speed refrigerated centrifuge.

4.6 Overhead stirrer.

4.7 Burette. The capacity is 10 mL, and the minimum scale is 0.05 mL.

4.8 Burette. The capacity is 25 mL or 50 mL, and the minimum scale is 0.1 mL.

5.1 Sample preparation

Strong light shall be avoided during the sample preparation process. After preparation,

the oil and fat shall be stored in a sealed container and measured as soon as possible.

5.1.1 Animal and vegetable oils and fats

For liquid samples, shake the closed container containing the sample, mix thoroughly,

and then take a sample directly; for solid samples, select a representative sample and

place it in a closed container, mix well, and then take a sample. If necessary, place the

container containing the solid sample in a constant temperature water bath, and heat it

until the sample begins to melt; let it completely melt at this temperature, shake and

mix well, and take a sample for measurement immediately while the sample is in liquid

state.

5.1.2 Oil products

5.1.2.1 Edible hydrogenated oil, shortening, cocoa butter substitute

5.1.2.2 Margarine

Place the sample in a closed container, heat it in an electric constant-temperature drying

oven at 60 °C to 70 °C until it melts, shake and mix, continue heating until the

emulsification breaks down into layers, and filter the oil layer through the rapid

qualitative filter paper into a beaker. The filtrate in the beaker is the sample to be tested,

and the sample to be tested shall be clarified. Take a sample and measure it immediately

while the sample to be tested is in a liquid state.

5.1.2.3 Non-dairy cream

Take a representative sample in a beaker, add about 5 times the sample volume of

petroleum ether, and stir for 2 minutes by using an overhead stirrer to mix evenly. While

stirring, add anhydrous sodium sulfate of about 1.6 times the mass of the sample,

continue stirring and mixing for 5 minutes, remove the beaker, and let the solution stand

for 5 minutes to allow the petroleum ether to layer (if emulsification occurs, cover the

top of the beaker with a layer of plastic wrap, and place the beaker in a water bath of

not higher than 40 °C for 10 minutes to stratify the petroleum ether). Pour out the

supernatant, add about 2 times the sample volume of petroleum ether to the beaker, and

repeat the above stirring and standing operations; combine the petroleum ethers, filter,

and transfer the filtrate into a brown rotary evaporation bottle; in a water bath of not

higher than 40 degrees C, use a rotary evaporator to evaporate the petroleum ether to dryness

under reduced pressure.

5.2 Sample determination

Sample determination shall be avoided under direct sunlight. Weigh 2 g~3 g of the

prepared sample (accurate to 0.001 g), place it in a 250 mL iodine flask, add 30 mL of

chloroform-glacial acetic acid solution, and shake the sample gently until it is

completely dissolved. Accurately add 1.00 mL of saturated potassium iodide solution,

plug the bottle cap tightly, shake gently for 0.5 min, and place in a dark place for 3 min.

Take out and add 100 mL of water, shake well and immediately use sodium thiosulfate

standard titration solution (when the estimated peroxide value is 0.15 g/100 g and below,

use 0.002 mol/L standard titration solution; when the estimated peroxide value is greater

than 0.15 g/100 g, use 0.01 mol/L standard titration solution) to titrate the precipitated

iodine. When the solution turns to light yellow, add 1 mL of starch indicator, continue

titrating, and shake vigorously until the blue color of the solution disappears, that is the

end point.

6.1 When the peroxide value is expressed as the mass fraction of peroxide equivalent

to iodine, it is calculated according to formula (1).

6.2 When the peroxide value is expressed in millimoles of active oxygen in 1 kg of the

sample, it is calculated according to formula (2).

9.1 Reagents

9.2 Reagent preparation

9.3 Preparation of standard solution

The preparation is the same as 3.3.

10.1 Balance. The sensitivities are 0.01 g, 0.001 g, and 0.0001 g, respectively.

10.2 Electric constant-temperature drying oven.

10.3 Potentiometric titrator.

10.4 Magnetic stirrer.

11.1 Sample preparation

The preparation is the same as 5.1.1 and 5.1.2.2.

11.2 Sample determination

Weigh 5 g of the prepared sample (accurate to 0.001 g) and place it into the titration

cup of the potentiometric titrator, add 50 mL of isooctane-glacial acetic acid solution,

and shake gently to completely dissolve the sample. If the solubility of the sample is

poor (such as stearin or animal fat), first add 20 mL of isooctane to the titration cup,

shake gently to dissolve the sample, then add 30 mL of glacial acetic acid, and mix well.

Accurately add 1.00 mL of saturated potassium iodide solution to the titration cup, start

the magnetic stirrer, and react at a suitable stirring speed for 60 s+/-1 s. Immediately add