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This standard replaces GB/T5538-2005 Animal and Vegetable Fats and Oils - Determination of Peroxide Value, SN/T 0801.3-2011 Animal and Vegetable Fats and Oils for Export - Method for the Determination of Peroxide Value and Section 4.2 Peroxide value specified in GB/T5009.37-2003 Method for Analysis of Hygienic Standard of Edible Oils.
Compared with Section 4.2 “Peroxide value” specified in GB/T5009.37- 2003, the main changes are as follows:
——The standard is renamed as “National Food Safety Standard - Determination of Peroxide Value in Foods”;
——The concentration of standard titration solution of sodium thiosulfate in Method I is modified;
——Method II "Colorimetry" is deleted and replaced by "Potentiometric Titration";
——The scope of application of the methods is added;
——The section of "Sample preparation" is added.
National Food Safety Standard -
Determination of Peroxide Value in Foods
1 Scope
This standard specifies two determination methods for peroxide value in foods: titration and potentiometric titration.
Method I in this standard is applicable to edible animal and vegetable fats and oils, edible fat and oil products, foods made of wheat flour, cereal, nuts and other vegetable food through processing techniques such as frying, puffing, baking, brewing and sauting, as well as those made of animal food through the processing techniques such as quick freezing, dry processing and salting away; Method II is applicable to animal and vegetable fats and oils and margarine with the measurement range of 0 g/100g ~ 0.38 g/100g.
This standard is not applicable to determination of embedded fat and oil products like vegetable fat powder.
Method 1 Titration
2 Theory
The oil and fat specimen prepared will be dissolved in trichloromethane and glacial acetic acid, during which the peroxide will react with potassium iodide to produce iodine that will be titrated by sodium thiosulfate standard solution. The amount of peroxide value shall be expressed by the mass fraction of the peroxide equivalent to iodine or the mill mole quantity of the active oxygen in 1 kg of the sample.
3 Reagents and Materials
Unless otherwise specified, analytically-pure reagents and Class III water (defined in GB/T 6682) are adopted for the purpose of this method.
3.1 Reagents
3.1.1 Glacial acetic acid (CH3COOH).
3.1.2 Trichloromethane (CHCl3).
3.1.3 Potassium iodide (KI).
3.1.4 Sodium thiosulfate (Na2S2O3·5H2O).
3.1.5 Petroleum ether: with boiling range of 30℃~60℃.
3.1.6 Anhydrous sodium sulfate (Na2SO4).
3.1.7 Soluble starch.
3.1.8 Potassium dichromate (K2Cr2O7): the working chemical.
3.2 Reagents preparation
3.2.1 Trichloromethane - glacial acetic acid mixed solution (volume ratio 40 + 60): measure 40mL of trichloromethane, add 60mL of glacial acetic acid and then mix uniformly.
3.2.2 Potassium iodide saturated solution: weigh 20g of potassium iodide, put in 10mL of cooled water which is newly boiled, shake up and store in the brown bottle which shall be kept in a dark place for standby. Ensure that saturated potassium iodide crystallization exists in the solution. Inspection prior to use: add 1.00 mL of potassium iodide saturated solution and two drops of 1% starch indicator into the mixed solution of trichloromethane and glacial acetic acid, if it turns blue which can only be eliminated with more than 1 drop of 0.01 mol/ L sodium thiosulfate solution, the potassium iodide solution can't be put into service and shall be prepared afresh.
3.2.3 1% starch indicator: weigh 0.5g of the soluble starch, add a small amount of water to make it into paste, pour into 100mL of boiling water while stirring, then boil and mix up and then cool it down for standby; prepare immediately before use.
3.2.4 Processing of petroleum ether: take 100mL of petroleum ether and put it into a distillation flask, then evaporate it to dryness with a rotary evaporator under reduced pressure in the water bath with the temperature below 40℃. Wash the distillation flask with 30mL of trichloromethane - glacial acetic acid mixed solution by several times and merge the washing solutions into a 250 mL iodine flask. Put in exact 1.00 mL of saturated potassium iodide solution, plug up the bottle cover, gently shake for 0.5 min and place it in the dark for 3min, after which add into 1.0 mL of the starch indicator and mix well. If it doesn't turn blue, the petroleum ether can be used for specimen preparation; and if blue appears after it is mixed well with 1.0 mL of the starch indicator, the reagent shall be replaced.
3.3 Preparation of standard solutions
3.3.1 Sodium thiosulfate standard solution (0.1 mol/L): weigh 26g of sodium thiosulfate (Na2S2O3·5H2O), add into 0.2g of anhydrous sodium carbonate, dissolve them in 1,000mL of pure water, boil slowly for 10 min and cool it down. Place it for two weeks before filtration and calibration.
3.3.2 Sodium thiosulfate standard solution (0.01mol/L): it shall be made by diluting the reagent prepared in 3.3.1 with cooled water which is newly boiled just before use.
3.3.3 Sodium thiosulfate standard solution (0.002mol/L): it shall be made by diluting the reagent prepared in 3.3.1 with cooled water which is newly boiled just before use.
4 Instruments and Apparatuses
4.1 Iodine flask: 250 mL.
4.2 Burette: 10mL, with minimum scale of 0.05 mL.
4.3 Burette: 25mL or 50mL, with minimum scale of 0.1 mL.
4.4 Balance: with sensibility of 1 mg and 0.01mg.
4.5 Electrothermal constant-temperature dry oven
4.6 Rotary evaporator.
Note: all the wares used for this method shall be free from reducing or oxidizing substances. Do not oil the surface of ground glass.
5 Analysis Steps
5.1 Specimen preparation
Avoid strong light in sample preparation process and try the best to avoid taking into air.
5.1.1 Animal and vegetable fats and oils
As for liquid samples, shake the closed vessel containing specimen sufficiently and uniformly and then sample directly, as for solid sample, select a representative specimen and put it into a closed vessel, then mix well and sample.
5.1.2 Fat and oil products
5.1.2.1 Edible hydrogenated oil, shortening and cocoa butter substitute
As for liquid samples, shake the closed vessel containing specimen sufficiently and uniformly and then sample directly, as for solid sample, select a representative specimen and put it into a closed vessel, then mix well and sample. If necessary, put the closed vessel which contains solid specimen into the constant-temperature dry oven, heat slowly until it just melts, then shake and mix well, and then sample immediately for determination while the specimen is in liquid state.
5.1.2.2 Margarine
Put the sample into a closed vessel, heat it in a constant-temperature dry oven at the temperature of 60℃ ~ 70℃ until it melts , shake and mix well, then continue heating it until emulsion breaking and layering, at which time filter the oil layer into a beaker through rapid qualitative filter paper. The filtrate in the beaker is the specimen to be tested which shall be clear.
Take samples immediately for determination while the specimen to be tested is in liquid state.
5.1.3 Foods made of wheat flour, cereal, nuts and other vegetable foods through the processing techniques such as frying, puffing, baking, brewing and sauting
Take the edible part of the representative sample drawn from all the samples, pestle in the glass mortar, and put the pestled sample into a wide mouth bottle, add in the petroleum ether (3.2.4) 2~3 times the volume of the sample, shake up and mix well, then leave it standstill and leaching for more than 12h. After that filter with a funnel containing anhydrous sodium sulfate, evaporate the petroleum ether to dryness with a rotary evaporator under reduced pressure in the water bath with the temperature below 40℃. The residue is the specimen to be tested.
5.1.4 Foods made of animal foods through the processing techniques such as quick freezing, dry processing and salting away
Take the edible part of the representative sample drawn from all the samples, grind it and mix well, then put it into a wide mouth bottle, add in the petroleum ether (3.2.4) 2~3 times the volume of the sample, shake up and mix well, then leave it standstill and leaching for more than 12h. After that filter with a funnel containing anhydrous sodium sulfate, evaporate the petroleum ether to dryness with a rotary evaporator under reduced pressure in the water bath with the temperature below 40℃. The residue is the specimen to be tested.
5.2 Determination of the specimen
Avoid determining the specimen in direct sunlight. Weigh 2g~3g (to the nearest of 0.001 g) of the specimen prepared in Clauses "5.1.1 ~ 5.1.4", place it into a 250 mL iodine flask, add in trichloromethane - glacial acetic acid mixed solution, then gently shake to make the specimen fully dissolved. Put in exact 1.00 mL of saturated potassium iodide solution, plug up the bottle cover and gently shake for 0.5 min, then place it in the dark for 3min. Take it out and add into 100mL of water, shake well and titrate the iodine that is separated out with sodium thiosulfate standard solution (with 0.002 mol/L standard solution if the estimated peroxide value is 0.15 g/100g and below; with 0.01 mol/L standard solution if the estimated peroxide value is greater than 0.15g/100g) until it turns light yellow, then add in 1mL of starch indicator to continue titrating, and shake violently until the blue in the solution disappears. Carry out blank test at the same time. The volume of 0.01 mol/L sodium thiosulfate solution consumed for the blank test, V0 shall not exceed 0.1 mL.
Foreword i
1 Scope
2 Theory
3 Reagents and Materials
4 Instruments and Apparatuses
5 Analysis Steps
6 Expression of Analysis Results
7 Accuracy
8 Theory
9 Reagents and Materials
10 Instruments and Apparatuses
11 Analysis Steps
12 Expression of Analysis Results
13 Accuracy
