This standard supersedes "National Food Safety Standard - Determination of Ash in Foods" (GB 5009.4-2010), "Inspection of Grain and Oils - Methods for Determination of Ash Content" (GB/T 5505-2008), "Starch - Determination of Ash" (GB/T 22427.1-2008), "Meat and Meat Products - Determination of Total Ash" (GB/T 9695.18-2008), "Determination of Ash Content in Edible Mushroom" (GB/T 12532-2008), "Determination of Total Ash in Oilseed Residues" (GB/T 9824-2008), "Inspection of Grain and Oils - Determination of Insoluble Dietary Fiber in Cereals" (GB/T 9825-2008), "Spices and Condiments - Determination of Total Ash" (GB/T 12729.7-2008), "Spices and Condiments - Determination of Water-insoluble Ash" (GB/T 12729.8-2008), "Spices and Condiments - Determination of Acid-insoluble Ash" (GB/T 12729.9-2008), "Animal and Vegetable Fats and Oils - Determination of Ash" (GB/T 17375-2008), "Cereals, Pulses and By-products - Determination of Ash Yield by Incineration" (GB/T 22510-2008), "Tea - Determination of Total Ash Content" (GB/T 8306-2013), "Tea - Determination of Water-soluble Ash and Water-insoluble Ash Content" (GB/T 8307-2013), "Tea - Determination of Acid-insoluble Ash Content" (GB/T 8308-2013), "Method for the Determination of Total Ash of Tea for Import and Export" (SN/T 0925-2000), "Method for the Determination of Water-soluble Ash and Water-insoluble Ash of Tea for Import and Export" (SN/T 0921-2000), "Method for the Determination of Acid-insoluble Ash of Tea for Import and Export" (SN/T 0923-2000) and "Determination of Fruit Juice- Total Ash" (NY 82.8-1988).
Compared with GB 5009.4-2010, this standard has the following main modifications:
- Determinations of ash content in starch and its derivatives are added according to GB/T 22427.1-2008;
- Determinations of water-soluble ash, water-insoluble ash, acid-soluble ash and acid-insoluble ash content in some foods are added according to GB/T 12729.8-2008, GB/T 12729.9-2008, GB/T 8307-2013 and GB/T 8308-2013.
National Food Safety Standard
Determination of Ash in Foods
食品安全國家標準
食品中灰分的測定
1 Scope
In this standard, Method I specifies the method for determination of ash in foods; Method II specifies the method for determination of water-soluble ash and water-insoluble ash in foods; Method III specifies the method for determination of acid-insoluble ash in foods.
In this standard, Method I is applicable to the determination of ash in foods (as for the determination of ash in starchy foods, this method is applicable to the starch and modified starch with mass fraction of ash not greater than 2%); Method II is applicable to the determination of water-soluble ash and water-insoluble ash in foods; Method III is applicable to the determination of acid-insoluble ash in foods.
Method I: Determination of Total Ash in Foods
2 Principle
The inorganic substance remained after burning the foods is referred to as ash content. The value of ash content shall be calculated with the mass after burning and weighing.
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 Magnesium acetate [(CH3COO)2Mg·4H2O].
3.1.2 Concentrated hydrochloric acid (HCl).
3.2 Reagent preparation
3.2.1 Magnesium acetate solution (80g/L): weigh 8.0g magnesium acetate, dissolve it with water, scale the volume to 100mL and mix it uniformly.
3.2.2 Magnesium acetate solution (240g/L): weight 24.0g magnesium acetate, dissolve it with water, scale the volume to 100mL and mix it uniformly.
3.2.3 10% hydrochloric acid solution: measure 24mL analytically-pure concentrated hydrochloric acid and dilute it to 100mL with distilled water.
4 Instruments and Apparatus
4.1 High temperature furnace: maximum service temperature≥950℃.
4.2 Analytical balance: with sensibility of 0.1mg, 1mg and 0.1g.
4.3 Silica or porcelain crucible.
4.4 Dryer (with desiccant).
4.5 Electric hot plate.
4.6 Thermostat water bath: with temperature control precision of ±2℃.
5 Analysis Steps
5.1 Crucible pretreatment
5.1.1 Foods with high phosphorus content and other foods
Take an appropriate size of silica or porcelain crucible, put it in the high temperature furnace and burn it for 30min at 550℃±25℃, cool it to about 200℃, take out, place it into a dryer and cool for 30min, weigh the crucible exactly. Burn the crucible repeatedly till the mass difference of two successive weighs does not exceed 0.5mg, and the weighed value is the constant weight.
5.1.2 Starchy food
Wash it with boiling diluted hydrochloric acid, large volume of tap water and distilled water successively. Place the clean crucible into the high temperature furnace, burn it for 30min at 900℃±25℃, cool it down to ambient temperature in the dryer, and weigh it, accurate to 0.0001g.
5.2 Specimen weighing
Foods with high phosphorus content and other foods: weigh 2g~3g specimen (accurate to 0.0001g) with ash content greater than or equal to 10g/100g, and 3g~10g specimen (accurate to 0.0001g, specimen mass may be appropriately increased for the sample with lower ash content) with ash content less than or equal to 10g/100g. Starchy food: rapidly weigh 2g~10g sample (at least 5g for potato starch, wheaten starch and rice starch, 10g for corn starch and cassava starch), accurate to 0.0001g. Distribute the sample in the crucible uniformly without compaction.
5.3 Determination
5.3.1 Bean, meat, egg, aquatic product, milk and their products with high phosphorus content
5.3.1.1 Weigh the specimen, then add 1.00mL magnesium acetate solution (240g/L) or 3.00mL magnesium acetate solution (80g/L) to moisten the specimen completely. Place it still for 10min, evaporate the moisture on water bath, heat it on electric hot plate on low heat to make the specimen be fully carbonized till it is smokeless, then place it in the high temperature furnace to burn it for 4h at 550℃±25℃. Cool it to about 200℃, then take out and cool it in the dryer for 30min; if some carbon granules are discovered in the ignition residue before weighing, a small amount of water shall be dropped into the specimen to moisten it and loosen the block, evaporate the moisture and burn again till there is no carbon granule, which represents that the specimen is completely incinerated and allowed to be weighed. Burn the crucible repeatedly till the mass difference of two successive weighs does not exceed 0.5mg, and the weighed value is the constant weight.
5.3.1.2 Pipet 3 portions of magnesium acetate solutions with same concentration and volume as 5.3.1.1 for three reagent blank tests. Where the standard deviation of the test results in three tests is less than 0.003g, the arithmetic average shall be taken as the blank value. Where the standard deviation is greater than or equal to 0.003g, blank test shall be conducted again.
5.3.2 Starchy food
Put the crucible at high temperature furnace mouth or on the electric hot plate, cover half and carefully heat it to make the sample be fully carbonized till it is smokeless under ventilation condition; place the crucible into the high temperature furnace immediately and increase the temperature to 900℃±25℃, maintain this temperature till the remaining carbon is totally disappeared, generally the incineration will be completed in 1h, cool it to about 200℃, then take out and cool it in the dryer for 30min; where there are carbon granules in the ignition residue before weighing, a small amount of water shall be dropped into the specimen to moisten it and loosen the block, evaporate the water content and burn again till there is no carbon granule, which represents that the specimen is completely incinerated and allowed to be weighed. Burn the crucible repeatedly till the mass difference of two successive weighs does not exceed 0.5mg, and the weighed value is the constant weight.
5.3.3 Other foods
The liquor and semisolid specimens shall be evaporated dry on boiling water bath. The solid or evaporated specimen shall be heated on electric hot plate with soft fire to make it be fully carbonized till it is smokeless, then place it in the high temperature furnace and burn for 4h at 550℃±25℃. Cool it to about 200℃, then take out and cool it in the dryer for 30min; where there are carbon granules in the ignition residue before weighing, a small amount of water shall be dropped into the specimen to moisten it and loosen the block, evaporate the moisture and burn again till there is no carbon granule, which represents that the specimen is completely incinerated and allowed to be weighed. Burn the crucible repeatedly till the mass difference of two successive weighs does not exceed 0.5mg, and the weighed value is the constant weight.
6 Expression of Analysis Results
6.1 Calculated in specimen mass
6.1.1 The ash content in specimen added with magnesium acetate solution is calculated according to Formula (1):
(1)
Where,
X1 - the ash content in specimen with magnesium acetate solution, g/100g;
m1 - the mass of crucible and ash, g;
m2 - the mass of crucible, g;
m0 - the mass of magnesium oxide (product of magnesium acetate after burning), g;
m3 - the mass of crucible and specimen, g;
100 - the unit conversion coefficient.
6.1.2 The ash content in the specimen without magnesium acetate solution is calculated according to Formula (2):
(2)
Where,
X2 - the ash content in the specimen without magnesium acetate solution, g/100g;
m1 - the mass of crucible and ash, g;
m2 - the mass of crucible, g;
m3 - the mass of crucible and specimen, g;
100 - the unit conversion coefficient.
6.2 Calculated in dry matter
6.2.1 The ash content in specimen with magnesium acetate solution is calculated according to Formula (3):
(3)
Where,
X1 - the ash content in specimen with magnesium acetate solution, g/100g;
m1 - the mass of crucible and ash, g;
m2 - the mass of crucible, g;
m0 - the mass of magnesium oxide (product of magnesium acetate after burning), g;
m3 - the mass of crucible and specimen, g;
ω - the dry matter content (mass fraction) in specimen, %;
100 - the unit conversion coefficient.
6.2.2 The ash content in specimen without magnesium acetate solution is calculated according to Formula (4):
(4)
Where,
X2 - the ash content in specimen without magnesium acetate solution, g/100g;
m1 - the mass of crucible and ash, g;
m2 - the mass of crucible, g;
m3 - the mass of crucible and specimen, g;
ω - the dry matter content (mass fraction) in specimen, %;
100 - the unit conversion coefficient.
Where the ash content in specimen ≥10g/100g, three significant digits shall be reserved; where the ash content in specimen <10g/100g, two significant digits shall be reserved.
Foreword I
1 Scope
2 Principle
3 Reagents and Materials
4 Instruments and Apparatus
5 Analysis Steps
6 Expression of Analysis Results
7 Precision
8 Principle
9 Reagents and Materials
10 Instruments and Apparatus
11 Analysis Steps
12 Expression of Analysis Results
13 Precision
14 Principle
15 Reagents and Materials
16 Instruments and Apparatus
17 Analysis Steps
18 Expression of Analysis Results
19 Precision
