This standard supersedes "National Food Safety Standard Determination of Moisture in Foods"(GB 5009.3-2010), "Starch - Determination of Moisture Content - Oven-drying Method" (GB/T 12087-2008), "Instant Tea in Solid Form - Part 3: Determination of Moisture Content" (GB/T 18798.3-2008), "Cereals and Cereal Products - Determination of Moisture Content - Routine Reference Method" (GB/T 21305-2007) and "Inspection of Grain, Oilseeds - Methods for Determination of Moisture Content"(GB/T 5497-1985), "Tea-Determination of Moisture Content"(GB/T 8304-2013), "Spices and Condiments - Determination of Moisture Content - Entrainment Method"(GB/T 12729.6), "Meat and Meat Products - Determination of Moisture Content"(GB/T 9695.15-2008), "Method for Determination of Dry Matter and Water Content in Fruit and Vegetable Products"(GB/T 8858-1988) and "Method for the Determination of Moisture of Tea for Import and Export"(SN/T 0919-2000).
Compared with GB 5009.3-2010, the main changes in this standard are as follows:
- The application scopes of Method I (Direct Drying Method), Method II (Drying Method under Reduced Pressure), Method III (Distillation Method), and Method IV (Karl Fischer Volumetric Method) are modified;
- The reagent, precision, notes and Analysis steps in Method I (Direct Drying Method) are modified;
- The Analysis steps in Method III (Distillation Method) are modified;
- The text description of Karl Fischer Coulometric Method in Method IV (Karl Fischer Method) is deleted.
National Food Safety Standard
Determination of Moisture Content
in Foods
食品安全國(guó)家標(biāo)準(zhǔn) 食品中水分的測(cè)定
1 Scope
This standard specifies the method for determination of moisture in foods.
In this standard, Method I (Direct Drying Method) is applicable to the determination of moisture in foods at 101~105℃ such as vegetables, cereal and its products, aquatic products, bean products, dairy products, meat products, pot-stewed products, grain (moisture content: lower than 18%), oilseeds (water content: lower than 13%), starch and tea, while it's not applicable to the sample with moisture content less than 0.5g/100g. Method II (Drying Method under Reduced Pressure) is applicable to the determination of moisture content in sample labile at high temperature and that with much moisture, e.g. sugar and gourmet powder, while it's not applicable to the determination of moisture content in candy added with other ingredient (e.g. milk candy and soft candy) added, and also the sample (excluding sugar and gourmet powder) with moisture content less than 0.5g/100g. Method III (Distillation Method) is applicable to the determination of moisture in foods with much moisture and volatile constituents, e.g. fruits, spices, condiments and meat and meat products, while it's not applicable to the sample with moisture content less than 1g/100g. Method IV (Karl Fischer Method) is applicable to the determination of foods with trace moisture, while it's not applicable to the determination of moisture in foods with oxidizer, reductant, basic oxide, hydroxide, carbonate and boric acid etc. Karl Fischer Volumetric Method is applicable to the sample with moisture content larger than 1.0×10-3g/100g.
Method I: Direct Drying Method
2 Principle
Depending on the physical property of the moisture in foods, determine the reduced weight in sample due to drying at 101.3kPa (one atmosphere) under 101~105℃ with volatilization method, including hygroscopic water, partial crystal water and the substance that can volatilize under the same condition, and then work out the moisture content with the values obtained by weighing the sample before and after drying.
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 Sodium hydroxide (NaOH).
3.1.2 Hydrochloric acid (HCl).
3.1.3 Sea sand.
3.2 Reagent preparation
3.2.1 Hydrochloric acid solution (6mol/L): measure 50mL hydrochloric acid and dilute it to 100mL with water.
3.2.2 Sodium hydroxide solution (6mol/L): weigh 24g sodium hydroxide and dissolve it into water and dilute to 100mL.
3.2.3 Sea sand: take the sea sand, river sand, quartz sand or the similar, from which the soil has been washed out, boil it first for 0.5h with hydrochloric acid solution (6mol/L), wash it with water till it's neutral, and then boil it for another 0.5h with sodium hydroxide solution (6mol/L), wash it till it's neutral, dry it at 105℃ finally for future use.
4 Instruments and Apparatus
4.1 Flat aluminum or glass weighing bottle.
4.2 Electric thermostatic drying oven
4.3 Dryer: with effective desiccant.
4.4 Balance: with sensibility of 0.1mg.
5 Analysis Steps
5.1 Solid specimen: take one clean flat aluminum or glass weighing bottle and put it into a drying oven of 101~105℃ with the bottle cap supported on the bottle rim slantly, heat the weighing bottle in drying box for 1.0h, take it out and cover the bottle well, cool it in a dryer for 0.5h, weigh it, and then dry it repeatedly till the mass difference before and after drying does not exceed 2mg, and the weighed mass is the constant weight of this weighing bottle. Rapidly grind the uniformly mixed specimen into particle (less than 2mm), thereof, for those samples that are not easy to be grinded, cut them up possibly, weigh about 2~10g specimen (accurate to 0.0001g) and put them into this weighing bottle, keeping the thickness of samples not exceeding 5mm (keeping the thickness not exceeding 10mm where the specimen is loose), cover the bottle and weigh the bottle accurately, and then put this bottle into a 101~105℃ drying oven with the bottle cap slantly supported on the bottle rim, dry the samples in this drying oven for 2~4h, cover the bottle well, take it out and cool the bottle in a dryer for 0.5h, subsequently, weigh the bottle. Whereafter, put this bottle into a drying oven to dry it at 101~105℃ for about 1h, take it out and cool it in a dryer for 0.5h, and then weigh it again after taking it out. Repeat the above operation till the mass difference of the bottle in two successive weighs does not exceed 2mg, and the final weighed value is the constant weight.
Note: in the final calculation, the smaller one of two obtained constant weights shall be taken.
5.2 Semisolid or liquid specimen: take one clean weighing bottle, add 10g sea sands (the mass may be increased properly during the test as required) and a stick of small glass rod into the bottle, place the bottle into a drying oven at 101~105℃, dry it for 1.0h and take it out, weigh it after cooling it in a dryer for 0.5h, and dry it repeatedly till it reaches a constant weight. Whereafter, weigh 5~10g specimen (accuracy to 0.0001g) and put them into a weighing bottle, stir them to be uniform with the small glass rod and put on boiling water bath to evaporate them to dryness, pay attention to mixing them during the evaporating process, wipe away the water drops at the bath bottom, put the bottle into a 101~105℃ drying oven for 4h, cover the bottle well and cool it in a dryer for 0.5h after taking it out, and weigh the bath after taking it out. Whereafter, put this bottle into a drying oven to dry it at 101~105℃ for about 1h, take it out and cool it in a dryer for 0.5h, and then weigh it again. Repeat the above operation till the mass difference of the bottle in two successive weighs does not exceed 2mg, and the final weighed value is the constant weight.
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 Instruments and Apparatus
10 Analysis Steps
11 Expression of Analysis Results
12 Precision
13 Principle
14 Reagents and Materials
15 Instruments and Apparatus
16 Analysis Steps
17 Expression of Analysis Results
18 Precision
19 Principle
20 Reagents and Materials
21 Instruments and Apparatus
22 Analysis Steps
23 Expression of Analysis Results
24 Precision
