GB 5009.5-2025 PDF English
US$245.00 · In stock · Download in 9 secondsGB 5009.5-2025: National food safety standard - Determination of protein in food Delivery: 9 seconds. True-PDF full-copy in English & invoice will be downloaded + auto-delivered via email. See step-by-step procedureStatus: Valid GB 5009.5: Evolution and historical versions
| Standard ID | Contents [version] | USD | STEP2 | [PDF] delivery | Name of Chinese Standard | Status |
| GB 5009.5-2025 | English | 245 |
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National food safety standard - Determination of protein in food
| Valid |
| GB 5009.5-2016 | English | 85 |
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National food safety standard - Determination of protein in foods
| Valid |
| GB 5009.5-2010 | English | 359 |
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National food safety standard -- Determination of protein in foods
| Obsolete |
| GB/T 5009.5-2003 | English | 279 |
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3 days
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Determination of protein in foods
| Obsolete |
| GB/T 5009.5-1985 | English | 199 |
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2 days
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Method for determination of protein in foods
| Obsolete |
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GB 5009.5-2025: National food safety standard - Determination of protein in food---This is an excerpt. Full copy of true-PDF in English version (including equations, symbols, images, flow-chart, tables, and figures etc.), auto-downloaded/delivered in 9 seconds, can be purchased online: https://www.ChineseStandard.net/PDF.aspx/GB5009.5-2025
GB
NATIONAL STANDARD OF THE
PEOPLE’S REPUBLIC OF CHINA
National Food Safety Standard – Determination of Protein
in Foods
Issued on. MARCH 16, 2025
Implemented on. SEPTEMBER 16, 2025
Issued by. National Health Commission of the People’s Republic of China;
State Administration for Market Regulation.
Table of Contents
Foreword... 3
1 Scope... 4
2 Principle... 4
3 Reagents and Materials... 4
4 Instruments and Equipment... 5
5 Analysis Steps... 6
6 Expression of Analysis Results... 8
7 Precision... 9
8 Others... 9
9 Principle... 9
Foreword
This Standard replaced GB 5009.5-2016 National Food Safety Standard - Determination of
Protein in Foods.
Compared with GB 5009.5-2016, the major changes of this Standard are as follows.
--- Modify the scope of the standard;
--- Modify Method I the sampling volume and standard titration solution concentration of
the Kjeldahl method;
--- Add Method II the storage conditions and time of the standard solution and color
developer;
--- Modify Method III the scope and detection limit of the combustion method;
--- Add Appendix B combustion method calibration curve;
--- Modify the expression of analysis results and Appendix C protein conversion coefficient
table;
--- Modify the precision.
National Food Safety Standard – Determination of Protein
in Foods
1 Scope
This Standard specifies the method for determination of protein in foods.
This Standard is applicable to the determination of protein in foods.
Method I Kjeldahl Method
2 Principle
The protein in food is decomposed under catalytic heating conditions; and the produced
ammonia combines with sulfuric acid to form ammonium sulfate. Alkalinization distillation
frees the ammonia, which is absorbed by boric acid and titrated with sulfuric acid or
hydrochloric acid standard titration solution. The nitrogen content is calculated based on the
consumption of sulfuric acid or hydrochloric acid, and then multiplied by the conversion
coefficient to obtain the protein content.
3 Reagents and Materials
Unless otherwise specified, all reagents used in this method are analytically pure, and water is
Grade-3 water specified in GB/T 6682.
3.1 Reagents
3.2 Preparation of reagents
3.2.1 Boric acid solution (20 g/L). Weigh 20 g of boric acid; dissolve in water and dilute to
1,000 mL.
3.2.2 Sodium hydroxide solution (400 g/L). Weigh 40 g of sodium hydroxide; dissolve in water;
cool and dilute to 100 mL.
4 Instruments and Equipment
4.1 Analytical balance. With sensitivity of 1 mg.
4.2 Nitrogen determination distillation apparatus. as shown in Appendix A.
4.3 Pipette. 10 mL, 25 mL and 50 mL.
4.4 Nitrogen determination bottle. 100 mL, 250 mL and 500 mL.
4.5 Digestion furnace. ≥420℃.
4.6 Semi-automatic Kjeldahl nitrogen analyzer or fully automatic Kjeldahl nitrogen analyzer.
4.7 Homogenizer.
4.8 Crusher.
5 Analysis Steps
5.1 Kjeldahl method
5.2 Fully automatic or semi-automatic Kjeldahl method
Weigh 0.2 g ~ 2 g of solid specimen, 2 g ~ 5 g of semi-solid specimen, (accurate to 0.001 g),
10 g (mL) ~ 25 g (mL) (equivalent to 30 mg ~ 40 mg nitrogen) of liquid specimen; and then
add 0.4 g of copper sulfate, 6 g of potassium sulfate and 20 mL of sulfuric acid to the digestion
furnace for digestion. When the temperature of the digestion furnace reaches 420 ℃, continue
digestion for at least 1 h.
6 Expression of Analysis Results
The protein content in the specimen is calculated according to Formula (1).
When the protein content is ≥1 g/100 g or 1 g/100 mL, the result shall be retained 3 significant
figures; when the protein content is < 1 g/100 g or 1 g/100 mL, the result shall be retained 2
significant figures.
7 Precision
When the protein content in the sample is ≤10 g/100 g or 10 g/100 mL, the absolute difference
between two independent determination results obtained under repeatability conditions shall
not exceed 10% of the arithmetic mean.
8 Others
When using 0.05 mol/L hydrochloric acid titration solution, the sample weight is 5.0 g or 5.0
mL; and the detection limit of nitrogen in this method is 0.008 g/100 g or 0.008 g/100 mL.
Method II Spectrophotometry
9 Principle
The protein in food is decomposed under catalytic heating conditions. The ammonia produced
by the decomposition combines with sulfuric acid to form ammonium sulfate, which reacts with
acetylacetone and formaldehyde in a sodium acetate-acetic acid buffer solution at pH 4.8 to
form a yellow 3,5-diacetyl-2,6-dimethyl-1,4-dihydropyridine compound.
10 Reagents and Materials
Unless otherwise specified, the reagents used in this method are analytically pure, and the water
is Grade-3 water specified in GB/T 6682.
10.1 Reagents
10.2 Preparation of reagents
10.4 Preparation of standard solutions
10.4.1 Standard ammonium sulfate stock solution (by nitrogen) (1.0 g/L). Weigh 0.4720 g of
ammonium sulfate dried at 105°C for 2 h; dissolve in water and dilute to 100 mL; and mix well.
Each milliliter of this solution is equivalent to 1.0 mg of nitrogen. It can be stored at 4°C for 1
month.
10.4.2 Standard ammonium sulfate working solution (0.10 mg/mL). Accurately pipette 10.00
mL of standard ammonium sulfate stock solution (1.0 g/L) into a 100 mL volumetric flask;
dilute to the mark with water; and mix well. Each milliliter of this solution is equivalent to 0.1
mg of nitrogen. Prepare it before use.
11 Instruments and Equipment
11.1 Spectrophotometer.
11.2 Electro-thermostatic water bath. 100℃ ±1℃.
11.3 pH meter. With accuracy of 0.01.
11.4 10 mL stoppered glass colorimetric tube.
11.5 Analytical balance. With sensitivity of 1 mg and 0.1 mg.
11.6 Nitrogen determination bottle. 100 mL, 250 mL and 500 mL.
11.7 Homogenizer.
11.8 Crusher.
12 Analysis Steps
12.1 Preparation of specimen
The same as 5.1.1.
12.2 Determination of moisture
The same as 5.1.2.
12.3 Digestion of specimen
Weigh 0.1 g ~ 0.5 g of solid specimen, 0.2 g ~ 1 g (accurate to 0.01 g) of semi-solid specimen,
1 mL(g) ~ 5 mL(g) of liquid specimen; transfer into a dry 100 mL or 250 mL nitrogen
determination bottle. Add 0.1 g of copper sulfate, 1 g of potassium sulfate and 5 mL of sulfuric
acid; shake gently; place a small funnel at the mouth of the bottle; and place the nitrogen
determination bottle at a 45° angle on an asbestos net with small holes. Heat slowly; and when
the contents are completely carbonized and the foam stops completely, increase the fire and
keep the liquid in the bottle slightly boiling until the liquid becomes blue-green, clear and
transparent; and continue heating for 0.5 h~1 h. Remove the nitrogen determination bottle and
cool it to room temperature. Carefully add 20 mL of water and transfer all the contents to a 100
mL volumetric flask. Wash the inner wall of the nitrogen determination bottle with a small
amount of water; add the washing solution to the volumetric flask; add water to the scale, mix
well and set aside. Perform a blank test at the same time.
12.5 Drawing of standard curve
Pipette 0.00 mL, 0.05 mL, 0.10 mL, 0.20 mL, 0.40 mL, 0.60 mL, 0.80 mL and 1.00 mL of
standard ammonium sulfate working solution (equivalent to 0.00 μg, 5.00 μg, 10.0 μg, 20.0 μg,
40.0 μg, 60.0 μg, 80.0 μg and 100.0 μg of nitrogen) and place them in 10 mL colorimetric tubes
respectively. Add 4.0 mL of sodium acetate-acetic acid buffer solution and 4.0 mL of color
developer; dilute to the mark with water; and mix well. Heat in a 100 ℃ water bath for 15 min.
12.6 Determination of specimen
Pick 0.50 mL ~ 2.00 mL (equivalent to nitrogen < 100 μg) of specimen solution and the same
amount of reagent blank solution; and place them in 10 mL colorimetric tubes, respectively.
Add 4.0 mL of sodium acetate-acetic acid buffer solution and 4.0 mL of color developer; dilute
to the scale with water; and mix well. Heat in a 100 ℃ water bath for 15 min.
13 Expression of Analysis Results
The protein content in the specimen is calculated according to Formula (2).
14 Precision
When the protein content in the sample is ≤10 g/100 g or 10 g/100 mL, the absolute difference
between two independent determination results obtained under repeatability conditions shall
not exceed 10% of the arithmetic mean.
15 Others
When the sample weight is 5.0g or 5.0mL, the detection limit of nitrogen in this method is
0.0001g/100g or 0.0001g/100mL.
Method III Combustion Method
16 Principle
The specimen burns at a high temperature of 900℃~1,200℃. During the combustion process,
a mixed gas is generated. Interfering gases such as carbon and sulfur and salts are absorbed by
the absorption tube; and nitrogen oxides are completely reduced to nitrogen. The formed
nitrogen gas flow is detected by a thermal conductivity detector (TCD).
17 Reagents and Materials
17.1 Oxygen (O2). purity ≥99.995%.
17.2 Carrier gas (CO2, He, Ar, etc.). Purity ≥99.995%.
17.3 Nitrogen-containing standard substances. aspartic acid (C4H7NO4), urea (CH4N2O), purity
≥99%. Or nitrogen-containing standard substances certified by the state and awarded with
standard substance certificates.
17.4 Nitrogen-free aluminum foil, tin capsule, nitrogen-free plastic capsule or stainless-steel
crucible.
......
Source: Above contents are excerpted from the full-copy PDF -- translated/reviewed by: www.ChineseStandard.net / Wayne Zheng et al.
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