Determination of non-protein nitrogen content in milk and dairy products

GB/ T 21704-2008

———————————————————————————————————————

Determination of non-protein nitrogen content in milk and dairy products

Determination of   Non-protein-nitrogencontentin   Milk   And   Dairy   Products

( ISO 8968-4 : 2001/IDF   20-4:2001 , Milk - Determinationof   Nitrogencontent - Part

4: Determination of   Non-protein-nitrogencontent , MOD)

2008-04-09   Released 2008-07-01   Implementation

——————————————————————————————————

General Administration of Quality Supervision, Inspection and Quarantine of the People's Republic of China

China National Standardization Administration

GB /T 21704-2008

before          Word

This standard is modified to adopt ISO   8968-4 :2001/IDF 20-4:2001 "Detecting nitrogen content in milk   4th   Part: Detection of non-protein nitrogen content (English version) .

This standard is based on   ISO 8968-4 : 2001/IDF   20-4:2001 redrafting, according to   GB/T20001.4-2001 "Standard

Write rules    Part 4: Chemical Analysis Methods" The structure of the original standard was modified.

This standard was proposed by the Ministry of Agriculture of the People's Republic This standard is under the jurisdiction of the National Animal Husbandry Standardization Technical Committee.

This standard was drafted: Food Quality Supervision, Inspection and Testing Center of the Ministry of Agriculture (Shanghai) .

The main drafters of this standard: Meng Hao, Zheng Guanshu, Han Wei, Wu Hao, Zhu Jianxin.

Determination of non-protein nitrogen content in milk and dairy products

1          Scope This standard specifies methods for the determination of non-protein nitrogen in milk and dairy products. This standard applies to.

GB /T   21704-2008

4

The detection limit of this method is 3.5 × 10 ˉ

g/100g.

2    Normative reference

The terms in the following documents become the terms of this standard by reference to this standard. For dated reference documents, which subsequently some amendments (not including errata content) or revisions do not apply to this standard, however, encourage the use of these files according to whether the parties to the agreement are the zui new version. Any undated reference document, its new

This version G B / T 50 is adapted to a 09 - 00 2 standard

. Food hygiene inspection method      Physical and chemical part      General

Determination of protein in foods GB/T5009.5-2003

GB/T6682                     Analytical laboratory water specifications and test methods ( GB/T6682-1992, neq   ISO 3696 :

1987)

3    Terms and Definitions The following terms and definitions apply to this standard.

3.

1    Non-protein nitrogen content non-protein-nitrogen   Content

The content of nitrogen other than protein.

4    principle

The protein is precipitated with a 15% trichloroacetic acid solution, and the filtrate is digested and distilled.   0.01mol / L of hydrochloric acid titration, an amount calculated nitrogen content, the nitrogen content of the sample is the nonprotein.

5    Reagents and materials

Analytically pure reagents are used unless otherwise specified.

5.1     Water: Level 1 water specified in GB/T6682.

5.2 Sucrose ( C

1 2 H 22 O 11 ): The mass fraction of nitrogen is not more than 0.002% and cannot be dried in an oven before use.

5.3 Trichloroacetic acid solution: 150g / L, weighed   15.0g of trichloroacetic acid ( CCl 3 COOH ), dissolved and diluted with water

Mix 100mL and mix.                                                                         to

5.4     Standard titration solution of hydrochloric acid [ c(HCl)=0.01mol/L]: Preparation calibration according to Appendix B of GB/T5009.1-2003

carried out.

5.5     The remaining reagents are the same   GB/T5009.5-2003   Medium reagent.

5.6    Quantitative filter paper: medium speed.

6    Instruments and equipment commonly used in equipment and the following.

6.1                    Analytical balance: Sensitivity 0.0001 g.

6.2      Homogenizer: speed   6000r/min～ 18000   r/min.

6.3    A nitrogen distillation unit, or a nitrogen analyzer.

7    Analysis step

7.1    Sample preparation Milk and dairy products stored in the refrigerator should be taken out before the test and reached room temperature.

7.1.1     Liquid sample

Accurately weigh 10g of sample, accurate to 0.0001g, and place it in a pre-weighed beaker for testing.

GB /T 21704-2008

7.1.2     Solid sample

Accurately weigh 10g of the sample to the nearest 0.0001g and place it in a beaker. Milk powder added to 90mL   Warm water (5.1), uniform stirring; stirred heated cheese was added 40mL (5.1), homogenizer (6.2) was dissolved homogenate; warm melted butter. draw

10 mL was weighed in a previously weighed beaker and tested.

7.2     Precipitation, filtration

Measure 40mL   Trichloroacetic acid solution (5.3), added to the above sample beaker (7.1), a shake, said measured precisely. It was allowed to stand for 5 min , filtered at medium speed filter paper (5.6), and the clear filtrate was collected.

7.3     Determination

Accurately weigh 20g of filtrate to the nearest 0.0001g, and replace it with 0.01mol/L hydrochloric acid standard titration solution (5.4)

The 0.1mol/L hydrochloric acid standard titration solution is carried out according to the provisions of GB/T5009.5-2003 *.

7.4     Blank determination

Accurately weigh 0.1g sucrose (5.2) in a beaker and add 16mL   Trichloroacetic acid solution (5.3), 7 into the press operation. 2 lines, 7. 3 as a blank value.

8     Result calculation

The content of non-protein nitrogen in the sample is expressed by mass fraction, and the value is expressed in %, calculated according to formula (1):

1.4007c( V 1 - V 0   )( m 2 -0.065 m 1 ) X=

m 3   m 1

............(1)