BS EN ISO 16634-2-2016 Food products Determination of the total nitrogen content by combustion according to the Dumas principle and calculation of the crude protein content Cereals.pdf

1、BS EN ISO 16634-2:2016Food products Determination of thetotal nitrogen content bycombustion according tothe Dumas principle andcalculation of the crude proteincontentPart 2: Cereals, pulses and milled cerealproducts (ISO 16634-2:2016)BSI Standards PublicationWB11885_BSI_StandardCovs_2013_AW.indd 1 1

2、5/05/2013 15:06BS EN ISO 16634-2:2016 BRITISH STANDARDNational forewordThis British Standard is the UK implementation of EN ISO16634-2:2016. It supersedes DD CEN ISO/TS 16634-2:2009 which iswithdrawn.The UK participation in its preparation was entrusted to TechnicalCommittee AW/4, Cereals and pulses

3、.A list of organizations represented on this committee can beobtained on request to its secretary.This publication does not purport to include all the necessaryprovisions of a contract. Users are responsible for its correctapplication. The British Standards Institution 2016. Published by BSI Standar

4、dsLimited 2016ISBN 978 0 580 87691 2ICS 67.050; 67.060Compliance with a British Standard cannot confer immunity fromlegal obligations.This British Standard was published under the authority of theStandards Policy and Strategy Committee on 30 June 2016.Amendments issued since publicationDate Text aff

5、ectedEUROPEAN STANDARD NORME EUROPENNE EUROPISCHE NORM EN ISO 16634-2 June 2016 ICS 67.060; 67.050 Supersedes CEN ISO/TS 16634-2:2009English Version Food products - Determination of the total nitrogen content by combustion according to the Dumas principle and calculation of the crude protein content

6、 - Part 2: Cereals, pulses and milled cereal products (ISO 16634-2:2016) Produits alimentaires - Dtermination de la teneur en azote total par combustion selon le principe Dumas et calcul de la teneur en protines brutes - Partie 2: Crales, lgumineuses et produits craliers de mouture (ISO 16634-2:2016

7、) Lebensmittelerzeugnisse - Bestimmung des Gehaltes an Gesamtstickstoff mit dem Verbrennungsverfahren nach Dumas und Berechnung des Gehaltes an Rohprotein - Teil 2: Getreide, Hlsenfrchte und gemahlene Getreideerzeugnisse (ISO 16634-2:2016) This European Standard was approved by CEN on 12 May 2016. C

8、EN members are bound to comply with the CEN/CENELEC Internal Regulations which stipulate the conditions for giving this European Standard the status of a national standard without any alteration. Up-to-date lists and bibliographical references concerning such national standards may be obtained on ap

9、plication to the CEN-CENELEC Management Centre or to any CEN member. This European Standard exists in three official versions (English, French, German). A version in any other language made by translation under the responsibility of a CEN member into its own language and notified to the CEN-CENELEC

10、Management Centre has the same status as the official versions. CEN members are the national standards bodies of Austria, Belgium, Bulgaria, Croatia, Cyprus, Czech Republic, Denmark, Estonia, Finland, Former Yugoslav Republic of Macedonia, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, L

11、atvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Romania, Slovakia, Slovenia, Spain, Sweden, Switzerland, Turkey and United Kingdom. EUROPEAN COMMITTEE FOR STANDARDIZATION COMIT EUROPEN DE NORMALISATION EUROPISCHES KOMITEE FR NORMUNG CEN-CENELEC Management Centre: Avenue M

12、arnix 17, B-1000 Brussels 2016 CEN All rights of exploitation in any form and by any means reserved worldwide for CEN national Members. Ref. No. EN ISO 16634-2:2016 EBS EN ISO 16634-2:2016EN ISO 16634-2:2016 (E) 3 European Foreword This document (EN ISO 16634-2:2016) has been prepared by Technical C

13、ommittee ISO/TC 34 “Food products“ in collaboration with Technical Committee CEN/TC 338 “Cereal and cereal products” the secretariat of which is held by AFNOR. This European Standard shall be given the status of a national standard, either by publication of an identical text or by endorsement, at th

14、e latest by December 2016, and conflicting national standards shall be withdrawn at the latest by December 2016. Attention is drawn to the possibility that some of the elements of this document may be the subject of patent rights. CEN and/or CENELEC shall not be held responsible for identifying any

15、or all such patent rights. This document supersedes CEN ISO/TS 16634-2:2009. According to the CEN-CENELEC Internal Regulations, the national standards organizations of the following countries are bound to implement this European Standard: Austria, Belgium, Bulgaria, Croatia, Cyprus, Czech Republic,

16、Denmark, Estonia, Finland, Former Yugoslav Republic of Macedonia, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Romania, Slovakia, Slovenia, Spain, Sweden, Switzerland, Turkey and the United Kingdom. Endorsemen

17、t notice The text of ISO 16634-2:2016 has been approved by CEN as EN ISO 16634-2:2016 without any modification. BS EN ISO 16634-2:2016ISO 16634-2:2016(E)Foreword ivIntroduction v1 Scope . 12 Normative references 13 Terms and definitions . 14 Principle 25 Reagents 26 Apparatus . 37 Sampling 38 Prepar

18、ation of the test sample . 39 Procedure. 49.1 General . 49.2 Test portion 49.3 Control of oxygen supply 49.4 Calibration 59.5 Determination . 59.6 Detection and data processing 510 Calculation and expression of results . 610.1 Calculation 610.1.1 Nitrogen content 610.1.2 Crude protein content . 610.

19、2 Expression of results 611 Precision . 611.1 Interlaboratory tests 611.2 Repeatability . 711.3 Reproducibility . 711.4 Critical difference 711.4.1 Comparison of two groups of measurements in the same laboratory 711.4.2 Comparison of two groups of measurements in two different laboratories 811.5 Unc

20、ertainty . 812 Test report . 8Annex A (informative) Flowchart for a basic Dumas apparatus 9Annex B (informative) Schematic diagrams of suitable types of Dumas apparatus 10Annex C (informative) Equipment calibration 13Annex D (informative) Results of interlaboratory tests 15Bibliography .22 ISO 2016

21、All rights reserved iiiContents PageBS EN ISO 16634-2:2016ISO 16634-2:2016(E)ForewordISO (the International Organization for Standardization) is a worldwide federation of national standards bodies (ISO member bodies). The work of preparing International Standards is normally carried out through ISO

22、technical committees. Each member body interested in a subject for which a technical committee has been established has the right to be represented on that committee. International organizations, governmental and non-governmental, in liaison with ISO, also take part in the work. ISO collaborates clo

23、sely with the International Electrotechnical Commission (IEC) on all matters of electrotechnical standardization.The procedures used to develop this document and those intended for its further maintenance are described in the ISO/IEC Directives, Part 1. In particular the different approval criteria

24、needed for the different types of ISO documents should be noted. This document was drafted in accordance with the editorial rules of the ISO/IEC Directives, Part 2 (see www.iso.org/directives).Attention is drawn to the possibility that some of the elements of this document may be the subject of pate

25、nt rights. ISO shall not be held responsible for identifying any or all such patent rights. Details of any patent rights identified during the development of the document will be in the Introduction and/or on the ISO list of patent declarations received (see www.iso.org/patents).Any trade name used

26、in this document is information given for the convenience of users and does not constitute an endorsement.For an explanation on the meaning of ISO specific terms and expressions related to conformity assessment, as well as information about ISOs adherence to the WTO principles in the Technical Barri

27、ers to Trade (TBT) see the following URL: Foreword - Supplementary informationThe committee responsible for this document is ISO/TC 34, Food products, Subcommittee SC 4, Cereals and pulses.This first edition cancels and replaces ISO/TS 16634-2:2009, which has been technically revised.ISO 16634 consi

28、sts of the following parts, under the general title, Food products Determination of the total nitrogen content by combustion according to the Dumas principle and calculation of the crude protein content: Part 1: Oilseeds and animal feeding stuffs Part 2: Cereals, pulses and milled cereal productsiv

29、ISO 2016 All rights reservedBS EN ISO 16634-2:2016ISO 16634-2:2016(E)IntroductionFor a long time, the Kjeldahl method has been the most frequently used method for the determination of the protein content of food products. In recent years, the Dumas method has gained importance compared to the Kjelda

30、hl method because it is faster and does not use dangerous chemicals. Although the principles of the two methods are different, both measure the nitrogen content of the product. Nitrogen content can be converted into protein content by using an appropriate factor. The value of this factor varies depe

31、nding on the relative amounts of different proteins and their amino-acid composition in a given product.Neither the Dumas nor the Kjeldahl method distinguishes between protein and non-protein nitrogen. In most cases, results obtained by the Dumas method are slightly higher than those of the Kjeldahl

32、 method. This is because the Dumas method measures almost all of the non-protein nitrogen, whereas the Kjeldahl method measures only a part of it.Taking into consideration that the protein content of a product calculated by both methods only approximates to the true value, it is a matter of discreti

33、on which one is accepted. The best solution is to use a second factor for the elimination of the systematic error caused by the non-protein nitrogen content of the different products.However, this second factor has to be determined for each product like the existing factors which indicate the ratio

34、of the protein content to the nitrogen content. ISO 2016 All rights reserved vBS EN ISO 16634-2:2016BS EN ISO 16634-2:2016Food products Determination of the total nitrogen content by combustion according to the Dumas principle and calculation of the crude protein content Part 2: Cereals, pulses and

35、milled cereal products1 ScopeThis part of ISO 16634 specifies a method for the determination of the total nitrogen content and the calculation of the crude protein content of cereals, pulses and milled cereal products.This method, like the Kjeldahl method (see References 1 and 6), does not distingui

36、sh between protein nitrogen and non-protein nitrogen. For the calculation of the protein content, various conversion factors are used (see 3.2).2 Normative referencesThe following documents, in whole or in part, are normatively referenced in this document and are indispensable for its application. F

37、or dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies.ISO 712, Cereals and cereal products Determination of moisture content Reference methodISO 6540, Maize Determination of moisture content (on m

38、illed grains and on whole grains)ISO 24557, Pulses Determination of moisture content Air-oven method3 Terms and definitionsFor the purposes of this document, the following terms and definitions apply.3.1nitrogen contentmass fraction of the total nitrogenNote 1 to entry: Determined by the procedure s

39、pecified in this part of ISO 16634.Note 2 to entry: The mass fraction is expressed as a percentage.3.2crude protein contentnitrogen content (3.1) multiplied by a factorNote 1 to entry: A 5,7 factor is generally used for cereals for human food (such as wheat, rye and their milled products) and 6,25 f

40、or malting barley and cereals for feed and other products falling within the scope of this part of ISO 16634.Note 2 to entry: The factors for calculation of the crude protein content from the total nitrogen content are derived from the Kjeldahl method, which is the reference method for the determina

41、tion of total nitrogen content.INTERNATIONAL STANDARD ISO 16634-2:2016(E) ISO 2016 All rights reserved 1BS EN ISO 16634-2:2016ISO 16634-2:2016(E)4 PrincipleSamples are converted into gases by heating in a combustion tube. Interfering components are removed from the resulting gas mixture. The nitroge

42、n compounds in the gas mixture, or a representative part of them, are converted to molecular nitrogen which is quantitatively determined by a thermal-conductivity detector. The nitrogen content is calculated by a microprocessor.5 ReagentsUse only reagents of recognized analytical grade or reagents o

43、f equivalent purity as specified by instrument manufacturers. Except for the reference materials (5.12), all reagents shall be free from nitrogen.5.1 Carrier gas(es), use either 5.1.1 or 5.1.2.5.1.1 Carbon dioxide, as pure as possible, but with a minimum CO2volume fraction of 99,99 %.5.1.2 Helium, a

44、s pure as possible, but with a minimum He volume fraction of 99,99 %.5.2 Oxygen, as pure as possible, but with a minimum O2volume fraction of 99,99 %.5.3 Sulfur dioxide and halogen absorbent, to eliminate any sulfur from the sample e.g. lead chromate (PbCrO4) or steel wool.5.4 Copper oxide/platinum

45、catalyst, for the post-combustion tube.Platinum catalyst 5 % of Pt on alumina (Al2O3) is blended with CuO in the ratio 1 part:7 parts or 1 part:8 parts in accordance with the manufacturers recommendations.To prevent separation as a result of the different bulk densities of the two materials, it is r

46、ecommended not to prepare the mixture before filling the tube, but to pour the platinum catalyst and copper oxide simultaneously into the post-combustion tube using a suitable funnel.5.5 Silver or copper wool.This shall be disaggregated before being inserted into the post-combustion or reduction tub

47、e.5.6 Silica (quartz) or glass wool or cotton wool, as recommended by the instrument manufacturer.5.7 Copper or tungsten (wire, cuttings, turnings or powder), for the reduction tube.The use of copper or tungsten in one of these forms can improve the precision of analytical results for samples with l

48、ow nitrogen contents (about 1 % mass fraction).5.8 Diphosphorus pentoxide (P2O5) or granulated magnesium perchlorate Mg(ClO4)2, or another suitable drying agent, to fill the drying tubes.5.9 Hollow corundum spheres or aluminium oxide pellets, for the combustion tube.5.10 Copper oxide (CuO), as filli

49、ng material for the combustion tube.5.11 Sodium hydroxide (NaOH), on a support material.2 ISO 2016 All rights reservedBS EN ISO 16634-2:2016ISO 16634-2:2016(E)5.12 Aspartic acid (C4H7NO4) or ethylenediaminetetraacetic acid (C10H16N2O8) or glutamic acid (C5H9NO4) or hippuric acid (C9H9NO3) standard, or other suitable reference materials with a known, constant, certified nitrogen content.The minimum recovery should preferably be 99 % mass fraction.5.13 Light petroleum, with a boiling range between 30 C and 60 C, or acetone or