1、BSI Standards PublicationBS EN ISO 8968-1:2014Milk and milk products Determination of nitrogencontentPart 1: Kjeldahl principle and crude proteincalculationBS EN ISO 8968-1:2014 BRITISH STANDARDNational forewordThis British Standard is the UK implementation of EN ISO 8968-1:2014. It supersedes BS 62
2、48-7:1982, BS EN ISO 8968-2:2002,BS EN ISO 8968-1:2002 and DD ISO/TS 17837:2008, which are withdrawn.The UK participation in its preparation was entrusted to Technical Committee AW/5, Chemical analysis of milk and milk products.A list of organizations represented on this committee can be obtained on
3、 request to its secretary.This publication does not purport to include all the necessary provisions of a contract. Users are responsible for its correct application. The British Standards Institution 2014.Published by BSI Standards Limited 2014ISBN 978 0 580 77839 1ICS 67.100.10Compliance with a Bri
4、tish Standard cannot confer immunity from legal obligations.This British Standard was published under the authority of the Standards Policy and Strategy Committee on 28 February 2014.Amendments/corrigenda issued since publicationDate T e x t a f f e c t e dEUROPEAN STANDARD NORME EUROPENNE EUROPISCH
5、E NORM EN ISO 8968-1 February 2014 ICS 67.100.10 Supersedes EN ISO 8968-1:2001, EN ISO 8968-2:2001English Version Milk and milk products - Determination of nitrogen content - Part 1: Kjeldahl principle and crude protein calculation (ISO 8968-1:2014) Lait et produits laitiers - Dtermination de la ten
6、eur en azote - Partie 1: Mthode Kjeldahl et calcul de la teneur en protines brutes (ISO 8968-1:2014) Milch und Milcherzeugnisse - Bestimmung des Stickstoffgehaltes - Teil 1: Kjeldahl-Verfahren und Berechnung des Rohproteingehaltes (ISO 8968-1:2014) This European Standard was approved by CEN on 18 Ja
7、nuary 2014. CEN 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 o
8、btained on application 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
9、 CEN-CENELEC 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, Irel
10、and, Italy, Latvia, 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 Cen
11、tre: Avenue Marnix 17, B-1000 Brussels 2014 CEN All rights of exploitation in any form and by any means reserved worldwide for CEN national Members. Ref. No. EN ISO 8968-1:2014 EBS EN ISO 8968-1:2014EN ISO 8968-1:2014 (E) 3 Foreword This document (EN ISO 8968-1:2014) has been prepared by Technical C
12、ommittee ISO/TC 34 “Food products” in collaboration with Technical Committee CEN/TC 302 “Milk and milk products - Methods of sampling and analysis” the secretariat of which is held by NEN. This European Standard shall be given the status of a national standard, either by publication of an identical
13、text or by endorsement, at the latest by August 2014, and conflicting national standards shall be withdrawn at the latest by August 2014. 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 respons
14、ible for identifying any or all such patent rights. This document supersedes EN ISO 8968-1:2001, EN ISO 8968-2:2001. According to the CEN-CENELEC Internal Regulations, the national standards organizations of the following countries are bound to implement this European Standard: Austria, Belgium, Bul
15、garia, Croatia, Cyprus, Czech Republic, 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, T
16、urkey and the United Kingdom. Endorsement notice The text of ISO 8968-1:2014 has been approved by CEN as EN ISO 8968-1:2014 without any modification. BS EN ISO 8968-1:2014ISO 8968-1:2014(E)IDF 20-1:2014(E) ISO and IDF 2014 All rights reserved iiiContents PageForewords .v1 Scope . 12 Normative refere
17、nces 13 Terms and definitions . 14 Principle 25 Reagents 26 Apparatus . 37 Sampling 58 Preparation of test sample . 58.1 Whole, partially skimmed or skimmed liquid milk . 58.2 Hard, semi-hard and processed cheese . 58.3 Dried milk and dried milk products . 59 Procedures 69.1 Traditional method . 69.
18、2 Block digestion method . 79.3 Blank test . 99.4 Recovery tests . 1010 Calculation and expression of results 1110.1 Calculation . 1110.2 Expression of results . 1211 Precision 1311.1 Interlaboratory tests .1311.2 Liquid milk, whole milk and skimmed milk 1311.3 Hard, semi-hard and processed cheese 1
19、411.4 Dried milk and dried milk products 1412 Test report 14Annex A (informative) Test portion .15Annex B (informative) Collaborative trials 16Bibliography .18BS EN ISO 8968-1:2014ISO 8968-1:2014(E)ForewordsISO (the International Organization for Standardization) is a worldwide federation of nationa
20、l standards bodies (ISO member bodies). The work of preparing International Standards is normally carried out through ISO 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. Internation
21、al organizations, governmental and non-governmental, in liaison with ISO, also take part in the work. ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters of electrotechnical standardization.The procedures used to develop this document and those intended f
22、or its further maintenance are described in the ISO/IEC Directives, Part 1. In particular the different approval criteria 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. www.iso.org/d
23、irectivesAttention is drawn to the possibility that some of the elements of this document may be the subject of patent 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 th
24、e Introduction and/or on the ISO list of patent declarations received. www.iso.org/patentsAny trade name used 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 c
25、onformity assessment, as well as information about ISOs adherence to the WTO principles in the Technical Barriers to Trade (TBT) see the following URL: Foreword - Supplementary informationThe committee responsible for this document is ISO/TC 34, Food and food products, Subcommittee SC 5, Milk and mi
26、lk products and the International Dairy Federation (IDF) and is being published jointly by ISO and IDF.This second edition of ISO 8968-1|IDF 20-1 cancels and replaces the first edition of ISO 8968-1| IDF 20-1:2001, ISO 8968-2|IDF 20-2:2001, ISO 5549:1978/IDF 92:1979 and ISO/TS 17837| IDF/RM 25:2008
27、which have been technically revised.IDF 20-1:2014(E)iv ISO and IDF 2014 All rights reservedBS EN ISO 8968-1:2014ISO 8968-1:2014(E)The International Dairy Federation (IDF) is a worldwide federation of the dairy sector with a National Committee in every member country. Every National Committee has the
28、 right to be represented on the IDF Standing Committees carrying out the technical work. IDF collaborates with ISO in the development of standard methods of analysis and sampling for milk and milk products.Draft International Standards adopted by the Standing Committees are circulated to the Nationa
29、l Committees for voting. Publication as an International Standard requires approval by at least 50 % of IDF National Committees casting a vote.Attention is drawn to the possibility that some of the elements of this document may be the subject of patent rights. IDF shall not be held responsible for i
30、dentifying any or all such patent rights.Any trade name used in this document is information given for the convenience of users and does not constitute an endorsement.ISO 8968-1|IDF 20-1 was prepared by the International Dairy Federation and Technical Committee ISO/TC 34, Food products, Subcommittee
31、 SC 5, Milk and milk products. It is being published jointly by ISO and IDF.The work was carried out by the IDF-ISO Project Group on Nitrogen, of the Standing Committee on Analytical Methods for Composition (SCAMC), under the aegis of its project leaders: Mr. R. Johnson (NZ), Mr. J. Romero (US), Dr.
32、 Barbano (US), Dr. Orlandini (IT), and Mr. Psathas (CY). This second edition of ISO 8968-1|IDF 20-1 cancels and replaces the first edition of ISO 8968-1| IDF 20-1:2001, ISO 8968-2|IDF 20-2:2001, ISO 5549:1978/IDF 92:1979 and ISO/TS 17837| IDF/RM 25:2008 which have been technically revised.IDF 20-1:2
33、014(E) ISO and IDF 2014 All rights reserved vBS EN ISO 8968-1:2014BS EN ISO 8968-1:2014Milk and milk products Determination of nitrogen content Part 1: Kjeldahl principle and crude protein calculationWARNING The use of this International Standard might involve the use of hazardous materials, operati
34、ons, and equipment. This International Standard does not purport to address all the safety risks associated with its use. It is the responsibility of the user of this International Standard to establish appropriate safety and health practices and determine the applicability of local regulatory limit
35、ations prior to use.1 ScopeThis International Standard specifies a method for the determination of the nitrogen content and crude protein calculation of milk and milk products by the Kjeldahl principle, using traditional and block digestion methods.The methods are applicable to: liquid cows (whole,
36、partially skimmed or skimmed milk), goats and sheeps whole milk; hard, semi-hard and processed cheese; dried milk and dried milk products (including milk-based infant formulae, milk protein concentrate, whey protein concentrate, casein and caseinate). The methods are not applicable to samples contai
37、ning ammonium caseinate.NOTE Inaccurate crude protein results will be obtained if non-milk sources of nitrogen are present in the products specified in this International Standard.2 Normative referencesThe following documents, in whole or in part, are normatively referenced in this document and are
38、indispensable to its application. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies.ISO 385, Laboratory glassware BurettesISO 8655-3, Piston-operated volumetric apparatus Part 3: Piston buret
39、tes3 Terms and definitionsFor the purposes of this document, the following terms and definitions apply.3.1nitrogen contentmass fraction of nitrogen determined by the specified procedureNote 1 to entry: It is expressed as a percentage.INTERNATIONAL STANDARDISO 8968-1:2014(E)IDF 20-1:2014(E) ISO and I
40、DF 2014 All rights reserved 1BS EN ISO 8968-1:2014ISO 8968-1:2014(E)3.2crude protein contentmass fraction of crude protein calculated as specifiedNote 1 to entry: It is expressed as a percentage.4 PrincipleA test portion is digested with a mixture of concentrated sulfuric acid and potassium sulfate.
41、 Using copper sulfate (II) as a catalyst to thereby convert any organic nitrogen present to ammonium sulfate. The function of the potassium sulfate is to elevate the boiling point of the sulfuric acid and to provide a stronger oxidizing mixture for digestion. Excess sodium hydroxide is added to the
42、cooled digest to liberate ammonia. The liberated ammonia is steam distilled into the excess boric acid solution and titration with hydrochloric acid standard volumetric solution is carried out. The nitrogen content is calculated from the amount of ammonia produced.5 ReagentsUse only reagents of reco
43、gnized analytical grade, unless otherwise specified, and distilled or demineralized water or water of equivalent purity.NOTE The solutions specified in this procedure might be different than those required for the operation of automated titrators. An effort is made to address those, but it is the re
44、sponsibility of the operator to follow the directions of the equipment manufacturer.5.1 Potassium sulfate (K2SO4), nitrogen free.5.2 Copper (II) sulfate pentahydrate solution, c(CuSO4.5H2O) = 5,0 g/100 ml.Dissolve 5,0 g of copper(II) sulfate pentahydrate in water in a 100 ml one-mark volumetric flas
45、k. Dilute to the mark with water and mix.5.3 Sulfuric acid (H2SO4), with a mass fraction of between 95 % and 98 %, nitrogen-free (approximately 20= 1,84 g/ml).5.4 Sodium hydroxide (NaOH) solution, nitrogen-free, containing 50 g of sodium hydroxide per 100 g.With automated distillation systems, other
46、 mass fractions of sodium hydroxide may be used, provided an excess of sodium hydroxide is dispensed to the distillation mixture; for example, a mass fraction of 40 % sodium hydroxide solution may be used instead of a mass fraction of 50 %, where plugging of the automated flow system is a problem. T
47、he total volume of such sodium hydroxide solution should be considered in order to maintain the suitable distillation volumes.5.5 Indicator solutionDissolve 0,1 g of methyl red in 95 % (volume fraction) ethanol in a 50 ml one-mark volumetric flask (6.16). Dilute to 50 ml with ethanol and mix. Dissol
48、ve 0,5 g of bromocresol green in 95 % (volume fraction) ethanol in a 250 ml one-mark volumetric flask (6.16). Dilute to 250 ml with ethanol and mix. Mix one part of the methyl red solution with five parts of the bromocresol green solution or combine and mix all of both solutions.5.6 Boric acid solut
49、ion, c(H3BO3) = 40,0 g/l.Dissolve 40,0 g of boric acid (H3BO3) in 1 l of hot water in a 1 000 ml one-mark volumetric flask (6.16). Allow the flask and its contents to cool to 20 C. Adjust to the mark with water, add 3 ml of the indicator IDF 20-1:2014(E)2 ISO and IDF 2014 All rights reservedBS EN ISO 8968-1:2014ISO 8968-1:2014(E)solution (5.5) and mix. Store the solution, which will be light orange in colour, in a borosilicate glass bottle. Protect the solution from light and sources of ammonia fume during storage.With automated distillation
