1、June 2014Translation by DIN-Sprachendienst.English price group 13No part of this translation may be reproduced without prior permission ofDIN Deutsches Institut fr Normung e. V., Berlin. Beuth Verlag GmbH, 10772 Berlin, Germany,has the exclusive right of sale for German Standards (DIN-Normen).ICS 67
2、.100.10!%2N“2156143www.din.deDDIN EN ISO 8968-1Milk and milk products Determination of nitrogen content Part 1: Kjeldahl principle and crude protein calculation(ISO 8968-1:2014);English version EN ISO 8968-1:2014,English translation of DIN EN ISO 8968-1:2014-06Milch und Milcherzeugnisse Bestimmung d
3、es Stickstoffgehaltes Teil 1: Kjeldahl-Verfahren und Berechnung des Rohproteingehaltes (ISO 8968-1:2014);Englische Fassung EN ISO 8968-1:2014,Englische bersetzung von DIN EN ISO 8968-1:2014-06Lait et produits laitiers Dtermination de la teneur en azote Partie 1: Mthode Kjeldahl et calcul de la teneu
4、r en protines brutes (ISO 8968-1:2014);Version anglaise EN ISO 8968-1:2014,Traduction anglaise de DIN EN ISO 8968-1:2014-06SupersedesDIN EN ISO 8968-1:2002-06 andDIN EN ISO 8968-2:2002-06www.beuth.deIn case of doubt, the German-language original shall be considered authoritative.Document comprises 2
5、5 pages05.14 DIN EN ISO 8968-1:2014-06 2 A comma is used as the decimal marker. National foreword This document (EN ISO 8968-1:2014) has been prepared by Technical Committee ISO/TC 34 “Food products” (Secretariat: AFNOR, France), Subcommittee SC 5 “Milk and milk products” (Secretariat: NEN, Netherla
6、nds) in collaboration with Technical Committee CEN/TC 302 “Milk and milk products Methods of sampling and analysis” (Secretariat: NEN, Netherlands). The responsible German body involved in its preparation was the Normenausschuss Lebensmittel und landwirtschaftliche Produkte (Food and Agricultural Pr
7、oducts Standards Committee), Working Committee NA 057-05-13 AA Milch und Milcherzeugnisse Probenahme- und Untersuchungsverfahren. The DIN Standards corresponding to the International Standards referred to in this document are as follows: ISO 707 DIN EN ISO 707 ISO 5725-1 DIN ISO 5725-1 ISO 5725-2 DI
8、N ISO 5725-2 Amendments This standard differs from DIN EN ISO 8968-1:2002-06 and DIN EN ISO 8968-2:2002-06 as follows: a) the title of the standard has been amended; b) the scope has been amended and rendered more precise; c) information on automated distillation systems has been included; d) the ap
9、paratus to be used has been updated and supplemented; e) Equation (3) has been added to calculate the recovery; f) Annex A (informative) “Test portion” has been added; g) Annex B (informative) “Collaborative trials” has been added; h) the standard has been technically and editorially revised and bro
10、ught in line with current rules of presentation. Previous editions DIN 10334: 1989-11 DIN 10334-1: 1980-06 DIN 10334-2: 1981-10 DIN EN ISO 8968-1: 2002-06 DIN EN ISO 8968-2: 2002-06 DIN EN ISO 8968-1:2014-06 3 National Annex NA (informative) Bibliography DIN EN ISO 707, Milk and milk products Guidan
11、ce on sampling DIN ISO 5725-1, Accuracy (trueness and precision) of measurement methods and results Part 1: General principles and definitions DIN ISO 5725-2, Accuracy (trueness and precision) of measurement methods and results Part 2: Basic method for the determination of repeatability and reproduc
12、ibility of a standard measurement method DIN EN ISO 8968-1:2014-06 4 This page is intentionally blank EUROPEAN STANDARD NORME EUROPENNE EUROPISCHE NORM EN ISO 8968-1February 2014 ICS 67.100.10 Supersedes EN ISO 8968-1:2001, EN ISO 8968-2:2001English Version Milk and milk products - Determination of
13、nitrogen content -Part 1: Kjeldahl principle and crude protein calculation(ISO 8968-1:2014)Lait et produits laitiers - Dtermination de la teneur en azote -Partie 1: Mthode Kjeldahl et calcul de la teneur enprotines brutes (ISO 8968-1:2014)Milch und Milcherzeugnisse - Bestimmung des Stickstoffgehalte
14、s - Teil 1: Kjeldahl-Verfahren und Berechnung des Rohproteingehaltes (ISO 8968-1:2014) This European Standard was approved by CEN on 18 January 2014. CEN members are bound to comply with the CEN/CENELEC Internal Regulations which stipulate the conditions for giving this European Standard the status
15、of a national standard without any alteration. Up-to-date lists and bibliographical references concerning such national standards may be obtained on application to the CEN-CENELEC Management Centre or to any CEN member. This European Standard exists in three official versions (English, French, Germa
16、n). 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 Management Centre has the same status as the official versions. CEN members are the national standards bodies of Austria, Belgium, Bulgaria, Croatia,
17、 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, Turkey and Unite
18、d Kingdom. EUROPEAN COMMITTEE FOR STANDARDIZATIONCOMIT EUROPEN DE NORMALISATIONEUROPISCHES KOMITEE FR NORMUNGCEN-CENELEC Management Centre: 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
19、8968-1:2014 EContents Page Forewords . 3 1 Scope . 4 2 Normative references. 4 3 Terms and definitions 4 4 Principle 5 5 Reagents . 5 6 Apparatus 6 7 Sampling . 8 8 Preparation of test sample 8 8.1 Whole, partially skimmed or skimmed liquid milk 8 8.2 Hard, semi-hard and processed cheese 8 8.3 Dried
20、 milk and dried milk products 8 9 Procedures 9 9.1 Traditional method . 9 9.2 Block digestion method 10 9.3 Blank test 12 9.4 Recovery tests 13 10 Calculation and expression of results . 14 10.1 Calculation 14 10.2 Expression of results . 15 11 Precision . 16 11.1 Interlaboratory tests. 16 11.2 Liqu
21、id milk, whole milk and skimmed milk . 16 11.3 Hard, semi-hard and processed cheese 17 11.4 Dried milk and dried milk products 17 12 Test report . 17 Annex A (informative) Test portion 18 Annex B (informative) Collaborative trials 19 Bibliography 21 2DIN EN ISO 8968-1:2014-06EN ISO 8968-1:2014 (E)Fo
22、reword This document (EN ISO 8968-1:2014) has been prepared by Technical Committee 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
23、 the status of a national standard, either by publication of an identical 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
24、the subject of patent rights. CEN and/or CENELEC shall not be held responsible 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 coun
25、tries are bound to implement this European Standard: Austria, Belgium, Bulgaria, 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, Po
26、land, Portugal, Romania, Slovakia, Slovenia, Spain, Sweden, Switzerland, Turkey 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. 3DIN EN ISO 8968-1:2014-06EN ISO 8968-1:2014 (E)WARNING The use of this Inte
27、rnational Standard might involve the use of hazardous materials, operations, 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 he
28、alth practices and determine the applicability of local regulatory limitations 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 blo
29、ck digestion methods.The methods are applicable to: liquid cows (whole, 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,
30、 casein and caseinate). The methods are not applicable to samples containing 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, i
31、n whole or in part, are normatively referenced in this document and are 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 Buret
32、tesISO 8655-3, Piston-operated volumetric apparatus Part 3: Piston burettes3 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 perce
33、ntage.4DIN EN ISO 8968-1:2014-06EN ISO 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. Using copper
34、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 cooled digest
35、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 recognized analyti
36、cal 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 responsibility o
37、f 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 flask. Dilute to t
38、he 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 mass fraction
39、s 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. The total volum
40、e 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. Dissolve 0,5 g of br
41、omocresol 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 solution, c(H3BO3)
42、= 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 5DIN EN ISO 8968-1:2014-06EN ISO 8968-1:2014 (E)solution (5.5) and mix. Stor
43、e 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 systems, other boric acid concentrations may be used after validating accordingly.If using the electronic pH en
44、d point titration, the addition of the indicator solution to the boric acid solution may be omitted. On the other hand, the change in colour may also be used as a check on proper titration procedures.5.7 Hydrochloric acid standard volumetric solution, c(HCI) = (0,1 0,0005) mol/l.It is recommended to
45、 purchase this material prestandardized by the manufacturer, which meets, or exceeds, these specifications. Often, the systematic errors (which can be avoided) introduced by an analyst diluting a concentrated stock acid and then determining the molarity of the acid, cause poor reproducibility perfor
46、mance of the method in this part. The analyst should not use a solution for titration that has a higher concentration than 0,1 mol/l, because this will reduce the total titration volume per sample and the uncertainty in readability of the burette will become a larger percentage of the value. This wi
47、ll have a negative impact on the method repeatability and reproducibility performance. If sulfuric acid is substituted for hydrochloric acid, the solution should have a concentration of 0,05 0,000 3 mol/l.5.8 Ammonium sulfate (NH4)2SO4, minimum assay 99,9 % (mass fraction) on dried material.Immediat
48、ely before use, dry the ammonium sulfate at 102 C 2 C for not less than 2 h. Cool to room temperature in a desiccator.5.9 Tryptophan (C11H12N2O2) or lysine hydrochloride (C6H15ClN2O2), minimum assay 99 % (mass fraction).Do not dry these reagents in an oven before use.5.10 Sucrose, with a mass fracti
49、on of nitrogen of not more than 0,002 %.Do not dry the sucrose in an oven before use.6 ApparatusUsual laboratory apparatus and, in particular, the following.6.1 Water bath, capable of maintaining a water temperature between 38 C and 40 C.6.2 Analytical balance, capable of weighing to the nearest 0,1 mg.6.3 Burette or automatic pipette, capable for delivering 1,0 ml portions of the copper sulfate solution (5.2).6.4 Graduated measuring cylinders, of
