1、March 2009DEUTSCHE NORM English price group 12No part of this standard 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 67.100.10!$VW$“1515201ww
2、w.din.deDDIN EN ISO 7208Skimmed milk, whey and buttermilk Determination of fat content Gravimetric method (Reference method) (ISO 7208:2008)English version of DIN EN ISO 7208:2009-03Magermilch, Molke und Buttermilch Bestimmung des Fettgehaltes Gravimetrisches Verfahren (Referenzverfahren) (ISO 7208:
3、2008)Englische Fassung DIN EN ISO 7208:2009-03SupersedesDIN EN ISO 7208:2000-01www.beuth.deDocument comprises 21 pagesDIN EN ISO 7208:2009-03 2 National foreword This standard has been prepared by Technical Committee ISO/TC 34 “Food products” (Secretariat: AFNOR, France), Subcommittee SC 5 “Milk and
4、 milk products” (Secretariat: NEN, Netherlands) 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 landwirtsch
5、aftliche Produkte (Food and Agricultural Products Standards Committee), Technical Committee Milch und Milchprodukte Probenahme- und Untersuchungsverfahren. Based on the results of parallel voting, ISO 7208:2008 has been adopted as a European Standard. For reasons of environmental and worker protecti
6、on, the German employers liability insurance associations and inspectorates forbid the open evaporation of diethyl ether, which this standard allows as an alternative method. One way of reducing risks is to substitute diethyl ether with an equivalent amount of tert-butyl methyl ether (t-BME). This d
7、eviation from the specified procedure is to be stated in the test report. The DIN Standards corresponding to the International Standards referred to in this document are as follows: ISO 707 DIN EN ISO 707 ISO 835 DIN EN ISO 835 ISO 1042 DIN EN ISO 1042 ISO 4788 DIN EN ISO 4788 Amendments This standa
8、rd differs from DIN EN ISO 7208:2000-01 as follows: a) Clause 1 “Scope” has been rendered more precise. b) Clause 2 “Normative references” and clause 7 “Sampling” have been revised. c) The standard has been revised in form and substance and brought in line with the current rules of presentation. d)
9、The bibliography has been updated. Previous editions DIN EN ISO 7208: 2000-01 DIN EN ISO 7208:2009-03 3 National Annex NA (informative) Bibliography DIN EN ISO 707, Milk and milk products Guidance on sampling DIN EN ISO 835, Laboratory glassware Graduated pipettes DIN EN ISO 1042, Laboratory glasswa
10、re One-mark volumetric flasks DIN EN ISO 4788, Laboratory glassware Graduated measuring cylinders DIN EN ISO 7208:2009-03 4 This page is intentionally blank EUROPEAN STANDARDNORME EUROPENNEEUROPISCHE NORMEN ISO 7208October 2008ICS 67.100.10 Supersedes EN ISO 7208:1999 English VersionSkimmed milk, wh
11、ey and buttermilk - Determination of fatcontent - Gravimetric method (Reference method)(ISO 7208:2008)Lait crm, srum et babeurre - Dtermination de lateneur en matire grasse - Mthode gravimtrique(Mthode de rfrence) (ISO 7208:2008)Magermilch, Molke und Buttermilch - Bestimmung desFettgehaltes - Gravim
12、etrisches Verfahren(Referenzverfahren) (ISO 7208:2008)This European Standard was approved by CEN on 14 October 2008.CEN members are bound to comply with the CEN/CENELEC Internal Regulations which stipulate the conditions for giving this EuropeanStandard the status of a national standard without any
13、alteration. Up-to-date lists and bibliographical references concerning such nationalstandards may be obtained on application to the CEN 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 t
14、ranslationunder the responsibility of a CEN member into its own language and notified to the CEN Management Centre has the same status as theofficial versions.CEN members are the national standards bodies of Austria, Belgium, Bulgaria, Cyprus, Czech Republic, Denmark, Estonia, Finland,France, German
15、y, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal,Romania, Slovakia, Slovenia, Spain, Sweden, Switzerland and United Kingdom.EUROPEAN COMMITTEE FOR STANDARDIZATIONCOMIT EUROPEN DE NORMALISATIONEUROPISCHES KOMITEE FR NORMUNGManage
16、ment Centre: rue de Stassart, 36 B-1050 Brussels 2008 CEN All rights of exploitation in any form and by any means reservedworldwide for CEN national Members.Ref. No. EN ISO 7208:2008: EContents Page Foreword3 1 Scope 4 2 Normative references 4 3 Terms and definitions .4 4 Principle5 5 Reagents.5 6 A
17、pparatus .5 7 Sampling.6 8 Preparation of test sample7 9 Procedure .7 9.1 Test portion 7 9.2 Blank tests7 9.3 Preparation of fat-collecting vessel.8 9.4 Determination.8 10 Calculation and expression of results.10 10.1 Calculation10 10.2 Expression of results 10 11 Precision.11 11.1 Interlaboratory t
18、est 11 11.2 Repeatability.11 11.3 Reproducibility.11 12 Test report 11 Annex A (informative) Notes on procedures 11 Annex B (informative) Alternative procedure using fat-extraction tubes with siphon or wash-bottle fittings .14 Bibliography 17 2EN ISO 7208:2008 (E) DIN EN ISO 7208:2009-03 EN ISO 7208
19、:2008 (E) 3 Foreword This document (EN ISO 7208:2008) has been prepared by Technical Committee ISO/TC 34 “Agricultural 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 Europea
20、n Standard shall be given the status of a national standard, either by publication of an identical text or by endorsement, at the latest by April 2009, and conflicting national standards shall be withdrawn at the latest by April 2009. Attention is drawn to the possibility that some of the elements o
21、f this document may be 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 7208:1999. According to the CEN/CENELEC Internal Regulations, the national standards organizations of the following cou
22、ntries are bound to implement this European Standard: Austria, Belgium, Bulgaria, Cyprus, Czech Republic, Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Romania, Slovakia, Slovenia, Sp
23、ain, Sweden, Switzerland and the United Kingdom. Endorsement notice The text of ISO 7208:2008 has been approved by CEN as an EN ISO 7208:2008 without any modification. DIN EN ISO 7208:2009-03 WARNING The use of this International Standard may involve hazardous materials, operations and equipment. Th
24、is International Standard does not purport to address all the safety problems associated with its use. It is the responsibility of the user of this International Standard to establish safety and health practices and determine the applicability of regulatory limitations prior to use. 1 Scope This Int
25、ernational Standard specifies the reference method for the determination of the fat content of liquid skimmed milk, whey and buttermilk. It is a particularly accurate gravimetric method especially for the purpose of establishing the operating efficiency of cream separators. This International Standa
26、rd also specifies the reference method for establishing correction tables for procedures with skimmed milk butyrometers. NOTE When a high accuracy of determination is not required, the method specified in ISO 1211IDF 12is suitable. 2 Normative references The following referenced documents are indisp
27、ensable for the application of this document. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies. ISO 835, Laboratory glassware Graduated pipettes ISO 1042, Laboratory glassware One-mark volum
28、etric flasks ISO 3889IDF 219, Milk and milk products Specification of Mojonnier-type fat extraction flasks ISO 4788, Laboratory glassware Graduated measuring cylinders 3 Terms and definitions For the purposes of this document, the following terms and definitions apply. 3.1 fat content of skimmed mil
29、k, whey and buttermilk mass fraction of substances determined by the procedure specified in this International Standard NOTE The fat content is expressed as a percentage mass fraction. 4EN ISO 7208:2008 (E) DIN EN ISO 7208:2009-03 4 Principle An ammoniacal ethanolic solution of a test portion is ext
30、racted with diethyl ether and light petroleum. The solvents are removed by distillation or evaporation. The mass of the substances extracted is determined. NOTE This is usually known as the Rse-Gottlieb principle. 5 Reagents Use only reagents of recognized analytical grade, unless otherwise specifie
31、d, and only distilled or demineralized water or water of equivalent purity. The reagents shall leave no appreciable residue when the determination is carried out by the method specified (see 9.2.2). 5.1 Ammonia solution, containing a mass fraction of NH3of approximately 25 % (20= 910 g/l). NOTE If a
32、mmonia solution of this concentration is not available, a more concentrated solution of known concentration may be used (see 9.4.2). 5.2 Ethanol (C2H5OH), or ethanol denatured by methanol, containing a volume fraction of ethanol of at least 94 %. (See Clause A.5.) 5.3 Congo red solution Dissolve 1 g
33、 of Congo red (C32H22N6Na2O6S2) in water in a 100 ml one-mark volumetric flask (6.14). Make up to the mark with water. NOTE The use of this solution, which allows the interface between the solvent and aqueous layers to be seen more clearly, is optional (see 9.4.3). Other aqueous indicator solutions
34、can be used provided that they do not affect the result of the determination. 5.4 Diethyl ether (C2H5OC2H5), free from peroxides (see Clause A.3), containing no more than 2 mg/kg of antioxidants, and complying with the requirements for the blank test (see 9.2.2, Clauses A.1 and A.4). WARNING The use
35、 of diethyl ether can lead to hazardous situations. Observe current safety precautions for handling, use, and disposal. 5.5 Light petroleum, with any boiling range between 30 C and 60 C or, as equivalent, pentane (CH3CH23CH3) with a boiling point of 36 C and complying with the requirements for the b
36、lank test (see 9.2.2, Clauses A.1 and A.4). The use of pentane is recommended because of its higher purity and consistent quality. 5.6 Mixed solvent. Shortly before use, mix equal volumes of diethyl ether (5.4) and light petroleum (5.5). 6 Apparatus WARNING Since the determination involves the use o
37、f volatile flammable solvents, all electrical apparatus employed shall comply with legislation relating to the hazards in using such solvents. Usual laboratory equipment and, in particular, the following. 6.1 Analytical balance, capable of weighing to the nearest 1 mg, with a readability of 0,1 mg.
38、5EN ISO 7208:2008 (E) DIN EN ISO 7208:2009-03 6.2 Centrifuge, capable of holding the fat-extraction flasks or tubes (6.6) and capable of spinning at a rotational frequency of 500 min1to 600 min1to produce a radial acceleration of 80g to 90g at the outer end of the flasks or tubes. The use of the cen
39、trifuge is optional but recommended (see 9.4.6). 6.3 Distillation or evaporation apparatus, for distilling the solvents and ethanol from the boiling or conical flasks, or evaporating from beakers and dishes (see 9.4.13) at a temperature not exceeding 100 C. 6.4 Drying oven, electrically heated, with
40、 ventilation port(s) fully open, capable of being maintained at a temperature of 102 C 2 C throughout its working space. The oven shall be fitted with a suitable thermometer. 6.5 Water bath, capable of being maintained at a temperature of between 35 C and 40 C. 6.6 Mojonnier-type fat-extraction flas
41、ks, as specified in ISO 3889IDF 219. NOTE It is also possible to use fat-extraction tubes, with siphon or wash-bottle fittings, but then the procedure is different. The alternative procedure is given in Annex B. The fat-extraction flasks shall be provided with good quality cork bungs or stoppers of
42、other material (e.g. silicone rubber or polytetrafluoroethylene) unaffected by the reagents used. Cork bungs shall be extracted with the diethyl ether (5.4), kept in water at a temperature of 60 C or more for at least 15 min, and shall then be allowed to cool in the water so that they are saturated
43、when used. 6.7 Rack, for holding the fat-extraction flasks (or tubes) (6.6). 6.8 Wash bottle, suitable for use with the mixed solvent (5.6). A plastics wash bottle shall not be used. 6.9 Fat-collecting vessels, such as boiling flasks (flat-bottomed), of capacities 125 ml to 250 ml, conical flasks, o
44、f capacity 250 ml, or metal dishes. If metal dishes are used, they shall be of stainless steel, flat-bottomed with a diameter of 80 mm to 100 mm and a height of approximately 50 mm. 6.10 Boiling aids, fat-free, of non-porous porcelain or silicon carbide (optional when metal dishes are used). 6.11 Me
45、asuring cylinders, of capacities 5 ml and 25 ml, complying with the requirements of ISO 4788, class A, or any other apparatus suitable for the product concerned. 6.12 Pipettes, graduated, of capacity 10 ml, complying with the requirements of ISO 835, class A. 6.13 Tongs, made of metal, for holding f
46、lasks, beakers or dishes. 6.14 Volumetric flask, one-mark, of capacity 100 ml, complying with the requirements of ISO 1042, class A. 7 Sampling A representative sample should have been sent to the laboratory. It should not have been damaged or changed during transport or storage. Sampling is not par
47、t of the method specified in this International Standard. A recommended sampling method is given in ISO 707IDF 501. Store laboratory samples at a temperature between 2 C and 6 C from the time of sampling to the time of commencing the procedure. 6EN ISO 7208:2008 (E) DIN EN ISO 7208:2009-03 8 Prepara
48、tion of test sample Warm the test sample to a temperature between 35 C and 40 C by means of the water bath (6.5), if necessary. Gently mix the test sample thoroughly by repeatedly inverting the sample bottle without causing frothing or churning. Cool the test sample quickly to approximately 20 C. NO
49、TE A reliable value for the fat content cannot be expected: a) if the milk is churned; b) when a distinct smell of free fatty acids is perceptible; c) if during or after preparation of the test sample, white particles are visible on the walls of the sample bottle or fat droplets float on the surface of the sample. 9 Procedure NOTE 1 In the determination, two test portions (9.1) are extracted in two Mojonnier-type fat-extraction flasks (6.6). The extracts of the two flasks are poured into one prepared fa
