BS ISO 2446-2008 Milk - Determination of fat content《牛奶 脂肪含量的测定》.pdf

1、BS ISO 2446:2008ICS 67.100.10NO COPYING WITHOUT BSI PERMISSION EXCEPT AS PERMITTED BY COPYRIGHT LAWBRITISH STANDARDMilk Determinationof fat contentThis British Standardwas published underthe authority of theStandards Policy andStrategy Committee on 30September 2008 BSI 2008ISBN 978 0 580 63333 1Amen

2、dments/corrigenda issued since publicationDate CommentsBS ISO 2446:2008National forewordThis British Standard is the UK implementation of ISO 2446:2008. Itsupersedes BS 696-2:1989 which is withdrawn.The UK participation in its preparation was entrusted to TechnicalCommittee AW/5, Chemical analysis o

3、f milk and milk products.A list of organizations represented on this committee can be obtained onrequest to its secretary.This publication does not purport to include all the necessary provisionsof a contract. Users are responsible for its correct application.Compliance with a British Standard canno

4、t confer immunityfrom legal obligations.BS ISO 2446:2008Reference numbersISO 2446:2008(E)IDF 226:2008(E)ISO and IDF 2008INTERNATIONAL STANDARD ISO2446IDF226Second edition2008-09-01Milk Determination of fat content Lait Dtermination de la teneur en matire grasse BS ISO 2446:2008ISO 2446:2008(E) IDF 2

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8、m the ISO Central Secretariat at the address given below. COPYRIGHT PROTECTED DOCUMENT ISO and IDF 2008 All rights reserved. Unless otherwise specified, no part of this publication may be reproduced or utilized in any form or by any means, electronic or mechanical, including photocopying and microfi

9、lm, without permission in writing from either ISO or IDF at the respective address below. ISO copyright office International Dairy Federation Case postale 56 CH-1211 Geneva 20 Diamant Building Boulevard Auguste Reyers 80 B-1030 Brussels Tel. + 41 22 749 01 11 Tel. + 32 2 733 98 88 Fax + 41 22 749 09

10、 47 Fax + 32 2 733 04 13 E-mail copyrightiso.org E-mail infofil-idf.org Web www.iso.org Web www.fil-idf.org Published in Switzerland ii ISO and IDF 2008 All rights reservedBS ISO 2446:2008ISO 2446:2008(E) IDF 226:2008(E) ISO and IDF 2008 All rights reserved iiiForeword ISO (the International Organiz

11、ation 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 technical committees. Each member body interested in a subject for which a technical committee has been established

12、 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 closely with the International Electrotechnical Commission (IEC) on all matters of electrotechnical standardization. I

13、nternational Standards are drafted in accordance with the rules given in the ISO/IEC Directives, Part 2. The main task of technical committees is to prepare International Standards. Draft International Standards adopted by the technical committees are circulated to the member bodies for voting. Publ

14、ication as an International Standard requires approval by at least 75 % of the member bodies casting a vote. Attention 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

15、rights. ISO 2446IDF 226 was prepared by Technical Committee ISO/TC 34, Food products, Subcommittee SC 5, Milk and milk products, and the International Dairy Federation (IDF). It is being published jointly by ISO and IDF. This second edition of ISO 2446IDF 226 cancels and replaces the first edition (

16、ISO 2446:1976), of which it constitutes a minor revision. BS ISO 2446:2008ISO 2446:2008(E) IDF 226:2008(E) iv ISO and IDF 2008 All rights reservedForeword IDF (the International Dairy Federation) is a non-profit organization representing the dairy sector worldwide. IDF membership comprises National

17、Committees in every member country as well as regional dairy associations having signed a formal agreement on cooperation with IDF. All members of IDF have the right to be represented at the IDF Standing Committees carrying out the technical work. IDF collaborates with ISO in the development of stan

18、dard methods of analysis and sampling for milk and milk products. Draft International Standards adopted by the Action Teams and Standing Committees are circulated to the National Committees for voting. Publication as an International Standard requires approval by at least 50 % of the IDF National Co

19、mmittees 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 identifying any or all such patent rights. ISO 2446IDF 226 was prepared by the International Dairy Federation (IDF) and

20、 Technical Committee ISO/TC 34, Food products, Subcommittee SC 5, Milk and milk products. It is being published jointly by IDF and ISO. All work was carried out by the former Joint ISO/IDF/AOAC Group of Experts (E40-E301) which is now part of the Joint ISO-IDF Action Team on Fat, of the Standing Com

21、mittee on Main components in milk. BS ISO 2446:2008INTERNATIONAL STANDARD ISO 2446:2008(E)IDF 226:2008(E) ISO and IDF 2008 All rights reserved 1Milk Determination of fat content 1 Scope This International Standard specifies the Gerber method for the determination of the fat content of milk and inclu

22、des guidance on the determination of the appropriate capacity of the milk pipette and on the determination of the corrections to apply to the results if the milk is not of average fat content (see 6.1). The procedure for checking the capacity of the milk pipette is specified in Annex A. The method i

23、s applicable to liquid milk, whole or partially skimmed, raw or pasteurized. With modifications, details of which are given, it is also applicable to: a) milk containing certain preservatives (see Clause 11); b) milk that has undergone the process of homogenization, in particular sterilized milk and

24、 ultra heat-treated (UHT) milk (see Clause 12); c) skimmed milk (see Clause 13). NOTE The result obtained by the procedure specified in Clause 12 (modified for milk that has undergone homogenization) may be slightly high. 2 Normative references The following referenced documents are indispensable fo

25、r 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 488IDF 105, Milk Determination of fat content Gerber butyrometers ISO 1211IDF 1, Milk Determination

26、of fat content Gravimetric method (Reference method) 3 Terms and definitions For the purposes of this document, the following terms and definitions apply. 3.1 Gerber method empirical procedure which gives a value for fat content either as a mass fraction or as a mass concentration depending on the c

27、apacity of the milk pipette used that is the same as, or has a known relationship to, the value obtained by the reference method specified in ISO 1211IDF 1 NOTE The mass fraction is expressed in grams of fat per 100 g of milk and the mass concentration in grams of fat per 100 ml of milk. BS ISO 2446

28、:2008ISO 2446:2008(E) IDF 226:2008(E) 2 ISO and IDF 2008 All rights reserved4 Principle The milk fat in a butyrometer is separated by centrifuging after dissolving the protein with sulfuric acid, the separation being aided by the addition of a small quantity of iso-amyl alcohol. The butyrometer is g

29、raduated to give a direct reading of fat content. 5 Reagents Use only reagents of recognized analytical grade, unless otherwise specified, and only distilled or demineralized water or water of equivalent purity. 5.1 Sulfuric acid 5.1.1 Requirements The sulfuric acid shall have a density at 20 C of (

30、1,816 0,004) g/ml, which corresponds to approximately (90,4 0,8) % mass fraction H2SO4. The acid shall be colourless, or not darker in colour than pale amber, shall be free from suspended matter and shall be found suitable for use when tested as specified in 5.1.2. 5.1.2 Suitability test 5.1.2.1 Pur

31、pose of test Sulfuric acid can satisfy the specific requirements of 5.1.1 for density and appearance and yet be unsuitable for the Gerber method. Therefore, check the suitability of the acid before use by means of the following comparative test with a standard sulfuric acid. 5.1.2.2 Standard sulfuri

32、c acid Add sulfuric acid e.g. w(H2SO4) = 98 % mass fraction; 20= 1,84 g/ml to water to obtain a solution with a density within the range specified in 5.1.1. NOTE Approximately 1 l of standard sulfuric acid is obtained by adding 908 ml of 98 % mass fraction sulfuric acid to 160 ml of water, checking

33、the density of the diluted acid with a suitable hydrometer and adjusting the density, if necessary, by adding a small volume of water or 98 % mass fraction acid. 5.1.2.3 Comparison procedure Determine in duplicate the fat content of four samples of whole milk with average fat content by the Gerber m

34、ethod specified, using butyrometers whose scale errors are less than 0,01 % and standard iso-amyl alcohol (5.2.6.2). In one of each pair of duplicates use 10 ml of the sulfuric acid under test and in the other use 10 ml of the standard sulfuric acid (5.1.2.2). Keep the butyrometers in a random order

35、 from the shaking stage onwards. Take the readings to the nearest 0,01 % fat (read by at least two persons). The mean fat content of the four milk samples obtained with the sulfuric acid under test shall not differ by more than 0,015 % fat from the mean value obtained using the standard sulfuric aci

36、d. BS ISO 2446:2008ISO 2446:2008(E) IDF 226:2008(E) ISO and IDF 2008 All rights reserved 35.2 Iso-amyl alcohol 5.2.1 Composition A volume fraction of at least 98 % of the “iso-amyl” alcohol shall consist of the primary alcohols 3-methylbutan-1-ol and 2-methylbutan-1-ol, the only permissible major im

37、purities being 2-methylpropan-1-ol and butan-1-ol. It shall be free from secondary pentanols, 2-methylbutan-2-ol, furan-2-al (furfural, furan-2-carboxaldehyde, 2-furaldehyde), gasoline (petrol) and derivatives of benzene. Not more than a trace of water shall be present. 5.2.2 Physical appearance The

38、 iso-amyl alcohol shall be clear and colourless. 5.2.3 Density The iso-amyl alcohol shall have a density at 20 C of 0,808 g/ml to 0,818 g/ml. 5.2.4 Furan-2-al and other organic impurities When 5 ml of the iso-amyl alcohol is added to 5 ml of the sulfuric acid (5.1), no more than a yellow or light-br

39、own colour shall develop. 5.2.5 Distillation range When the iso-amyl alcohol is distilled at a pressure of 101,3 kPa1), a volume fraction of not less than 98 % shall distil below 132 C and a volume fraction of not more than 5 % below 128 C. There shall be no solid residue after distillation. If the

40、atmospheric pressure during the distillation is lower or higher than 101,3 kPa, the specified temperatures should be decreased or increased, respectively, by 0,3 C/kPa. 5.2.6 Suitability test 5.2.6.1 Purpose of test An iso-amyl alcohol can satisfy the requirements of 5.2.1 to 5.2.5, yet be unsuitabl

41、e for the Gerber method. Therefore, check the suitability of the iso-amyl alcohol before use by means of the following comparative test with a standard amyl alcohol. 5.2.6.2 Standard iso-amyl alcohol Distil an iso-amyl alcohol satisfying the requirements of 5.2.1 to 5.2.5, using a suitable fractiona

42、tion column, and collect a fraction within a boiling range of 2 C between 128 C and 131,5 C (see 5.2.5, paragraph 2). Apply the following tests to the fraction: a) when analysed by gas-liquid chromatography, a volume fraction of at least 99 % shall consist of 3-methylbutan-1-ol and 2-methylbutan-1-o

43、l only traces of impurities other than 2-methylpropan-1-ol and butan-1-ol shall be present; 1) 1 kPa = 10 mbar. BS ISO 2446:2008ISO 2446:2008(E) IDF 226:2008(E) 4 ISO and IDF 2008 All rights reservedb) when fractionally distilled, the first 10 % and the last 10 % collected, when compared using the p

44、rocedure specified in 5.2.6.3, shall give values for the fat content of milk that do not differ by more than 0,015 % fat. If the fraction satisfies both these tests, it can be regarded as standard iso-amyl alcohol. The standard iso-amyl alcohol can be used for several years, provided that it is kept

45、 in the dark in a cool place. 5.2.6.3 Comparison procedure Determine in duplicate the fat content of four samples of whole milk with average fat content by the Gerber method specified, using butyrometers whose scale errors are less than 0,01 % and standard sulfuric acid (5.1.2.2). In one of each pai

46、r of duplicates, use 1 ml of the iso-amyl alcohol under test, and in the other use 1 ml of the standard iso-amyl alcohol (5.2.6.2). Keep the butyrometers in a random order from the shaking stage onwards. Take the readings to the nearest 0,01 % fat (read by at least two persons). The mean fat content

47、 of the four milk samples obtained with the iso-amyl alcohol under test shall not differ by more than 0,015 % fat from the mean value obtained using the standard iso-amyl alcohol. Instead of the iso-amyl alcohol specified, an artificial iso-amyl alcohol or an iso-amyl alcohol substitute, coloured if

48、 desired, may be used, provided that its use has been demonstrated by experiment not to lead to any significant differences in the results of the determination. 6 Apparatus 6.1 Milk pipette. 6.1.1 The milk pipette shall be of the single graduation line, bulb type, and its capacity shall be defined a

49、s the volume, in millilitres, of water at 20 C (27 C in tropical countries) delivered by the pipette when emptied as specified in Annex A. The capacity of the pipette, determined by the method specified in Annex A, shall not differ from the nominal capacity, established according to 6.1.3, by more than 0,03 ml. 6.1.2 The capacity of the milk pipette shall be such that, when the pipette is used as specified in 9.2 (i.e. using the top of the milk meniscus when adjusting the milk to the graduation line) and w