BS ISO 5546-2010 Caseins and caseinates - Determination of pH (Reference method)《酪蛋白和酪蛋白酸盐 pH值的测定(基准方法)》.pdf

1、BS ISO 5546:2010ICS 67.100.99NO COPYING WITHOUT BSI PERMISSION EXCEPT AS PERMITTED BY COPYRIGHT LAWBRITISH STANDARDCaseins and caseinates Determination of pH(Reference method)This British Standard was published under the authority of the Standards Policy and Strategy Committee on 31 July2010 BSI 201

2、0ISBN 978 0 580 70099 6Amendments/corrigenda issued since publicationDate CommentsBS ISO 5546:2010National forewordThis British Standard is the UK implementation of ISO 5546:2010. Itsupersedes BS 6248-4:1982 which is withdrawn.The UK participation in its preparation was entrusted to TechnicalCommitt

3、ee AW/5, Chemical analysis of 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

4、with a British Standard cannot confer immunityfrom legal obligations.BS ISO 5546:2010Reference numbersISO 5546:2010(E)IDF 115:2010(E)ISO and IDF 2010INTERNATIONAL STANDARD ISO5546IDF115Second edition2010-06-01Caseins and caseinates Determination of pH (Reference method) Casines et casinates Dtermina

5、tion du pH (Mthode de rfrence)BS ISO 5546:2010ISO 5546:2010(E) IDF 115:2010(E) PDF disclaimer This PDF file may contain embedded typefaces. In accordance with Adobes licensing policy, this file may be printed or viewed but shall not be edited unless the typefaces which are embedded are licensed to a

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10、sels Tel. + 41 22 749 01 11 Tel. + 32 2 733 98 88 Fax + 41 22 749 09 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 2010 All rights reservedBS ISO 5546:2010ISO 5546:2010(E) IDF 115:2010(E) ISO and IDF

11、 2010 All rights reserved iiiForeword ISO (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 technical committees. Each member body interest

12、ed 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 closely with the International Electrotechnical Co

13、mmission (IEC) on all matters of electrotechnical standardization. International 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 techn

14、ical committees are circulated to the member bodies for voting. Publication 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 s

15、hall not be held responsible for identifying any or all such patent rights. ISO 5546IDF 115 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

16、 edition of ISO 5546IDF 115 cancels and replaces the first edition (ISO 5546:1979), of which it constitutes a minor revision. BS ISO 5546:2010ISO 5546:2010(E) IDF 115:2010(E) iv ISO and IDF 2010 All rights reservedForeword IDF (the International Dairy Federation) is a non-profit organization represe

17、nting the dairy sector worldwide. IDF membership comprises National 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 on the IDF Standing Committees carrying out the

18、technical work. IDF collaborates with ISO in the development of standard methods of analysis and sampling for milk and milk products. The main task of Standing Committees is to prepare International Standards. Draft International Standards adopted by the Standing Committees are circulated to the Nat

19、ional Committees for endorsement prior to publication as an International Standard. 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 subjec

20、t of patent rights. IDF shall not be held responsible for identifying any or all such patent rights. ISO 5546IDF 115 was prepared by the International Dairy Federation (IDF) and Technical Committee ISO/TC 34, Food products, Subcommittee SC 5, Milk and milk products. It is being published jointly by

21、IDF and ISO. All work was carried out by the former Joint ISO-IDF Action Team on Minor compounds, now part of the Standing Committee on Analytical methods for composition. This edition of ISO 5546|IDF 115 cancels and replaces IDF 115A:1989, of which it constitutes a minor revision. BS ISO 5546:2010I

22、NTERNATIONAL STANDARD ISO 5546:2010(E)IDF 115:2010(E) ISO and IDF 2010 All rights reserved 1Caseins and caseinates Determination of pH (Reference method) 1 Scope This International Standard specifies a reference method for the determination of the pH of all types of casein (acid caseins and rennet c

23、aseins) and of caseinates. 2 Terms and definitions For the purposes of this document, the following terms and definitions apply. 2.1 pH of caseins and caseinates pH, at 20 C, of an aqueous extract of casein or an aqueous solution of caseinate, as determined by the procedure specified in this Interna

24、tional Standard 3 Principle The pH of an aqueous extract of casein or an aqueous solution of caseinate is determined electrometrically using a pH meter. 4 Reagents Unless otherwise stated, use only reagents of recognized analytical grade and recently distilled water that has been protected from carb

25、on dioxide absorption. 4.1 Buffer solutions, for calibration of the pH meter (5.2). Two standard buffer solutions with pH values at 20 C, which are known to the second decimal place and which bracket the pH value of the sample under test, e.g. a phthalate buffer solution of approximately pH 4 and a

26、borax buffer solution of approximately pH 9. In addition, a phosphate buffer solution of approximately pH 7 may be used. 5 Apparatus Usual laboratory equipment and in particular the following. 5.1 Balance, accurate to the nearest 0,1 g. 5.2 pH meter, minimum sensitivity 0,05 pH unit, with a suitable

27、 glass electrode and a calomel or other reference electrode. 5.3 Thermometer, accurate to the nearest 0,5 C. BS ISO 5546:2010ISO 5546:2010(E) IDF 115:2010(E) 2 ISO and IDF 2010 All rights reserved5.4 Conical flask, capacity 100 ml, fitted with a ground-glass stopper. 5.5 Beaker, capacity 50 ml. 5.6

28、Grinding device, for grinding the laboratory sample, if necessary (see 7.4), without producing undue heat and loss or absorption of moisture. A hammer mill shall not be used. 5.7 Test sieve, wire cloth, diameter 200 mm, nominal size of openings 500 m, with receiver, ISO 3310-12. 5.8 Mixer. 5.9 Beake

29、r, for the mixer (5.8), capacity at least 250 ml. 6 Sampling Sampling is not part of the method specified in this International Standard. A recommended sampling method is given in ISO 707|IDF 501. It is important that the laboratory receive a truly representative sample which has not been damaged or

30、 changed during transport or storage. 7 Preparation of test sample 7.1 Thoroughly mix the laboratory sample by repeatedly shaking and inverting the container (if necessary, after having transferred all of the laboratory sample to an airtight container of sufficient capacity to allow this operation t

31、o be carried out). 7.2 Transfer about 50 g of the thoroughly mixed laboratory sample to the test sieve (5.7). 7.3 If the 50 g portion passes through the sieve completely or almost completely, use for the determination the sample as prepared in 7.1. 7.4 Otherwise, grind the 50 g portion, using the gr

32、inding device (5.6), until it passes through the sieve. Immediately transfer all the sieved sample to an airtight container of sufficient capacity and mix thoroughly by repeatedly shaking and inverting. During these operations, take precautions to avoid any change in the water content of the product

33、. 7.5 After the test sample has been prepared, initiate the procedure (see Clause 8) as soon as possible. 8 Procedure 8.1 Calibration of pH meter Adjust the temperature of the buffer solution (4.1) to 20 C and calibrate the pH meter in accordance with the manufacturers instructions. The calibration

34、should be carried out while the flasks are standing for 20 min (see 8.2.1 and 8.2.2). If a series of samples is being tested, check the calibration of the pH meter with one or more of the standard buffer solutions at least every 30 min. BS ISO 5546:2010ISO 5546:2010(E) IDF 115:2010(E) ISO and IDF 20

35、10 All rights reserved 38.2 Preparation of test solution 8.2.1 Caseins Weigh, to the nearest 0,1 g, into the conical flask (5.4), 5,0 g of the test sample (see Clause 7), add 30 ml of water previously adjusted to 20 C and stopper the flask. (If desired, 7,0 g of the test sample and 42 ml of water ma

36、y be taken.) Shake the flask by hand for 10 s and allow to stand for 20 min at about 20 C. 8.2.2 Caseinates Transfer to the beaker (5.9) 95 ml of water, add 5,0 g of the test sample (see Clause 7), and mix using the mixer (5.8) for 30 s. Allow to stand for 20 min at about 20 C. 8.3 Measurement of pH

37、 8.3.1 Caseins Decant the supernatant liquid into the beaker (5.5) and immediately determine the pH of this liquid, using the pH meter (5.2), after having rinsed the glass electrode carefully with water. 8.3.2 Caseinates Pour about 20 ml of the solution into the beaker (5.5) and immediately determin

38、e the pH of this liquid, using the pH meter (5.2), after having rinsed the glass electrode carefully with water. 9 Expression of results 9.1 Caseins Record, as the pH of the aqueous extract of casein, the value read from the dial of the pH meter to at least one decimal place. 9.2 Caseinates Record,

39、as the pH of the aqueous solution of caseinate, the value read from the dial of the pH meter to at least two decimal places. 10 Precision 10.1 Repeatability The difference between two single results obtained on identical test material by one analyst using the same apparatus within a short time inter

40、val will exceed 0,1 pH unit for casein extracts and 0,05 pH unit for caseinate solutions on average not more than once in 20 cases in the normal and correct operation of the method. BS ISO 5546:2010ISO 5546:2010(E) IDF 115:2010(E) 4 ISO and IDF 2010 All rights reserved10.2 Reproducibility The differ

41、ence between two single and independent results obtained by two operators working in different laboratories on identical test material will exceed 0,3 pH unit for casein extracts and 0,15 pH unit for caseinate solutions on average not more than once in 20 cases in the normal and correct operation of

42、 the method. 11 Test report The test report shall contain at least the following information: a) all the information necessary for the complete identification of the sample; b) the sampling method used, if known; c) the test method used, including a reference to this International Standard (ISO 5546

43、|IDF 115:2010); d) any operating conditions not specified in this International Standard, or regarded as optional, as well as details of any incidents that may have influenced the result(s); e) the test result(s) obtained; f) if the repeatability has been checked, the final quoted result obtained. B

44、S ISO 5546:2010ISO 5546:2010(E) IDF 115:2010(E) ISO and IDF 2010 All rights reserved 5Bibliography 1 ISO 707|IDF 50, Milk and milk products Guidance on sampling 2 ISO 3310-1, Test sieves Technical requirements and testing Part 1: Test sieves of metal wire cloth BS ISO 5546:2010ISO 5546:2010(E) IDF 1

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