BS-6248-7-1982 ISO-5549-1978.pdf
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1、BRITISH STANDARD BS 6248-7: 1982 ISO 5549:1978 Caseins and caseinates Part 7: Method for determination of protein content (reference method) ISO title: Caseins and caseinates Determination of protein content (Reference method) NOTEThis Part should be read in conjunction with Part 1 “General introduc
2、tion, including preparation of laboratory samples”, published separately. UDC 637.147.2.045:543.865 Licensed Copy: sheffieldun sheffieldun, na, Wed Dec 06 13:15:01 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS 6248-7:1982 This British Standard, having been prepared under the direction of the Dairyin
3、g Standards Committee, was published under the authority of the Board of BSI and comes into effect on 30 June 1982 BSI 12-1999 The following BSI references relate to the work on this standard: Committee reference DAC/3 Draft for comment 76/53486 DC ISBN 0 580 12751 6 Amendments issued since publicat
4、ion Amd. No.Date of issueComments Licensed Copy: sheffieldun sheffieldun, na, Wed Dec 06 13:15:01 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS 6248-7:1982 BSI 12-1999i Contents Page National forewordii 1Scope and field of application1 2References1 3Definition1 4Principle1 5Reagents1 6Apparatus1 7Sa
5、mpling1 8Procedure1 9Expression of results3 10Test report3 Publications referred toInside back cover Licensed Copy: sheffieldun sheffieldun, na, Wed Dec 06 13:15:01 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS 6248-7:1982 ii BSI 12-1999 National foreword This Part of BS 6248, which has been prepare
6、d under the direction of the Dairying Standards Committee, is identical with ISO 5549:1978 “Caseins and caseinates Determination of protein content (Reference method)”, prepared by ISO/TC 34, Agricultural food products, of the International Organization for Standardization (ISO) in cooperation with
7、the International Dairy Federation (IDF) and the Association of Official Analytical Chemists (AOAC). Terminology and conventions. The text of the International Standard has been approved as suitable for publication as a British Standard without deviation. Some terminology and certain conventions are
8、 not identical with those used in British Standards; attention is especially drawn to the following. The comma has been used throughout as a decimal marker. In British Standards it is current practice to use a full point on the baseline as the decimal marker. Where the words “International Standard”
9、 appear, referring to this standard, they should be read as “British Standard”. Related British Standards for ISO 3310-1 and ISO/R 707, referred to in the text, are respectively BS 410:1976 “Specification for test sieves” and BS 809:1974 “Methods for sampling milk and milk products”. With reference
10、to 6.12, a wire cloth test sieve of aperture size 500 4m, complying with BS 410:1976 is suitable. With reference to clause 7, the methods for sampling given in BS 809:1974 may be employed. Additional information 1) With reference to clause 5, water complying with BS 3978:1966 “Water for laboratory u
11、se” is suitable. 2) With reference to paragraph 3 of 8.5.2, the contents of the flask should be thoroughly mixed before any heat is applied in order to avoid excessive bumping. Textual error. When adopting the text of the International Standard, the textual error given below was discovered. It has b
12、een marked in the text and has been reported to ISO in a proposal to amend the text of the International Standard. In 8.4, line 2, “0,1 g” should read “0,1 mg”. A British Standard does not purport to include all the necessary provisions of a contract. Users of British Standards are responsible for t
13、heir correct application. Compliance with a British Standard does not of itself confer immunity from legal obligations. Cross-references International StandardCorresponding British Standard ISO 5550:1978aBS 6248 Caseins and caseinates Part 8:1982 Method for determination of water content (reference
14、method) (Identical) a As ISO 5550 has been published, the footnote to clause 2 is no longer applicable. Summary of pages This document comprises a front cover, an inside front cover, pages i and ii, pages 1 to 4, an inside back cover and a back cover. This standard has been updated (see copyright da
15、te) and may have had amendments incorporated. This will be indicated in the amendment table on the inside front cover. Licensed Copy: sheffieldun sheffieldun, na, Wed Dec 06 13:15:01 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS 6248-7:1982 BSI 12-19991 1 Scope and field of application This Internat
16、ional Standard specifies a reference method for the determination of the protein content of caseins and caseinates, excluding those containing ammonium caseinate or other ammonium compounds, or other nitrogenous non-protein compounds. 2 References ISO/R 707, Milk and milk products Sampling. ISO 3310
17、-I, Test sieves Technical requirements and testing Part I: Metal wire cloth. ISO 5550, Caseins and caseinates Determination of water content (Reference method)1). 3 Definition protein content of caseins and caseinates the nitrogen content as determined by the procedure described in this Internationa
18、l Standard, multiplied by 6,38 and expressed as a percentage by mass 4 Principle Digestion of a test portion with a mixture of potassium sulphate and sulphuric acid, in the presence of copper(II) sulphate as catalyst, to convert organic nitrogen into ammoniacal nitrogen. Distillation and absorption
19、of the ammonia in boric acid solution. Titration with standard volumetric hydrochloric acid solution. Multiplication of the result by the factor 6,38. 5 Reagents All reagents shall be of recognized analytical quality. The water used shall be distilled water or water of at least equivalent purity. 5.
20、1 Sulphuric acid, concentrated, 20 1,84 g/ml. 5.2 Potassium sulphate, anhydrous (K2SO4). 5.3 Copper(II) sulphate pentahydrate (CuSO4.5H2O) 5.4 Sucrose (C12H22O11) 5.5 Boric acid, 40 g/l solution. 5.6 Sodium hydroxide, concentrated aqueous solution, 30 % (m/m). 5.7 Hydrochloric acid, approximately 0,
21、1 N standard volumetric solution, standardized against sodium tetra-borate decahydrate (Na2B4O7.10H2O) or anhydrous sodium carbonate (Na2CO3). 5.8 Mixed indicator Mix equal volumes of a 2 g/l solution of methyl red in at least 95 % (V/V) ethanol and a 1 g/l solution of methylene blue in at least 95
22、% (V/V) ethanol. 6 Apparatus 6.1 Analytical balance 6.2 Kjeldahl flask, 500 ml capacity. 6.3 Digestion apparatus to hold the Kjeldahl flask (6.2) in an inclined position and with a heating device which will not heat the part of the flask above the surface of the liquid contents. 6.4 Condenser with s
23、traight inner tube. 6.5 Outlet tube with safety bulb connected to the lower end of the condenser (6.4) by a ground glass joint or a rubber tube. If rubber tubing is used, the glass ends must be near one another. 6.6 Splash-head connected to the Kjeldahl flask (6.2) and to the condenser (6.4) by soft
24、, close-fitting rubber stoppers. 6.7 Conical flask, 500 ml capacity. 6.8 Graduated cylinders, 50 ml and 100 ml capacity. 6.9 Burette, 50 ml capacity, graduated in 0,1 ml. 6.10 Boiling aids 6.10.1 For the digestion: small pieces of hard porcelain, or glass beads. 6.10.2 For the distillation: freshly
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