《BS-6248-7-1982 ISO-5549-1978.pdf》由会员分享，可在线阅读，更多相关《BS-6248-7-1982 ISO-5549-1978.pdf（10页珍藏版）》请在三一文库上搜索。
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
25、calcined pieces of pumice. 6.11 Grinding device, for grinding the laboratory sample, if necessary (see 8.1.4), without development of undue heat and without loss or absorption of moisture. A hammer-mill shall not be used. 6.12 Test sieve, wire cloth, diameter 200 mm, nominal size of aperture 500 4m,
26、 with receiver, complying with ISO 3310-I. 7 Sampling See ISO/R 707. 8 Procedure 8.1 Preparation of the test sample 8.1.1 Thoroughly mix the laboratory sample by repeatedly shaking and inverting the container (if necessary, after having transferred all of the laboratory sample to an air-tight contai
27、ner of sufficient capacity to allow this operation to be carried out). 8.1.2 Transfer about 50 g of the thoroughly mixed laboratory sample to the test sieve (6.12). 8.1.3 If the 50 g portion directly passes or almost completely passes the sieve, use for the determination the sample as prepared in 8.
28、1.1. 1) At present at the stage of draft. Licensed Copy: sheffieldun sheffieldun, na, Wed Dec 06 13:15:01 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS 6248-7:1982 2 BSI 12-1999 8.1.4 Otherwise, grind the 50 g portion, using the grinding device (6.11), until it passes the sieve. Immediately transfer
29、 all the sieved sample to an air-tight 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. 8.1.5 After the test sample has been prepared, the determination should b
30、e proceeded with as soon as possible. 8.2 Test for presence of non-protein nitrogen If the presence of ammonium caseinate or other ammonium compounds is suspected, carry out the following test. Add to 1 g of sample in a small conical flask, 10 ml of water and 100 mg of magnesium oxide. Rinse down an
31、y magnesium oxide adhering to the walls and close the flask with a cork stopper, inserting a piece of red litmus paper between the stopper and the neck of the flask. Mix the contents of the flask carefully and heat the flask in a water bath at 60 to 65 C. If the litmus paper colours blue within 15 m
32、in, ammonia is present, and the method is not applicable (see clause 1). 8.3 Blank test At the same time as the determination of the nitrogen content of the sample, perform a blank determination using 0,5 g of the sucrose (5.4) instead of the test portion, using the same apparatus, the same quantiti
33、es of all reagents and the same procedure as described in 8.5. If the result of the blank determination exceeds 0,5 ml of 0,1 N acid, the reagents shall be checked and the impure reagent or reagents purified or replaced. 8.4 Test portion Transfer to the Kjeldahl flask (6.2) 0,3 to 0,4 g of the test
34、sample (8.1), weighed to the nearest 0,1 g2). 8.5 Determination 8.5.1 Transfer to the flask a few pieces of porcelain or a few glass beads (6.10.1) and about 15 g of the anhydrous potassium sulphate (5.2). Add 0,2 g of the copper(II) sulphate (5.3) and wash down the neck of the flask with a little w
35、ater. Add 20 ml of the concentrated sulphuric acid (5.1). Mix the contents of the flask. Heat gently on the digestion apparatus (6.3) until any frothing has ceased. Boil gently until the solution is clear and a pale green-blue colour persists. During heating, shake the flask from time to time. Conti
36、nue the boiling, regulating the heating so as to condense the vapours in the middle of the flask neck. Continue the heating for 90 min, avoiding local overheating. Allow to cool to room temperature. Carefully add about 200 ml of water and a few pieces of pumice (6.10.2). Mix and cool again. 8.5.2 Tr
37、ansfer into the conical flask (6.7) 50 ml of the boric acid solution (5.5) and 4 drops of the indicator (5.8). Mix. Place the conical flask under the condenser (6.4) so that the tip of the outlet tube (6.5) is immersed in the boric acid solution. Using a graduated cylinder (6.8), add to the Kjeldahl
38、 flask 80 ml of the sodium hydroxide solution (5.6). During this operation, hold the flask in an inclined position so that the sodium hydroxide solution runs down the side of the flask to form a bottom layer. Immediately connect the Kjeldahl flask to the condenser by means of the splash-head (6.6).
39、Gently rotate the Kjeldahl flask to mix its contents. Boil gently at first, avoiding any frothing. Continue the distillation so that 150 ml of distillate are collected in approximately 30 min. The distillate should have a temperature below 25 C. About 2 min before the end of the distillation, lower
40、the conical flask so that the tip of the outlet tube is no longer immersed in the acid solution, and rinse the tip with a little water. Stop heating, remove the outlet tube and rinse its outer and inner walls with a little water, collecting the washings in the conical flask. 2) See national foreword
41、 for details of textual error. Licensed Copy: sheffieldun sheffieldun, na, Wed Dec 06 13:15:01 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS 6248-7:1982 BSI 12-19993 8.5.3 Titrate the distillate in the conical flask, using the standard volumetric hydrochloric acid solution (5.7). 9 Expression of res
42、ults 9.1 Method of calculation and formula 9.1.1 The protein content of the sample, expressed as a percentage by mass, is equal to where V1is the volume, in millilitres, of the standard volumetric hydrochloric acid solution (5.7) used in the determination (8.4); V2is the volume, in millilitres, of t
43、he standard volumetric hydrochloric acid solution (5.7) used in the blank test (8.3); Tis the normality of the standard volumetric hydrochloric acid solution (5.7); mis the mass, in grams, of the test portion. Calculate the protein content to the nearest 0,1 %. 9.1.2 To calculate the protein content
44、 of the sample on the dry basis, as a percentage by mass, multiply the result obtained in accordance with 9.1.1 by where M is the water content of the sample determined according to ISO 5550. 9.2 Precision 9.2.1 Repeatability The difference between two single results obtained on identical test mater
45、ial by one analyst using the same apparatus within a short time interval will exceed 0,5 g of protein per 100 g of product on average not more than once in 20 cases in the normal and correct operation of the method. 9.2.2 Reproducibility The difference between two single and independent results obta
46、ined by two operators working in different laboratories on identical test material will exceed 1,0 g of protein per 100 g of product on average not more than once in 20 cases in the normal and correct operation of the method. 10 Test report The test report shall show the method used and the result o
47、btained; it shall also mention all operating conditions not specified in this International Standard, or regarded as optional, as well as any circumstances that may have influenced the result. The report shall include all details necessary for complete identification of the sample. Licensed Copy: sh
48、effieldun sheffieldun, na, Wed Dec 06 13:15:01 GMT+00:00 2006, Uncontrolled Copy, (c) BSI 4 blank Licensed Copy: sheffieldun sheffieldun, na, Wed Dec 06 13:15:01 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS 6248-7:1982 BSI 12-1999 Publications referred to See national foreword. Licensed Copy: sheff
49、ieldun sheffieldun, na, Wed Dec 06 13:15:01 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS 6248-7: 1982 ISO 5549:1978 BSI 389 Chiswick High Road London W4 4AL BSI British Standards Institution BSI is the independent national body responsible for preparing British Standards. It presents the UK view on standards in Europe and at the international level. It is incorporated by Royal Charter. Revisions British Standards are updated by amendment or revision. Users of British Standards should make sure that they possess the latest amendments or editions. It is the co