《BS-6248-6-1982.pdf》由会员分享,可在线阅读,更多相关《BS-6248-6-1982.pdf(10页珍藏版)》请在三一文库上搜索。
1、BRITISH STANDARD BS 6248-6: 1982 Caseins and caseinates Part 6: Method for determination of lactose content (photometric method) NOTEThis Part should be read in conjunction with Part 1 “General introduction, including preparation of laboratory samples”, published separately. UDC 637.147.2.044:543.42
2、:547.458.227.3 Licensed Copy: sheffieldun sheffieldun, na, Wed Dec 06 13:15:01 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS 6248-6:1982 This British Standard, having been prepared under the direction of the Dairying Standards Committee, was published under the authority of the Board of BSI and come
3、s 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 79/53463 DC ISBN 0 580 12750 8 Foreword This Part of BS 6248, which has been prepared under the direction of the Dairying Standards Committee, is re
4、lated to ISO 5548:1980 “Caseins and caseinates Determination of lactose content Photometric method”, prepared by ISO/TC 34, Agricultural food products, of the International Organization for Standardization (ISO) in cooperation with the International Dairy Federation (IDF) and the Association of Offi
5、cial Analytical Chemists (AOAC). This British Standard differs from ISO 5548 principally in its inclusion of safety warnings in 5.6 and 8.5.1. However, for ease of reproduction the ISO text has been used, with changes made as appropriate. Some terminology and certain conventions are not identical wi
6、th 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. A British Standard does not purport to include all the ne
7、cessary provisions of a contract. Users of British Standards are responsible for their correct application. Compliance with a British Standard does not of itself confer immunity from legal obligations. Summary of pages This document comprises a front cover, an inside front cover, pages i and ii, pag
8、es 1 to 4, an inside back cover and a back cover. This standard has been updated (see copyright date) and may have had amendments incorporated. This will be indicated in the amendment table on the inside front cover. Amendments issued since publication Amd. No.Date of issueComments Licensed Copy: sh
9、effieldun sheffieldun, na, Wed Dec 06 13:15:01 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS 6248-6:1982 BSI 12-1999i Contents Page ForewordInside front cover 1Scope and field of application1 2References1 3Definition1 4Principle1 5Reagents1 6Apparatus1 7Sampling1 8Procedure1 9Expression of results3
10、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 ii blank Licensed Copy: sheffieldun sheffieldun, na, Wed Dec 06 13:15:01 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS 6248-6:1982 BSI 1
11、2-19991 1 Scope and field of application This British Standard describes a photometric method for the determination of the lactose and other soluble carbohydrates content of caseins and caseinates containing less than 2.0 % of total soluble carbohydrates. 2 References The publications referred to in
12、 this standard are listed on the inside back cover. 3 Definition lactose content of caseins and caseinates the content of total soluble carbohydrates, expressed as anhydrous lactose as a percentage by mass, determined by the procedure described in this British Standard 4 Principle Dissolution of a t
13、est portion a) in hot water in the case of caseinates; b) in hot water with the addition of sodium hydrogen carbonate in the case of acid casein; c) in hot water with the addition of pentasodium triphosphate in the case of rennet casein. Precipitation of the casein with acetic acid and sodium acetat
14、e solution at pH 4,6, followed by filtration to obtain a protein-free solution of the carbohydrates. Addition of phenol solution and concentrated sulphuric acid to an aliquot portion of the filtrate, thus producing a colour which is proportional to the amount of carbohydrate present, and photometric
15、 measurement at a wavelength of 490 nm. 5 Reagents All reagents shall be of recognized analytical quality. The water used shall be distilled water or water of at least equivalent purity. NOTEWater complying with BS 3978 is suitable. 5.1 Sodium hydrogen carbonate (NaHCO3) (for analysis of acid casein
16、). 5.2 Pentasodium triphosphate (Na5P3O10) (for analysis of rennet casein). 5.3 Hydrochloric acid or sulphuric acid, c(HCl) or c(1/2 H2SO4) = 0,1 mol/l. 5.4 Acetic acid, 100 g/l solution. 5.5 Sodium acetate solution, c(CH3COONa) = 1 mol/l. 5.6 Phenol, 80 % (m/m) solution. Heat a mixture of 8 g of ph
17、enol and 2 g of water until the mixture is homogeneous. WARNING NOTE. Appropriate precautions to protect the eyes and skin should be taken. 5.7 Sulphuric acid, concentrated, (20 1,84 g/ml). 5.8 Lactose, 20 g/l solution. Weigh 2,105 0,001 g of lactose monohydrate, corresponding to 2,00 g of anhydrous
18、 lactose, into a 100 ml volumetric flask, dissolve in water, make up to volume and mix well. Store the solution at 0 C. 6 Apparatus Usual laboratory equipment, and in particular: 6.1 Analytical balance 6.2 Conical flasks, of capacity 100 ml. 6.3 One-mark pipettes, of capacity 1, 2 and 10 ml. 6.4 Mic
19、ropipettes, of capacity 0,2 ml, with 0,001 ml divisions. 6.5 Graduated pipettes, of capacity 25 ml. 6.6 Test tubes, of capacity about 40 ml, with ground necks and fitted with ground glass stoppers. 6.7 Automatic dispenser, capable of dispensing 5 ml of concentrated sulphuric acid within 1 s. 6.8 Wat
20、er bath, capable of being controlled at 60 to 70 C. 6.9 Photometer, suitable for making measurements at a wavelength of 490 nm, provided with cells of optical path length 1 to 2 cm. 6.10 Mixer, suitable for mixing inside the test tubes (6.6), with a stirrer resistant to strong acid. 6.11 Grinding de
21、vice, for grinding the laboratory sample, if necessary (see 8.1.4), without development of undue heat and without loss of moisture. A hammer-mill shall not be used. 6.12 Test sieve, wire cloth, diameter 200 mm, nominal size of aperture 500 4m, with receiver, complying with BS 410. 6.13 Volumetric fl
22、asks, of capacity 100 ml. 6.14 Water bath, capable of being controlled at 20 C. 7 Sampling See BS 809 and BS 6248-1. 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
23、 of the laboratory sample to an air-tight container of sufficient capacity to allow this operation to be carried out). Licensed Copy: sheffieldun sheffieldun, na, Wed Dec 06 13:15:01 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS 6248-6:1982 2 BSI 12-1999 8.1.2 Transfer about 50 g of the thoroughly m
24、ixed laboratory sample to the test sieve (6.12). 8.1.3 If the 50 g portion passes completely or almost completely through the sieve, use for the determination the sample prepared in 8.1.1. 8.1.4 Otherwise, grind the 50 g portion, using the grinding device (6.11), until it passes through the sieve. I
25、mmediately transfer 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, carry o
26、ut the determination (8.5) as soon as possible. 8.2 Preparation of a blank solution Prepare a blank solution containing 0,1 0,001 g of sodium hydrogen carbonate or 0,1 0,001 g of pentasodium triphosphate, as appropriate, using the same apparatus, the same reagents in the same amounts, and the same p
27、rocedure as described in 8.4.2 to 8.5.1 inclusive, but omitting the test portion and omitting those operations in connection with the presence of a test portion. NOTEFor the most accurate results, prepare the blank solution, the test solution and the standard solutions for the calibration graph (see
28、 8.6) simultaneously. 8.3 Test portion Weigh, to the nearest 1 mg, about 1 g of the test sample (8.1) into a conical flask (6.2). 8.4 Test solution 8.4.1 In the case of acid casein, add 0,1 0,001 g of the sodium hydrogen carbonate (5.1). In the case of rennet casein, add 0,1 0,001 g of the pentasodi
29、um triphosphate (5.2). 8.4.2 Add 25 ml of water, place in the water bath (6.8), controlled at 60 to 70 C, and mix occasionally by shaking. 8.4.3 When the test portion is completely dissolved generally this takes 10 to 15 min cool and add successively: 15 ml of water; 8 ml of the hydrochloric acid or
30、 sulphuric acid solution (5.3); 1 ml of the acetic acid solution (5.4). Stopper and mix the contents by shaking after each addition. 8.4.4 Leave for 5 min and then add 1 ml of the sodium acetate solution (5.5). Mix by shaking. 8.4.5 Allow the casein precipitate to settle, then filter through a dry f
31、ilter paper. Discard the first few millilitres of the filtrate. 8.5 Determination 8.5.1 Pipette 2 ml of the filtrate (8.4.5) into a test tube (6.6), add 0,2 ml of the phenol solution (5.6) by means of a micropipette (6.4), and mix by shaking. Then add from the automatic dispenser (6.7), in less than
32、 1 s, 5 ml of the concentrated sulphuric acid (5.7), directing the stream of acid against the liquid surface rather than against the side of the test tube in order to obtain good mixing. Immediately mix, using the mixer (6.10), and allow to stand for 15 min. Cool for 5 min in the water bath (6.14) a
33、t 20 C. Wipe the tube and proceed immediately as described in 8.5.2. WARNING NOTE. The addition of the concentrated sulphuric acid produces a violent reaction which should be contained within the test tube. Appropriate precautions should be taken, particularly to protect the eyes and skin, in case o
34、f splashing. 8.5.2 Measure the absorbance of the solution (8.5.1) at 490 nm using the blank solution (8.2) as reference. 8.5.3 If the absorbance is above the upper limit of the calibration graph (see 8.6), repeat steps 8.5.1 and 8.5.2, using 2 ml of a suitable dilution of the filtrate (8.4.5) instea
35、d of 2 ml of the filtrate itself. NOTEIf such a dilution is made, the formula given in 9.1 has to be modified accordingly. 8.6 Preparation of calibration graph 8.6.1 Pipette 10 ml of the lactose solution (5.8) into a 100 ml volumetric flask (6.13) and dilute to the mark with water (solution A); 1 ml
36、 of solution A corresponds to 2 mg of anhydrous lactose. Prepare three standard solutions by pipetting 1, 2 and 3 ml of solution A into three 100 ml volumetric flasks and making up the volumes with water. The anhydrous lactose concentrations of the standard solutions obtained are respectively 20, 40
37、 and 60 4g/ml. 8.6.2 Using four test tubes (6.6), proceed in accordance with 8.5.1, but replace the 2 ml of filtrate respectively by 2 ml of each of the three standard solutions and by 2 ml of water. 8.6.3 Measure the absorbances of the three standard matching solutions using the solution obtained b
38、y treatment of the 2 ml of water as the reference liquid. 8.6.4 Construct a calibration graph by plotting the absorbances of the standard matching solutions against their anhydrous lactose concentrations in micrograms per millilitre. Draw the best-fitting line through the calibration points. License
39、d Copy: sheffieldun sheffieldun, na, Wed Dec 06 13:15:01 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS 6248-6:1982 BSI 12-19993 9 Expression of results 9.1 Method of calculation and formula The lactose content of the sample, expressed as anhydrous lactose as a percentage by mass, is equal to where c
40、is the concentration, in micrograms per millilitre, of anhydrous lactose in the test solution (8.4.5), read from the calibration curve (8.6.4); mis the mass, in grams, of the test portion (8.3). 9.2 Repeatability1) For lactose contents less than or equal to 0,2 % (m/m), the difference between two si
41、ngle results found on identical test material by one analyst using the same apparatus within a short time-interval will exceed 0,03 g of lactose per 100 g of product on average not more than once in 20 cases in the normal and correct operation of the method. 9.3 Reproducibility1) For lactose content
42、s less than or equal to 0,2 % (m/m), the difference between two single and independent results found by two operators working in different laboratories on identical test material will exceed 0,04 g of lactose per 100 g of product on average not more than once in 20 cases in the normal and correct op
43、eration of the method. 10 Test report The test report shall show the method used and the result obtained. It shall also mention all operating conditions not specified in this British Standard, or regarded as optional, as well as any circumstances that may have influenced the result. The report shall
44、 include all details necessary for complete identification of the sample. 1) At higher lactose contents, this difference will be proportionately greater. c 106 - -50 m - -100 Licensed Copy: sheffieldun sheffieldun, na, Wed Dec 06 13:15:01 GMT+00:00 2006, Uncontrolled Copy, (c) BSI 4 blank Licensed C
45、opy: sheffieldun sheffieldun, na, Wed Dec 06 13:15:01 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS 6248-6:1982 BSI 12-1999 Publications referred to BS 410, Specification for test sieves. BS 809, Methods for sampling milk and milk products. BS 3978, Water for laboratory use. BS 6248, Caseins and cas
46、einates. BS 6248-1, General introduction, including preparation of laboratory samples. Licensed Copy: sheffieldun sheffieldun, na, Wed Dec 06 13:15:01 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS 6248-6: 1982 BSI 389 Chiswick High Road London W4 4AL BSI British Standards Institution BSI is the inde
47、pendent 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 th
48、ey possess the latest amendments or editions. It is the constant aim of BSI to improve the quality of our products and services. We would be grateful if anyone finding an inaccuracy or ambiguity while using this British Standard would inform the Secretary of the technical committee responsible, the
49、identity of which can be found on the inside front cover. Tel: 020 8996 9000. Fax: 020 8996 7400. BSI offers members an individual updating service called PLUS which ensures that subscribers automatically receive the latest editions of standards. Buying standards Orders for all BSI, international and foreign standards publications should be addressed to Customer Services. Tel: 020 8996 9001. Fax: 020 8996 7001. In response to orders for international standards, it is BSI policy to supply the BSI implementation of thos
链接地址:https://www.31doc.com/p-3772951.html