1、BRITISH STANDARD CONFIRMED APRIL 1993 BS 1743-7.2: 1982 ISO 6092:1980 Methods for Analysis of dried milk and dried milk products Part 7: Determination of the titratable acidity of dried milk Section 7.2 Routine method ISO title: Dried milk Determination of titratable acidity (Routine method) IMPORTA
2、NT NOTE. It is essential that this Part be read in conjunction with Part1 “General introduction, including preparation of laboratory samples”, published separately. UDC 637.143.074:664.97:543.241.5BS1743-7.2:1982 This British Standard, having been prepared under the directionof the Dairying Standard
3、s Committee, was published under the authority ofthe Board of BSI and comes intoeffect on 29January 1982 BSI 08-1999 The following BSI references relate to the work on this standard: Committee reference DAC/3 Draftfor comment 77/52606 DC ISBN 0 580 12517 3 Amendments issued since publication Amd. No
4、. Date of issue CommentsBS1743-7.2:1982 BSI 08-1999 i Contents Page National foreword ii 1 Scope and field of application 1 2 References 1 3 Definition 1 4 Principle 1 5 Reagents 1 6 Apparatus 1 7 Sampling 1 8 Procedure 1 9 Expression of results 2 10 Comparison with the reference method 2 11 Test re
5、port 2 Publications referred to Inside back coverBS1743-7.2:1982 ii BSI 08-1999 National foreword This Part of BS 1743, which has been prepared under the direction of the Dairying Standards Committee, is identical with ISO 6092:1980 (including erratum published 1981-09-01) “Dried milk Determination
6、of titratable acidity (Routine method)”, prepared by ISO/TC 34, Agricultural food products, of the International Organization for Standardization (ISO). The method described in this International Standard has been developed jointly with the International Dairy Federation (IDF) and Association of Off
7、icial Analytical Chemists, USA (AOAC). The methods described in this Section 7.2 and in Section 7.1 of BS 1743 together constitute a revision of the method of determining titratable acidity of dried milk described in clause 8 of BS 1743:1968. The method given in BS1743:1968 is therefore superseded a
8、nd has been deleted from that standard. The routine method described in this Section differs from the method describedin BS 1743:1968 in that a) titration of reconstituted dried milk is with 0.1 mol/l sodium hydroxide solution to a phenolphthalein end-point using a cobalt sulphate reference colour s
9、olution (instead of with N/9 sodium hydroxide solution to a phenolphthalein end-point using a rosaniline acetate reference colour solution) and b) titratable acidity is expressed as millilitres of0.1 mol/l sodium hydroxide solution per 10 g of solids-not-fat (instead of grams of lactic acid per 100
10、g of dried milk. 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 not identical with those used in British Standards; attention is especially drawn t
11、o 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” appear, referring to this standard, they should be read as “British Standard”. With
12、 reference to clause 7, the methods for sampling given in BS 809:1974 “Methods for sampling milk and milk products” which is related to ISO/R 707, may be employed. With reference to the note to 8.2, the fat content may be determined in accordance with the method given in BS 1743:1968 “Methods for th
13、e analysis of dried milk and dried milk products” which is related to ISO/R 1736. A British Standard does not purport to include all the necessary provisions of a contract. Users of British Standards are responsible for their correct application. Compliance with a British Standard does not of itself
14、 confer immunity from legal obligations. Cross-references International Standard Corresponding British Standard ISO 6091:1980 BS 1743 Methods for analysis of dried milk and dried milk products Part 7 Determination of titratable acidity of dried milk Section 7.1:1982 Reference method (Identical) Summ
15、ary of pages This document comprises a front cover, an inside front cover, pages i and ii, pages1and 2, 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 fro
16、nt cover.BS1743-7.2:1982 BSI 08-1999 1 1 Scope and field of application This International Standard specifies a routine method for the determination of the titratable acidity of all types of dried milk. 2 References ISO/R 707, Milk and milk products Sampling. ISO/R 1736, Dried milk Determination of
17、fat content (Reference method). ISO 6091, Dried milk Determination of titratable acidity (Reference method). 3 Definition titratable acidity of dried milk the number of millilitres of 0,1 mol/l sodium hydroxide solution required to neutralize, in the presence of phenolphthalein, a quantity of the re
18、constituted milk corresponding to 10 g of solids-not-fat, until the appearance of a pink coloration 4 Principle Preparation of reconstituted milk by addition of water to a test portion of dried milk corresponding accurately to 5 g of solids-not-fat. Titration with0,1mol/l sodium hydroxide solution u
19、sing phenolphthalein as indicator and cobalt(II) sulphate as reference colour solution. Multiplication of the number of millilitres used in the titration by the factor 2, in order to obtain the number of millilitres in terms of 10 g of solids-not-fat. The amount of sodium hydroxide solution required
20、 is a function of the amount of natural buffering substances present in the product, and of developed or added acid or alkaline substances. 5 Reagents All reagents shall be of recognized analytical quality. Water shall be distilled or deionized water, freed from carbon dioxide by boiling for 10 min
21、before use. 5.1 Sodium hydroxide, standard volumetric solution, c(NaOH) = 0,1 0,000 2 mol/l. 1) 5.2 Reference colour solution Dissolve 3 g of cobalt(II) sulphate heptahydrate (CoSO 4 .7H 2 O) in water and make up to 100 ml. 5.3 Phenolphthalein solution Dissolve 2 g of phenolphthalein in 75 ml of 95
22、% (V/V) ethanol and add 20 ml of water. Add the sodium hydroxide solution (5.1) until 1 drop gives a faint pink coloration, and make up to 100 ml of water. 6 Apparatus 6.1 Analytical balance 6.2 Burette, graduated in 0,1 ml and with an accuracy of 0,05 ml. 6.3 Pipettes, of capacity 2 ml. 6.4 Measuri
23、ng cylinders, of capacity 50 ml. 6.5 Conical flasks, of capacity 100 or 150 ml, with ground necks and ground glass stoppers. 7 Sampling See ISO/R 707. 8 Procedure 8.1 Preparation of the test sample Transfer the sample to a clean, dry container (provided with an air-tight lid) of capacity about twice
24、 the volume of the sample. Close the container immediately, and thoroughly mix the contents by repeatedly shaking and inverting the container. During these operations, exposure of the sample to the atmosphere should be avoided as far as possible, to minimize adsorption of water. 8.2 Test portion Wei
25、gh (500/a) 0,01 g of the test sample (8.1) into each of two conical flasks (6.5), a being the solids-not-fat content of the sample, expressed as a percentage to two decimal places. NOTEThe solids-not-fat content of the sample may be calculated by subtracting the fat content (determined in accordance
26、 with ISO/R 1736) and the moisture content 2)from100. 8.3 Determination 8.3.1 Prepare reconstituted milk by adding 50 ml ofwater at about 20 C to the test portion (8.2) andagitating vigorously. Allow to stand for about20min. 8.3.2 Add to one of the conical flasks 2 ml of the reference colour solutio
27、n (5.2) to obtain a colour standard, and mix by slight swirling. 1) Hitherto expressed as “0,1 0,000 2 N standard volumetric solution”. 2) A method for the determination of moisture content is specified in IDF Standard No. 26, Determination of the water content of dried milk, which is currently unde
28、r revision by a joint ISO/IDF/AOAC group of experts.BS1743-7.2:1982 2 BSI 08-1999 If a series of determinations on similar products isto be carried out, this colour standard may be used throughout. However it should be discarded after 2h. 8.3.3 Add 2 ml of the phenolphthalein solution (5.3) to the s
29、econd conical flask, and mix by slight swirling. 8.3.4 Titrate the contents of the second conical flask, while swirling, by adding the sodium hydroxide solution (5.1) from the burette (6.2) until a faint pink colour similar to that of the colour standard persists for about 5 s. The titration should
30、be completed within 45 s. Record the volume, in millilitres, of sodium hydroxide solution used, to the nearest 0,05 ml. 9 Expression of results 9.1 Method of calculation and formula The titratable acidity is equal to 2 V where V is the volume, in millilitres, of the sodium hydroxide solution (5.1) u
31、sed for titration (8.3.4). Express the result to one decimal place. 9.2 Repeatability The difference between the results of two determinations carried out simultaneously or in rapid succession by the same analyst shall not exceed 0,4 ml of 0,1 mol/l sodium hydroxide solution per 10 g of solids-not-f
32、at. 10 Comparison with the reference method Verify at intervals whether this routine method gives results in adequate agreement with those obtained using the reference method specified in ISO 6091. 11 Test report The test report shall show the method used and the result obtained. It shall also menti
33、on any operating conditions not specified in this International Standard, or regarded as optional, as well as any circumstances that may have influenced the result. The test report shall include all details required for the complete identification of the sample.BS1743-7.2:1982 BSI 08-1999 Publicatio
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