1、BRITISH STANDARD BS 1741-10.1: 1989 Methods for Chemical analysis of liquid milk and cream Part 10: Determination of titratable acidity Section 10.1 Method for liquid milk NOTEThis Section should be read in conjunction with Part1 “General introduction including preparation of samples”, published sep
2、arately. UDC 637.12+637.148.074:543BS 1741-10.1:1989 This British Standard, having been prepared under the directionof the Dairying Standards Committee, was published under the authorityofthe Board of BSIandcomes intoeffect on 28 February 1989 BSI 07-1999 The following BSI references relate to the w
3、ork on this standard: Committee reference DAC/3 Draft for comment 86/52566 DC ISBN 0 580 16826 3 Committees responsible for this British Standard The preparation of this British Standard was entrusted by the Dairying Standards Committee (DAC/-) to Technical Committee DAC/3, upon which the following
4、bodies were represented: AFRC Institute of Food Research, Reading Laboratory Association of British Preserved Milk Manufacturers Association of Public Analysts Association of Public Analysts of Scotland Creamery Proprietors Association Dairy Trade Federation Department of Trade and Industry (Laborat
5、ory of the Government Chemist) Ice Cream Alliance Limited Intervention Board for Agricultural Produce Joint Committee of the Milk Marketing Board and the Dairy Trade Federation Milk Marketing Board Milk Marketing Board for Northern Ireland Ministry of Agriculture, Fisheries and Food Royal Associatio
6、n of British Dairy Farmers Royal Society of Chemistry Society of Chemical Industry Society of Dairy Technology Amendments issued since publication Amd. No. Date of issue CommentsBS1741-10.1:1989 BSI 07-1999 i Contents Page Committees responsible Inside front cover Foreword ii 1 Scope 1 2 Definition
7、1 3 Principle 1 4 Reagents 1 5 Apparatus 1 6 Sampling 1 7 Procedure 1 8 Expression of results 1 9 Precision 2 10 Test report 2 Publications referred to Inside back coverBS 1741-10.1:1989 ii BSI 07-1999 Foreword This Section of BS1741has been prepared under the direction of the Dairying Standards Com
8、mittee. It is a revision of the method described in clause12 of BS1741:1963, which is deleted by amendment. This Section of BS1741introduces the expression of results in the form of titratable acidity in millilitres equivalent to sodium hydroxide solution used as well as retaining the alternative of
9、 expressing titratable acidity in terms of grams per100mL of “lactic acid”. This Section also introduces precision data. 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 wit
10、h 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, pages1 and2, an inside back cover and a back cover. This standard has been updated (see copyright date) and may have had amen
11、dments incorporated. This will be indicated in the amendment table on the inside front cover.BS1741-10.1:1989 BSI 07-1999 1 1 Scope This Section of BS1741describes a method for the determination of the titratable acidity of liquid milk. NOTEThe titles of the publications referred to in this standard
12、 are listed on the inside back cover. 2 Definition For the purposes of this Section of BS1741the following definition applies. titratable acidity of milk the number of millilitres of0.1mol/L sodium hydroxide solution required to neutralize10mL of sample, using phenolphthalein as indicator alternativ
13、ely, the titratable acidity of milk can be expressed as the number of millilitres of 0.111mol/L sodium hydroxide solution required to neutralize10mL of sample, using phenolphthalein as indicator, the result being expressed asg/100mL “lactic acid” NOTEIt has been the practice for many years to expres
14、s the titratable acidity in the terminology “lactic acid”g/100mL. It is well known that the titratable acidity is not due solely to the actual lactic acid content as natural buffering substances contribute to the quantity of sodium hydroxide solution used. 3 Principle Milk is titrated with0.1mol/L s
15、odium hydroxide solution or0.111mol/L sodium hydroxide solution using phenolphthalein as indicator and cobalt (II) sulphate as reference colour solution. 4 Reagents NOTESee BS1741-1. 4.1 Water, complying with grade3 of BS3978and freed from carbon dioxide by boiling. 4.2 Sodium hydroxide solution, ei
16、ther c (NaOH)=0.1mol/L, or c (NaOH)=0.111mol/L. 4.3 Reference colour solution. Dissolve1.5g of cobalt(II) sulphate heptahydrate (CoSO 4 .7H 2 O) in water and dilute to100mL. 4.4 Phenolphthalein solution. Dissolve1g of phenolphthalein in110mL of 95% (V/V) ethanol and add80mL water. Add the sodium hyd
17、roxide solution (4.2) until one drop gives a faint pink colouration and dilute to200mL with water. 5 Apparatus 5.1 Ordinary laboratory apparatus 5.2 Burette, of capacity10mL, graduated to0.02mL, complying with BS846, classB and fitted with a soda-lime guard tube. 5.3 Pipettes, of capacity1mL and10mL
18、, complying with BS1583, classB. 5.4 Porcelain basins, two, white, of capacity60mL, with a short glass stirring rod. 6 Sampling Take a representative sample of the liquid milk to be tested using, where appropriate, the procedures described in BS1741-1. 7 Procedure 7.1 Number of determinations Carry
19、out duplicate determinations using two test portions taken from the same test sample. NOTEWhen the method is being used for routine purposes, single determinations may be appropriate. However the analyst should undertake periodically duplicate determinations to verify that results complying with the
20、 repeatability requirements (see clause 9) are being obtained. 7.2 Test portions Pipette10mL of the test sample (see clause 6) into each of the two porcelain basins (5.4). 7.3 Control sample Prepare the control sample by stirring in1mL of the reference colour solution (4.3) into one of the prepared
21、porcelain basins (see 7.2). 7.4 Determination To the second prepared porcelain basin, stir in1mL of the phenolphthalein solution (4.4) and rapidly titrate using the appropriate sodium hydroxide solution (4.2), by first adding1mL of the sodium hydroxide solution and then continuing, drop by drop, unt
22、il the colour matches the pink tint of the control sample (see 7.3). The titration time shall not exceed30s. Record the volume, in millilitres, to the nearest0.02mL. NOTEThe titration should be undertaken as quickly as possible. If necessary, a ranging test to determine the approximate volume of sod
23、ium hydroxide solution can be undertaken. 8 Expression of results 8.1 If0.1mol/L sodium hydroxide solution is used for the determination, the titratable acidity of the test sample, expressed in millilitres, is equal to the volume of the sodium hydroxide solution used in the titration. Take as the re
24、sult the arithmetic mean of the results of two determinations provided that the requirement for repeatability (see clause 9) is satisfied. Express the result to the nearest0.02mL.BS 1741-10.1:1989 2 BSI 07-1999 8.2 If0.111mol/L sodium hydroxide solution is used for the determination, the titratable
25、acidity of the sample, expressed asg/100mL “lactic acid”, is given by the expression where V is the volume of sodium hydroxide solution used in the titration (inmL). Take as the result the arithmetic mean of the results of two determinations provided that the requirement for repeatability (see claus
26、e 9) is satisfied. Express the result to three decimal places. 9 Precision NOTEThe precision data were obtained from a collaborative study undertaken in1986, involving twelve laboratories and three milks (skimmed, semi-skimmed and full fat). 9.1 Repeatability The difference between the values obtain
27、ed from two determinations carried out simultaneously or in rapid succession by the same analyst using the same apparatus shall not exceed0.06mL or 0.006g/100mL “lactic acid”. 9.2 Reproducibility The difference between the results obtained on samples of the same test material by two different analys
28、ts in different laboratories (where each result is the mean of two values that comply with the repeatability requirement) should not exceed0.2mL or0.02g/100mL “lactic acid”. 10 Test report The test report shall be in accordance with BS1741-1. V 10 -BS1741-10.1:1989 BSI 07-1999 Publications referred
29、to BS 846, Specification for burettes. BS 1583, Specification for one-mark pipettes. BS 1741, Methods for the chemical analysis of liquid milk and cream. BS 1741-1, General introduction including preparation of samples. BS 1741-10.1: 1989 BSI 389 Chiswick High Road London W4 4AL BSIBritishStandardsI
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