1、BRITISH STANDARD BS 1741-10.2: 1989 Methods for Chemical analysis of liquid milk and cream Part 10: Determination of titratable acidity Section 10.2 Method for cream NOTEThis Section should be read in conjunction with Part 1 “General introduction including preparation of samples”, published separate
2、ly. UDC 637.12 + 637.148.074:543BS1741-10.2:1989 This British Standard, having been prepared under the directionof the Dairying Standards Committee, was published under the authority ofthe Board of BSI and comes intoeffect on 28 February 1989 BSI 07-1999 The following BSI references relate to the wo
3、rk on this standard: Committee reference DAC/3 Draft for comment 86/53333 DC ISBN 0 580 16808 5 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 b
4、odies 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 (Laborato
5、ry 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 Association
6、 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 CommentsBS1741-10.2:1989 BSI 07-1999 i Contents Page Committees responsible Inside front cover Foreword ii 1 Scope 1 2 Definition 1
7、 3 Principle 1 4 Reagents 1 5 Apparatus 1 6 Sampling 1 7 Procedure 1 8 Expression of results 1 9 Repeatability 2 10 Test report 2 Publications referred to Inside back coverBS1741-10.2:1989 ii BSI 07-1999 Foreword This Section of BS 1741 has been prepared under the direction of the Dairying Standards
8、 Committee. It is a revision of the method described in clause 19 of BS1741:1963, which is deleted by amendment. This Section of BS 1741 introduces the expression of results in the form of titratable acidity in millilitres equivalent to sodium hydroxide solution used as well as retaining the alterna
9、tive of expressing titratable acidity in terms of grams per 100 g of “lactic acid”. 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 itse
10、lf confer immunity from legal obligations. Summary of pages This document comprises a front cover, an inside front cover, pages i and ii, pages1 and 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 in
11、dicated in the amendment table on the inside front cover.BS1741-10.2:1989 BSI 07-1999 1 1 Scope This section of BS 1741 describes a method for the determination of the titratable acidity of cream. NOTEThe titles of the publications referred to in this standard are listed on the inside back cover. 2
12、Definition For the purposes of this Section of BS 1741 the following definition applies. titratable acidity of cream the number of millilitres of 0.1 mol/L sodium hydroxide solution required to neutralize 10 g of sample, using phenolphthalein as indicator alternatively, the titratable acidity of cre
13、am can be expressed as the number of millilitres of 0.111 mol/L sodium hydroxide solution required to neutralize 10 g of sample, using phenolphthalein as indicator the result being expressed as g/100 g “lactic acid” NOTEIt has been the practice for many years to express the titratable acidity in the
14、 terminology “lactic acid” g/100 g. 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 Cream is titrated with 0.1 mol/L sodium hydroxide solution or
15、 0.111 mol/L sodium hydroxide solution using phenolphthalein as indicator and cobalt(II) sulphate as reference colour solution. 4 Reagents NOTESee BS 1741-1. 4.1 Water, complying with grade 3 of BS 3978 and freed from carbon dioxide by boiling. 4.2 Sodium hydroxide solution, either c(NaOH)=0.1 mol/L
16、, or c(NaOH) = 0.111 mol/L. 4.3 Reference colour solution. Dissolve 1.5 g of cobalt(II) sulphate heptahydrate (CoSO 4 .7H 2 O) in water and dilute to 100 mL. 4.4 Phenolphthalein solution. Dissolve 1 g of phenolphthalein in 110 mL of 95% (V/V) ethanol and add 80 mL of water. Add the sodium hydroxide
17、solution (4.2) until one drop gives a faint pink colouration and dilute to 200 mL with water. 5 Apparatus 5.1 Ordinary laboratory apparatus 5.2 Burette, of capacity 10 mL, graduated to0.02mL, complying with BS 846, class B and fitted with a soda-lime guard tube. 5.3 Pipettes, of capacity 2 mL and 10
18、 mL, complying with BS 1583, class B. 5.4 Porcelain basins, two, white, of capacity 60 mL, with a short glass stirring rod. 6 Sampling Take a representative sample of the cream to be tested using, where appropriate, the procedures described in BS 1741-1. 7 Procedure 7.1 Number of determinations Carr
19、y 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 t
20、he repeatability requirement (seeclause 9) are obtained. 7.2 Test portions Weigh 10 0.01 g of the test sample (see clause 6) into each of the two porcelain basins (5.4). Add10mL of water and mix by stirring. 7.3 Control sample Prepare the control sample by stirring in 2 mL of the reference colour so
21、lution (4.3) into one of the prepared porcelain basins (see 7.2). 7.4 Determination To the second prepared porcelain basin, stir in 2 mL of the phenolphthalein solution (4.4) and rapidly titrate using the appropriate sodium hydroxide solution (4.2), by first adding 1 mL of the sodium hydroxide solut
22、ion and then continuing, drop by drop, until the colour matches the pink tint of the control sample (see 7.3). The titration time shall not exceed 30 s. Record the volume, in millilitres, to the nearest 0.02 mL. NOTEThe titration should be undertaken as quickly as possible. If necessary, a ranging t
23、est to determine the approximate volume of sodium hydroxide solution can be undertaken. 8 Expression of results 8.1 If 0.1 mol/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 hydroxid
24、e solution used in the titration. Take as the result 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 nearest 0.02 mL.BS1741-10.2:1989 2 BSI 07-1999 8.2 If 0.111 mol/L sodium hydroxide solu
25、tion is used for the determination, the titratable acidity of the sample, expressed as g/100 g “lactic acid”, is given by the expression where V is the volume of sodium hydroxide solution used in the titration (in mL). Take as the result the arithmetic mean of the results of two determinations provi
26、ded that the requirement for repeatability (see clause 9) is satisfied. Express the result to three decimal places. 9 Repeatability The difference between the values obtained from two determinations carried out simultaneously or in rapid succession by the same analyst using the same apparatus shall
27、not exceed 0.06 mL or 0.006 g/100 g “lactic acid”. 10 Test report The test report shall be in accordance with BS 1741-1. V 10 -BS1741-10.2:1989 BSI 07-1999 Publications referred to BS 846, Specification for burettes. BS 1583, Specification for one-mark pipettes. BS 1741, Methods for chemical analysi
28、s of liquid milk and cream. BS 1741-1, General introduction including preparation of samples . BS 1741-10.2: 1989 BSI 389 Chiswick High Road London W4 4AL BSIBritishStandardsInstitution BSI is the independent national body responsible for preparing BritishStandards. It presents the UK view on standa
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