1、BRITISH STANDARD BS 1741-7.1: 1989 Methods for Chemical analysis ofliquid milk and cream Part 7: Determination of lactose content Section 7.1 Reference method UDC 637.12 + 637.148.074:543:620.1BS1741-7.1:1989 This British Standard, having been prepared under the directionof the Dairying Standards Co
2、mmittee, was published under the authority ofthe Board of BSI and comes intoeffect on 31 July 1989 BSI 08-1999 The following BSI references relate to the work on this standard: Committee reference DAC/3 Draft for comment 86/54969 DC ISBN 0 580 17100 0 Committees responsible for this British Standard
3、 The preparation of this British Standard was entrusted by the Dairying Standards Committee (DAC/-) to Technical Committee DAC/3, upon which the following bodies were represented: AFRC Institute of Food Research (Reading Laboratory) Association of British Preserved Milk Manufacturers Association of
4、Public Analysts Association of Public Analysts of Scotland Creamery Proprietors Association Department of Trade and Industry (Laboratory of the Government Chemist) Ice Cream Alliance Limited Intervention Board for Agricultural Produce Joint Committee of the Milk Marketing Board and the Dairy Trade F
5、ederation Milk Marketing Board Milk Marketing Board for Northern Ireland Ministry of Agriculture, Fisheries and Food Royal Association of British Dairy Farmers Royal Society of Chemistry Society of Chemical Industry Society of Dairy Technology Amendments issued since publication Amd. No. Date of iss
6、ue CommentsBS1741-7.1:1989 BSI 08-1999 i Contents Page Committees responsible Inside front cover Foreword ii 1 Scope 1 2 Definition 1 3 Principle 1 4 Reagents 1 5 Apparatus 1 6 Sampling 1 7 Setting up the polarimeter 1 8 Calibration of the polarimeter 2 9 Procedure 2 10 Expression of results 2 11 Pr
7、ecision 3 12 Test report 3 Publications referred to Inside back coverBS1741-7.1:1989 ii BSI 08-1999 Foreword This Section of BS 1741 has been prepared under the direction of the Dairying Standards Committee. Part7 comprises two Sections, published separately, which together supersede clause9 of BS17
8、41:1963, which is deleted by amendment. This Section describes a polarimetric method for use for reference purposes. Section7.2 describes a titrimetric method for use for routine purposes. NOTEThis Part should be read in conjunction with Part 1 “General introduction, including preparation of samples
9、”, published separately. 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 confer immunity from legal obligations. Summary of pages
10、 This document comprises a front cover, an inside front cover, pagesi andii, pages1 to4, 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.BS1741
11、-7.1:1989 BSI 08-1999 1 1 Scope This Section of BS1741 describes a reference method for the determination of the lactose content of liquid milk of all types. Preserved samples may be analysed by this procedure provided that it can be shown that the preservative does not interfere with the determinat
12、ion. NOTEThe titles of the publications referred to in this standard are listed on the inside back cover. 2 Definition For the purposes of this Section of BS1741 the following definition applies. lactose content the lactose content, as determined under the conditions specified in this Section of BS1
13、741, expressed as a percentage by mass of the anhydrous lactose in the sample 3 Principle The method entails deproteinisation and removal of the fat from the milk, followed by measurement of the optical rotation of the clarified sample solution. 4 Reagents NOTESee BS1741-1. 4.1 General. Use reagents
14、 of recognized analytical grade, where available. 4.2 Water, complying with grade3 of BS3978. 4.3 Clarifying reagent. Dissolve125g of zinc acetate dihydrate (CH 3COO) 2Zn.2H 2 O) and 62.5g of dodecatungstophosphoric acid (H 3PO 812WO 3 ) in about500mL of water (4.2). Transfer to a1000mL one-mark vol
15、umetric flask and add100mL of glacial acetic acid (CH 3 COOH). Swirl to mix and dilute to the mark with water (4.2). Mix well. NOTEThe solution may appear slightly turbid. 4.4 Standard sucrose solution. Heat for1h a quantity of finely ground sucrose (C 12 H 22 O 11 ) at a depth of not greater than20
16、mm in a dish placed in an oven maintained at102 1 C. Allow to cool to room temperature in a desiccator and weigh2.600 0.001g in a glass weighing boat. Transfer, using water, to a100mL one-mark volumetric flask. Add water to within a few millilitres of the of the mark, stopper and swirl to mix and co
17、mplete the dissolution. Place the flask in the water bath (5.5) at20 0.5 C and, when the solution has reached the bath temperature, dilute to the mark with water and mix. NOTEThis solution is stable for1day. 5 Apparatus 5.1 Analytical balance, capable of weighing to an accuracy of 0.1mg. 5.2 One-mar
18、k volumetric flasks, capacity50mL and1000mL, complying with class B of BS1792. 5.3 Polarimeter. A semi-automatic or manual instrument capable of being read to0.01 angular or a fully automatic electronic instrument with digital read-out, having an accuracy of not less than0.01 angular shall be used.
19、The wavelength of the polarized light beam shall be589.44 nm (sodium D-line). The instrument shall have a compartment capable of holding a jacketed polarimeter tube (5.4). Instruments shall be operated according to the manufacturers instructions. NOTE 1In this standard a polarimeter is referred to w
20、here the instrument measures angular degrees of rotation. A saccharimeter is a polarimeter calibrated to measure degrees of rotation according to the International Sugar Scale. (One ISS degree of rotation =0.34626 angular degrees.) NOTE 2On 1 July 1988 a new “degrees Z” scale was adopted. Scales on
21、polarimeters and saccharimeters were previously calibrated in “degrees S”. Values in S on the old scale can be converted to Z on the new scale by multiplying the S value by the factor0.99971. Because the magnitude of the change is small it is not necessary to install new scales on existing instrumen
22、ts. However it is important to know which scale has been used to calibrate the quartz control plate and, if necessary, to convert readings to the new Z scale. 5.4 Polarimeter tube, jacketed, 200mm optical path length. 5.5 Temperature controlled water bath and circulator, capable of maintaining a wat
23、er temperature of20 0.5 C. 5.6 Quartz control plate, polarimetric reference standard, 8.5 angular rotation certificated by the National Physical Laboratory, Teddington, Middlesex. NOTE 1The quartz control plate should be fitted with a water jacket. NOTE 2See note 2 to5.3. 6 Sampling Take a represent
24、ative sample of the milk to be tested using, where appropriate, the procedures described in BS1741-1. 7 Setting up the polarimeter 7.1 Connect the water bath circulating pump (5.5) with tubing to the jacketed polarimeter tube (5.4) in its position in the polarimeter (5.3). Check that the water tempe
25、rature in the jacket or in the return tube is20 0.5 C. Mark the polarimeter tube in such a way that its placing in the instrument is always the same and not reversed.BS1741-7.1:1989 2 BSI 08-1999 7.2 Fill the polarimeter tube with water (4.2) whose temperature has been adjusted to20 0.5 C, place it
26、in the instrument and take the reading. If the reading is not0.00 0.02 angular, disassemble the tube, clean the parts, reassemble and retest with further water. NOTEOvertightening of the tube end fittings, causing strain in the glass windows, is a common cause of incorrect zeroing. 8 Calibration of
27、the polarimeter NOTEThe calibration of the polarimeter should be carried out as and when necessary prior to a batch of analyses or at least weekly. The calibration is most conveniently carried out with a certificated quartz control plate (5.6) or alternatively with a standard sucrose solution (4.4).
28、 8.1 Calibration with standard sucrose solution Place the flask containing the standard sucrose solution (4.4), together with a flask containing water (4.2), in the water bath at20 0.5 C and allow them to equilibrate thermally. Remove the flask containing the water, rinse the polarimeter tube three
29、or four times with small quantities of the water, then fill the tube, place it in the polarimeter and take the reading in accordance with7.2. Remove the polarimeter tube and empty it. Remove the flask containing the standard sucrose solution from the bath, dry the outside of the flask and rinse the
30、polarimeter tube with the sucrose solution three or four times and then fill the tube. Place the polarimeter tube in the instrument and take the reading. The optical rotation for the standard sucrose solution prepared accurately is3.462 angular; if the reading is not within 0.01 angular of this valu
31、e, recheck the zero setting for water at20 0.5 C, prepare fresh standard sucrose solution (4.4) and recalibrate. 8.2 Calibration with a certificated quartz control plate Connect the jacket of the certificated quartz plate(5.6) to the water circulator maintained at20 0.5 C. Place the plate in the ins
32、trument and allow5min for thermal equilibration. Take the reading. If the reading does not agree with the standard rotation given on the quartz control plate to within the tolerance stated in the certificate, adjust the instrument if necessary, making reference to the instrument manual. 9 Procedure
33、9.1 Carry out duplicate determinations using two test portions from the same test sample. 9.2 Weigh to the nearest0.01g about20mL of theprepared sample (see clause6) into a50mL one-mark volumetric flask (5.2). Add5mL of the clarifying reagent (4.3) and, without mixing, carefully dilute to the mark w
34、ith water, avoiding the formation of foam. Stopper and mix by several inversions of the flask. Allow to stand and after15min filter through a fluted filter paper, rejecting the first few millilitres of filtrate. Collect the remaining clear filtrate in a clean dry bottle or conical flask. Stopper the
35、 bottle or flask and place in the water bath (5.5) maintained at20 0.5 C at such a depth that the collected filtrate is below the level of the water in the bath. Place a similar stoppered bottle or flask containing water (4.2) in the bath. Allow the contents to equilibrate with the bath temperature.
36、 Remove the water sample and carry out a check on the zero setting as described in7.2. Remove the clarified milk sample from the bath and wipe the container dry. Empty the polarimeter tube and rinse it three or four times with the sample solution and then fill the tube. Place the tube in the instrum
37、ent and take the reading. 10 Expression of results Calculate the anhydrous lactose content, expressed as a percentage by mass, using the expression: where: Take as the result the arithmetic mean of the results of two determinations provided that the requirement for repeatability (see11.1) is satisfi
38、ed. Express the result to two decimal places. NOTEThe lactose monohydrate content, expressed as a percentage by mass, can be obtained by multiplying the result by1.053. A is the optical rotation of the clarified sample solution in angular degrees on the Z scale (see note2 to5.3); R is the specific r
39、otation of anhydrous lactose, which is55.48when measured at589.44nm and20 C; m is the mass of the test portion of milk, in g; F is the percentage (m/m) of fat in the milk sample, determined in accordance with BS1741-3 or BS696; P is the percentage (m/m) of protein in the milk sample, calculated by m
40、ultiplying the nitrogen content, determined in accordance with BS1741-5.1 or BS1741-5.2, by6.38.BS1741-7.1:1989 BSI 08-1999 3 11 Precision NOTEThe precision data were obtained from a collaborative study undertaken in1968 and involving12 laboratories and three milks (skimmed, semi-skimmed and full fa
41、t). 11.1 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 not exceed0.04% (m/m). 11.2 Reproducibility The difference between the results obtained on samples of the sam
42、e test material by two different analysts in different laboratories (where each result is the mean of two values that comply with the repeatability requirement) should not exceed0.07% (m/m). 12 Test report The test report shall be in accordance with BS1741-1.4 blankBS1741-7.1:1989 BSI 08-1999 Public
43、ations referred to BS 696, Specification for Gerber method for the determination of fat in milk and milk products. BS 1741, Methods for chemical analysis of liquid milk and cream. BS 1741-1, General introduction, including preparation of samples. BS 1741-3, Determination of fat content of liquid mil
44、k. BS 1741-5, Determination of the nitrogen content of liquid milk. BS 1741-5.1, Reference method. BS 1741-5.2, Routine method 1) . BS 1741-7, Determination of lactose content. BS 1741-7.2, Routine method 2) . BS 1792, Specification for one-mark volumetric flasks. BS 3978, Specification for water fo
45、r laboratory use. 1) In preparation. 2) Referred to in the foreword only.BS 1741-7.1: 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 standards in Europe and at th
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