1、BRITISH STANDARD BS 4938-1: 1982 Dirt content of milk Part1: Method for the determination of dirt content (reference method) UDC 637.12.068.07BS4938-1:1982 This British Standard, having been prepared under the directionof the Dairying Standards Committee, was published under the authorityofthe Board
2、 ofBSIandcomes into effect on 31 December1982 BSI 12-1999 First published as BS4938 March1973 First Part revision December 1982 The following BSI references relate to the work on this standard: Committee reference DAC/3 Draft for comment79/55241 DC ISBN 0 580 13047 9 Cooperating organizations The Da
3、irying Standards Committee, under whose direction this British Standard was prepared, consists of representatives from the following: Commonwealth Bureau of Dairy Science and Technology Creamery Proprietors Association* Dairy Trade Federation* Department of Health and Social Security Department of I
4、ndustry (Laboratory of the Government Chemist)* Institute of Food Science and Technology Intervention Board for Agricultural Produce* Joint Committee of the Milk Marketing Board and the Dairy Trade Federation* Local Authorities Organization Milk Marketing Board* Milk Marketing Board for Northern Ire
5、land* Milking Machine Manufacturers Association Ministry of Agriculture, Fisheries and Food* National Farmers Union National Institute for Research in Dairying* Office of the High Commissioner for NewZealand Process Plant Association Royal Association of British Dairy Farmers* Scottish Dairy Trade F
6、ederation Ltd. Scottish Milk Marketing Board Society of Chemical Industry* Society of Dairy Technology* UnitedKingdom Dairy Association West of Scotland Agricultural College The organizations marked with an asterisk in the above list, together with the following, were directly represented on the Tec
7、hnical Committee entrusted with the preparation of this British Standard: Association of British Manufacturers of Milk Powder Association of Condensed Milk Manufacturers Association of Public Analysts British Food Manufacturing Industries Research Association Department of Agriculture (Government of
8、 Northern Ireland) Hannah Research Institute Ice Cream Alliance Limited Royal Society of Chemistry University of Reading Amendments issued since publication Amd. No. Date of issue CommentsBS4938-1:1982 BSI 12-1999 i Contents Page Cooperating organizations Inside front cover Foreword ii 0 Introductio
9、n 1 1 Scope 1 2 Definitions 1 3 Principle 1 4 Reagents 2 5 Apparatus 2 6 Preparation of test sample 2 7 Procedure 2 8 Expression of results 3 9 Test report 4 Appendix A Information on interpretation of results: a discussion ofrecommendations of the Society for Analytical Chemistry 5 Appendix B Bibli
10、ography 5 Publications referred to Inside back coverBS4938-1:1982 ii BSI 12-1999 Foreword This Part ofBS4938 has been prepared under the direction of the Dairying Standards Committee and together with Part2 supersedesBS4938:1973 which is withdrawn. The1973 edition of this standard described a rapid
11、routine method for determining sediment in milk by filtration. In reviewing that method it was decided that it should be replaced by a reference method and a rapid method, published separately. Furthermore, it was agreed that what these methods determined would be more appropriately described as “di
12、rt” and “visible dirt”, rather than sediment. The reference method determines dirt (moist), by centrifuging followed by chemical treatment of the deposit obtained, as microlitres per litre of milk whereas the rapid method determines visible dirt by filtration and the use of photographic standard fil
13、ter discs, as milligrams per litre of milk. It would be desirable for both methods to measure dirt in the same state and in the same units of concentration, but factors inherent in the methods make it impossible to achieve this. The results obtained by the reference method are expressed on a volume/
14、volume basis whereas the preparation of the milk samples containing “standard” amounts of dirt (for use in preparing the photographic standards used in the rapid method) can only be carried out accurately on a mass/volume basis. (Seealso Hoyle,1977.) The relationship between results obtained by the
15、reference method and the rapid method is discussed inAppendixA ofBS4938-2:1982. 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 c
16、onfer immunity from legal obligations. Summary of pages This document comprises a front cover, an inside front cover, pagesi andii, pages1 to6, 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
17、in the amendment table on the inside front cover.BS4938-1:1982 BSI 12-1999 1 0 Introduction The method currently used in the UK to determine, for official purposes, the amount of dirt (extraneous insoluble matter) in milk is that described in the “Report of the Sub-Committee on Dirt in Milk” publish
18、ed by the Analytical Methods Committee of the Society of Public Analysts and Other Analytical Chemists 1)(Tankard Hanson,1973). In the method of the Society for Analytical Chemistry (SAC), the insoluble particulate matter in a test portion of milk (with added preservative) is allowed to settle by gr
19、avity for5days in a sedimentation vessel, to the outlet at the bottom of which is attached a graduated centrifuge tube. The special vessels and tubes required are specified inBS736. The tube is then centrifuged to collect in the narrow graduated part the insoluble material (sediment), which is then
20、washed successively with water, dilute ammonia solution, water, dilute hydrochloric acid, and water, with centrifuging after each treatment, to remove any non-extraneous matter. The volume of the remaining insoluble matter, i.e.dirt, is recorded and expressed as parts by volume of moist dirt in10000
21、0 parts by volume of the milk; dirt content is now usually expressed as4L/L (parts per million by volume of the milk). The SAC method purports to determine dirt, i.e.“all matters insoluble in and foreign to milk as it leaves the cows udder”, and in this method, “the bulk of micro-organisms will be r
22、emoved from the sediment”. Surprisingly, there is no mention in the description of the method that the dirt finally measured will be free from somatic cells, as it should be according to the SACs definition of dirt since these cells are not “foreign to” milk but are always present to varying degree.
23、 However, Harding, Morris N is the speed (in r/min). 5.9 Suction device, consisting of a glass tube of4mm internal diameter (with the bottom end upturned by10mm) connected to a water pump. 5.10 Pasteur pipettes, of length approximately225mm, fitted with rubber or plastics bulbs (teats). 5.11 Water b
24、ath, capable of operating at temperatures in the range35 to65 C with an accuracy of 1 C. 5.12 Wash bottle, of capacity500mL, containing water at20 C to25 C. 5.13 Centrifuge tube, conical, of capacity15mL. 5.14 Wintrobe tube, complying withBS4316 but with the overall length (external) reduced from111
25、 0.5mm to approximately60mm. NOTE 1The Wintrobe tube is shortened to facilitate its centrifuging, the removal of dirt for examination, and its cleaning. NOTE 2The internal diameter (bore) of a Wintrobe tube is2.55 0.15mm and the capacity of the tube (when shortened as described above) is approximate
26、ly0.3mL. 5.15 Magnifier NOTEA folding pocket type, with25mm lens(es) is suitable. 5.16 Microscope, of low to medium power. 6 Preparation of test sample Take a laboratory sample of sufficient volume to provide a test portion of800mL (see7.1). NOTEGeneral guidance on the sampling of milk is given inBS
27、809. This guidance has been shown to be satisfactory when taking milk samples, for determination of dirt content, from road tankers (Harding estimate the height if the surface of the deposit is uneven or sloping. If two Wintrobe tubes have been used (seenote1 to7.12), record the combined height of t
28、he deposits. 7.14 Identify, if possible, the major constituents of the dirt (see2.1). NOTEUse of a microscope will assist in the identification. For further aid in the identification, seeTankard V 1 is the volume of the moist dirt (inmL) in the Wintrobe tube, i.e.;r 2 h; r is the radius of the bore of the Wintrobe tube (incm), i.e.0.1275cm; h is the height of the moist dirt (incm) in the Wintrobe tube; is taken as3.1416. Round the value obtained for dirt content to the nearest14L/L. NOTEIf necessary, seethe rounding rule inBS1957. D = (V 1 10 6 )/V 0 = (r 2 h 10 6 )/V 0 = 63.84h
