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1、BRITISH STANDARD BS 1742-3: 1990 ISO 1737:1985 Methods for Chemical analysis of condensed milks Part 3: Determination of fat content Licensed Copy: sheffieldun sheffieldun, na, Fri Nov 24 08:01:36 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS 1742-3:1990 This British Standard, having been prepared u
2、nder the direction of the Dairying Standards Policy Committee, was published under the authority of the Board of BSI and comes into effect on 29 June 1990 BSI 12-1999 The following BSI references relate to the work on this standard: Committee reference DAC/3 Draft for comment 84/53133 DC ISBN 0 580
3、18260 6 Committees responsible for this British Standard The preparation of this British Standard was entrusted by the Dairying Standards Policy Committee (DAC/-) to Technical Committee DAC/3, upon which the following bodies were represented: AFRC Institute of Food Research (Reading Laboratory) Asso
4、ciation of British Preserved Milk Manufacturers Association of 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 Jo
5、int 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 of British Dairy Farmers Royal Society of Chemistry Society of Chemical Industry Society of Dairy Tech
6、nology Amendments issued since publication Amd. No.Date of issueComments Licensed Copy: sheffieldun sheffieldun, na, Fri Nov 24 08:01:36 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS 1742-3:1990 BSI 12-1999i Contents Page Committees responsibleInside front cover National forewordii 0Introduction1 1S
7、cope and field of application1 2References1 3Definition1 4Principle1 5Reagents1 6Apparatus1 7Sampling2 8Procedure2 9Expression of results5 10Notes on procedure5 11Test report6 Annex A Alternative procedure using fat-extraction tubes with siphon or wash-bottle fittings7 Figure 1 Before decantation4 F
8、igure 2 After decantation4 Figure 3 Example of extraction tubes8 Publications referred toInside back cover Licensed Copy: sheffieldun sheffieldun, na, Fri Nov 24 08:01:36 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS 1742-3:1990 ii BSI 12-1999 National foreword NOTEThis Part should be read in conjun
9、ction with Part 1 “General introduction, including preparation of test samples”, which is published separately. This Part of BS 1742, which has been prepared under the direction of the Dairying Standards Policy Committee, is identical with ISO 1737:1985 “Evaporated milk and sweetened condensed milk
10、Determination of fat content Gravimetric method (Reference method)”, published by the International Organization for Standardization (ISO). The method described in the International Standard was developed jointly with the International Dairy Federation (IDF) and the Association of Official Analytica
11、l Chemists (AOAC). This Part supersedes clause 5 of BS 1742:1951, which is deleted by amendment. Additional information. The term “evaporated milk” as used in ISO 1737 should be construed as meaning “unsweetened condensed milk” as defined in Part 1 of this British Standard. Although not specified in
12、 the standard it is strongly recommended that duplicate determinations are undertaken. Provided that the duplicate values, calculated as described in 9.1, comply with the repeatability requirements of 9.2.1, the result should be reported as the mean value, and in such cases, the test report (see cla
13、use 11) should include a reference to the fact that such a result has been reported. When results reported are the mean of two values that comply with the repeatability requirement, the difference between the results reported for fat content, obtained on samples of the same test material by two diff
14、erent analysts in two different laboratories, should not exceed the relevant values stated in 9.2.2. 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
15、 does not of itself confer immunity from legal obligations. Cross-references International StandardCorresponding British Standard ISO 707:1985BS 809:1985 Methods for sampling of milk and milk products (Identical) ISO 1211:1984BS 1741 Methods for chemical analysis of liquid milk and cream Part 3:1987
16、 Determination of fat content of liquid milk (Identical) ISO 3889:1977BS 5522:1977 Specification for milk and milk products determination of fat content Mojonnier-type fat extraction flasks (Identical) Summary of pages This document comprises a front cover, an inside front cover, pages i and ii, pag
17、es 1 to 8, 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. Licensed Copy: sheffieldun sheffieldun, na, Fri Nov 24 08:01:36 GMT+00:00 2006, Unc
18、ontrolled Copy, (c) BSI BS 1742-3:1990 BSI 12-19991 0 Introduction This second edition of ISO 1737 has been prepared within the framework of producing a series of methods, which are harmonized to the greatest possible extent, for the gravimetric determination of the fat content of milk, milk product
19、s and milk-based foods. The revision is based on the revised Rse-Gottlieb method for milk specified in ISO 1211, comprising a number of modifications to improve the precision of the method. A more complete explanation of these modifications to the basic Rse-Gottlieb procedure is given in the introdu
20、ction to ISO 1211.1) 1 Scope and field of application This International Standard specifies the reference method for the determination of the fat content of all types of evaporated milk and sweetened condensed milk (liquid unsweetened and sweetened concentrated milks). 2 References ISO 707, Milk and
21、 milk products Methods of sampling. ISO 3889, Milk and milk products Determination of fat content Mojonnier-type fat extraction flasks. 3 Definition fat content of evaporated milk and sweetened condensed milk all the substances determined by the method specified in this International Standard it is
22、conventionally expressed as a percentage by mass 4 Principle Extraction of an ammoniacal ethanolic solution of a test portion with diethyl ether and light petroleum, removal of the solvents by distillation or evaporation, and determination of the mass of the substances extracted which are soluble in
23、 light petroleum. (This is usually known as the Rse-Gottlieb principle.) 5 Reagents All reagents shall be of recognized analytical grade and shall leave no appreciable residue when the determination is carried out by the method specified. The water used shall be distilled water or water of at least
24、equivalent purity. To test the quality of the reagents, carry out a blank test as specified in 8.3. Use an empty fat-collecting vessel, prepared as specified in 8.4, for mass control purposes. The reagents shall leave no residue greater than 0,5 mg (see 10.1). If the residue of the complete reagent
25、blank test is greater than 0,5 mg, determine the residue of the solvents separately by distilling 100 ml of the diethyl ether and light petroleum respectively. Use an empty control vessel to obtain the real mass of residue, which shall not exceed 0,5 mg. Replace unsatisfactory reagents or solvents,
26、or redistil solvents. 5.1 Ammonia solution, containing approximately 25 % (m/m) of NH3, 20 = 910 g/l. NOTEIf ammonia solution of this concentration is not available, a more concentrated solution of known concentration may be used (see 8.5.2). 5.2 Ethanol, or ethanol denatured by methanol, at least 9
27、4 % (V/V). (See 10.5.) 5.3 Congo-red solution Dissolve 1 g of Congo-red in water and dilute to 100 ml. NOTEThe use of this solution, which allows the interface between the solvent and aqueous layers to be seen more clearly, is optional (see 8.5.3). Other aqueous colour solutions may be used provided
28、 that they do not affect the result of the determination. 5.4 Diethyl ether, free from peroxides (see 10.3), and containing no or not more than 2 mg of antioxidants per kilogram, and complying with the requirements for the blank test (see clause 5, and also 10.1 and 10.4). 5.5 Light petroleum, havin
29、g any boiling range between 30 and 60 C. 5.6 Mixed solvent, prepared shortly before use by mixing equal volumes of the diethyl ether (5.4) and the light petroleum (5.5). 6 Apparatus WARNING Since the determination involves the use of volatile flammable solvents, electrical apparatus employed may be
30、required to comply with legislation relating to the hazards in using such solvents. Usual laboratory equipment, and in particular 1) ISO 1211, Milk Determination of fat content Gravimetric method (Reference method). Licensed Copy: sheffieldun sheffieldun, na, Fri Nov 24 08:01:36 GMT+00:00 2006, Unco
31、ntrolled Copy, (c) BSI BS 1742-3:1990 2 BSI 12-1999 6.1 Analytical balance 6.2 Centrifuge, in which the fat-extraction flasks or tubes (6.6) can be spun at a rotational frequency of 500 to 600 min1 to produce a gravitational field of 80 g to 90 g at the outer end of the flasks or tubes. NOTEThe use
32、of the centrifuge is optional but recommended (see 8.5.6). 6.3 Distillation or evaporation apparatus, to enable the solvents and ethanol to be distilled from the fat-collecting flasks or to be evaporated from beakers and dishes (see 8.5.9 and 8.5.13) at a temperature not exceeding 100 C. 6.4 Drying
33、oven, electrically heated, with ventilation port(s) fully open, capable of being maintained at 102 2 C throughout the working space. The oven shall be fitted with a suitable thermometer. 6.5 Water-baths 6.5.1 Water-bath, capable of being maintained at 30 to 40 C. 6.5.2 Water-bath, capable of being m
34、aintained at 40 to 60 C. 6.6 Mojonnier-type fat-extraction flasks, as specified in ISO 3889. NOTEIt is also possible to use fat-extraction tubes (or flasks) with siphon or wash-bottle fittings, but the procedure is then different and is specified in the Annex. The long inner limb of the fitting may
35、have a hooked end if desired. The flasks (or tubes, see the note) shall be provided with good quality bark corks or stoppers of other material for example silicone rubber or PTFE2). unaffected by the reagents used. Bark corks shall be extracted with the diethyl ether (5.4), kept in water at 60 C or
36、more for at least 15 min, and shall then be allowed to cool in the water so that they are saturated when used. 6.7 Rack, to hold the fat-extraction flasks (or tubes) (see 6.6). 6.8 Wash bottle, suitable for use with the mixed solvent (5.6). A plastic wash bottle shall not be used. 6.9 Fat-collecting
37、 vessels, for example boiling flasks (flat-bottomed) of capacity 125 to 250 ml, conical beakers of capacity 250 ml, or metal dishes. If metal dishes are used, they shall preferably be of stainless steel, shall be flat-bottomed, preferably with a spout, and shall have a diameter of 80 to 100 mm and a
38、 height of approximately 50 mm. 6.10 Boiling aids, fat-free, of non-porous porcelain or silicon carbide, or glass beads (optional in the case of metal dishes). 6.11 Measuring cylinders, of capacities 5 and 25 ml. 6.12 Pipettes, graduated, of capacity 10 ml. 6.13 Tongs, made of metal, suitable for ho
39、lding flasks, beakers or dishes. 7 Sampling See ISO 707. All laboratory samples shall be kept at a temperature of 0 to 4 C from the time of sampling to the time of commencing the procedure. In the case of samples in sealed cans, store the closed cans at a temperature below 20 C. 8 Procedure NOTEThe
40、alternative procedure using fat-extraction tubes with siphon or wash-bottle fittings (see the note to 6.6) is described in the Annex. 8.1 Preparation of the test sample 8.1.1 Evaporated milk Shake and invert the container. Open the container, pour the milk slowly into a second container (provided wi
41、th an airtight lid) and mix by repeated transfer, taking care to incorporate in the sample any fat or other constituent adhering to the wall and ends of the first container. Finally transfer the milk as completely as possible to the second container. If necessary, in the case of samples in sealed ca
42、ns, condition the unopened can in the water-bath (6.5.2) at 40 to 60 C. Remove and shake the can vigorously every 15 min. After 2 h, remove the can and allow to cool to room temperature. Remove the lid entirely and thoroughly mix the contents of the can by stirring with a spoon or spatula. (If fat s
43、eparates, do not test the sample.) 8.1.2 Sweetened condensed milk Open the container and thoroughly mix the milk with a spoon or spatula. Use an up and down rotary movement in such a way that the top layers and the contents of the lower corners of the container are moved and mixed. Take care to inco
44、rporate in the sample any milk adhering to the wall and ends of the container. 2) Polytetrafluoroethylene. Licensed Copy: sheffieldun sheffieldun, na, Fri Nov 24 08:01:36 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS 1742-3:1990 BSI 12-19993 Transfer the milk as completely as possible to a second co
45、ntainer (provided with an airtight lid). Close the container. If necessary, in the case of samples in sealed cans, condition unopened can in the water-bath (6.5.1) at 30 to 40 C. Open the can, scrape out all milk adhering to the interior of the transfer to a dish large enough to permit stirring thor
46、oughly, and mix until the whole mass is homogeneous. In the case of a sample in a collapsible tube, open the tube, and transfer the contents to a jar. Then cut open the tube and scrape out all material adhering to the interior and add to the contents of the jar. 8.2 Test portion Mix the test sample
47、(8.1) by stirring (in the case of sweetened condensed milk) or gently inverting the bottle three or four times (in the case of evaporated milk) and immediately weigh, to the nearest 1 mg, directly or by difference, into a fat extraction flask (6.6), 4 or 5 g of the test sample of evaporated milk or
48、2,0 to 2,5 g of the test sample of sweetened condensed milk The test portions shall be delivered as completely as possible into the lower (small) bulb of the extraction flask (6.6). 8.3 Blank test Carry out a blank test simultaneously with the determination, the same procedure and same reagents, but
49、 replacing the dispersed test portion as in 8.5.1 by 10 ml of water (see 10.2). 8.4 Preparation of fat-collecting vessel Dry a vessel (6.9) with a few boiling aids (6.10) in the oven (6.4) for 1 h (see note 1). Allow the vessel to cool (protected from dust) to the temperature of the weighing room (glass vessel for at least 1 h, metal dish for at least 0,5 h) (see note 2). Using tongs (6.13) (to avoid, in particular, temperature variations), place the vessel on the balance and weigh to the nearest 0,1 mg. NOTE 1Boiling aids are desirab