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1、BRITISH STANDARD BS 7142-1: 1989 ISO 8381:1987 Methods for Analysis of milk-based products Part 1: Determination of fat content of milk-based infant foods by the Rse-Gottlieb gravimetric method UDC 637.1.074:543.8 + 637.14 053.2:543.851.062 Licensed Copy: London South Bank University, London South B
2、ank University, Fri Dec 08 13:51:23 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS 7142-1:1989 This British Standard, having been prepared under the direction of the Dairying Standards Policy Committee, was published under the authority of the Board of BSI and comes into effect on 29 September 1989 B
3、SI 11-1999 The following BSI references relate to the work on this standard: Committee reference DAC/3 Draft for comment 86/52584 DC ISBN 0 580 17379 8 Committees responsible for this British Standard The preparation of this British Standard was entrusted by the Dairying Standards Policy Committee (
4、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 Public Analysts Association of Public Analysts of Scotland Creamery Proprietors Association De
5、partment 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 Federation Milk Marketing Board Milk Marketing Board for Northern Ireland Ministry of Agriculture
6、, 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 issueComments Licensed Copy: London South Bank University, London South Bank University, Fri Dec 08
7、13:51:23 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS 7142-1:1989 BSI 11-1999i Contents Page Committees responsibleInside front cover National forewordii 0Introduction1 1Scope and field of application1 2References1 3Definition1 4Principle1 5Reagents1 6Apparatus2 7Sampling2 8Procedure3 9Expression o
8、f results5 10Notes on procedure6 11Test report7 Annex Alternative procedure using fat-extraction tubes with siphon or wash-bottle fitting9 Bibliography8 Figure 1 Before decantation4 Figure 2 After decantation4 Figure 3 Examples of extraction tubes10 Publications referred toInside back cover Licensed
9、 Copy: London South Bank University, London South Bank University, Fri Dec 08 13:51:23 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS 7142-1:1989 ii BSI 11-1999 National foreword This Part of BS 7142 has been prepared under the direction of the Dairying Standards Policy Committee. It is identical wit
10、h ISO 8381:1987 “Milk-based infant foods Determination of fat content Rse-Gottlieb gravimetric method (Reference method)”, prepared by ISO/TC 34, Agricultural food products, of the International Organization for Standardization (ISO). The method described in ISO 8381 was developed jointly with the I
11、nternational Dairy Federation (IDF) and the Association of Official Analytical Chemists (AOAC). Terminology and conventions. The text of the International Standard has been approved as suitable for publication as a British Standard without deviation. Some terminology and certain conventions are not
12、identical with those used in British Standards; attention is drawn especially to the following. The comma has been used as a decimal marker. In British Standards it is current practice to use a full point on the baseline as the decimal marker. The symbol “l” has been used to denote litre (and in its
13、 submultiples). In British Standards, it is current practice to use the symbol “L”. Wherever the words “International Standard” appear, referring to this standard, they should be read as “Part of BS 7142”. Additional information. Although not specified in the ISO text, it is strongly recommended tha
14、t 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 clause 11) should include a reference to the fa
15、ct 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 different analysts in two different laboratories
16、, should not exceed the value stated in 9.2.2. With reference to the Bibliography, copies of International Dairy Federation Report No. 51 may be obtained from the United Kingdom Dairy Association, Giggs Hill Green, Thames Ditton, Surrey. Cross-references International StandardCorresponding British S
17、tandard 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 Determination of fat content of liquid milk (Identical) ISO 3889:1977BS 5522:1977 Specification for milk and milk product
18、s determination of fat content Mojonnier-type fat extraction flasks (Identical) ISO 5725:1986BS 5497 Precision of test methods Part 1:1987 Guide for the determination of repeatability and reproducibility for a standard test method by inter-laboratory tests (Identical) ISO 8262-1:1987BS 7142 Methods
19、for analysis of milk-based products Part 2:1989 Determination of fat content of milk-based infant foods by the Weibull-Berntrop gravimetric method (Identical) Licensed Copy: London South Bank University, London South Bank University, Fri Dec 08 13:51:23 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS
20、7142-1:1989 BSI 11-1999iii 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 pag
21、es This document comprises a front cover, an inside front cover, pages i to iv, pages 1 to 10, 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.
22、 Licensed Copy: London South Bank University, London South Bank University, Fri Dec 08 13:51:23 GMT+00:00 2006, Uncontrolled Copy, (c) BSI iv blank Licensed Copy: London South Bank University, London South Bank University, Fri Dec 08 13:51:23 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS 7142-1:1989
23、 BSI 11-19991 0 Introduction This International Standard has been prepared within the framework of producing a series of reference methods, which are harmonized to the greatest possible extent, for the gravimetric determination of the fat content of milk, milk products and milk-based foods. These me
24、thods are based on either the Rse-Gottlieb (RG), or the Weibull-Berntrop (WB) or the Schmid-Bondzynski-Ratzlaff (SBR) principle. For this International Standard, dealing with milk-based infant foods containing no or not more than 5 % (m/m) (in the dry matter) of starch or dextrin, or vegetable, frui
25、t, meat, etc., a method based on the RG principle has been chosen because a) for products containing a high percentage of lactose and other carbohydrates, such as milk-based infant foods, an RG procedure with dissolution in ammonia is, in principle, preferable to a method employing a hydrochloric ac
26、id digestion (Schmid-Bondzynski-Ratzlaff or Weibull-Berntrop method). This preference is based on the fact that in the acid digestion, ether-soluble substances and a great quantity of charred material that impedes the extraction are formed from the carbohydrates; b) many types of infant foods are mi
27、lk-based and contain no or not more than a few per cent of starch or dextrin; therefore they can be examined by the RG method. In the case of products containing more than 5 % (m/m) (in the dry matter) of starch or dextrin, or vegetable, fruit, meat, etc., recourse has to be made to a method utilizi
28、ng the Weibull-Berntrop principle1). The details of the determination are based on the revised RG method for milk specified in ISO 12112), comprising a number of modifications to improve the precision of the method. An explanation of these modifications is given in the introduction to ISO 1211. 1 Sc
29、ope and field of application This International Standard specifies the reference method for the determination of the fat content of liquid, concentrated and dried milk-based infant foods containing no or not more than 5 % (m/m) (in the dry matter) of starch or dextrin, or vegetable, fruit, meat, etc
30、. (Malto-dextrins without higher molecular mass dextrins, which are often present in infant foods, do not disturb the RG extraction even when present in high percentages.) NOTEIf the product does not dissolve completely in ammonia owing to the presence of more than a few per cent of starch or dextri
31、n, or to the presence of hard lumps, or if it contains free fatty acids in significant quantities, the result of the determination will be too low. In the case of such products, recourse should be made to a method utilizing the Weibull-Berntrop principle1). 2 References ISO 707, Milk and milk produc
32、ts Methods of sampling. ISO 3889, Milk and milk products Determination of fat content Mojonnier-type fat extraction flasks. 3 Definition fat content of milk-based infant foods all the substances determined by the method specified in this International Standard it is expressed as a percentage by mass
33、 4 Principle Extraction of an ammoniacal ethanolic solution of the liquid, diluted or dissolved 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 light petroleum.
34、 (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 equivalent purity
35、. 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 (see 10.1). The reagents shall leave no residue greater than 0,5 mg. If the residue of the complete reagent blank test is gre
36、ater 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 distil the solvents if they
37、 do not meet this requirement. 5.1 Ammonia solution, containing approximately 25 % (m/m) of NH3, 20 . 910 g/l. 1) See ISO 8262-1, Milk products and milk-based foods Determination of fat content by the Weibull-Berntrop gravimetric method (Reference method) Part 1: Infant foods. 2) ISO 1211, Milk Dete
38、rmination of fat content Gravimetric method (Reference method). Licensed Copy: London South Bank University, London South Bank University, Fri Dec 08 13:51:23 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS 7142-1:1989 2 BSI 11-1999 NOTEIf ammonia solution of this concentration is not available, a mor
39、e concentrated solution of known concentration may be used (see 8.5.2). 5.2 Ethanol, or ethanol denatured by methanol, at least 94 % (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
40、 solvent and aqueous layers to be seen more clearly, is optional (see 8.5.4). Other aqueous colour solutions may be used provided 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/kg of antioxidants and
41、complying with the requirements for the blank test (see the introductory paragraphs to clause 5, and also 10.1 and 10.4). 5.5 Light petroleum, having 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
42、 petroleum (5.5). 6 Apparatus WARNING Since the determination involves the use of volatile flammable solvents, electrical apparatus employed may be required to comply with legislation relating to the hazards in using such solvents. Usual laboratory equipment, and in particular 6.1 Analytical balance
43、 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 an acceleration of 80 g to 90 g at the outer end of the flasks or tubes. NOTEThe use of the centrifuge is optional but recommended (see 8.5.7). 6.3 Distillation or e
44、vaporation apparatus, to enable the solvents and ethanol to be distilled from the fat-collecting flasks or to be evaporated from beakers and dishes (see 8.5.10 and 8.5.14) at a temperature not exceeding 100 C. 6.4 Drying oven, electrically heated, with ventilation port(s) fully open, capable of bein
45、g maintained at 102 2 C throughout the working space. The oven shall be fitted with a suitable thermometer. 6.5 Water-baths, capable of being maintained at the following temperatures: 40 to 60 C (see 8.1.1); 30 to 40 C (see 8.1.2); 40 to 50 C (see 8.5.1); 60 to 70 C (see 8.5.3). 6.6 Mojonnier-type f
46、at-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 that specified in the Annex. The long inner limb of the fitting may have a hooked end if desired. The flasks
47、 (or tubes, see the note) shall be provided with good quality bark corks or stoppers of other material (for example silicone rubber or PTFE3) unaffected by the reagents used. Bark corks shall be washed with the diethyl ether (5.4), kept in water at 60 C or more (but not boiling) for at least 15 min,
48、 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 vessels, for example boi
49、ling 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 made of stainless steel, shall be flat-bottomed, preferably with a spout, and shall have a diameter of 80 to 100 mm and a 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