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1、BRITISH STANDARD BS 770-3:1989 ISO 1735:1987 Methods for Chemical analysis of cheese Part 3: Determination of fat content (reference method) NOTEThis Part should be read in conjunction with Part 1 “General introduction”, published separately. UDC 637.3.074:543.85:001.4:620.1 Licensed Copy: London So
2、uth Bank University, London South Bank University, Fri Dec 08 13:50:26 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS 770-3:1989 This British Standard, having been prepared under the direction of the Dairying Standards Committee, was published under the authority of the Board of BSI and comes into ef
3、fect on 28 April 1989 BSI 12-1999 First published February 1976 First revision April 1989 The following BSI references relate to the work on this standard: Committee reference DAC/3 Draft for comment 86/53330 DC ISBN 0 580 17098 5 Committees responsible for this British Standard The preparation of t
4、his 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 Public Analysts Assoc
5、iation 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 Federation Milk Market
6、ing 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 issueComments Licensed Co
7、py: London South Bank University, London South Bank University, Fri Dec 08 13:50:26 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS 770-3:1989 BSI 12-1999i Contents Page Committees responsibleInside front cover National forewordii 0Introduction1 1Scope and field of application1 2References1 3Definitio
8、n1 4Principle1 5Reagents1 6Apparatus2 7Sampling2 8Procedure3 9Expression of results5 10Notes on procedure6 11Test report7 Annex Alternative procedure using fat-extraction tubes with siphon or wash-bottle fittings8 Figure 1 Before decantation4 Figure 2 After decantation4 Figure 3 Examples of extracti
9、on tubes9 Publications referred toInside back cover Licensed Copy: London South Bank University, London South Bank University, Fri Dec 08 13:50:26 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS 770-3:1989 ii BSI 12-1999 National foreword This Part of BS 770 has been prepared under the direction of th
10、e Dairying Standards Committee. It is identical with ISO 1735:1987 “Cheese and processed cheese products Determination of fat content Gravimetric method (Reference method)”, published by the International Organization for Standardization (ISO). The method described in the International Standard was
11、developed jointly with the International Dairy Federation (IDF) and the Association of Official Analytical Chemists (AOAC). This edition replaces BS 770-3:1976, which is withdrawn. Terminology and conventions. The text of the International Standard has been approved as suitable for publication as a
12、British Standard without deviation. Some terminology and certain conventions are not 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 bas
13、eline as the decimal marker. Wherever the words “International Standard”, appear, referring to this standard, they should be read as “Part of BS 770”. The symbol “l” has been used to denote litre (and in its submultiples). In British Standards it is current practice to use the symbol “L”. Additional
14、 information. With reference to clause 0, it is intended to implement ISO 8262-3 as an identical British Standard. With reference to 8.1, FAO/WHO standards may be obtained from Her Majestys Stationery Office, PO Box 276, London SW8 5DT. Although not specified in the standard it is strongly recommend
15、ed that duplicate determinations are undertaken. Provided that the duplicate values, calculated as described in 9.1, comply with the repeatability requirement 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 t
16、he 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 different analysts in two different laborat
17、ories, should not exceed the value stated in 9.2.2. Cross-references International StandardCorresponding British Standard ISO 707:1985BS 809:1985 Methods for sampling of milk and milk products (Identical) ISO 3889:1977BS 5522:1977 Specification for milk and milk products Determination of fat content
18、 Mojonnier-type fat extraction flasks (Identical) ISO 5534:1985BS 770 Methods for chemical analysis of cheese Part 10:1986 Determination of total solids content (reference method) (Identical) ISO 5725:1986BS 5497 Precision of test methods Part 1:1987 Guide for the determination of repeatability and
19、reproducibility for a standard test method by inter-laboratory tests (Identical) Licensed Copy: London South Bank University, London South Bank University, Fri Dec 08 13:50:26 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS 770-3:1989 BSI 12-1999iii A British Standard does not purport to include all t
20、he 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 This document comprises a front cover, an inside front cover, pages i to iv,
21、 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. Licensed Copy: London South Bank University, London South Bank University, Fri
22、 Dec 08 13:50:26 GMT+00:00 2006, Uncontrolled Copy, (c) BSI iv blank Licensed Copy: London South Bank University, London South Bank University, Fri Dec 08 13:50:26 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS 770-3:1989 BSI 12-19991 0 Introduction This second edition of ISO 1735 has been prepared w
23、ithin 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 methods are based on either the Rse-Gottlieb (RG), or the Weibull-Berntrop (WB
24、) or the Schmid-Bondzynski-Ratzlaff (SBR) principle. A method based on the SBR principle, involving digestion with hydrochloric acid, has been chosen because a) many types of cheese and cheese products do not readily dissolve in ammonia and it is therefore not practical to examine them according to
25、a method based on the RG principle as used for milk and most milk products; b) ripened cheeses contain, owing to fat splitting, free fatty acids which are not extracted from an ammoniacal solution; c) all cheeses and cheese products, owing to their low lactose contents (mostly less than 5 % (m/m) of
26、 the dry matter), can be examined according to the SBR principle with good precision. Generally speaking, the method is not suitable as a reference method for fresh cheese types, such as cottage cheese and quarg, which have higher lactose contents of up to 25 % (m/m) of the non-fat solids. Difficult
27、ies may also be expected with some types of fresh cheese, especially cottage cheese, because of their extreme inhomogeneity and the impracticability of attaining homogeneity of the test sample. In such cases, the WB method in ISO 8262-31), using a larger mass of test portion, is to be preferred. The
28、 same holds for fresh cheeses with added fruit, syrup, “muesli”, etc. 1 Scope and field of application This International Standard specifies the reference method for the determination of the fat content of all types of cheese and processed cheese products having lactose contents below 5 % (m/m) of t
29、he non-fat solids. 2 References ISO 707, Milk and milk products Methods of sampling. ISO 3889, Milk and milk products Determination of fat content Mojonnier-type fat extraction flasks. ISO 5534, Cheese and processed cheese Determination of total solids content (Reference method). 3 Definition For th
30、e purposes of this International Standard, the following definition applies. fat content of cheese and processed cheese products all the substances determined by the method specified in this International Standard it is expressed as a percentage by mass 4 Principle Digestion of a test portion with h
31、ydrochloric acid, addition of ethanol and subsequent extraction of the acid-ethanolic solution 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. (This is usua
32、lly known as the Schmid-Bondzynski-Ratzlaff 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
33、. 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
34、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
35、 do not meet this requirement. 1) ISO 82623, Milk products and milk-based foods Determination of fat content by the Weibull-Berntrop gravimetric method (Reference method) part 3: Special cases Licensed Copy: London South Bank University, London South Bank University, Fri Dec 08 13:50:26 GMT+00:00 20
36、06, Uncontrolled Copy, (c) BSI BS 770-3:1989 2 BSI 12-1999 5.1 Hydrochloric acid solution, 20 1,125 g/ml. Dilute 675 ml of concentrated hydrochloric acid (20= 1,18 g/ml) to 1 000 ml with water. 5.2 Ethanol, or ethanol denaturated by methanol, at least 94 % (V/V). (See 10.5.) 5.3 Diethyl ether, free
37、from peroxides (see 10.3) and containing no or not more than 2 mg/kg of antioxidants and complying with the requirements for the blank test (see the introductory paragraphs to clause 5, and also 10.1 and 10.4). 5.4 Light petroleum, having any boiling range between 30 and 60 C. 5.5 Mixed solvent, pre
38、pared shortly before use by mixing equal volumes of the diethyl ether (5.3) and the light petroleum (5.4). 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
39、using such solvents. Usual laboratory equipment, and in particular 6.1 Analytical balance 6.2 Centrifuge, in which the stoppered fat-extraction flasks or tubes (6.6) can be spun at a rotational frequency of 500 to 600 min 1 to produce an acceleration of 80 g to 90 g at the outer end of the flasks or
40、 tubes. NOTEThe use of the centrifuge is optional but recommended (see 8.5.7). 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 8.5.10 and 8.5.13) at a temperature not exceedi
41、ng 100 C. 6.4 Drying oven, electrically heated, with ventilation port(s) fully open, capable of being maintained at a temperature of 102 2 C throughout the working space. The oven shall be fitted with a suitable thermometer; or Vacuum drying oven, capable of being maintained at a temperature of 70 t
42、o 75 C and a pressure less than 66 mbar (50 mmHg). 6.5 Boiling water bath or hotplate (see 8.5.2) 6.6 Mojonnier-type fat-extraction flasks, as specified in ISO 3889 (but see the note to 8.5.2). NOTEIt is also possible to use fat-extraction tubes (or flasks) with siphon or wash-bottle fittings, but t
43、he 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 (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 b
44、y the reagents used. Bark corks shall be washed with the diethyl ether (5.3), kept in water at 60 C or more (but not boiling) 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.
45、8 Wash bottle, suitable for use with the mixed solvent (5.5). A plastic wash bottle shall not be used. 6.9 Fat-collecting 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 preferabl
46、y 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
47、 cylinders, of capacities 5 and 25 ml. 6.12 Pipettes, graduated, of capacity 10 ml. 6.13 Tongs, made of metal, suitable for holding flasks, beakers or dishes. 6.14 Sheets of cellulose film, unlacquered, soluble in hydrochloric acid, 0,03 to 0,05 mm thick and of dimensions approximately 50 mm 75 mm.
48、The sheets shall be inert under the test conditions. 6.15 Appropriate grinding or grating device, easy to clean, for preparing the sample. 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. 2) P
49、olytetrafluoroethylene. Licensed Copy: London South Bank University, London South Bank University, Fri Dec 08 13:50:26 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS 770-3:1989 BSI 12-19993 8 Procedure NOTEThe 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 sample3) Before the analysis, remove the rind or smear or mouldy surface layer of the cheese in such a way as to obtain a sample representative of the cheese as it is