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1、BRITISH STANDARD BS 6248-10: 1986 ISO 5543:1986 Incorporating Amendment No. 1 Caseins and caseinates Part 10: Method for determination of fat (gravimetric reference method) NOTEThis Part should be read in conjunction with Part 1 “General introduction, including preparation of laboratory samples”, pu
2、blished separately. UDC 637.142.2.04:543.21:547.915 Licensed Copy: sheffieldun sheffieldun, na, Wed Dec 06 13:27:02 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS 6248-10:1986 This British Standard, having been prepared under the direction of the Dairying Standards Committee, was published under the
3、authority of the Board of BSI and comes into effect on 31 December 1986 BSI 12-1999 The following BSI references relate to the work on this standard: Committee reference DAC/3 Draft for comment 76/53486 DC ISBN 0 580 15580 3 Committees responsible for this British Standard The preparation of this Br
4、itish 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 Association
5、 of Public Analysts of Scotland Creamery Proprietors Association Dairy Trade Federation 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 Feder
6、ation 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 University of Reading Amendments issued since publication Am
7、d. No.Date of issueComments 5868July 1988Indicated by a sideline in the margin Licensed Copy: sheffieldun sheffieldun, na, Wed Dec 06 13:27:02 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS 6248-10:1986 BSI 12-1999i Contents Page Committees responsibleInside front cover National forewordii 0Introduct
8、ion1 1Scope and field of application1 2References1 3Definition1 4Principle1 5Reagents1 6Apparatus and materials2 7Sampling2 8Procedure2 9Expression of results5 10Notes on procedure5 11Test report6 Annex Alternative procedure using fat-extraction tubes with siphon or wash-bottle fittings (see for exa
9、mple Figure 3)7 Figure 1 Before decantation4 Figure 2 After decantation4 Figure 3 Examples of extraction tubes8 Publications referred toInside back cover Licensed Copy: sheffieldun sheffieldun, na, Wed Dec 06 13:27:02 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS 6248-10:1986 ii BSI 12-1999 National
10、 foreword This Part of BS 6248, which has been prepared under the Dairying Standards Committee, is identical with ISO 5543:1986 “Caseins and caseinates Determination of fat content Gravimetric method (Reference method)”, prepared by ISO/TC 34, Agricultural food products, of the International Organiz
11、ation for Standardization (ISO) in cooperation with the International Dairy Federations (IDF) and the Association of Official Analytical Chemists (AOAC). This Part of BS 6248 supersedes clause 10 of BS 1416:1962 “Methods for sampling and analysis of rennet casein” and clause 11 of BS 1417:1963 “Meth
12、ods for the sampling and analysis of acid casein”, which are deleted by amendment. 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 identical wit
13、h those used in British Standards; attention is drawn especially to the following. The comma has been used throughout as a decimal marker. In British Standards it is current practice to use a full point on the baseline as the decimal marker. Wherever the words “International Standard” appear, referr
14、ing to this standard, they should be read as “British Standard”. The symbol “ml” has been used to denote millilitre. In British Standards it is current practice to use the symbol “mL”. In British Standards it is current practice to use the spelling “sulphur”, etc. instead of “sulfur”, etc. A British
15、 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. Cross-references International StandardCorrespondi
16、ng British Standard ISO 707:1985BS 809:1985 Methods for sampling of milk and milk products (Identical) ISO 3889:1977BS 5522:1977 Milk and milk products Determination of fat content Mojonnier-type fat extraction flasks (Identical) ISO 5550:1978BS 6248 Caseins and caseinates Part 8:1982 Method for det
17、ermination of water content (reference method) (Identical) Summary of pages This document comprises a front cover, an inside front cover, pages i and ii, pages 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.
18、 This will be indicated in the amendment table on the inside front cover. Licensed Copy: sheffieldun sheffieldun, na, Wed Dec 06 13:27:02 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS 6248-10:1986 BSI 12-19991 0 Introduction This International Standard has been prepared within the framework of produ
19、cing a series of methods, which are harmonized to the greatest possible extent, for the gravimetric determination of the fat content of milk, milk products and milk-based food. A method based on the principle of Schmid-Bondzynski-Ratzlaff (SBR), involving digestion with hydrochloric acid, has been c
20、hosen, because: a) many caseins do not readily dissolve in ammonia, either because they contain or consist of hard lumps, or because they are not soluble, or are only poorly soluble, as such (for example rennet casein), and therefore cannot be examined according to the method based on the Rse-Gottli
21、eb (RG) principle as used for milk and most milk products; b) all caseins and caseinates, due to their low lactose content less than 5 % (m/m) of the dry matter, can be examined according to the SBR principle. This has the advantage over the Weibull method in that the method can be carried out using
22、 the same apparatus as that specified for the RG method and, at the same time, is less time consuming; c) methods based on the SBR principle have already found wide application in many countries as official or standardized methods for the examination of all caseins and caseinates. 1 Scope and field
23、of application This International Standard specifies the reference method for the determination of the fat content of all types of caseins and caseinates. 2 References ISO 707, Milk and milk products Methods of sampling. ISO 3889, Milk and milk products Determination of fat content Mojonnier-type fa
24、t extraction flasks. ISO 5550, Caseins and caseinates Determination of water content (Reference method). 3 Definition fat content of caseins and caseinates all the substances determined by the method specified in this International Standard it is expressed as a percentage by mass 4 Principle Digesti
25、on of a test portion with hydrochloric 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 lig
26、ht petroleum. (This is usually 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
27、 at least 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 (see 10.1). The reagents shall leave no residue greater than 0,5 mg. If the residue of the complet
28、e reagent 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
29、solvents, or redistil solvents. 5.1 Hydrochloric acid solution, 20= 1,125 g/ml. (See also note to 8.5.1.) Dilute 675 ml of hydrochloric acid (20= 1,18 g/ml) to 1 000 ml with water. 5.2 Ethanol, or ethanol denatured by methanol, at least 94 % (V/V). (See 10.5.) 5.3 Diethyl ether, free from peroxides
30、(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, prepared shortly b
31、efore use by mixing equal volumes of the diethyl ether (5.3) and the light petroleum (5.4). Licensed Copy: sheffieldun sheffieldun, na, Wed Dec 06 13:27:02 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS 6248-10:1986 2 BSI 12-1999 5.6 Congo-red solution Dissolve 1 g of Congo-red in water and dilute to
32、 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 8.5.4) and only useful with products giving colourless or only slightly coloured digests. Other aqueous colour solutions may be used provided that they d
33、o not affect the result of the determination. 6 Apparatus and materials 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
34、, 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 min1 to produce a gravitational field of 80 g to 90 g at the outer end of the flasks or tubes. NOTEThe use of the centrifuge is
35、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 8.5.12) at a temperature not exceeding 100 C. 6.4 Drying oven, electrically h
36、eated, with ventilation port(s) fully open, capable of being maintained at 102 2 C throughout the working space and fitted with a suitable thermometer; or vacuum drying oven, capable of being maintained at 70 to 75 C, at a pressure less than 66 mbar (50 mmHg). 6.5 Boiling water bath or hotplate (see
37、 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 the procedure is then different and is specified in the Annex. The long inner limb of the
38、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 PTFF1) unaffected by the reagents used. Bark corks shall be washed with the diethyl ether (5.3), kept in water at
39、 60 C or 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 (5.5). A plastic wash bottle shall not be used. 6.9 Fat-c
40、ollecting 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
41、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 ml. 6.13 Tongs, made of metal, suitabl
42、e for holding flasks, beakers or dishes. 6.14 Grinding device, for grinding the laboratory sample if necessary. This device should be such that no undue heat will be developed and no loss of moisture occurs. (A hammer mill shall not be used.) 6.15 Test sieve, of woven wire cloth, diameter 200 mm, no
43、minal size of openings 500 4m, with receiver, complying with the requirements of ISO 565. 6.16 Container with lid, airtight, of capacity such that the test sample can be mixed by shaking. 7 Sampling See ISO 707. The laboratory sample shall be stored in a securely closed air-tight container. 8 Proced
44、ure 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 sample 8.1.1 Thoroughly mix the laboratory sample (clause 7), if necessary after transferring all of it to an airtight contain
45、er of suitable capacity, by repeatedly shaking and inverting the container. 8.1.2 Transfer 50 g of the laboratory sample to the test sieve (6.15). If it does not pass completely through the sieve, use the grinding device to achieve this condition. Immediately transfer all the sieved sample to the co
46、ntainer (6.16) and mix thoroughly in the closed container. During these operations, take precautions to avoid any change in the water content of the product. 1) ploytetrafluoroethylene Licensed Copy: sheffieldun sheffieldun, na, Wed Dec 06 13:27:02 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS 6248-
47、10:1986 BSI 12-19993 8.1.3 After the test sample has been prepared, proceed with the determination (8.5) as soon as possible. If the 50 g portion directly passes, or nearly completely passes, the sieve, use the prepared test sample (see 8.1.1) for the determination. 8.2 Test portion Mix the test sam
48、ple (8.1) by gently stirring, or by rotating and inverting the container. Immediately weigh, to the nearest 1 mg, directly or by difference, into a fat-extraction flask (6.6), or into a 100 ml beaker or flask, 2 to 3 g of the test sample. The test portion shall be delivered as completely as possible
49、 into the lower (small) bulb of the extraction flask. 8.3 Blank test Carry out a blank test simultaneously with the determination, using the same procedure and same reagents, but omitting the test portion as in 8.5.1 (see 10.2). 8.4 Preparation of fat-collecting vessel Dry a vessel (6.9) containing 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.