ISO-1854-1999.pdf

A Reference number ISO 1854:1999(E) INTERNATIONAL STANDARD ISO 1854 Third edition 1999-10-01 Whey cheese Determination of fat content Gravimetric method (Reference method) Fromage de sérum Détermination de la teneur en matière grasse Méthode gravimétrique (Méthode de référence) Copyright International Organization for Standardization Provided by IHS under license with ISO Licensee=NASA Technical Standards 1/9972545001 Not for Resale, 04/19/2007 22:23:55 MDTNo reproduction or networking permitted without license from IHS -,-,- ISO 1854:1999(E) © ISO 1999 All rights reserved. Unless otherwise specified, no part of this publication may be reproduced or utilized in any form or by any means, electronic or mechanical, including photocopying and microfilm, without permission in writing from the publisher. International Organization for Standardization Case postale 56 CH-1211 Genève 20 Switzerland Internetisoiso.ch Printed in Switzerland ii Contents 1 Scope1 2 Normative reference1 3 Term and definition .1 4 Principle1 5 Reagents.2 6 Apparatus.2 7 Sampling.3 8 Preparation of test sample3 9 Procedure.4 9.1 Test portion.4 9.2 Blank tests.4 9.3 Preparation of fat-collecting vessel4 9.4 Determination5 10 Calculation and expression of results.7 10.1 Calculation.7 10.2 Expression of results .7 11 Precision.7 11.1 Interlaboratory test.7 11.2 Repeatability7 11.3 Reproducibility8 12 Test report8 Annex A (informative) Notes on procedures9 Annex B (informative) Alternative procedure using fat-extraction tubes with siphon or wash-bottle fittings 11 Bibliography14 Copyright International Organization for Standardization Provided by IHS under license with ISO Licensee=NASA Technical Standards 1/9972545001 Not for Resale, 04/19/2007 22:23:55 MDTNo reproduction or networking permitted without license from IHS -,-,- © ISOISO 1854:1999(E) iii Foreword ISO (the International Organization for Standardization) is a worldwide federation of national standards bodies (ISO member bodies). The work of preparing International Standards is normally carried out through ISO technical committees. Each member body interested in a subject for which a technical committee has been established has the right to be represented on that committee. International organizations, governmental and non-governmental, in liaison with ISO, also take part in the work. ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters of electrotechnical standardization. International Standards are drafted in accordance with the rules given in the ISO/IEC Directives, Part 3. Draft International Standards adopted by the technical committees are circulated to the member bodies for voting. Publication as an International Standard requires approval by at least 75 % of the member bodies casting a vote. International Standard ISO 1854 was prepared by Technical Committee ISO/TC 34, Agricultural food products, Subcommittee SC 5, Milk and milk products, in collaboration with the International Dairy Federation (IDF) and AOAC International, and will also be published by these organizations. This third edition cancels and replaces the second edition (ISO 1854:1987), which has been technically revised. Annexes A and B of this International Standard are for information only. Copyright International Organization for Standardization Provided by IHS under license with ISO Licensee=NASA Technical Standards 1/9972545001 Not for Resale, 04/19/2007 22:23:55 MDTNo reproduction or networking permitted without license from IHS -,-,- Copyright International Organization for Standardization Provided by IHS under license with ISO Licensee=NASA Technical Standards 1/9972545001 Not for Resale, 04/19/2007 22:23:55 MDTNo reproduction or networking permitted without license from IHS -,-,- INTERNATIONAL STANDARD © ISOISO 1854:1999(E) 1 Whey cheese Determination of fat content Gravimetric method (Reference method) WARNING: The use of this International Standard may involve hazardous materials, operations and equipment. This standard does not purport to address all the safety problems associated with its use. It is the responsibility of the user of this standard to establish safety and health practices and determine the applicability of regulatory limitations prior to use. 1 Scope This International Standard specifies the reference method for the determination of fat content of whey cheese. NOTE If the whey cheese does not dissolve completely in the ammonia or if it contains free fatty acids in significant quantities (only in exceptional cases and then noticeable by a distinct smell), the result of the determination will be too low. With such products recourse should be made to a method utilizing the Weibull-Berntrop principle (see ISO 8262-3). 2 Normative reference The following normative document contains provisions which, through reference in this text, constitute provisions of this International Standard. For dated references, subsequent amendments to, or revisions of, this publications do not apply. However, parties to agreement based on this International Standard are encouraged to investigate the possibility of applying the most recent edition of the normative document indicated below. For undated references, the latest edition of the normative document referred to applies. Members of ISO and IEC maintain registers of currently valid International Standards. ISO 3889, Milk and milk products Determination of fat content Mojonnier-type fat extraction flasks. 3 Term and definition For the purposes of this International Standard, the following term and definition apply. 3.1 fat content of whey cheese mass fraction of substances determined by the procedure specified in this International Standard. NOTE The fat content is expressed as a mass fraction, in percent formerly given as % (m/m). 4 Principle An ammoniacal ethanolic solution of a test portion is extracted with diethyl ether and light petroleum. The solvents are removed by distillation or evaporation. The mass of the substances extracted is determined. NOTE This is usually known as the Röse-Gottlieb principle. Copyright International Organization for Standardization Provided by IHS under license with ISO Licensee=NASA Technical Standards 1/9972545001 Not for Resale, 04/19/2007 22:23:55 MDTNo reproduction or networking permitted without license from IHS -,-,- ISO 1854:1999(E) © ISO 2 5 Reagents Use only reagents of recognized analytical grade, unless otherwise specified, and distilled or demineralized water or water of equivalent purity. The reagents shall leave no appreciable residue when the determination is carried out by the method specified (see 9.2.2). 5.1 Ammonia solution, containing a mass fraction of NH3 of approximately 25 % (20 = 910 g/l). NOTE If ammonia solution of this concentration is not available, a more concentrated solution of known concentration may be used (see 9.4.3). 5.2 Ethanol (C2H5OH), or ethanol denatured by methanol, containing a volume fraction of ethanol of at least 94 %. (See A.5.) 5.3 Congo red solution Dissolve 1 g of Congo red in water in a 100 ml one-mark volumetric flask (6.14). Dilute to the mark with water. NOTE The use of this solution, which allows the interface between the solvent and aqueous layers to be seen more clearly, is optional (see 9.4.4). Other aqueous colour solutions may be used provided that they do not affect the result of the determination. 5.4 Diethyl ether (C2H5OC2H5), free from peroxides (see A.3), containing no more than 2 mg/kg of antioxidants, and complying with the requirements for the blank test (see 9.2.2, A.1 and A.4). NOTE The use of diethyl ether could lead to hazardous situations. Due to expected changes in safety regulations studies are ongoing to replace diethyl ether by another reagent provided that it does not affect the end result of the determination. 5.5 Light petroleum, with any boiling range between 30 °C and 60 °C or, as equivalent, pentane (CH3CH23CH3) with a boiling point of 36 °C and complying with the requirements for the blank test (see 9.2.2, A.1 and A.4). NOTE The use of pentane is recommended because of its higher purity and constant quality. 5.6 Mixed solvent Shortly before use, mix equal volumes of diethyl ether (5.4) and light petroleum (5.5). 6 Apparatus WARNING: Since the determination involves the use of volatile flammable solvents, all electrical apparatus employed shall comply with legislation relating to the hazards in using such solvents. Usual laboratory equipment and, in particular, the following. 6.1 Analytical balance, capable of weighing to the nearest 1 mg, with a readability of 0,1 mg. 6.2 Centrifuge, capable of holding the fat-extraction flasks or tubes (6.6) and capable of spinning at a rotational frequency of 500 min1 to 600 min1 to produce a radial acceleration of 80 g to 90 g at the outer end of the flasks or tubes. NOTE The use of the centrifuge is optional but recommended (see 9.4.7). 6.3 Distillation or evaporation apparatus, for distilling the solvents and ethanol from the boiling or conical flasks, or evaporating from beakers and dishes (see 9.4.14) at a temperature not exceeding 100 °C. 6.4 Drying oven, electrically heated, with ventilation port(s) fully open, capable of being maintained at a temperature of 102 °C ± 2 °C throughout its working space. Copyright International Organization for Standardization Provided by IHS under license with ISO Licensee=NASA Technical Standards 1/9972545001 Not for Resale, 04/19/2007 22:23:55 MDTNo reproduction or networking permitted without license from IHS -,-,- © ISOISO 1854:1999(E) 3 The oven shall be fitted with a suitable thermometer. 6.5 Water bath, capable of boiling water. 6.6 Mojonnier-type fat extraction flasks, as specified in ISO 3889. NOTE It is also possible to use fat-extraction tubes, with siphon or wash-bottle fittings, but then the procedure is different. The alternative procedure is given in annex B. The fat-extraction flasks shall be provided with good quality bark corks or stoppers of other material e.g. silicone rubber or polytetrafluoroethylene (PTFE) unaffected by the reagents used. Bark corks shall be extracted with the diethyl ether (5.4), kept in water at a temperature of 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, for holding the fat-extraction flasks (or tubes) (6.6). 6.8 Wash bottle, suitable for use with the mixed solvent (5.6). A plastics wash bottle shall not be used. 6.9 Fat-collecting vessels, such as boiling flasks (flat-bottomed), of capacities 125 ml to 250 ml, conical flasks, of capacity 250 ml, or metal dishes. If metal dishes are used, they shall be of stainless steel, flat-bottomed with a diameter of 80 mm to 100 mm and a height of approximately 50 mm. 6.10 Boiling aids, fat-free, of non-porous porcelain or silicon carbide (optional when metal dishes are used). 6.11 Measuring cylinders, of capacities 5 ml and 25 ml. 6.12 Pipettes, graduated, of capacity 10 ml. 6.13 Tongs, made of metal, for holding flasks, beakers or dishes. 6.14 Appropriate grinding device. 6.15 Volumetric flasks, one-mark, of capacity 100 ml. 7 Sampling Sampling is not part of the method specified in this International Standard. A recommended sampling method is given in ISO 707. It is important that the laboratory receive a sample which is truly representative and has not been damaged or changed during transport or storage. 8 Preparation of test sample Prepare the test sample using an appropriate device (6.14). Quickly mix the ground or grated mass and, if possible, grind it a second time. Again mix thoroughly. Clean the device after preparing each test sample. If the test sample cannot be ground or grated, mix it thoroughly by intensive kneading, for example with a pestle in a mortar. The danger of moisture loss during grinding or grating of the sample should be avoided as far as practically possible. Copyright International Organization for Standardization Provided by IHS under license with ISO Licensee=NASA Technical Standards 1/9972545001 Not for Resale, 04/19/2007 22:23:55 MDTNo reproduction or networking permitted without license from IHS -,-,- ISO 1854:1999(E) © ISO 4 Keep the prepared test sample in an airtight sample container until the time of analysis, which should be carried out on the same day. If delay is unavoidable, take every precaution to ensure proper storage of the test sample. When refrigerated, ensure that any condensation of moisture on the inside surface of the container is thoroughly and uniformly reincorporated into the test sample. 9 Procedure NOTE 1 If it is required to check whether the repeatability limit (11.2) is met, carry out two single determinations in accordance with 9.1 to 9.4 NOTE 2 An alternative procedure using fat-extraction tubes with siphon or wash-bottle fittings (see note in 6.6) is given in annex B. 9.1 Test portion Mix the test sample (clause 8) by gently stirring or rotating and inverting the sample container several times. Immediately weigh to the nearest 1 mg, about 3 g of the prepared test sample, directly or by difference, in a fat- extraction flask (6.6). Transfer the test portion as completely as possible into the lower (small) bulb of the extraction flask. 9.2 Blank tests 9.2.1 Blank test for method Carry out a blank test simultaneously with the determination using the same procedure and same reagents, but replacing the dissolved test portion in 9.4.1 by 10 ml of water (see A.2). If the value obtained in the blank test regularly exceeds 1,0 mg, check the reagents if this has not been recently done (9.2.2). Corrections of more than 2,5 mg should be mentioned in the test report. 9.2.2 Blank test for reagents To test the quality of the reagents, carry out a blank test as specified in 9.2.1. Additionally use an empty fat- collecting vessel, prepared as specified in 9.3, for mass control purposes. The reagents shall leave no residue greater than 1,0 mg (see A.1). If the residue of the complete reagent blank test is greater than 1,0 mg, determine the residue of the solvents separately by distilling 100 ml of the diethyl ether and light petroleum, respectively. Use an empty fat-collecting vessel, prepared for control purposes as described above, to obtain the real mass of residue which shall not exceed 1,0 mg. Very occasionally, the solvents may contain volatile matter which is strongly retained in fat. If there are indications of the presence of such substances, carry out blank tests on all the reagents and for each solvent using a fat- collecting vessel with about 1 g of