1、raising standards worldwideNO COPYING WITHOUT BSI PERMISSION EXCEPT AS PERMITTED BY COPYRIGHT LAWBSI Standards PublicationBS ISO 27871:2011Cheese and processed cheese Determination of thenitrogenous fractionsBS ISO 27871:2011 BRITISH STANDARDNational forewordThis British Standard is the UK implement
2、ation of ISO 27871:2011.The UK participation in its preparation was entrusted to TechnicalCommittee AW/5, Chemical analysis of milk and milk products.A list of organizations represented on this committee can beobtained on request to its secretary.This publication does not purport to include all the
3、necessaryprovisions of a contract. Users are responsible for its correctapplication. BSI 2011ISBN 978 0 580 69768 5ICS 67.100.30Compliance with a British Standard cannot confer immunity fromlegal obligations.This British Standard was published under the authority of theStandards Policy and Strategy
4、Committee on 30 November 2011.Amendments issued since publicationDate Text affectedBS ISO 27871:2011Reference numbersISO 27871:2011(E)IDF 224:2011(E)ISO and IDF 2011INTERNATIONAL STANDARD ISO27871IDF224First edition2011-10-15Cheese and processed cheese Determination of the nitrogenous fractions From
5、ages et fromages fondus Dtermination des fractions azotes BS ISO 27871:2011ISO 27871:2011(E) IDF 224:2011(E) COPYRIGHT PROTECTED DOCUMENT ISO and IDF 2011 All rights reserved. Unless otherwise specified, no part of this publication may be reproduced or utilized in any form or by any means, electroni
6、c or mechanical, including photocopying and microfilm, without permission in writing from either ISO or IDF at the respective address below. ISO copyright office International Dairy Federation Case postale 56 CH-1211 Geneva 20 Silver Building Boulevard Auguste Reyers 70/B B-1030 Brussels Tel. + 41 2
7、2 749 01 11 Tel. + 32 2 733 98 88 Fax + 41 22 749 09 47 Fax + 32 2 733 04 13 E-mail copyrightiso.org E-mail infofil-idf.org Web www.iso.org Web www.fil-idf.org Published in Switzerland ii ISO and IDF 2011 All rights reservedBS ISO 27871:2011ISO 27871:2011(E) IDF 224:2011(E) ISO and IDF 2011 All righ
8、ts reserved iiiForeword 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 subjec
9、t 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)
10、 on all matters of electrotechnical standardization. International Standards are drafted in accordance with the rules given in the ISO/IEC Directives, Part 2. The main task of technical committees is to prepare International Standards. Draft International Standards adopted by the technical committee
11、s 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. Attention is drawn to the possibility that some of the elements of this document may be the subject of patent rights. ISO shall not be he
12、ld responsible for identifying any or all such patent rights. ISO 27871IDF 224 was prepared by Technical Committee ISO/TC 34, Food products, Subcommittee SC 5, Milk and milk products, and the International Dairy Federation (IDF). It is being published jointly by ISO and IDF. BS ISO 27871:2011ISO 278
13、71:2011(E) IDF 224:2011(E) iv ISO and IDF 2011 All rights reservedForeword IDF (the International Dairy Federation) is a non-profit organization representing the dairy sector worldwide. IDF membership comprises National Committees in every member country as well as regional dairy associations having
14、 signed a formal agreement on cooperation with IDF. All members of IDF have the right to be represented on the IDF Standing Committees carrying out the technical work. IDF collaborates with ISO in the development of standard methods of analysis and sampling for milk and milk products. The main task
15、of Standing Committees is to prepare International Standards. Draft International Standards adopted by the Standing Committees are circulated to the National Committees for endorsement prior to publication as an International Standard. Publication as an International Standard requires approval by at
16、 least 50 % of IDF National Committees casting a vote. Attention is drawn to the possibility that some of the elements of this document may be the subject of patent rights. IDF shall not be held responsible for identifying any or all such patent rights. ISO 27871IDF 224 was prepared by the Internati
17、onal Dairy Federation (IDF) and Technical Committee ISO/TC 34, Food products, Subcommittee SC 5, Milk and milk products. It is being published jointly by IDF and ISO. All work was carried out by the ISO-IDF Project Group on Nitrogen fractions of the Standing Committee on Analytical Methods for Compo
18、sition under the aegis of its project leader, Mr. P. Trossat (FR). BS ISO 27871:2011INTERNATIONAL STANDARD ISO 27871:2011(E)IDF 224:2011(E) ISO and IDF 2011 All rights reserved 1Cheese and processed cheese Determination of the nitrogenous fractions 1 Scope This International Standard specifies a met
19、hod for determining the nitrogenous fractions in cheeses and processed cheese from cow milk. 2 Normative references The following referenced documents are indispensable for the application of this document. For dated references, only the edition cited applies. For undated references, the latest edit
20、ion of the referenced document (including any amendments) applies. ISO 8968-1IDF 20-1, Milk Determination of nitrogen content Part 1: Kjeldahl method ISO 8968-2IDF 20-2, Milk Determination of nitrogen content Part 2: Block-digestion method (Macro method) 3 Abbreviated terms TN total nitrogen mass fr
21、action g(N)/100 g SN soluble nitrogen mass fraction g(N)/100 g TCA-SN soluble nitrogen content in trichloroacetic acid g(N)/100 g PTA-SN soluble nitrogen content in phosphotungstic acid g(N)/100 g 4 Principle The fractions are obtained after separation by precipitation of the insolubles in a medium
22、having a pH of 4,4 (SN) or in 12 % trichloroacetic acid (TCA-SN) or in 5 % phosphotungstic acid (PTA-SN). The nitrogen content in each fraction is determined in the filtrates thus obtained in accordance with the procedures specified in ISO 8968-1IDF 20-1 or ISO 8968-2IDF 20-2. BS ISO 27871:2011ISO 2
23、7871:2011(E) IDF 224:2011(E) 2 ISO and IDF 2011 All rights reserved5 Reagents Use only reagents of recognized analytical grade, unless otherwise specified. 5.1 Water, ISO 36964, grade 3 or equivalent purity. 5.2 Trisodium citrate dihydrate solution, c(C6H5Na3O72H2O) = 0,5 mol/l. Weigh 147,05 g of tr
24、isodium citrate dihydrate in a 1 000 ml one-mark volumetric flask (6.8). Shake to dissolve. Make up to the mark with water and mix again. 5.3 Hydrochloric acid solution, c(HCl) = 1 mol/l. 5.4 Trichloroacetic (C2HCl3O2) acid solution (TCA), with a mass-volume fraction of 24 % of TCA. 5.5 Phosphotungs
25、tic acid (H3PW12O40xH2O)solution (PTA), with a mass-volume fraction of 25 % of PTA. 5.6 Sulfuric acid (H2SO4) solution, with a mass fraction of 25 % of H2SO4(20 1,84 g/ml). Prepare the sulfuric acid solution by very carefully adding and mixing 260 g of 98 % H2SO4into 740 g of water. Use the solution
26、 obtained in the nitrogen determination. 6 Apparatus Usual laboratory equipment and in particular the following. 6.1 Grinding device or grating device, easy to clean, appropriate for preparing the test sample. 6.2 Analytical balance, capable of weighing to 1 mg, with a readability of 0,1 mg. 6.3 Hom
27、ogenizer and mixer e.g. Ultraturrax type T251), equipped with a rotor capable forming a 10 m to 50 m suspension. 6.4 Beakers, capacity 250 ml. 6.5 Measuring cylinders, capacities 50 ml, 100 ml, and 200 ml respectively, ISO 47885, class A. 6.6 Water bath, capable of maintaining a temperature of 45 C
28、5 C. 6.7 Magnetic stirrers, equipped with bar magnets (optional). 6.8 One-mark volumetric flasks, capacities 100 ml and 200 ml, ISO 10423, class A. 6.9 Graduated pipettes, capacities 15 ml, 20 ml and 50 ml, ISO 8352, class A. 6.10 pH meter, accurate to 0,01 unit of pH. 6.11 Glass funnels. 6.12 Filte
29、rs, of porosity 8 m e.g. Whatman 402). 1) Ultraturrax type T25 is an example of a suitable product available commercially. This information is given for the convenience of users of this document and does not constitute an endorsement by ISO or IDF of this product. BS ISO 27871:2011ISO 27871:2011(E)
30、IDF 224:2011(E) ISO and IDF 2011 All rights reserved 37 Sampling A representative sample should be sent to the laboratory. It should not have been damaged or changed during transport or storage. Sampling is not part of the method specified in this International Standard. A recommended sampling metho
31、d is given in ISO 707IDF 501. 8 Procedure 8.1 Preparation of test sample Prior to analysis, remove the rind, the smear or the mouldy surface layer of the cheese in such a way as to obtain a test sample representative of the cheese as it is usually consumed. Grind or grate the test sample by using an
32、 appropriate grinding or grating device (6.1). Mix the ground mass quickly. If necessary, e.g. for semi-hard and hard cheese, grind the mixture a second time and mix thoroughly. Preferably, cut the hard and semi-hard cheese into cubes of side 15 mm. Grind or grate the test sample as previously descr
33、ibed. Clean the device after preparing each sample. If the test sample cannot be ground or grated, mix it thoroughly by intensive kneading, e.g. with a pestle in a mortar. Avoid moisture loss. Store the prepared test sample in an airtight container until commencing the analysis. Preferably, however,
34、 analyse the samples as soon as possible after grinding. If delay is unavoidable, take all precautions to ensure proper preservation of the test sample. If refrigerated, bring the test sample to room temperature. Thoroughly mix the sample (to obviate a well-documented transfer of moisture within the
35、 cheese that occurs during cooling and warming). Ensure that any condensation of moisture on the inside surface of the container is thoroughly and uniformly re-incorporated into the test sample. Do not examine ground cheese showing unwanted mould growth or signs of deterioration. 8.2 Determination o
36、f the different fractions 8.2.1 Total nitrogen (TN) Take a test portion of crushed cheese (8.1), depending on the assumed nitrogen content of the cheese and in order to obtain 0,025 g of nitrogen per digestion tube. Determine the total nitrogen content in accordance with the procedure specified in I
37、SO 8968-1IDF 20-1 or ISO 8968-2IDF 20-2. 8.2.2 Preparation of the citrate solution of cheese Weigh, to the nearest 1 mg, approximately 20 g of crushed cheese (8.1) in a 250 ml beaker. Using a measuring cylinder, add 100 ml of citrate solution (5.2) and mix. Place the mixture in the water bath (6.6)
38、maintained at 45 C for 15 min while shaking regularly (manually or by using a magnetic stirrer). If using a bar magnet (6.7), take care to rinse the latter in order to avoid losses. Using the homogenizer and mixer (6.3), crush until obtaining a homogeneous suspension. Rinse the rotor of the crusher
39、and homogenizer with water (5.1) while collecting the rinsings in the beaker. Place the obtained mixture in the water bath (6.6) maintained at 45 C until completely dissolved for 1 h maximum. If small, undissolved pieces still persist, further homogenize the mixture using the homogenizer (6.3). Then
40、 rinse the rotor as previously specified while collecting the rinsings again. 2) Example of a suitable product available commercially. This information is given for the convenience of users of this document and does not constitute an endorsement by ISO or IDF of this product. Alternative products ma
41、y be used if they can be shown to lead to comparable results. BS ISO 27871:2011ISO 27871:2011(E) IDF 224:2011(E) 4 ISO and IDF 2011 All rights reservedQuantitatively transfer the contents of the beaker into a 200 ml one-mark volumetric flask (6.8). Rinse the beaker while collecting the rinsings in t
42、he flask. Mix and let the mixture cool to room temperature. Make up to the mark with water (5.1). The dissolution of processed cheeses can also be conducted in water (5.1). 8.2.3 Preparation of the SN fraction Using a graduated pipette (6.9), introduce 50 ml of the citrate solution of cheese obtaine
43、d in 8.2.2 into a beaker. Add approximately 11 ml of hydrochloric acid solution (5.3). Check the pH and adjust, if necessary, to 4,4 0,05. Quantitatively transfer into a 100 ml one-mark volumetric flask (6.8). Make up to the mark with water (5.1) and mix. Filter (6.12) the solution. Using a graduate
44、d pipette (6.9), transfer 15 ml of filtrate into the digestion tube. Carry out the digestion and determine the SN content in accordance with the procedure specified in ISO 8968-1IDF 20-1 or ISO 8968-2IDF 20-2. 8.2.4 Preparation of the TCA-SN fraction Using a graduated pipette (6.9), introduce 50 ml
45、of the citrate solution of cheese obtained in 8.2.2 into a 100 ml one-mark volumetric flask (6.8). Make up to the mark with 24 % TCA solution (5.4) and mix. Filter (6.12) the solution. Using a graduated pipette (6.9), transfer 20 ml of filtrate into the digestion tube. Carry out the digestion and de
46、termine the TCA-SN content in accordance with the procedure specified in ISO 8968-1IDF 20-1 or ISO 8968-2IDF 20-2. 8.2.5 Preparation of the PTA-SN fraction Using a graduated pipette (6.9), introduce 50 ml of the citrate solution of cheese obtained in 8.2.2 into a 100 ml one-mark volumetric flask (6.
47、8). Add 20 ml of the 25 % PTA solution (5.5) and mix. Make up to the mark with 25 % sulfuric acid solution (5.6). Filter (6.12) the solution. Using a graduated pipette (6.9), transfer 20 ml of filtrate into the digestion tube. Carry out the digestion and determine the PTA-SN content in accordance wi
48、th the procedure specified in ISO 8968-1IDF 20-1 or ISO 8968-2IDF 20-2. NOTE The weighing of the test portions of citrate solution and filtrate (for digestion) is allowed in 8.2.3, 8.2.4 and 8.2.5 under the conditions which the final dilutions are realized as a mass fraction (instead of a volume fra
49、ction). 8.3 Blank test Simultaneously with the determination of the test sample, carry out a blank test using the same procedure as specified in 8.2.3 to 8.2.5, but omitting the test portion (citrate solution without cheese). 9 Calculation and expression of results 9.1 Calculation Calculate the soluble nitrogen of the different nitrogenous fractions of the test sample, wSN,expressed in grams of nitrogen per 100 g of test sample, using the following equation: sbrSNw1, 4 0 0 7 ( )VVcwf BS ISO
