1、BRITISH STANDARD BS ISO 15323:2002 Dried milk protein products Determination of nitrogen solubility index ICS 67.100.10 BS ISO 15323:2002 This British Standard, having been prepared under the direction of the Consumer Products and Services Sector Policy and Strategy Committee, was published under th
2、e authority of the Standards Policy and Strategy Committee on 8 October 2002 BSI 8 October 2002 ISBN 0 580 40509 5 National foreword This British Standard reproduces verbatim ISO 15323:2002 and implements it as the UK national standard. The UK participation in its preparation was entrusted to Techni
3、cal Committee AW/5, Milk and milk products, which has the responsibility to: A list of organizations represented on this committee can be obtained on request to its secretary. Cross-references The British Standards which implement international publications referred to in this document may be found
4、in the BSI Catalogue under the section entitled “International Standards Correspondence Index”, or by using the “Search” facility of the BSI Electronic Catalogue or of British Standards Online. This publication does not purport to include all the necessary provisions of a contract. Users are respons
5、ible for its correct application. Compliance with a British Standard does not of itself confer immunity from legal obligations. aid enquirers to understand the text; present to the responsible international/European committee any enquiries on the interpretation, or proposals for change, and keep the
6、 UK interests informed; monitor related international and European developments and promulgate them in the UK. Summary of pages This document comprises a front cover, an inside front cover, the ISO title page, pages ii to iv, pages 1 to 6, an inside back cover and a back cover. The BSI copyright dat
7、e displayed in this document indicates when the document was last issued. Amendments issued since publication Amd. No. Date Comments Reference numbers ISO 15323:2002(E) IDF 173:2002(E)INTERNATIONAL STANDARD ISO 15323 IDF 173 First edition 2002-09-01 Dried milk protein products Determination of nitro
8、gen solubility index Poudres de protines lactiques Dtermination de lindice de solubilit de lazote BSISO15323:2002BSISO15323:2002iiIS:32351 O2002(E) ID:371 F2002(E) I SO dna ID 2002 F All irhgts seredevr iiiForeword ISO (the International Organization for Standardization) is a worldwide federation of
9、 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. Int
10、ernational 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 t
11、he rules given in the ISO/IEC Directives, Part 3. The main task of technical committees is to prepare International Standards. Draft International Standards adopted by the technical committees are circulated to the member bodies for voting. Publication as an International Standard requires approval
12、by at least 75 % of the member bodies casting a vote. Attention is drawn to the possibility that some of the elements of this International Standard may be the subject of patent rights. ISO shall not be held responsible for identifying any or all such patent rights. ISO 15323 IDF 173 was prepared by
13、 Technical Committee ISO/TC 34, Food products, Subcommittee SC 5, Milk and milk products, and the International Dairy Federation (IDF), in collaboration with AOAC International. It is being published jointly by ISO and IDF and separately by AOAC International. Annex A of this International Standard
14、is for information only. BSISO15323:2002iiiIS:32351 O2002(E) ID:371 F2002(E) vi I SO dna ID 2002 F All irhgts seredevrForeword IDF (the International Dairy Federation) is a worldwide federation of the dairy sector with a National Committee in every member country. Every National Committee has the ri
15、ght to be represented on the IDF Standing Committees carrying out the technical work. IDF collaborates with ISO and AOAC International in the development of standard methods of analysis and sampling for milk and milk products. Draft International Standards adopted by the Action Teams and Standing Co
16、mmittees are circulated to the National Committees for voting. Publication as an International Standard requires approval by at least 50 % of National Committees casting a vote. ISO 15323 IDF 173 was prepared by Technical Committee ISO/TC 34, Food products, Subcommittee SC 5, Milk and milk products,
17、 and the International Dairy Federation (IDF), in collaboration with AOAC International. It is being published jointly by ISO and IDF and separately by AOAC International. All work was carried out by the Joint ISO/IDF/AOAC Action Team, Physical properties of dried milk products, under the aegis of i
18、ts project leader, Dr P. Paquin (CA). BSISO15323:2002ivINTENRATIONAL TSANDADR IS:32351 O2002(E) ID:371 F2002(E)I SO dna ID 2002 F All irhgts seredevr 1Dried milk protein products Determination of nitrogen solubility index 1 Scope This International Standard specifies a method for the determination o
19、f the nitrogen solubility index (NSI) of dried milk protein products. This determination is a means of assessing the solubility of nitrogen-containing compounds. 2 Normative references The following normative documents contain provisions which, through reference in this text, constitute provisions o
20、f this International Standard. For dated references, subsequent amendments to, or revisions of, any of these publications do not apply. However, parties to agreements based on this International Standard are encouraged to investigate the possibility of applying the most recent editions of the normat
21、ive documents 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 8968-1 IDF 20-1, Milk Determination of nitrogen content Part 1: Kjeldahl method ISO 8968-
22、2 IDF 20-2, Milk Determination of nitrogen content Part 2: Block-digestion method (Macro method) 3 Term and definition For the purposes of this International Standard, the following term and definition applies. 3.1 nitrogen solubility index ratio of the nitrogen content of the supernatant liquid aft
23、er centrifuging an aqueous dispersion of the test sample to the nitrogen content of the aqueous dispersion before centrifuging, determined by the method specified in this International Standard NOTE The nitrogen solubility index (NSI) is expressed as a percent. 4 Principle A test portion of a dried
24、milk protein product is dispersed in water at a fixed pH value and the nitrogen content of the dispersion is determined. Part of the dispersion is centrifuged and the nitrogen content of the filtered supernatant liquid is determined. The ratio between the two nitrogen contents obtained is calculated
25、. 5 Reagents Use only reagents of recognized analytical grade, unless otherwise specified, and glass-distilled water or water of at least equivalent purity. 5.1 Sodium hydroxide, c(NaOH) = 0,1 mol/l approximately. 5.2 Hydrochloric acid, c(HCl) = 0,1 mol/l approximately. 5.3 Reagents for the determin
26、ation of nitrogen, according to ISO 8968-1 IDF 20-1 or ISO 8968-2 IDF 20-2. BSISO15323:20021IS:32351 O2002(E) ID:371 F2002(E) 2 I SO dna ID 2002 F All irhgts seredevr6 Apparatus Usual laboratory equipment and, in particular, the following. 6.1 Analytical balance, capable of weighing to the nearest 0
27、,001 g. 6.2 Beaker, of capacity 250 ml. 6.3 One-mark volumetric flask, of capacity 100 ml. 6.4 Measuring cylinder, of capacity 100 ml. 6.5 Small glass funnels. 6.6 Wash bottle. 6.7 Magnetic stirrer. 6.8 Fixed-angle centrifuge, temperature controlled to maintain a temperature of 22 C 2 C and capable
28、of producing a radial acceleration of 3 000 g at the bottom of the centrifuge tubes. 6.9 Centrifuge tubes, of capacity 50 ml. 6.10 pH-meter, capable of reading to 0,05 pH units. 6.11 Filter paper, medium grade (Whatman No. 1 1)or equivalent is suitable). 7 Sampling It is important that the laborator
29、y receive a sample which is truly representative and has not been damaged or changed during transport or storage. Sampling is not part of the method specified in this International Standard. A recommended sampling method is given in ISO 707 (IDF 50). Store the test sample in such a way that deterior
30、ation and change in its composition are prevented. 8 Preparation of test sample Thoroughly mix the test sample by repeatedly rotating and inverting the test sample container. Keep the test sample in the container to prevent water uptake. If necessary, transfer the sample to a tightly closed containe
31、r of sufficient size to do this effectively. 9 Procedure 9.1 Test portion Weigh, to the nearest 0,001 g, an amount of the prepared test sample (clause 8) which is equivalent to about 1 g of protein (0,16 g of nitrogen) into the beaker (6.2). 1) Whatman No. 1 is an example of a suitable product avail
32、able commercially. This information is given for the convenience of users of this International Standard and does not constitute an endorsement by ISO or IDF of this product. BSISO15323:20022IS:32351 O2002(E) ID:371 F2002(E) I SO dna ID 2002 F All irhgts seredevr 39.2 Determination 9.2.1 Gradually a
33、dd water at a temperature of 22 C 2 C to the test portion to a total volume of about 75 ml. Stir the mixture, while adding the water, and break up any lumps. Adjust the pH (6.10) of the dispersion to pH 7,00 0,55 with sodium hydroxide (5.2) or hydrochloric acid (5.3), if necessary. Rinse the pH elec
34、trode with some water. Stir the dispersion with a magnetic stirrer (6.7) at a temperature of 22 C 2 C for 2 h. Readjust the pH to 7,0 after 1 h of stirring, if necessary. 9.2.2 Transfer the dispersion to the 100 ml volumetric flask (6.3). Wash out the contents of the beaker carefully into the volume
35、tric flask. Make up to the mark with water and mix thoroughly. 9.2.3 Take a suitable size aliquot portion of the dispersion (9.2.2). Immediately determine its nitrogen content by using the Kjeldahl method according to ISO 8968-1 IDF 20-1 or ISO 8968-2 IDF 20-2. Low-solubility products (e.g. dried la
36、ctalbumin) tend to produce poor repeatability values. In such cases, the nitrogen content should be determined in the powder sample from those products as such. The obtained nitrogen content should be used in the calculation instead. The moisture content of the test sample can influence the result.
37、9.2.4 Allow the remaining dispersion to stand for 2 min. Decant, using the measuring cylinder (6.4), 35 ml of the dispersion into a centrifuge tube (6.9). Centrifuge (6.8) at the required rotational frequency to produce a radial acceleration of 3 000 g at 22 C for 10 min. Decant the supernatant liqu
38、id through the filter paper (6.11). Take care not to transfer any sediment to the filter. 9.2.5 Take a suitable aliquot of the filtered supernatant liquid (9.2.4). Determine the nitrogen content of the supernatant liquid in it by using the Kjeldahl method according to ISO 8968-1 IDF 20-1 or ISO 8968
39、-2 IDF 20-2. 10 Calculation and expression of results 10.1 Calculation Calculate the nitrogen solubility index, NSI, using the following equation. s d NSI 100 w = w % where NSI is the nitrogen solubility index of the sample, expressed as a percent; w Sis the nitrogen content of the supernatant liqui
40、d obtained in 9.2.5, expressed as grams per 100 ml; w dis the nitrogen content of the dispersion obtained in 9.2.3, expressed as grams per 100 ml. 10.2 Expression of results Express the results to one decimal place. 11 Precision 11.1 Interlaboratory test Details of an interlaboratory test on the pre
41、cision of the method are summarized in annex A. The values derived from this interlaboratory test may not be applicable to concentration ranges and matrices other than those given. NOTE IDF 135 provides specific guidance for interlaboratory tests on methods of analysis and milk products. It is based
42、 on ISO 5725. BSISO15323:20023IS:32351 O2002(E) ID:371 F2002(E) 4 I SO dna ID 2002 F All irhgts seredevr11.2 Repeatability The absolute difference between two independent single test results, obtained using the same method on identical test material in the same laboratory by the same operator using
43、the same equipment within a short interval of time, will in not more than 5 % of cases be greater than the repeatability limit, r, for each type of protein powder as given in Table A.1. 11.3 Reproducibility The absolute difference between two single test results, obtained using the same method on id
44、entical test material in different laboratories with different operators using different equipment, will in not more than 5 % of cases be greater than the reproducibility limit, R, for each type of protein powder as given in Table A.1. 12 Test report The test report shall specify: a) all information
45、 necessary for the complete identification of the sample; b) the sampling method used, if known; c) the test method used, with reference to this International Standard; d) all operational details not specified in this International Standard, or regarded as optional, together with details of any inci
46、dents which may have influenced the test result(s); e) the test result(s) obtained or, if the repeatability has been checked, the final result obtained. BSISO15323:20024IS:32351 O2002(E) ID:371 F2002(E) I SO dna ID 2002 F All irhgts seredevr 5Annex A (informative) Results of an interlaboratory trial
47、 An international collaborative test was carried out on three types of protein powder as given in Table A.1. The test was organized by joint ISO/IDF/AOAC action team (JAT), Measurement of functional properties of dried milk products. The results obtained were subjected to statistical analysis in acc
48、ordance with ISO 5725 2)to give the precision data shown in Table A.1 and have been published (see reference 6). Table A.1 Precision data for different types of protein powder Repeatability Reproducibility Product Number of laboratories Mean NSI value r s rRSD R s RRSD Whey protein concentrate 10 92
49、,16 % 3,00 1,06 1,15 8,61 3,04 3,30 Co-precipitate 11 85,31 % 1,87 0,66 0,77 2,58 0,91 1,07 Caseinate 13 100,37 % 1,87 0,66 0,66 2,71 0,96 0,96 2) The precision data were obtained using ISO 5725:1986 (now withdrawn). BSISO15323:20025IS:32351 O2002(E) ID:371 F2002(E) 6 I SO dna ID 2002 F All irhgts seredevrBibliography 1 ISO 707, Milk and milk products Guidance on sampling 2 ISO 5725:1986, Precision of test methods Determina
