BS ISO 17997-1-2005 Milk - Determination of casein-nitrogen content - Indirect method (Reference method)《乳 酪蛋白氮含量测定 间接方法(参照法)》.pdf

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1、BRITISH STANDARD BS ISO 17997-1:2004 Milk Determination of casein-nitrogen content Part 1: Indirect method (Reference method) ICS 67.100.10 BS ISO 17997-1:2004 This British Standard was published under the authority of the Standards Policy and Strategy Committee on 14 January 2005 BSI 14 January 200

2、5 ISBN 0 580 45363 4 National foreword This British Standard reproduces verbatim ISO 17997-1:2004 and implements it as the UK national standard. The UK participation in its preparation was entrusted to Technical Committee AW/5, Milk and milk products, which has the responsibility to: A list of organ

3、izations 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 in the BSI Catalogue under the section entitled “International Standards Correspondence Inde

4、x”, 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 responsible for its correct application. Compliance with a British Standard does not of itself conf

5、er 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 UK interests informed; monitor related international and European developments and promulga

6、te them in the UK. Summary of pages This document comprises a front cover, an inside front cover, the ISO title page, pages ii to v, a blank page, pages 1 to 8, an inside back cover and a back cover. The BSI copyright notice displayed in this document indicates when the document was last issued. Ame

7、ndments issued since publication Amd. No. Date Comments Reference numbers ISO 17997-1:2004(E) IDF 29-1:2004(E)INTERNATIONAL STANDARD ISO 17997-1 IDF 29-1 First edition 2004-09-15 Milk Determination of casein-nitrogen content Part 1: Indirect method (Reference method) Lait Dtermination de la teneur e

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11、he unlikely veent that a problem relating to it is f,dnuo lpsaei efnmro tI ehStneC Olar Scerteirata ta teh serddas igleb nevow. ii BSISO179971:2004 iiiForeword ISO (the International Organization for Standardization) is a worldwide federation of national standards bodies (ISO member bodies). The wor

12、k 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-governme

13、ntal, 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 2. The m

14、ain 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 by at least 75 % of the member bodies casting a vote. A

15、ttention is drawn to the possibility that some of the elements of this document may be the subject of patent rights. ISO shall not be held responsible for identifying any or all such patent rights. ISO 17997-1IDF 29-1 was prepared by Technical Committee ISO/TC 34, Food products, Subcommittee SC 5, M

16、ilk 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. ISO 17997IDF 29 consists of the following parts, under the general title Milk Determination of casein- nit

17、rogen content: Part 1: Indirect method (Reference method) Part 2: Direct method BSISO179971:2004iv Foreword 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 right to be represent

18、ed 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 Committees are circul

19、ated to the National Committees for voting. Publication as an International Standard requires approval by at least 50% of IDF National Committees casting a vote. ISO 17797-1IDF 29-1 was prepared by Technical Committee ISO/TC 34, Food products, Subcommittee SC 5, Milk and milk products, and the Inter

20、national 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 on Nitrogen compounds, of the Standing Committee on Main components in milk. Th

21、is edition of ISO 17997-1IDF 29-1, together with ISO 17997-2IDF 29-2, cancels and replaces the first edition of IDF 29:1964, which has been technically revised. ISO 17997IDF 29 consists of the following parts, under the general title Milk Determination of casein- nitrogen content: Part 1: Indirect m

22、ethod (Reference method) Part 2: Direct method BSISO179971:2004 vIntroduction This part of ISO 17997IDF 29 is a classical reference method for the indirect determination of the casein- nitrogen content of milk. No collaborative study data were available for this method when publishing the first edit

23、ion of IDF 29:1964. Recent research has been completed to develop a better defined indirect reference method. A routine method for the direct measurement of the casein-nitrogen content of milk is given in ISO 17997-2IDF 29-2. Both parts of ISO 17997IDF 29 have been collaboratively studied and a refe

24、rence to the obtained precision data is now included in each part. BSISO179971:2004blankNITERNATNOIAL STANDARD IS-79971 O1:(4002E) ID-92 F1:(4002E)1Milk Determination of casein-nitrogen content Part 1: Indirect method (Reference method) WARNING The use of the method and equipment described in this s

25、tandard may involve hazardous materials, operations and equipment. This standard does not purport to address all the safety risks associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of loc

26、al regulatory limitations prior to use. 1 Scope This part of ISO 17997IDF 29 specifies a reference method for the indirect determination of the casein- nitrogen content of bovine milk. The method can be modified for milk from other species or liquid dairy products. NOTE Casein nitrogen will decrease

27、 with milk storage time due to casein breakdown even at 4 C. The casein nitrogen of heat-treated milk will be artificially high because of whey-protein denaturation. 2 Normative references The following referenced documents are indispensable for the application of this document. For dated references

28、, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies. ISO 648:1977, Laboratory glassware One-mark pipettes ISO 1042:1998, Laboratory glassware One-mark volumetric flasks ISO 8968-1IDF 20-1, Milk Determination of ni

29、trogen content Part 1: Kjeldahl method ISO 8968-2IDF 20-2, Milk Determination of nitrogen content Part 2: Block-digestion method (Macro method) 3 Terms and definitions For the purposes of this document, the following terms and definitions apply. 3.1 non-casein-nitrogen content mass fraction of subst

30、ances determined according to the procedures specified in this part of ISO 17997IDF 29 BSISO179971:20042 3.2 casein-nitrogen content mass fraction of substances determined according to the procedures specified in this part of ISO 17997IDF 29 NOTE Both the non-casein-nitrogen content and the casein-n

31、itrogen content are expressed as a mass fraction in percent. 4 Principle The total-nitrogen content of a test sample is determined by the method of either ISO 8968-1IDF 20-1 or ISO 8968-2IDF 20-2. Casein is precipitated from a separate test portion of the same milk by the addition of acetic acid and

32、 sodium acetate solutions, such that the final pH of the mixture is approximately 4,6. The precipitated milk casein is removed by filtration, so the remaining filtrate contains the non-casein-nitrogen components. The nitrogen content of the filtrate is determined by the procedure described in ISO 89

33、68-1IDF 20-1 or ISO 8968-2IDF 20-2. The casein-nitrogen content is calculated as the difference between the total-nitrogen content and the non-casein-nitrogen content of the milk. 5 Reagents Use only reagents of recognized analytical grade and glass-distilled water or water of at least equivalent pu

34、rity. 5.1 Reagents for determination of total nitrogen. Use the reagents specified in ISO 8968-1IDF 20-1 or ISO 8968-2IDF 20-2. 5.2 Acetic acid solution, c(CH 3 CO 2 H) = 1,75 mol/l. Using a volumetric pipette (6.6), add 10,0 ml of glacial acetic acid in a 100 ml volumetric flask (6.3). Dilute to th

35、e mark with water. 5.3 Sodium acetate solution, c(CH 3 CO 2 Na) = 1 mol/l. Dissolve 8,20 g of sodium acetate or 13,60 g of sodium acetate trihydrate in water in a 100 ml volumetric flask (6.3). Dilute to the mark with water. The sodium acetate solution may be stored at room temperature for one week

36、or at between 0 C and 4 C for 6 months. 6 Apparatus Usual laboratory equipment and, in particular, the following. 6.1 Apparatus for determination of total nitrogen. Use that specified in ISO 8968-1IDF 20-1 or ISO 8968-2IDF 20-2. 6.2 Water bath, capable of maintaining a temperature of 38 C to 40 C. 6

37、.3 One-mark volumetric flasks, with stoppers, of capacity 100 ml, conforming to ISO 1042:1998, class A. 6.4 Bottle-top dispenser, capable of delivering 75 ml of water (optional). 6.5 Graduated measuring cylinder, of capacity up to 100 ml. BSISO179971:2004 36.6 One-mark volumetric pipettes, of capaci

38、ty 1 ml, 10 ml and 50 ml, conforming to ISO 648:1977, class A. 6.7 Filter funnel, made of glass or plastic, of diameter 75 mm. 6.8 Filter paper, of diameter 15 cm, nitrogen-free (e.g. Whatman No. 1 1)or equivalent). Pleat before use. 6.9 Conical flasks, or equivalent, of capacity 100 ml. 6.10 Analyt

39、ical balance, capable of weighing to the nearest 0,1 mg. 6.11 Automatic pipettor or (adjustable) micropipette, capable of delivering 1,0 ml (optional). 7 Sampling It is important that the laboratory receive a sample which is truly representative and has not been damaged or changed during transport o

40、r storage. Sampling is not part of the method specified in this part of ISO 17997IDF 29. A recommended sampling method is given in ISO 707. 8 Preparation of test sample Warm the test sample in the water bath (6.2) set at between 38 C and 40 C to melt the milk fat so that a representative test portio

41、n of milk can be removed from the test sample. Gently mix the sample immediately prior to removal and weighing of the test portion (see 9.1 and 9.2). 9 Procedure 9.1 Determination of total nitrogen Determine the total-nitrogen content of the test sample (Clause 8), w N , expressed as a mass fraction

42、 in percent, by using the procedure as described in ISO 8968-1IDF 20-1 or ISO 8968-2IDF 20-2. 9.2 Determination of non-casein nitrogen 9.2.1 Test portion 9.2.1.1 Weigh, to the nearest 0,1 mg, approximately 10 g of the prepared test sample (Clause 8) into a 100 ml volumetric flask (6.3). Immediately

43、add 75 ml of water, preheated to 38 C, using a bottle-top dispenser (6.4) or a measuring cylinder (6.5). Additional samples may be weighed and water added at this point. However, care shall be taken to finish step 9.2.1.2 within 30 min after adding the test portion to the volumetric flask. NOTE This

44、 30-min time limit is to minimize proteolytic degradation of casein during sample preparation. 1) Whatman No. 1 is an example of a product available commercially. This information is given for the convenience of users of this part of ISO 17997|IDF 29 and does not constitute an endorsement by ISO or

45、IDF of this product. BSISO179971:20044 9.2.1.2 Using a volumetric pipette (6.6) or an automatic pipettor or (adjustable) micropipette (6.11), add 1 ml of acetic acid solution (5.2) to the flask. Stopper the flask and swirl to mix the contents. Place the flask for 10 min in the water bath (6.2) set a

46、t between 38 C and 40 C. Using another volumetric pipette (6.6) or an automatic pipettor or (adjustable) micropipette (6.11), add 1 ml of sodium acetate solution (5.3) to the flask and swirl to mix. Cool the flask and its contents to 20 C. Dilute to the mark with water at 20 C. Stopper the flask and

47、 invert to mix. Let the precipitate settle. Filter the contents of the flask using a filter funnel (6.7) and a pleated filter paper (6.8). Collect the entire filtrate in a 100 ml conical flask (6.9). The filtrate shall be clear and free of particulate matter. If not, repeat the procedure starting fr

48、om 9.2.1 with a new test portion. NOTE This method uses a fixed volume addition of acetic acid and sodium acetate solutions for every sample. This will not achieve an exact pH of 4,6 for every milk sample. However, it is a practical compromise that has been used traditionally for analysis of bovine

49、milks, particularly when a large number of samples are to be analysed. pH variation in the range between 4,5 and 5,0 has been shown to have a negligible influence on the final result (see Reference 8). The alternative is to monitor the pH as acid is added to the sample with the appropriate temperature adjustments for pH-meter calibration. In this case, the exact dilution of each test portion should be meas