1、 Reference numbers ISO 3976:2006(E) IDF 74:2006(E) ISO and IDF 2006INTERNATIONAL STANDARD ISO 3976 IDF 74 Second edition 2006-03-01 Milk fat Determination of peroxide value Matire grasse laitire Dtermination de lindice de peroxyde ISO 3976:2006(E) IDF 74:2006(E) PDF disclaimer This PDF file may cont
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7、ww.iso.org Web www.fil-idf.org Published in Switzerland ii ISO and IDF 2006 All rights reservedISO 3976:2006(E) IDF 74:2006(E) ISO and IDF 2006 All rights reserved iii Contents Page Foreword iv 1 Scope 1 2 Terms and definitions .1 3 Principle1 4 Reagents.1 5 Apparatus .2 6 Sampling.3 7 Preparation o
8、f test sample3 7.1 General3 7.2 Anhydrous milk fat, anhydrous butteroil, butteroil, ghee .3 7.3 Butter 4 8 Procedure (see Annex A) .4 8.1 Precautions to avoid oxidation and disturbed recording of extinction .4 8.2 Reagent blank 4 8.3 Test sample blank4 8.4 Test portion 5 8.5 Extinction coefficient o
9、f the red iron(III) complex5 9 Calculation and expression of results.6 9.1 Calculation6 9.2 Expression of test results.7 10 Precision.7 10.1 Interlaboratory test 7 10.2 Repeatability.7 10.3 Reproducibility.7 11 Test report 7 Annex A (informative) Summary of the procedure and examples of calculations
10、.8 Annex B (informative) Interlaboratory trial .9 Annex C (informative) Comparison trial10 Bibliography 13 ISO 3976:2006(E) IDF 74:2006(E) iv ISO and IDF 2006 All rights reservedForeword ISO (the International Organization for Standardization) is a worldwide federation of national standards bodies (
11、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, go
12、vernmental 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/IE
13、C Directives, Part 2. 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 by at least 75 % of the memb
14、er 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 held responsible for identifying any or all such patent rights. ISO 3976 IDF 74 was prepared by Technical Committee ISO/TC 34, Food product
15、s, Subcommittee SC 5, Milk and milk products, and the International Dairy Federation (IDF). It is being published jointly by ISO and IDF. This edition of ISO 3976 IDF 74 cancels and replaces ISO 3976:1977, which has been technically revised. A comparison of the results using the new reagent (methano
16、l/1-decanol/n-hexane mixture) with those found using chloroform/methanol is given in Annex C. ISO 3976:2006(E) IDF 74:2006(E) ISO and IDF 2006 All rights reserved v Foreword IDF (the International Dairy Federation) is a worldwide federation of the dairy sector with a National Committee in every memb
17、er country. Every National Committee has 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. Draft International Standards adopted by the Acti
18、on Teams and Standing Committees are circulated to the National Committees for voting. Publication as an International Standard requires approval by at least 50 % of the IDF National Committees casting a vote. Attention is drawn to the possibility that some of the elements of this document may be th
19、e subject of patent rights. IDF shall not be held responsible for identifying any or all such patent rights. ISO 3976 IDF 74 was prepared by the International Dairy Federation (IDF) and Technical Committee ISO/TC 34, Food products, Subcommittee SC 5, Milk and milk products. It is being published joi
20、ntly by IDF and ISO. All work was carried out by the Joint ISO-IDF Action Team on Fat, of the Standing Committee on Main components of milk, under the aegis of its project leader, Mr A. van Reusel (BE). This edition of ISO 3976 IDF 74 cancels and replaces IDF 74A:1991, which has been technically rev
21、ised. A comparison of the results using the new reagent (methanol/1-decanol/n-hexane mixture) with those found using chloroform/methanol is given in Annex C. INTERNATIONAL STANDARD ISO 3976:2006(E) IDF 74:2006(E) ISO and IDF 2006 All rights reserved 1 Milk fat Determination of peroxide value WARNING
22、 The use of this International Standard may involve the use of hazardous materials, operations, and equipment. This International 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 a
23、nd health practices and determine the applicability of local regulatory limitations prior to use. 1 Scope This International Standard specifies a method for the determination of the peroxide value of anhydrous milk fat. The method is suitable for anhydrous milk fat having a peroxide value up to 1,3
24、mmol of oxygen per kilogram. NOTE For milk fat samples with peroxide values between 0,5 mmol and 1,3 mmol of oxygen per kilogram, an extended procedure (see Annex A) is used. For milk fat samples with peroxide values of more than 1,3 mmol of oxygen per kilogram, an iodine/thiosulfate method can be u
25、sed (e.g. AOAC 920.160). 2 Terms and definitions For the purposes of this document, the following terms and definitions apply. 2.1 peroxide value amount of substance determined by the procedure specified in this International Standard NOTE The peroxide value is expressed as millimoles of oxygen per
26、kilogram. 3 Principle A test portion is dissolved in a mixture of methanol/1-decanol/n-hexane, then iron(II) chloride and ammonium thiocyanate are added. The peroxides oxidize the iron(II) which forms a red iron(III) complex with the ammonium thiocyanate. The amount of substance is calculated from a
27、 photometric determination of the red iron(III) complex, after a fixed period of reaction. 4 Reagents Use only reagents of recognized analytical grade, unless otherwise specified, and distilled or demineralized water or water of at least equivalent purity. 4.1 Methanol/1-decanol/n-hexane mixture, in
28、 ratio 3:2:1 (volume fraction). Mix 2 volume parts of 1-decanol with 1 volume part of n-hexane. Add 3 volume parts of anhydrous methanol to that mixture and mix again. ISO 3976:2006(E) IDF 74:2006(E) 2 ISO and IDF 2006 All rights reservedThe mixture is flammable and has an unpleasant odour. Therefor
29、e, it is recommended to work in a fume cupboard and to wear gloves. Petroleum ether with a boiling range at between 60 C and 80 C may be used instead of n-hexane. 4.2 Iron(II) chloride (FeCl 2 ) solution, c(Fe 2+ ) 1 mg/ml. Prepare the iron(II) chloride solution in indirect, dimmed light. Dissolve a
30、pprox. 0,4 g of barium chloride dihydrate (BaCl 2 2H 2 O) in about 50 ml water. Then dissolve approx. 0,5 g of iron(II) sulfate heptahydrate (FeSO 4 7H 2 O) in about 50 ml water. Slowly pour the barium chloride solution, with constant stirring, into the iron(II) sulfate solution. Add about 2 ml of h
31、ydrochloric acid solution I (4.5) and mix again. Allow the precipitate of barium sulfate to settle or centrifuge the mixture until the upper liquid layer is clear. Decant the thus-obtained clear solution into a brown bottle. Do not store the solution for more than 1 week. Alternatively, the iron(II)
32、 chloride solution may be prepared by dissolving approximately 0,35 g of iron(II) chloride tetrahydrate (FeCl 2 4H 2 O) in about 100 ml water. Add 2 ml of hydrochloric acid solution I (4.5) and mix. 4.3 Ammonium thiocyanate solution. Dissolve approx. 30 g of ammonium thiocyanate (NH 4 SCN) in water.
33、 Dilute with water to 100 ml. If the solution is not colourless, wash the solution several times with small amounts (e.g. 5 ml portions) of iso-amyl alcohol (3-methylbutan-1-ol). 4.4 Iron(III) chloride (FeCl 3 ) standard solution, c(Fe) = 10 g/ml. Dissolve 0,500 g of iron powder in about 50 ml of hy
34、drochloric acid solution I (4.5) in a 500 ml one-mark volumetric flask. Add 1 ml to 2 ml of hydrogen peroxide solution (4.7). Remove the excess of hydrogen peroxide by boiling for 5 min. Cool to room temperature. Dilute to the 500 ml mark with water and mix. The iron(III) chloride solution containin
35、g 1 g/l of Fe may also be prepared from standardized chemicals available commercially. Transfer, using a pipette, 1 ml of the obtained solution to a 100 ml one-mark volumetric flask. Dilute to the 100 ml mark with methanol/1-decanol/n-hexane mixture (4.1) and mix. 4.5 Hydrochloric acid solution I, a
36、pprox. c(HCl) = 10 mol/l. 4.6 Hydrochloric acid solution II, approx. c(HCl) = 0,2 mol/l. Dilute 2 ml of hydrochloric acid solution I (4.5) with water to 100 ml. 4.7 Hydrogen peroxide solution (H 2 O 2 ), of mass fraction approx. 30 %. 4.8 Dilute nitric acid (HNO 3 ), of mass fraction approx. 10 %. 5
37、 Apparatus Usual laboratory apparatus and, in particular, the following. 5.1 Glassware. Clean all glassware by soaking in dilute nitric acid (4.8) for 24 h. Rinse the glassware four times with tap water and four times with distilled or equivalent water before drying it in the oven (5.10) set at 100
38、C for 1 h. ISO 3976:2006(E) IDF 74:2006(E) ISO and IDF 2006 All rights reserved 3 The cleanliness of the glassware is of utmost importance. Other cleaning procedures may also be used if they give the same result. 5.2 Analytical balance, capable of weighing to the nearest 1 mg, with a readability of
39、0,1 mg. 5.3 Dispenser device, capable of accurately delivering 9,9 ml, 9,6 ml, 9,4 ml, 8,9 ml, 8,4 ml and 7,9 ml of methanol/1-decanol/n-hexane mixture (4.1). 5.4 Dispenser device, capable of accurately delivering 0,5 ml, 1,0 ml, 1,5 ml and 2,0 ml of iron(III) chloride standard solution (4.4). 5.5 M
40、icropipettes, capable of accurately delivering 0,05 ml of ammonium thiocyanate solution (4.3), of iron(II) chloride solution (4.2) and of hydrochloric acid solution II (4.6) respectively. 5.6 Photometer, capable of measuring at a wavelength near to 500 nm. 5.7 Cells with caps, suitable for the photo
41、meter (5.6), resistant to all reagents used in the procedure. 5.8 Glass test tubes, provided with ground glass stoppers. 5.9 Oven, electrically heated, capable of operating at between 40 C and 45 C. 5.10 Oven, electrically heated, capable of operating at 100 C 2 C. 5.11 Centrifuge, capable of produc
42、ing a radial acceleration of at least 350 g, with a swing-out rotor (e.g. a so-called Gerber centrifuge). 5.12 Centrifuge tubes, suitable for using in the centrifuge (5.11). 5.13 Glass funnels, with folded filter paper (medium grade). 5.14 Bottles, suitable for using with the reagents. 6 Sampling A
43、representative sample should have been 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 method is given in ISO 707 IDF 50. 7 Preparation of test sample 7
44、.1 General Carry out all preparations in indirect subdued light. 7.2 Anhydrous milk fat, anhydrous butteroil, butteroil, ghee If necessary, completely liquefy the test sample (see IDF 68A for details) by warming the unopened container at the lowest temperature necessary to achieve liquefaction. Mix
45、the liquefied sample, while avoiding the inclusion of air in the sample as far as possible. Proceed with the determination immediately and while the test sample is still liquid. ISO 3976:2006(E) IDF 74:2006(E) 4 ISO and IDF 2006 All rights reserved7.3 Butter Add an appropriate quantity of test sampl
46、e to a centrifuge tube (5.12). Melt the sample in the oven (5.9) set at between 40 C and 45 C. Separate the fat by centrifuging at a radial acceleration of at least 350 g for 5 min. Filter the warm separated butterfat through a glass funnel (5.13) with a folded dry filter paper in the oven (5.9) set
47、 at between 40 C and 45 C. The filtered butterfat shall be clear and visibly free from water and non-fatty compounds. Proceed with the determination without any delay while the test sample is still liquid. 8 Procedure (see Annex A) 8.1 Precautions to avoid oxidation and disturbed recording of extinc
48、tion 8.1.1 Avoid any exposure of the test sample to light. Carry out the test in indirect light, subdued as much as is practicable. 8.1.2 Perform all optical extinction measurements at the wavelength of maximal extinction of the red iron(III) complex, i.e. near to 500 nm. 8.1.3 Perform all optical e
49、xtinction measurements in cells (5.7) which are closed immediately after filling. From the moment of closure, allow the closed cells stand for 10 min to obtain equilibrium in the mixture before reading the extinction. NOTE Evaporation of the solvent might produce condensation on the upper walls of the cells. By reintegrating the bulk liquid, this condensation creates a diffraction of the light beam by the different solvent streaks resulting in a fluctuating extinction. The 10-min waiting time is needed to obtain eq
