1、BRITISH STANDARDBS ISO 3976:2006Milk fat Determination of peroxide valueICS 67.100.10g49g50g3g38g50g51g60g44g49g42g3g58g44g55g43g50g56g55g3g37g54g44g3g51g40g53g48g44g54g54g44g50g49g3g40g59g38g40g51g55g3g36g54g3g51g40g53g48g44g55g55g40g39g3g37g60g3g38g50g51g60g53g44g42g43g55g3g47g36g58BS ISO 3976:200
2、6This British Standard was published under the authority of the Standards Policy and Strategy Committee on 30 June 2008 BSI 2008ISBN 978 0 580 54299 2National forewordThis British Standard is the UK implementation of ISO 3976:2006. The UK participation in its preparation was entrusted to Technical C
3、ommittee AW/5, Chemical analysis of milk and milk products.A list of organizations represented on this committee can be obtained on request to its secretary.This publication does not purport to include all the necessary provisions of a contract. Users are responsible for its correct application.Comp
4、liance with a British Standard cannot confer immunity from legal obligations.Amendments/corrigenda issued since publicationDate CommentsReference numbersISO 3976:2006(E)IDF 74:2006(E)INTERNATIONAL STANDARD ISO3976IDF74Second edition2006-03-01Milk fat Determination of peroxide value Matire grasse lai
5、tire Dtermination de lindice de peroxyde BS ISO 3976:2006ii iiiContents Page Foreword iv 1 Scope 1 2 Terms and definitions .1 3 Principle1 4 Reagents.1 5 Apparatus .2 6 Sampling.3 7 Preparation of test sample3 7.1 General3 7.2 Anhydrous milk fat, anhydrous butteroil, butteroil, ghee .3 7.3 Butter 4
6、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 of the red iron(III) complex5 9 Calculation and expression of results.6 9.1 Calculation6 9.2 Expression of
7、 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.8 Annex B (informative) Interlaboratory trial .9 Annex C (informative) Comparison trial10 Bibliography 1
8、3 BS ISO 3976:2006iv 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
9、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
10、 (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 main task of technical committees is to prepare International Standards. Draft International Standards adopted by the technical com
11、mittees 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
12、 be held responsible for identifying any or all such patent rights. ISO 3976IDF 74 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. This edition of ISO
13、3976IDF 74 cancels and replaces ISO 3976:1977, which has been technically revised. 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. BS ISO 3976:2006vForeword IDF (the International Dairy Federation
14、) is a worldwide federation of the dairy sector with a National Committee in every member 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
15、 sampling for milk and milk products. Draft International Standards adopted by the Action 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. Att
16、ention 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 3976IDF 74 was prepared by the International Dairy Federation (IDF) and Technical Committee ISO/TC 3
17、4, 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 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 editio
18、n of ISO 3976IDF 74 cancels and replaces IDF 74A:1991, which has been technically revised. 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. BS ISO 3976:2006blank1Milk fat Determination of peroxide
19、value WARNING 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 appropr
20、iate safety and 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 val
21、ue up to 1,3 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 me
22、thod can be used (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 o
23、f oxygen per 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 calc
24、ulated from a 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-hexan
25、e mixture, in 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. BS ISO 3976:20062 The mixture is flammable and has an unpleasant odour. Therefore, it is recommended to work in a fume
26、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 (FeCl2) solution, c(Fe2+) 1 mg/ml. Prepare the iron(II) chloride solution in indirect, dimmed light. Dissolve approx. 0,4 g of barium chloride dihydrate (
27、BaCl22H2O) in about 50 ml water. Then dissolve approx. 0,5 g of iron(II) sulfate heptahydrate (FeSO47H2O) 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 hydrochloric acid solution I (4.5) and mix again. Al
28、low 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) chloride solution may be prepared by dissolving ap
29、proximately 0,35 g of iron(II) chloride tetrahydrate (FeCl24H2O) 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 (NH4SCN) in water. Dilute with water to 100 ml. If the solution is not colo
30、urless, 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 (FeCl3) standard solution, c(Fe) = 10 g/ml. Dissolve 0,500 g of iron powder in about 50 ml of hydrochloric acid solution I (4.5) in a 500 ml one-mark volum
31、etric 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 containing 1 g/l of Fe may also be prepared from standardized chemic
32、als 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, approx. c(HCl) = 10 mol/l. 4.6 Hydrochloric acid solution II
33、, 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 (H2O2), of mass fraction approx. 30 %. 4.8 Dilute nitric acid (HNO3), of mass fraction approx. 10 %. 5 Apparatus Usual laboratory apparatus and, in particular, the fol
34、lowing. 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 C for 1 h. BS ISO 3976:20063The cleanliness of the glassware is o
35、f 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 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 met
36、hanol/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 Micropipettes, capable of accurately delivering 0,05 ml of ammonium thiocyanate solution (4.3), of iron(II) chloride sol
37、ution (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 photometer (5.6), resistant to all reagents used in the procedure. 5.8 Glass test tubes, provided with ground glass stoppers
38、. 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 producing a radial acceleration of at least 350 g, with a swing-out rotor (e.g. a so-called Gerber centrifuge). 5.12 Centrifu
39、ge 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 representative sample should have been sent to the laboratory. It should not have been damaged or changed during transp
40、ort or storage. Sampling is not part of the method specified in this International Standard. A recommended sampling method is given in ISO 707IDF 50. 7 Preparation of test sample 7.1 General Carry out all preparations in indirect subdued light. 7.2 Anhydrous milk fat, anhydrous butteroil, butteroil,
41、 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 the liquefied sample, while avoiding the inclusion of air in the sample as far as possible. Proceed with the determinati
42、on immediately and while the test sample is still liquid. BS ISO 3976:20064 7.3 Butter Add an appropriate quantity of test sample 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 f
43、or 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 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
44、 the test sample is still liquid. 8 Procedure (see Annex A) 8.1 Precautions to avoid oxidation and disturbed recording of extinction 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 mea
45、surements at the wavelength of maximal extinction of the red iron(III) complex, i.e. near to 500 nm. 8.1.3 Perform all optical extinction 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
46、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
47、. The 10-min waiting time is needed to obtain equilibrium between the solvent and the vapour phase. 8.2 Reagent blank 8.2.1 Add, using the dispenser (5.3), 9,90 ml of methanol/1-decanol/n-hexane mixture (4.1) to the test tube (5.8). 8.2.2 Add, using a micropipette (5.5), 0,05 ml of ammonium thiocyan
48、ate solution (4.3) to the mixture in the test tube and mix. 8.2.3 Add, using a micropipette (5.5), 0,05 ml of iron(II) chloride solution (4.2) to the mixture in the test tube and mix again. 8.2.4 Transfer the obtained reagent blank mixture to a photometer cell (5.7). Close the cell with a cap and al
49、low it stand for 10 min to obtain equilibrium in the mixture. Measure the extinction, E1, of the reagent blank against the methanol/1-decanol/n-hexane mixture (4.1). Perform the reagent blank determination at least four times. 8.2.5 The obtained results (E1) shall be within a range of 0,010 extinction units. The mean reagent blank extinction (Em) shall not exceed 0,030 units. If the above requirements are not fulfilled, check the photometric procedure, the glassware and the reagents. Correct the procedure or replace what is necessary. 8.3 Test sample blank
