DIN 10479-1-2000 Butyrometric determinations of the fat content of milk and milk products - Part 1 General guidance on the use of butyrometric methods and technical specification f.pdf

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1、ICS 67.100.01Butyrometrische Bestimmung des Fettgehaltes von Milch und Milch-produkten Teil 1: Allgemeine Anleitung fr die Anwendungbutyrometrischer Verfahren und technische Lieferbedingungen frAmylalkoholIn keeping with current practice in standards published by the International Organization for S

2、tandardization(ISO), a comma has been used throughout as the decimal marker.ForewordThis standard has been prepared by Technical Committee Chemische und physikalische Milchuntersuchungof the Normenausschuss Lebensmittel und landwirtschaftliche Produkte (Foodstuffs and AgriculturalProducts Standards

3、Committee) and is based on DIN 10330 and ISO 11870.AmendmentsThis standard differs from the June 1977 edition of DIN 10330 in that editorial changes have been made andreferences have been updated.Previous editionDIN 10330: 1977-06.IntroductionReference methods for determining the fat content of milk

4、 and milk products are time-consuming andexperience is required to obtain reliable results. Butyrometric methods are simpler to perform and make itpossible to determine rapidly the fat content of a wide variety of milk products. Two of these methods, theGerber method for milk and the Van Gulik metho

5、d for cheese, are covered by international standards. Theapparatus required for these methods has also been standardized (see Bibliography). Other butyrometricmethods and butyrometers are in use in various countries, but are not the subject of standards.Although there is only one reference method fo

6、r each type of product, there are a number of butyrometricmethods. Furthermore, standard methods are used for products outside their scope, but establishingstandard methods for the entire product range would result in an ever-increasing number of standards. It wastherefore decided at international l

7、evel to prepare general guidelines on butyrometric methods while retainingthe standards on which this standard is based.1 ScopeThis standard provides a basis for extending the scope of existing standard butyrometric methods of fatdetermination to cover various milk products, and specifies the proced

8、ure for all butyrometric analyses andthe most important requirements relating to their performance. It also gives information on validatingbutyrometric methods using the appropriate reference methods.Appendix A stipulates the requirements for amyl alcohol.Ref. No. DIN 10479-1 : 2000-06English price

9、group 08 Sales No. 010803.01DEUTSCHE NORM June 200010479-1Continued on pages 2 to 6. No part of this translation may be reproduced without the prior permission ofDIN Deutsches Institut fr Normung e. V., Berlin. Beuth Verlag GmbH, 10772 Berlin, Germany,has the exclusive right of sale for German Stand

10、ards (DIN-Normen).Butyrometric determination of fat content of milkand milk productsGeneral guidance on the use of butyrometric methods andrequirements for amyl alcoholTranslation by DIN-Sprachendienst.In case of doubt, the German-language original should be consulted as the authoritative text.Super

11、sedes DIN 10330,June 1977 edition.Page 2DIN 10479-1 : 2000-062 Normative referencesThis standard incorporates, by dated or undated reference, provisions from other publications. These normativereferences are cited at the appropriate places in the text, and the titles of the publications are listed b

12、elow. Fordated references, subsequent amendments to or revisions of any of these publications apply to this standardonly when incorporated in it by amendment or revision. For undated references, the latest edition of thepublication referred to applies.DIN 10329 Determination of fat content of cream

13、by Roeder gravimetric methodDIN 10330 Butyrometric determination of fat content of milk and milk productsDIN 10332 Determination of fat content of cream by Schulz and Kley methodDIN EN ISO 707 : 1997 Milk and milk products Guidance on samplingISO 2446 : 1976 Milk Determination of fat content (routin

14、e method)ISO 3433 : 1975 Cheese Determination of fat content (Van Gulik method)ISO 8196-1 : 2000 Milk Definition and evaluation of the overall accuracy of indirect methods of milkanalysis Part 1: Analytical attributes of indirect methodsISO 8196-2: 2000 Milk Definition and evaluation of the overall

15、accuracy of indirect methods of milkanalysis Part 2: Calibration and quality control in the dairy laboratoryISO 11870 : 2000 Milk and milk products Determination of fat content General guidance on the useof butyrometric methodsLebensmittel- und Bedarfsgegenstndegesetz (German Foodstuffs Act), as of

16、1 August 1997, BGBl. (GermanFederal Law Gazette), I, No. 63, pp. 229623193 Standard butyrometric methodsStandard butyrometric methods are specified in ISO 2446 and ISO 3433.4 PrincipleAll butyrometric methods follow a standard procedure, regardless of the product to be analysed:a) the proteins and,

17、consequently, the fatty spherule membrane are dissolved;b) the fat is separated from the product by centrifuging in a butyrometer, a small amount of amyl alcohol ora suitable substitute being added to promote separation;c) the fat values are read off directly as a percentage, corrected if necessary,

18、 on the butyrometer scale.5 Reagents5.1 GeneralUnless otherwise specified, only analytical grade reagents and distilled or demineralized water or water ofequivalent quality shall be used.The following reagents shall be used.5.2 Pure, colourless or pale amber sulfuric acid, H2SO4, free of impurities.

19、5.2.1 Sulfuric acid, H2SO4, having a density of (1,818 0,003) g/ml at 20 C, for analyzing milk and milkproducts having a similar water content or whose water content has been appropriately adjusted (e.g. condensedmilk, and cream in the Schulz and Kley method (see DIN 10332) or in the Khler method).T

20、he use of higher or lower acid concentrations is inadvisable since more concentrated sulfuric acid attacks theamyl alcohol at 65 C and forms olefins by eliminating water. Lower concentrations lessen the oxidative effect,but the dissolution of the fatty spherule membrane may be incomplete and lumps m

21、ay form.5.2.2 Sulfuric acid, having a density of (1,522 0,005) g/ml at 20 C, for analysing cheese and productshaving a lower water content than milk (cream by the Roeder method (see DIN 10329).5.3 Amyl alcohol, as specified in appendix A, or a substitute which has been shown to give the same testres

22、ults as amyl alcohol.6 ApparatusIn addition to standard laboratory equipment, the following shall be used.6.1 Butyrometer and stopper, suitable for the method used and thoroughly cleaned to remove any fatresidues.6.2 Apparatus for dispensing the required volumes of acid and amyl alcohol with adequat

23、e repeatability.6.3 Centrifuge, suitable for use with a butyrometer, having a meter capable of indicating the speed to thenearest 70 min1and preferably with vertical rather than horizontal loading. It shall be capable of maintainingthe contents of the butyrometer at 30 C to 50 C after centrifuging.N

24、OTE 1: A heated centrifuge shall be used.Page 3DIN 10479-1 : 2000-06The loaded centrifuge shall be capable of achieving a relative centrifugal acceleration of (350 50) g at the outerend of the butyrometer stopper within two minutes. This acceleration is achieved at the specified speeds incentrifuges

25、 having the effective radii (horizontal distance between the centre of the centrifuge spindle and theouter end of the butyrometer stopper) shown in table 1.Table 1Effective radius, R,Speed, N,mmin number of revolutionsper minute ( 70)240 1140245 1130250 1120255 1110260 1100265 1090270 1080275 107030

26、0 1020325 980NOTE 2: The relative centrifugal acceleration, aZen, rel, of a centrifuge is given by the following equation:aZen, rel= 1,12 . 106RN2whereR is the effective horizontal radius, in mm;N is the speed, in number of revolutions per minute.6.4 Pipette or analytical balance, capable of dispens

27、ing the required sample volume with the necessaryaccuracy.6.5 Thermostatically controlled water bath, capable of maintaining the required temperature to within 2 C and deep enough to accommodate the butyrometers vertically with their measurement scales completelyimmersed.7 SamplingAs in DIN EN ISO 7

28、07.8 Sample preparationSample preparation shall be as specified in the relevant reference method for each product to be analyzed.9 ProcedureFollow the appropriate procedure for the product and method (Gerber method for milk, Teichert method forcondensed milk, buttermilk and milk powder, Schulz-Kley

29、and Khler methods for cream, Khler method for icecream (see Bibliography).First introduce 10 ml of sulfuric acid into the butyrometer, then use a pipette or other metering device to coverthe sulfuric acid with a layer of the homogenized analytical sample having a suitable thickness for thebutyromete

30、r, taking care not to mix the acid and product, since this will prevent the required digestiontemperature being reached when the mixture is subsequently shaken. Finally, add 1 ml of amyl alcohol.Seal the butyrometers and shake them vigorously. If they contain products (e.g. milk powder) requiring a

31、longerdigestion time, place them in a hot water bath (at 65 C) until digestion is complete.Centrifuge for the specified time at the specified centrifugal acceleration. Before taking a reading, keep thebutyrometer in a water bath at precisely 65 C for not less than five minutes. Read the butyrometer

32、immediatelyafter it has been removed from the water bath, otherwise the contents will cool, their volume will decrease andthe fat values found will be unduly low. To read the butyrometer, hold it vertically at eye level and hold the stopperstill.If the fat is cloudy or dark in colour, white or black

33、 material is deposited at the bottom of the fat column or thephase separation is not clearly visible, the fat content values shall be considered unreliable and the analysisrepeated.Page 4DIN 10479-1 : 2000-06To determine fat in cheese by the Van Gulik method, in cream by the Roeder gravimetric metho

34、d and in butterby the butyrometric method, first weigh the sample into a suitable glass beaker for the butyrometer, place thebeaker in the butyrometer and then introduce the required quantity of sulfuric acid.10 Handling the butyrometerAfter taking the reading, invert the butyrometers and place them

35、 in a holder with the stoppers uppermost. Afterabout 30 minutes, the fat from the flask and the scale tube will have risen to beneath the stopper. While the tubesare still hot, remove the butyrometer stoppers carefully, holding the open end of the butyrometer near the bottomof a sink. Wash the still

36、 hot, empty tubes using a suitable detergent and shake them vigorously; do not use abottle brush. Immerse the butyrometers in water containing detergent, and fill, empty and vigorously shake themseveral times, paying particular attention to the small flask. Then fill the tubes with hot water, vigoro

37、usly shakethem and then empty them three times. Finally, shake the tubes very vigorously and leave them to dry upsidedown. They can be used while still damp, but it is important to shake them again immediately before use in orderto remove any remaining water droplets.11 Validation of a butyrometric

38、method using the appropriate reference methodRegardless of the product being analyzed, all butyrometric methods are empirical and it is essential to establishthat the result is equivalent to that given by the reference method. Every laboratory shall therefore validate itsbutyrometric method by compa

39、rison with the appropriate reference method. It may be assumed that thebutyrometric methods, apparatus and reagents specified in standards and manuals (e.g. collection of officialmethods under article 35 of the Lebensmittel- und Bedarfsgegenstndegesetz) have been harmonized so as toensure that the r

40、esults are very close or identical to those obtained by the reference methods.If a butyrometric method is to be applied to products outside its scope, a comparison with the reference methodshall be undertaken and the routine method shall be modified, if necessary, by altering, for example, thefollow

41、ing parameters:a) concentration of the acid;b) temperature of the water bath;c) dimensions of the butyrometer (volume of body, length or cross section of the scale section, shape andthe graduation scale).The absolute difference between the result obtained by the (modified) routine method and that ob

42、tained by thereference method shall be used to judge whether the agreement is satisfactory and shall be as small as possible.Once conditions are found for the routine method that give results comparable to those of the reference method,the equivalence shall be confirmed by performing further analyse

43、s on several samples using the two methods.The results from each series of samples can be compared with the aid of the conventional t-test.NOTE: This test presupposes that the variances of the two methods are equal, and this shall be checked in caseof doubt.Since the ideal conditions found may be va

44、lid only for a limited concentration range of the product to be analyzed,the full range for which the routine method is used shall be checked. This can be done by duplicate analysesusing both methods (routine and reference methods) on samples covering the whole range of fat contents. Theequivalence

45、of the two methods shall then be determined by comparing the results for each sample using thet-test. If necessary, the results for the whole range can be used to prepare a correction table (cf. ISO 8196).In laboratories that always analyze the same type of product produced by the same method, the a

46、greement ofthe results obtained by the butyrometric method with those obtained by the reference method shall be as closeas possible and the absolute difference shall be approximately zero.If the fat content of products of the same type, but of different origin, has to be determined in a laboratory,

47、it maybe very difficult to modify the butyrometric method so that a value is obtained in every case that is identical tothe result of the reference method.Standardized butyrometric methods shall also be regularly checked because such methods, in addition to theother possible causes for variation, ar

48、e subject to errors themselves.Page 5DIN 10479-1 : 2000-06Appendix ATechnical delivery conditions for amyl alcoholA.1 GeneralAmyl alcohol is used in butyrometric determinations of the fat content of milk and milk products to facilitatephase separation. Its composition has a crucial effect on the pre

49、cision of the analytical results. In order to obtainresults comparable to those of the reference methods by butyrometric methods, the amyl alcohol used shall haveexactly specified properties.A.2 RequirementsA.2.1 CompositionAt least 98 % (V/V) of the amyl alcohol shall consist of the primary alcohols 3-methyl-1-butanol and 2-methyl-1-butanol. The only allowable major impurities are 2-methyl-1-propanol and 1-butanol. The amyl alcohol shallbe free of secondary amyl alcohols, 2-methyl-2-butanol, furfuraldehyde, benzine, benzene and its derivati