ISO TS 22113-2012 Milk and milk products - Determination of the titratable acidity of milk fat《牛奶和乳制品 乳脂滴定酸度的测定》.pdf

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1、 Access to Additional Content for ISO/TS 22113 First edition, Dated: 07/01/2012 (Click here to view the publication) This Page is not part of the original publication This page has been added by IHS as a convenience to the user in order to provide access to additional content as authorized by the Co

2、pyright holder of this document Click the link(s) below to access the content and use normal procedures for downloading or opening the files. ISO/TS 22113 Files Information contained in the above is the property of the Copyright holder and all Notice of Disclaimer an ISO Technical Specification (ISO

3、/TS) represents an agreement between the members of a technical committee and is accepted for publication if it is approved by 2/3 of the members of the committee casting a vote. An ISO/PAS or ISO/TS is reviewed after three years in order to decide whether it will be confirmed for a further three ye

4、ars, revised to become an International Standard, or withdrawn. If the ISO/PAS or ISO/TS is confirmed, it is reviewed again after a further three years, at which time it must either be transformed into an International Standard or be withdrawn. Attention is drawn to the possibility that some of the

5、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/TS 22113|IDF/RM 204 was prepared by Technical Committee ISO/TC 34, Food products, Subcommittee SC 5, Milk and milk products, and the International Dairy

6、 Federation (IDF). It is being published jointly by ISO and IDF. ISO/TS 22113:2012(E) IDF/RM 204:2012(E) ISO and IDF 2012 All rights reserved vForeword IDF (the International Dairy Federation) is a non-profit organization representing the dairy sector worldwide. IDF membership comprises National Com

7、mittees in every member country as well as regional dairy associations having signed a formal agreement on cooperation with IDF. All members of IDF have the right to be represented on the IDF Standing Committees carrying out the technical work. IDF collaborates with ISO in the development of standar

8、d methods of analysis and sampling for milk and milk products. The main task of Standing Committees is to prepare International Standards. Draft International Standards adopted by the Standing Committees are circulated to the National Committees for endorsement prior to publication as an Internation

9、al Standard. Publication as an International Standard requires approval by at least 50 % of IDF National Committees casting a vote. In other circumstances, particularly when there is an urgent market requirement for such documents, a Standing Committee may decide to publish an other type of normativ

10、e document which is called by IDF: Reviewed method. Such a method represents an agreement between the members of a Standing Committee and is accepted for publication if it is approved by at least 50 % of the committee members casting a vote. A Reviewed method is equal to an ISO/PAS or ISO/TS and wil

11、l, therefore, also be published jointly under ISO conditions. Attention 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/TS 22113|IDF/RM 204 was prepared by

12、 the International Dairy Federation (IDF) and Technical Committee ISO/TC 34, Food products, Subcommittee SC 5, Milk and milk products. It is being published jointly by IDF and ISO. All work was carried out by Joint ISO-IDF Project Group (C01) on Determination of titratable acidity of fat (BDI method

13、) of the Standing Committee on Analytical Methods for Composition (SCAMC) under the aegis of its project leader, P. Trossat (FR). TECHNICAL SPECIFICATION ISO/TS 22113:2012(E) IDF/RM 204:2012(E) ISO and IDF 2012 All rights reserved 1Milk and milk products Determination of the titratable acidity of mi

14、lk fat 1 Scope This Technical Specification specifies a routine method for determining the titratable acidity of milk fat. The method is applicable to milk fat obtained from: a) raw milk; b) heat-treated milk; c) milk reconstituted from milk powder; d) cream with any fat content, provided the produc

15、t is diluted so as to obtain a mass fraction of between 4 % and 6 % fat. The method is not applicable to fermented milk or milk that has undergone bacterial or enzymatic damage. NOTE 1 The titration procedure can also be applied to fat separated from several other dairy products. NOTE 2 This Technic

16、al Specification is designed for batches of test samples of between five and several hundred test portions per day. 2 Principle An amount of sample is thoroughly mixed with a solution containing sodium tetraphosphate and a surface- active agent. The mixture is heated in a boiling water bath to obtai

17、n separation of fat. A known quantity of extracted fat is dissolved in an organic solvent and titrated with alcoholic alkali. 3 Reagents Use only reagents of recognized analytical grade, unless otherwise specified, and distilled or demineralized water or water of equivalent purity. 3.1 Phosphoric ac

18、id solution, c(H 3 PO 4 ) 1 mol/l. 3.2 BDI 1 )reagent. Dissolve 70 g of sodium tetraphosphate in about 700 ml distilled water without additional warming and mix. 1) The acronym “BDI” stands for Bureaux of Dairy Industries; this organization first developed this method. ISO/TS 22113:2012(E) IDF/RM 20

19、4:2012(E) 2 ISO and IDF 2012 All rights reservedAdd 30 g of octylphenylpoly(ethyleneglycol) 2 )and mix again. Adjust the pH to 6,6 with phosphoric acid solution (3.1), if needed. Dilute to 1 l with water and mix. If necessary, readjust the pH with phosphoric acid solution (3.1). If stored in a refri

20、gerator and in the dark, the BDI reagent is stable for 1 month. NOTE Sodium tetraphosphate is a polyphosphate containing sodium tetraphosphate (NaPO 3 ) 4as the main component besides some other polyphosphates. 3.3 Thymol blue solution, c(C 27 H 30 O 5 S) 0,1 g/l in propan-2-ol. Dissolve 0,1 g sodiu

21、m salt of thymol blue in 100 ml of propan-2-ol to prepare a stock solution. Directly before use, dilute one volume of the stock solution with nine volumes of propan-2-ol. 3.4 Fat solvent solution. Mix one volume of thymol blue solution (3.3) with four volumes light petroleum with a boiling range bet

22、ween 60 C and 80 C. The fat solvent solution can be stored in the dark for up to 1 month. 3.5 Potassium hydrogen phthalate solution, c(KHC 8 H 4 O 4 ) 0,01 mol/l. Dissolve 1,021 1 g of potassium hydrogen phthalate in a 500 ml one-mark volumetric flask (4.11). Dilute to the 500 ml mark with water and

23、 mix. 3.6 Tetra-n-butylammonium hydroxide solution, c(C 16 H 37 NO) 0,01 mol/l in a propan-2-ol and methanol mixture. Dilute one volume of tetra-n-butylammonium hydroxide, c(C 4 H 9 ) 4 NOH 0,1 mol/l in a propan-2-ol and methanol mixture, with nine volumes of propan-2-ol to obtain a final concentrat

24、ion of c(C 16 H 37 NO) 0,01 mol/l. The concentration of the tetra-n-butylammonium hydroxide solution may change on storage and when being transferred to the burette. For these reasons, determine the actual concentration of the solution to four decimal places before use by titration against a standar

25、d solution of potassium hydrogen phthalate (3.5) using the thymol blue solution (3.3) as indicator. If the burette is fitted with a facility to exclude the entry of carbon dioxide, the concentration is stable for 1 month. 3.7 Pilot fat and reference fat. 3.7.1 Pilot fat. Melt some anhydrous milk fat

26、 (e.g. 1 000 g) having a fat acidity level of between 0,5 mmol/100 g and 1,0 mmol/100 g of fat. Divide the melted anhydrous milk fat sample into subsamples (e.g. of 5 g each). If stored in a freezer at 20 C or below, the pilot fat subsamples can be kept for at least 2 years. The pilot fat samples ca

27、n be used for checking the reproducibility of the results obtained by the titration procedure (7.2), either during a single work session or between work sessions over a long period of time (several months to years). 3.7.2 Reference fat. Reference fat samples consist of milk fat of low fat acidity (b

28、asic fat) spiked with increasing levels of palmitic acid (C 16 ) within the range 0,5 mmol/100 g to 1,5 mmol/100 g per 100 g fat. 2) Triton X-100 is an example of a suitable product available commercially. This information is given for the convenience of users of this document, and does not constitu

29、te an endorsement by ISO and IDF of this product. ISO/TS 22113:2012(E) IDF/RM 204:2012(E) ISO and IDF 2012 All rights reserved 3The accuracy of the titration procedure can be checked by using the regression Equation (1): 16 (C )bb (1) where b(C 16 ) is the amount of palmitic acid, expressed in mmol

30、per 100 g fat, added to the basic fat; b is the BDI value of the spiked samples decreased by the BDI value of the basic fat (blank). The preparation and the guidelines for use of these reference fat samples are described in Annex C. 4 Apparatus Usual laboratory equipment and, in particular, the foll

31、owing. 4.1 Delivery pipettes or syringes, capacities 10 ml, 25 ml, and 50 ml. 4.2 Fat separation tubes, consisting of a bulk vat surmounted by a narrow stem for collecting the small quantity of fat extracted from the reagent mixture. The diameter of the stem shall be large enough to allow the calibr

32、ated syringe (4.5) to take a fat sample. Models of fat separation tubes are given in Annex A. Butyrometers according to ISO 3432|IDF 221 3can also be used. NOTE The fat separation is enhanced by centrifugation, especially in tubes with narrow stems. 4.3 Water bath, capable of maintaining a temperatu

33、re of 45 C 1C. 4.4 Boiling water bath, capable of maintaining a temperature of 95 C. 4.5 Calibrated syringe, adjustable and capable of delivering a known quantity of milk fat of about 0,25 g at 45 C, being accurate to 2 mg of milk fat. NOTE From experience, transfer of a quantity of fat can be done

34、accurately and conveniently by using a positive displacement pipette. 4.6 Titration vessel, capacity of between 10 ml and 100 ml depending on the volumes of test samples to be titrated in one titration run, provided with a stirring device. 4.7 Microburette, graduated in divisions of at least 0,002 m

35、l. 4.8 Nitrogen supply, free of carbon dioxide. 4.9 Gas washbottle, containing light petroleum with a boiling range of 60 C to 80 C, connected to the nitrogen supply (4.8) and the titration vessel (4.6). 4.10 Colorimeter, with dip-probe, suitable for measuring at a wavelength of between 600 nm and 6

36、20 nm, connectable to the titration vessel (4.6). 4.11 One-mark volumetric flasks, capacities 100 ml to 500 ml, ISO 1042, 2class A. NOTE 1 The titration vessel (4.6), the microburette (4.7) for delivering the non-aqueous titrant tetra-n-butylammonium hydroxide (3.6), the nitrogen supply (4.8) throug

37、h a gas washbottle (4.9) and the dip-probe connected to the colorimeter (4.10) are assembled in a typical device (see Annex B) for consecutive titration of several samples in one and the same volume of fat solvent. NOTE 2 A simpler device for manual titration and visual determination of the endpoint

38、 of titration can be set up without a colorimeter with dip-probe. ISO/TS 22113:2012(E) IDF/RM 204:2012(E) 4 ISO and IDF 2012 All rights reserved5 Sampling Sampling is not part of the method specified in this Technical Specification. A recommended sampling method is given in ISO 707|IDF 50. 1It is im

39、portant the laboratory receive a truly representative sample which has not been damaged or changed during transport or storage. 6 Preparation of test samples 6.1 Storage and preservation The milk or cream test samples shall have been stored and transported at 0 C to 4 C (milk powder can be stored at

40、 ambient temperature) and be analysed within 36 h. For prolonged storage or storage in a refrigerator at 5 C, it is recommended that test samples be preserved by means of hydrogen peroxide at a final concentration of 0,2 g/l H 2 O 2 . In this case, the test samples can be stored for 4 days. 6.2 Pret

41、reatment of test sample 6.2.1 Milk sample Mix gently by inverting the test sample several times, without increasing its temperature. 6.2.2 Cream sample Dilute cream sample using the corresponding skim milk or water to obtain a mass fraction of between 4 % and 6 % fat. Using water to dilute cream res

42、ults in an underestimation of the free fatty acid (FFA) level compared to the parent milk. In these cases, use a correction programme to obtain accurate results (see Reference 8). 6.2.3 Milk powder sample Dissolve around 13 g of milk powder in a 100 ml one-mark volumetric flask (4.11). Add 60 ml of

43、water and mix using a mixer at room temperature for 70 min. Dilute to the 100 ml mark with water and mix. 7 Procedure 7.1 Separation of fat Mix 3,5 parts ( 3 %) of test sample (milk, cream diluted or reconstituted milk powder) (6.2) to 1 part ( 1,5 %) of BDI reagent (3.2) in the tube for fat separat

44、ion using the following amounts: a) when using a MONED tube (4.2), mix 31 ml + 1 ml of test sample (6.2) and 8,9 ml + 0,1 ml of BDI reagent (3.2); b) when using a Van Gulik butyrometer (4.2), mix 16,0 ml + 0,5 ml of test sample (6.2) and 4,5 ml + 0,1 ml of BDI reagent (3.2); c) when using other tubes, mix volume fractions of the test sample (6.2) and the BDI reagent in ratio 3,5 + 1 using volumes such that a fat column exists in the stem of the extraction tube (4.2). Immediately after filling, close the fat separation tube and mix its content.