BS 4401-2-1980 Methods of test for meat and meat products - Determination of nitrogen content (reference method)《肉及肉制品试验方法 第2部分 氮含量测定(比对法)》.pdf

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1、BRITISH STANDARD BS4401-2: 1980 ISO937:1978 Methods of test for Meat and meat products Part2: Determination of nitrogen content (reference method) ISO title: Meat and meat products Determination of nitrogen content (Reference method) UDC637.5:664.91/.94:543.846BS4401-2:1980 This British Standard, ha

2、ving been prepared under the directionof the Food and Agriculture Standards Committee,was published underthe authority of the Executive Board and comes intoeffect on 31 July 1980 BSI 04-1999 First published January 1969 First revision July 1980 The following BSI references relate to the work on this

3、 standard: Committee reference FAC/6 Draft for comment79/50881DC ISBN 0 580 11486 4 Cooperating organizations The Food and Agriculture Standards Committee, under whose direction this British Standard was prepared, consists of representatives from the following Government departments and scientific a

4、nd industrial organizations: Agricultural Co-operation and Marketing Services Agricultural Research Council, Meat Research Institute* British Food Manufacturing Industries Research Association* British Industrial Biological Research Association Ltd. Campden Food Preservation Research Association Con

5、sumer Standards Advisory Committee of BSI Department of Agriculture and Fisheries for Scotland Department of Agriculture (Government of Northern Ireland) Department of Industry (Laboratory of the Government Chemist)* Flour Milling and Baking Research Association Food Manufacturers Federation Incorpo

6、rated Institute of Brewing Local Authority Coordinating Body of Trading Standards Ministry of Agriculture, Fisheries and Food* National Farmers Union* National Farmers Union of Scotland Tobacco Advisory Council The organizations marked with an asterisk in the above list, together with the following,

7、 were directly represented on the committee entrusted with the preparation of this British Standard: Bacon and Meat Manufacturers Association British Poultry Federation Limited Chemical Society, Analytical Division Institute of Meat Licensed Animal Slaughterers and Salvage Association Meat and Lives

8、tock Commission National Federation of Meat Traders Association (Inc) Public Health Laboratory Service Society of Chemical Industry Ulster Farmers Union Amendments issued since publication Amd. No. Date of issue CommentsBS4401-2:1980 BSI 04-1999 i Contents Page Cooperating organizations Inside front

9、 cover National foreword ii 1 Scope and field of application 1 2 Reference 1 3 Definition 1 4 Principle 1 5 Reagents 1 6 Apparatus 1 7 Sample 1 8 Procedure 2 9 Expression of results 3 10 Notes on procedure 3 11 Test report 3 Publications referred to Inside back coverBS4401-2:1980 ii BSI 04-1999 Nati

10、onal foreword This Part of this British Standard is identical with ISO937-1978 “Meat and meat products Determination of nitrogen content (Reference method)” published by the International Organization for Standardization (ISO) and prepared by Subcommittee6, Meat and meat products, of Technical Commi

11、ttee34, Agricultural food products. BS4401-2was first published in1969 and was related to ISO/R937-1969. Following publication of an international standard dealing with methods for sampling meat and meat products, ISO/R937-1969 was revised and was published as ISO937-1978. This first revision of BS4

12、401-2 has been published to align the British Standard with the text of ISO937-1978. Other Parts of this British Standard are: Part1: Determination of ash (identical with ISO936); Part3: Determination of moisture content (technically equivalent to ISO1442); Part4: Determination of total fat content

13、(includes a method technically equivalent to ISO1443); Part5: Determination of free fat content (technically equivalent to ISO1444); Part6: Determination of chloride content (technically equivalent to ISO/R1841); Part7: Determination of nitrate content (related to ISO3091); Part8: Determination of n

14、itrite content (related to ISO2918); Part9: Measurement of pH (identical with ISO2917); Part10: Determination of total phosphorus content (identical with ISO2294); Part11: Determination of L()-hydroxyproline content (reference method) (identical with ISO3496); Part12: Determination of starch content

15、 of meat products (reference method) (identical with ISO5554); Part13: Determination of glucono-delta-lactone content (reference method) (identical with ISO4133); Part14: Determination of L-(+)-glutamic acid content (reference method) (identical with ISO4134). Terminology and conventions. The text o

16、f the international standard has been approved as suitable for publication, without deviation, as a British Standard. Some terminology and certain conventions are not identical with those used in British Standards; attention is especially drawn to the following: Wherever the words “International Sta

17、ndard” appear, referring to this publication, they should be read as “British Standard”. The comma has been used throughout as a decimal marker. In British Standards it is current practice to use a full point on the baseline as the decimal marker. NOTE 1The general reference to ISO3100 in clause2 an

18、d7.1 applies at present only to ISO3100/I-1975 which is related to BS5348-1:1976; subsequent Parts of ISO3100 are expected to be published as dual-numbered Parts of BS5348. NOTE 2The reference to ISO1871 in footnote1) to clause1 is for information only and the lack of an equivalent British Standard

19、therefore does not affect the validity of this standard. With reference to6.3, a burette complying with the requirements of BS846 “Burettes and bulb burettes” will satisfy the relevant requirements of ISO/R385. Cross-references International standard Corresponding British Standard ISO3100 (see note)

20、 BS5348 Methods for sampling meat and meat productsBS4401-2:1980 BSI 04-1999 iii Additional information. With reference to clause5, water complying with the requirements of BS3978 “Water for laboratory use” is suitable. With reference to6.6, if asbestos is used as part of the heating device, attenti

21、on is drawn to the importance of preventing the release of asbestos fibres. A British Standard does not purport to include all the necessary provisions of a contract. Users of British Standards are responsible for their correct application. Compliance with a British Standard does not of itself confe

22、r immunity from legal obligations. Summary of pages This document comprises a front cover, an inside front cover, pages i to iv, pages1to4, an inside back cover and a back cover. This standard has been updated (see copyright date) and may have had amendments incorporated. This will be indicated in t

23、he amendment table on theinside front cover.iv blankBS4401-2:1980 BSI 04-1999 1 1 Scope and field of application This International Standard specifies a reference method for the determination of the nitrogen content of meat and meat products 1) . 2 Reference ISO3100, Meat and meat products Sampling.

24、 3 Definition nitrogen content of meat and meat products the quantity of nitrogen corresponding to the ammonia produced and determined under the conditions specified below 4 Principle Digestion of a test portion with concentrated sulphuric acid, using copper(II) sulphate as a catalyst, to convert or

25、ganic nitrogen to ammonium ions; alkalisation, distillation of the liberated ammonia into an excess of boric acid solution, titration with hydrochloric acid to determine the ammonia bound by the boric acid, and calculation of the nitrogen content of the sample from the amount of ammonia produced. 5

26、Reagents All reagents shall be of recognized analytical quality. The water used shall be distilled water or water of at least equivalent purity. 5.1 Copper(II) sulphate pentahydrate (CuSO 4 .5H 2 O). 5.2 Potassium sulphate (K 2 SO 4 ), anhydrous. 5.3 Sulphuric acid, 201,84g/ml. 5.4 Sodium hydroxide

27、solution, carbonate-free, containing approximately33g of sodium hydroxide (NaOH) per100g of solution. Dissolve500g of sodium hydroxide in1000ml of water. 5.5 Boric acid solution. Dissolve40g of boric acid (H 3 BO 3 ) in water and dilute to1000ml. 5.6 Hydrochloric acid,0,1N standard volumetric soluti

28、on, the normality being known to four decimal places. 5.7 Indicator solution: mixed indicator (methyl red-methylene blue) 2) , prepared by dissolving2g of methyl red and1g of methylene blue in1000 ml of95 % (V/V) ethanol. The colour change of this indicator solution occurs at a pH of5,4. Store the i

29、ndicator solution in a brown bottle in a dark and cool place. 5.8 Boiling regulators 5.8.1 For the digestion Glass beads, silicon carbide or splinters of hard porcelain. 5.8.2 For the distillation Silicon carbide or freshly ignited pieces of pumice stone. 6 Apparatus Usual laboratory apparatus not o

30、therwise specified, and the following items: 6.1 Mechanical meat mincer, laboratory size fitted with a plate with holes of diameter not exceeding4mm. 6.2 Greaseproof paper, pieces about9cm 6cm. 6.3 Burette,50ml, complying with ISO/R385, class A. 6.4 Kjeldahl flask, of not more than800ml capacity, pr

31、ovided, if desired, with a pear-shaped glass bulb loosely fitting on top of the neck. 6.5 Steam distillation apparatus or, alternatively, ordinary distillation apparatus. 6.6 Heating device, on which the Kjeldahl flask can be heated in an inclined position in such a way that the source of heat touch

32、es only that part of the flask wall which is below the liquid level. For gas heating, a suitable device is a plate of asbestos provided with a circular hole, so that only the lower part of the flask is exposed to the free flame. 6.7 Effective suction device, for the acid fumes evolved during the dig

33、estion. 6.8 Analytical balance. 7 Sample 7.1 Proceed from a representative sample of at least200g. See ISO3100. 7.2 Store the sample in such a way that deterioration and change in composition are prevented. Preservatives, if any, should not contain nitrogen compounds in measurable amounts. 1) See al

34、so ISO1871, Agricultural food products General directions for the determination of nitrogen by the Kjeldahl method. 2) Sometimes known as Tashiro indicator.BS4401-2:1980 2 BSI 04-1999 8 Procedure 8.1 Preparation of the test sample Homogenize the sample by passing it at least twice through the meat m

35、incer (6.1) and mixing. Keep it in a completely filled, air-tight, closed container and store it in such a way that deterioration and change in composition are prevented. Analyse the sample as soon as possible after homogenization, but always within24h. 8.2 Test portion Place a few boiling regulator

36、s(5.8) into the Kjeldahl flask(6.4), then add about15g of the anhydrous potassium sulphate(5.2) and0,5g of the copper(II) sulphate(5.1). Weigh, to the nearest0,001g, about2g (or1,5g in the case of a sample rich in fat) of the test sample(8.1) on a piece of greaseproof paper(6.2). Transfer the grease

37、proof paper and the test portion to the Kjeldahl flask. 8.3 Determination Add25ml of the sulphuric acid(5.3) to the Kjeldahl flask. Mix by gently swirling the liquid. If desired, a pear-shaped glass bulb may be inserted into the neck of the flask with its tapering end downwards. Place the flask in a

38、n inclined position (at an angle of about40 from the vertical position) on the heating device(6.6). At first heat the flask gently until foaming has ceased and the contents have become completely liquefied. Then digest by boiling vigorously, occasionally rotating the flask, until the liquid has beco

39、me completely clear and of a light blue-green colour. Keep the liquid boiling for another90min. The total digestion time should not be less than2h. Take care that no condensed liquid runs down the outside of the flask. Prevent the escape of too much sulphuric acid caused by overheating during the di

40、gestion, as this is likely to result in a loss of nitrogen. Cool to about40 C and cautiously add about50ml of water. Mix and allow to cool. Pour into a conical flask, of capacity about500ml,50ml of the boric acid solution(5.5) from a measuring cylinder, add4 drops of the indicator solution(5.7), mix

41、 and place the flask under the condenser of the distillation apparatus(6.5) so that the outlet of the adapter dips into the liquid. Treat the contents of the Kjeldahl flask in one of the following ways: a) In the case of steam distillation Transfer the contents of the Kjeldahl flask to the distillat

42、ion apparatus and rinse the flask with about50ml of water. Add100ml of the sodium hydroxide solution(5.4) by means of a measuring cylinder, pouring carefully along the inclined neck of the flask so that the two layers in the flask do not mix. Immediately attach the flask to the splash-head of the di

43、stillation apparatus. Heat the alkaline liquid by passing steam through it until boiling and keep it so for20min. At first heat gently to minimize foaming. The collected volume of distillate should be at least150ml. b) In the case of ordinary distillation Cautiously dilute the contents of the Kjelda

44、hl flask with about300ml of water and swirl. If desired, transfer to a1litre flask. After about15min, add100ml of the sodium hydroxide solution(5.4) by means of a measuring cylinder, pouring carefully along the inclined neck of the flask so that the two layers in the flask do not mix. Immediately at

45、tach the flask to the splash-head of the distillation apparatus. Distil at least,150ml of liquid, even if the mixture bumps irregularly. Continue the distillation until the mixture starts bumping or until250ml of distillate has been collected. Make sure that the distillate is cooled effectively, and

46、 prevent the boric acid solution from becoming warm. In either case, lower the conical flask just before terminating the distillation, so that the outlet of the adapter is above the liquid level. Rinse the outlet of the adapter above the liquid (internally and externally) with a little water. Verify

47、 the completion of the ammonia distillation with red litmus paper, wetted with distilled water; its colour should not be affected by the liquid dripping from the condenser. Stop heating. If the distillation is found to be incomplete, carry out a new determination, carefully following the instruction

48、s. Titrate the contents of the conical flask with the hydrochloric acid solution(5.6). Record the volume of hydrochloric acid solution required, estimated to the nearest0,02ml. Carry out two determinations on test portions taken from the same test sample. 8.4 Blank test Always perform a blank test (

49、in duplicate) when fresh batches of reagents, or freshly prepared solutions are used. It is advisable to carry out a blank test occasionally for reagents and solutions which have already been in use for some time. Carry out this blank test according to8.3, taking a piece of greaseproof paper(6.2) only.BS4401-2:1980 BSI 04-1999 3 9 Expression of results 9.1 Method of calculation and formula The nitrogen content of the sample, expressed as a percentage by mass, is equal to where V 0 is the volume, in millilitres, of0,1N hydrochlor