1、BRITISH STANDARD BS 4325-6: 1989 ISO 5506: 1988 Methods for Analysis of oilseed residues Part 6: Determination of urease activity of soya bean products ISO title: Soya bean products Determination of urease activity UDC 633.85 157.63.002.6:543.8 + 635.853.52 157.63.002.6:577.15:543.866:543.25BS 4325-
2、6:1989 This British Standard, having been prepared under the directionof the Food and Agriculture Standards Policy Committee, was published underthe authority of the Board ofBSI and comes into effect on 29September 1989 BSI10-1999 First published March1980 First revision September1989 The following
3、BSI references relate to the work on this standard: Committee reference FAC/17 Draft (ref. 88/53838) announced inBSI News September 1988 ISBN 0 580 17380 1 Committees responsible for this British Standard The preparation of this British Standard was entrusted by the Food and Agriculture Standards Po
4、licy Committee (FAC/-) to Technical Committee FAC/17, upon which the following bodies were represented: British Food Manufacturing Industries Research Association Department of Trade and Industry (Laboratory of the Government Chemist) FOSFA International Grain and Feed Trade Association Internationa
5、l Association of Seed Crushers Intervention Board for Agricultural Produce Ministry of Agriculture, Fisheries and Food National Farmers Union National Institute of Agricultural Botany Overseas Development Natural Resources Institute Royal Society of Chemistry Seed Crushers and Oil Processors Associa
6、tion Tropical Growers Association Amendments issued since publication Amd. No. Date of issue CommentsBS 4325-6:1989 BSI 10-1999 i Contents Page Committees responsible Inside front cover National foreword ii Introduction 1 1 Scope 1 2 Normative references 1 3 Definition 1 4 Principle 1 5 Reagents 1 6
7、 Apparatus 1 7 Sampling 1 8 Preparation of the test sample 2 9 Procedure 2 10 Expression of results 2 11 Test report 2 Publications referred to Inside back coverBS 4325-6:1989 ii BSI 10-1999 National foreword This Part of BS 4325 has been prepared under the direction of the Food and Agriculture Stan
8、dards Policy Committee. It is identical with ISO 5506:1988 “Soya bean products Determination of urease activity”, published by the International Organization for Standardization (ISO), and in the preparation of which the United Kingdom played a full part. It is a revision of BS 4325-6:1980, which is
9、 withdrawn, and from which it differs principally in that the presentation has been changed to produce a clearer and more logical text, and that it is now recommended that samples having a fat content of higher than 10% (m/m) be defatted by cold extraction. Terminology and conventions. The text of t
10、he International Standard has been approved as suitable for publication as a British Standard without deviation. Some terminology and certain conventions are not identical with those used in British Standards; attention is drawn especially to the following. The comma has been used as a decimal marke
11、r. In British Standards it is current practice to use a full point on the baseline as the decimal marker. The symbol “l” has been used to denote litre (and in its submultiples). In British Standards it is current practice to use the symbol “L”. Wherever the words “International Standard” appear, ref
12、erring to this standard, they should be read as “Part of BS 4325”. Additional information. With reference to clause5, water complying with grade 3 of BS 3978 “Specification for water for laboratory use” is suitable. In relation to 6.1, requirements for suitable test sieves are given in BS 410 “Speci
13、fication for test sieves”. Textual errors. When adopting the text of the International Standard, the textual errors given below were discovered. They have been marked in the text and have been reported to ISO in a proposal to amend the text of the International Standard. In clause 2 and clause 7 ISO
14、 5505 should be read as ISO5500. 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 confer immunity from legal obligations. Cross-re
15、ferences International Standard Corresponding British Standard BS 4325 Methods for analysis of oilseed residues ISO 771:1977 Part 1:1978 Determination of moisture and volatile matter content (Technically equivalent) ISO 5502:1983 Part 9:1984 Preparation of test samples (Identical) ISO 5500:1986 BS 6
16、606:1987 Methods for sampling oilseed residues (Identical) Summary of pages This document comprises a front cover, an inside front cover, pagesi andii, pages1 and 2, an inside back cover and a back cover. This standard has been updated (see copyright date) and may have had amendments incorporated. T
17、his will be indicated in the amendment table on the inside front cover.BS 4325-6:1989 BSI 10-1999 1 Introduction The method specified in this International Standard is based on the property of soya bean products of being able to liberate ammoniacal nitrogen from a urea solution when they have not be
18、en sufficiently cooked. 1 Scope This International Standard specifies a method of determining the urease activity of products derived from soya beans. The method allows inadequate cooking of these products to be detected. It applies to products having a urease activity of less than 1mg of nitrogen p
19、er gram of product as received, under the conditions specified. For more active products, the method applies provided that the mass of the test portion is reduced (see note 1 to9.1). 2 Normative references The following standards contain provisions which, through reference in this text, constitute p
20、rovisions of this International Standard. At the time of publication, the editions indicated were valid. All standards are subject to revision, and parties to agreements based on this International Standard are encouraged to investigate the possibility of applying the most recent editions of the sta
21、ndards listed below. Members of IEC and ISO maintain registers of currently valid International Standards. ISO 771:1977, Oilseed residues Determination of moisture and volatile matter content. ISO 5502:1983, Oilseed residues Preparation of test samples. ISO 5505:1986, Oilseed residues Sampling 1) .
22、3 Definition For the purposes of this International Standard, the following definition applies. 3.1 urease activity amount of ammoniacal nitrogen liberated per minute under the operating conditions specified in this International Standard, expressed as milligrams of nitrogen per gram of the product
23、as received 4 Principle Mixing of a ground test portion with a buffered urea solution. After keeping the mixture for 30 min at30 C, neutralization of the ammonia liberated, with an excess of hydrochloric acid solution, and back-titration with standard volumetric sodium hydroxide solution. 5 Reagents
24、 All the reagents shall be of analytical quality and the water used shall be distilled water or water of equivalent purity. 5.1 Urea, buffer solution (pH 6,9 to 7,0). Prepare a buffer solution by dissolving 4,45 g of disodium hydrogen phosphate dihydrate (Na 2 HPO 4 2H 2 O) and 3,40g of potassium di
25、hydrogen phosphate (KH 2 PO 4 ) in water and making up to 1000ml. Dissolve 30g of urea (NH 2 CONH 2 ) in the buffer solution. The solution thus prepared has a storage life of1month. 5.2 Hydrochloric acid, 0,1 mol/l solution. 5.3 Sodium hydroxide, standard volumetric solution, c(NaOH) = 0,1 mol/l. 6
26、Apparatus Usual laboratory apparatus and, in particular, the following. 6.1 Sieve, of 200 4m aperture size. 6.2 Apparatus for potentiometric titration 2) , or pHmeter, sensitive to the nearest 0,02 pH unit, withan automatic burette and magnetic stirrer. 6.3 Titration flask 6.4 Thermostatically contr
27、olled water-bath, capable of being controlled at 30 C 0,5 C. 6.5 Test tubes, 18 mm in diameter and 150 mm in length, fitted with a ground-in stopper. 6.6 Pipettes, of 10 ml capacity. 6.7 Grinding device, capable of grinding without significant heating (for example a ball mill). 6.8 Chronometer 6.9 A
28、nalytical balance 7 Sampling Sampling shall be carried out in accordance with 1)ISO 5505. 1) See national foreword for details of textual errors. 2) An automatic titration apparatus allows more reproducible results to be obtained.BS 4325-6:1989 2 BSI 10-1999 8 Preparation of the test sample See ISO
29、5502:1983 and particularly subclause5.4. Using the grinding device (6.7), grind 10g of the sample for analysis to particles which pass completely through the sieve (6.1). 9 Procedure 9.1 Test portion Transfer into a test tube (6.5) about 0,2g of the test sample (clause8), weighed to the nearest 0,1m
30、g. NOTE 1For samples of very high activity, the test portion may be reduced to 0,05 g. NOTE 2It is recommended that samples having a fat content of more than 10 % (m/m) be defatted previously by cold extraction. 9.2 Determination Using a pipette (6.6), add 10ml of the buffered urea solution (5.1). S
31、topper the tube immediately and shake vigorously. Place the test tube in the water-bath (6.4) at30 C 0,5 C and keep it there for 30min measured with the chronometer (6.8). Using a pipette (6.6), immediately add 10 ml of the hydrochloric acid solution (5.2), cool rapidly to20 C and transfer the conte
32、nts of the test tube quantitatively into the titration flask (6.3), rinsing the test tube twice with5ml portions of water. Titrate immediately and rapidly with the sodium hydroxide solution (5.3) to pH4,70, preferably using the potentiometric apparatus (6.2). 9.3 Number of determinations Carry out t
33、wo determinations on test portions from the same test sample. 9.4 Blank test Introduce into a test tube (6.5) 10ml of the buffered urea solution (5.1) and 10ml of the hydrochloric acid solution (5.2), measured with a pipette (6.6). Rapidly add a test portion equal to that used for the main determina
34、tion, weighed to the nearest0,1mg. Stopper the tube immediately and shake vigorously. Place the test tube in the water-bath (6.4) at30 C 0,5 C and keep it there for30min measured with the chronometer (6.8). Cool to20 C, transfer the contents of the test tube to the titration flask (6.3) as specified
35、 in 9.2, and titrate with the sodium hydroxide solution (5.3) to pH4,70. 10 Expression of results 10.1 Method of calculation The urease activity, U, expressed in milligrams of nitrogen liberated per minute per gram of the product as received, is given by the formula where Take as the result the arit
36、hmetic mean of the two determinations, if the requirement for repeatability (see10.2) is satisfied. Express the result to two decimal places. NOTE 1If a preliminary drying was carried out (see clause8), modify the calculation accordingly. NOTE 2If the urease activity is to be expressed in relation t
37、o the dry material, it is then equal to where 10.2 Repeatability The difference between the values of two determinations, carried out in rapid succession by the same analyst using the same equipment on the same test sample, shall not exceed10% of the arithmetric mean value. 11 Test report The test r
38、eport shall specify the method used and the result obtained. It shall also mention all operating details not specified in this International Standard, or regarded as optional, together with details of any incidents which may have influenced the result. The test report shall include all information n
39、ecessary for the complete identification of the sample. V 0is the volume, in millilitres, of 0,1 mol/l sodium hydroxide solution used for the blank test (9.4); V 1is the volume, in millilitres, of 0,1 mol/l sodium hydroxide solution used in the determination (9.2); m is the mass, in grams, of the te
40、st portion (9.1); c is the exact concentration, in moles per litre, of the sodium hydroxide solution used. U is the urease activity calculated using the formula above; H is the moisture and volatile matter content of the product, as a percentage by mass, determined in accordance with ISO771. U 14c V
41、 0 V 1 () 30m - = U 100 100H - BS 4325-6:1989 BSI 10-1999 Publications referred to See national foreword.BS 4325-6: 1989 ISO5506: 1988 BSI 389 Chiswick High Road London W4 4AL BSIBritishStandardsInstitution BSI is the independent national body responsible for preparing BritishStandards. It presents
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