BS 6049-3-1994 Methods of test for tea - Determination of water extract《茶叶试验方法 第3部分 水萃取物测定》.pdf

1、BRITISH STANDARD BS6049-3: 1994 ISO 9768:1994 Incorporating Amendment No.1 Methods of test for Tea Part3: Determination of water extractBS6049-3:1994 This British Standard, having been prepared under the directionof the Consumer Products and Services Sector Board, was published under theauthority of

2、 the Standards Boardand comes into effect on 15 December 1994 BSI 05-1999 First published December 1980 Second edition November 1990 Third edition December 1994 The following BSI references relate to the work on this standard: Committee reference AW/8 Draft for comment 92/56272 DC ISBN 0 580 23531 9

3、 Committees responsible for this British Standard The preparation of this British Standard was entrusted by the Consumer Products and Services Sector Board to Technical Committee AW/8, upon which the following bodies were represented: Campden Food and Drink Research Association Ministry of Agricultu

4、re, Fisheries and Food Natural Resources Institute Tea Trade Technical Committee United Kingdom Tea Association Amendments issued since publication Amd. No. Date Comments 10193 October 1998 Indicated by a sideline in the marginBS 6049-3:1994 BSI 05-1999 i Contents Page Committees responsible Inside

5、front cover National foreword ii 1 Scope 1 2 Normative reference 1 3 Definition 1 4 Principle 1 5 Apparatus 1 6 Sampling 1 7 Preparation of test sample 1 8 Procedure 1 9 Calculation 2 10 Precision 2 11 Test report 2 Annex A (informative) Statistical results of interlaboratory tests on tea 3 List of

6、references Inside back coverBS 6049-3:1994 ii BSI 05-1999 National foreword This Part of BS6049 has been prepared under the direction of the Consumer Products and Services Sector Board. It supersedes the 1990 edition of BS6049-3, which is withdrawn, and implements an agreement, to which the UK was a

7、 party, reached in Subcommittee8, Tea, of Technical Committee TC34, Agricultural food products, of the International Organization for Standardization (ISO). The UK also provides the secretariat for the Subcommittee. This Part of BS6049 is identical with ISO9768:1994 Tea Determination of water extrac

8、t. The principal difference between this Part of BS6049 and the 1990 edition is that provision has been made for grinding very large leaf teas before the determination. The details of statistical results of interlaboratory tests given in Annex A are supplied for information only. Cross-references Th

9、is standard describes a method of test only and should not be referred to as a specification defining limits of purity. Reference to the standard should indicate that the method of test used is in accordance with BS6049-3. A British Standard does not purport to include all the necessary provisions o

10、f 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. International standard Corresponding British Standard ISO1573:1980 BS6049 Methods of test for tea Part2:1981 Determina

11、tion of loss in mass at103C (Identical) ISO1839:1980 BS5987:1980 Methods for sampling tea (Identical) ISO5725:1986 BS5497 Precision of test methods Part1:1987 Guide for the determination of repeatability and reproducibility for a standard test method by inter-laboratory tests (Identical) Summary of

12、pages This document comprises a front cover, an inside front cover, pagesi andii, pages1 to4, 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 the amendment table on the inside front cover.I

13、SO 9768:1994(E) BSI 05-1999 1 1 Scope This International Standard specifies a method for the determination of the water extract from tea. 2 Normative reference The following standard contains provisions which, through reference in this text, constitute provisions of this International Standard. At t

14、he time of publication, the edition indicated was 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 edition of the standard indicated below. Members of IEC and ISO mai

15、ntain registers of currently valid International Standards. ISO1573:1980, Tea Determination of loss in mass at103C. 3 Definition For the purposes of this International Standard, the following definition applies. 3.1 water extract the soluble matter extracted from a test portion by boiling water, und

16、er the conditions specified in this International Standard, expressed as a percentage by mass on a dry basis 4 Principle Extraction of soluble matter from a test portion of the product by means of water boiling under reflux. Filtration, washing, drying and weighing of the hotwater-insoluble residue.

17、 Calculation of the water extract. 5 Apparatus Usual laboratory apparatus and, in particular, the following. 5.1 Oven, constant-temperature and fan-assisted, capable of being operated at103C 2 C. 5.2 Crucible, made of sintered borosilicate glass, of porosity grade P160 (pore size index1004m to 1604m

18、),40mm in diameter and of70ml capacity. 5.3 Desiccator, containing an efficient desiccant. 5.4 Flask, of500ml capacity, fitted with a reflux condenser. 5.5 Filter flask, of1litre capacity, for vacuum filtration. 5.6 Test sieves, of nominal aperture size1,4mm and3mm. 5.7 Analytical balance, capable o

19、f weighing to an accuracy of0,001g. 6 Sampling It is important that the laboratory receive a sample which is truly representative and has not been damaged or changed during transport or storage. Sampling is not part of the method specified in this International Standard. A recommended sampling metho

20、d is given in ISO1839. 1) 7 Preparation of test sample Use a test sample of known dry matter content, determined using the method specified in ISO1573. Teas of which60% or more is retained on a1,4mm sieve shall be ground to pass a3mm sieve prior to analysis. 8 Procedure NOTE 1If it is required to ch

21、eck whether the repeatability requirement is met, carry out two determinations on the same test sample. 8.1 Preparation of the crucible Heat the clean crucible(5.2) for1h in the oven(5.1) set at103 C. Cool in the desiccator(5.3) and weigh to the nearest0,001g. 8.2 Test portion Weigh, to the nearest0

22、,001 g,2g of the test sample (clause7) into the flask(5.4). 8.3 Determination Add to the test portion(8.2)200 ml of hot distilled water, or water of at least equivalent purity, and reflux over low heat for1h, rotating the flask occasionally. Filter hot under vacuum through the prepared crucible (8.1

23、) using the filter flask(5.5). Repeatedly wash out the flask with hot distilled water, transferring all the insoluble residue into the crucible. Finally, wash the residue with200ml of hot distilled water. Dry the residue by suction. Heat the crucible and its contents in the oven(5.1) set at103C for1

24、6h (i.e.overnight). Cool in the desiccator(5.3) and weigh to the nearest0,001g. 1) ISO1839:1980, Tea Sampling.ISO 9768:1994(E) 2 BSI 05-1999 9 Calculation The water extract yielded by the test sample, expressed as a percentage by mass on a dry basis, is given by the formula where 10 Precision See An

25、nex A for statistical results of interlaboratory tests. 10.1 Repeatability The absolute difference between two independent test results, obtained using the same method on identical test material in the same laboratory by the same operator using the same equipment within a short interval of time, sho

26、uld not be greater than1,0% (m/m). 10.2 Reproducibility The absolute difference between two single test results, obtained using the same method on identical test material in different laboratories with different operators using different equipment, should not be greater than2,5% (m/m). 11 Test repor

27、t The test report shall specify the method in accordance with which sampling was carried out, if known, the method used, the test result obtained, and if the repeatability has been checked, the final quoted result obtained. It shall also mention all operating details not specified in this Internatio

28、nal Standard, or regarded as optional, together with details of any incidents which may have influenced the result. The test report shall include all information necessary for the complete identification of the sample. m 0 is the mass, in grams, of the testportion; m 1 is the mass, in grams, of the

29、dried insoluble residue; w is the dry matter content, expressed as a percentage by mass, of the test sample. It is equal to100minus the loss in mass at103C determined using the method specified in ISO1573. m 0 w ()m 1 100 () m 0 w -100 ISO 9768:1994(E) BSI 05-1999 3 Annex A (informative) Statistical

30、 results of interlaboratory tests on tea Four interlaboratory tests, carried out between 1984 and 1989 under the auspices of the International Organization for Standardization, gave the following statistical results (evaluated in accordance with ISO5725 2) . Year 1984 1986 1988 1989 Number of labora

31、tories 7 21 16 10 Number of samples 3 6 6 3 Repeatability, r 0,877 to1,259 0,677 to1,114 1,37 to1,60 0,50 to0,63 Reproducibility, R 1,252 to1,422 1,871 to2,934 4,69 to6,19 1,02 to1,45 2) ISO 5725:1986, Precision of test methods Determination of repeatability and reproducibility for a standard test m

32、ethod by inter-laboratory tests.4 blankBS 6049-3:1994 BSI 05-1999 List of references See national foreword.BS 6049-3: 1994 ISO 9768:1994 BSI 389 Chiswick High Road London W4 4AL BSIBritishStandardsInstitution BSI is the independent national body responsible for preparing BritishStandards. It present

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