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1、| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | BRITISH STANDARD BS EN 1788 : 1997 The Eur
2、opean Standard EN 1788 : 1996 has the status of a British Standard ICS 67.020 NO COPYING WITHOUT BSI PERMISSION EXCEPT AS PERMITTED BY COPYRIGHT LAW Foodstuffs Detection of irradiated food from which silicate minerals can be isolated Method by thermoluminescence Licensed Copy: sheffieldun sheffieldu
3、n, na, Fri Nov 17 08:44:01 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS EN 1788 : 1997 This British Standard, having been prepared under the direction of the Consumer Products and Services Sector Board, was published under the authority of the Standards Board and comes into effect on 15 June 1997 B
4、SI 1997 The following BSI references relate to the work on this standard: Committee reference AW/-/3 Draft for comment 95/500046 DC ISBN 0 580 27446 2 Amendments issued since publication Amd. No.DateText affected Committees responsible for this British Standard The preparation of this British Standa
5、rd was entrusted to Technical Panel AW/-/3, Food analysis Horizontal methods, upon which the following bodies were represented: Association of Public Analysts Food and Drink Federation Institute of Food Science and Technology Laboratory of the Government Chemist Ministry of Agriculture, Fisheries an
6、d Food Royal Society of Chemistry Licensed Copy: sheffieldun sheffieldun, na, Fri Nov 17 08:44:01 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS EN 1788 : 1997 BSI 1997i Contents Page Committees responsibleInside front cover National forewordii Foreword2 Text of EN 17883 Licensed Copy: sheffieldun sh
7、effieldun, na, Fri Nov 17 08:44:01 GMT+00:00 2006, Uncontrolled Copy, (c) BSI ii BSI 1997 BS EN 1788 : 1997 National foreword This British Standard has been prepared under the direction of Technical Panel AW/-/3 and is the English language version of EN 1788 : 1996 Foodstuffs Detection of irradiated
8、 food from which silicate minerals can be isolated Method by thermoluminescence, published by the European Committee for Standardization (CEN). EN 1788 was produced as a result of international discussions in which the United Kingdom took an active part. Cross-reference Publication referred toCorres
9、ponding British Standard EN ISO 3696 : 1995BS EN ISO 3696 : 1995 Water for analytical laboratory use. Specification and test methods Compliance with a British Standard does not of itself confer immunity from legal obligations. Summary of pages This document comprises a front cover, an inside front c
10、over, pages i and ii, the EN title page, pages 2 to 14, an inside back cover and a back cover. Licensed Copy: sheffieldun sheffieldun, na, Fri Nov 17 08:44:01 GMT+00:00 2006, Uncontrolled Copy, (c) BSI CEN European Committee for Standardization Comite Europe en de Normalisation Europa isches Komitee
11、 fu r Normung Central Secretariat: rue de Stassart 36, B-1050 Brussels 1996 Copyright reserved to CEN members Ref. No. EN 1788 : 1996 E EUROPEAN STANDARDEN 1788 NORME EUROPE ENNE EUROPA ISCHE NORM December 1996 ICS 67.020 Descriptors: Foodstuffs, irradiated foodstuffs, ionizing radiation, food analy
12、sis, detection of irradiation treatment, silicate minerals, thermoluminescence English version Foodstuffs Detection of irradiated food from which silicate minerals can be isolated Method by thermoluminescence Produits alimentaires De tection des aliments ionise s dont les mine raux silicate s peuven
13、t e tre isole s Me thode par thermoluminescence Lebensmittel Nachweis von bestrahlten Lebensmitteln, von denen Silikatmineralien isoliert werden ko nnen Verfahren mittels Thermolumineszenz This European Standard was approved by CEN on 1996-12-05. CEN members are bound to comply with the CEN/CENELEC
14、Internal Regulations which stipulate the conditions for giving this European Standard the status of a national standard without any alteration. Up-to-date lists and bibliographical references concerning such national standards may be obtained on application to the Central Secretariat or to any CEN m
15、ember. This European Standard exists in three official versions (English, French, German). A version in any other language made by translation under the responsibility of a CEN member into its own language and notified to the Central Secretariat has the same status as the official versions. CEN memb
16、ers are the national standards bodies of Austria, Belgium, Denmark, Finland, France, Germany, Greece, Iceland, Ireland, Italy Luxembourg, Netherlands, Norway, Portugal, Spain, Sweden, Switzerland and United Kingdom. Licensed Copy: sheffieldun sheffieldun, na, Fri Nov 17 08:44:01 GMT+00:00 2006, Unco
17、ntrolled Copy, (c) BSI Page 2 EN 1788 : 1996 BSI 1997 Foreword This European Standard has been prepared by CEN/TC 275, Food analysis Horizontal methods, the Secretariat of which is held by DIN. This European Standard was elaborated on the basis of a protocol developed following a concerted action su
18、pported by the Commission of European Union (XII C.5). Experts and laboratories from EU and EFTA countries contributed jointly to the development of this protocol. This European Standard shall be given the status of a national standard, either by publication of an identical text or by endorsement, a
19、t the latest by June 1997, and conflicting national standards shall be withdrawn at the latest by June 1997. According to the CEN/CENELEC Internal Regulations, the national standards organizations of the following countries are bound to implement this European Standard: Austria, Belgium, Denmark, Fi
20、nland, France, Germany, Greece, Iceland, Ireland, Italy, Luxembourg, Netherlands, Norway, Portugal, Spain, Sweden, Switzerland and the United Kingdom. Contents Page Foreword2 1Scope3 2Normative references3 3Definitions3 4Principle3 5Reagents4 6Apparatus4 7Sampling technique4 8Procedure4 9Evaluation6
21、 10Limitations7 11Validation7 12Test report7 Annexes A(normative) Estimation of blank levels8 B(normative) Practical example for defining temperature intervals of the TL heating unit9 C(informative) Examples for TL glow curves using various readers10 D(informative) Bibliography12 Licensed Copy: shef
22、fieldun sheffieldun, na, Fri Nov 17 08:44:01 GMT+00:00 2006, Uncontrolled Copy, (c) BSI Page 3 EN 1788 : 1996 BSI 1997 1 Scope This European Standard specifies a method for the detection of irradiation treatment of food by thermoluminescence analysis of contaminating silicate minerals. This method i
23、s applicable to those foodstuffs from which a sufficient amount of silicate minerals can be isolated. The method has been successfully tested in inter-laboratory tests with herbs and spices as well as their mixtures, 1 to 3, and shrimps 4, 5. From other studies, including an inter-laboratory test on
24、 fresh fruits and vegetables, it may be concluded that the method, after suitable modification, is applicable to a large variety of foods including seafood 6 to 38. At present, this standard pertains only to the detection of the irradiation treatment of herbs, spices, their mixtures, and shrimps. 2
25、Normative references This European Standard incorporates by dated and undated reference, provisions from other publications. These normative references are cited at the appropriate places in the text and the publications are listed hereafter. For dated references, subsequent amendments to or revisio
26、ns of any of these publications apply to this European Standard only when incorporated in it by amendment or revision. For undated references the latest edition of the publication referred to applies. EN ISO 3696 : 1995Water for analytical laboratory use Specification and test methods (ISO 3696 : 19
27、87) 3 Definitions For the purposes of this standard, the following definitions apply. 3.1 thermoluminescence (TL) The light emission which occurs on heating a solid material, in addition to black body radiation, due to the thermally stimulated release of trapped charge carriers. 3.2 TL intensity The
28、 amount of light detected per unit temperature interval at a given heating rate. The integrated TL intensity over a stated temperature interval is measured in photon counts or coulombs. 3.3 glow curve The variation of TL intensity with temperature. The integral of the glow curve is expressed in coun
29、ts or coulombs depending on the apparatus used. 3.4 glow 1 The glow curve recorded from the minerals of the prepared sample as received. 3.5 glow 2 The glow curve recorded from the minerals of the prepared sample after measurement of glow 1 and a subsequent exposure to a fixed known dose of radiatio
30、n for the purpose of normalization. 3.6 TL glow ratio The ratio of integrated TL intensities of glow 1 to glow 2, evaluated over a stated temperature interval. 3.7 Minimum Detectable integrated TL intensity Level (MDL) The full process blank level (glow 1) plus three standard deviations (full proces
31、s blank levels should be measured in parallel with sample extractions using portions of the same stock solutions and following the procedure in all stages) defines the MDL, which should be consistent with freedom from contamination of discs, glassware and reagents. 3.8 background of the TL reader In
32、tegrated TL intensity measured without sample disc over the whole temperature range studied. 4 Principle Silicate minerals contaminating food products store energy by charge trapping processes as a result of exposure to ionizing radiation. Releasing such energy, by controlled heating of isolated sil
33、icate minerals, gives rise to measurable TL glow curves. Silicate minerals are therefore isolated from the food products, mostly by a density separation step. In order not to obscure the TL, the isolated silicate minerals should be as free as possible of organic constituents of the food. A first glo
34、w of the separated mineral extracts is recorded (glow 1). Since various amounts or types of minerals (quartz, feldspar, etc.) exhibit very variable integrated TL intensities after irradiation, a second TL glow (glow 2) of the same sample after exposure to a fixed dose of radiation is necessary to no
35、rmalize the TL response. The TL glow ratio, thus obtained, is used to indicate the irradiation treatment of the food, since the population of irradiated samples in principle yields higher TL glow ratios than those of unirradiated samples. Glow shape parameters offer additional evidence for identifyi
36、ng irradiated foods. This method of TL analysis relies only on the silicate minerals which can be separated from various foods and is principally not influenced by the kind of food product. Licensed Copy: sheffieldun sheffieldun, na, Fri Nov 17 08:44:01 GMT+00:00 2006, Uncontrolled Copy, (c) BSI Pag
37、e 4 EN 1788 : 1996 BSI 1997 1) c is the substance concentration. 2) Corning 7/59, Schott KG 1, and Schott BG 39are examples of suitable products available commercially. This information is given for the convenience of users of this standard and does not constitute an endorsement by CEN of these prod
38、ucts. 5 Reagents 5.1 General Use only reagents of recognized analytical grade. Water shall be of at least grade 3 according to EN ISO 3696 : 1995. All reagents shall be kept free from particulate contamination throughout the procedure. 5.2 Sodium polytungstate, Na6H2W12O40xH2O solution, with a densi
39、ty of 2 g/ml. The solution may be recovered and purified for re-use 2. 5.3 Hydrochloric acid, c1)(HCl) = 1 mol/l. 5.4 Ammonium hydroxide solution, c (NH4OH) = 1 mol/l. 5.5 Acetone. 5.6 Nitrogen gas, oxygen-free, for flushing the TL heating chamber. 5.7 Silicone spray (optional). 5.8 Ethanol. 6 Appar
40、atus 6.1 General All laboratory surfaces and glassware should be carefully cleaned. Use usual laboratory apparatus, and in particular the following. 6.2 TL reader, with glow curve recording facility and data evaluation; heating rate: about 6 C/s; maximum temperature required: at least 350 C; equippe
41、d with a suitable photomultiplier tube, e.g. a bi-alkali photocathode photomultiplier tube, in combination with filters to reject black body radiation. Acceptable filter combinations are Corning 7/59+ Schott KG 1 filters, or Schott BG 392), or equivalent. 6.3 Stainless steel discs, or shallow cups h
42、aving a diameter to suit the TL reader (usually about 9 mm up to 10 mm), and a thickness of 0,25 mm up to 0,5 mm. 6.4 Radiation source, capable of irradiating samples with a defined radiation dose before measurement of glow 2. In the inter-laboratory tests on herbs, spices, their mixtures, and shrim
43、ps 1 to 5, various sources delivering 60Co-g-rays have been employed at a fixed radiation dose of 1 kGy. NOTE 1. Other fixed doses may be suitable. NOTE 2. Alternatives to 60Co-g-rays may be used, provided they have been found to be satisfactory. 6.5 Ultrasonic bath, capable of fitting several beake
44、rs of 150 ml. 6.6 Nylon disposable sieves, comprising e.g.: 6.6.1 Mini-sieve set (51 mm in diameter), consisting of 2 rings between which the nylon sieve cloth is clamped. 6.6.2 Nylon sieve cloth, with pore sizes of 125 mm and 250 mm. 6.7 Centrifuge, supplied with a swing-out rotor and suitable glas
45、s tubes, e.g. of 10 ml to 15 ml capacity with pointed bottom; providing a centrifugal acceleration of about 1000g at the outer end of the tubes. 6.8 Vortex, for centrifuge tubes (optional). 6.9 Vacuum pump (optional). 6.10 Laboratory oven, set to (505) C. 7 Sampling technique Whenever possible, the
46、sample is taken from a light-protected position in the food consignment, since the TL intensity decreases on exposure to light. Before analysis, samples should be protected against light exposure. Store them in the dark. Avoid exposure of samples to temperatures in excess of 100 C, since heating red
47、uces TL intensity. 8 Procedure 8.1 General Several procedures for mineral separation may be used, e.g. handpicking, rinsing by water, density separation and/or acid hydrolysis. It should be ascertained that the mineral isolation procedure does not affect the qualitative classification as to whether
48、the food has been irradiated or not, when compared with the procedures described below which have been found satisfactory. The isolated silicate minerals should be free of organic material. The presence of organic matter could induce spurious (non radiation-induced) luminescence, or in extreme cases
49、, could obscure TL. Samples with organic residues are blackened by the TL measurement process. Furthermore, during isolation, the minerals should be protected against light exposure, i.e., not exposed to strong light or unnecessarily kept exposed to light, to prevent optical bleaching. It may be favourable to use subdued light conditions. Some authors prefer to work under safelight conditions. However, the inter-laboratory tests with herbs, spices, their mixtures, and shrimps 1 to 5, demonstrate that prot
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