1、BRITISH STANDARD Foodstuffs - Thermoluminescence detection of irradiated food from which silicate minerals can be isolated The European Standard EN 1788:200 1 has the status of a British Standard ICs 67.050 BS EN 1788:200 1 NO COPYING WITHOUT BSI PERMISSION EXCEPT AS PERMITTED BY COPYRIGHT LAW BS EN
2、 1788:2001 Amd.No. National foreword Date Comments This British Standard is the official English language version of EN 1788:2001. It supersedes BS EN 1788: 1997 which is withdrawn. The UK participation in its preparation was entrusted to Technical Committee AW/-/3, Food analysis - Horizontal method
3、s, which has the responsibility to: - - aid enquirers to understand the text; present to the responsible European committee any enquiries on the interpretation, or proposals for change, and keep the UK interests informed; monitor related international and European developments and promulgate them in
4、 the UK. - A list of organizations represented on this committee can be obtained on request to its secretary. Cross-references The British Standards which implement international or European publications referred to in this document may be found in the BSI Standards Catalogue under the section entit
5、led “International Standards Correspondence Index”, or by using the “Find” facility of the BSI Standards Electronic Catalogue. 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. Complian
6、ce with a British Standard does not of itself confer immunity from legal obligations. This British Standard. havinp. - been prepared under the direction of the Consumer Products and Services Sector Summary of pages This document comprises a front cover, an inside front cover, the EN title page, Poli
7、cy and Strategy Committee, was published under the authority of the Standards Policy and Strategy Committee on 3 December 200 1 pages 2 to 18, an inside back cover and a back cover. The BSI copyright date displayed in this document indicates when the document was last issued. O BSI 3 December 200 1
8、ISBN O 580 38328 8 EUROPEAN STANDARD NORME EUROPENNE EUROPISCHE NORM EN 1788 October 2001 ICs 67.050 Supersedes EN 1788:1996 English version Foodstuffs - Thermoluminescence detection of irradiated food from which silicate minerals can be isolated Produits alimentaires - Dtection par thermoluminescen
9、ce daliments ioniss dont peuvent tre extraits des minraux silicats Lebensmittel - Thermolumineszenzvetfahren zum Nachweis von bestrahlten Lebensmitteln, von denen Silikatmineralien isoliert werden knnen This European Standard was approved by CEN on 18 August 2001 CEN members are bound to comply with
10、 the CENKENELEC 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 Management Centre o
11、r to any CEN member. 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 Management Centre has the same status as the official versio
12、ns. CEN members are the national standards bodies of Austria, Belgium, Czech Republic, Denmark, Finland, France, Germany, Greece, Iceland, Ireland, Italy, Luxembourg, Netherlands, Norway, Portugal, Spain, Sweden, Switzerland and United Kingdom. EUROPEAN COMMITTEE FOR STANDARDIZATION EUROPISCHES KOMI
13、TEE FR NORMUNG COMIT EUROPEN DE NORMALISATION Management Centre: rue de Stassart, 36 B-1050 Brussels O 2001 CEN All rights of exploitation in any form and by any means reserved worldwide for CEN national Members. Ref. No. EN 1788:2001 E EN 1788:2001 (E) Contents Foreword 2 1 2 3 4 5 6 7 8 9 10 11 12
14、 Scope 3 Normative references 3 Terms and definitions 3 Principle 4 Reagents . 4 Apparat us .4 Sampling technique . 5 Procedure . 6 Eva1 uat io n .9 Limitations 10 Validation 10 Test report 11 Annex A (normative) Estimation of blank levels 12 Annex B (informative) Practical example for defining temp
15、erature intervals of the TL heating unit . 13 Annex C (informative) Examples for TL glow curves using various readers 14 Bibliography 16 Foreword This European Standard has been prepared by Technical Committee CEN/TC 275 “Food analysis - Horizontal methods“, the secretariat of which is held by DIN.
16、This European Standard replaces EN 1788:1996. This European Standard shall be given the status of a national standard. either by publication of an identical text or by endorsement, at the latest by April 2002, and conflicting natioi?al standards shall be withdrawn at the latest by April 2002. This d
17、ocument was elaborated on the basis of a protocol developed following a concerted action supported by the Commission of European Union (XII C.5). Experts and laboratories from E.U. and EFTA countries, contributed jointly to the development of this protocol. This predecessor of this document has been
18、 prepared under a mandate given to CEN by the Commission of the European Communities and the European Free Trade Association. WARNING : The use of this standard may involve hazardous materials, operations and equipment. This standard does not purport to address all the safety problems associated wit
19、h its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use. The annex A is normative ; the annexes B and C are informative. According to the CENKENELEC Internal Regulatio
20、ns, the national standards organizations of the following countries are bound to implement this European Standard: Austria, Belgium, Czech Republic, Denmark, Finland, France, Germany, Greece, Iceland, Ireland, Italy, Luxembourg, Netherlands, Norway, Portugal, Spain, Sweden, Switzerland and the Unite
21、d Kingdom. 2 EN 1788:2001 (E) 1 Scope This European Standard specifies a method for the detection of irradiation treatment of food and/or food ingredients by thermoluminescence analysis of contaminating silicate minerals. This method is applicable to those foodstuffs from which a sufficient amount o
22、f silicate minerals can be isolated. The method has been successfully tested in interlaboratory tests with herbs and spices as well as their mixtures I to 3, shellfish including shrimps and prawns 4 to 6, both fresh and dehydrated fruits and vegetables 7 to 9, and potatoes IO. Other studies Il to 46
23、 demonstrate that the method is applicable to a large variety of foodstuffs. 2 Normative references This European Standard incorporates by dated or undated reference, provisions from other publications. These normative references are cited at the appropriate places in the text and the publications a
24、re listed hereafter. For dated references, subsequent amendments to or revisions 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 (including amendments)
25、. EN IS0 3696, Water for analytical laboratory use - Specification and test methods (IS0 3696). 3 Terms and definitions For the purposes of this European Standard, the following terms and definitions apply. 3.1 thermoluminescence (TL) light emission which occurs on heating a solid material in additi
26、on to black body radiation, due to the thermally stimulated release of trapped charge carriers 3.2 TL intensity 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
27、 glow curve variation of TL intensity with temperature. The integral of the glow curve is expressed in counts or coulombs depending on the apparatus used. 3.4 Glow 1 glow curve recorded from the minerals of the prepared sample 3.5 Glow 2 glow curve recorded from the minerals of the prepared sample a
28、fter measurement of Glow 1 and a subsequent exposure to a fixed known dose of radiation for the purpose of normalization 3.6 TL glow ratio 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)
29、full process blank level (Glow 1) plus three standard deviations over a stated temperature interval (full process blank levels should be measured in parallel with sample extractions using portions of the same stock solutions and following the procedure at all steps) defines the MDL, which should be
30、consistent with freedom from luminescent contamination of discs, glassware and reagents (see Annex A) 3 EN 1788:2001 (E) 3.8 background of the TL reader integrated TL intensity measured without sample disc over the whole temperature range studied 4 Principle Silicate minerals contaminating foodstuff
31、s store energy by charge trapping processes as a result of exposure to ionizing radiation. Releasing such energy, by controlled heating of isolated silicate minerals, gives rise to measurable TL glow curves. Silicate minerals are therefore isolated from the foodstuffs, mostly by a density separation
32、 step. In order not to obscure the TL, the isolated silicate minerals should be as free of organic constituents as possible. A first glow of the separated mineral extracts is recorded (Glow 1). Since various amounts and/or types of minerals (quartz, feldspar etc.) exhibit very variable integrated TL
33、 intensities after irradiation, a second TL glow (Glow 2) of the same sample after exposure to a fixed dose of radiation is necessary to normalize the TL response. The TL glow ratio, thus obtained, is used to indicate radiation treatment of the food, since the population of irradiated samples on pri
34、nciple yields higher TL glow ratios than that of unirradiated samples. Glow shape parameters offer additional evidence for identifying irradiated foods. This method of TL analysis relies solely on the silicate minerals which can be separated from various foods and is not principally influenced by th
35、e kind of food product. 5 Reagents 5.1 General Only use reagents of recognized analytical grade. Water shall be of at least grade 3 in accordance with EN IS0 3696. All reagents shall be kept free from particulate contamination throughout the procedure. 5.2 Sodium polytungstate Na6H2W12040 x H20 solu
36、tion with a density of 2 g/mI. The solution may be recovered and purified for re-use 2. 5.3 Hydrochloric acid, substance concentration c(HCI) = 1 mol/l and/or 4 mol/l to 6 mol/l (for special cases) 5.4 Ammonium hydroxide solution, e.g. c(NH40H) = 1 mol/l 5.5 Acetone 5.6 Nitrogen gas, oxygen free, fo
37、r flushing the TL heating chamber 5.7 Silicone spray (optional) 5.8 Ethanol 6 Apparatus 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 evaluatio
38、n; heating rate: about 6 “C/s; maximum temperature required: at least 350 OC; equipped with a suitable photomultiplier tube, e.g. a bi-alkali photocathode photomultiplier tube, in 4 EN 1788:2001 (E) combination with filters to reject black body radiation. Acceptable filter combinations are Corning 7
39、/59C3 + Schott KG IC3 filters or Schott BG 39C3) , or equivalent. 6.3 Stainless steel discs or shallow cups having 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 discs or cups with isolated minera
40、ls at a defined radiation dose before measurement of Glow2. In the interlaboratory tests on herbs, spices and their mixtures I to 3, shellfish 4 to 6, fresh and dehydrated fruits and vegetables 7 to 9, various sources delivering GoCo-y-rays have been employed at a fixed radiation dose of 1 kGy. In t
41、he interlaboratory test on potatoes IO GoCo-y-rays at a fixed dose of only 250 Gy have been used. NOTE 1 Other fixed doses can be suitable. NOTE 2 Alternatives to GoCo-y-rays can be used, provided they have been found satisfactory. 6.5 U It rasoni c bath capable of fitting several beakers of 150 ml.
42、 For larger sample volumes, e.g. with dehydrated fruits and vegetables or larger fruits or potatoes, an ultrasonic bath, capable of fitting several beakers of 1000 ml may be advantageous. 6.6 Nylon disposable sieves, comprised of e.g.: 6.6.1 clamped. Mini-sieve set (e.g. diameter 50 mm), consisting
43、of two rings between which the nylon sieve cloth is 6.6.2 Nylon sieve cloth, with pore sizes of 125 pm and 250 pm. 6.7 Centrifuge supplied with a swing-out rotor and suitable glass tubes, e.g. of 10 ml to 15 ml capacity with pointed bottom; providing a centrifugal acceleration of about 1000 g at the
44、 outer end of the tubes. 6.8 Vortex for centrifuge tubes (optional) 6.9 Vacuum pump (optional) 6.10 Laboratory oven, set to (50 f 5) “C. 6.11 Reflux apparatus 6.12 Scalpel and forceps 7 Sampling technique Whenever possible, the sample should be taken from a Iight-protected position in the food consi
45、gnment, since the TL intensity decreases on exposure to light. Before analysis, samples should be protected against light exposure and be stored in the dark. Avoid exposure of samples to temperatures in excess of 100 OC, since heating reduces TL intensity. 1) Corning 7/59, Schott KG I and Schott BG
46、39 are 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 products. 5 EN 1788:2001 (E) 8 Procedure 8.1 General Several procedures for mineral separation may be used, e.g.
47、 handpicking, rinsing by water, density separation and/or hydrolysis. The procedures for mineral isolation described in 8.2 have been found to be satisfactory. For any other procedure, it has to be ascertained that the mineral isolation procedure does not affect the qualitative classification. The i
48、solated silicate minerals should be free of organic material. The presence of organic matter could induce spurious (non-radiation induced) luminescence, or in extreme cases could obscure TL. Samples with organic residues are blackened by the TL measurement process. Furthermore, during isolation the
49、minerals should be protected against light exposure, .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 interlaboratory tests with herbs, spices, their mixtures, shrimps I to 5, fresh and dehydrated fruits and vegetables 7, 9 and potatoes IO demonstrate that protection from strong light under usual laboratory conditions may prove satisfactory. The quantity of
