Foodstuffs - Thermoluminescence detection of irradiated food from which silicate minerals can be isolated

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 of silicate minerals can be isolated.
The method has been successfully tested in interlaboratory tests with herbs and spices as well as their mixtures [1] to [3], shellfish including shrimps and prawns [4] to [6], both fresh and dehydrated fruits and vegetables [7] to [9], and potatoes [10]. Other studies [11] to [46] demonstrate that the method is applicable to a large variety of foodstuffs.

Lebensmittel - Thermolumineszenzverfahren zum Nachweis von bestrahlten Lebensmitteln, von denen Silikatmineralien isoliert werden können

Diese Europäische Norm legt ein Verfahren fest, das zum Nachweis einer Behandlung von Lebensmitteln mit ionisierenden Strahlen durch Messung der Thermolumineszenz (TL) an mineralischen, silikathaltigen Verunreini-gungen geeignet ist. Das Verfahren ist auf Lebensmittel anwendbar, von denen eine ausreichende Menge an Silikatmineralien isoliert werden kann.
Das Verfahren wurde in Ringversuchen erfolgreich an Kräutern und Gewürzen bzw. Gewürzmischungen [1] bis [3], an Krebs- und Weichtieren einschließlich Garnelen [4] bis [6] sowohl an frischem als auch an getrocknetem Obst und Gemüse [7] bis [9] sowie an Kartoffeln [10] geprüft. Weitere Untersuchungen [11] bis [46] haben gezeigt, dass das Verfahren auf viele verschiedene Lebensmittel angewandt werden kann.

Produits alimentaires - Détection par thermoluminescence d'aliments ionisés dont peuvent être extraits des minéraux silicatés

La présente Norme européenne spécifie une méthode de détection de traitement ionisant appliquée à des produits alimentaires par analyse de la thermoluminescence des minéraux silicatés contaminant l'aliment. Cette méthode s'applique aux produits alimentaires à partir desquels il est possible d'isoler une quantité suffisante de minéraux silicatés.
La méthode a été appliquée avec succès lors d'essais interlaboratoires conduits sur des aromates, des épices, leurs mélanges, [1] à [3], sur des crustacés incluant les crevettes et les langoustes [4] à [6], sur des légumes et des fruits, frais ou déshydratés [7] à [9], et sur des pommes de terre [10]. D'autres études [11] à [46] montrent que cette méthode est applicable à une grande variété d'aliments.

Živila - Termoluminescenčna detekcija obsevane hrane, iz katere je mogoče izolirati silikatne minerale

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Publication Date
09-Oct-2001
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2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.Lebensmittel - Thermolumineszenzverfahren zum Nachweis von bestrahlten Lebensmitteln, von denen Silikatmineralien isoliert werden könnenProduits alimentaires - Détection par thermoluminescence d'aliments ionisés dont peuvent etre extraits des minéraux silicatésFoodstuffs - Thermoluminescence detection of irradiated food from which silicate minerals can be isolated67.050Splošne preskusne in analizne metode za živilske proizvodeGeneral methods of tests and analysis for food productsICS:Ta slovenski standard je istoveten z:EN 1788:2001SIST EN 1788:2002en01-junij-2002SIST EN 1788:2002SLOVENSKI

STANDARDSIST EN 1788:19981DGRPHãþD
SIST EN 1788:2002

EUROPEAN STANDARDNORME EUROPÉENNEEUROPÄISCHE NORMEN 1788October 2001ICS 67.050Supersedes EN 1788:1996English versionFoodstuffs - Thermoluminescence detection of irradiated foodfrom which silicate minerals can be isolatedProduits alimentaires - Détection par thermoluminescenced'aliments ionisés dont peuvent être extraits des minérauxsilicatésLebensmittel - Thermolumineszenzverfahren zumNachweis von bestrahlten Lebensmitteln, von denenSilikatmineralien isoliert werden könnenThis European Standard was approved by CEN on 18 August 2001.CEN members are bound to comply with the CEN/CENELEC Internal Regulations which stipulate the conditions for giving this EuropeanStandard the status of a national standard without any alteration. Up-to-date lists and bibliographical references concerning such nationalstandards may be obtained on application to the Management Centre or to any CEN member.This European Standard exists in three official versions (English, French, German). A version in any other language made by translationunder the responsibility of a CEN member into its own language and notified to the Management Centre has the same status as the officialversions.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 STANDARDIZATIONCOMITÉ EUROPÉEN DE NORMALISATIONEUROPÄISCHES KOMITEE FÜR NORMUNGManagement Centre: rue de Stassart, 36

B-1050 Brussels© 2001 CENAll rights of exploitation in any form and by any means reservedworldwide for CEN national Members.Ref. No. EN 1788:2001 ESIST EN 1788:2002

EN 1788:2001 (E)2ContentsForeword........................................................................................................................................................21Scope.........................................................................................................................................................32Normative references.................................................................................................................................33Terms and definitions..................................................................................................................................34Principle........................................................................................................................................................45Reagents.......................................................................................................................................................46Apparatus.....................................................................................................................................................47Sampling technique......................................................................................................................................58Procedure......................................................................................................................................................69Evaluation......................................................................................................................................................910Limitations...................................................................................................................................................1011Validation.....................................................................................................................................................1012Test report...................................................................................................................................................11Annex A (normative)

Estimation of blank levels....................................................................................................12Annex B (informative)

Practical example for defining temperature intervals of the TL heating unit...............13Annex C (informative)

Examples for TL glow curves using various readers......................................................14Bibliography.............................................................................................................................................................16ForewordThis European Standard has been prepared by Technical Committee CEN/TC 275 "Food analysis - Horizontalmethods", the secretariat of which is held by DIN.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 orby endorsement, at the latest by April 2002, and conflicting national standards shall be withdrawn at the latest byApril 2002.This document was elaborated on the basis of a protocol developed following a concerted action supported by theCommission of European Union (XII C.5). Experts and laboratories from E.U. and EFTA countries, contributedjointly to the development of this protocol.This predecessor of this document has been prepared under a mandate given to CEN by the Commission of theEuropean Communities and the European Free Trade Association.WARNING : The use of this standard may involve hazardous materials, operations and equipment. This standarddoes not purport to address all the safety problems associated with its use. It is the responsibility of the user of thisstandard to establish appropriate safety and health practices and determine the applicability of regulatorylimitations prior to use.The annex A is normative ; the annexes B and C are informative.According to the CEN/CENELEC Internal Regulations, the national standards organizations of the followingcountries 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 United Kingdom.SIST EN 1788:2002

EN 1788:2001 (E)31 ScopeThis European Standard specifies a method for the detection of irradiation treatment of food and/or foodingredients by thermoluminescence analysis of contaminating silicate minerals. This method is applicable to thosefoodstuffs from which a sufficient amount of silicate minerals can be isolated.The method has been successfully tested in interlaboratory tests with herbs and spices as well as their mixtures [1]to [3], shellfish including shrimps and prawns [4] to [6], both fresh and dehydrated fruits and vegetables [7] to [9],and potatoes [10]. Other studies [11] to [46] demonstrate that the method is applicable to a large variety offoodstuffs.2 Normative referencesThis European Standard incorporates by dated or undated reference, provisions from other publications. Thesenormative references are cited at the appropriate places in the text and the publications are listed hereafter. Fordated references, subsequent amendments to or revisions of any of these publications apply to this EuropeanStandard only when incorporated in it by amendment or revision. For undated references the latest edition of thepublication referred to applies (including amendments).EN ISO 3696, Water for analytical laboratory use – Specification and test methods (ISO 3696).3 Terms and definitionsFor the purposes of this European Standard, the following terms and definitions apply.3.1thermoluminescence (TL)light emission which occurs on heating a solid material in addition to black body radiation, due to the thermallystimulated release of trapped charge carriers3.2TL intensityamount of light detected per unit temperature interval at a given heating rate. The integrated TL intensity over astated temperature interval is measured in photon counts or coulombs.3.3glow curvevariation of TL intensity with temperature. The integral of the glow curve is expressed in counts or coulombsdepending on the apparatus used.3.4Glow 1glow curve recorded from the minerals of the prepared sample3.5Glow 2glow curve recorded from the minerals of the prepared sample after measurement of Glow 1 and a subsequentexposure to a fixed known dose of radiation for the purpose of normalization3.6TL glow ratioratio of integrated TL intensities of Glow 1 to Glow 2, evaluated over a stated temperature interval3.7Minimum Detectable integrated TL- intensity Level (MDL)full process blank level (Glow 1) plus three standard deviations over a stated temperature interval (full processblank levels should be measured in parallel with sample extractions using portions of the same stock solutions andfollowing the procedure at all steps) defines the MDL, which should be consistent with freedom from luminescentcontamination of discs, glassware and reagents (see Annex A)SIST EN 1788:2002

EN 1788:2001 (E)43.8background of the TL readerintegrated TL intensity measured without sample disc over the whole temperature range studied4 PrincipleSilicate minerals contaminating foodstuffs store energy by charge trapping processes as a result of exposure toionizing radiation. Releasing such energy, by controlled heating of isolated silicate minerals, gives rise tomeasurable TL glow curves.Silicate minerals are therefore isolated from the foodstuffs, mostly by a density separation step. In order not toobscure the TL, the isolated silicate minerals should be as free of organic constituents as possible. A first glow ofthe separated mineral extracts is recorded (Glow 1). Since various amounts and/or types of minerals (quartz,feldspar etc.) exhibit very variable integrated TL intensities after irradiation, a second TL glow (Glow 2) of the samesample 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 ofirradiated samples on principle yields higher TL glow ratios than that of unirradiated samples. Glow shapeparameters offer additional evidence for identifying irradiated foods. This method of TL analysis relies solely on thesilicate minerals which can be separated from various foods and is not principally influenced by the kind of foodproduct.5 Reagents5.1 GeneralOnly use reagents of recognized analytical grade. Water shall be of at least grade 3 in accordance withEN ISO 3696. All reagents shall be kept free from particulate contamination throughout the procedure.5.2 Sodium polytungstate Na6[H2W12O40] x H2O solution with a density of 2 g/ml. The solution may berecovered and purified for re-use [2].5.3 Hydrochloric acid, substance concentration c(HCl) = 1 mol/l and/or 4 mol/l to 6 mol/l (for specialcases)5.4 Ammonium hydroxide solution, e.g. c(NH4OH) = 1 mol/l5.5 Acetone5.6 Nitrogen gas, oxygen free, for flushing the TL heating chamber5.7 Silicone spray (optional)5.8 Ethanol6 Apparatus6.1 GeneralAll laboratory surfaces and glassware should be carefully cleaned. Use usual laboratory apparatus and, inparticular, the following:6.2 TL readerwith glow curve recording facility and data evaluation; heating rate: about 6 °C/s; maximum temperature required:at least 350 °C; equipped with a suitable photomultiplier tube, e.g. a bi-alkali photocathode photomultiplier tube, inSIST EN 1788:2002

EN 1788:2001 (E)5combination with filters to reject black body radiation. Acceptable filter combinations are Corning 7/59® + SchottKG 1® filters or Schott BG 39®1) , or equivalent.6.3 Stainless steel discsor shallow cups having a diameter to suit the TL reader (usually about 9 mm up to 10 mm) and a thickness of 0,25mm up to 0,5 mm.6.4 Radiation sourcecapable of irradiating discs or cups with isolated minerals at a defined radiation dose before measurement ofGlow 2. In the interlaboratory tests on herbs, spices and their mixtures [1] to [3], shellfish [4] to [6], fresh anddehydrated fruits and vegetables [7] to [9], various sources delivering 60Co-y-rays have been employed at a fixedradiation dose of 1 kGy. In the interlaboratory test on potatoes [10] 60Co-y-rays at a fixed dose of only 250 Gy havebeen used.NOTE 1 Other fixed doses can be suitable.NOTE 2 Alternatives to 60Co-y-rays can be used, provided they have been found satisfactory.6.5 Ultrasonic bathcapable of fitting several beakers of 150 ml. For larger sample volumes, e.g. with dehydrated fruits and vegetablesor 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 Mini-sieve set (e.g. diameter 50 mm), consisting of two rings between which the nylon sieve cloth isclamped.6.6.2 Nylon sieve cloth, with pore sizes of 125 µm and 250 µm.6.7 Centrifugesupplied 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 outer end of the tubes.6.8 Vortex for centrifuge tubes (optional)6.9 Vacuum pump (optional)6.10 Laboratory oven, set to (50 ± 5) °C.6.11 Reflux apparatus6.12 Scalpel and forceps7 Sampling techniqueWhenever possible, the sample should be taken from a light-protected position in the food consignment, since theTL intensity decreases on exposure to light.Before analysis, samples should be protected against light exposure and be stored in the dark. Avoid exposure ofsamples to temperatures in excess of 100 °C, since heating reduces TL intensity.

1)Corning 7/59®, Schott KG 1® and Schott BG 39® are examples of suitable products available commercially. Thisinformation is given for the convenience of users of this standard and does not constitute an endorsement by CEN of theseproducts.SIST EN 1788:2002

EN 1788:2001 (E)68 Procedure8.1 GeneralSeveral procedures for mineral separation may be used, e.g. handpicking, rinsing by water, density separationand/or hydrolysis. The procedures for mineral isolation described in 8.2 have been found to be satisfactory. For anyother procedure, it has to be ascertained that the mineral isolation procedure does not affect the qualitativeclassification.The isolated silicate minerals should be free of organic material. The presence of organic matter could inducespurious (non-radiation induced) luminescence, or in extreme cases could obscure TL. Samples with organicresidues are blackened by the TL measurement process.Furthermore, during isolation the minerals should be protected against light exposure, i.e. not exposed to stronglight or unnecessarily kept exposed to light, to prevent optical bleaching. It may be favourable to use subdued lightconditions. Some authors prefer to work under safelight conditions. However, the interlaboratory tests with herbs,spices, their mixtures, shrimps [1] to [5], fresh and dehydrated fruits and vegetables [7], [9] and potatoes [10]demonstrate that protection from strong light under usual laboratory conditions may prove satisfactory.The quantity of silicate minerals required for TL analysis, is approximately 0,1 mg to 5 mg. The minimum quantityrequired depends on the outcome of Glow 2. The lowest acceptable integrated TL intensity for Glow 2, shall be atleast 10 times the MDL, see also 8.4.6.8.2 Isolation of silicate minerals from food8.2.1 Preconcentration step of minerals8.2.1.1 Herbs, spices and their mixturesPreconcentration of minerals by wet sieving is recommended for most samples using the following procedure. Insome cases (depending on the particular sample) this preconcentration procedure can be omitted. In this caseplace 0,5 g to 1 g of the sample in a suitable centrifuge tube (6.7) and proceed immediately to the densityseparation step (as described in 8.2.2).For the preconcentration, suspend 3 g to 20 g of the sample (depending on the degree of mineral contamination) ina 100 ml to 150 ml glass beaker with 50 ml to 100 ml water added.Treat the sample in the beaker with ultrasound (6.5) for about 5 min to loosen the adhering minerals.Sieve the sample in portions through a 250 µm nylon mesh (for coarse samples like aromatic herbs) or through a125 µm nylon mesh (6.6) (for fine samples like ground spices) into a large beaker (e.g. 500 ml to 1000 ml), rinsingthe minerals through with water each time e.g. using a strong jet of water from a wash bottle. Discard theconstituents retained by the sieve cloth. Use a fresh nylon sieve cloth for each sample. Allow to settle for about 5min.Decant most of the water from the large beaker together with as much organic material as possible, leaving theminerals in only a few millilitres of water. If there are still fairly large amounts of organic material left, add water to adepth of 1 cm to 2 cm, swirl, wait for about 5 s to 10 s to let the minerals settle again and then decant again.Repeat this step until only small amounts of organic material are left together with the minerals.Transfer the mineral fraction to a centrifuge tube (6.7), e.g. using a Pasteur pipette.Centrifuge for 1 min at 1000 g. Alternatively allow sedimentation for 5 min. Decant off or remove the water bysuction, leaving the mineral fraction behind.8.2.1.2 ShellfishNOTE Minerals can be associated with various parts of shellfish including the intestines. Intestinally entrained minerals arepreferred for analysis. Intestines are found as a 1 mm to 2 mm broad dark tube on the convex side of shrimps and prawns, andin the interior of molluscs.Cut the skin carefully using a scalpel and remove the intestine by means of forceps. Transfer intestines of severalanimals to a Petri dish and cut with a scalpel. After adding some drops of water, separate minerals from intestinalmembranes. Transfer minerals e.g. using a Pasteur pipette to a suitable, e. g. 10 ml to 15 ml centrifuge tube.Alternatively, place the sliced intestinal tracts into a beaker (e.g. 150 ml), treat with ultrasound for about 15 min andsieve the sample in portions through a 250 µm nylon mesh into a large beaker (e.g. 500 ml to 1000 ml), rinsing theminerals through with water each time e.g. using a strong jet of water from a wash bottle. Discard the residualsample from the sieve. Use a fresh nylon sieve cloth for each sample. Allow to settle for about 5 min to 10 min.SIST EN 1788:2002

EN 1788:2001 (E)7Decant most of the water from the large beaker, leaving the minerals in only a few millilitres of water. Transfer themineral fraction to a centrifuge tube (6.7), e.g. using a Pasteur pipette.Centrifuge for about 1 min at 1000 g. Alternatively allow sedimentation for 5 min. Decant off or remove the water bysuction, leaving the mineral fraction behind.A further alternative to separate minerals from shellfish is hydrolysis. A procedure for acid hydrolysis which hasbeen tested in an interlaboratory trial is described in 8.2.3.8.2.1.3 Fresh fruits and vegetables including potatoesIf enough minerals can be isolated just by collection or washing, put them in a centrifuge tube (6.7) and proceedimmediately to the density separation step (as described in 8.2.2). Otherwise, preconcentration of minerals by wetsieving is recommended using the following procedure.Place the sample (one or more fruits, vegetables or potatoes, depending on the degree of mineral contamination)into one or more glass beakers, e.g. of 1000 ml, and add enough water to cover the sample.Treat the sample in the beaker with ultrasound for about 5 min to loosen the adhering minerals. Remove fruits,vegetables or potatoes, rinsing with water as needed to recover the minerals and proceed as described in 8.2.1.1,paragraph 5 and following. It is recommended to sieve the minerals through a 250 µm nylon mesh to remove verycoarse mineral grains or organic parts.8.2.1.4 Dehydrated fruits and vegetablesPreconcentration of minerals by wet sieving is recommended for most samples using the following procedure.Place 50 g to 200 g of the sample (depending on the degree of mineral contamination) into one or more glassbeakers, e.g. of 1000 ml, and add enough water to cover the sample.Treat the sample in the beaker with ultrasound for about 5 min (to loosen the adhering minerals) and proceed asdescribed in 8.2.1.1, paragraph 4 and following.To increase recovery of minerals from dehydrated fruits and vegetables, the settling time in the beaker can beextended to 10 min. During this first preconcentration step, use many rinsing steps to remove organic material.8.2.2 Density separation step to free the minerals from organic materialAdd 5 ml of sodium polytungstate solution (5.2) to the mineral fraction in the centrifuge tube (6.7). Shake vigorously(Vortex) and agitate in an ultrasonic bath for about 3 min (e.g. in case of 8.2.1.3) or 5 min to 15 min (e.g. in case of8.2.1.1).Centrifuge for 2 min at 1000 g. Silicate minerals (density 2,5 g/ml to 2,7 g/ml) will sediment whereas organiccomponents will float.Carefully overlay the polytungstate solution with water to facilitate removal of the organic material. Extract theupper water layer and the organic material either by decantation or vacuum suction, leaving the minerals behind inthe lower polytungstate layer. If necessary, clean the centrifuge tube side by wiping with a small moist tissue. If notall organic material is removed, overlay the polytungstate solution with water again and repeat extraction.Alternatively, decant off the polytungstate solution and the organic material, and if necessary, clean the centrifugetube side by wiping with a small moist tissue.In the case of dehydrated fruits and vegetables, some samples, e.g. apples, form a gel in the polytungstate layer.Instead of immediately extracting the upper water layer, it is recommended to leave the centrifuge tube overnight(room temperature, stoppered tube) and extract the water layer the next day. Add an additional 2 ml to 3 ml ofpolytungstate solution, shake vigorously (Vortex) and agitate with ultrasound (for about 5 min to 15 min). Centrifugefor 2 min at 1000 g, overlay the polytungstate solution with water, and leave the tube overnight. Although part of thegel now still may be in the upper part of the polytungstate layer, it can be more easily extracted, leaving the mineralfraction at the bottom.Extract the sodium polytungstate layer, being careful to leave the mineral fraction behind. If too much organicmaterial is still present, put further sodium polytungstate solution and repeat the procedure. The sodiumpolytungstate solution can be collected and purified for re-use [2].Wash the minerals twice to remove the tungstate residues by filling the centrifuge tube with water, allow theminerals to settle or centrifuge briefly at 1000 g and remove the water.To dissolve carbonates adhering to the silicate minerals, add 1 ml to 2 ml of hydrochloric acid c(HCl) = 1 mol/l (5.3),agitate, and leave for 10 min. If necessary, increase the amount and/or concentration of hydrochloric acid.Especially for potatoes, it is recommended to add at least 5 ml of hydrochloric acid of c(HCl) = 4 mol/l.SIST EN 1788:2002

EN 1788:2001 (E)8Neutralize the acid using the ammonium hydroxide solution (5.4), fill up the centrifuge tube with water, allow theminerals to settle or centrifuge briefly. Remove the supernatant and wash the mineral residue twice with water.To displace the residual water, add about 3 ml of acetone (5.5) and agitate. If the acetone becomes turbid, removeit and add fresh acetone.8.2.3 Acid hydrolysis silicate extraction for shellfishNOTE It has been shown in an interlaboratory study on shellfish [6] that this technique produced higher yields and lowerbackground luminescence of the unirradiated samples compared with physical density separation.Either the whole sample or intestinal tract removed from the whole sample with a scalpel and forceps, can be usedin this process.Place 10 g to 20 g of the whole sample or 10 mg to 20 mg of the intestinal tract in a round bottomed flaskcontaining 200 ml of 6 mol/l hydrochloric acid for the whole sample or 20 ml for the intestinal tract sample. Refluxthe whole sample for 2 h to 3 h. For intestines, heating to 50 °C for 15 min to 30 min is sufficient. During digestionthe solution changes from colourless to a clear brown solution.After cooling, add slowly 400 ml (40 ml for the intestines) of water. Leave the solution for 15 min to allow theminerals to settle.Decant off the solution carefully to leave minerals at the bottom of the flask or if preferred remove the hydrochloricacid by rotary evaporation to leave remaining minerals.Carefully transfer the minerals to a centrifuge tube where they are washed thoroughly twice with water. Rinse theminerals with acetone to remove any traces of water (as in 8.2.2).8.3 Fixing the minerals on discs for TL measurementCarefully clean stainless steel discs (6.3), e. g. by rinsing in water, ultrasonic agitation, two to three washings inacetone, a second ultrasonic treatment, drying in an oven, and storage under dust free conditions. (The cleaningprocedure may be checked as described in annex A.)Transfer the isolated minerals in acetone to a disc using a Pasteur pipette. After suction of the mineral suspensioninto the pipette, the minerals will immediately sediment to the outlet of the pipette and can then be easilytransferred dropwise (allow the acetone to evaporate in between) in an adequate amount to the disc. Store thediscs overnight at 50 °C in a laboratory oven (6.10).As an alternative to dropping minerals on the disc, transfer the mineral suspension in acetone to one or a set ofclean flat bottomed tubes each containing a clean stainless steel disc. Place these tubes upright in a laboratoryoven at 50 °C overnight. The acetone will dry off, leaving a deposit of minerals adhering to the discs.The deposit of minerals can be fixed on the disc by using silicone spray (5.7).8.4 Thermoluminescence (TL) measurements8.4.1 GeneralFor comparison of different analyses, identical measuring conditions should be assured. Measure the backgroundof the TL reader (3.8) regularly and ensure that it remains at the same level. Clean the optical filter and the heatingplate (planchet) regularly with ethanol.To reduce spurious TL, flush the TL heating chamber with nitrogen (5.6), at a constant flow rate during eachmeasurement.8.4.2 Measurement conditionsThe following instrument settings have been found satisfactory.Initial temperature:70 °CHeating rate:6 °C/sFinal temperature:350 °C to 500 °C8.4.3 Measurement of Glow 1Place the disc with the mineral deposit (as prepared in 8.3) on the heating plate of the TL reader (6.2), and glow itunder the specified conditions.SIST EN 1788:2002

EN 1788:2001 (E)98.4.4 Irradiation for the purpose of normalizationAfter measurement of Glow 1, irradiate the discs with the mineral deposit with a defined radiation dose using theradiation source (6.4).With herbs and spices and their mixtures [1] to [3], and shellfish [4] to [6], fresh and dehydrated fruits andvegetables [7] to [9], which are irradiated in commercial practice for decontamination purposes with radiation dosesnear or above 1 kGy, the interlaboratory tests have shown that a fixed radiation dose of about 1 kGy with a 60Co-y-source proves satisfactory. The commercial irradiation of potatoes for sprout inhibition is carried out with radiationdoses in the range of 50 Gy to 150 Gy. The interlaboratory test with potatoes [10] has shown that a dose of 250 Gywith 60Co-y-rays proves satisfactory for potatoes as a normalizing dose. It shall be noted that the TL limits (8.4.7)and classification criteria (see clause 9) depend on the radiation dose used for normalization.NOTE

Some studies indicate that suitable alternatives to 60Co-y-rays may be used, see e.g. [2], [7] and [23].The applied radiation dose for normalization should be controlled by adequate dosimetry.The discs should be packed in a manner which protects them from loss of material, exposure to light or crosscontamination. It is essential that the minerals on the discs to be irradiated, and subsequently measured for Glow 2,are identical with the minerals measured during Glow 1. If significant loss of minerals occurs, the discs should berejected. This may be checked by visual inspection or by weighing of the discs.After irradiation of the discs, store them overnight at 50 °C in the laboratory oven (6.10) before recording Glow 2.8.4.5 Measurement of Glow 2Measure Glow 2 under the same conditions as Glow 1 (8.4.2).8.4.6 Estimation of MDLMeasure full process blank levels in parallel with sample extractions using portions of the same stock solutions andfollowing the procedure at all stages. Calculate the MDL in accordance with 3.7. Contamination will be indicated byhigher blank levels [31].8.4.7 TL limits for Glow 2For samples with a Glow 2 lower than 10 times the MDL, evaluated over a stated temperature interval, noassessment can be made of whether irradiation treatment of the food product has occurred.If the TL of Glow 2 approximates the counting saturation limit, reject the sample and repeat the analysis using asmaller amount of minerals. Alternatively, a restrictive aperture or a neutral density filter to reduce count rate maybe effective (both for Glow 1 and Glow 2).9 EvaluationThe identification of irradiated foods and food ingredients by TL analysis depends on the

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