OPTIMISATION OF THE PHOTOSTIMULATED
OPTIMISATION OF THE PHOTOSTIMULATED LUMINESCENCE (PSL)TESTS TO DETECT IRRADIATED DIETARY SUPPLEMENTSCONTRACT NUMBER A05010TASK 1 : REVIEW OF EXISTING DATA SETSD.C.W. Sanderson, L.A. Carmichael, S.FiskAugust 2008
CONTENTS1. Introductionp12. Review of existing data sets including dietary supplements which haveBeen analysed with PSL, calPSL and TLp22.1 Identification of data sets2.2 Qualitative examination of PSL and TL outcomes2.3 Quantitative summary data for each PSL and TL category2.4 Graphical analysis of PSL and TL correspondencep2p3p9p 113. Discussion4. Referencesp 19p 20Appendix A - Samples by Survey, PSL and TL outcomep 22Appendix B – Summary tables of mis-matched outcomesp32i
LIST OF TABLESTable 2.1 Summary of surveys examined in this projectTable 2.2. Comparison of PSL and TL outcomes for 280 dietary supplement samplesfrom survey dataTable 2.3. Comparison of PSL and TL outcomes for 113 dietary supplement samplesfrom survey data where CalPSL data are availableTable 2.4. Comparison of PSL and TL outcomes for 554 dietary supplement samplesfrom routine analysisTable 2.5 Summary statistics for all 280 survey samples classified by PSL/TLcategoryTable 2.6. Summary statistics for 113 survey samples with calPSL, classified byPSL/TL categoryTable A1 FSA 2001Table A2 FSA 2003Table A3 FSAI 2002Table A4 FSAI 2003Table A5 FSAI 2005Table A6 Denmark 2003Table A7 Denmark 2005Table A8 Norway 2003Table A9 Norway 2004Table A10 Belgian Consumer Association 2003Table B1 Summary of dietary supplement results in the ten surveysTable B2a Mis-match results from the FSA2001/2 surveyTable B2b Mis-match results from the FSA2003 surveyTable B2c Mis-match results from the FSAI 2002 surveyTable B2d Mis-match results from the FSAI 2003 surveyTable B2e Mis-match results from the FSAI 2005 surveyTable B3 : Comparison of PSL/TL outcome with sample form for 53 samples wherethis is recorded.ii
LIST OF FIGURESFigure 2.1 Concordance plot for all 4 surveys showing comparison between aliquotsFigure 2.2. Calibrated PSL plot for 113 survey samplesFigure 2.3 TL and PSL scatter plotsFigure 2.4 Comparison of PSL screening and calPSL with TL glow ratioiii
SUMMARYThis report forms the first deliverable of project A05010 aimed at optimising thephotostimulated luminescence screening method for dietary supplements. The workfollows a series of surveys of undeclared irradiated foods conducted since 2001 whichhave shown substantial evidence of irradiated ingredients and products within thedietary supplement field. Over the same period producers and retailers have alsoconducted significant studies of raw materials in support of regulatory compliance.The dietary supplements themselves are a very diverse product set. Whereas theEN13751 photostimulated luminescence (PSL) method, and EN1788thermoluminescence (TL) were originally developed and validated for herbs, spices,seafoods and fruits and vegetables, their application to dietary supplements hasresulted in extension of the fields of application; in some cases to poorly definedsample matrices whose luminescence sensitivities are not well established. While theTL method involves explicit separation of silicate phases followed by sensitivitycalibrated TL analysis, PSL screening in its simplest form searches for radiationinduced luminescence from essentially unprepared samples. While EN13751recommends the use of the calibrated PSL protocol for materials of unknownsensitivity, this has not always been followed in studies of dietary supplements, andmay in any case be of limited use in complex mixtures of diverse ingredients.In this study it is intended to explore the possibilities of developing pre-concentrationtechniques to improve PSL performance with products whose sensitivities are limitedby low mineral concentrations. Also, once mineral concentrates are available, toexplore the potential of using depletion–rate analysis and multi-wavelengthstimulation to enhance the method. In the initial stage a review has been conducted ofavailable data sets where PSL data had been collected together with TL data fromdietary supplements and their ingredients. The correspondence between both methodshas been examined and combinations identified where different types of mixedoutcomes were encountered. From 10 official survey sets a subset of 280 samples wasexamined for which PSL screening and TL analysis were available. Within these asubset of 113 samples was identified where calibrated PSL was also available.Drawing on routine analysis conducted at SUERC since 2001 a further set of 554samples with PSL screening and TL data has also been considered. Qualitativecorrespondence has been cross-tabulated, confirming the existence of data sets wherePSL screening outcomes and TL analytical outcomes diverge. Quantitative analysis ofthe sensitivities of both PSL and TL, where available, and the outcomes confirms thatlack of luminescence sensitivity, coupled to a low concentration of irradiated materialin a mixture accounts for many of these cases. Other scenarios where PSL may bedetecting irradiated materials present in water-soluble or acid-soluble phases that arenot present in TL samples have also been considered, as has the possibility thatsamples with high geological residual signals might mask TL detection of minorirradiated components.The data sets accumulated provide a context for selection of samples for investigationof pre-concentration and serve as a reference for later parts of the project.iv
1. IntroductionPhoto-stimulated luminescence (PSL) and thermoluminescence (TL) methods fordetection of irradiated food (using standards EN17887 and EN137518 respectively)were initially developed for herbs and spices, but have subsequently been extendedto a number of other product categories, such as shellfish. Validation studies4 havebeen conducted on many of these, but in principle the methods can be applied to anyfoods containing silicate minerals. Dietary (herbal) supplements are among theproducts covered by the provisions of the Food Safety Act19 unless they are clearlymedicinal products for the treatment or prevention of disease. Therefore labellingregulations apply and detection of undeclared irradiation is an issue. Use ofluminescence detection techniques over a number of years both by industry and ingovernment surveys has led to a belief that there is a significant number of apparentmis-matches in classification when more than one of the techniques is used. Thisproject aims to assess whether the incidence of mis-match is in fact significant, andalso to understand why such outcomes arise and to investigate methods of reducingthe incidence.Photo-stimulated luminescence was developed as a screening test to identify sampleswhich require further analysis by a method which takes account of sensitivity toionising radiation, such as calibrated PSL (calPSL) or TL1-4. Extensive experience (inrelation to herbs, spices, shellfish, fruit and vegetables) from validation studies4, FSAproject E01068 to develop a proficiency testing scheme for these methods5, and morethan 3000 commercial analyses performed at SUERC since 1996 shows that in mostinstances (more than 95%) where this procedure is followed, the two techniques are inagreement, but with dilute mixtures or materials with low mineral load it has beenoccasionally observed that TL evidence of irradiation can occur in conjunction withnegative PSL. There are also cases of non-negative PSL signals which are notassociated with TL evidence of irradiation, but these are rarer still.Extension of the techniques to materials other than those originally subjected to interlaboratory trials appears to have increased the incidence of such mis-matches, as doesincreased blending. In particular, dietary supplements, which are often either multiingredient and/or contain highly processed extracts with few minerals, but which havebeen found6 to be frequently irradiated, require further study.Apparent mis-matches arise when positive or intermediate PSL screening of a sampleleads to further investigation by TL which does not reveal an irradiated component, orwhere positive TL analysis is associated with negative PSL. Such outcomes havebeen observed in commercial samples analysed at SUERC and also in surveys.Commercial submissions with negative PSL are not often referred for TL, soinstances of the second form of discrepancy are largely confined to survey evidence,where TL analysis of a random selection of samples giving negative PSL has beenperformed. It should not, however, be assumed that TL is always correct in suchinstances, since there are circumstances, such as the presence of water-soluble PSLbearing salts or large geological signals, where a positive PSL will be correct evenwhen not corroborated by TL. Therefore, apparent mis-matches should be examinedon a case by case basis.1
Where TL is not associated with a PSL signal, the cause may be low sensitivity,dilution of the irradiated component by blending, loss of PSL signal, or physical formof sample.An investigation20 was undertaken in 1999 to study the impact of blending on herbsand spices. Sensitivity variation was also incorporated into the study protocol. A totalof 162 blended samples was produced for analysis. Standardised and validatedprocedures were used for all analyses. As expected, detection rates were lower fordiluter or less sensitive materials. At 10% concentration, PSL detection rate was100% and TL 98%. At 1% concentration, PSL detection rate was 68% and TL 75%.At 0.1% concentration, PSL detection rate was 33% and TL 54%.This demonstrates that there is a significant possibility of non- detection for both PSLand TL methods at low concentration and that there is a difference between PSL andTL detection rates at any given concentration. When assessing mis-matches, thepossibility of blending therefore needs to be taken into account, particularly wheresensitivity is likely to be low.The work described below includes the initial identification of existing data sets atSUERC which contain dietary supplements, review of these data sets, examination ofPSL versus TL outcomes, and of sample groups/types associated with different PSLscreening and TL outcomes. This report also summarises these investigations andpotential future work.2. Review of existing data sets including dietary supplements which have beenanalysed with PSL, calPSL and TL.As a first step, luminescence data from dietary supplements available at SUERC havebeen identified. Data sets reviewed included surveys conducted by SUERC between2001 and 2005 for the Food Standards Agency6,9, for National Authorities in Ireland,Denmark and Norway, and for a consortium of European Consumer Organisations, aswell as samples routinely examined in response to individual submissions from otherorganisations between 2001 and 2008.The surveys together comprised 1007 analyses, of which 427 were from dietarysupplement samples. Of these, 280 samples had both PSL screening and TL analysis.Full calibrated PSL data sets in combination with TL analysis were available for 113of these samples. These data sets have been examined in detail in this study. Bothqualitative and quantitative descriptive analyses are presented below, with full detailsat the level of individual samples presented in Appendices.Between 2001 and 2008 routine analyses were performed from 7967 samples, ofwhich 5182 were classified as dietary supplements and their excipients. Normallythese would have been submitted to SUERC for either PSL screening analysis or forTL analysis. The combination of PSL screening and TL analytical data exists in ourdatabase for 554 samples. The qualitative correspondence between PSL screeningoutcomes and TL outcomes has been reviewed for these cases.2
2.1 Identification of data setsTen data sets from the surveys, which included dietary supplements, were identifiedas summarised below. Where these also contained other materials, that has beennoted, together with the total number of samples submitted in each product category.The techniques used are also tabulated for each of these surveys.Number Submittingbody1UK s and spices(203), shellfish (202),dietary supplements(138)Dietary supplements(47)PSL, calPSLand TL2003UK FoodStandardsAgency2002Dietary supplements3Food Safety(24)Authority ofIreland2003Dietary supplements4Food Safety(26)Authority ofIreland2005Dietary supplements5Food Safety(20)Authority ofIreland6Norwegian2003/4Herbs and spices (10),Food Safetyshellfish (10), dietaryAuthoritysupplements (10)2004/5Shellfish (13), dietary7Norwegiansupplements (21)Food SafetyAuthority2003Dietary supplements8Danish(40)Veterinary andFoodAdministration2005Dietary supplements9Danish(22)Veterinary andFoodAdministration2004Herbs and spices (79),10Belgian Foodshellfish (65), dietaryCommissionsupplements (79)(samples fromBelgium, Italy,Spain andPortugal)Table 2.1: Summary of surveys examined in this project2PSL, calPSLand TLPSL and TLPSL and TLPSL and TLPSL, calPSLand TLPSL, calPSLand TLPSL and TLPSL and TLPSL and TLThe data sets reviewed thus comprised a total of 1007 samples of which 292 wereherbs and spices, 290 were shellfish and 427 were dietary supplements. All sampleswere screened using PSL; for four of the surveys calPSL analyses were also3
performed on all samples, giving a total of 216 dietary supplement cases where PSLsensitivity could be considered along with the outcomes of PSL screening. Of these113 samples were also passed on to TL analysis. The surveys examined comprise 2conducted by the UK Food Standards Agency6,9, 3 for the Food Safety Authority ofIreland10-12, 2 each for the Norwegian Food Safety Authority13-14and the DanishVeterinary and Food Administration, Regional Veterinary and Food ControlAuthority15-16 and also one organised by the Belgian Consumer Association withsamples submitted by equivalent bodies in Italy, Spain and Portugal as well asBelgium17The selection criterion for progressing to TL varied from survey to survey. In all ofthe studies samples with intermediate or positive PSL progressed to TL analysis.In the FSA studies 10% of samples with negative PSL screening outcomes were alsoselected for TL analysis. In the Irish studies 10-12 , all samples underwent TL analysis.In the Danish studies15-16 samples had been pre-screened using the DEFT/APCmethod, and were then submitted for TL analysis; PSL analyses being conductedinformally by SUERC at the same time. The PSL outcomes of samples which werenot selected by DEFT/APC are unknown.For both the FSA surveys, samples were purchased by Trading Standards Officers in5 regions of the UK (Yorkshire, Oxfordshire, Wales, Northern Ireland, Scotland)according to an explicit schedule. 138 dietary supplements were purchased out of atotal of 543 samples in 200 product categories in 2001. Following the discovery thatof the dietary supplement samples analysed, 44 were identified as being irradiated and14 as containing an irradiated ingredient. This lead to a follow-up survey in 2003,conducted again under enforcement conditions, looking at the same products wherepossible. 47 products were purchased by Trading Standards Officers, and analysedat SUERC.The Food Safety Authority of Ireland also conducted surveys on dietary supplementsprompted by the high incidence of irradiation of herbal supplements in the FSA2001/2 survey. Twenty-four herbal supplements were bought “off the shelf” fromhealth stores, a supermarket and a pharmacy. These herbal supplements were in eithercapsule or tablet form. Both PSL and TL methods were used for the analysis of thesesamples. Ten of the 24 samples had either been irradiated (4) or contained andirradiated component (6).In the second Irish survey, twenty-six herbal supplements and substances werepurchased “off the shelf”. Again, the herbal supplements were in capsule or tabletform. All samples underwent both PSL screening and TL analyses. Ten of thesamples tested were described as “herbal substances” because they were presented forsale as powders or in leaf form rather than as packaged doses. 13 of the 26 samplestested were found to have been irradiated: a total of 11 of the 16 herbal supplements(5 irradiated and 6 containing an irradiated component) and 2 of the 10 herbalsubstances, both containing an irradiated component.A further Irish survey targeting herbal supplements that had previously been shown tobe either irradiated or to have an irradiated component was carried out in 2005. Atotal of 20 herbal products were purchased “off the shelf”. Of the 23 samples thatwere identified as having been irradiated in previous surveys five were unavailable4
(discontinued or out of stock) and therefore two extra herbal supplements wereincluded. The products included both supplements and substances. No distinction wasmade between these categories in the FSAI’s final report. Of the eight productspreviously identified as irradiated in both 2002 and 2003, four of these were againfound to be irradiated, three contained an irradiated component and one was negative.Of the 11 products identified as having an irradiated component in 2002 and 2003,one was irradiated and the remainder contained irradiated components.Two surveys in Denmark were prompted by the FSA disclosure that unlabelledirradiated dietary supplements were to be found in the UK market. In 2003 106herbal food supplements (either capsules, tablets or powder) were identified as beingworthy of examination and examples of each were purchased by the 11 DanishRegional Laboratories, from the importer or manufacturer where possible18.All 106 products were screened using DEFT/APC. 40 samples had a DEFT/APC logdifference of 4.0 or greater, defined in EN1378321 as indicating irradiation. These 40samples were then analysed using both PSL and TL at SUERC, leading to 5 positive,6 intermediate and 28 negative PSL screening results. All these samples alsounderwent TL analysis, leading to 15 irradiated results (11 positive and 4 containingirradiated components). This was interpreted 18 as evidence that DEFT/APC producesa lot of “false positives”, but since due to study protocol it was not possible tocompare luminescence analyses with negative DEFT/APC, the incidence of “falsenegatives” cannot be assessed here. It was also observed that some clean productsand/or those with only minor irradiated ingredients produced TL signals associatedwith negative PSLIn a follow-up survey in 2005, 22 samples were submitted to SUERC for analysis.Sample types corresponded to those in the earlier survey. PSL screening showed that21 of these samples were negative and one was intermediate. TL was performed onall 22 samples, with 16 negative outcomes, 4 positives and 2 containing irradiatedcomponents. .Small numbers of samples (10 and 21 respectively) were examined in two Norwegiangovernment surveys in 2003 and 2004. Only those samples with non-negative PSLwere progressed to TL, 12 samples in total; there were no random negatives selectedfor this survey.Four EU countries (Belgium, Italy, Spain and Portugal) provided samples for aninvestigation co-ordinated by the Belgian Consumer Association in 2003. Herbs,spices and shellfish were examined as well as 79 dietary supplements. Instructionsfor purchase were provided for collaborators in each country. The samples were eithercapsules, tablets or tea bags. Only those samples with non-negative PSL wereprogressed to TL, no random 10% of negative PSL screening were put forward forTL.As indicated above, not all surveys use all 3 techniques, and the selection criteria forthe studies may introduce some elements of bias relative to the full range of marketedproduct.5
An initial examination of PSL screening correspondence with TL outcome wasperformed to identify cases where mismatched outcomes were obtained. Theincidence of negative PSL outcome followed by TL identification of irradiatedcomponents was repre
Photo-stimulated luminescence was developed as a screening test to identify samples which require further analysis by a method which takes account of sensitivity to ionising radiation, such as calibrated PSL (calPSL) or TL1-4. Extensive experience (in relation to herbs, spices, shell
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