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1、 W - - - - - - - - - 7 - -7- - -7 - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - W W D - w - - - - EN 13751:2009 (E) 2 Contents Page Foreword 3 1 Scope 4 2 Terms and definitions .4 3 Principle 5 4 Reagents .6 5 Apparatus .6 6 Sampling technique .6 7 Procedure .7 8 Eval
2、uation .8 9 Limitations . 10 10 Validation . 10 11 Test report . 11 Bibliography . 12 EN 13751:2009 (E) 3 Foreword This document (EN 13751:2009) has been prepared by Technical Committee CEN/TC 275 “Food analysis - Horizontal methods”, the secretariat of which is held by DIN. This European Standard s
3、hall be given the status of a national standard, either by publication of an identical text or by endorsement, at the latest by January 2010, and conflicting national standards shall be withdrawn at the latest by January 2010. Attention is drawn to the possibility that some of the elements of this d
4、ocument may be the subject of patent rights. CEN and/or CENELEC shall not be held responsible for identifying any or all such patent rights. This document supersedes EN 13751:2002. According to the CEN/CENELEC Internal Regulations, the national standards organizations of the following countries are
5、bound to implement this European Standard: Austria, Belgium, Bulgaria, Cyprus, Czech Republic, Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Romania, Slovakia, Slovenia, Spain, Sweden
6、, Switzerland and the United Kingdom. EN 13751:2009 (E) 4 1 Scope This European Standard specifies a method for the detection of irradiated foods using photostimulated luminescence (PSL). The technique described here comprises an initial measurement of PSL intensity which may be used for screening p
7、urposes, and a calibration method to determine the PSL sensitivity to assist classification. It is necessary to confirm a positive screening result using calibrated PSL or another standardised (e.g. EN 1784 to EN 1788) or validated method. The method has been successfully tested in interlaboratory t
8、rials using shellfish and herbs, spices and seasonings 1. From other studies it may be concluded that the method is applicable to a large variety of foods 2, 3, 4. 2 Terms and definitions For the purposes of this document, the following terms and definitions apply. 2.1 photostimulated luminescence P
9、SL radiation specific phenomenon resulting from energy stored by trapped charge carriers NOTE Release of this stored energy by optical stimulation can result in a detectable luminescence signal. 2.2 PSL intensity amount of light detected during photostimulation, in photon count rate 2.3 screening PS
10、L initial PSL PSL intensity recorded from the sample as received or following preparation 2.4 calibrated PSL PSL intensity recorded from the test sample following irradiation to a known dose, after initial PSL measurement 2.5 thresholds values of PSL intensity used for classification. In screening m
11、ode, two thresholds, a lower threshold (T1) and an upper threshold (T2) are used to classify the sample 2.6 negative PSL result PSL intensity below the lower threshold (less than T1) 2.7 intermediate PSL result PSL intensity between the upper and the lower threshold (greater than or equal to T1, les
12、s than or equal to T2) 2.8 positive PSL result PSL intensity above the upper threshold (greater than T2) EN 13751:2009 (E) 5 2.9 dark count photon count rate from the photomultiplier with an empty chamber in the absence of stimulation 2.10 light count photon count rate with a reference light source
13、(e.g. 14C loaded scintillant, or equivalent) in the sample chamber 2.11 empty chamber run PSL intensity measured from an empty sample chamber to ensure absence of contamination of the chamber 3 Principle 3.1 General Mineral debris, typically silicates or bioinorganic materials such as calcite which
14、originate from shells or exoskeletons, or hydroxyapatite from bones or teeth, can be found on most foods. These materials store energy in charge carriers trapped at structural, interstitial or impurity sites, when exposed to ionising radiation. Excitation spectroscopy has shown that optical stimulat
15、ion of minerals releases charge carriers 5, 6, 7. It has subsequently been shown that the same spectra can be obtained from whole herb and spice samples and other foods using photostimulation 2, 8, 9. PSL measurements do not destroy the sample, therefore whole samples, or other mixtures of organic a
16、nd inorganic material, can be measured repeatedly. PSL signals, however, decrease if the same sample is measured repeatedly. The methodology comprises screening (initial) PSL measurements to establish the status of the sample (see 2.3) and an optional second measurement following a calibration radia
17、tion dose to determine the PSL sensitivity of the sample (see 2.4). 3.2 Screening PSL For screening (see 2.3) the signal levels are compared with two thresholds (see 2.5). The majority of irradiated samples produce a strong signal above the upper threshold level. Signals below the lower threshold su
18、ggest that the sample has not been irradiated. Signal levels between the two thresholds, intermediate signals, show that further investigations are necessary. The use of thresholds produces an effective screening method which can also be backed up by calibration, by TL as described in EN 1788 or ano
19、ther validated method, e.g. 3, 4, 8. 3.3 Calibrated PSL For calibration, the sample is exposed to a defined radiation dose after the initial PSL measurement, and then re-measured. Irradiated samples show only a small increase in PSL after this radiation exposure, whereas unirradiated samples usually
20、 show a substantial increase in PSL signal after irradiation. EN 13751:2009 (E) 6 4 Reagents 4.1 Aerosol silicone grease, e.g. Electrolube SC0200H1) 4.2 Water, deionized 5 Apparatus 5.1 PSL system, e.g. SURRC PPSL Irradiated food screening system1) 10, 11, 12, 13, comprising sample chamber, stimulat
21、ion source, pulsed stimulation and synchronised photon counting system. For instrumental set-up, see 7.4. NOTE For the interlaboratory tests, the SURRC PPSL system has been used. 5.2 Disposable Petri-dishes NOTE For the interlaboratory tests, 5 cm Petri-dishes have been used. 5.3 Radiation source, c
22、apable of irradiating samples with a defined radiation dose before measurement of calibrated PSL. In the interlaboratory tests on shellfish and herbs, spices and their mixtures 1, sources delivering 60Co-rays have been employed at a fixed radiation dose of 1 kGy. Alternative sources may be used prov
23、iding they have been found satisfactory. NOTE Other fixed doses can be suitable. 5.4 14C-Source (optional) 5.5 Laminar flow cabinet (optional) 5.6 Air duster (optional) 6 Sampling technique Whenever possible, the sample is taken from a light-protected position in the food consignment, since the PSL
24、intensity decreases on exposure to light. Before analysis, samples should be protected against light exposure. Store them in the dark. 1) Electrolube SC0200H and Scottish Universities Research and Reactor Center Pulsed Photostimulated Luminescence (SURRC PPSL) are examples of products available comm
25、ercially. This information is given for the convenience of users of this standard and does not constitute an endorsement of CEN of these products. Equivalent products may be used if they can be shown to lead to equivalent results. EN 13751:2009 (E) 7 7 Procedure 7.1 General All dispensing and handli
26、ng of samples should be carried out under subdued lighting whenever possible. Samples are dispensed into disposable Petri-dishes and introduced to the system. Samples should be handled with care to avoid cross-contamination during dispensing. It is recommended that samples are dispensed individually
27、, under a laminar flow cabinet (5.5), and fresh tissue is placed on the bench for each sample. The Petri-dish should be covered with a lid to reduce the possibility of contamination. 7.2 Preparation of herb, spice and seasoning samples Samples are dispensed into clean Petri-dishes, in duplicate. If
28、these test samples lead to inconsistent classifications, a further four aliquots shall be dispensed and classification based on the highest two results. Some samples can require a minimum of preparation; e.g. vanilla pods may need to be cut to fit the dish and wrappings should be removed. Samples ca
29、n either be dispensed in a thick layer within the Petri-dish or in a thin layer, applied to a dish already sprayed with silicone grease (4.1) to fix the sample. Thicker layer samples are less likely to be affected by bleaching; subsurface minerals can be exposed by gentle agitation. NOTE Thin layer
30、samples can also be dispensed into planchets or other shallow containers suitable for irradiation with 90Sr or other sources. If a gamma source is used for calibration either dispensing method is suitable. 7.3 Preparation of shellfish 7.3.1 General PSL analysis can be conducted using whole samples i
31、ncluding shell, shelled whole samples and dissected intestines or minerals extracted by flushing with water (4.2). If enough sample material is available, it is recommended that samples be divided into at least six portions, i.e. six Petri-dishes. 7.3.2 Whole samples Whole samples including shell ca
32、n be placed as received in the Petri-dish. In some cases it can be necessary to cut the shellfish to fit the Petri-dish. If the intestinal tract is visible, it is preferable to place this uppermost. 7.3.3 Shelled whole samples Shelled whole samples can be placed whole in the Petri-dish, again with t
33、he intestinal tract facing upwards, using as many individual shellfish as will fit in the Petri-dish. 7.3.4 Shellfish intestines Shellfish intestines can be found as a thin dark tube on the convex side of prawns or shrimps, and in the interiors of molluscs. Using a scalpel, slice the flesh open and
34、with tweezers remove the intestinal tract. Repeat this technique on several samples of shellfish (recommended: 6 intestines per Petri-dish). 7.4 Instrumental Set-Up This section describes the set-up of the SURRC PPSL system, as an example. EN 13751:2009 (E) 8 The system is used in conjunction with a
35、 computer for setting individual measurement parameters (cycle time, thresholds and data recording conditions) for recording quantitative photon counts. NOTE 1 The system can be used in a stand-alone mode, with simple push button controls, for preliminary measurements. However, the validated procedu
36、res which are the subject of this standard apply only to quantitative measurements performed in conjunction with a computer. The instrumental set-up procedure includes checks on dark count (2.9) and light count (2.10), establishing measurement parameters and checks on irradiated and unirradiated sta
37、ndard materials. For herbs and spices tested in the interlaboratory trial 1, the threshold settings of T1 = 700 counts/60 s and T2 = 5 000 counts/60 s have been shown to be satisfactory. These thresholds refer to the use of 5 cm Petri- dishes. For shellfish tested in the interlaboratory trial 1, the
38、 threshold settings of T1 = 1 000 counts/60 s and T2 = 4 000 counts/60 s have been shown to be satisfactory. NOTE 2 The threshold levels are based on results of interlaboratory tests and further experience. They might need to be adjusted in dependence of the PSL sensitivity of the samples, the sensi
39、tivity of the instrument and the surface area of the samples (size of petri-dishes). It has been shown that e.g. pepper, nutmeg and clove are less sensitive to PSL. An empty chamber test (2.11) should be run to ensure that the chamber is free from contamination. This step should be repeated periodic
40、ally, e.g. at least every 10 samples and also after samples with positive results. An air duster (5.6) can be used to clean the sample chamber. 7.5 Screening Measurements Run the test samples and record the results over the specified measurement time. The results should be classified according to th
41、e pre-set thresholds 2.6 to 2.8. 7.6 Calibrated Measurements After screening, the sample should be covered to prevent loss of material or contamination, either with the lid of the Petri-dish or, in the case of planchets or shallow containers, some other suitable means. During handling, care should b
42、e taken not to shake the sample. The sample should then be exposed to a defined radiation dose (e.g. 1 kGy or a dose comparable to the expected treatment dose). After irradiation, all further handling should take place under subdued lighting whenever possible. After storage overnight at ambient temp
43、erature (chilled storage is recommended for shellfish and other perishable materials), perform calibrated measurements according to 7.4 and 7.5. 8 Evaluation 8.1 Negative result 8.1.1 Screening PSL Negative results (counts less than T1) indicate that the sample is unlikely to be irradiated. For irra
44、diated samples with insufficient PSL sensitivity, negative results can also occur. 8.1.2 Calibrated PSL Negative calibrated results (calibrated results reading less than T1) are indicative of insufficient PSL sensitivity. These are unusual in herbs and spices and should always be associated with negative screening results. With