Identification of irradiated foods by the thermoluminescence of mineral contamination

Summary This investigation assessed the radiation-induced thermoluminescence (TL) of food minerals for identifying irradiated foods. Mineral contamination, rather than the inherent mineral content, of foods was studied. Positive identification of foods given 1–10-kGy doses depends on the contents and composition of the mineral contamination and the time span between irradiation and TL analysis. All 20 irradiated spice and herb samples could be identified without comparing them with unirradiated material. Three out of 60 lots of spices and herbs examined so far were so pure that the mineral contents were too low to allow TL analysis. If the soil where potatoes are grown contains feldspars, sprout inhibition treatment with 100–200-Gy doses can also be detected for up to one year, using the 90–250° C low-temperature part of the TL spectrum for evaluation.

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Die Identifizierung strahlenbehandelter Lebensmittel anhand der Thermolumineszenz mineralischer Verunreinigungen

Zusammenfassung Gegenstand dieser Untersuchung ist die strahleninduzierte Thermolumineszenz (TL) der in Lebensmitteln enthaltenen Mineralien als Mittel zur Identifizierung strahlenbehandelter Lebensmittel. Untersucht wird nicht der Eigengehalt der Lebensmittel an Mineralien, sondern die Mineralienkontamination. Die positive Identifizierung von Lebensmitteln, die mit einer Dosis von 1–10 kGy bestrahlt worden waren, ist abhängig vom Gehalt und der Zusammensetzung der Mineralienkontamination sowie von der Zeitspanne zwischen Bestrahlung und TL-Analyse. Noch nach Ablauf von maximal einem halben Jahr konnten sämtliche Gewürzund Kräuterproben (insgesamt 20 Stück) ohne irgendwelche Vergleiche mit unbestrahltem Material identifiziert werden. Von insgesamt 60 bisher überprüften Losen waren drei so sauber, daß ihr Mineraliengehalt für eine TL-Analyse nicht ausreichte. Wenn der Boden eines Kartoffelfelds Feldspate enthält, kann auch die Keimhemmungsbehandlung der Kartoffeln mit Dosen von 100 bis 200 Gy noch bis nach Ablauf von einem Jahr erkannt werden; für die Bewertung wird dabei der Niedrigtemperaturanteil des TL-Spektrums im Bereich von 90 bis 250 °C herangezogen.

     

Applicability of thermoluminescence techniques to identify irradiated seafoods using different methods of mineral separation: An interlaboratory blind trial

Thermoluminescence (TL) technique for identifying γ-irradiated (0–10 kGy) anchovies (dried), kelp (dried), and mackerel (fresh) was validated in an interlaboratory blind trial. Different irradiation detection laboratories were involved by using 2 methods of mineral separation (density separation and acid hydrolysis) for the analysis. Key TL parameters, including the TL glow-curve shape, intensity, and the TL ratio (TL₁/TL₂) were used to characterize the irradiation status. All irradiated samples exhibited an intense TL peak at approximately 200°C, which was absent in non-irradiated samples. TL glow curve interpretations were also confirmed by determining the TL ratio. Different participating laboratories reported 89–100% correct results. Both methods of mineral separation were equally effective; however, some variation was observed in the results from different laboratories for irradiated mackerel, which might be due to a lack of isolated minerals, differences in personnel expertise, and different TL instruments.     

Identification of a gamma-irradiated ingredient (garlic powder) in Korean barbeque sauce by thermoluminescence analysis

Thermoluminescence (TL) analysis was applied to identify gamma-irradiated garlic powder in Korean barbeque sauce before and after pasteurization (85 °C, 30 min), when blended in different ratios (1%, 3%, and 5%). The sauce sample with nonirradiated garlic powder gave a background glow curve. However, the sample blended with irradiated ingredient (1 and 10 kGy) showed typical TL glow curves at temperatures of 150 to 200 °C. The identification properties of sauce samples were more influenced by blending ratios than by irradiation doses, showing that 3% and 5% added samples produced glow curves at 150 to 250 °C. After pasteurization of the samples containing the irradiated ingredient, TL glow intensity decreased but did not change its shape or temperature range. As a result, the pasteurization of Barbeque sauces containing irradiated ingredients had reduced TL glow intensity, but the shape and temperature range of glow curve were still able to provide information required for confirming irradiation treatment. PRACTICAL APPLICATION: To monitor the irradiated food in international market, thermoluminescence (TL) analysis is considered most promising identification technique because of its sensitivity and long-term stability. In this study the applicability of TL analysis to detect an irradiated ingredient (garlic powder) added in low quantity to a food matrix (sauce) was investigated. The effect of processing (pasteurization) on TL results was also evaluated.     

辐照食品分析检测技术的研究进展

本文介绍了国内外辐照食品检测技术的研究进展，着重对化学分析法、电子自旋共振(ESR)法及热释光分析(TL)法进行了阐述，并对今后辐照食品检测技术的研究提出了建议。     

Import control of irradiated foods by the thermoluminescence method

Summary A thermoluminescence (TL) method was applied for the import control of irradiated foods. The method is based on the determination of the TL of mineral contaminants in foods. Detection of irradiation was incorporated in official Finnish control procedures in spring 1990. For foodstuffs with a reduced microbe content and in which no fumigant residues are found, possible irradiation is investigated by the TL method. The minerals are separated from the foods in different ways: picking is used for spices; water rinsing for herbs, spices, berries and mushrooms; high-density liquid to separate the organic material from the mineral fraction in seafood; and carbon tetrachloride for foods forming gels with water. To date about 140 food samples have been analysed for control purposes: 50 samples of herbs and spices, 25 samples of berries and mushrooms and 65 samples of seafood. Of these, 14 samples of herbs and spices and 5 samples of seafood were shown to have been irradiated. Differences in TL intensity between irradiated and unirradiated samples were at least 1 and usually 3–4 orders of magnitude.

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Einfuhrkontrolle bestrahlter Lebensrnittel mit Hilfe der Thermoluminescenz-Methode

Zusammenfassung Eine Thermoluminescenz-Methode (TL) wurde für die Einfuhrkontrolle bestrahlter Lebensmittel verwendet. Diese Methode basiert auf der Messung der Thermoluminescenz von in den Lebensmitteln vorhandenen mineralischen Verunreinigungen. Diese Methode, eine Bestrahlung festzustellen, wurde im Frühjahr 1990 in das offizielle finnische Kontrollverfahren aufgenommen. Lebensmittel mit reduziertem Mikrobengehalt, ohne feststellbare Begasungsrückstände werden mit der TL-Methode auf eventuelle Bestrahlung überprüft. Die mineralischen Stoffe werden mit verschiedenen Verfahren aus den Lebensmitteln abgetrennt. Dabei werden bei Gewürzen die mineralischen Partikel manuell entnommen, bei Kräutern, Gewürzen, Beeren und Pilzen werden diese mit Wasser abgespült, bei Meeresfrüchten wird mit hochkonzentrierter Lösung behandelt und das organische Material wird von der anorganischen Fraktion bei Lebensmitteln, die mit Wasser gelieren, mit Kohlenstofftetrachlorid abgetrennt. Bis jetzt sind zu Kontrollzwecken etwa 140 Lebensmittelproben analysiert worden: 50 Kräuter- und Gewürzproben, 25 Beeren- und Champignonproben und 65 Proben von Meeresfrüchten. Dabei konnte bei 14 Kräuter- und Gewürzproben sowie bei 5 Proben von Meeresfrüchten eine Bestrahlung nachgewiesen werden. Zwischen den bestrahlten und den unbestrahlten Proben zeigten sich in der TL-Intensität Unterschiede von mindestens einer, meist jedoch von drei bis zu vier Größenordnungen.

     

热释光法在辐照食品检测中出现假阳性问题的探讨

目的探讨热释光法在辐照食品检测中出现假阳性的问题。方法按照标准EN1788-2001《食品与硅酸盐矿物隔绝的食品的辐射检验热致发光法》,采用热释光法对深海鱼加工产品进行辐照食品检测。结果与花椒粉等典型辐照样品不同,深海鱼加工产品虽然检测结果为阳性,但其谱图与典型辐照样品谱图存在一定差异。主要表现为一次发光曲线中,典型辐照样品谱图的发光峰下降舒缓,峰型符合正态分布;而深海鱼加工产品的发光峰下降陡峭,并不符合正态分布。据此,怀疑热释光法对深海鱼加工产品的检测分析结果实为假阳性。结论建议在对深海鱼产品进行辐照检测时,谨慎选用热释光法或采用其他检测方法如气相色谱分析碳氢化合物法进行复验。     

茶叶辐照的热释光分析研究

不采用二次辐照,将TL 分析法应用于辐照茶叶的定性鉴定。分离并收集茶叶中黏附的硅酸盐,采用热释光剂量仪测量获得硅酸盐的热释光发光曲线,比较未辐照与辐照不同剂量茶叶的热释光发光曲线的积分强度、峰值和峰值温度等特征参数。未辐照茶叶的热释光发光曲线的积分强度小于50、峰值小于0.4、峰值温度大于260℃;反之,辐照茶叶的热释光发光曲线的积分强度大于50000、峰值大于600、峰值温度位于160～190℃。TL 分析法能判别出茶叶的辐照与否,尤其对不能满足参比剂量辐照条件的样品很有帮助。     

Effect of Drying Treatment on Physical Identification Characteristics of Irradiated Seasonings

The effect of different drying treatments such as spray drying and vacuum drying on the sensitivity of physical detection methods (photostimulated luminescence (PSL), electron spin resonance (ESR), and thermoluminescence (TL)) was investigated for four types of irradiated seasonings. The slurry feed of each seasoning was exposed to γ-ray irradiation at doses of 0, 5, 10 kGy before being subjected to drying process. Spray drying was applied to beef and soybean seasoning while garlic and broth seasoning were exposed to vacuum drying according to routine protocols adopted in the industry. The samples were analyzed by PSL as a rapid screening method followed by validated methods including ESR spectroscopy and TL analysis. The PSL photon counts drastically dropped in all irradiated samples after both drying processes. No ESR signal was obtained from any of the irradiated seasonings before or after the drying applications. All the irradiated seasoning samples produced typical TL glow curves between the specific temperature range of 150–250 °C. However, the shape, peak, and intensity of TL glow curves were greatly affected particularly after the spray drying treatment. In conclusion, the dry treatment can significantly affect the irradiation detection characteristics in seasoning samples.     

纸质食品包装材料的矿物油迁移研究进展

食品中的矿物油污染物是指石油来源的C10~C50烃类化合物, 包括烷烃矿物油(mineral oil saturated hydrocarbons, MOSH)和芳烃矿物油(mineral oil aromatic hydrocarbons, MOAH)2大类。近年来的研究表明, 食品中的矿物油污染物主要来源于食品的回收纸包装材料迁移。本文综述了国外近十年来纸质包装材料的矿物油迁移研究情况, 包括纸质包装材料迁移的矿物油分析方法——液相色谱-气相色谱联用法; 矿物油迁移至食品的2种方式: 气态扩散迁移和包装材料接触迁移; 降低矿物油迁移的技术方法, 即食品包装纸质材料的回收工艺, 向包装纸质中添加活性炭等吸附剂以及增加阻隔层以阻挡矿物油的迁移。旨在为相关企业和机构提供数据与技术参考。     

2014年陕西省市售食品中重金属污染调查及评价

目的对陕西省6类食品中铅、镉、汞、砷的含量进行检测,并对其污染状况做出综合评价,从而为陕西省开展食品安全评估和采取针对性的控制措施提供科学依据。方法在陕西省境内10个地市的大型农贸市场、批发市场和超市,采集粮食562份、蔬菜340份、水果174份、肉类228份、蛋类144份和奶类108份,6类食品共1 556份。利用电感耦合等离子体质谱法(ICP-MS)测定铅(Pb)、镉(Cd)的含量,应用GB/T 5009.11—2003《食品中总砷及无机砷的测定》中氢化物原子荧光法测定砷(As)的含量,利用测汞仪直接测定汞(Hg)的含量,采用单项污染指数及综合污染指数对不同类食品中铅、镉、汞、砷的污染状况做出评价,并对陕西省居民经此6类食品摄入铅、镉、汞、砷的人体健康风险进行描述。结果陕西省6类食品中,铅、汞含量均值最高的都是肉类,分别为0.049 0和0.003 3 mg/kg,镉、砷含量均值最高的是粮食类,含量均值均为0.025 0 mg/kg;利用单项污染指数和综合污染指数对6类食品中铅、镉、汞、砷含量进行评价,均可评价为安全、清洁;由6类食品摄入铅、镉、汞、砷的安全限值(MOS)1。结论陕西省6类食品不同程度的受到了铅、镉、汞、砷的污染,但总体污染程度较低,铅、镉、汞、砷对食品安全影响的风险较低。     

An improved method to identify irradiated rice by EPR spectroscopy and thermoluminescence measurements

Minimal change in irradiated foods with low dose treatment makes the identification process a difficult task. Two independent physical methods, electron paramagnetic resonance (EPR) spectroscopy and thermoluminescence (TL) detection were employed for detection of irradiation treatment on Basmati rice. EPR investigation of 0.5–2.0 kGy irradiated rice samples showed a short lived, asymmetric, dose dependent spectrum (g = 2.005), characterised by the radicals of irradiated starch. However, this signal disappears with time. The present work explores the possibility to identify irradiated rice by the relaxation characteristics and thermal behaviour of the radicals. This study reports for the first time that the different microwave saturation behaviours of the signal (g = 2.004) in irradiated and non-irradiated rice samples provide an important clue to identify radiation treatment beyond the period when the radiation specific EPR spectral lines have disappeared. TL investigation involving scanning electron microscopy/energy dispersive X-ray analysis (SEM/EDX) of the poly-minerals isolated from the rice samples allowed to discriminate clearly between irradiated and non-irradiated samples even after a prolonged period of storage.     

Synthesis,characterisation and use of 2-tetradecylcyclobutanone together with other cyclobutanones as markers for irradiated liquid whole egg

The synthesis and characterisation of 2-tetradecylcyclobutanone (TCB) is described. Both 2-dodecykyclobutanone and TCB were shown to be present in liquid whole egg irradiated at doses of 2.5 and 10.0 kGy. These compounds were absent from the unirradiated pasteurised samples. Using gas chromatography and infrared spectroscopy, there was also evidence for the presence in irradiated egg of 2-tetradeccnyl- and 2-tetradecadienylyclobutanone which are formed from oleic and linoleic acids, respectively. Authentic standards for these unsaturated cyclobutanones were not available commercially but the presence of 2-tetra-decenylcyclobutanone was substantiated by hydrogenating the egg extracts so converting this unsaturated cyclobutanone to TCB. Saturated and unsaturated cyclobutanones appear to be specific products of irradiation and are potential markers for detection of irradiated liquid egg and probably other fat-containing foods.     

Identification of Irradiated Shellfish Using Well-Characterized Thermoluminescence Properties of Biogenic Minerals Present in the Exoskeletons

The shellfish exoskeleton is mainly composed of carbonate minerals with very minute traces of silicate minerals. Feldspar (silicate mineral) has outstanding thermoluminescence (TL) characteristics, whereas carbonate minerals could lead to the false detection of irradiation history. The silicate minerals present in the biogenic exoskeleton matrix of shellfish (Corbicula and Melanian snail) were targeted for their TL properties after separating through different acid treatments of shell samples. Excellent TL results for the TL glow curve shape, intensity, and TL ratio (TL₁/TL₂) were obtained where the clear discrimination of irradiation treatment (0, 2, and 4 kGy) was possible. The results were compared to the whole shell powder samples, feldspar, and calcite standard minerals to present a better understanding of their luminescence characteristics. The developed TL method showed the potential to successfully identify irradiated shellfish for the regulatory requirements.     

Characteristics of DNA Comet, Photostimulated Luminescence, Thermoluminescence and Hydrocarbon in Perilla Seeds Exposed to Electron Beam

ABSTRACT: Detection characteristics of perilla seeds exposed to electron beam doses of 0 to 2 kGy were investigated. DNA comet assay, photostimulated luminescence (PSL) and thermoluminescence (TL) measurements, and hydrocarbon determinations by GC-MS were carried out. The irradiated samples showed comets with longer tails (152 ± 6 mm) than did nonirradiated samples (35 ± 11 mm). PSL values (photon counts) for the irradiated samples were more than 7865; whereas those of nonirradiated samples were less than 294. TL ratios (Glow 1/Glow 2) obtained from nonirradiated samples were less than 0.01 and above 0.48 from irradiated ones. The prominent radiation-induced hydrocarbons were 16:2, 16:3, 17:1, and 17:2, of which 16:2 was the most abundant.     

Effect of γ-irradiation on physical quality attributes and identification properties of different sauces

Gamma-irradiated (0, 1, and 10 kGy) ketchup (KTP), barbeque sauce (BBQ), and sweet chili sauce (SWC) were identified using photostimulated-luminescence (PSL) and thermoluminescence (TL) analysis and characterized for physical properties like Brix, consistency, and color. PSL-based screening showed negative results for all nonirradiated samples, while intermediated results were found for irradiated samples. Routine density separation method for mineral extraction provided better TL results; however, alkaline and acid hydrolysis could ease the process with acceptable results. A slight decrease in consistency of all the samples was observed. Brix of KTP remained unchanged, while increase of same was obvious in BBQ and SWC following irradiation. The Hunter L* value of the γ-irradiated sauces decreased except SWC samples, and the a* and b* values showed a general increase compared to the non-irradiated samples. The studied methods have potential to successfully identify and characterize the irradiated sauces for technical and regulatory requirements.     

Changes in thermoluminescence properties of minerals separated from irradiated potatoes and garlic during long-term storage under different light conditions

The effect of different light conditions on the specificity and reliability of thermoluminescence (TL) analysis to detect irradiated samples (potatoes and garlic) during 2?years of storage was investigated. The silicate minerals separated from the nonirradiated samples provided a low-intensity TL glow curve with a maximum peak after 300?°C demonstrating the absence of an irradiation history. The TL glow curve from the irradiated samples provided easy discrimination with TL glow curves of high intensity and maximum peak in temperatures range of 160?C185?°C. The results were also confirmed by calculating the TL ratio (TL₁/TL₂) through normalization (re-irradiation) step. The key parameters of the TL analysis including the TL intensity, TL glow curve shape, and the TL ratio exhibited a time-dependent change. The bleaching effect of different light conditions was also significant, which was most prominent in the case of natural light with a prominent decrease in the TL intensity and ratio. The maximum TL glow peak also showed a shift towards the higher temperature. However, all irradiated samples, irrespective of the storage conditions and time, were easily discernable from the nonirradiated ones considering the shape and intensity of the TL glow curve.     

Mineral oil polyaromatic hydrocarbons in foods, e.g. from jute bags, by on-line LC-solvent evaporation (SE)-LC-GC-FID

 On-line and automated LC-SE-LC-GC-FID was used for the analysis of polyaromatic hydrocarbons in foods contaminated with mineral oil products. The detection limit for a fraction was around 1 mg/kg. Batching oil from jute bags introduces two-ring and three-ring aromatic compounds into foods (shown for rice), and environmental contamination of fish introduces primarily two-ring compounds. For other foods containing mineral oil material from unknown sources, the analysis provided important information about the type of oil involved (shown for a sample of linseed oil, a safflower oil and a chocolate). Received: 26 February 1996 / Revised version: 3 June 1996     

Some limitations of the comet assay to detect the treatment of seeds with ionising radiation

DNA fragmentation, detected by microgel electrophoresis of single cells, is applied as a marker for irradiation treatment of seeds. Seeds may be treated with ionising radiation for the purpose of insect disinfestation or microbial control. Various seeds treated with radiation doses in the range of 0-5 kGy were analysed. After electrophoresis, irradiated cells--with a large number of DNA strandbreaks--showed tailing and appeared as distinct comets, whereas non-irradiated cells appeared nearly circular or with only slight comet tails. Shape, length and intensity of comets were dose-dependent. Although DNA comet assay has now been adopted as an official European Standard (EN 13784) to detect irradiated foodstuffs, the method discloses several limitations. Identification was successful for buckwheat, linseed, melon, nigella, poppy, sesame and sunflower seeds, but caused problems for fennel, fenugreek, millet and mustard seeds. In some foods, many comets were also detected in the non-irradiated samples, mimicking an irradiation treatment. The use of the DNA comet assay as a screening method for irradiated food, therefore, has its restraints, but for a number of foods it serves as a rapid and inexpensive test.     

Development and single laboratory validation for thermoluminescence detection of irradiated foods using X-ray irradiation

The thermoluminescence (TL) method using X-rays was investigated for the purpose of detection of irradiated food, and the method was validated at a single laboratory level. A small X-ray irradiator was developed as an alternative radiation source for normalization, and X-ray irradiation conditions equivalent to gamma-ray irradiation from (60)Co were established. Gamma-ray irradiated spices were used for the method validation. The detection limits (MDL) and lower limit of integrated TL intensities (MDL×10) for the spices were checked and the separation of silicate minerals from the spices was confirmed to be sufficient for TL analysis. There was no significant difference in TL glow ratio obtained using two sets of X-ray irradiation equipment including the newly developed equipment. Repeatability and intermediate precision showed no influence of analysts, X-ray irradiation equipments, or measurement days on the TL ratios. From these results, this detection method was validated in a single laboratory.     

FLAVOR SENSITIVITY OF SELECTED ANIMAL PROTEIN FOODS TO GAMMA RADIATION

Raw protein foods derived from 20 different species of animals of different biological classifications were irradiated with gamma irradiation over a range of doses. The intensity of irradiated flavor developed in each case was determined by an expert panel. Relative flavor sensitivities and threshold doses were estimated.