Applicability of different analytical methods for the identification of γ-irradiated fresh mushrooms during storage

Photostimulated luminescence (PSL), thermoluminescence (TL), and electron spin resonance (ESR) analyses were performed to identify γ-irradiated (0, 1,2, and 3 kGy) fresh mushrooms (oyster, king oyster, and shiitake mushrooms) during storage at 5°C. PSL analysis gave negative results [<700 photon counts (PCs)] for the nonirradiated and intermediate (700–5,000 PCs) or positive results (>5,000 PCs) for the irradiated samples. The shape, intensity, and occurrence of TL glow curve in a typical temperature range (150–250°C) along with TL ratio (TL₁/TL₂) provided sufficient information to confirm the irradiation history of samples. Storage resulted in a negligible fading effect on PSL and TL characteristics. X-ray diffraction analysis showed the abundance of feldspar and quartz minerals in the separated dust from mushrooms. In detailed ESR analysis employing different sample pre-treatments, all samples were silent for radiation-specific ESR signals giving only a central signal (g=2.005) that showed an increase in intensity upon irradiation.     

Electron seed dressing of barley—aspects of its verification

Seeds (e.g. cereal grains) are treated with low energy electrons for seed dressing to inactivate phytopathogenic organisms on their surface and in the seed coat. To verify the electron treatment of barley by e-ventus^® technology, three physical detection methods were investigated: photostimulated luminescence (PSL), thermoluminescence (TL) and electron spin resonance (ESR). Influencing factors such as storage time and temperature, geographic origin of samples and light exposure were studied. All three detection methods proved to be suitable, with PSL being the most convenient. But also ESR by measuring the barley husks offered a simple and rapid verification. Although TL was more laborious to perform, it was highly reliable. PSL was able to classify electronically dressed seeds after storage times of at least 12–13 months independent of storage temperatures, assayed in the range of 5–23 °C. The applicability of ESR after storage was dependent on the measuring system used and on storage temperature. At room temperature the advanced E-Scan? spectrometer allowed verification of treatment for at least 7.5 months, whereas the EMS 104 spectrometer was applicable only up to 2 months of storage. Storage temperatures of 5 °C markedly prolonged the verifiability of treatment. Using TL, treated samples stored at room temperature could be easily verified for at least 13 months. Fading of the PSL signal of treated barley was observed under the influence of light, the extent of fading being influenced by illuminance but not by treatment of the samples with high or low energy electrons. Contrary to PSL, TL and ESR were found to be still applicable for the detection of treated barley exposed to light.     

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.     

Identification of gamma-irradiated ingredients in liquid seasonings by thermoluminescence analysis: an interlaboratory blind trial

An interlaboratory blind trial was conducted to validate the thermoluminescence (TL)-based identification of gamma-irradiated (0, 1, and 10 kGy) ingredients (garlic powder) in liquid seasonings. Two kinds of forty (20 each) coded samples containing irradiated ingredients at blending ratio of 0–3 % were processed in a food industry and sent to two different irradiation detection laboratories. The garlic powders were also analyzed by both laboratories as reference materials. Irradiated garlic powder provided a strong TL peak at about 200 °C, which was absent in the non-irradiated ones, and the results were also confirmed by determining the TL ratio (TL₁/TL₂). In the blind trial of sauces containing an irradiated ingredient, 75–80 % validated results were reported. The problematic results were observed for the samples containing low quantities of 1 kGy-irradiated ingredients. The TL ratios of all sauce samples were <0.1 irrespective of their irradiation history, where the evaluation was made using the glow curve shapes and intensities. Low amounts of irradiated ingredients could be effectively detected; however, the lower detection limits need to be established after getting a better understanding of the complex TL glow curve results.     

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。     

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.     

Dose dependence and fading effect of the thermoluminescence signals in γ-irradiated paprika

The thermoluminescence (TL) method can be used to discriminate irradiated and non-irradiated paprika. This study reports the polymineral composition of the dust adhered to paprika; radiation-specific luminescence is emitted by the inorganic material (mainly quartz, feldspars and calcite). On the basis of the shape of the TL curves (or glow curves) some physical parameters are evaluated. Natural TL curves, from non-irradiated samples, show three very low intensity peaks while induced TL curves, from irradiated paprika, seem to consist of five overlapping peaks. TL spectra reveal a very important difference in intensity and in the position of the peaks between irradiated and non-irradiated paprika. Fading observations of TL after irradiation at 5, 10 and 21 kGy, show the same behaviour in all the cases: an initial rapid decay to maintain a certain stability from 300–400 h onwards. © 1998 SCI.     

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.     

Detection of irradiation treatment in dried mushrooms by photostimulated luminescence,EPR spectroscopy and thermoluminescence measurements

Detection of the irradiation treatment of nine species of dried mushrooms commercially available employing photostimulated luminescence (PSL), electron paramagnetic resonance spectroscopy (EPR/ESR) and thermoluminescence (TL) is described. PSL is adaptable to six to seven species shortly after irradiation, but the PSL signal decays with storage and may render detection impossible. After 4 months of storage, six species could still be well identified by PSL if the radiation dose was higher than 5 kGy. EPR spectroscopy enabled detection with five to six species, both cellulose and crystalline sugar-like radicals being observed. For some mushrooms, hat or leg parts showed a different response and some lots could not be identified at all. TL - although being more cumbersome - allowed unequivocal identification of all species of investigated mushrooms. It is concluded that dried mushrooms exposed to ionising radiation can be successfully detected by at least one of the analytical methods investigated.     

Comparison of three methods for detection of herbal food supplement irradiation

A survey for irradiation of 106 herbal food supplements was carried out in Denmark in 2003. The results from three methods, two screening methods and a specific method, were compared: Direct epifluorescent filter technique/aerobic plate count (DEFT/APC), photostimulated luminescence (PSL) and thermoluminescence (TL) standardised by Comité Européen de Normalisation (CEN). Forty samples screened positive with the DEFT/APC method. However, the TL method could only confirm irradiation of 15 samples, 11 samples wholly irradiated and 4 samples with a minor irradiated ingredient. Thus, the DEFT/APC method gave a large number of false positive results, although the number of false negative results probably was very low. Only 7 of the 15 confirmed irradiated samples screened positive with the PSL screening method, the samples with low photon counts escaping detection. For 10% of the samples also the TL method was lacking in sensitivity, as not enough minerals could be isolated to get a signal over the minimum detection level. For such clean herbal food supplements no suitable method exists at all among the CEN standardised methods for irradiation detection.     

Analysis of irradiated jujube (Zizyphus jujuba) by photostimulated luminescence and electron spin resonance spectroscopy

Possibility of photostimulated luminescence (PSL) and electron spin resonance (ESR) to detect γ-irradiation of jujube (Zizyphus jujuba) was investigated. The jujube samples were exposed to γ-irradiation at doses of 1, 3, 5, and 10 kGy. The PSL results showed that jujube exposed to at 1 kGy or more had a photon count of greater than 5,000 count/60 sec (positive), while the non-irradiated jujube yielded a photon count of less than 700 photon count/60 sec (negative). However, physical parameters (light exposure, storage, and thermal treatment) of irradiated jujube samples gave a strong effect on the PSL signal, resulting in decrease of the photon counts from the initial counts. ESR spectroscopy analysis of irradiated jujube revealed specific signals derived from cellulose radicals, and irradiation caused a significant increase in the ESR signal intensity of the jujube samples without any changes in the spectral patterns. Light exposure, storage, and thermal treatment of jujube resulted in significant decreases in the ESR signal intensities of cellulose radicals.     

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.     

Inter-Laboratory study to define the temperature interval for a thermoluminescence heating unit used to identify irradiated food

EN 1788:2001 suggests defining the temperature range for the thermoluminescence (TL) heating unit to calculate the TL ratio (TL₁/TL₂). In the present study, practical temperature ranges were established by using well-characterized lithium fluoride (LiF, TLD-100®) at 4 different research institutes in Korea. Temperature ranges differed according to models of TLD heating unit, which were wide in the case of RISØ (160–249°C) as compared with Harshaw (155–232°C) TLD readers. The silicate minerals separated from irradiated turmeric samples were measured to check these intervals on a practical basis. The X-ray diffraction (XRD) analysis of separated minerals showed that quartz and feldspar minerals were the main source of well-characterized TL glow curve following irradiation. The TL glow peaks from the separated minerals were narrower in Harshaw than RISØ TLD readers. The TL ratios determined after re-irradiation (1 kGy) for the tested minerals, using the pre-defined temperature intervals, provided the satisfactory results.     

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。     

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.     

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.     

电子自旋共振波谱法对干果类辐照食品的鉴定

研究电子自旋共振波谱法对干果类辐照食品的鉴定。分析开心果、核桃、桂圆的电子自旋共振波谱特征和样品干燥温度对信号强度的影响。结果表明：电子自旋共振特征峰信号强度与吸收剂量呈正相关,检测限为0.5kGy;进一步干燥时,开心果和核桃的最佳温度为40℃,桂圆的最佳温度为55℃;电子自旋共振特征峰的信号强度受微波功率影响,检测开心果、核桃、桂圆最佳的微波功率依次为0.59、0.37、0.24mW。通过电子自旋共振特征峰可判定干果是否经过辐照处理。     

Improved Electron Spin Resonance Spectroscopy with Different Sample Treatments to Identify Irradiated Sprout Seeds

Irradiation helps to reduce microbial load in sprout seeds and prevents the outbreak of sprout-related foodborne illness. In food materials of plant origins, irradiation produces free radicals in cellulose and crystalline sugars which could serve as irradiation detection markers in electron spin resonance (ESR) analysis. In the present research, radiation-induced free radicals were studied in the seeds of alfalfa and broccoli irradiated at 0, 2, 4, and 6 kGy. The effect of three different sample pretreatments, namely freeze-drying, alcoholic extraction, and nitric acid extraction (5, 10, and 15 %), was also investigated. Freeze-dried and alcoholic-extracted samples lacked radiation-induced ESR spectral characteristics. However, the sample treatment with 5 % nitric acid was found most appropriate to obtain clear evidence of irradiation. These findings indicate the possible need for different sample pretreatments for clear or improved ESR spectral features.     

Pulsed photostimulated- and thermo-luminescence investigations of γ ray-irradiated herbs

In this study, physical detection methods like pulsed photo-stimulated luminescence (PPSL) and thermoluminescence (TL) were investigated to indentify γ-ray irradiation treatment of some medicinal herbs. Dried herbal samples consisting of root, rhizome, cortex, fruit, seed, flower, spike, ramulus, folium and whole plant of nineteen different herbs were irradiated using a 60Co irradiator at 0–50 kGy. Fifteen non-irradiated control samples had photon counts (PCs) less than the lower threshold value (700 counts/60 s). The photon counts of four non-irradiated samples (roots of osterici, angelica gigas, liriope, and whole plant of taraxaci herba) were between the lower and upper threshold values (700–5000 counts/60 s). However, PCs of all the irradiated samples were found to be higher than the upper threshold value (5000 counts/60 s), clearly screening them out from the non-irradiated ones. Even after 12 weeks of storage PPSL signals of all irradiated samples were observed to be higher than the upper threshold value, making it possible to distinguish them from the non-irradiated control samples. The first TL glow curves (TL₁) for the non-irradiated samples were of very low intensity at about 250–300 °C. Irradiated samples (5–50 kGy) showed a higher peak at around 150–250 °C. TL ratios [ratio of the integrated areas of the first (TL₁) and second (TL₂) glow], measured after re-irradiation for the TL₁-tested samples at 1 kGy, were found to be less than 0.1 for the non-irradiated samples and higher than 0.1 for the irradiated ones. TL ratios for all irradiated samples measured after 12 weeks of storage under dark condition at (23 ± 2 °C) were apparent for distinguishing them from the non-irradiated controls.     

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.