Identification of irradiated foods by the thermoluminescence of mineral contamination

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 degrees C low-temperature part of the TL spectrum for evaluation.     

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.

     

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.     

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。     

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.     

Microbiological safety of irradiated foods

This paper attempts to summarize relevant information on microbiological safety of irradiated foods in the light of previous reports of expert committees and current literature references. After a brief survey of the relative radiation resistance of food-borne microorganisms, the importance of microbial load for dose requirement, and the role of post-irradiation conditions, it addresses the following questions: Could selective changes in the microflora, caused by non-sterilizing radiation doses, make known pathogens more likely to occur, or bring into prominence unfamiliar pathogens? Is it probable that 'mutational' (including adaptive) changes might make pathogens more virulent, more harmful, or more difficult to recognize, and could new pathogens arise in this way? Is it possible that development of radiation-resistant strains might render the antimicrobial irradiation processes ineffective? The present survey of relevant scientific evidence related to these questions reaffirms the basic conclusion of earlier reviews, that microbiological safety of irradiated food is fully comparable with that of foods preserved by other acceptable preservation methods. Similar to other preservation processes, gains in microbiological or keeping quality attained by food irradiation can be and must be safeguarded by proper control in the food irradiation facilities and by proper care of the product before and after processing.     

Increased supercooling in irradiated foods

The supercooling temperatures of γ-irradiated and control cod, mushroom, and two chicken samples were measured using a Differential Scanning Calorimeter (DSC). The mean supercooling temperatures were significantly lower in three out of the four samples of the irradiated foods, suggesting that the effect might be the result of irradiation. There was high variability between samples and a possible dependence on spoilage which require further investigation to assess the potential of the test for detecting irradiated foods.     

The identification of irradiated crustaceans and evaluation of the dose by thermoluminescence: Intercomparison between two methods for extracting minerals

The thermoluminescence (TL) is one of the physical methods recommended by the European Committee for Standardization, for the identification of irradiated food from which silicate minerals can be extracted. The efficacy of the method strongly depends on the quantity and purity of the extracted minerals, and therefore on the extraction procedure. In this work we applied the TL for the identification of crustacean Nephrops norvegicus irradiated at 0.5?1.5?3.0 kGy, comparing two different procedures for extracting minerals: by means of a density gradient or with acid hydrolysis. The identification of the irradiation treatment was always achieved with both procedures, without any false positive. A dose reconstruction method was also set up and tested. A little preference should be given to the acid hydrolysis extraction procedure, that requires less quantity of food sample and reagents, as well as less time to be carried out, and gives a satisfactory reconstruction of dose.     

辐照食品检测技术方法与标准

对辐照食品检测的目的、原理以及建立检测方法的要求进行系统归纳,对不同辐照食品检测方法和国内外标准制定情况进行比较.发现目前还不存在一种适用于所有辐照食品检测的方法,现有的方法各有优劣.同时并指明我国辐照食品检测技术今后的研究和发展方向.     

GC-MS测定富含油脂类食品中氯丙醇的方法研究

建立了油脂类食品中氯丙醇含量的气相色谱-质谱法（GC-MS）联用技术检测方法,对油辣椒、腐乳、火锅底料以及鸡辣椒等食品中氯丙醇含量进行检测。结果表明：在10～500 μg/L范围内,3-氯-1,2-丙二醇（3-MCPD）的质量浓度与峰面积呈良好的线性关系,相关系数R2为0.999 5,方法检出限（LOD）为4.7 μg/kg,定量限（LOQ）为10.2 μg/kg,平均加标回收率在86.2%～108.5%,精密度试验测定得相对标准偏差（RSD,n=6）为4.26%。表明该方法准确、可靠、稳定,能够满足油脂类食品中氯丙醇含量的检测要求。     

凝胶色谱法测定保健食品中免疫球蛋白IgG

建立了凝胶色谱法测定保健食品中免疫球蛋白IgG含量的方法。采用紫外检测器,测定波长280 nm;色谱柱为Zorbax GF-250,柱温为20℃,流动相为0.01 mol/L KH2PO4+0.1 mol/L K2HPO4+0.15 mol/LNa2SO4(pH 6.0),流速为1.0 ml/min;样品调pH值为4.6沉淀酪蛋白及变性乳清蛋白后过滤分离。本方法的最低检测限为1 mg/g,标准曲线的相关系数为0.9999,回收率在97.2%～103.2%,RSD为1.38%。     

酶重量法测定食品中膳食纤维含量方法的改进

对酶重量法测定食品中总膳食纤维、不溶性膳食纤维和可溶性膳食纤维含量的方法进行了改进,利用磷酸缓冲液取代了价格较高的MESI-TR IS缓冲液,并在过滤过程中采用热过滤法以加快过滤速度。利用改进法对燕麦片和红枣粉为原料与传统测定方法进行了比较,结果表明,两种方法测定结果基本一致。同时,对改进法在不同实验室进行了对比测定,发现该方法稳定性较好,可以代替传统的AOAC测定方法。     

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.     

RP-HPLC法测定食品中胆固醇含量的研究

目的建立一种快速、准确的RP-HPLC法测定胆固醇含量的方法。方法样品在60℃水浴锅里磁力搅拌皂化45 min,用石油醚提取后浓缩,无水乙醇定容后,用戴安C18色谱柱(4.6 mm×250 mm,5μm)进行分离,甲醇作为流动相,1 mL/min流速进行等度洗脱。结果方法的线性范围为10～400μg/mL,r=1.000,检出限为20.6μg/g,相对标准偏差为0.66%～2.12%,回收率范围为92.5%～100.2%。结论该方法快速、准确、精密度高,适用于食品中胆固醇的检测。     

Folate concentrations of fast foods measured by trienzyme extraction method

Folate concentrations in common fast foods containing beef were measured using a new trienzyme folate extraction method and compared to the values using traditional folate conjugase. A total of 56 fast foods were purchased from local restaurants after the 1998 mandate of folic acid fortification in enriched cereal grains. One serving of hamburger, sandwich, pizza (one eighth of a 30-cm pizza) and Mexican foods contained a mean of 314 (±98, S.D.), 401 (±115), 221 (±45) and 282 (±126) μg of folate, respectively. Breakfast items provided the lowest folate amount among the foods (165±89 μg per serving). These values are markedly higher than those in the literature most likely due to the mandate of folic acid fortification in cereal-grain products and the use of the new folate extraction technique. We hope that the information presented here is a useful means to accurately calculate dietary folate intake.     

Microwave vacuum drying of foods with temperature control by power modulation

Microwave power modulation during drying was evaluated to guarantee mild temperatures, reducing burning spots when producing sweet potatoes snacks. Samples were peeled, sliced, blanched, and microwave vacuum dried with (MWVDc) and without (MWVD) controlling the temperature (60 °C) with a PID system. MWVD used constant power, while MWVDc adjusted the power input based on samples' temperature target. Moisture content was reduced from 4.5 g g⁻¹ (db) to 0.4 g g⁻¹ (db), resulting in water activity lower than 0.55. MWVD processing time was about 80, 15, and 10 min at 300, 1500, and 2700 W, respectively, resulting in dried samples with dark areas due to hot spots. The power modulation in MWVDc resulted in intermediary drying time (50 min) and uniform color products without burnings. This study demonstrated that automated temperature control leads to high-quality sweet potato chips by microwave processing.     

转基因食品定量检测方法的验证

按欧盟联合研究中心(Joint Reaserch Center,JRC)的欧盟网络转基因实验室(European Network of GMO laboratories,ENGL)方法验证工作组编制的指南文件的要求,对《GB/T 19495.5—2004转基因产品检测核酸定量PCR检测方法》进行方法验证。分别验证了脱氧核糖核酸(deoxyribonucleic acid,DNA)提取质量,方法的准确度、重复性和相对定量限4个指标。经过验证,选用的DNA提取试剂盒提取质量合格;检测值在可接受参考值的±25%内,准确度良好;相对可重复性标准偏差均小于25%,重复性良好;相对定量限为0.1%转基因含量。依照指南对国标进行了验证,结果证明该指南在实验室进行方法验证中具有指导性作用。     

微波消解-原子荧光法测定婴儿食品中的砷

目的：建立微波消解-原子荧光法测定婴儿食品中砷的方法。方法：婴儿食品采用微波消解,双道氢化物发生原子荧光法测定样品中的砷。结果：砷的质量浓度在0μg/L～160.0μg/L范围内与原子荧光强度呈良好的线性关系,相关系数为0.999 2,方法检出限为0.038 2μg/L,回收率为93.47%~98.51%。结论：方法简...     

固相萃取-高效液相色谱法测定食品中痕量花粉红染料

本实验建立了测定食品中痕量花粉红色素的高效液相色谱方法.样品经正己烷等溶液提取,经过中性氧化铝柱净化,以甲醇和水溶液为流动相进行色谱分离,在激发波长550 nm,发射波长580 nm的荧光条件下检测.花粉红的浓度在0.5～10.0 μg/ L 范围内与其色谱峰面积的线性关系良好( r=0.999),在1、5、10 μg/kg添加水平时的回收率为56.3 %～80.1%,RSD为2.8 %～5.7%.方法的定量检出限为1.0 μg/kg.