Identification of irradiated pulses by thermoluminescence of the contaminating minerals

Thermoluminescence (TL) response of contaminating minerals from six samples of pulses commonly consumed in Pakistan has been studied for identification of irradiation treatment. The samples were irradiated by Co-60 gamma rays at 0.3, 0.5 and 1.0 kGy, or by 10 MeV electrons using an accelerator at 0.75 and 2.2. kGy. Generally, the TL intensity for minerals separated from irradiated samples was higher than for unirradiated samples. To normalize the results, separated minerals deposited on stainless steel discs were re-irradiated by a normalizing dose and TL response was redetermined. The ratio of the area of the first glow curve to the second glow curve was more than 0.8 for all irradiated samples and less than 0.33 for most of the unirradiated samples. For those unirradiated samples where the ratio of the glow curves was more then 0.03, the shapes of the glow curves were compared. Taking this criterion into consideration, all 21 unirradiated and irradiated samples of pulses were identified correctly. Therefore, a normalization procedure by re-irradiation of minerals and analysis of TL glow curve shapes lead to unequivocal identification of radiation treatment of pulses.     

Accredited laboratory for detection of irradiated foods in Poland

The history of the development and the role of the Accredited Laboratory for Detection of Irradiated Foods in the national quality food control system are described. The analytical methods for the detection of irradiation in foods adapted and accredited in the Laboratory are enumerated and discussed.     

Thermoluminescence detection of Korean traditional foods exposed to gamma and electron-beam irradiation

Thermoluminescence(TL) analysis was applied to detect irradiated Korean traditional condiments and soup mixes containing salt(NaCl). These food items, which are commercially irradiated in Korea, showed a consistently high correlation(R²) between the absorbed doses and the corresponding TL responses. It was proved that table salt played a role as an in-built indicator in TL measurements and its concentration in test samples was proposed as a correction factor for varying conditions of TL measurements. Pre-established threshold values were successfully adopted to identify 167 coded samples of Ramen soup mixes, both non-irradiated and irradiated with gamma and electron-beam energy. The TL intensity of irradiated soup mixes decreased with the lapse of time, but was still distinguishable from that of the non-irradiated samples at the fourth month of ambient storage. Expected estimates of absorbed doses, 2.85 and 4.75 kGv were obtained using a quadratic equation with average values of 1.57 and 4.90 kGy, respectively.     

Improvement of the ESR detection of irradiated food containing cellulose employing a simple extraction method

Fruit may be irradiated at rather low doses, below 1 kGy in combination treatments or for quarantine purposes. To improve the ESR detection sensitivity of irradiated fruit de Jesus et al. (Int. J. Food Sci. Technol. 34 (1999) 173.) proposed extracting the fruit pulp with 80% ethanol and measuring the residue with ESR using low power (0.25 mW) for detection of ‘cellulosic’ radicals. An improvement in ESR sensitivity using the extraction procedure could be confirmed in this paper for strawberries and papayas. In most cases, a radiation dose of 0.5 kGy could be detected in both fruits even after 2–3 weeks storage. In addition, some herbs and spices were also tested, but only for a few of them the ESR detection of the ‘cellulosic’ signal was improved by previous alcoholic extraction.

As an alternative to ESR measurements, other detection methods like DNA Comet Assay and thermoluminescence were also tested.     

Comparative identification of irradiated herbs by the methods of electron paramagnetic resonance and thermoluminescence

Non irradiated and γ-irradiated dry herbs savoury (Savoury), wild thyme (Thymus serpollorium) and marjoram (Origanum) with absorbed dose of 8 kGy have been investigated by the methods of elecrtron paramagnetic resonance (EPR) and thermoluminescence (TL). Non-irradiated herbs exhibit only one weak siglet EPR signal whereas in irradiated samples its intensity increase and in addition two satelite lines are recorded. This triplet EPR spectrum is attributed to cellulose free radical generated by irradiation. It has been found that upon keeping the samples under the normal stock conditions the life-time of the cellulose free radical in the examined samples is ∼60–80 days. Thus the conclusion has been made that the presence of the EPR signal of cellulose free radical is unambiguous indication that the sample under study has been irradiated but its absence can not be considered as the opposite evidence. In the case when EPR signal was absent the method of TL has been used to give the final decision about the previous radiation treatment of the sample.     

Petitioning process for irradiated foods and animal feeds in North America

Sales of irradiated foods clearly indicate that North Americans consumers appreciate the value of irradiated foods. All irradiated foods offered for sale have sold well. The results of North American consumer attitude surveys can be used to predict acceptance of quality irradiated foods, especially when improved food safety is the perceived benefit. Consumers perceive the most benefit when irradiation is used to improve food safety or to reduce the chemicals used on foods. Information about irradiation seems to increase consumer willingness to buy. Consumer activists continue to attempt to prevent the sale of labelled irradiated foods, but they have not been successful.     

Identification of irradiated foods by monitoring radiolytically produced hydrocarbons

Many countries allow the treatment of foods with low doses of ionizing radiation to reduce microbial and insect infestations, inhibit maturation, and extend shelf life. Therefore, a reliable method is needed to identify irradiated foods and to determine their compliance with respect to allowable absorbed radiation dose. Several approaches for the identification of irradiated foods have been developed such as measurement of radiolytic products, chemiluminescence, and thermoluminescence, and the use of electron spin resonance spectroscopy to measure free radicals trapped in bone. A method for the determination of radiolytically produced hydrocarbons was developed in our laboratory to evaluate the utility of monitoring these compounds as indicators of food irradiation. The method involves the extraction of the radiolytic hydrocarbons from foods and their quantitation by gas chromatography. Concentrations of the radiolytically produced hydrocarbons increased linearly with radiation doses ranging from 0 to 6 kGy. The limit of detection appears to be approximately 1 kGy. The method was found to be useful for the identification of gamma-irradiated foods such as shrimp, frog legs, pork, beef, and poultry. Results of the method evaluation studies of these food matrices as well as factors affecting hydrocarbon production and determination will be presented.     

A sensitive method for quantification of the insecticide spinetoram in 13 different plant- and animal-type foods by ultra-high performance liquid chromatography-tandem mass spectrometry

We developed a simple, sensitive and rapid analytical method for simultaneous quantification of spinetoram (XDE-175-L and XDE-175-J) residue in foods originating from plants (cucumber, cabbage, eggplant, pepper, bayberry, mango, rice, wheat, and codonopsis) or animals (eggs, milk, pork, and chicken). The method was validated by ultra-high performance liquid chromatography coupled to tandem mass spectrometry, run in the positive-ion mode with selected reaction monitoring. Briefly, the samples were extracted with acetonitrile and purified via dispersive solid-phase extraction with octadecylsilane, primary secondary amine, or graphitized carbon black, used either singly or in combination. The method provides good linearity (R² ≥ 0.9956) and outstanding performance (trueness and recovery percentages 80.1–111.3%; intra-day/inter-day precision of 1.2–9.7% and 3.9–12.9%). For all food matrices, the limit of quantification was 0.125 µg kg^–1 for XDE-175-L and 0.375 µg kg^–1 for XDE-175-J. We also validated the applicability of the method using 130 samples obtained from commercial sources, which revealed trace amounts of spinetoram in 28 of those samples. The data indicated that the method yields reproducible results and is sufficiently sensitive for the detecting trace amounts of spinetoram in plant- and animal-type foods.     

Supercritical fluid extraction for the detection of 2-dodecylcyclobutanone in low dose irradiated plant foods

Supercritical carbon dioxide extraction [152 bar (15,200 kPa), 80 degrees C, 4 ml min(-1), 60 min], performed on lipids (2 g) previously extracted from irradiated plant foods, allowed a selective extraction of 2-dodecylcyclobutanone and its further detection by gas chromatography-mass spectrometry in 50 Gy irradiated cowpeas and 100 Gy irradiated rice. However, because of the higher quantities of lipid impurities in these test samples compared to those present in meat samples, a longer and slightly more polar capillary column than the one proposed in the official standard EN 1785 method should be used to obtain a satisfactory resolution.     

Activated aluminum oxide selectively retaining long chain n-alkanes: Part II. Integration into an on-line high performance liquid chromatography-liquid chromatography-gas chromatography-flame ionization detection method to remove plant paraffins for the determination of mineral paraffins in foods and environmental samples

Aluminum oxide activated by heating to 300-400 °C retains n-alkanes with more than about 20 carbon atoms, whereas iso-alkanes largely pass non-retained (with characteristics described in more detail in Part I). This property is useful for the analysis of mineral oil contamination of foods and other matrices: it enables the removal of plant n-alkanes, typically ranging from C₂₃ to C₃₃, when they disturb the analysis of mineral paraffins (usually almost exclusively consisting of iso-alkanes). An on-line HPLC-LC-GC-FID method is proposed in which a first silica gel HPLC column isolates the paraffins from the bulk of edible oils or extracts and is backflushed with dichloromethane. In a second separation step, a 10 cm × 2 mm i.d. column packed with activated aluminum oxide separates the long chain n-alkanes from the fraction of the iso-alkanes which is transferred to GC-FID by the on-column interface and the retention gap technique. The retained n-alkanes are removed by flushing with iso-octane.     

Rapid detection of irradiated frozen hamburgers

DNA comet assay can be employed as a rapid and inexpensive screening test to check whether frozen ground beef patties (hamburgers) have been irradiated as a means to increase their safety by eliminating pathogenic bacteria, e.g. E. coli O157:H7. Such a detection procedure will provide an additional check on compliance with existing regulations, e.g. enforcement of labelling and rules in international trade. Frozen ready prepared hamburgers from the market place were ‘electron irradiated’ with doses of 0, 1.3, 2.7, 4.5 and 7.2 kGy covering the range of potential commercial irradiation. DNA fragmentation in the hamburgers was made visible within a few hours using the comet assay, and non-irradiated hamburgers could be easily discerned from the irradiated ones. Even after 9 months of frozen storage, irradiated hamburgers could be identified. Since DNA fragmentation may also occur with other food processes (e.g. temperature abuse), positive screening tests shall be confirmed using a validated method to specifically prove an irradiation treatment, e.g. EN 1784 or EN 1785.     

食品中磷的检测方法

磷是人体内的重要元素之一,对人体生命活动有十分重要的作用,如何快速、简便、准确、灵敏地检测食品中磷的含量已经引起了世界各国的重视.本文总结了前人的研究工作,概述了近年来食品中总磷及有机磷农药的检测研究进展,分析了各种检测方法的优势和局限性,展望了未来该领域研究的发展趋势.     

Ionic liquids as mobile phase additives in high-performance liquid chromatography with electrochemical detection: Application to the determination of heterocyclic aromatic amines in meat-based infant foods

The beneficial effects of several ionic liquids (ILs) as mobile phase additives in high-performance liquid chromatography with electrochemical detection for the determination of six heterocyclic aromatic amines (HAs) have been evaluated for first-time. The studied ionic liquids were 1-butyl-3-methylimidazolium tetrafluoroborate (BMIm-BF₄), 1-hexyl-3-methylimidazolium tetrafluoroborate (HMIm-BF₄) and 1-methyl-3-octylimidazolium tetrafluoroborate (MOIm-BF₄). Several chromatographic parameters have been evaluated in the presence or absence of ILs, or using ammonium acetate as the most common mobile phase additive, with three different C18 stationary phases. The effect of the acetonitrile content was also addressed. In general, best resolution, lower peak-widths (up to 72.1% lower) and lower retention factors are obtained when using ILs rather than ammonium acetate as mobile phase additives. The main improvement was obtained in the baseline noise, being 360% less noisy for BMIm-BF₄, 310% for HMIm-BF₄, and 227% for MOIm-BF₄, when compared to ammonium acetate at +1000 mV. Different chromatographic methods using the best conditions for each IL were also evaluated and compared. Finally, the best chromatographic conditions using 1 mM of BMIm-BF₄ as mobile phase additive, the Nova-Pak^® C18 column, 19% (v/v) of acetonitrile content in the mobile phase, and +1000 mV in the ECD, have been applied for the chromatographic analysis of six HAs contained in meat-based infant foods. The whole extraction method of meat-based infant foods using focused microwave-assisted extraction and solid-phase extraction has also been optimized. Extraction efficiencies up to 89% and detection limits ranged between 9.30 and 0.165 ng g⁻¹ have been obtained under optimized conditions.     

毛细管区带电泳-间接紫外检测法快速测定食品中乳糖、蔗糖、葡萄糖和果糖

建立了毛细管区带电泳-间接紫外检测快速测定食品中乳糖、蔗糖、葡萄糖和果糖的方法。以水或5 mmol/L醋酸为样品提取液,未涂层熔融石英毛细管(30.2 cm(有效长度20 cm)×50 μm)为分离柱,4 mmol/L山梨酸钾+10 mmol/L磷酸钠+30 mmol/L NaOH(pH 12.56)+0.5 mmol/L十六烷基三甲基溴化铵(CTAB)为分离缓冲液,在-8 kV下分离,于254 nm波长下检测,10 min内实现了食品中上述4种糖的同时分离与测定。乳糖、蔗糖、葡萄糖和果糖的检出限(S/N=3)分别为50、75、25和25 mg/L,定量限(S/N=10)分别为150、225、75和75 mg/L,回收率在87.0%~107.0%之间,相对标准偏差在1.2%~4.7%之间。整个实验过程未使用有机溶剂。用该法测定了9种食品样品及1个质控样品,结果表明该法简单、快速、准确,适用于食品中乳糖、蔗糖、葡萄糖和果糖的日常测定。     

Study of effective factors in detection of irradiated food using thermoluminescence based on the models of reference minerals

In the thermoluminescence (TL) detection method for irradiated foods, accurate standards have been developed for detecting irradiated foods. The standard method describes that emission maximum temperature (T1i) and TL ratio for non-heated or non-mixed sample can be in the range of 150–250 °C and more than 0.1, respectively, when it was irradiated food. But when irradiated food is heated up to 200 °C, or mixed up with non-irradiated stuffs, T1i and TL ratio would not drop in the range. Here we examined the effects of the two processes, heating and mixing with non-irradiated food, on T1i and G1/G1k ratio (ratio of G1 and average G1 for 1-kGy-irradiated JF2, this value is modeled after TL ratio) using a model consisting of irradiated and non-irradiated geochemical standards of feldspar (JF1, JF2, PF, etc.). T1i temperatures for irradiated JF1, JF2, and PF ranged from 163 to 175 °C, while those for the non-irradiated JF2 ranged from 253 to 263 °C. T1i temperatures for 5-kGy-irradiated and preheated JF2 for 10 s, 20 s, and 30 s at 180 °C were 215, 225, and 231 °C, respectively.When JF2 was irradiated from 100 Gy to 5 kGy, the T1i was almost constant at any doses. G1/G1k ratios at 100, 200, and 500 Gy were 0.15, 0.23, and 0.60, respectively. G1/G1k ratio was proportional to the given dose at the integration temperature ranges.The TS sample, which originated from farm soil in Tanegashima Island, gave the same results as JF2. T1is for 5-kGy-irradiated and preheated JF2 for 20 s at 150, 180, and 200 °C were 197, 225, and 246 °C, respectively. Longer and higher preheating resulted in higher T1i. Longer and higher preheating extremely reduced the G1/G1k ratio, and in some cases the ratio was less than 0.1. This means TL ratio is useless in determination of the standard for irradiated food.Peak temperatures for JF2 in mixture of 5-kGy-irradiated to non-irradiated (1.25–5%) were 261–263 °C (non-irradiated portion, T1n) and 177–180 °C (irradiated portion T1i). The peak positions are almost the same as those of original components and would not be affected by the mixing ratio. But TL ratio could not be used to determine irradiated food because mixing would reduce it remarkably.Some of the glow curves were simulated by a computer program.In conclusion, T1i/n is a key factor in an irradiated food determination practice for sample containing feldspar, rather than TL ratio.     

Immunochemical-based method for detection of hazelnut proteins in processed foods

A competitive enzyme-linked immunosorbent assay (ELISA) was developed to detect hazelnut by using polyclonal antibodies generated against a protein extract of roasted hazelnut. No cross-reactivity was observed in tests against 39 commodities, including many common allergens, tree nuts, and legumes. Hazelnut protein standard solutions at 0.45 ng/mL [inhibition concentration (IC80) of the competitive test] were clearly identified by the ELISA. An extraction and quantification method was developed and optimized for chocolate, cookies, breakfast cereals, and ice cream, major food commodities likely to be cross-contaminated with undeclared hazelnut during food processing. No sample cleanup was required when extracts were diluted 10-fold. Recovery results were generated with blank matrixes spiked at 4 levels from 1 to 10 microg/g hazelnut protein. With the developed extraction and sample handling procedure, hazelnut proteins were recovered at 64-83% from chocolate and at 78-97% from other matrixes. A confirmatory technique was developed with sodium dodecyl sulfate-polyacrylamide gel electrophoresis and Western transfer. The developed methods were applied to a small market survey of chocolate products and allowed the identification of undeclared hazelnut in these products.     

A simple method for determination of erythritol,maltitol, xylitol,and sorbitol in sugar‐free chocolates by capillary electrophoresis with capacitively coupled contactless conductivity detection

In this work, a novel and simple analytical method using capillary electrophoresis (CE) with capacitively coupled contactless conductivity detection (C⁴D) is proposed for the determination of the polyols erythritol, maltitol, xylitol, and sorbitol in sugar‐free chocolate. CE separation of the polyols was achieved in less than 6 min, and it was mediated by the interaction between the polyols and the borate ions in the background electrolyte, forming negatively charged borate esters. The extraction of the polyols from the samples was simply obtained using ultra‐pure water and ultrasonic energy. Linearity was assessed by calibration curves that showed R² varying from 0.9920 to 0.9976. The LOQs were 12.4, 15.9, 9.0, and 9.0 μg/g for erythritol, maltitol, xylitol, and sorbitol, respectively. The accuracy of the method was evaluated by recovery tests, and the obtained recoveries varied from 70 to 116% with standard deviations ranging from 0.2 to 19%. The CE‐C⁴D method was successfully applied for the determination of the studied polyols in commercial samples of sugar‐free chocolate.     

On the morphology of some irradiated ultra high molecular weight polyethylenes

The morphology of various grades of ultra high molecular weight polyethylene (UHMWPE), prepared for use in orthopaedic implants, has been examined using differential scanning calorimetry (DSC), wide and small angle X-ray diffraction (WAX and SAX) and Raman spectroscopy. Preparation included gamma irradiation at various dose rates and mechanical annealing, and post-irradiation changes were of particular interest. The experimental results are interpreted in terms of previous proposals that UHMWPE is best considered as a three phase material, fully amorphous, all-trans amorphous and fully crystalline. The all-trans amorphous material is thought to be interfacial. The phase analysis shows that the age related increase in crystallinity occurs through conversion of all-trans material to fully crystalline, and there is little change in the total amorphous content of the polymers. SAX patterns show a change in the sharpness of the main diffraction peak and the emergence of a second diffraction peak at a higher q value, and this is considered to arise from crystallisation of all-trans amorphous material. Increasing the irradiation dose rate has a similar effect on the crystallography as does ageing the material. Mechanically annealed polymer also shows a similar trend towards a bimodal crystal population, accompanied by a reduction in interfacial material.     

Determination of heterocyclic aromatic amines by capillary high-performance liquid chromatography with diode array detection in ready-to-eat cooked ham treated with electron-beam irradiation

Heterocyclic aromatic amines (HAs) are a group of mutagenic and carcinogenic substances present in significant amounts in cooked meat and fish that can potentially be formed during food processing operations. This paper proposes a capillary liquid chromatography method with diode array detection for the trace-level determination of three HAs, namely, MeIQx (2-amino-3,8-dimethylimidazo[4,5-f]quinoxaline), norharman (9H-pyrido[3,4-b]indole) and harman (1-methyl-9H-pyrido[3,4-b]indole), in ready-to-eat (RTE) cooked ham processed by electron-beam (accelerated electrons) irradiation to eliminate pathogenic microorganisms and to extend its shelf-life. The HAs selected have frequently been detected and quantified in a wide range of food and could be potential markers to indicate the presence of these toxic compounds. The method is based on the separation in an Inertsil C(8) capillary column (150 mm x 0.3-mm internal diameter, 3 microm) by gradient elution mode using a mixture of acetonitrile and 30 mM ammonium acetate pH 4.5 buffer as the mobile phase. Detection was at 250 and 265 nm and, to improve sensitivity, large injection volumes (20 microL) and on-column focusing techniques based on the injection of HA samples in low organic solvent strength solutions were employed. A simple and short solid-phase extraction and purification procedure was also optimized for sample preparation. Nonirradiated and irradiated RTE cooked ham samples at doses between 1 and 8 kGy were analyzed. HAs were not detected in any of the samples analyzed; so both types of samples were spiked at concentration levels in the range 5-25 ng g(-1), which may be found in meat products. The quality parameters of the method developed in the food matrix were established, and detection limits around 0.3 ng g(-1) were obtained. Spiked recoveries between 70 and 79% (n = 3 for each spiked level) relative standard deviations between 1 and 5% were also obtained, showing the effectiveness of the proposed method.     

双气相色谱-双脉冲火焰光度法高通量检测动物性食品中有机磷农药残留及其代谢产物

建立了动物性食品中包括代谢产物在内的54种有机磷农药残留及其代谢产物的双气相色谱-双脉冲火焰光度检测器(GC-PFPD)检测方法。动物组织样品经丙酮提取后以二氯甲烷进行液-液萃取,经凝胶渗透色谱净化后采用配有双脉冲火焰光度检测器的气相色谱仪测定。采用外标法定量,有机磷农药的响应与其浓度在线性范围内均呈良好的线性关系,相关系数在0.9905～0.9999之间。分别在空白鸡肉、羊肉、牛肉和猪肉样品中添加低、中和高3个加标水平的标准品进行了回收试验,回收率在50.5%～128.1%之间,相对标准偏差(n=6)在1.1%～25.5%之间,证明该方法的精密度和准确度良好。各有机磷农药的检出限在0.001～0.170 mg/kg之间,定量限在0.002～0.455 mg/kg之间。对从市场采集的动物组织样品进行了测定,检出敌敌畏、乙拌磷亚砜等有机磷农药残留。本方法灵敏度高、特异性强,且能同时检测有机磷农药多残留及其代谢产物,能够更加真实地反映动物性食品中有机磷农药的残留水平。