Thermoluminescence of contaminating minerals for the detection of radiation treatment of dried fruits

Several types of dry fruits (pistachio nut, dried apricot, almond and raisins) have been investigated for detection of their radiation treatment by gamma rays or electron beam using thermoluminescence (TL) measurements. These samples were irradiated to 1.0–3.0 kGy (gamma rays) or 0.75–3.9 kGy (10 MeV electron beam). Thermoluminescence glow curves for the contaminating minerals separated from the dry fruits were recorded between the temperature range of 50°C and 500°C. In all the cases, the intensity of TL signal for the irradiated dry fruits was 1–3 orders of magnitudes higher than the TL intensity of the corresponding unirradiated control samples allowing clear distinction between the irradiated and unirradiated samples. These results were normalized by re-irradiating the mineral grains with a gamma-ray dose of 1.0 kGy, and a second glow curve was recorded. The ratio of intensity of the first glow curve (TL₁) to that after the normalization dose (TL₂), i.e. (TL₁/TL₂) was determined and compared with the recommended threshold values. These parameters, together with comparison of the shape of the first glow curve, gave unequivocal results about the radiation treatment of the dry fruit samples.     

The application of different detection methods for irradiated dried anchovy and shrimp

Three different techniques, photostimulated luminescence (PSL), electron spin resonance (ESR) and thermoluminescence (TL) were applied for the detection of dried anchovy and shrimp exposed to electron beam at 0–10 kGy. PSL values for irradiated samples were more than 5000 photon counts/60 s, upper threshold (T₂), whereas those of non-irradiated samples were <700 counts (lower threshold, T₁) in anchovy and intermediate values of T₁–T₂ in shrimp. ESR measurements using both the whole samples did not show any signals specific to irradiation. However, in the case of anchovy it was possible to use bone for ESR detection, showing typical signals (g=2.002, 1.998). Minerals separated from both the samples for TL measurement showed that non-irradiated samples were characterised by glow curves situated at about 300°C with low intensity, while all irradiated samples showed glow peaked at about 200°C and its intensity was high enough to be discriminated from the non-irradiated ones. Furthermore, normalization by a re-irradiation enhanced the reliability of detection results of TL. In conclusion, a multi-step detection using different methods enhances confidence in the detection of irradiated food.     

The identification of irradiated seasoned filefish (Thamnaconus modestus) by different analytical methods

Dried seasoned filefish (Thamnaconus modestus) was irradiated at 0–10 kGy and the identification of irradiation treatment was investigated by analyzing the characteristics of thermoluminescence (TL), hydrocarbon (HC), and 2-alkylacyclobutanone (2-ACB). The TL (TL₁), glow curve of the irradiated samples peaked at approximately 150 °C with high intensity, but that of the non-irradiated samples peaked at about 300 °C with little intensity, thus making it possible to discriminate between irradiated and non-irradiated samples. Moreover, TL ratio (TL₁/TL₂), through normalization steps, enhanced the reliability of the TL₁ results. Six kinds of HCs and three kinds of 2-ACBs quantitatively determined for the samples linearly increased in proportion to irradiation doses. In particular, two HCs like 1-hexadecane and 1,7-hexadecadine, and three ACBs, such as 2-dodecylcyclobutanone, 2-(5′-tetradeceyl)cyclobutanone, and 2-tetradecylcyclobutanone, were identified only in the irradiated samples as radiation-induced markers.     

Effect of γ-radiation on ointment cold cream

In this paper, Co-60γ ray was used to irradiate the ointment cold cream at room temperature (25°C). We also used FTIR, GC and thin film chromatogram to analyse various irradiated samples. It was found that the ointment cold cream can be irradiated at dose of 5–35 kGy and at dose rate from 0.2 to 0.6 kGy/h at room temperature (25°C) without evident decomposition. At dose of 5–15 kGy, the number of bacteria can be reduced to hygienic standard value. The radiation sterilization is a safe method for killing the bacteria in the ointment cold cream.     

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.     

Thermoluminescence analyses of irradiated dried sea foods using different methods of mineral separation

This research was conducted to find the most suitable parameters to separate minerals from irradiated dried shrimps and mussels (0 and 5 kGy) for thermoluminescence analysis using density separation and modified acid hydrolysis (at 50 °C with continuous agitation) methods. Nonirradiated samples gave TL glow curve of low intensity with peak after 300 °C except dried mussel sample, which gave false positive result. This problem was absent in minerals separated by acid hydrolysis. TL ratios of all nonirradiated samples were <0.1 irrespective of method used for mineral separation. Minerals separated from irradiated samples by density separation showed very high intensity of TL glow peak before 200 °C, where results from irradiated dried shrimp samples were better because of good availability of minerals. The minerals separated from irradiated samples by acid hydrolysis showed slightly low TL intensity and glow curve peak was found at about 200 °C. However, acid hydrolysis method was less laborious and required less sample weight as compared to density separation method. TL ratios of all irradiated samples were >0.1 confirming the quality of minerals on TL discs.     

Potential use of the activation energy value calculated from the thermoluminescence glow curves to detect irradiated food

We herein report on the calculation of the activation energy (E _a) from the thermoluminescence (TL) glow curves performed by the initial rise method that allows us to discriminate between irradiated and non-irradiated sesame seeds. E _a values of natural TL (0.68 ± 0.03 eV) and gamma-induced TL (never lower than 0.82 ± 0.02 eV) appear as a complementary criterion to be used differentiating between irradiated and non-irradiated foodstuffs with the position and the intensity of the main peak of the TL emission. In addition, E _a values taken from irradiated sesame samples at different doses (1, 5 and 10 kGy) and stored up to 15 months after being processed were compared to a ‘positive’ Spanish blend (i.e. at least one component was commercially irradiated).     

Sunna 535-nm photo-fluorescent film dosimeter response to different environmental conditions

Evaluations on the influence of environmental variabilities on the red fluorescence component of the Sunna Model γ photo-fluorescent dosimeter^TM have previously been reported. This present paper describes the environmental effects on the response of the green fluorescence component of the same dosimeter, which is manufactured using the injection molding technique. The results presented include temperature, relative humidity, and light influences both during and after irradiation. The green fluorescence signal shows a significant dependence on irradiation temperature below room temperature at 1%/°C. Above room temperature (approximately 24–60°C), the irradiation temperature effect varies from −0.1%/°C to 1.0%/°C, depending on the absorbed dose level. For facilities with irradiation temperatures between 30°C and 60°C and absorbed dose levels above 10 kGy, irradiation temperature effects are minimal. Light-effects results indicate that the dosimeter is influenced by ultraviolet and blue wavelengths during irradiation as well as during the post-irradiation stabilization period (approximately 22 h), requiring the use of light-tight packaging. Results also show that the dosimeter exhibits negligible effects from ambient moisture during and after irradiation when in the range of 33–95% relative humidity.     

Application of thermoluminescence measurements to detect low dose gamma-irradiated table grapes

A major factor hampering the introduction of ionizing radiation as an alternative quarantine treatment to chemical fumigation for fruit and vegetables is the lack of reliable, simple and inexpensive post-treatment methods to confirm this low dose irradiation treatment. Considering this purpose, thermoluminescence (TL) measurements of the wind blown dust naturally adhered to the surface of table grapes, was surveyed. Two doses, 0.5 and 1.0 kGy, were studied, applied to the main Chilean table grape export varieties: Thompson Seedless and Flame Seedless.

TL measurements were carried out over 78 days for Thompson Seedless and 62 days for Flame Seedless varieties, both stored at 1 ± 1°C (usual handling of this fruit). TL response fading of dust samples stored at room temperature was also followed over 125 days. The TL response values obtained from the irradiated samples exceeded at least 3 times the highest ones obtained from the unirradiated counterparts. The treatment, even for the lower γ-radiation dose applied, could be properly detected well above the shipping and marketing time for this Chilean export fruit (2–8 weeks). This method also has the advantage of using relatively inexpensive equipment.     

Identification of low amount of irradiated spices (red pepper,garlic, ginger powder) with luminescence analysis

For the identification of irradiated food, current analysis methods have limitations regarding presence and stability of radiation-induced markers. In this study, different spice blends with small quantity of different irradiated (0, 1 and 10 kGy) spice powders, such as red pepper, garlic or ginger, were investigated using PSL and TL techniques. In PSL-based screening analysis, the spice blends containing 10% of irradiated materials (1 or 10 kGy) were determined as intermediate or positive. In TL results, the blends containing 1% of 1 or 10 kGy-irradiated spices showed the typical TL glow curves that could be interpreted as positive. The blends with irradiated garlic powder provided more good results where identification was possible at 0.5% mixing of irradiated sample. However, the TL ratios of all spice blends were <0.1 and only TL glow curve shape and intensity may be used to discriminate the samples having irradiated component.     

Identification of irradiation treatment of spices by thermoluminescence of contaminating minerals

Five spices, cumin, coriander, clove, cinnamon and black pepper were irradiated by gamma-ray doses of 1.0 and 5.0 kGy and thermoluminescence (TL) method was used for identification of the irradiation treatment. The TL response of the minerals isolated from irradiated samples was much higher as compared to the mineral particles from unirradiated control samples. For the normalisation of results the separated minerals were reirradiated to a normalisation dose of 1.0 kGy and the TL glow curve was recorded a second time. By comparing the glow curves of irradiated and unirradiated samples, finding the ratio of the areas of first and second glow curves (TL₁/TL₂) and comparing the shapes of the glow curves, all the irradiated and unirradiated samples were identified correctly.     

Characterization of radiation-induced luminescence properties and free radicals for the identification of different gamma-irradiated teas

Two kinds (20 each) of gamma-irradiated (0, 5, and 10 kGy) tea samples, blended powders and packed in sachets (tea bags), were investigated using photostimulated luminescence (PSL), thermoluminescence (TL), and electron spin resonance spectroscopy (ESR) to identify their irradiation status. PSL-based rapid screening was possible for all the control samples except for one packed and two powdered samples. The irradiated samples presented a good dose-dependent PSL count except two powdered samples with very low PSL sensitivity. TL analysis provided the most reliable results, in which all the irradiated samples were identified using a well-defined high-intensity TL glow curve in a temperature range of 150–250 °C. The TL results were also confirmed by determining the TL ratio (TL₁/TL₂), which was <0.1 in all the non-irradiated samples and >0.1 in the irradiated ones. ESR spectroscopy was effective for only 3 packed and 6 powdered samples showing the radiation-induced cellulosic and sugar radical signals, respectively.

The effect of irradiation of fresh pork loins on the protein quality and microbiological changes in aerobically—or vacuum-packaged

The effect of γ-irradiation on the physico-chemical, organoleptic and microbiological properties of pork was studied, during 43 d of storage at 4°C. Irradiation treatments were carried out under air or vacuum packaging on fresh pork loins at a dose of 6 kGy, at two dose-rates: 2 and 20 kGy/h. Regardless of the type of packaging and dose-rate of irradiation, all irradiated pork samples were prevented from bacterial spoilage during 43 d. Meat redness and texture of irradiated loins were well preserved during storage especially when samples were stored under vacuum. The physico-chemical and organoleptic changes in pork loins appeared to be relatively little affected by the 6 kGy dose.     

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.     

Reduction of Escherichia coli 0157:H7 in shredded iceberg lettuce by chlorination and gamma irradiation

Lettuce was inoculated with a six-strain cocktail of acid-adapted Escherichia coli 0157:H7 at a level of 1×10⁷ CFU/g. Following chlorination at 200 μg/ml, the lettuce was irradiated at 0.15, 0.38, or 0.55 kGy using a ⁶⁰Co source. Survival of E. coli 0157:H7, aerobic mesophiles and yeast and molds were measured over a period of 10 days. For quality analysis, chlorinated lettuce was subjected to irradiation at 0.33 and 0.53 kGy and stored at 1.0°C, 4.0°C or 7.0°C. Changes in texture and color were determined by instrumental means and changes in flavor, odor, and visual quality were determined by sensory testing.

Chlorination plus irradiation at 0.55 kGy produced a 5.4−log reduction in E. coli 0157:H7 levels. Chlorination alone reduced the E. coli 0157:H7 counts by 1–2 logs. Irradiation at 0.55 kGy was also effective in reducing standard plate counts and yeast and mold counts. Irradiation at this level did not cause softening of lettuce and sensory attributes were not adversely affected. In general, appearance and flavor were affected more by the length of storage than by temperature conditions. The 5+log reduction in E. coli counts and lack of adverse effects on sensory attributes indicate that low-dose irradiation can improve the safety and shelf-life of fresh-cut iceberg lettuce for retail sale or food service.     

Identification of gamma-irradiated Chinese herbs by thermoluminescence analysis

The feasibility of thermoluminescence (TL) to differentiate irradiated Chinese medicinal herbs from non-irradiated was investigated. Thirty different dried Chinese herbs were tested, including root, flower, ramulus, rhizome, cortex, and whole plant samples. Irradiation of Chinese herbs was associated with strong TL peaks at ~150–250 °C, while TL curves of non-irradiated herbs had very low intensities above 250 °C, which was also confirmed by the TL ratio (non-irradiated, TL₁/TL₂ < 0.1). The ability to determine the irradiation dose by the TL method was influenced by the amount and types of minerals in the samples. All levels of irradiation doses could be detected when between 0.1 and 1.0 kGy, except for three herbs at 0.1 kGy dose. Different blends with small quantities (0.1–10 %) of irradiated herbs were also tested in this study. Samples with powder mixtures containing 1 % irradiated components could be differentiated (TL₁/TL₂ > 0.1) except for sterculia lychnophora, semen cassia, flos inulae, and anemone root. TL ratios of some herbs indicated irradiation (TL₁/TL₂ > 0.1) even if the irradiated components were as low as 0.1 %. Thus we demonstrated that TL analysis had excellent sensitivity and reliability for the identification of irradiated Chinese herbs.     

Photo-luminescence of Risø B3 and PVB films for application in radiation dosimetry

Risø B3 film dosimeters (23 μm) prepared from poly(vinyl butyral) (PVB) incorporating pararosaniline cyanide, as the radiation-sensitive element and PVB films (25 μm) prepared from PVB without any additives are investigated for γ-radiation measurement using spectrofluorimetry based on their emission properties. The unirradiated Risø B3 film when excited at 554 nm shows an emission band at 602 nm while PVB film shows an emission band at 305 nm when excited at 235 nm wavelength. The fluorescence intensity of both emission bands decreases with the increase of absorbed dose due to the damage caused by ionizing radiation. The useful dose range of Risø B3 film extends up to 120 kGy while that of PVB film extends up to 60 kGy. The response of Risø B3 film increases with the increase of relative humidity during irradiation while that of PVB has less effect in the humidity range of 20–70%. The percent uncertainty associated with the measurement of the dose response was found to be ±3% (1σ) for both films. Risø B3 and PVB films show good post-irradiation stability in dark and indirect daylight where the deviation in the response overall a 2-month storage period was found to be ±5% for Risø B3 and ±2% for PVB.     

Thermoluminescence analysis for testing the irradiation of spices

Thermoluminescence signals of irradiated and unirradiated spices and herbs are due to inorganic matter grains adhering to the surfaces. This study reports the mineral composition of this dust being, mainly quartz, calcite and philosilicates; it shows the differences between samples exposed and non-exposed to -radiation on the basis of TL signals after long storage periods (1–16 months). A saturation process in the TL signal is found when the samples absorb doses higher than 5 kGy. Finally, the TL glow curve intensities do not suffer significant changes with the dose rate of the -source used in the radiation process.     

Effect of gamma radiation on growth and survival of common seed-borne fungi in India

The present work describes radiation-induced effects of major seeds like Oryza sativa Cv-2233, Oryza sativa Cv-Shankar, Cicer arietinum Cv-local and seed-borne fungi like Alternaria sp., Aspergillus sp., Trichoderma sp. and Curvularia sp. ⁶⁰Co gamma source at 25 °C emitting gamma ray at 1173 and 1332 keV energy was used for irradiation. Dose of gamma irradiation up to 3 kGy (0.12 kGy/h) was applied for exposing the seed and fungal spores. Significant depletion of the fungal population was noted with irradiation at 1–2 kGy, whereas germinating potential of the treated grain did not alter significantly. However, significant differential radiation response in delayed seed germination, colony formation of the fungal spores and their depletion of growth were noticed in a dose-dependent manner. The depletion of the fungal viability (germination) was noted within the irradiation dose range of 1–2 kGy for Alternaria sp. and Aspergillus sp., while 0.5–1 kGy for Trichoderma sp. and Curvularia sp. However, complete inhibition of all the selected fungi was observed above 2.5 kGy.     

Raman scattering study of highly fluorinated graphite

Raman spectra of highly fluorinated C_xF samples (1<x<2) prepared at room temperature and 515°C were measured. C_xF samples prepared at room temperature exhibited two Raman bands at 1593–1583 and 1555–1542 cm⁻¹. Graphite samples fluorinated at 515°C for 1 and 2 min also gave similar bands at 1581–1580 and 1550–1538 cm⁻¹. However, graphite samples fluorinated from 15 min to 10 h at 515°C no longer showed such spectra. The Raman peaks shifted to lower frequencies with increasing fluorine concentration in C_xF. This trend is due to the weakening of the C---C bonds of the graphene layers. Observation of both kinds of Raman bands suggests the coexistence of two highly fluorinated phases, C₂F and C₁F, in the samples. The process of formation of graphite fluoride is discussed on the basis of the Raman spectra of C_xF samples obtained at 515°C.