Polymerization of calcium caseinates solutions induced by gamma irradiation

Solutions of calcium caseinate (5%) combined with propylene glycol (PG) or triethylene glycol(TEG) (0, 2.5% and 5%) and used for the development of edible films and coatings, were irradiated at doses between 0 to 128 kGy. Solutions were chromatographed through toyopearl HW 55F resin to observe the effect of irradiation on cross-link reactions. In unirradiated calcium caseinate solutions, two peaks could be observed (fractions 30 and 37) while samples irradiated at 64 kGy and 128 kGy showed one shifted peak at fraction 32 and 29 respectively. No effect of the plasticizers was observed. According to proteins standards of knowed molecular weights, the molecular weight of calcium caseinate increased approximately 10 times when irradiated at 128 kGy and 5 times when irradiated at 64 kGy. The physico-chemical properties of bio-films prepared with the irradiated solutions, demonstrated that tensile strength at break increased with increase of irradiation dose. A maximum dose was obtained at 16 kGy.     

Antimicrobial properties of natural substances in irradiated fresh poultry

This study was undertaken to determine if a combined treatment (marinating in natural plant extracts or vacuum) with irradiation could have a synergetic effect, in order to reduce the dose required for complete elimination of Salmonella on fresh poultry. The effect of these combined treatments on the shelf-life extension was also evaluated. The fresh chicken legs were irradiated at 0, 3 and 5 kGy. The poultry underwent microbial analysis(mesophilic and Salmonella detection). For each treatment, the total microbial count decreased with increase of irradiation dose. The marinating treatment have a synergistic effect with irradiation treatment to reduce the total microbial count and controlling the proliferation during storage at 4°C. Irradiation of fresh chicken pieces with a dose of 3 kGy appears to be able to extend the microbial shelf-life by a factor of 2. When the chicken is marinating and irradiated at 3 kGy or when irradiated at 5 kGy without marinating, the microbial shelf-life is extended by a factor of 7 to 8. No Salmonella was found during all the experiment in the chicken in air and marinated. However, a presence of Salmonella was found in samples irradiated at 5 kGy under vacuum, in unirradiated samples and samples irradiated at 3kGy in air and under vacuum.     

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.     

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.     

Electron beam irradiated polyamide-6,6 films—II: mechanical and dynamic mechanical properties and water absorption behavior

Electron beam irradiation of poly(iminohexamethylene-iminoadipoyl) (Polyamide-6,6) films was carried out over a range of irradiation doses (20–500 kGy) in air. The mechanical properties were studied and the optimum radiation dose was 200 kGy, where the ultimate tensile stress (UTS), 10% modulus, elongation at break (EB) and toughness showed significant improvement over the unirradiated film. At a dose of 200 kGy, the UTS was improved by 19%, the 10% modulus by 9% and the EB by 200% over the control. The dynamic mechanical properties of the films were studied in the temperature region 303–473 K to observe the changes in the glass transition temperature (T_g) and loss tangent (tan δ) with radiation dose. The storage modulus of the film receiving a radiation dose of 200 kGy was higher than the unirradiated film. The water uptake characteristics of the Polyamide-6,6 films were investigated. The water uptake was less for the films that received a radiation dose of 200 and 500 kGy than the unirradiated film. The role of crystallinity, crosslinking and chain scission in affecting the tensile, dynamic mechanical and water absorption properties was discussed.     

Effect of gamma irradiation on microbiological,chemical and sensory characteristics of licorice root product

Licorice root products were irradiated at doses of 0, 5, 10, 15 and 20 kGy in a ⁶⁰Co package irradiator. Irradiated and unirradiated samples were stored at room temperatures. Microbial population on product, chemical changes and sensory properties of produced solution of licorice root products were evaluated after 0 and 12 months of storage. The results indicated that gamma irradiation reduced the counts of microorganisms on licorice root products. D₁₀ of total count and klebsiella spp. were about 1.4 and 0.7 kGy, respectively. The mineral ions (Na, Ca and K) concentration in solution produced from irradiated products were lower than non-irradiated ones. Glycyrrhezinic acid and maltose concentration in solution produced from irradiated products were higher than non-irradiated ones. Sensory evaluation indicated that no significant differences (P<0.05) were found between solution produced from irradiated and unirradiated products in color, flavor, texture, or taste.     

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.     

Detection of irradiation treatment of foods using DNA ‘comet assay’

Microgel electrophoresis of single cells (DNA comet assay) has been investigated to detect irradiation treatment of some food samples. These samples of fresh and frozen rainbow trout, red lentil, gram and sliced almonds were irradiated to 1 or 2 kGy using 10 MeV electron beam from a linear accelerator. Rainbow trout samples yielded good results with samples irradiated to 1 or 2 kGy showing fragmentation of DNA and, therefore, longer comets with no intact cells. Unirradiated samples showed shorter comets with a significant number of intact cells. For rainbow trout stored in a freezer for 11 days the irradiated samples can still be discerned by electrophoresis from unirradiated samples, however, the unirradiated trouts also showed some longer comets besides some intact cells. Radiation treatment of red lentils can also be detected by this method, i.e. no intact cells in 1 or 2 kGy irradiated samples and shorter comets and some intact cells in unirradiated samples. However, the results for gram and sliced almond samples were not satisfactory since some intact DNA cells were observed in irradiated samples as well. Probably, incomplete lysis has led to these deviating results.     

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.     

Effect of high-dose irradiation on quality characteristics of ready-to-eat chicken breast

High-dose (higher than 30 kGy) irradiation has been used to sterilize specific-purposed foods for safe and long-term storage. The objective of this study was to investigate the effect of high-dose irradiation on the quality characteristics of ready-to-eat chicken breast in comparison with those of the low-dose irradiation. Ready-to-eat chicken breast was manufactured, vacuum-packaged, and irradiated at 0, 5, and 40 kGy. The populations of total aerobic bacteria were 4.75 and 2.26 Log CFU/g in the samples irradiated at 0 and 5 kGy, respectively. However, no viable cells were detected in the samples irradiated at 40 kGy. On day 10, bacteria were not detected in the samples irradiated at 40 kGy but the number of bacteria in the samples irradiated at 5 kGy was increased. The pH at day 0 was higher in the samples irradiated at 40 kGy than those at 0 and 5 kGy. The 2-thiobarbituric acid reactive substance (TBARS) values of the samples were not significantly different on day 0. However, on day 10, the TBARS value was significantly higher in the samples irradiated at 40 kGy than those at 0 and 5 kGy. There was no difference in the sensory scores of the samples, except for off-flavor, which was stronger in samples irradiated at 5 and 40 kGy than control. However, no difference in off-flavor between the irradiated ones was observed. After 10 days of storage, only the samples irradiated at 40 kGy showed higher off-flavor score. SPME-GC–MS analysis revealed that 5 kGy of irradiation produced 2-methylbutanal and 3-methylbutanal, which were not present in the control, whereas 40 kGy of irradiation produced hexane, heptane, pentanal, dimethly disulfide, heptanal, and nonanal, which were not detected in the control or the samples irradiated at 5 kGy. However, the amount of compounds such as allyl sulfide and diallyl disulfide decreased significantly in the samples irradiated at 5 kGy and 40 kGy.     

Effect of γ-irradiation on cotton-cellulose

The effect of high-energy irradiation on cotton-cellulose was studied in inert atmosphere and in the presence of oxygen. A decrease in the degree of polymerization from 1200 to 330 was measured after irradiation with a dose of 15 kGy (dose rate 100 Gy/h) and further gradual decrease was measured when the dose was increased up to 100 kGy. At lower doses a slight increase in crease recovery angle was found as compared to the unirradiated sample. In the FTIR spectra of the same sample the appearance of the absorbance of carbonyl groups (band at 1730–1750 cm⁻¹) was found as a consequence of the oxidative degradation. Cracks on the surface of the fibers were observed by scanning electron microscope on samples irradiated with doses higher than 100 kGy.     

Pectin- and gelatin-based film: effect of gamma irradiation on the mechanical properties and biodegradation

Agricultural by-products, pectin and gelatin, were used to prepare a biodegradable film. The film casting solution including the pectin and gelatin was irradiated at 0, 10, 20, and 30 kGy to investigate the irradiation effect on the mechanical properties of the film. The tensile strength of the 10 kGy-irradiated film was the highest among the treatments but the elongation at break, water vapour permeability, and swelling ratio were the lowest. Hunter color L^*- and a^*-values decreased but the b^*-value increased as the irradiation dose increased. The total organic carbon content produced from the Paenibacillus polymyxa and Pseudomonas aeruginosa also showed that the film of 10 kGy-irradiated was lower than those of 0, 20, and 30 kGy-irradiated films. In conclusion, irradiation of the film casting solution at 10 kGy increased the mechanical properties of the pectin and gelatin based film. To manufacture the film by agricultural by-products, however, the irradiation dose of the film casting solution should be determined to achieve better mechanical properties.     

DNA comet assay: A simple screening technique for identification of some irradiated foods

DNA Comet Assay method was carried out to detect irradiation treatment of some foods like meat, spices, beans and lentils. The fresh meat of cow and duck were irradiated up to radiation doses of 3 kGy, the spices (cardamoms and cumin black) were irradiated to radiation doses of 5, 10, 15 and 20 kGy while the beans (black beans and white beans) and lentils (red and green lentils) were irradiated to 0.5 and 1 kGy. All the foods were then analyzed for radiation treatment using simple microgel electrophoresis of single cells or nuclei (DNA Comet Assay). Sedimentation, lysis and staining times were adjusted to get optimized conditions for correct and easy analysis of each food. Using these optimized conditions, it was found out that radiation damaged DNA showed comets in case of irradiated food samples, whereas in non-treated food samples, round or conical spots of stained DNA were visible. Shape, length and intensity of these comets were also radiation dose dependent. Screening of unirradiated and irradiated samples by Comet Assay was successful in the case of all the foods under consideration under the optimized conditions of assay. Therefore, for different kinds of irradiated foods studied in the present study, the DNA Comet Assay can be used as a rapid, simple and inexpensive screening test.     

Effect of gamma irradiation on linear low density polyethylene/magnesium hydroxide/sepiolite composite

Radiation crosslinking is generally used to improve the thermo-mechanical properties of the composites. A study has been carried out to investigate the effect of gamma radiation on the thermo-mechanical properties of linear low density polyethylene containing magnesium hydroxide (MH) and sepiolite (SP) as non-halogenated flame retardant additives. The developed composites are irradiated at different doses upto maximum of 150 kGy. Infrared spectra of the irradiated composites reveal the reduction in the intensity of O-H band with increase in the absorbed doses, thus indicates a distinct structural change in MH at higher doses. The thermogravimetric analysis results of unirradiated and composites irradiated at low doses (≤75 kGy) show two steps weight loss, which is changed to single step at higher doses with lower thermal stability. The melting temperature (T_m) and crystallization temperature (T_c) of irradiated composites are lowered with irradiation whereas Vicat softening temperature (VST) is increased. The increasing trend in gel content with increase in the absorbed dose confirms the presence of crosslinked network. The mechanical properties, results show significant improvement in the modulus of irradiated composites. The results also confirm that MH gradually loses its OH functionality with irradiation.     

Radiation degradation of polypropylene

Post-irradiation degradation of isotactic polypropylene irradiated by Co⁶⁰-γ-ray has been followed for 12 months. Effects of irradiation doses (10–100 kGy) up on the change of the structure and mechanical properties as well as flowability of this polymer has been studied. Carbonyl index increases with increasing post-irradiation time. The rate of which was much higher for doses above 50 kGy. Tensile strength declines with time and those samples irradiated above 50 kGy become quite brittle, just after irradiation. Results reveal that post-irradiation degradation of polypropylene irradiated by γ-ray occurs via chain scission mechanism.     

Investigation of the irradiation history of the Iranian dates and pistachio nuts using thermoluminescence technique

Three different varieties of Iranian fresh dates and five types of raw and salted pistachio nuts have been tested for identification of irradiation histories. Doses of 2.5, 5, 7.5 and 10 kGy from a gamma cell Gc-220 have been administrated to the samples under investigation.TL response versus dose for date and for pistachio nuts have been obtained. The effect of added ingredients such as salt in pistachio nuts, and moisture in date samples on the TL response have been studied. The fading of TL intensity of the irradiated dates and pistachio nuts have also been measured. Based on the latter results, it appears possible to identify the irradiated dates (10 kGy), within (1–2) months post-irradiation.In the salted pistachio nuts, the salt itself gives a very significant and distinguishable response. In the unsalted case, however, the difference between the irradiated and unirradiated samples seem difficult to detect due to partial overlapping of the respective responses.     

Molecular-topological and thermal properties of gamma-irradiated alternating carbon monoxide-ethylene copolymer

Gamma-irradiation to a dose of up to 2000 kGy does not lead to substantial changes in the topological structure of a carbon monoxide copolymer with ethylene, thereby suggesting it high radiation resistance. The topological structure of unirradiated and irradiated copolymer samples is polyblock in nature having four crystalline phases as the branching “junctions” in the pseudo-network structure of its amorphous block. Copolymer molecular flow begins after completion of melting of its high-melting fraction and at an onset flow temperature of 484 ± 4 K regardless of the absorbed radiation dose. The irradiated and unirradiated copolymer releases the same gaseous products upon heating, and the irradiation itself does not affect the onset temperature of effective gas evolution.     

An electron spin resonance study of gamma-irradiated grapes

The ESR spectra of the seeds, skins and stalks of unirradiated and γ-irradiated Cape black grapes have been obtained. In the spectra of all parts of the grape a single line (g ca. 2.004) is observed both before and after irradiation. New spectral features are observed after irradiation with doses of between 2 and 10 kGy. Some of these features decline in intensity over a period of several days. However, in the case of stalks, new spectral features are readily observed over the shelf-life of the fruit and in samples irradiated to a dose of only 2kGy.     

Thermoluminescence characteristics of minerals from irradiated potatoes of different origins of production

Thermoluminescence (TL) characteristics were investigated for minerals, which were separated from potatoes irradiated at 0–1 kGy of different origins of production in Korea. The polyminerals analyzed by X-ray diffractometer were mainly composed of quartz and feldspar, and showed varied contents with producing origins, that contributed to typical TL responses to irradiation. The glow curve of irradiated samples at 0.05–1 kGy peaked at approximately 200°C with high intensity, but that of non-irradiated potatoes was observed at approximately 300°C with low intensity. Discrimination between irradiated (more than 0.05 kGy) and non-irradiated samples was possible just on the basis of the first glow curve, however, normalization of results through a re-irradiation step greatly improved their reliability. The signal intensity of TL decreased with the lapse of post-irradiation time under different storage conditions (0±0.5°C/dark room, 25±5°C/dark room and 25±5°C/naturally lighted room) but was still distinguishable from that of the non-irradiated sample even after one year.     

Effects of gamma rays on a restored painting from the XVIIth century

The subject of this study is a Peruvian painting from the 17th century, which has been recently restored and then contaminated by mould. It received different unsuccessful treatments. Therefore, radiation process was suggested as an alternative once it is an effective technology for decontamination and conservation purposes. The aim of this study is to investigate the influence of irradiation process on the original painting and on the products used in the restoration process. These products were irradiated with ⁶⁰Co gamma rays applying doses in the range of 6–25 kGy. The polymeric materials were characterized by thermal analysis techniques before and after irradiation. The colour of the pigments irradiated and non-irradiated were compared by spectrophotometric analysis. Small samples removed of the original painting were also irradiated and investigated. The results obtained until now allowed concluding that the irradiation with the appropriated dose of 6.0 kGy, according to the literature, will not damage the restored painting.