The application of high dose food irradiation in South Africa

During the 1950s to the end of the 1970s the United States Army developed the basic methodology to produce shelf-stable irradiated meat, seafood and poultry products. These products are normally packed without gravy, sauce or brine, as liquid is not required to sterilize the product as in the canning process. This leads to the distinctive “dried cooked” taste normally associated with roasts opposed to the casserole taste usually associated with tinned meats. The Biogam group at the Atomic Energy Corporation of South Africa is currently producing shelf-stable irradiated meats on a commercial basis. The meats are cooked, chilled, portioned, vacuum packed and irradiated to the required minimum dose of 45 kGy at a temperature of between −20 and −40°C to ensure absolute sterility even under tropical conditions. The product is packaged in a high quality four layer laminate pouch and will therefore not rust or burst even under adverse weather conditions and can be guaranteed for more than two years as long as the integrity of the packaging is maintained. Safari operators in remote parts of Africa, mountaineers, yachtsmen, canoeists and geological survey teams currently use shelf-stable irradiated meat products produced in South Africa.     

Improvement of microbiological safety of sous-vide meals by gamma radiation

Experimental batches of smoked-cured pork in stewed beans sauce were inoculated with spores of psychrotrophic Bacillus cereus, more heat and radiation resistant than spores of non-proteolytic C. botulinum. After vacuum packaging, the meals were treated with combinations of pasteurizing heat treatments and gamma irradiation of 5 kGy. Prior and after treatments, and periodically during storage at 10°C, total aerobic and total anerobic viable cell counts, and selectively, the viable cell counts of B. cereus and sulphite-reducing clostridia have been determined. The effects of the treatment order as well as addition of nisin to enhance the preservative efficiency of the physical treatments were also studied. Heat-sensitization of bacterial spores surviving irradiation occurred. The quality-friendly sous-vide cooking in combination with this medium dose gamma irradiation and/or nisin addition increased considerably the microbiological safety and the keeping quality of the meals studied. However, approx. 40% loss of thiamin content occurred as an effect of combination treatments, and adverse sensorial effects may also limit the feasible radiation doses or the usable concentrations of nisin.     

The effect of gamma irradiation on physicochemical and microbiological quality of fresh pork loins

Radiation treatments were carried out under air on fresh pork loins at doses of 2, 4 and 8 kGy and the loins were evaluated for deamidation, solubility, sulphydryl content and surface hydrophobicity. Deamidation was significantly (P0.05) affected by the treatment with 98% deamidation at a dose of 8 kGy. No significant changes (P>0.05) were noted in sulphydryl content under the same conditions. The increase in deamidation was accompanied by a decrease in hydrophobicity and an increase in protein solubility. γ-Irradiation also reduced the number of microorganisms in the meat. Mesophiles were more resistant to the irradiation treatment than psychrotrophs and Pseudomonas.     

The influence of molecular orientation on the crosslinking/oxidative behaviour of iPP exposed to gamma radiation

This paper presents a study of the influence of structural peculiarities, uniaxial orientation and fibrillar structure on the radiation-induced changes in iPP. For the purposes of this study, iPP was oriented via solid-state stretching at elevated temperature to various draw ratios and, later on, gamma irradiated in air. In order to investigate orientation- and/or radiation-induced structural changes, optical microscopy (OM), scanning electron microscopy (SEM), wide angle X-ray scattering (WAXS), differential scanning calorimetry (DSC), infrared spectroscopy (IR) and gel measurements were employed. To quantify the degree of molecular orientation, Herman’s orientation function (f_c), was used. IR spectroscopy and gel measurements were used to determine the changes in the oxidative degradation and degree of network formation, respectively. Sol-gel analysis was studied in detail using the Charlesby-Pinner (C-P) equation. The radiation-induced changes in the structure and evolution of oxygen-containing species were also studied through dielectric loss (tan δ) analysis in a wide frequency range; the polar groups that were introduced by irradiation in apolar iPP were considered as tracer groups. Conclusions derived according to different methods were compared. Presented results reveal two different radiation-induced dynamics; gamma irradiation of initial and fully developed fibrillar iPP structures leads to significantly different crosslinking and/or oxidation response.     

ESR studies on poly(vinyl chloride) irradiated at medium and high doses

Room temperature gamma irradiation at medium (1-100 kGy) or high (0.9-25 MGy) doses induces different radicals into pure or industrial poly(vinyl chloride) (PVC); the various ESR signals differ by their shapes and/or values of their g-factors and/or peak-to-peak widths but do not give precise information on the chemical structures of the different radicals as the spectra are only poorly resolved. However, looking at the ESR parameters of the different signals and their evolution during natural ageing of the samples, allows us to make correlations between the radio-induced lines in industrial PVC and the ones induced in pure PVC or in PVC additives.     

Effect of gamma irradiation on the microbiological quality and on the functional properties of proteins in dry red kidney beans (Phaseolus vulgaris)

Gamma-irradiation was found to affect the physicochemical properties of dry red kidney beans. The highest dose used (8 kGy) significantly (P0.05) modified the extent of deamidation, the number of sulfhydryl groups, as well as the solubility and the hydrophobicity of the protein. Deamidation, protein solubility and hydrophobicity all increased with the irradiation dose while the number of sulfhydryl groups was reduced by the treatment. Furthermore, irradiation also affected the outgrowth of natural filamentous fungi contaminants present on the dry beans. A dose of 1.5 kGy reduced the number of filamentous fungi by 2 log cycles immediately after treatment. However, the highest dose used (3 kGy) did not eliminate the filamentous fungi completely. Moreover, the filamentous fungi population was a lot less diversified on the irradiated samples. Species of Aspergillus sp. and Penicillium sp. were more abundant on the unirradiated beans while the beans irradiated at 3 kGy contained were predominantly infected by species of Rhizopus sp. , Cladosporium sp. and Alternaria sp.     

The effect of ionizing radiation on microbiological decontamination of medical herbs and biologically active compounds

Several thousand tons of medical herbs are produced annually by pharmaceutical industry in Poland. This product should be of highest quality and microbial purity. Recently, chemical methods of decontamination are recognized as less safe, thus irradiation technique was chosen to replace them in use. In the Institute of Nuclear Chemistry and Technology the national program on the application of irradiation to the decontamination of medical herbs is in progress now. The purpose of the program is to elaborate, on the basis of research work, the facility standards and technological instructions indispensable for the practice of radiation technology.     

Chemical, sensory and microbiological changes of gamma irradiated coconut cream powder

A study was carried out to determine optimum decontamination dose for a locally manufactured coconut cream powder. Samples were gamma irradiated (0–15 kGy) and ageing process was achieved using GEER oven at 60 °C for 7 days, which is equivalent to one-year storage at room temperature. Iodine value (IV), ranging from 4.8 to 6.4, was not affected by radiation doses and storage, however peroxide value and thiobarbituric acid (TBA) generally increased with radiation doses. In most samples, peroxide value (meq/kg) reduced after storage, whilst the TBA (mg malonaldehyde/kg), indicator for product quality, slightly increased. The sensory evaluation conducted using 25 taste panellists indicated that scores on odour, creamy taste and overall acceptance for all irradiated samples at more than 5 kGy were significantly lower (P<0.05) than the control. However, the panellists could not detect any significant differences among the irradiation doses (P>0.05). All stored products were significantly different in colour, creamy taste, odour and overall acceptance (P<0.05) when compared to the non-stored non-irradiated control. Microbiological count of the samples prior to irradiation was in the range of 1×10²–1.7×10³ cfu/g with no detection of Salmonella sp. and Escherichia coli. No microbial colonies were detected after irradiation. Based on the TBA and overall sensory acceptance, gamma irradiation of 5 kGy was found to be the optimum dose and lower doses can be considered to decontaminate coconut cream powder.     

Influence of gamma radiation on microbiological parameters of the ethanolic fermentation of sugar-cane must

The influence of gamma radiation on reducing the population of some bacteria Bacillus and Lactobacillus that usually contaminate the sugar-cane must and its effects on acidity of the medium and viability of the yeast during fermentation were evaluated. The treatment with gamma radiation reduced the bacterial load of the sugar-cane must. Consequently, the volatile acidity produced during the fermentation of the must decreased and the viability of the yeast afterwards added increased.     

Impact of gamma-irradiation on some mass transfer driven operations in food processing

The effect of gamma-irradiation pretreatment on some mass transfer driven operations such as dehydration, osmotic dehydration and rehydration, commonly used in food processing, was studied. Applied irradiation up to 12.0 kGy resulted in decrease in hardness of the samples, as indicated by texture analysis. The effective diffusion coefficients of water and solute determined for dehydration, osmotic dehydration as well as for rehydration using a Fickian diffusion model. The effective diffusion coefficients for water (in case of osmotic dehydration and dehydration) and solid diffusion (in case of osmotic dehydration) were found to increase exponentially with doses of gamma-irradiation (G) according to an equation of the form D=A exp(−B/G), where A and B are constants. Microstructures of irradiated-carrot samples revealed that the exposure of carrot to gamma irradiation resulted in the breakage of cell wall structure, thereby causing softening of irradiated samples and facilitating mass transfer during dehydration and osmotic dehydration. The rehydration characteristics showed that gamma-irradiated sample did not absorb as much water as control, probably due to loss of cell integrity.     

The effect of gamma irradiation on the viscosity of two barley cultivars for broiler chicks

Seeds of two barley cultivars (Local Black and Shoaa) were gamma irradiated at 0, 10, 50, 100, 150 and 200 kGy doses using Cobalt-60 source to decrease the viscosity. The viscosity was determined in the flour of the seeds using Ostwald U-tube viscometer. The viscosity values were reduced by 25%, 50%, 65%, 72% and 74% in Local Black barley cultivar, while, in Shoaa cultivar the reductions were 15%, 30%, 52%, 69% and 67% at 10, 50, 100, 150 and 200 kGy, respectively. The chemical compositions of the seeds were determined in all treatments.     

The electron dose monitoring and control system in EB radiation processing for wires and cables

This paper introduces a close-loop microcomputer control system used for EB radiation processing of wires and cables, which is based on the measurements and calculations of the absorbed dose distribution of 0.6–2.0 MeV electrons in circular compound materials. The calculation of electron energy deposition in 4-layer media is carried out by the bipartition model of electron transport.

The design ideas, system configuration and implementation of this control system governed by a 586 personal computer under windows 98 OS are described in this paper. The field operation results such as control precision and step response curves of this system are also given. The control system has been used for EB radiation processing of wires.     

Stability of a salicylate-based poly(anhydride-ester) to electron beam and gamma radiation

The effect of electron beam and gamma radiation on the physicochemical properties of a salicylate-based poly(anhydride-ester) was studied by exposing polymers to 0 (control), 25 and 50 kGy. After radiation exposure, salicylic acid release in vitro was monitored to assess any changes in drug release profiles. Molecular weight, glass transition temperature and decomposition temperature were evaluated for polymer chain scission and/or crosslinking as well as changes in thermal properties. Proton nuclear magnetic resonance and infrared spectroscopies were also used to determine polymer degradation and/or chain scission. In vitro cell studies were performed to identify cytocompatibility following radiation exposure. These studies demonstrate that the physicochemical properties of the polymer are not substantially affected by exposure to electron beam and gamma radiation.     

Gamma radiation induced synthesis of gold nanoparticles in aqueous polyvinyl pyrrolidone solution and its application for hydrogen peroxide estimation

Gold nanoparticles (Au nps) have been synthesized in aqueous solution of polyvinyl pyrrolidone (PVP) by gamma radiolysis from HAuCl₄·3H₂O precursor and in presence of small concentrations of Ag⁺, 2-propanol and acetone. The effect of different experimental parameters, such as concentration of reactant, molecular weight of PVP on nanoparticle formation was studied. TEM image confirmed that spherical Au nps were formed when PVP of molecular weight 360,000 Da was used as capping agent. H₂O₂ is a reactant in the enzyme catalyzed reaction of o-phenylene diamine (o-PDA). The reaction product has a weak absorption in the yellow region of the spectrum. When this product interacts with Au nps, it leads to enhancement of the absorption peak. The nanoparticles synthesized by radiation method were used for estimation of H₂O₂. The absorbance value of this peak at λ_max was observed to change with H₂O₂ concentration, which was monitored for estimation of H₂O₂. The response is linear in the range of 2.5×10⁻⁶ mol dm⁻³ to 2×10⁻⁴ mol dm⁻³ and 1×10⁻⁷ mol dm⁻³ to 3×10⁻⁶ mol dm⁻³ H₂O₂ in two separate sets of experimental parameters with detection limit 1×10⁻⁷ mol dm⁻³.     

Effect of chemical structure on the properties of some hydrogels prepared by using gamma radiation polymerization

Several hydrogels were prepared using radiolytic polymerization of aqueous solutions of acrylamide or acrylamide containing appropriate comonomer such as acrylic acid, maleic acid, itaconic acid, and maleic anhydride. The hydrogels have been prepared at an irradiation dose of 30 kGy. The effects of the chemical structure of the monomer(s) and crosslinking agents on the yield of homopolymer(s) or copolymers have been studied. These crosslinking agents include N, N′‐methylene dimethacrylate (MDA) and N, N′‐methylene bisallyamide (MBA). The hydrogels obtained were characterized using swelling technique, thermal and spectroscopic analysis. The results obtained showed that the prepared samples are able to reject sodium ions and are not able to recover the Basic Blue Dye from their aqueous solution. © 2005 John Wiley & Sons, Ltd.     

Effects of gamma irradiation on chemical composition and ruminal protein degradation of canola meal

Gamma irradiation of canola meal (at doses of 25, 50 and 75 kGy) could alter its ruminal protein degradation characteristics by cross-linking of the polypeptide chains. This processing resulted in decrease (linear effect, P<0.001) of ruminal protein degradation and increase (linear effect, P<0.001) of intestinal protein digestibility. The results showed that gamma irradiation at doses higher than 25 kGy can be used as a cross-linking agent to improve protein properties of supplements in ruminant nutrition.     

Comparative study on degradation of ethylene-propylene rubber for nuclear cables from gamma and beta irradiation

Considering safety is the priority concern of nuclear power plants, equipment qualification testing of the nuclear components manufactured should be paid special attention to. Thereinto, equivalent conversion (1:1) from the absorbed beta doses to gamma doses is a rule of thumb for irradiation qualification testing of the polymers used as nuclear cables, however whether it is reasonable and applicable to Chinese domestic polymers still requires investigation. In this paper, both gamma and beta irradiation testing with the actual dose rates and total absorbed doses in China Advanced Passive (CAP) series nuclear power plant was performed upon one domestically manufactured ethylene-propylene rubber intended for nuclear cable insulation in China. The mechanical and the electrical properties before and after irradiation were measured to compare the extent and the trend of degradation between the two irradiation types, and related oxidation degradation mechanism especially its attenuation along the thickness was quantitatively addressed.     

Comparative effects of gamma irradiation and phosphine fumigation on the quality of white ginseng

The hygienic, physicochemical, and organoleptic qualities of white ginseng were monitored during 6 months under accelerated conditions (40°C, 90% r.h.) by observing its microbial populations, disinfestation, and some quality attributes following either gamma irradiation at 2.5–10 kGy or commercial phosphine (PH₃) fumigation. In a comparative study, both treatments were found to be effective for disinfecting the stored samples. Phosphine showed no appreciable decontaminating effects on microorganisms contaminated including coliforms, while 5 kGy irradiation was sufficient to control all microorganisms related to the quality of the packed samples. Irradiation at 5 kGy caused negligible changes in physicochemical attributes of the samples, such as ginsenosides, amino acids, fatty acids, and organoleptic properties, whereas phosphine fumigation was found detrimental to sensory flavor (P<0.01). Quality deterioration occurred in the commercially-packed samples was in the following order: the control, 10 kGy-, phosphine-, and 2.5–5 kGy-treated samples. Accordingly, irradiation at <5 kGy was found to be an effective alternative to phosphine fumigation for white ginseng.     

Effect of gamma irradiation on the thermal and rheological properties of grain amaranth starch

Physical properties of starch from two cultivars of gamma-irradiated grain amaranth with different amylose content were investigated. Pasting viscosities decreased continuously with the increase in dosages of irradiation. Furthermore, different irradiation dosages resulted in modification of the thermal properties and crystallinity of starch. Dynamic oscillation on shear was also employed, temperature and frequency sweeps showed that changes in storage modulus and loss modulus were significant, with Tibet Yellow producing more elastic gels as compared to Hy030 at different irradiation dosages.     

Effects of gamma irradiation on solid and lyophilised phospholipids

The effects of gamma irradiation (25 kGy) as a sterilisation method for phospholipids (distearoylphosphatidylcholine and distearoylphosphatidylglycerol) were investigated. ³¹P-NMR revealed minor chemical degradation of the phospholipids but lower dynamic viscosity and pseudoplasticity, lower turbidity, higher diffusion constant, smaller size, more negative zeta potential and changes in the phase transition behaviour of the subsequently produced liposomes were observed. The observed changes could to some extent be explained by the irradiation-induced degradation products (distearoylphosphatidic acid, fatty acids, lysophospholipids).