Effect of dose rate on inactivation of microorganisms in spices by electron-beams and gamma-rays irradiation

Total aerobic bacteria in spices used in this study were determined to be 1 × 10⁶ to 6 × 10⁷ per gram. A study on the inactivation of microorganisms in spices showed that doses of 6–9kGy of EB (electron-beams) or γ-irradiation were required to reduce the total aerobic bacteria in many However, a little increase of resistance was observed on the inactivation of total aerobic bacteria in many spices in case of EB irradiation. These difference of radiation sensitivities between EB and γ-rays was explained by dose rate effect on oxidation damage to microorganisms from the results of radiation sensitivities of Bacillus pumilus and B. megaterium spores at dry conditions. On the other hand, these high dose rate of EB irradiation suppressed the increase of peroxide values in spices at high dose irradiation up to 80 kGy. However, components of essential oils in spices were not changed even irradiated up to 50 kGy with EB and γ-rays.     

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.     

Volatile compounds and odor preferences of ground beef added with garlic and red wine,and irradiated with charcoal pack

Irradiation is the most efficient non-thermal technology for improving hygienic quality and extending the shelf-life of food products. One of the adverse effects of food irradiation, however, is off-flavor production, which significantly affects the sensory preferences for certain foods. In this study, garlic (5%, w/w) and red wine (1:1, w/w) were added to ground beef to increase the radiation sensitivity of pathogens and improve meat odor/flavor. Samples were irradiated at 0 or 5 kGy in the presence of charcoal pack. SPME-GC–MS analysis was performed to measure the changes in the volatile compounds and sensory characteristics of the samples. The amount of total volatile compounds produced from ground beef was greater when the sample was irradiated. When garlic and red wine were added to the ground beef, the amount of volatile compounds significantly increased, and the amount of volatile compounds increased even further after irradiation. However, when the samples were irradiated with charcoal pack, the amount of volatile compounds decreased significantly. Sensory evaluation indicated that charcoal pack significantly increased the odor preferences for both irradiated and non-irradiated ground beef added with garlic. These results indicated that addition of charcoal pack to ground beef could reduce off-odor problems induced by irradiation, and this effect was consistent even when certain additives such as garlic and red wine were added.     

Food irradiation in Hungary: commercial processing and development work

The result of an experiment with irradiated frozen poultry meat is presented. The purpose of the experiment was to prove the benefit of irradiation treatment for elimination of pathogenic bacteria such as Salmonella and Campylobacter. We found that an average dose of 4.5 kGy kills the bacteria in the meat. Agroster was involved in an EU project on the identification of irradiation treatment of spices and data from this project are presented. Commercial irradiation of spices has been used for more than 15 years in Hungary, proving the benefit of this technology     

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.     

Effects of irradiation on trans fatty acids formation in ground beef

In order to give the consumer the assurance that meat processed by irradiation is a safe product, a great deal of research has been developed in the world. The effect of irradiation on the hygienic quality of meat and meat products is considered as related to the control of meat-borne parasites of humans; elimination of pathogens from fresh meat and poultry; and elimination of pathogens from processed meat. Lipid oxidation and associated changes are the major causes of the quality deterioration of meat during storage. Irradiation of lipids induces the production of free radicals, which react with oxygen, leading to the formation of carbonyls, responsible for alterations in food nutritional and sensorial characteristics. Trans fatty acids are present in ground beef and can also be formed during its processing. Interestingly, the trans fatty acids, due to their chemical and physical characteristics, show more resistance to the oxidizing process. This property motivated us to investigate the level of the trans fatty acids, as well as the level of oxidation in irradiated ground beef. Irradiation of ground beef was performed by gamma rays from a ⁶⁰Co source. The applied radiation doses were 0; 1.0; 2.0; 3.0; 4.0; 5.0; 6.0; 7.0 and 8.0 kGy. Lipid peroxidation in terms of TBA number and carbonyl content was monitored during storage. The sample characteristics and trans fatty acids composition were measured, following irradiation and after 60 and 90 days of storage at –10°C.     

Reduction of irradiation off-odor and lipid oxidation in ground beef by α-tocopherol addition and the use of a charcoal pack

A combination of a charcoal pack during irradiation and α-tocopherol addition into ground beef was applied to eliminate an irradiation characteristic off-odor and to retard the lipid oxidation caused by the irradiation process. Ground beef was mixed with 200 ppm α-tocopherol and gamma irradiated with 0, 5, and 10 kGy with or without a charcoal pack present during the irradiation treatment. The pH of the control group was lower than that of α-tocopherol and charcoal pack treatment initially but increased rapidly and showed higher pH at day 7. Addition of α-tocopherol with or without charcoal pack addition showed lower 2-thiobarbituric acid reactive substances values in irradiated ground beef at days 3 and 7 compared to those without addition. The color of ground beef was not significantly affected by the treatment. However, odor preference result showed that 10 kGy-irradiated ground beef with a combination of charcoal pack and α-tocopherol addition had higher scores than the control group regardless of irradiation. Solid-phase microextraction (SPME) gas chromatograph/mass spectrometry (GC/MS) analysis identified various volatile compounds that were created by irradiation of ground beef. These compounds were reduced or eliminated when a charcoal pack was used during the irradiation process. The results of the present study imply that combination of packaging with a charcoal pack during the irradiation process and addition of α-tocopherol into ground beef is a good method to effectively eliminate an irradiation off-odor and retard the lipid oxidation development in ground beef caused by irradiation.     

Comparison of the efficacy of gamma and UV irradiation in sanitization of fresh carrot juice

As there is no pasteurization procedure for the manufacture of fresh vegetable juice, both industry and consumers have sought a method for improving the storage stability and shelf-life of this category of products. In this study, the effects of commercially available, non-thermal pasteurization processes, such as gamma and UV irradiation, were compared for their efficacy in sanitizing fresh carrot juice (FCJ). FCJ was manufactured, packaged, and gamma irradiated with doses of 0, 1, 3, and 5 kGy. The manufactured FCJ was also passed through 4 UV light lamps at doses of 3.67, 4.69, and 6.50 kGy. The total aerobic bacterial count of the FCJ approached the legal limit (10⁵ CFU/mL) after manufacturing. Both treatments were effective in reducing the number of total aerobic bacteria, and the reduced number was maintained during storage for 7 days. Gamma irradiation was more effective in suppressing microbial growth during storage. When the doses for UV treatment and gamma irradiation were higher, the inactivation effects were higher. The reduction of ascorbic acid content was greater upon gamma irradiation than UV treatment. No difference was found in the contents of flavonoids and polyphenols in FCJ after either treatment. After 3 days of refrigerated storage, the sensory scores of gamma- or UV-irradiated FCJ were superior to those of the control. The results indicate that both non-thermal treatments were effective in improving storage stability and extending shelf-life, but gamma irradiation was slightly better in suppressing microbial growth after treatment.     

DNA analysis of a radiotolerant bacterium Pantoea agglomerans by FT-IR spectroscopy

A radiation tolerance strain, Pantoea agglomerans was isolated from γ-irradiated carrot samples (Daucus carota). D₁₀ determination showed that the radioresistance of this bacterium is five-fold higher than Escherichia coli, both belonging to the family of Enterobacteriaceae. DNA isolated from untreated and irradiated bacterial cells was analyzed by FT-IR spectroscopy to investigate the radiotolerance of this bacterium. At doses <5 kGy, an alteration of the interbase hydrogen networks was observed and characterized mainly by an increase of bands assigned to the carbonyl non-pairing and the free amine groups. Moderate breakage of the DNA backbone and damage of the osidic structure were also observed. Similar spectral profiles were noticed at doses ≥5 kGy, but additional increase of the band intensity of CC and CN suggests damages of nucleobases. High number of asymmetric PO₂⁻ and upper shift of symmetric PO₂⁻ are indicative of DNA strand breaks. Osidic damages were evidenced by decrease of the absorption bands ascribed to deoxyribosyl moieties and by appearance of C–OH band. DNA degradation at high irradiation doses was also noticed by electrophoresis using agarose gel. It appeared that DNA underwent covalent cross-linking, as revealed by agglomeration of DNA in the wells of agarose gel.     

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.     

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.     

Effects of low-level gamma irradiation on the characteristics of fermented pork sausage during storage

The effect of gamma irradiation (0.5, 1, 2, and 4 kGy) on the quality of vacuum-packaged dry fermented sausages during refrigerated storage was evaluated. At Day 0 of irradiation, the pH, redness (CIE a^?), yellowness (CIE b^?), 2-thiobarbituric acid-reactive substances (TBARS) and volatile basic nitrogen (VBN) values of samples irradiated at 2 and 4 kGy were higher (p<0.05), but the CIE L^? values (lightness) were lower than those of the non-irradiated control (p<0.05). At<1 kGy irradiation, however, the pH, CIE L^?, CIE a^? and CIE b^?-value of samples were not significantly influenced by irradiation. The CIE a^?, and CIE b^?-values of samples irradiated at 2 and 4 kGy decreased with the increase of storage time. The VBN, TBARS, and CIE L^?-values of samples irradiated at 4 kGy were not changed significantly during refrigerated storage for 90 days (p>0.05). The total plate counts (TPC) and lactic acid bacteria (LAB) in the samples irradiated at 4 kGy were significantly lower (p<0.01) than those with lower irradiation doses. At the end of storage, the TPC, coliform, and LAB in the samples were not increased after irradiation at 1, 0.5 and 1 kGy, respectively. TPC and LAB were not detected in samples irradiated at 4 kGy at Day 90. In addition, no coliform bacteria were found in samples irradiated at 1 kGy during refrigerated storage. Sensory evaluation indicated that the rancid flavor of samples irradiated at 4 kGy was significantly higher, but aroma and taste scores were lower than those of the control at Day 3 of storage. Irradiation of dry fermented sausages at 2 kGy was the best conditions to prolong the shelf-life and decrease the rancid flavor without significant quality deterioration.     

Shelf-life extension of preservative-free hydrated feed using gamma pasteurization and its effect on growth performance of eel

Hydrated feed (HF) promotes the growth performance and shortens the feeding time of fish by increasing the efficiency of digestion. However, the shelf-life of HF is a concern due to its relatively higher water content. In this study, radiation pasteurization was applied to improve the shelf-life and microbiological quality of HF for fish farming. Preservative-free HF containing 25% moisture was gamma-irradiated and its microbiological and nutritional properties evaluated in addition to a practical feeding trial carried out using eel. The viable counts of bacteria and fungi in HF were 10⁶ and 10⁴ CFU/g, respectively. All coliform bacteria and yeast in HF were eliminated by irradiation at a dose of 5 kGy, and total aerobic bacteria were eliminated at 10 kGy. The shelf-life of the preservative-free and irradiated (10 kGy) HF was estimated as 6 months under ambient conditions. The nutritional composition of HF was stable up to 10 kGy of irradiation. Based on a feeding trial, it was proven that eel fed HF had about 20% higher growth rate than that fed dried feed.     

Quality properties of sausage made with gamma irradiated natural casing from intestine of pork or lamb

Quality properties in emulsion-type sausage stuffed into irradiated natural casing were studied. The numbers of total aerobic bacteria, Enterococci and coliform bacteria in the sausage prepared with irradiated natural pork and lamb casing were significantly decreased or eliminated compared to those prepared with the nonirradiated control. The 2-thiobarbituric acid reactive substances (TBARS) value in the sausage with irradiated natural casing did not change significantly during storage with minor exceptions. The total working force of shear of the sausages were decreased in both irradiated casings but the sensory evaluation showed no difference. Therefore, the gamma irradiation was a useful technique to sanitize the natural pork and lamb casings and to extend the shelf-life of the sausage made with natural casings during distribution.     

Improvement of shelf stability and processing properties of meat products by gamma irradiation

To evaluate the effects of gamma irradiation on the processing properties of meat products, emulsion-type sausage, beef patties and pork loin ham were manufactured. Most contaminated bacteria were killed by 3 kGy-irradiation to raw ground beef, and sausage can be manufactured with desirable flavor, a reduction of NaCl and phosphate, and extension of shelf life using gamma irradiation on the raw meat. The beef patties were manufactured with the addition of antioxidants (200 ppm), BHA, ascorbyl palmitate, -tocopherol, or β-carotene, and gamma-irradiation. Retardation of lipid oxidation appeared at the patties with an antioxidant. A dose of 5 kGy was observed to be as effective as the use of 200 ppm NaNO₂ to provide and maintain the desired color of the product during storage. After curing, irradiation, heating and smoking could extensively prolong the shelf life of the hams.     

Use of gamma-irradiation technology in combination with edible coating to produce shelf-stable foods

This research was undertaken to determine the effectiveness of low-dose gamma-irradiation combined with edible coatings to produce shelf-stable foods. Three types of commercially distributed food products were investigated: precooked shrimps, ready to cook pizzas, and fresh strawberries. Samples were coated with various formulations of protein-based solutions and irradiated at total doses between 0 and 3 kGy. Samples were stored at 4°C and evaluated periodically for microbial growth. Sensorial analysis was also performed using a nine-point hedonic scale to evaluate the organoleptic characteristics (odor, taste and appearance). The results showed significant (p0.05) combined effect of gamma-irradiation and coating on microbial growth (APCs and Pseudomonas putida). The shelf-life extension periods ranged from 3 to 10 days for shrimps and from 7 to 20 days for pizzas, compared to uncoated/unirradiated products. No significant (p>0.05) detrimental effect of gamma-irradiation on sensorial characteristics (odor, taste, appearance) was observed. In strawberries, coating with irradiated protein solutions resulted in significant reduction of the percentage of mold contamination.     

Effect of gamma radiation on microbial population of natural casings

The high microbial load of fresh and dry natural casings increases the risk of meat product contamination with pathogenic microorganisms, agents of foodborn diseases.

The aim of this work is to evaluate the killing effect of gamma radiation of the resident microbial population of pork and beef casings, to improve their hygiene and safety.

Portions of fresh pork (small intestines and colon) and dry beef casings were irradiated in a Cobalt 60 source with with absorbed doses of 1,2,5 and 10 kGy.

The D₁₀ values of total aerobic microorganisms in the pork casings were 1.65 kGy for colon and 1.54 kGy for small intestine. The D₁₀ value found in beef dry casings (small intestine) was 10.17 kGy. Radurization with 5 kGy was able to reduce, at least, 6 logs the coliform bacteria in pork casings. The killing effect over faecal Streptococci was 4 logs for pork fresh casings and 2 logs for beef dry casings. Gamma radiation with 5 kGy proved to be a convenient method to reduce substantially the microbial population of pork fresh casings. Otherwise, the microbial population of beef dry casings still resisted to 10 kGy.     

Effect of dose rate of gamma irradiation on biochemical quality and browning of mushrooms Agaricus bisporus

In order to enhance the shelf-life of edible mature mushrooms Agaricus bisporus, 2 kGy ionising treatments were applied at two different dose rates: 4.5 kGy/h (I⁻) and 32 kGy/h (I⁺). Both I⁺ and I⁻ showed 2 and 4 days shelf-life enhancement compared to the control (C). Before day 9, no significant difference (p>0.05) in L^* value was detected in irradiated mushrooms. However, after day 9, the highest observed L^* value (whiteness) was obtained for the mushrooms irradiated in I⁻. Analyses of phenolic compounds revealed that mushrooms in I⁻ contained more phenols than I⁺ and C, the latter containing the lower level of phenols. The polyphenol oxidase (PPO) activities of irradiated mushrooms, analysed via catechol oxidase and dopa oxidase substrates, resulted in being significantly lowered (p0.05) compared to C, with a further decrease in I⁺. Analyses of the enzymes indicated that PPO activity was lower in I⁺, contrasting with its lower phenol concentration. Ionising treatments also increased significantly (p0.05) the phenylalanine ammonia-lyase (PAL) activity. The observation of mushrooms cellular membranes, by electronic microscopy, revealed a better preserved integrity in I⁻ than in I⁺. It is thus assumed that the browning effect observed in I⁺ was caused by both the decompartimentation of vacuolar phenol and by the entry of molecular oxygen into the cell cytoplasm. The synergetic effect of the residual active PPO and the molecular oxygen, in contact with the phenols, allowed an increased oxidation rate and, therefore, a more pronounced browning in I⁺ than in I⁻.     

Effects of organic acids,amino acids and ethanol on the radio-degradation of patulin in an aqueous model system

The effects of organic acids, amino acids, and ethanol on the radio-degradation of patulin by gamma irradiation in an aqueous model system were investigated. The patulin, dissolved in distilled water at a concentration of 50 ppm, was practically degraded by the gamma irradiation at the dose of 1.0 kGy, while 33% of the patulin remained in apple juice. In the aqueous model system, the radio-degradation of patulin was partially inhibited by the addition of organic acids, amino acids, and ethanol. The proportions of remaining patulin after irradiation with the dose of 1.0 kGy in the 1% solution of malic acid, citric acid, lactic acid, acetic acid, ascorbic acid, and ethanol were 31.4%, 2.3%, 31.2%, 6.1%, 50.8%, and 12.5%, respectively. During 30 days of storage, the remaining patulin was reduced gradually in the solution of ascorbic acid and malic acid compared to being stable in other samples. The amino acids, serine, threonine, and histidine, inhibited the radio-degradation of patulin. In conclusion, it was suggested that 1 kGy of gamma irradiation (recommended radiation doses for radicidation and/or quarantine in fruits) is effective for the reduction of patulin, but the nutritional elements should be considered because the radio-degradation effects are environment dependent.     

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.