Irradiation of Food, Current Legislation Framework, and Detection of Irradiated Foods

Raman Spectroscopic and Sensory Evaluation of Cocoa Liquor Prepared with Ecuadorian Cocoa Beans Treated with Gamma Irradiation or Induced Electromagnetic Field Fermentation

Cocoa liquor is the primary precursor of the worldwide highly appreciated commodity chocolate. Its quality depends on several factors, such as the type of cocoa, the fermentation process, and the control of the contaminants in the fermented beans. This study aims to evaluate whether the induced magnetic field treatment during the fermentation process or the pathogen reduction with gamma irradiation after the fermentation affect the characteristics of the cocoa liquor obtained from Ecuadorian cocoa beans. For this purpose, liquor samples from controls (standard process), from beans treated with an induced magnetic field up to 80 mT, and from beans irradiated with nominal doses up to 3 kGy were characterized through Raman spectroscopic analysis and sensorial evaluation. The most relevant bands of the cocoa liquor were assigned according to reports from the literature, spectroscopic data, and chemometrics. The spectra corresponding to different treatments and doses were visually very similar, but they could be discriminated using OPLS-DA models, where the most intense Raman signals were attributed to the lipid components. The sensorial evaluation rated the presence of floral, fruity, almondy, acid, and bitter flavors, along with astringency and intense aroma, and these attributes exhibited variable behavior depending on the dose of the irradiation or magnetic treatment. Therefore, both treatments may exert an influence on cocoa beans and, therefore, on the cocoa liquor quality.

Human Salmonellosis: A Continuous Global Threat in the Farm-to-Fork Food Safety Continuum

Salmonella is one of the most common zoonotic foodborne pathogens and a worldwide public health threat. Salmonella enterica is the most pathogenic among Salmonella species, comprising over 2500 serovars. It causes typhoid fever and gastroenteritis, and the serovars responsible for the later disease are known as non-typhoidal Salmonella (NTS). Salmonella transmission to humans happens along the farm-to-fork continuum via contaminated animal- and plant-derived foods, including poultry, eggs, fish, pork, beef, vegetables, fruits, nuts, and flour. Several virulence factors have been recognized to play a vital role in attaching, invading, and evading the host defense system. These factors include capsule, adhesion proteins, flagella, plasmids, and type III secretion systems that are encoded on the Salmonella pathogenicity islands. The increased global prevalence of NTS serovars in recent years indicates that the control approaches centered on alleviating the food animals' contamination along the food chain have been unsuccessful. Moreover, the emergence of antibiotic-resistant Salmonella variants suggests a potential food safety crisis. This review summarizes the current state of the knowledge on the nomenclature, microbiological features, virulence factors, and the mechanism of antimicrobial resistance of Salmonella. Furthermore, it provides insights into the pathogenesis and epidemiology of Salmonella infections. The recent outbreaks of salmonellosis reported in different clinical settings and geographical regions, including Africa, the Middle East and North Africa, Latin America, Europe, and the USA in the farm-to-fork continuum, are also highlighted.

Effects of Spray Drying, Freeze Drying and Gamma Irradiation on the Antioxidant Activities of Camel and Cow Milk Fractions

This work aimed to establish an integrated approach to investigate the total phenolic content and antioxidant activities of dried skim camel and cow milk and their fractions. The milk fractions were obtained by acid or enzymatic coagulation followed by spray drying (inlet temperature/outlet temperature: 125 ± 2 °C/90 ± 2 °C) or freeze drying (−50 °C, 0.05 mbar) coupled or not to gamma irradiation (at 5, 11, 22 kGy). The results showed that the total phenolic content (measured in gallic acid equivalent, GAE) varied depending on the drying technique. The freeze-drying process corresponded to the highest values of total phenolic compounds, with 247.23 ± 2.08 mg GAE/100 g powder for the β-casein fraction of camel milk (βC CaM) and 621.13 ± 4.16 mg GAE/100 g powder for the β-casein fraction of cow milk (βC CoM). Compared to spray-dried fractions, freeze-dried fractions showed generally higher ferric reducing antioxidant power for both camel milk and cow milk. The highest values of free radical scavenging activity were seen in the spray-dried β-casein fractions of camel milk (βC CaM) and cow milk (βC CoM) and in the freeze-dried acid whey of cow and camel milk (AW CaM and AW CaM). Freeze-dried acid whey (AW CaM and AW CoM) appeared to be less sensitive to gamma irradiation at 5 and 11 kGy.

Effect of 60Co γ-rays on dried figs adsorption isotherms and thermodynamic properties

Irradiation is one of the promising food preservation techniques, but few are known about its impact on foods' water vapor change. In this research, the impact of gamma irradiation on moisture adsorption isotherms of dried figs, one of the most emblematic foods of the Mediterranean diet, at increasing doses (0, 1, 1.5, and 2 kGy) was investigated. The isotherms data of equilibrium points displayed a sigmoid-shaped curve of the type II pattern for both controlled and irradiated dried figs, with a notable effect of irradiation on equilibrium moisture content, which revealed a decreasing pattern as irradiation dose and temperature increase. This effect was also seen in data fitting, where GAB model showed the best prediction statistics for control samples, while Peleg model displayed the most suitable samples irradiated at 1 and 1.5 kGy, then the Enderby model for those treated with 2 kGy. Results of Net isosteric heat of adsorption suggested that high irradiation dose increases the spontaneity of moisture adsorption. Hence, gamma irradiation exhibited a significant effect on the water-specific surface area of which the magnitude was proportional to the increasingly applied doses. This effect was also visibly significant on the optimum water activity [a_w (op)] for proper dried fig storage. Indeed, a_w was about 0.4243 for control samples, which is much higher compared to irradiated ones (a_w = 0.2). Information from this research suggests that gamma irradiation at a dose up to 2 kGy extended the dried figs' shelf life. Since many aspects related to the impact of gamma irradiation on the moisture adsorption isotherms and thermodynamic properties of dried figs as well as in other foods have yet to be further investigated, this study provides interesting results that may be a useful reference for future research direction.

Effect of Various Doses of Electron Beam Irradiation Treatment on the Quality Characteristics of Vacuum-Packed Dry Fermented Sausage during Refrigerated Storage

In this study, we investigated the effect of electron beam irradiation on the physicochemical, microbiological, and sensory attributes of dry fermented sausage during 8 weeks of refrigerated storage at 4°C. The five doses of e-beam irradiation applied were: 0 kGy (control) and 1, 2, 3, and 4 kGy. All the experimental treatments led to a significant decrease in pH values during the storage period of 60 days (P<0.05). The 2-kGy treatment caused a significant (P<0.05) decrease in pH value, bacterial growth (total plate count, Listeria monocytogenes, Salmonella Typhimurium, and Escherichia coli), and thiobarbituric acid-reactive substances values than other irradiated fermented sausage batches during the study. Irradiation did not affect the water activity value of the fermented sausage samples. For color characteristics, 3 kGy exhibited significantly lower (P<0.05) L* (lightness) values than other irradiation treatments. A similar trend of significantly lower (P<0.05) a* (redness) and b* (yellowness) values was observed in all irradiated treatments than in the control. All the treatments showed no significant differences (P>0.05) in scores in sensory attributes (color and sourness); however, fermented sausage irradiated with 3 kGy had the highest sensory characteristics (overall acceptability) at the end of the storage period. In conclusion, 1, 2, and 3 kGy irradiation treatments can be beneficial for inhibiting lipid oxidation, controlling microbial growth, and maintaining sensory attributes of fermented sausage during storage, thereby enhancing their food safety and shelf stability.

The Effects of Thermal Pasteurisation, Freeze-Drying, and Gamma-Irradiation on the Antibacterial Properties of Donor Human Milk

The most common pasteurisation method used by human milk banks is Holder pasteurisation. This involves thermal processing, which can denature important proteins and can potentially reduce the natural antimicrobial properties found in human milk. This study assesses the application of a hybrid method comprised of freeze-drying followed by low-dose gamma-irradiation for nonthermal donor human milk pasteurisation. Freeze-drying donor human milk followed by gamma-irradiation at 2 kGy was as efficient as Holder pasteurisation in the reduction of bacterial inoculants of Staphylococcus aureus (10⁶ cfu/mL) and Salmonella typhimurium (10⁶ cfu/mL) in growth inhibition assays. These assays also demonstrated that human milk naturally inhibits the growth of bacterial inoculants S. aureus, S. typhimurium, and Escherichia coli. Freeze drying (without gamma-irradiation) did not significantly reduce this natural growth inhibition. By contrast, Holder pasteurisation significantly reduced the milk’s natural antimicrobial effect on S. aureus growth after 6 h (−19.8% p = 0.01). Freeze-dried and then gamma-irradiated donor human milk showed a strong antimicrobial effect across a dose range of 2–50 kGy, with only a minimal growth of S. aureus observed after 6 h incubation. Thus, a hybrid method of freeze-drying followed by 2 kGy of gamma-irradiation preserves antimicrobial properties and enables bulk pasteurisation within sealed packaging of powderised donor human milk. This work forwards a goal of increasing shelf life and simplifying storage and transportation, while also preserving functionality and antimicrobial properties.

Cobalt-60 and electron beam irradiation-induced lipid oxidation in largemouth bass (Micropterus salmoides)

BACKGROUND

Irradiation can cause lipid oxidation of fish. This study aimed to examine the effect of radiation (method, dose and dose rate) on the acid value (AV), peroxide value (PV), thiobarbituric acid reactive substances (TBARS) content and fatty acid profile of fresh and freeze-dried largemouth bass flesh.

RESULTS

AV, PV and TBARS presented a dose-dependent increase in fish meat for both cobalt-60 (⁶⁰ Co) and electron beam (EB) irradiation. With a 6 kGy dose of radiation, all measured indices in the ⁶⁰ Co group were significantly higher than those in the EB group (P < 0.05 or P < 0.01). With a 3 kGy dose of radiation, AV, PV and TBARS in the 200 Gy min^-1 dose rate group were significantly lower than those in the 2 and 80 Gy min^-1 groups (P < 0.05). After ⁶⁰ Co irradiation, AV, PV and TBARS in most fresh samples were significantly higher than those in freeze-dried samples (P < 0.01). And ⁶⁰ Co irradiation decreased the unsaturated fatty acid (UFA) content in fresh samples and increased the UFA content in freeze-dried samples. Our study indicated that ⁶⁰ Co irradiation, particularly at a low dose rate, accelerated lipid oxidation in fish meat. A large amount of muscle moisture enhances the amount of UFA loss in fish meat during ⁶⁰ Co irradiation.

CONCLUSIONS

A low dose (3 kGy) of EB irradiation, a high dose rate (200 Gy min^-1 ) of ⁶⁰ Co irradiation or freeze-drying treatment can alleviate the lipid oxidation of largemouth bass meat. © 2020 Society of Chemical Industry.

Comparison between irradiating and autoclaving citrus wastes as substrate for solid-state fermentation by Aspergillus aculeatus

Agricultural or food processing wastes cause serious environmental burden and economic losses. Solid-state fermentation using these wastes is an attractive option to valorize these wastes. However, conventional autoclaving of substrate may degrade nutrients and generate toxins. Unsterilization of the substrate will cause undesired microbial contamination. Therefore, we compared irradiation with autoclaving to treat citrus wastes as substrate for solid-state fermentation by Aspergillus aculeatus. By comparing microbial growth, enzymes tested and medium consumption, irradiated substrate had higher biomass and extracellular protein, more sugar consumption and higher enzyme production than those with autoclaved substrate. Irradiation prevented the generation of cell-inhibiting components such as 5-hydroxymethylfurfural (5-HMF) whereas preserved the flavonoids well that are often enzyme inducers. These findings suggest that irradiation of agricultural and food processing wastes as substrate has advantages over autoclaving for solid-state fermentation. SIGNIFICANCE AND IMPACT OF THE STUDY: This study proposes irradiation as an alternative to sterilize agricultural residues rich in nutrients and thermosensitive compounds, such as citrus wastes for fungal solid-state fermentation and production of enzymes.

Assessment of microbiological contamination in saengshik products from the Korean market and identification of the irradiation status

This study investigated the prevalence of microbiological contamination in commercial Saengshik products (samples SP-1 to SP-12) from the Korean market, and identified their irradiation status. SP-2, SP-8, and SP-12 showed less than 3.66 and 1.10 log colony forming units (CFU)/g in total plate and coliforms counts, respectively, while the remaining samples showed more than 4.70 and 2.35 log CFU/g, respectively. Four samples were positive on some of foodborne pathogenic bacteria (Clostridium perfringens, Escherichia coli O157:H7, and Bacillus cereus). SP-2, SP-8, and SP-12 contained no pathogenic bacteria and were suspected to have been irradiated. They were confirmed as positive using photostimulated luminescence (PSL) analysis. PSL positive results on samples SP-2, SP-8 and SP-12 were finally confirmed by the authentic thermoluminescence (TL) analysis on the basis of TL glow curve shape, intensity, temperature range of TL peak maxima and TL ratio (TL₁/TL₂).

Integrated effect of radiation processing and modified atmosphere packaging (MAP) on shelf life of fresh fig

Fresh figs have less shelf life due to the growth of yeasts and molds. The study aimed at extending the shelf life of fresh fig with the help of irradiation and modified atmosphere packaging (MAP). Effects of irradiation and MAP on the quality and shelf life of fresh fig were evaluated. Combined effect of irradiation and MAP on the quality of fresh fig was also studied. To optimize irradiation dose, 1, 2, 3 and 4 kGy doses were given to fresh fig. Firmness and overall acceptability of fresh fig were minimally affected by 1 kGy irradiation dose. Whereas, 2, 3 and 4 kGy had negative effects on firmness and overall acceptability score. Thus, 0.5 and 1 kGy were selected to evaluate the combined effect of irradiation and MAP. Fresh figs were packed in an atmosphere of 5% O₂, 10% CO₂, 85% N₂ and irradiated at 0.5 and 1 kGy doses. These atmospheric packed irradiated samples were stored at 5 °C for 15 days. Physico-chemical parameters, microbial quality and overall acceptability were monitored throughout the storage period at the interval of 5 days. Irradiation treatment did not prevent the firmness of fresh fig. Significant dissimilarities were observed between the irradiated and control fresh fig for all the parameters considered. The results indicated that MAP followed by irradiation doses of 0.5 and 1 kGy showed the best results for improving the quality and shelf-life of fresh fig.

Trends in microbial control techniques for poultry products

Fresh poultry meat and poultry products are highly perishable foods and high potential sources of human infection due to the presence of several foodborne pathogens. Focusing on the microbial control of poultry products, the food industry generally implements numerous preventive measures based on the Hazard Analysis and Critical Control Points (HACCP) food safety management system certification together with technological steps, such as refrigeration coupled to modified atmosphere packaging that are able to control identified potential microbial hazards during food processing. However, in recent years, to meet the demand of consumers for minimally processed, high-quality, and additive-free foods, technologies are emerging associated with nonthermal microbial inactivation, such as high hydrostatic pressure, irradiation, and natural alternatives, such as biopreservation or the incorporation of natural preservatives in packaging materials. These technologies are discussed throughout this article, emphasizing their pros and cons regarding the control of poultry microbiota and their effects on poultry sensory properties. The discussion for each of the preservation techniques mentioned will be provided with as much detail as the data and studies provided in the literature for poultry meat and products allow. These new approaches, on their own, have proved to be effective against a wide range of microorganisms in poultry meat. However, since some of these emergent technologies still do not have full consumer's acceptability and, taking into consideration the hurdle technology concept for poultry processing, it is suggested that they will be used as combined treatments or, more frequently, in combination with modified atmosphere packaging.

Molecular DNA-based detection of ionising radiation in meat

BACKGROUND

Ionising radiation induces molecular alterations, such as formation of ions, free radicals, and new stable molecules, and cleavage of the chemical bonds of the molecules present in food. Irradiation-treated meat should be labelled to control the process and to ensure free consumer choice. Therefore, sensitive analytical methods are required to detect the irradiation dose.

RESULTS

Meat samples were exposed to radiation doses of 0, 0.272, 0.497, 1.063, 3.64, 8.82 and 17.42 kGy in an industrial ⁶⁰ Co gamma cell. Primers were designed to amplify 998, 498 and 250-base pair (bp) regions of the 18S rRNA gene of nuclear DNA from the irradiated samples. A new DNA-based method was developed to quantify the radiation exposed to the unstored meat and the meat stored at -20 °C for 3 and 6 months. The method was able to detect meat samples stored and unstored with dose limits of 1.063 and 3.64 kGy, respectively.

CONCLUSION

The level of irradiation can be detected using primer pairs that target particularly different-sized sequences for DNA amplification by PCR. This method can be widely used for the analysis of not only meat samples, but also all biological materials containing DNA. © 2016 Society of Chemical Industry.

Tracking Human Adenovirus Inactivation by Gamma Radiation under Different Environmental Conditions

Adenovirus is the most prevalent enteric virus in waters worldwide due to its environmental stability, which leads to public health concerns. Mitigation strategies are therefore required. The aim of this study was to assess the inactivation of human adenovirus type 5 (HAdV-5) by gamma radiation in aqueous environments. Various substrates with different organic loads, including domestic wastewater, were inoculated with HAdV-5 either individually or in a viral pool (with murine norovirus type 1 [MNV-1]) and were irradiated in a Cobalt-60 irradiator at several gamma radiation doses (0.9 to 10.8 kGy). The infectivity of viral particles, before and after irradiation, was tested by plaque assay using A549 cells. D10 values (dose required to inactivate 90% of a population or the dose of irradiation needed to produce a 1 log10 reduction in the population) were estimated for each substrate based on virus infectivity inactivation exponential kinetics. The capability of two detection methods, nested PCR and enzyme-linked immunosorbent assay (ELISA), to track inactivated viral particles was also assessed. After irradiation at 3.5 kGy, a reduction of the HAdV-5 titer of 4 log PFU/ml on substrates with lower organic loads was obtained, but in highly organic matrixes, the virus titer reduction was only 1 log PFU/ml. The D10 values of HAdV-5 in high organic substrates were significantly higher than in water suspensions. The obtained results point out some discrepancies between nested PCR, ELISA, and plaque assay on the assessments of HAdV-5 inactivation. These results suggest that the inactivation of HAdV-5 by gamma radiation, in aqueous environments, is significantly affected by substrate composition. This study highlights the virucidal potential of gamma radiation that may be used as a disinfection treatment for sustainable water supplies.

IMPORTANCE

Human adenovirus (HAdV) is the most prevalent of the enteric viruses in environmental waters worldwide. The purposes of this study are to provide new insights on the inactivation of enteric virus by gamma irradiation and to introduce new concepts and reinforce the benefits and utility of radiation technologies as disinfection processes. This may be an effective tool to guarantee the reduction of viral pathogens and to contribute to public health and sustainable water supplies.

A new measurement approach of ionizing radiation in irradiated trout (Oncorhynchus mykiss) by Randomly Polymorphic DNA-Polymerase Chain Reaction

Trout (Oncorhynchus mykiss) were irradiated at doses of 0.250, 0.500, 1, 3, 5, 7 and 9 kGy in gamma cell. DNAs were extracted from the irradiated samples before and after storage. 1ERP primers were designed, and RAPD-PCR (Randomly Polymorphic DNA-Polymerase Chain Reaction) was applied to make randomly amplifications on the DNA of the irradiated samples. Agarose gel profiles of irradiated fish were obtained to determine change of band profiles. In addition, DNA fragmentation occurring in each dose was determined by comet assay for the verification of methodology developed in this study. The molecular methodology was developed to estimate ionizing radiation (IR) level in irradiated fish. This methodology allows the analysis of the trout irradiated up to the dose limit of around 0.5 kGy and stored for a period of three months.

Determination of irradiation dose and distinguishing between irradiated and non irradiated fish meat by real-time PCR

In this study, the effects of gamma irradiation on the DNA of fish (Oncorhynchus mykiss) by real-time PCR were studied. Fish (O. mykiss) were exposed to radiation doses of 0.250, 0.500, 1, 3, 5, 7, and 9 kGy in a gamma cell. Primers were designed for regions with different lengths of both nuclear and mitochondrial DNA, and each primer was used to amplify the DNA from irradiated samples. The amplicon curves for mitochondrial and nuclear DNA, and the correlations among the curves, were obtained. The Ct values for a 519 bp region of the 18S RNA gene on nuclear DNA correlated appropriately. Radiation doses applied to the fillets were estimated using the standard curve data obtained from the correlation values, and the DNA damage caused by each dose was calculated. As a consequence, a molecular methodology to analyze irradiated fish meat qualitatively and also for the estimation of administered dose was developed. This method allowed analysis of irradiated fish, which had been stored for up to 3 months with a dose limit of approximately 0.5 kGy.

Inactivation of internalized Salmonella Typhimurium in lettuce and green onion using ultraviolet C irradiation and chemical sanitizers

AIMS

The internalized human pathogens in fresh produce are not effectively removed during conventional washing, and therefore, it may cause foodborne illness when the produce is consumed raw. Thus, effective nonthermal processes are needed to prevent this risk.

METHODS AND RESULTS

Green fluorescence protein-tagged Salmonella Typhimurium was either sprayed on the surface of iceberg lettuce or injected into the bottom part (bulb) of green onions to induce bacterial internalization. The contaminated vegetables were collected after 2 days and subjected to surface disinfection. Different fluencies of UV-C radiation (75-900 mJ cm(-2)) and two fluencies of UV-C (450, 900 mJ cm(-2)) combined with chlorine and peracetic acid (PAA) were applied to the produce to examine the inactivation efficiency of internalized bacteria. A range of 1·96-2·52 log reduction in the internalized Salmonella was achieved when the lettuce was treated with higher UV-C fluency (150, 450, 900 mJ cm(-2)) or UV-C combined with chemical disinfectants. Significant reduction (1·00-1·49 log CFU g(-1)) in internalized Salmonella was observed in green onion treated with UV-C with the fluency of 150 or 900 mJ cm(-2) or UV-C-chlorine/PAA. No significant reduction was observed in either lettuce or green onion treatments when chlorine or PAA was used alone. The food quality measured with firmness was not changed during any treatments. However, a slight colour change was observed in lettuce only when UV-C was used at 900 mJ cm(-2).

CONCLUSION

High fluency UV-C can significantly inactivate the internalized Salmonella in lettuce and green onion while maintaining the food quality.

SIGNIFICANCE AND IMPACT OF THE STUDY

This research provides applicable research outcomes for developing nonthermal methods to inactivate internalized pathogens in fresh produce.

Analysis of organic acids in electron beam irradiated chestnuts (Castanea sativa Mill.): Effects of radiation dose and storage time

Since 2010, methyl bromide, a widely used fumigant was banned from the European Union under the Montreal Protocol guidelines, due to its deleterious effects on health and risk to the environment. Since then, many alternatives for chestnut conservation have been studied (hot water dip treatment being the most common), among them, electron beam irradiation has been proposed as being a safe, clean and cheap alternative. Herein, the effects of this radiation at different doses up to 6kGy and over storage up to 60days in the amounts and profile of nutritionally important organic acids were evaluated. Chestnuts contained important organic acids with quinic and citric acids as main compounds. Storage time, which is traditionally well accepted by consumers, caused a slight decrease on quinic (13-9mg/g), ascorbic (1.2-0.8mg/g), malic (5-4mg/g), fumaric (0.4-0.3mg/g) and total organic (33-26mg/g) acids content. Otherwise, irradiation dose did not cause appreciable changes, either individually or in total (28-27mg/g) organic acid contents. Electron beam irradiation might constitute a valuable alternative for chestnut conservation.

Effects of gamma irradiation on the viability and phenotypic characteristics of Salmonella Enteritidis inoculated into specific-pathogen-free eggs

The goal of this study was to determine the effects of various levels of gamma irradiation on the phenotypic characteristics of 20 strains of Salmonella Enteritidis inoculated separately into specific-pathogen-free shell eggs. Bacterial strains were inoculated into egg yolks and exposed to (60)Co radiation at doses of 0.49 to 5.0 kGy. The eggs were maintained at 25°C and analyzed for the presence of Salmonella on days 1, 2, 4, and 7, and the recovered Salmonella isolates were characterized biochemically. All strains were resistant to doses of 0.49, 0.54, 0.59, 0.8, and 1 kGy; colony counts were ≥10(5) CFU/ml of egg yolk except for one strain, which was detected at 96 h and at 7 days after irradiation at 1 kGy, with a population reduction of 2 log CFU/ml. For the other evaluated doses, 12 strains (60.0%) were resistant at 1.5 kGy and 7 strains (35.0%) were resistant at 3.0 kGy. Among all analyzed strains, 5.0 kGy was more effective for reducing and/or eliminating the inoculated bacteria; only two (10%) strains were resistant to this level of irradiation. Salmonella colony counts were significantly reduced (P < 0.01) with increasing doses from the day 1 to 7 of observation, when microbial growth peaked. Loss of mobility, lactose fermentation, citrate utilization, and hydrogen sulfide production occurred in some strains after irradiation independent of dose and postirradiation storage time. Increases in antibiotic susceptibility also occurred: seven strains became sensitive to β-lactams, two strains became sensitive to antifolates, and one strain each became sensitive to fluoroquinolone, phenicol, nitrofurans, tetracyclines, and aminoglycosides. The results indicate that up to 5.0 kGy of radiation applied to shell eggs inoculated with Salmonella Enteritidis at 4 log CFU per egg is not sufficient for complete elimination of this pathogen from this food matrix.