Frozen Ground Beef Research Articles

Experiments and simulations demonstrating the rapid ultrasonic rewarming of frozen tissue cryovials

The development of methods to safely rewarm large cryopreserved biological samples remains a barrier to the widespread adoption of cryopreservation. Here, experiments and simulations were performed to demonstrate that ultrasound can increase rewarming rates relative to thermal conduction alone. An ultrasonic rewarming setup based on a custom 444 kHz tubular piezoelectric transducer was designed, characterized, and tested with 2 ml cryovials filled with frozen ground beef. Rewarming rates were characterized in the -20 °C to 5 °C range. Thermal conduction-based rewarming was compared to thermal conduction plus ultrasonic rewarming, demonstrating a tenfold increase in rewarming rate when ultrasound was applied. The maximum recorded rewarming rate with ultrasound was 57° C/min, approximately 2.5 times faster than with thermal conduction alone. Coupled acoustic and thermal simulations were developed and showed good agreement with the heating rates demonstrated experimentally and were also used to demonstrate spatial heating distributions with small (<3° C) temperature differentials throughout the sample when the sample was below 0° C. The experiments and simulations demonstrate the potential for ultrasonic cryovial rewarming with a possible application to large volume rewarming, as faster rewarming rates may improve the viability of cryopreserved tissues and reduce the time needed for cells to regain normal function.

Prevalence and risk factors of potential pathogenicYersinia enterocoliticain Tunisian frozen ground beef through a shelf‐life monitoring protocol validation

This study aims to identify and determine the prevalence of Yersinia enterocolitica in ground beef meat during conservation process. In all, 180 sample-units of ground beef from three red meat processing companies were subjected to microbial analysis. The identification and prevalence rate of Y. enterocolitica in ground beef were performed using conventional culture methods and molecular identification based on the analysis of rpoB gene. The analytical method allowed the detection of 25 (14%) positive units and the identification of 15 Y. enterocolitica strains. Biogrouping classification allowed the assignment of all the isolates to the biotype 1A. However, the assessment of phenotypic virulence markers revealed that 9 out of 15 strains were presumptively virulent. The results revealed, for the first time, the evidence of Y. enterocolitica viability within Tunisian frozen beef meat and the need to consider the investigation of this bacterium within the analytical standards of meat products and their safety evaluation. Furthermore, the rpoB gene-based method is a rapid and sensitive technique to identify Y. enterocolitica strains in meat products. Novelty impact statement This work constitutes a first report of the prevalence of Yersinia enterocolitica in Tunisian frozen ground beef during conservation. The highest frequency number of positive samples was recorded at the end of the microbiological lifetime during the conservation meat process. In view of the detection of virulent markers among Y. enterocolitica 1A biogroup isolates, pathogenicity of this bacterial group should be investigated.

Oxidative stability in raw, cooked, and frozen ground beef using Epazote (Chenopodium ambrosioides L.)

This study investigated the potential of aqueous epazote (AE) and ethanolic extract of epazote (ETHE) as inhibitors of lipid oxidation in raw and cooked ground beef stored at 4 °C for 9 days as well as frozen beef patties stored at −18 °C for 90 days. Organic acids were identified in AE and ETHE using ultra-high-performance liquid chromatography-quadrupole time-of-flight (UHPLC-qTOF). Chemical composition, TBARS, pH, colour, sensory acceptability and intensity of oxidised flavour were analysed in the three different meat products. ETHE showed higher values in organic acid content than AE. In raw ground beef, ETHE inhibited lipid oxidation and received the highest score in the three sensorial attributes evaluated at the end of the storage period, whereas in cooked ground beef it showed the highest intensity of oxidised flavour. Regarding CTL, AE reduced lipid oxidation in the cooked ground beef as well as the frozen patties, with improved colour. Therefore, epazote may be a promising natural antioxidant source for use in meat.

CompactDry "Nissui" ETC for Enumeration of Enterococci in a Variety of Foods: AOAC Performance Tested MethodSM 111902.

The CompactDry "Nissui" ETC is a ready-to-use dry media sheet using a chromogenic medium with selective agents for the detection and enumeration of Enterococcus spp. After a 20-24 h incubation at 37 ± 1°C, Enterococcus colonies appear blue. The performance of the CompactDry "Nissui" ETC was compared to that of the Nordic Committee on Food Analysis (NMKL) reference method 68, Enterococcus, Determination in Foods and Feeds, for 10 matrixes including cream, custard, lettuce, parsley, pasta salad, frozen ground beef patties, fresh cooked prawns, sandwiches, raw beef, and tuna pate. Performance indicators included repeatability, difference of means (DOM), robustness and inclusivity/exclusivity. For all 30 materials (10 matrixes each inoculated at three levels), the relative standard deviation of repeatability (RSDr) was <10% for both methods. Most materials yielded RSDr <5%, with five materials between 5 and 10% for the CompactDry "Nissui" ETC method and ten materials between 5 and 10% for the NMKL 68 method. The DOM ranged from -0.240 (95% CI-0.363, -0.118) to 0.228 (95% CI 0.041, 0.415) log10 CFU/g, well within the -0.5 to 0.5 log10 CFU/g range generally accepted as microbiologically insignificant. Both the reference method and this method have limitations of the species detected. The CompactDry "Nissui" ETC was validated for the enumeration of Enterococcus species in cream, custard, lettuce, parsley, pasta salad, frozen ground beef patties, fresh cooked prawns, sandwiches, raw beef, and tuna pate.

Inactivation of Escherichia coli O157 and Salmonella Enteritidis in raw beef liver by gamma irradiation

Irradiation of ground beef and beef liver inoculated with Escherichia coli O157 466 and DT66 and Salmonella Enteritidis 3313 were performed with gamma rays from cobalt-60 at refrigerated and frozen temperatures under air- and vacuum-packaged conditions. Results showed that D10 values for all pathogens in frozen beef liver were higher than those in frozen ground beef samples, with significant differences observed between the D10 values of E. coli O157 466 and S. Enteritidis 3313 under air-packaged conditions, as well as in E. coli O157 DT66 and S. Enteritidis 3313 under vacuum-packaged conditions. To verify effective bacterial inactivation under high bacterial-contamination levels (105–107 CFU/g), survival/death interfaces of E. coli O157 DT66 and S. Enteritidis 3313 inoculated in beef liver under vacuum-packaged and frozen conditions were constructed, with results suggesting that doses from 5.3 kGy to 5.5 kGy and 8.2 kGy–8.5 kGy would be sufficient to kill 105 CFU/g of E. coli O157 and S. Enteritidis 3313, respectively, at a 95%–99% predicted confidence interval. These results suggested that food matrixes containing high amounts of antioxidants (such as beef liver) and treated under frozen and vacuum-packaged conditions require additional consideration and evaluation for applications of irradiation treatment.

THE MICROBIOLOGICAL STUDY OF MINCED MEAT IN SOME MARKETS IN ALEXANDRIA WITH REFERENCE TO ESCHERICHIA COLI O157 H: 7

This cross sectional study was carried out during a four months period from December, 2012 to March, 2013. A total of 140 fresh and frozen ground beef samples were purchased from local butchers and supermarkets in Alexandria. Each of the ground beef sample was analyzed for its microbiological quality (Aerobic plate count, total coliform count and E. coli count) as well as for the presence of E. coli O157:H7. Out of the 140 studied ground meat samples, 75(53.6%) proved to be unsatisfactory according to the three tested parameters. None out of 140 examined ground meat samples showed E. coli O157:H7.

Availability of Foods and Beverages in Supplemental Nutrition Assistance Program−Authorized Dollar Stores in a Region of North Carolina

BackgroundThere are >25,000 Supplemental Nutrition Assistance Program (SNAP)−authorized dollar stores throughout the United States; many are located in lower-income neighborhoods and provide an accessible food and beverage source for area residents. ObjectiveThe purpose of this research was to determine the percent of food deserts within 16 counties in North Carolina that include a SNAP dollar store; examine the types of foods and beverages at SNAP dollar stores in these counties; test whether the foods and beverages offered vary by SNAP dollar store chain; and test whether the foods and beverages available differ by rural and urban location. DesignThis cross-sectional study used a combination of publicly available data and primary data to investigate the research questions. Secondary data sources were obtained from the US Department of Agriculture’s SNAP retailer locator, the US Census, and the US Department of Agriculture’s Food Access Research Atlas. Availability of foods and beverages was assessed among a sample of 90 SNAP dollar stores in 16 counties in southern and western sections of North Carolina. Data were collected in June 2014. ResultsAbout half (52%) of the food deserts in the research area included a SNAP dollar store. Most of the sampled stores sold healthier food staples, such as frozen meats, brown rice, 100% whole-wheat bread, and dried beans. None of the stores sold fresh fruits or vegetables. Some of the foods and beverages offered (eg, frozen fruit, frozen unseasoned vegetables, nonfat or low-fat milk, frozen ground beef) varied by SNAP dollar store chain. The foods and beverages offered did not differ by rural or urban county location. ConclusionsSNAP dollar stores offer a number of healthy food staples; however, they do not sell fresh fruits or vegetables. Further food environment research should include dollar stores.

Quantitative and Qualitative Studies on Enterobacteriaceae in Ground Beef

120 packages of ground beef (40 each of fresh, frozen and frozen with Soya bean) were examined for the incidence of Enterobacteriaceae, Salmonella and E. coli. The incidence of Enterobacteriaceae was 100%, 75% and 87% in fresh, frozen and frozen with Soya ground beef respectively; and the mean counts were 6.3x104cfu/g, 1.4x102cfu/g and 1.6x103cfu/g respectively. E. coli, Klebsiella oxytoca, Serratia marcescens and Serratia liquefaiens could be isolated from fresh ground beef; Proteus vulgaries, E. coli and Enterobacter sakazakii was isolated from frozen ground beef, while in case of frozen ground beefwith Soya bean Klebsiella oxytoca, Proteus vulgaries, Citrobacter freundii, E. coli and Pantoea a gglomerans was isolated. The incidence of E. coli was 60%, 35%, 48% in fresh, frozen and frozen ground beef with Soya bean respectively. The incidence of Salmonellawas 0%, 10%, 15% in fresh, frozen and frozen ground beef with Soya bean respectively. E. coli strains were serologically identified into 20 O-typable strains and 37 O- untypable strains. The 20 O-typable strains were identified as O86, O119, O158 ,O145 and O115 .

Comparison of Baseline Bacterial Levels in Retail Ground Beef Originating from Different Regulatory, Processing, and Packaging Environments

The objectives of this study were to collect baseline measures of bacteria present in retail ground beef offered for sale in Saskatchewan and to assess differences associated with the licensing or regulatory environment of the packaging and processing facilities as indicated by package labeling. Packages of ground beef (n = 309) were purchased from May 2011 to May 2012. Retail samples were categorized as originating from facilities regulated by the federal government or licensed by the provincial government (n = 126), originating from facilities licensed by local health regions (n = 80), or having no inspection or source information on the package label (n = 103). Total aerobic plate counts and total Escherichia coli plate counts were determined using 3M Petrifilm methods. Total bacterial load was estimated using real-time quantitative PCR. The data were analyzed on a log scale using multivariable linear regression, accounting for season and whether the samples were fresh or frozen at purchase. Total aerobic plate counts and Escherichia coli plate counts were lower in samples from federally regulated or provincially licensed facilities than in samples from locally licensed facilities (P < 0.001 and P = 0.002, respectively) or in samples with no inspection information on the label (P < 0.001 and P = 0.011, respectively). Frozen ground beef from federally regulated or provincially licensed facilities had the lowest total bacterial load. Samples clearly labeled as packaged at federally regulated or provincially licensed facilities consistently had the lowest estimated bacterial levels.

Effects of ionizing irradiation and hydrostatic pressure on Escherichia coli O157:H7 inactivation, chemical composition, and sensory acceptability of ground beef patties

A randomized complete block design with three replications was utilized to determine the effects of ionizing irradiation and hydrostatic pressure on the inactivation of Escherichia coli O157:H7, volatile composition, and consumer acceptability ( n = 155) of frozen ground beef patties. E-beam and X-ray irradiation (2 kGy) inactivated E. coli O157:H7 below the limit of detection, while hydrostatic pressure treatment (300 mPa for 5 min at 4 °C) did not inactivate this pathogen. Solid-phase microextraction (SPME) was used to extract volatile compounds from treated ground beef patties. Irradiation and hydrostatic pressure altered the volatile composition ( P < 0.05) of the ground beef patties in respect to radiolytic products. However, results were inconclusive on whether these differences were great enough to use this method to differentiate between irradiated and non-irradiated samples in a commercial setting. Irradiation did not affect ( P > 0.05) consumer acceptability of ground beef patties when compared to untreated samples, but hydrostatic pressure caused decreased acceptability ( P < 0.05) when compared to other treatments.

Quantitative risk assessment for Escherichia coli O157:H7 in frozen ground beef patties consumed by young children in French households

A quantitative risk assessment for Escherichia coli O157:H7 in frozen ground beef patties consumed by children under 10 years of age in French households was conducted by a national study group describing an outbreak which occurred in France in 2005. Our exposure assessment model incorporates results from French surveys on consumption frequency of ground beef patties, serving size and consumption preference, microbial destruction experiments and microbial counts on patties sampled from the industrial batch which were responsible for the outbreak. Two different exposure models were proposed, respectively for children under the age of 5 and for children between 5 and 10 years. For each of these two age groups, a single-hit dose-response model was proposed to describe the probability of hemolytic and uremic syndrome (HUS) as a function of the ingested dose. For each group, the single parameter of this model was estimated by Bayesian inference, using the results of the exposure assessment and the epidemiological data collected during the outbreak. Results show that children under 5 years of age are roughly 5 times more susceptible to the pathogen than children over 5 years. Exposure and dose-response models were used in a scenario analysis in order to validate the use of the model and to propose appropriate guidelines in order to prevent new outbreaks. The impact of the cooking preference was evaluated, showing that only a well-done cooking notably reduces the HUS risk, without annulling it. For each age group, a relation between the mean individual HUS risk per serving and the contamination level in a ground beef batch was proposed, as a tool to help French risk managers.

Growth of Salmonella Serovars, Escherichia coli O157:H7, and Staphylococcus aureus during Thawing of Whole Chicken and Retail Ground Beef Portions at 22 and 30°C

Food regulatory agencies advise against thawing frozen meat and poultry at room temperature. In this study, whole chickens (1,670 g) and ground beef (453 and 1,359 g) were inoculated with Salmonella serovars, Escherichia coli O157:H7, and Staphylococcus aureus on the surface (all products) and in the center (ground beef). After freezing at −20°C for 24 h, products were thawed at 22 or 30°C for 9 h. Pathogen growth was predicted using product time and temperature data and growth values from the U.S. Department of Agriculture Agricultural Research Service Pathogen Modeling Program 7.0 predictive models of pathogen growth. No pathogen growth was predicted for whole chicken or 1,359 g of ground beef thawed at 30°C or 453 g of ground beef thawed at 22°C. Growth (≤5 generations) was predicted for 453 g of ground beef at 30°C. Inoculation study data corroborated the predictions. No growth occurred on whole chickens or 1,359-g portions of ground beef thawed at 30°C for 9 h. Pathogen numbers increased an average of 0.2 to 0.5 log on the surface of 453-g ground beef portions thawed for 9 h at 22 or 30°C. Our results suggest that thawing ≥1,670 g of whole chicken at ≤30°C for ≤9 h and thawing >453 g ground beef portions at ≤22°C for ≤9 h are not particularly hazardous practices. Thawing smaller portions at higher temperatures and/or for longer times cannot be recommended, however. Use of values derived from the Pathogen Modeling Program 7.0 model provided realistic predictions of pathogen growth during thawing of frozen ground beef and chicken.

Consumers Evaluate Frozen and Grilled Ground Beef and Turkey Product

Consumers are familiar with evaluating the acceptability of fresh and cooked ground beef in grocery stores and restaurants. Consumer acceptability of either fresh or frozen ground beef or ground beef blended with ground turkey has, however, received little attention. The acceptability of the blended beef turkey product is assumed to be relatively high given its origin from the traditional ground meats. Several different combinations of ground beef and ground turkey were evaluated for sensory color/texture differences in frozen and grilled forms by a 115-member consumer taste panel. Their evaluations of both frozen and grilled samples were influenced by previous experience with the combined product in the home and willingness to purchase the new product prior to evaluation of actual samples.

Influence of Freezing and Freezing Plus Acidic Calcium Sulfate and Lactic Acid Addition on Thermal Inactivation of Escherichia coli O157:H7 in Ground Beef

Undercooked ground beef is a leading vehicle for acquiring Escherichia coli O157:H7 infections through consumption of foods. Studies have been performed to determine the effect of freezing and the combined effect of freezing and addition of a mixture of 20% acidic calcium sulfate (final concentration of 0.4% in ground beef) and 10% lactic acid (final concentration of 0.2% in ground beef) (ACS-LA) on the thermal sensitivity of E. coli O157:H7 in ground beef. Five strains of E. coli O157: H7 were separately inoculated into ground beef and held at 5°C for up to 10 days or −20°C for up to 3 weeks then heated at 57, 60, 62.8, 64.3, and 68.3°C to determine rates of thermal inactivation. Results revealed that D-values (decimal reduction times) at equivalent temperatures for four of five E. coli O157:H7 strains were less in the previously frozen than in the refrigerated ground beef and that strains isolated from ground beef in 1993 and 1994 were generally more sensitive to thermal inactivation than those isolated in 1999 and 2000. Only one strain of E. coli O157:H7 was used to determine the effect of ACS-LA in previously frozen or refrigerated ground beef on rates of thermal inactivation. The addition of ACS-LA to ground beef at 20 ml/kg increased the thermal sensitivity of E. coli O157:H7 in both previously frozen and refrigerated ground beef, with greatest rates of inactivation occurring in previously frozen ground beef containing ACS-LA. D-values at 57°C obtained for E. coli O157:H7 in previously refrigerated and frozen ground beef containing ACS-LA and ACS-LA diluted by half were significantly (P < 0.05) less than those obtained in ground beef with no ACS-LA added. D-values at 60 and 62.8°C were consistently less in ACS-LA treated ground beef, but for most treatments the results were not significantly (P > 0.05) different than the controls. Results revealed that the addition of ACS-LA to ground beef, whether frozen or refrigerated, can reduce the temperature or time required to kill E. coli O157:H7 during heating.

Rapid detection of irradiated frozen hamburgers

DNA comet assay can be employed as a rapid and inexpensive screening test to check whether frozen ground beef patties (hamburgers) have been irradiated as a means to increase their safety by eliminating pathogenic bacteria, e.g. E. coli O157:H7. Such a detection procedure will provide an additional check on compliance with existing regulations, e.g. enforcement of labelling and rules in international trade. Frozen ready prepared hamburgers from the market place were ‘electron irradiated’ with doses of 0, 1.3, 2.7, 4.5 and 7.2 kGy covering the range of potential commercial irradiation. DNA fragmentation in the hamburgers was made visible within a few hours using the comet assay, and non-irradiated hamburgers could be easily discerned from the irradiated ones. Even after 9 months of frozen storage, irradiated hamburgers could be identified. Since DNA fragmentation may also occur with other food processes (e.g. temperature abuse), positive screening tests shall be confirmed using a validated method to specifically prove an irradiation treatment, e.g. EN 1784 or EN 1785.

Recovery of heat-stressed E. coli O157:H7 from ground beef and survival of E. coli O157:H7 in refrigerated and frozen ground beef and in fermented sausage kept at 7°C and 22°C

A study was undertaken to obtain information on survival of Escherichia coli O157:H7 in ground beef subjected to heat treatment, refrigeration and freezing and on survival of E. coli O157:H7 in fermented sausage kept at 7°C and 22°C. For the challenge test, a mixture of E. coli O157:H7 strains (EH 321, EH 385, EH 302) was used and enumeration was performed on an isolation medium suitable for recovery of stressed organisms: modified Levine's eosin methylene blue agar (mEMB). Heat resistance of E. coli O157:H7 decreased after pre-incubation at a reduced temperature.Escherichia coli O157:H7 was more susceptible to heat inactivation after storage at 7°C and die-off was even more enhanced if cultures were frozen prior to heat inactivation. The enhanced reduction of the pathogen at 56°C after prior storage under refrigeration was confirmed in a test with inoculated ground beef.Escherichia coli O157:H7 was able to survive in ground beef at 7°C for 11 days and at −18°C for 35 days showing maximal one log reduction during the storage period. Thus, ground beef contaminated with E. coli O157:H7 will remain a hazard even if the ground beef is held at low or freezing temperatures. At both 7°C and 22°C, a gradual reduction of E. coli O157:H7 was noticed in fermented sausage over the 35 days storage period resulting in a 2 log decrease of the high inoculum (106cfu 25 g−1). For the low inoculum (103cfu 25 g−1) a 2·5 log reduction was obtained in 7 and 28 days storage at respectively 22 and 7°C. Application of good hygienic practices and implementation of HACCP in the beef industry are important tools in the control of E. coli O157:H7.

Attempts to Isolate Helicobacter from Cattle and Survival of Helicobacter pylori in Beef Products

This study focused on important factors related to the potential of cattle and beef products to transmit Helicobacter pylori to humans. Mucosal samples were collected from the rumen and abomasum of 105 cattle and were plated on a selective medium to isolate Helicobacter spp.; none of the samples examined contained these bacteria. Studies were also conducted to determine how long H. pylori survives in refrigerated or frozen ground beef; results indicated that the microorganism dies rapidly in ground beef, whether refrigerated or frozen. Packaging in vacuum or air had little effect on survival of the organism. The number of H. pylori decreased in refrigerated samples from 3.3 log10 CFU/g on day 0 to 1.4 log10 CFU/g on day 6. H. pylori died even more rapidly when frozen, decreasing from 3.3 log10 CFU/g on day 0 to 0.5 log10 CFU/g on day 6. Retail beef cuts (n = 20) were also examined for the presence of H. pylori by direct plating on a selective medium and by incubation in an enriched broth followed by plating on a selective medium. None of the retail samples contained H. pylori. This research suggests that transmission of H. pylori from beef and beef products is not a primary factor in the high prevalence of this bacterium in humans.

The effect of high-dose-rate X-rays on E. coli 0157:H7 in ground beef

The emergence of pathogens in today's world has increased the need for new, portable, nonthermal sterilization technologies. The University of Missouri, Columbia in cooperation with the Institute of Electrophysics, Ekaterinburg, Russia, have built and tested a new accelerator based on solid-state opening switches for the disinfection of pathogens in food. The accelerator utilizes a new solid-state opening switch to generate 40 ns, 2OO-keV electron beam pulses. These pulses were then converted to Bremsstrahlung X-rays using an integral X-ray converter. The efficacy of treating E. coli 0157:H7. In ground beef was tested by irradiating frozen ground beef with the high-dose-rate 10/sup 7-6/ rads/s X-ray pulses. Comparison studies were also done with a Cobalt-60 source located at the Missouri University Research Reactor. The results of the study are presented in this paper.

Trained sensory panel and consumer evaluation of the effects of gamma irradiation on palatability of vacuum-packaged frozen ground beef patties.

The objectives for this experiment were to determine the effects of gamma irradiation on 1) the palatability of vacuum-packaged frozen ground beef patties by trained sensory panel and 2) consumer evaluation of the taste of hamburgers made with those patties. Boxes (4.5 kg) of frozen (-28 degrees C) ground beef patties (113.4 g/patty, 19% fat) from a commercial supplier were irradiated at a commercial gamma irradiation facility at one of three levels (0, 3.0, or 4.5 kGy). All boxes were stored at 28 degrees C for 27 to 29 d after irradiation before evaluation by a trained descriptive attribute sensory panel and for 62 to 104 d after irradiation before consumer evaluation. The trained panel evaluated grilled patties for ground beef aroma intensity, off-aroma, and off-flavor on 4-point scales (4 = intense, none, and none; 1 = none, intense, and intense, respectively) and ground beef flavor intensity, tenderness, and juiciness on 8-point scales (8 = extremely intense, tender, or juicy; 1 = extremely bland, tough, or dry). Control patties had more intense (P<.05) ground beef aroma (3.1 vs 2.6), less off-aroma (3.3 vs 2.6), and more intense ground beef flavor (4.9 vs. 4.3) than irradiated patties. However, there were no differences (P>.05) in any sensory trait between frozen ground beef patties treated with 3.0 or 4.5 kGy of gamma irradiation. There were no differences (P>.05) among treatments for tenderness (6.3, 6.6, and 6.7) or juiciness ratings (5.7, 5.9, and 5.9), respectively, for 0, 3.0, and 4.5 kGy. The consumers evaluated taste of a hamburger that included their choice of condiments on a 10-point scale (10 = excellent; 1 = terrible). Hamburgers made with patties treated with 4.5 kGy were rated lower (P<.05) in taste than hamburgers made with either control patties or those treated with 3.0 kGy (6.5, 6.6, and 6.2, respectively, for 0, 3.0, and 4.5 kGy); however, all doses were rated at some level of "fair." These results imply that hamburgers made from ground beef patties irradiated under the conditions of this experiment would encounter little, if any, consumer acceptance problems at the 3.0 kGy dose and only slightly greater problems at the 4.5 kGy dose.

Comparison of the Difco EZ Coli™ Rapid Detection System and Petrifilm™ Test Kit-HEC for Detection of Escherichia coli O157:H7 in Fresh and Frozen Ground Beef

The Difco EZ Coli™ Rapid Detection System was compared to the 3M Petrifilm™ method for detection of Escherichia coli O157:H7 in raw ground beef. Raw meatballs (25 g) were inoculated with 10 to 15 cells of Escherichia coli O157:H7, stored for various times and at different temperatures, and then stomached for 2 min in 225 ml of EZ Coli™ enrichment broth, which was then incubated at 42°C for 18 to 24 h. A 1-ml sample of the enrichment broth was loaded into the top of the detector tips and the remaining EZ Coli™ broth held at 35°C before streaking onto MacConkey sorbitol agar and tryptic soy agar with yeast extract. A duplicate set of meatballs were tested using the 3M Petrifilm™ Test Kit-HEC for hemorrhagic Escherichia coli O157:H7. In this method raw meatballs (25 g) were enriched for 6 h in modified EC broth containing novobiocin at 37°C prior to inoculation of the Petrifilm™E. coli Count Plates, which were incubated at 42°C for 18 h. The immunoblot ELISA was performed following this incubation. Presumptive positive isolates from both methods were confirmed using Oxoid E. coli Latex Agglutination and Difco Pasco ID Tripanels. Both methods permitted detection of 10 to 15 cells of E. coli O157:H7 per ml (i) immediately following inoculation, (ii) after 3 days of refrigerated storage at 8°C, and (iii) after 30 days in frozen storage at −20°C. The Difco EZ Coli™ Detection System proved to be a simpler and faster screening method with identification of negative and presumptive positive samples within 15 to 18 h