Interest in Aeromonas hydrophila as a food-borne and human pathogen is increasing. Isolation media from the clinical laboratory were evaluated for food use and either did not give quantitative recovery of A. hydrophila or did not permit ready differentiation of A. hydrophila from the background microflora. A new medium was developed which permitted quantitative recovery of A. hydrophila from foods. The medium consisted of phenol red agar base (Difco Laboratories), soluble starch (10gliter), and ampicillin (10 mg/liter). All foods surveyed contained A. hydrophila. Foods sampled included red ieats, chicken, raw milk, and seafood (fish, shrimp, scallops, crab, and oysters). The count of A. hydrophila at the time of purchase ranged from 1 x 102/g (lower limit of detection) to 5 x 105/g. In most instances, the count of A. hydrophila increased during 1 week of storage at 5°C. The starch-ampicillin agar developed permitted rapid quantitative recovery ofA. hydrophila from foods in the presence of very large numbers of competing microflora.

The benefits and concerns about treating foods with ionizing radiation are reviewed. Radioactivity cannot be induced in foods by treatment with gamma rays from 137Cs or 60Co, X-ray sources of 5 MeV or lower energy, or electrons of 10 MeV or lower energy. The evidence supports the safety and eficacy of using ionizing radiation for insect disinfestation of grains; dried spices, vegetables and fruits; and fresh fruit. Species and dose dependent phytotoxic and vitamin changes may occur in some fruits at greater doses than currently approved by the US. Food and Drug Administration. Irradiation can inactivate protozoan or helminth parasites and signijicantly decrease the probability of viable food-borne bacterial pathogens in fish, poultry, and red meats. The titers of amino acids, fatty acids, and vitamins of chicken meat sterilized by thermal, electron-beam, or gamma radiation are presented. On the whole, the data support the safety and eficacy of the process.

Longissimus dorsi from beef, pork, and lamb and turkey breast and leg meats were inoculated with Escherichia coli 0157:H7, Listeria monocytogenes, Salmonella spp., and Staphylococcus aureus, and the gamma radiation resistance of the pathogens were determined under identical conditions. At 5°C the respective radiation D-values of E. coli 0157:H7 and L. monocytogenes did not vary with the suspending meat. The Dvalue for a mixture of Salmonella spp. was significantly lower on pork than on beef, lamb, turkey breast, and turkey leg meats. The D-value for S. aureus was significantly lower on lamb and mechanically deboned chicken meat than on the other meats. All values were, nevertheless, within expected ranges.

Undercooked and raw meat has been linked to outbreaks of hemorrhagic diarrhea due to the presence of Escherichia coli 0157:H7; therefore, treatment with ionizing radiation was investigated as a potential method for the elimination of this organism. Response-surface methods were used to study the effects of irradiation dose (0 to 2.0 kGy), temperature (-20 to +20°C), and atmosphere (air and vacuum) on E. coli 0157:H7 in mechanically deboned chicken meat. Differences in irradiation dose and temperature significantly affected the results. Ninety percent of the viable E. coli in chicken meat was eliminated by doses of 0.27 kGy at +5C and 0.42 kGy at-5°C. Small, but significant, differences in radiation resistance by E. coli were found when finely ground lean beef rather than chicken was the substrate. Unlike nonirradiated samples, no measurable verotoxin was found in finely ground lean beef which had been inoculated with 104.8 CFU of E. coli 0157:H7 per g, irradiated at a minimum dose of 1.5 kGy, and temperature abused at 35°C for 20 h. Irradiation is an effective method to control this food-borne pathogen.

There have been several recent outbreaks of salmonellosis and infections with Escherichia coli O157:H7 linked to the consumption of raw sprouts. Use of ionizing radiation was investigated as a means to reduce or to totally inactivate these pathogens, if present, on the sprouts. The radiation D value, which is the amount of irradiation in kilograys for a 1-log reduction in cell numbers, for these pathogens was established using a minimum of five doses at 19 +/- 1 degrees C. Before inoculation, the sprouts were irradiated to 6 kGy to remove the background microflora. The sprouts were inoculated either with Salmonella spp. cocktails made with either meat or vegetable isolates or with E. coli O157:H7 cocktails made with either meat or vegetable isolates. The radiation D values for the Salmonella spp. cocktails on sprouts were 0.54 and 0.46 kGy, respectively, for the meat and vegetable isolates. The radiation D values for the E. coli O157:H7 cocktails on sprouts were 0.34 and 0.30 kGy, respectively, for the meat and vegetable isolates. Salmonella was not detected by enrichment culture on sprouts grown from alfalfa seeds naturally contaminated with Salmonella after the sprouts were irradiated to a dose of 0.5 kGy or greater. Ionizing radiation is a process that can be used to reduce the population of pathogens on sprouts.

Like alfalfa sprouts, broccoli sprouts can be a vehicle for bacterial pathogens, which can cause illness when they are consumed. The gamma irradiation process was used to reduce numbers of bacterial pathogens on broccoli sprouts and seeds, and the effect of this process on the seeds was studied. The irradiation destruct values for Salmonella sp. and for strains of Escherichia coli O157:H7 inoculated on broccoli seeds were determined. Results obtained in this study indicate that a dose of 2 kGy reduced total background counts for broccoli sprouts from 10(6) to 10(7) CFU/g to 10(4) to 10(5) CFU/g and increased the shelf life of the sprouts by 10 days. Yield ratio (wt/wt), germination percentage, sprout length, and thickness were measured to determine the effects of various irradiation doses on the broccoli seeds. Results show a decreased germination percentage at a dose level of 4 kGy, whereas the yield ratio (wt/wt), sprout length, and thickness decreased at the 2-kGy dose level. The radiation doses required to inactivate Salmonella sp. and strains of E. coli O157:H7 were higher than previously reported values. D-values, dose required for a 1-log reduction, for the nonvegetable and vegetable Salmonella sp. isolates were 0.74 and 1.10 kGy, respectively. The values for the nonvegetable and vegetable isolated strains of Escherichia coli O157:H7 were 1.43 and 1.11 kGy, respectively. With the irradiation process, a dose of up to 2 kGy can extend the shelf life of broccoli sprouts. A dose of > 2 kGy would have an adverse effect on the broccoli seed and decrease the yield of broccoli sprouts.

No abstract

Frankfurter is a generic term for a cured and cooked sausage, which may consist of almost any meat type and include a wide variety of nonmeat fillers and additives. When several “brands” or types of commercially available frankfurters were surface‐inoculated with Listeria monocytogenes and vacuum‐packed, gamma radiation D‐values ranged from 0.49 kGy to 0.71 kGy, with an average D‐value of 0.61 kGy. Differences in gamma radiation D‐value were observed for nine of twenty one pair‐wise comparisons (α= 0.01) as determined by analysis of covariance. Therefore, frankfurter formulation may affect radiation D‐values for surface inoculated L. monocytogenes. If low dose gamma irradiation, cold pasteurization, were to be used for control of L. monocytogenes on frankfurters, gamma radiation dosage should be based on individual product formulation.