The application of nucleic acid amplification methods to the detection of food-borne pathogens could be facilitated by concentrating the organisms from the food matrix before detection. This study evaluated the utility of metal hydroxide immobilization for the concentration of bacterial cells from dairy foods prior to detection by cultural and molecular methods. Using reconstituted nonfat dry milk (NFDM) as a model, two food-borne pathogens (Listeria monocytogenes and Salmonella enterica serovar Enteritidis) were concentrated from 25-ml samples by the sequential steps of clarification and high-speed centrifugation (designated primary concentration) and immobilization with zirconium hydroxide and low-speed centrifugation (designated secondary concentration). Sample volume reduction after immobilization with zirconium hydroxide was 50-fold, with total bacterial recoveries ranging from 78 to 96% of input for serovar Enteritidis and 65 to 96% of input for L. monocytogenes. Immobilized bacteria remained viable and could be enumerated by standard cultural procedures. When followed by RNA extraction and subsequent detection by reverse transcription (RT)-PCR, detection limits of 10 1 to 10 2 CFU/25 ml of reconstituted NFDM were achieved for both organisms. The bacterial-immobilization step was relatively nonspecific, resulting in recovery of >50% of the input cells when evaluated on a panel of representative bacterial strains of significance to foods. The method could be adapted to more complex dairy products, such as whole milk and ice cream, for which bacterial recoveries after immobilization ranged from 64 to >100%, with subsequent RT-PCR detection limits of >10 2 CFU/ml for whole milk and >10 1 CFU for ice cream for both serovar Enteritidis and L. monocytogenes. The bacterial-immobilization method is easy, rapid, and inexpensive and may have applications for the concentration of a wide variety of food-borne bacteria prior to detection by both conventional and alternative methods.

Vacuum-packaged frankfurters, inoculated with 24-h cultures of Listeria monocytogenes Scott A (approximately 10(9) CFU/ml) by injection into the packages, were held at pressures of 300, 500, and 700 MPa for up to 9 min. L. monocytogenes were washed from the surface of the frankfurter and plated onto brain heart infusion agar. During the time to achieve 300, 500, and 700 MPa (come-up time), L. monocytogenes populations decreased by 1, >3, and >5 logs, respectively. Additional inactivation of L. monocytogenes occurred while the samples were held at 300 and 500 MPa. A 5-log reduction in bacterial population was possible at all pressure treatments; however, pressurization at 700 MPa showed the fastest inactivation with L. monocytogenes reduced from 10(8) to 10(2) CFU/package during the come-up time. These results show that high-pressure processing may be a viable method for controlling foodborne pathogens in postprocessed, packaged frankfurters.

Eggshell conductance was measured and eggshell conductance constants were calculated for eggs from ostriches. In addition, egg water, yolk, albumen, shell, and total solids were measured in an effort to determine the maternal investment of ostrich eggs. The results of the study suggest that the optimal incubator humidity for ostrich eggs is less than 25% to allow a 15% loss of initial egg mass during the 45-d incubation period. This low humidity does not preclude increasing humidity during the actual hatching process. In addition, incubation temperatures need to be adjusted to allow a longer development time for the embryo to attain an adequate level of maturity to survive the plateau stage in oxygen consumption or to prevent the use of limited energy of the yolk to survive the anoxia of tucking and internal pipping. The optimal incubation temperature of ostrich eggs appears to be between 36.1 and 36.9 C.

The effects of two egg holding temperatures (15.5 and 26.7°C) and three wash-water temperatures (15.5, 32.2, and 48.9°C) on internal and external shell surface bacterial counts were tested by using a commercial-type egg-processing unit. Two experiments consisting of five trials, each of which included 360 eggs per treatment for a total of 2,160 per trial, were conducted during two seasons (summer and winter) for a total of 10 replicates per experiment. During the performance of each replicate, counts from tryptic soy agar (TSA) and MacConkey agar (MAC) were obtained from 10 egg samples which were collected prior to processing (prewash), immediately after washing (postwash), and after as-day cooling period at 7.2°C (postcool). No growth was observed on MAC plates in either experiment, indicating that fewer than 100 counts were detected. No significant differences (P > 0.05) were observed in the prewash, postwash, or postcool internal shell counts of eggs held at l5.5°C compared to internal counts of shells of eggs held at 26.7°C. Likewise, no significant differences (P > 0.05) were observed in the prewash, postwash, or postcool internal shell counts obtained from eggs washed in l5.5°C water compared with internal shell counts obtained from eggs washed in water at 32.2 or 48.9°C. On the basis of our data, spray washing eggs in l5.5°C water does not appear to increase internal shell bacterial counts. Because warm or hot wash water increases egg temperatures markedly, a reexamination of cold-water processing procedures may be in order.

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