IAFP 2009 Program Book and Abstract Book - AB180

of inhibition (ZOI) produced were measured. Furthermore, a five-isolate cocktail was required for both resistant and susceptible Salmonella. The ZOIs for each isolate were paired together, and median ZOIs were calculated separately for each Salmonella type. The Euclidean distances were calculated and normalized, and outliers were removed if their normalized distance was significantly higher than most other data points. Verification of outlier removal was also visually observed with scatter plots. The two data sets were partitioned, using hierarchical clustering with Euclidean distances. The results were plotted as dendrograms, and the specific isolates were then chosen. Results: For the case study, significant differences (P < 0.05) were observed in the diameter zones of inhibition for ACSSuT-resistant and susceptible Salmonella on both PCA (P = 0.025) and XLT4 (P = 0.046). The sample error for all resistant and susceptible Salmonella samples is 0.198 and 0.237, respectively. This high error rate is due to limited sample availability, illustrating the importance of a large sample size. Five isolates were then chosen for each cocktail based on their ZOI similarity in the dendrograms, because the behavior of these isolates are more likely to represent the behavior of serovars in the general Salmonella population. Significance: When statistical methods, such as the one discussed here, are applied to a study, the results are more valid. If all researchers were to embrace these types of sample selection methodologies, there would be fewer false positives and fewer misleading and irreproducible results, and it could even lead to increased perception and trust among professionals and the general public alike. P3-86 A Response Surface Model to Describe the Effect of Temperature and pH on the Growth of Bacillus cereus in Cooked Rice JI-YOUNG LEE, Sun-Kyung Heo and Sang-Do Ha Chung-Ang University, Food Science & Technology, Ansung-Si, Korea, South Introduction: A predictive model is being popularly applied to food industry to estimate Bacillus cereus growth and to determine the shelf life of cooked rice. Purpose: This study was performed to develop a predictive model for the growth rate of B. cereus in cooked rice using a response surface methodology (RSM). Methods: B. cereus F4810/72 producing an emetic toxin was used in this study. The growth curves as a function of storage temperature (10 to 40°C) and pH value (5.4 to 6.8) were fitted using a modified Gompertz equation and the relationship of the growth rate to the growth curves was modeled using an RSM quadratic polynomial equation. The RSM evaluation for describing the growth rate of B. cereus used both bias (Bf) and accuracy factors (Af). Results: The predicted growth of B. cereus in cooked rice varied from 0.01 h-1 at 10°C to 1.08 h-1 at 40°C. At the lower pH of 5.4, the growth of B. cereus was hardly observed regardless of storage temperature. The response surface quadratic polynomial equation was “Y = 0.330861 + 0.313648 × 1 + 0.212498 × 2 + 0.196629 × 1 × 2 + 0.037367 × 12 - 0.032263 × 22”. The predictive model was significant (P < 0.01) and the predicted values of the growth parameters obtained using the model equations were in good agreement with experimental values (R2 value of 0.9864). Both the Bf value (1.006) and the Af value (1.011) approached 1.0 and were within acceptable ranges. Therefore, the adequacy of the predictive model for B. cereus in cooked rice was verified by the validation data. Significance: Our model can be used as a reference in controlling B. cereus growth in cooked rice without the need for detection of the organism and may be of use to manufacturers of rice products for controlling B. cereus growth. P3-87 Growth of Escherichia albertii on Ground Beef Stored at Various Temperatures DSC KEILA L. PEREZ and T. Matthew Taylor Texas A&M University, Animal Science, College Station, TX, USA Introduction: Escherichia albertii is the newest species within the genus Escherichia and may represent an emergent foodborne pathogen. E. albertii has been cultured from stool samples of diarrheagenic children repeatedly and some strains are capable of synthesizing the pathogenesis factor intimin. The influence of food storage temperature on growth and survival of E. albertii in various foods has not been widely examined. Purpose: The objective of this study was to determine the growth characteristics of E. albertii on fresh raw ground beef as a function of storage temperature. Methods: Nalidixic acid-resistant strains of E. albertii (American Type Culture Collection 19982, 10457, and 9194) were individually inoculated on 150 g samples of ground beef to a concentration of 4.3 ± 0.7 log CFU/g. Aliquots (11 g) were prepared and incubated aerobically at 5°C, 22°C, or 35°C for 21, 7, or 3 days, respectively. E. albertii were enumerated following spread plating on MacConkey Agar supplemented with L-+-Rhamnose (10 g/l) and antibiotic (50 mg/l). The experiment was replicated three times. Means from like samples were generated and statistically significant differences assessed as a function of pathogen strain, days of incubation, and temperature of incubation (P < 0.05). Results: E. albertii 19982, 10457, and 9194 populations decreased by approximately 2.0, 1.6, and 0.9 log cycles following 21 days of storage at 5°C, respectively. Populations of E. albertii 19982, 10457, and 9194 recovered from beef incubated at 22°C and 35°C following 7 and 3 days of incubation, respectively, increased by 2.5, 3.6, and 3.7 log cycles and 3.9, 3.5, and 3.9 log cycles. Significance: E. albertii is able to flourish on nutrient-rich foods under conditions of abuse or at physiological temperature. However, data indicate that proper refrigeration of food products can assist in the prevention of growth of this potential foodborne pathogen. Further research on the ability of E. albertii strains to synthesize intimin along with its growth and survival on various other foods should be conducted. Poster 180 — Abstract Book

IAFP 2009 Program Book and Abstract Book

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