IAFP 2009 Program Book and Abstract Book - AB158

Purpose: Few reports quantify the growth rate of Salmonella on cut tomatoes, and only at a limited number of incubation temperatures. While modeling software (the pathogen modeling program — PMP and ComBase Predictor - CBP) can be used to predict Salmonella growth, no models have been validated for cut tomatoes. Our purpose was to build a mathematical model to describe the growth of Salmonella on cut tomatoes and to compare that model with other published Salmonella growth models. Methods: Whole red round tomatoes were dip inoculated with a cocktail of four Salmonella strains obtained from the Centers for Disease Control and Prevention (CDC). These strains are all human isolates associated with past tomato outbreaks. Inoculated tomatoes were dried overnight, cut with a sterile knife, placed in a sterile plastic bag, incubated at one of 10 different temperatures and plated on XLT4 agar for enumeration. Growth rates were calculated using DMFit. Results: A plot of the square root (SR) of growth rate (GR) was linear with temperature (T), such that SR(GR) = 0.026T 0.1065, (R2 = 0.9398). The growth rate was slightly faster than that predicted by CBP but slower than that predicted by PMP. , CBP would allow predictions at the pH of cut tomatoes (4.3), while the lowest pH available for Salmonella growth in the PMP was 5.6. Significance: The Salmonella in the cut tomato model created here provides a useful tool for estimating the risk posed by different abuse temperatures. The model also provides validation of CBP as a model for Salmonella growth in cut tomatoes. P3-27 High Pressure Processing to Reduce Salmonella enterica from Broth and Diced Tomatoes DSC JESSICA MAITLAND, Renee R. Boyer, Robert C. Williams and Joseph D. Eifert Virginia Tech, Blacksburg, VA, USA Introduction: Fresh and fresh-cut tomatoes have been associated with numerous outbreaks of salmonellosis in recent years. While the exact routes of contamination are unknown, high pressure processing (HPP) is being evaluated as a post harvest treatment to eliminate Salmonella. Purpose: The objectives of the study were to determine the effect of HPP at three pressures on reduction of S. enterica serovars Newport, Javiana, Braenderup and Anatum (clinical isolates from tomato outbreaks) in Tryptic Soy Broth and to determine the effect of HPP on reduction of the most pressure resistant S. enterica serovar from fresh diced tomatoes. Methods: Separate 5 ml portions of broth containing 8 log CFU/ml of each of the four serovars (made nalidixic acid resistant) were packaged in sterile stomacher bags and subjected to three different pressures (350, 450, and 550 MPa) for 120s. Diced tomatoes (150g) were inoculated with the most pressure resistant serovar as determined by the preceding work, to obtain 6 log CFU/g throughout the sample, and subjected to the same pressure treatments as described above. Treated broth and tomato samples (homogenized for 1 min) were surface plated onto Tryptic Soy Agar supplemented with nalidixic acid and incubated at 35°C for 48 h. Results: The most pressure resistant serovar of Salmonella evaluated was Braenderup. Subjecting the broth culture to 350, 450 and 550 MPa resulted in a 4.90, 6.10 and 7.45 log reduction in S. Braenderup, respectively. No significant reductions were seen in S. Braenderup concentrations in diced tomatoes when processed at 350 MPa. Significant reductions (P < 0.05) were seen at 450 (1.63 log CFU/g) and 550 MPa (3.65 log CFU/g). There were no differences in visual appearance between fresh diced and HPP diced tomatoes. Significance: HPP may be an effective post harvest strategy to reduce low levels of Salmonella contamination in diced tomatoes. P3-28 Factors Affecting Infiltration, Survival, and Growth of Salmonella on Inshell Pecans and Pecan Nutmeats DAVID A. MANN and Larry R. Beuchat University of Georgia, Griffin, GA, USA Introduction: Outbreaks of foodborne infections have been associated with consumption of tree nuts. Two outbreaks of salmonellosis associated with almonds and one outbreak of Escherichia coli O157:H7 infection associated with cashew nuts have been documented. Pecan handling and processing practices have potential for enhancing or compromising safety. However, factors that may affect infiltration, survival, and growth of foodborne pathogens on pecans have been given only meager research attention. Purpose: The purpose of this study was to determine (1) the effect of temperature on infiltration of Salmonella into inshell pecans; (2) survival characteristics of the pathogen on and in inshell pecans and pecan nutmeats as affected by temperature during long-term storage; and (3) survival and growth characteristics of Salmonella on high-aw nutmeats. Methods: Infiltration of Salmonella into inshell pecans as affected by temperature differential (nuts at -20, 4, 21, and 37°C; suspension at 21°C) was studied. Survival of the pathogen on and in dry inshell pecans, pecan halves, and pecan pieces during storage at -20, 4, 21, and 37°C was monitored. Survival and growth characteristics on high-aw (0.96 to 0.99) nutmeats held at 4, 21, 30, and 37°C were determined. Results: The rate of infiltration of water into inshell pecans was greater when pecans were at a temperature higher than that of the water. Salmonella was isolated from nutmeats of inshell pecans that had been immersed in a cell suspension, dried, and stored at 4°C for 4 weeks, indicating that the pathogen can infiltrate the nut, reach the edible portion, and survive. Populations of Salmonella on and in inshell pecans (nutmeat aw, 0.43 to 0.51; moisture, 3.2 to 3.6%) and nutmeats (aw, 0.53 to 0.63; moisture, 3.7 to 3.8%) stored for up to 36 weeks at -20 and 4°C decreased slightly; significant decreases occurred at 21 and 37°C but viable cells were detected. The pathogen grew at 21, 30, and 37°C but not at 4°C on high-aw (0.96 to 0.99) pecan halves, pieces, and granules. Significance: The ability of Salmonella to infiltrate pecans and survive for long periods of time, coupled with its ability to grow on high-aw nutmeats, emphasizes the importance of applying process treatments that will inactivate the pathogen. 158 — Abstract Book Poster

IAFP 2009 Program Book and Abstract Book

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