IAFP 2009 Program Book and Abstract Book - AB152

Results: Normal microflora in several batches of freshly-harvested spinach ranged as follows: 4 to 7 (ME), 5 to 7 (PS), 3 to 5 (YM), 0.5 to 2 (LA), and 4 to 6 (EN) log CFU/g. In 20% O2/3% CO2, normal microflora increased 1 to 2 log compared to initial levels, whether stored at 5 or 12°C during the 8-day storage period, while EC decreased by 0.5 to 1.5 log. In low oxygen, normal microflora levels remained unchanged at 5°C, while EC declined by 1 log. However at 12°C, EC levels remained stable or increased by approximately 0.5 log. The higher temperature and low oxygen conditions allowed increased survival of the pathogen, compared to survival at lower temperature and high oxygen conditions. Significance: Temperature and package atmosphere affect survival of E. coli. Other conditions may also minimize pathogen risk in packaged spinach. P3-11 Thermal Resistance of Heat-shocked Escherichia coli O157:H7, Salmonella and Listeria monocytogenes DSC in Dairy Compost RANDHIR SINGH, Xiuping Jiang and Feng Luo Clemson University, Dept. of Biological Science, Clemson, SC, USA Introduction: Proper composting, is critical for inactivation/killing of pathogens in animal wastes. However, persistence and survival of pathogens during composting has been reported. Purpose: To study thermal inactivation of heat-shocked E. coli O157:H7, Salmonella spp. and L. monocytogenes in dairy compost. Methods: Three strain mixture of E. coli O157:H7, Salmonella, and L. monocytogenes were heat-shocked at 47.5oC for 1 h, and then inoculated into the finished dairy compost (ca. 107 CFU/g). The non-heat-shocked cultures were served as control. Compost packed in pouches were placed in environmental chamber set at 50, 55 and 60oC with ca. 70% humidity. The surviving population of each species was analyzed in duplicate by direct plating or enrichment at predetermined time excluding the come-up time. The inactivation kinetic was modeled by mixed Weibull model. Results: The heat-shocked E. coli O157:H7, Salmonella and L. monocytogenes survived better (P < 0.05) at 50oC with log reduction of 2.67, 3.21 & 3.89 within 4 h in comparison to control cultures of 3.55, 4.77 and 5.09 log reduction, respectively. The heat-shocked cultures had 1.17, 1.85 and 2.1 log reduction within 1 h at 55°C for E. coli O157:H7, Salmonella and L. monocytogenes, respectively, whereas control cultures had 3.98, 5.6 & 4.7 log reductions, respectively. At 60°C, bacterial reduction was significant during the come-up time of 14 min between control and heat-shocked cultures of all three species. L. monocytogenes at all three temperatures exhibited extensive tailing in the survival curves. The mixed Weibull distribution model fitted well the survival curves of pathogens, with differences in the shape parameter of heat-shocked and control cultures. Significance: Our results suggest that heat-shock may extend the survival of pathogens at lethal temperature during composting and thereby promote survival through the composting process, which has the potential to result in contamination of fresh produce and the environment. P3-12 Evaluation of Physical Coverings Used to Reduce Escherichia coli O157:H7 Populations at the Surface of DSC Compost Heaps MARION W. SHEPHERD, Jinkyung Kim, Xiuping Jiang, Michael P Doyle and Marilyn C. Erickson . Clemson University, Dept. of Biological Sciences, Central, SC, USA Introduction: Minimal maintenance of compost heaps, including no heap turning, may result in extended survival of pathogens, as material near the compost surface lacks exposure to elevated temperatures. Purpose: The goal of this study was to apply physical coverings to control Escherichia coli O157:H7 at the surface of dairy composting heaps under field conditions. Methods: Two composting trials were conducted in the spring and summer seasons, each with four compost heaps composed primarily of a cow manure-sawdust mixture. Compost samples were inoculated with avirulent E. coli O157:H7 B6914 and packed into either Tyvek® bags or vented polystyrene trays and secured to the heaps. Two compost heaps were bisected; samples bags were placed at the east and west sections of each compost half and then covered with finished compost with 30 or 50% moisture at 15 or 30 cm thicknesses. Another heap was covered with ca. 13 cm of fresh hay, and the remaining heap was left uncovered, serving as the control. Populations of E. coli O157:H7 and Enterobacteriaceae were enumerated or enriched over pre-determined intervals. Results: Ca. 7 log CFU E. coli O157/g compost in the heap covered with 15 or 30 cm of finished compost (30% moisture) was eliminated within 21 and 5 days in composting trials 1 and 2, respectively. With other coverings, the pathogen was below detectable limits after 60 and 5 days of composting, in trials 1 and 2, respectively. In both trials, E. coli O157:H7 was detected in the control (uncovered) treatment through day 120. Within week one of composting, maximal temperatures at the interface between compost surface and compost coverings were achieved, ranging from 41 to 48°C in trial 1 and 47 to 50°C in trial 2. Significance: Our results demonstrated that covering compost heaps with finished compost or hay can expedite pathogen inactivation at the surface of heaps, thereby reducing the probability of environmental contamination. P3-13 Interaction of Escherichia coli O157:H7 with Growing Spinach Plants DSC SHUAIHUA PU, John C. Beaulieu, Witoon Prinyawiwatkul and Beilei Ge Louisiana State University, Dept. of Food Science, Baton Rouge, LA, USA Introduction: In recent years, there has been increasing incidence of foodborne outbreaks linked to fresh and freshcut fruits and vegetables in the United States. Particularly noteworthy was the 2006 Escherichia coli O157:H7 outbreak associated with pre-bagged baby spinach. To better ensure produce safety, research is urgently needed to fill critical knowledge gaps, especially regarding the route and mechanism of contamination. 152 — Abstract Book Poster

IAFP 2009 Program Book and Abstract Book

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