99D-32 |
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C.-A. HWANG and M. L. Tamplin. Microbial Food Safety Research Unit, USDA-ARS-Eastern Regional Research Center, 600 E. Mermaid Lane, Wyndmoor, PA 19038 Seafood salad has been identified as a ready-to-eat food with a relatively high incidence of contamination by Listeria monocytogenes; however, little is known about the behavior of this pathogen in seafood salad as a function of product pH and storage temperature. To produce data towards the development of a predictive growth model, a 6-strain cocktail of L. monocytogenes was inoculated onto the surface of a shrimp-crabmeat product, mixed with mayonnaise that was previously adjusted with NaOH to pH 3.7, 4.0, 4.4, 4.7 or 5.1, and then stored at 4°, 8° or 12°C under an aerobic atmosphere. L. monocytogenes grew at each combination of storage temperature and pH. At 4°C, the growth rate of L. monocytogenes at pH 3.7, 4.0, 4.4, 4.7, and 5.1 was 0.0107, 0.0112, 0.0113, 0.0103 and 0.0096 log cfu/h, respectively. Levels in the salad increased from 1.5 log cfu/g to 6.0-7.0 log cfu/g after 22 days of storage. At 8°C, the growth rate of L. monocytogenes was 0.0175, 0.0182, 0.0185, 0.0176, and 0.0155 log cfu/h at pH of 3.7, 4.0, 4.4, 4.7, and 5.1, respectively, reaching 7.0 log cfu/g in all samples after 16 days of storage. At 12°C, the growth rate of L. monocytogenes was 0.0283, 0.0222, 0.0220, 0.0235, and 0.0216 log cfu/h at pH of 3.7, 4.0, 4.4, 4.7, and 5.1, respectively, reaching 7.0 log cfu/g in all samples after 12 days of storage. At each storage temperature, the lag phase duration decreased with decreasing mayonnaise pH. These studies demonstrate that seafood salad supports the growth of L. monocytogenes over a wide range of pH values and storage temperatures that are relevant to commercial production practices.
Session 99D, Food Microbiology: General
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