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Title: HEAT INACTIVATION OF LISTERIA MONOCYTOGENES IN TSYE BROTH AND FRANKFURTER SLURRIES

Author
item SCHULTZE, K. - PURDUE UNIVERSITY
item LINTON, RICHARD - PURDUE UNIVERSITY
item SELBY, T. - PURDUE UNIVERSITY
item COUSIN, MARYBETH - PURDUE UNIVERSITY
item Tamplin, Mark
item Luchansky, John

Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: 12/1/2004
Publication Date: 7/1/2005
Citation: Schultze, K.K., Linton, R.H., Selby, T.L., Cousin, M., Tamplin, M.L., Luchansky, J.B. 2005. Heat inactivation of listeria monocytogenes in tsye broth and frankfurter slurries. Meeting Abstract. P20.

Interpretive Summary:

Technical Abstract: Ready-to-eat frankfurters are classified as very high risk products in the FDA/CFSAN Listeria monocytogenes (LM) Risk Assessment. Post-processing pasteurization of frankfurters has been proposed as a method to reduce the incidence of LM. In this research, the fate of LM was determined in synthetic media and in frankfurter slurries at post-processing pasteurization temperatures. The objective of this research was to compare the death rates of LM in tryptic soy and .6% yeast extract (TSYE) broth and frankfurter slurries. Hot dogs were blended with distilled water to make 8.5% and 10% frankfurter slurries. The slurries and TSYE (100 ml each) in round-bottom flasks were heated (55, 60, 65 deg C) in a water bath before inoculating with a five-strain cocktail of LM (~1 x 106 cells/ml). One-milliliter samples were pulled from flasks immediately and diluted in chilled peptone. Subsequent dilutions were done in unchilled peptone and pour-plated with TSYE and 1% pyruvate agar (TSYEP), and incubated at 37 deg C. Plates were overlaid with modified oxford (MOX) agar after 4 h and incubated for 44 hours at 37 deg C before counting. Inactivation rates (D-values) ranged from 0.29 min (10% slurry, 65 deg C) to 68.85 min (TSYE, 55 deg C). There was no difference (P<0.05) in log reductions between 8.5 and 10% slurries. Average D-values at all temperatures were higher in TSYE than in frankfurter slurries due to antimicrobial ingredients in franks, such as salt and nitrites. Most heat inactivation research is done in optimal broth systems instead of environments that simulate food products. These values might overestimate thermal death of LM in actual food products. Additional research comparing thermal death in frankfurters to broths needs to be done to investigate the effectiveness of using food systems to estimate thermal death.