|Tamplin, Mark - UNIV. OF TASMANIA|
Submitted to: Journal of Food Science and Technology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: June 7, 2007
Publication Date: September 1, 2007
Citation: Hwang, C., Tamplin, M. 2007. Modeling the Lag Phase and Growth Rate of Listeria monocytogenes in Ground Ham Containing Sodium Lactate and Sodium Diacetate at Various Storage Temperatures. Journal of Food Science and Technology. 72(7):M246-M253. Interpretive Summary: Several foodbrone illnesses caused by Listeria monocytogenes were linked to the consumption of refrigerated ready-to-eat (RTE) meat. Lactate and diacetate, two regulatory-permitted additives, have been reported to inhibit the growth of L. monocytogenes in RTE meat. This study examined a wider range of concentrations of lactate (1.0-4.2%) and diacetate (0.05-0.2%), and storage temperatures (0-45 degree C) on the growth of L. monocytogenes inoculated into a cooked ham product that was ground and sterilized. The time for the pathogen to start to grow (time to growth) and its growth rates afterward in ham as affected by the additives and storage temperature were determined. Results showed that lower storage temperatures or higher concentrations of lactate or diacetate increased the time to growth of L. monocytogenes in ham; the increase in time to grow by both additives was more significant at lower temperatures. The growth rates of L. monocytogenes in ham were lower at lower storage temperatures. The effect of higher concentrations of both additives in reducing growth rates was observed only at temperatures that were more optimal for growth of L. monocytogenes, i.e., 15 degree -35 degree C. Mathematical models describing the time to growth and growth rate were developed and validated. The models may be used as a reference by RTE meat producers to select the concentrations of lactate and diacetate for products similar to cooked ham to control the growth of L. monocytogenes over a wide range of temperatures during the manufacturing, distribution, and storage.
Technical Abstract: Refrigerated ready-to-eat (RTE) meats contaminated with L. monocytogenes were implicated in several listeriosis outbreaks. Lactate and diacetate have been shown to control L. monocytogenes in RTE meats. The objective of this study was to examine and model the effect of lactate (1.0-4.2%) and diacetate (0.05-0.2%) in irradiated ground ham on the lag phase duration (LPD, h) and growth rate (GR, log cfu/h) of L. monocytogenes at a wide range of temperatures (0-45 degree C). A 6-strain mixture of L. monocytogenes was inoculated into ground ham containing lactate and diacetate, and stored at various temperatures. A total of 19 combinations of these factors selected by a central composite design were examined. The LPD and GR of L. monocytogenes in ham as affected by lactate, diacetate and storage temperature were analyzed and described with mathematical equations. Resulting LPD and GR equations for storage temperatures within the range of 0 to 36 degree C significantly represented the experimental data with a regression coefficient of 0.97 and 0.96, respectively. Significant factors (p<0.05) that affected the LPD were temperature, lactate, diacetate, and the interactions of all three, whereas only temperature and the interactions between temperature and lactate and diacetate were significant on GR. At sub-optimal growth temperatures ( less than and equal to 12 degree C) the increase of lactate and diacetate concentrations, individually or in combination, extended the LPD. The effect of higher concentrations of both additives on reducing GR was observed only at temperatures that were more optimal for growth of L. monocytogenes, i.e., 15-35 degree C. The LPD and GR equations were validated in a separate experiment. These data may be used to assist in determining concentrations of lactate and diacetate in cooked ham products to control the growth of L. monocytogenes over a wide range of temperatures during the manufacturing, distribution and storage.