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Effects of Lactic Acid on the Growth Characteristics of Listeria monocytogenes on Cooked Ham Surfaces

Hwang, Cheng-An, Huang, Lihan, Sheen, Shiowshuh, Juneja, Vijay
Journal of food protection 2012 v.75 no.8 pp. 1404
Listeria monocytogenes, cooked foods, food surfaces, growth models, ham, lactic acid, mathematical models, microbial growth, product safety, risk, storage temperature
The surfaces of ready-to-eat meats are susceptible to post-processing contamination by Listeria monocytogenes. This study examined and modeled the growth characteristics of L. monocytogenes on the surface of cooked ham treated with lactic acid solutions (LA). Pieces of cooked ham inoculated with a 5-strain mixture of L. monocytogenes (ca. 3.0 log CFU/g) were immersed in 0, 0.5, 0.75, 1.0, 1.5 and 2.0% LA for 30 min, vacuum-packaged, and stored at 4, 8, 12, and 16 degrees Celsius. The immersion resulted in low levels of L. monocytogenes reduction (less than 0.7 log CFU/g) on ham surface indicated that the treatment was not a sufficient mean to reduce L. monocytogenes risk immediately after the treatment. During storage, no growth of L. monocytogenes occurred in ham treated with 1.5% LA at 4 and 8 degrees Celsius and with 2% LA at all temperatures. LA at 0.5-1.5% extended the lag phase duration (LPD) and reduced the growth rate (GR) of L. monocytogenes. Significant extension of LPD and GR reduction occurred in ham treated with greater than 1.25% LA. The GR of L. monocytogenes at 4 degrees Celsius was reduced from 0.214 log CFU/day in untreated ham to 0.131-0.059 log CFU/day in ham treated with 0.5-1.25% LA, whereas the GR was reduced from 0.569 log CFU/g to 0.402-0.117 CFU/day and from 0.938 log CFU/day to 0.742-0.216 log CFU/day at 8 and 12 degrees Celsius, respectively. The LPD and GR of L. monocytogenes as a function of LA concentration and storage temperature can be satisfactorily described by both polynomial and square-root-type models. Results from this study indicate that 1.5% LA immersion treatment may be used to control growth of L. monocytogenes on meat surface, and the models would help in selecting suitable LA immersion treatments for meat products to achieve desired product safety.