Eliminating Listeria monocytogenes in packed ready-to-eat poultry products by combining in-package pasteurization with nisin and/or lysozyme.

摘要

Listeria monocytogenes is a significant food-borne pathogen particularly associated with ready-to-eat (RTE) meat and poultry products which can grow and multiply at refrigeration temperatures. In-package pasteurization is an effective post-lethality intervention to reduce microbial contamination of RTE meat products. Enhancing the efficiency of in-package pasteurization is vital in reducing the L. monocytogenes population as well as in preserving the quality of the meat product.; The first section of the dissertation research evaluated the effect of product thickness on the surface heating rate and final surface temperature during in-package pasteurization of vacuum-packaged bologna. Three thicknesses (4, 12, and 20 mm), corresponding to 1, 3, and 5 slices of two types of bologna having different (13 and 18%) fat contents were subjected to in-package pasteurization at 4 temperatures (60, 70, 80, and 90°C). Surface heating rate was fastest in the thinnest (4 mm) and slowest in the thickest (20mm) samples for all 4 temperatures. Final surface temperature attained after 3 min was lower with increased thickness levels for all temperatures. More significant was the magnitude of the difference in the time required to attain a 5 log reductions in L. monocytogenes on the surface of bologna due to small difference in thickness. A difference of only 16 mm increased the time from 1.5 min to 9.5 min and 0.72 min to 4.12 min at 70 and 80°C, respectively.; Effect of surface application of nisin and/or lysozyme (5000 AU nisin/ml, 80 AU lysozyme/ml, and 5000 AU nisin + 80 AU lysozyme/ml) in combination with in-package pasteurization (60, 62.5 and 65°C) of RTE low fat turkey bologna on the inactivation of L. monocytogenes was the second objective investigated. Nisin-lysozyme combination and nisin treatments were effective in reducing the time required for a targeted reduction in L. monocytogenes population at 62.5 and 65°C, but not at 60°C.; Finally, the ability of in-package pasteurization at 65°C for 32 s combined with pre-surface application of nisin and/or lysozyme (antimicrobial treatments were of the same concentration mentioned above) to reduce L. monocytogenes populations, and to prevent the subsequent recovery and growth during refrigerated storage for 12 weeks on the surface of low fat turkey bologna was determined. Nisin and nisin-lysozyme treatments were effective in reducing the growth of L. monocytogenes to below detectable levels by 2-3 weeks of storage.