ELIMINATING LISTERIA MONOCYTOGENES IN PACKED READY-TO-EAT POULTRY PRODUCTS BY COMBINING IN-PACKAGE PASTEURIZATION WITH NISIN AND/OR LYSOZYME

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. 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

Effect of combining nisin and/or lysozyme with in-package pasteurization for control of Listeria monocytogenes in ready-to-eat turkey bologna during refrigerated storage

This study investigated the efficacy of in-package pasteurization combined with pre-surface application of nisin and/or lysozyme to reduce and prevent the subsequent recovery and growth of Listeria monocytogenes during refrigerated storage on the surface of low-fat turkey bologna. Sterile bologna samples were treated with solutions of nisin (2 mg/ml=5000 AU/ml), lysozyme (10 mg/ml=80 AU/ml) and a mixture of nisin and lysozyme (2 mg nisin+10 mg lysozyme/ml) before in-package pasteurization at 65 °C for 32 s. In-package pasteurization resulted in an immediate 3.5-4.2 log CFU/cm reduction in L. monocytogenes population for all treatments. All pasteurized treatments also resulted in a significant reduction of L. monocytogenes by 12 weeks compared to un-pasteurized bologna. In-package pasteurization in combination with nisin or nisin-lysozyme treatments was effective in reducing the population below detectable levels by 2-3 weeks of storage. Results from this study could have a significant impact for the industry since a reduction in bacterial population was achieved by a relatively short pasteurization time and antimicrobials reduced populations further during refrigerated storage

Effect of combining nisin and/or lysozyme with in-package pasteurization on thermal inactivation of Listeria monocytogenes in ready-to-eat turkey bologna

Achieving a targeted lethality with minimum exposure to heat and preservation of product quality during pasteurization is a challenge. The objective of this study was to evaluate the effect of nisin and/or lysozyme in combination with in-package pasteurization of a ready-to-eat low-fat turkey bologna on the inactivation of Listeria monocytogenes. Sterile bologna samples were initially treated with solutions of nisin (2 mg/ml = 5,000 AU/ml = 31.25 AU/cm), lysozyme (10 mg/ml = 80 AU/ml = 0.5 AU/cm), and a mixture of nisin and lysozyme (2 mg/ml nisin + 10 mg/ml lysozyme = 31.75 AU/cm). Bologna surfaces were uniformly inoculated with a Listeria suspension resulting in a population of approximately 0.5 log CFU/cm . Samples were vacuum packaged and subjected to heat treatment (60, 62.5, or 65°C). Two nonlinear models (Weibull and log logistic) were used to analyze the data. From the model parameters, the time needed to achieve a 4-log reduction was calculated. The nisin-lysozyme combination and nisin treatments were effective in reducing the time required for 4-log reductions at 62.5 and 65°C but not at 60°C. At 62.5°C, nisin-lysozyme-treated samples required 23% less time than did the control sample to achieve a 4-log reduction and 31% less time at 65°C. Lysozyme alone did not enhance antilisterial activity with heat. Results from this study can be useful to the industry for developing an efficient intervention strategy against contamination of ready-to-eat meat products by L. monocytogenes