Thesis (M.App.Sc.) - University of Queensland, 2004. / Includes bibliography.

Listeria monocytogenes is a pathogenic, psychrotrophic microorganism that is ubiquitous in nature. L. monocytogenes has been isolated from numerous meat products, both fresh and processed, the incidence of contamination varying greatly. The ability of Listeria to grow in meats depends on temperature, pH, water activity (a$ sb{ rm w}$), nutrients, species and numbers of competing microorganisms, gaseous conditions, and levels of additional barriers. Therefore, methods to control the growth of L.monocytogenes are of great importance to food processors since this organism can grow under a wide range of environmental and storage conditions. Two methods of control, in conjunction with temperature, were studied in this project: (i) modified atmosphere packaging (MAP) and (ii) chitosan, to determine the optimum levels of these "hurdles" needed to effectively control the outgrowth of L.monocytogenes in both model broth and agar systems and in fresh pork loin. On the basis of these preliminary studies, a combination of chitosan as a dipping solution and modified atmosphere packaging were investigated to control the growth of L.monocytogenes in fresh pork loin. Pork loin samples were dipped in a 0.2% chitosan solution for 60 seconds and packaged under various atmospheres in Cryovac bags and stored at 5, 10 and 15$ sp circ$C up to 28 days. Samples were monitored for physical, chemical and microbiological changes throughout the storage period. Optimum control over the growth of L. monocytogenes was achieved using a combination of 100%N$ sb2$ + an Ageless FX oxygen absorbent and dipping in a 0.2% chitosan solution. Based on these studies, a combination of 0.2% chitosan and MAP could be used to extend the shelf life of pork without adversely affecting color, odor and exudate loss while inhibiting the growth of the pathogenic microorganism, L.monocytogenes. (Abstract shortened by UMI.)

No description available.

Fresh pork loins were cut for three replications and randomly assigned to one of seven treatments: 1) polyvinylchloride (PVC) packaged, 2) vacuum packaged (Vac-pack), 3) 0.2 mL of Tris-Buffer, 4) 0.2 mL of high leghemoglobin high pH (HLbHpH), 5) 0.2 mL of high leghemoglobin low pH (HLbLpH), 6) 0.2 mL of low leghemoglobin high pH (LLbHpH), and 7) 0.2 mL of low leghemoglobin low pH (LLbLpH). Treatments 3 through 7 also were vacuum packaged. Leghemoglobin (Lb) protein treatments improved (P<0.05) the visual color of vacuum packaged pork at the point of purchase. CIE L* values were not affected by HLbHpH, LLbHpH or LLbLpH treatments. However, the HLbLpH treatment was lighter (P<0.05) than the vacuum packaged control treatments on days 3, 4, and 5. High Lb (HLb) treatments had a positive effect (P=0.0116) on the CIE a* values on the day of manufacture. HLbLpH treatment eIE b* values were higher (P<0.05) than Vac-pack and buffer controls from day 0 to day 5. On the day of processing, HLb treatments were higher (P=0.0637) in oxymyoglobin than low Lb treatments. Metmyoglobin of HLb treatments was higher (P<0.05) than the Vac-pack and the buffer treatments on the day of manufacture. pH did not affect (P>0.05) sensory or objective color, pigment state, purge or total psychrotrophic aerobic bacterial counts (TPC) throughout the study. Lb treatments TPC were lower (P<0.0l) than nontreated samples at all assessment times. / Master of Science