Degree Type


Date of Award


Degree Name

Doctor of Philosophy


Food Science and Human Nutrition

First Advisor

Dennis G. Olson


Radiation resistance of Listeria monocytogenes Scott A in ground pork patties, packaged in air and under vacuum, was studied. The patties were irradiated, using an electron accelerator, at the irradiation temperatures of 2°C and 48°C. Lower numbers of L. monocytogenes Scott A were recovered when irradiation was carried out at 2°C and the aerobic condition was secured during irradiation and recovery. The order of radiation sensitivity from low to high was obtained from the combination treatments of heated/vacuum > refrigerated/vacuum > heated/air > refrigerated/air suggesting a thermorestoration at 48°C. D-values of 0.42, 0.37, 0.36, 0.31 kGy were found from these treatments respectively;Storage-life extension of un-inoculated ground pork, irradiated at 1kGy, was studied utilizing similar treatments. Irradiation reduced mesophilic, psychrotrophic, and lactic acid bacteria by 1.5, 1.5, and 1.2 log cycles respectively. Non-irradiated samples, packaged in air, reached the spoilage level within 5 days (refrigerated samples) to 6 days (heated) when stored at 2°C. Their vacuum packaged counterparts reached the spoilage level between 16 (refrigerated) to 26 days (heated). Irradiation appeared to extend the storage-life of ground pork for an extra 18 and 25 days (total storage-life = 23 and 31 days) in the refrigerated/air and heated/air-packaged samples. In vacuum-packaged samples, irradiation added the storage-life of 9 (heated) and 10 days (refrigerated) to the total storage-life of 35 and 26 days;Sensory evaluation of ground pork receiving similar treatments was carried out. In uncooked samples, untrained panelists preferred (p 0.05) in irradiated samples, and particularly very high (13 mg malonaldehyde/1000 g on week 4) in the refrigerated/air-packaged pork. However, their flavor and aroma preference scores, were not significantly (p > 0.05) different. The treatment that showed the longest shelf-life and overall high preference scores, in all attributes, was vacuum packaging followed by irradiation at 48°C.



Digital Repository @ Iowa State University,

Copyright Owner

Usana Navanugraha



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157 pages