Degree Type


Date of Award


Degree Name

Doctor of Philosophy


Food Science and Human Nutrition

First Advisor

Dennis G. Olson

Second Advisor

Deland Myers


The effects of various modified gas atmospheres on the microbiological, physical and chemical characteristics of fresh red meats (pork chops, beef steak and ground beef) were studied. Fresh pork chops were packaged in air, vacuum or eleven modified gas atmospheres containing carbon dioxide and oxygen concentrations from 0% to 40%. Increasing the initial CO[subscript]2 concentration delayed growth of aerobic psychrotrophic and mesophilic bacteria, and Enterobacteriaceae, but slightly enhanced that of lactic acid bacteria. Increasing the initial O[subscript]2 concentration reduced growth of facultative anaerobic and anaerobic bacteria and enhanced growth of Brochotrix thermosphacta. In general, carbon dioxide had more influence on the microbiological storage life of the chops than oxygen. Increasing the CO[subscript]2 concentration also reduced the redness of the chops, increased purge losses and promoted lipid oxidation, but retarded the formation of volatile basic nitrogen. Increasing the O[subscript]2 concentration also increased lipid oxidation. Modified gas atmospheres with 20% CO[subscript]2 or more were superior to air for extending the microbiological storage life of fresh pork chops. Gas mixtures containing 40% CO[subscript]2 with or without O[subscript]2 had better performance than vacuum in delaying growth of psychrotrophic and mesophilic bacteria and Enterobacteriaceae during 21 days of storage. Vacuum was more effective in reducing lipid oxidation than modified atmospheres, but the latter greatly reduced purge losses;Listeria monocytogenes and Yersinia enterocolitica grew on inoculated pork chops stored in atmospheres consisting of three gas mixtures, vacuum and air. Doubling the CO[subscript]2 concentration reduced the growth rate of L. monocytogenes and increased that of Y. enterocolitica, but not significantly. Increasing the O[subscript]2 concentration reduced the growth rates of L. monocytogenes and Y. enterocolitica. Vacuum packaging was more effective than gas mixtures in slowing down the growth of L. monocytogenes or Y. enterocolitica;Fresh meat were treated with a mixture of color maintenance substances, packaged in a 50%CO[subscript]2/15%O[subscript]2/35%N[subscript]2 gas mixture, and stored at 2°C under conditions simulating wholesale distribution, followed by retail display at 2°C. The chemical treatment in combination with modified atmosphere storage did not select for the growth of naturally occurring pathogenic microorganisms. (Abstract shortened with permission of author.)



Digital Repository @ Iowa State University,

Copyright Owner

Wireko Manu-Tawiah



Proquest ID


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File Size

303 pages