Date of Award


Document Type


Degree Name

Doctor of Philosophy (PhD)

Legacy Department



Annel K. Greene

Committee Member

Thomas A. Hughes

Committee Member

Xiuping Jiang

Committee Member

Paul L. Dawson


This study tested enumeration techniques for high fat food matrices and determined thermal death times in rendering animal products. Standard Class O phosphate/magnesium chloride dilution buffer series (Dilution Series A) and a modified (pre-warmed to 32oC) lecithin phosphate dilution buffer series (Dilution Series B) were used to enumerate a Salmonella cocktail from both poultry and beef rendering materials. Results of this study indicate use of a modified lecithin buffer did not improve Salmonella enumeration accuracy from rendering materials. Instead, the results suggested use of xylose lysine deoxycholate agar (XLD) with either buffer system accurately enumerated Salmonella from rendering materials. The thermal death of four pathogenic strains of Salmonella recognized by the FDA as hazardous in animal feeds (Salmonella Choleraesuis (SC), Salmonella Enteriditis (SE), Salmonella Newport (SN), and Salmonella Dublin (SD)) was not a straight line decrease. After periods of appearing to be destroyed, some cultures reappeared at later treatment times. In thermal treatments up to 420 s at 240oF (115.6oC), SC was last detected at 120 s, SE at 120 s, SN at 300 s and SD at 360 s in inoculated beef rendering materials. In thermal treatments up to 420 s at 240oF (115.6oC), SC, SE, SN, and SD were last detected at 360 s, respectively, in inoculated poultry rendering materials. Controls indicated thermally resistant strains in the background of both beef and poultry rendering materials which when tested using standard FDA Bacteriological Analytical Manual (BAM) techniques indicated Salmonella . Hypotheses to explain the results of this study include: 1) thermally resistant sub-particles such as bone or tissue protected bacteria from thermal treatment; 2) presence of thermally resistant species in the background of rendering samples caused false positive results on BAM procedures; or 3) presence of thermally resistant Salmonella . Further research will need to be conducted at 240oF (115.6oC) for longer time intervals to ensure that SC, SE, SN and SD are destroyed and to identify the impact of particles on thermal conductivity through the rendering matrices. Additionally, future experimentation will be needed to verify that the microorganisms identified are indeed Salmonella or other another microorganism(s) cross-reacting as Salmonella .

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Microbiology Commons