Date of Award


Document Type


Degree Name

Master of Science (MS)

Legacy Department

Food, Nutrition, and Culinary Science

Committee Chair/Advisor

Greene, Annel K

Committee Member

Dawson , Paul L

Committee Member

Bodine , Ashby B


The non-pathogenic, heat stabile organism Geobacillus stearothermophilus was used during thermal death time testing of rendered poultry materials from three different rendering plants. G. stearothermophilus is an endospore–forming, Gram positive, thermophilic bacterium that is commonly used in the canning industry. A modification of the method of Kim and Naylor (1966) was used to prepare a G. stearothermophilus spore suspension. Uninoculated and inoculated rendering samples containing 50% fat and rendered crax were prepared. Lecithin and 2,3,5–triphenyl–2H–tetrazolium chloride (TTC) were used during sample enumeration to emulsify the high fat samples and to aid in detection of colonies, respectively. Commercial rendering cookers are reported to process in the temperature range of 240 to 290¡F (115.6 to 143.3¡C). In this experiment, 290¡F (143.3¡C) was used as the temperature in order to determine the maximum impact rendering could have on the heat stable G. stearothermophilus. The temperature selected for this experiment was the most rigorous rendering temperature reportedly used in commercial rendering cookers. Uninoculated and inoculated samples included unheated control and 0 min, 1 min and 2 min heat treatment at 290¡F (143.3¡C). Results of this study indicated that inoculation condition, time, inoculation & time combination, and sample, inoculation & time combination had a strong impact on bacterial populations. Sample & inoculation combination, replications within different sample & inoculation combination, sample difference, and sample and time combination had no significant effect or impact on data. Although G. stearothermophilus provided a valid thermal death time indicator for rendering processing, it may not be the best surrogate for use in the rendering industry for environmental studies since thermophilic bacterial colonies were detected in uninoculated controls. This research study is the first known study on use of surrogate bacteria as an indicator organism to validate the thermal treatment for the rendering industry. Further studies need to be done to provide more scientific data and explanation.

Included in

Food Science Commons



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