(Georgia Institute of Technology, 2018-04-26)
Richter, Stephanie
The poultry industry is an integral part of Georgia’s economy, accounting for more than half of the state’s agricultural output. In Georgia, more than 20 million pounds of broiler meat are produced daily. Poultry processing entails many phases, and this thesis focuses upon the immersion chilling step. The chilling phase is critical to reducing pathogen presence and ensuring meat product shelf-life. Immersion chilling consumes intense amounts of water and energy resources, and the industry is trying to discover more efficient approaches for processing. This thesis is based upon a multi-year project investigating ice slurry as an alternative chilling medium for the poultry industry. Ice slurry is composed of small characteristic length ice particles and a salt-brine solution that acts as a freezing point depressant. The salt is an important component in maintaining the ice slurry in a homogenous state (i.e., reduce ice agglomeration and media separation). Ice slurry is hypothesized to provide a disruptive scrubbing/abrasive phenomenon resulting in greater pathogen reduction compared to tradition chilled water medium.
Pathogen reduction experiments were conducted to determine the Salmonella pathogen reduction capability of chilled water and ice slurry on whole carcasses and wing-parts. Pathogen reduction experiments combined experimental factors of: peracetic acid (PAA) antimicrobial concentration, media salinity, time of immersion chilling, and air agitation levels. Treatment combinations were compared to discover the optimum relationship between factors resulting in the best reduction from STR concentrations pre- and post-chilling. The project also investigated the salt-uptake tendencies of whole carcasses during immersion chilling. Whole carcasses, without the giblets (WOGs) were chilled by either air chill, chilled water, or 4.5% salinity chilled water. Post-chilling, three sample types were collected per each carcass (breast skin, white meat, and dark meat). Results initially addressed salt-uptake concerns when ice slurry medium is used for immersion chilling. Initial findings indicated that salt concentrations increased in the skin, yet did not affect white or dark meat. The skin acts as a barrier that prevents salt penetration into the white and dark meat, furthering the consideration of ice slurry as a poultry chilling medium.
(Georgia Institute of Technology, 2017-12-14)
Hoffmann, Tobias
Vibrio cholerae is a human pathogen that causes the severe diarrheal disease cholera, but can also inhabit aquatic environments. The type-VI secretion system (T6SS) is a macromolecular contractile machine that injects neighboring cells with cytotoxic effector proteins. Clinical strains of V. cholerae express the T6SS only when exposed to high cell density and starvation conditions in the presence of chitin, a process regulated by the master regulator QstR. The atypical clinical strain V52 expresses its T6SS constitutively, a trait shared by many V. cholerae strains isolated from the environment. Recently it was discovered that the TfoY regulator controls T6SS expression independent of QstR in V52. In examining strains from environmental sources, I found that one constitutive environmental strain is also under TfoY control. However, I also uncovered that T6SS-mediated constitutive killing in four additional environmental strains was unaffected by a tfoY deletion. Furthermore, I demonstrated that other known regulators (TfoX, QstR, OscR) also played no role in T6SS expression in these strains. For example, the environmental strain BGT69 remains capable of T6SS-mediated killing when these four known T6SS regulators were deleted. These results suggest the presence of a novel regulatory pathway(s) for type-VI secretion in this and other environmental strains of V. cholerae.