Inactivation of Wild-type, Rifampicin-resistant, and Pressure-adopted Foodborne Bacteria of Public Health Concern and Microbial Spores Using Elevated Hydrostatic Pressure
Recent improvements in commercial feasibility of high pressure pasteurization units has promoted the technological acceptability across various sectors of food manufacturing, resulting in the requirement of extensive validation studies for effective adoption. The main curtailment of the technology is limited efficacy for inactivation of microbial spores. The first study of this dissertation investigated the decontamination of mesophilic background microflora and inoculated Salmonella in orange juice using elevated hydrostatic pressure. Various times (1 min to 10 min) and intensity levels (0 MPa to 380 MPa) of elevated hydrostatic pressure were used. Treatments below two minutes were less efficacious (p ≥ 0.05) against the pathogen and background microflora, in most time and pressure combinations. The second study is a summary of microbiological hurdle validation studies to investigate synergism of mild heat (up to 55 °C) and elevated hydrostatic pressure (up to 380 MPa) for decontamination of Listeria monocytogenes and natural background microflora in raw milk. Treatments below three minutes were less efficacious (p ≥ 0.05) against the pathogen and background microflora, in the most time and pressure combinations. Results of this study could influence a risk-based food safety management system and risk assessment analyses for mitigating the public health burden of listeriosis. The third study discussed growth of the two pathogenic species on abiotic surface and validates a decontamination intervention against wild-type and pressure-stressed phenotypes of the bacteria. Over 4.0 log CFU/cm2 multiplication (p<0.05) of the bacterial biofilms were observed with decontamination intervention more efficacious (p<0.05) on earlier stages of the aggregate cells relative to mature biofilms. The fourth study investigated synergism of elevated hydrostatic pressure, mild heat, and two antimicrobials (nisin and lysozyme) for inactivation of three spore suspensions. Results of this study indicate an optimized pressure-based intervention in presence of mild heat and antimicrobial agents that could be efficacious for inactivation of >99% of microbial spores. The last study investigated the effect of lactic acid and elevated pressure against wild-type and rifampicin-resistant O157 and non-O157 shiga toxin-producing Escherichia coli. Results of this study indicate lactic acid could appreciably enhance decontamination efficacy of high pressure against Shiga toxin-producing Escherichia coli.
Food Science|Public health
"Inactivation of Wild-type, Rifampicin-resistant, and Pressure-adopted Foodborne Bacteria of Public Health Concern and Microbial Spores Using Elevated Hydrostatic Pressure"
ETD Collection for Tennessee State University.