Date of Graduation

8-2023

Document Type

Dissertation

Degree Name

Doctor of Philosophy in Food Science (PhD)

Degree Level

Graduate

Department

Food Science

Advisor/Mentor

Subbiah, Jeyamkondan

Committee Member

Acuff, Jennifer C.

Second Committee Member

Atungulu, Griffiths G.

Third Committee Member

Villa-Rojas, Rossana

Fourth Committee Member

Li, Yanbin

Keywords

Antimicrobial intervention; Food safety; Low moisture foods; Salmonella

Abstract

High heat resistance and long survival of Salmonella in low moisture food ingredients (LMFIs) such as spices and seeds are concerning as they are typically consumed without cooking. Therefore, it is challenging to effectively inactivate pathogenic bacteria without negatively impacting the quality of the treated product. This dissertation aimed to develop and evaluate novel intervention technologies: in-package radiofrequency steaming and non-thermal gaseous technologies to improve the microbial safety of LMFIs. The dissertation can be divided into three parts. The first part of this dissertation on the thermal inactivation kinetics of Salmonella and a surrogate, Enterococcus faecium NRRL B-2354on black pepper powder indicated that microbial inactivation increased with increasing treatment temperature and water activity. Inoculation protocol also influenced the heat resistance of Salmonella where inoculation of black peppercorns pre-grinding had higher D-values compared to those inoculated post-grinding. The second part of this dissertation aimed at developing an in-package pasteurization process to inactivate Salmonella enterica in spices (black peppercorn) and herbs (dried basil leaves). During RF heating, the one-way steam vent enabled the accumulation of steam inside the package improving the heating uniformity before venting off excess steam. In-package radiofrequency steaming reduced Salmonella below detection levels on dried basil leaves within 35 s in a bottle sealed with a steam vent and 40 s in polymer packages with steam-vent and on black peppercorns within 155 s in a polymer package. A single intervention technology is not fit for all LMF matrices. Thermal processing would not be feasible for chia seeds due to the potential oxidation of fats and gelling in the presence of moisture. Therefore, the third part of the study explored non-thermal antimicrobial gaseous technologies, such as chlorine dioxide (ClO2), and ethylene oxide (EtO) gas on the decontamination of chia seeds. The developed response surface model suggested that an increase in gas concentration, relative humidity, and treatment time enhanced the microbial reduction on chia seeds. At gas concentration of 10 mg/L and 80% RH over a 5 h exposure period; Salmonella and E. faecium populations were reduced by 3.7 ± 0.2 and 3.2 ± 0.3 log CFU/g, respectively. Mild heating at 60 °C after ClO2 (90 %RH, 3 mg/L for 2 h) followed by ambient storage for seven days enhanced the inactivation to achieve 5-log reduction. The quality of treated products was not significantly impacted except for an increase in peroxide value after ClO2 treatment. EtO inactivation was faster than ClO2 treatment on chia seeds providing more than 5 log reduction of Salmonella within 10 minutes at 50% RH and 60 °C without significantly affecting its quality. E. faecium was a suitable surrogate for Salmonella in all intervention technologies investigated in this study. The developed predictive models would benefit food industries in identifying the process parameters for improving LMFIs safety without altering the nutritional and sensorial qualities of food.

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