The pathogenic microorganism Salmonella enterica has been associated with several outbreaks and recalls of spices, herbs, and seeds. To control these pathogens additional treatment methods, such as fumigation with chlorine dioxide (ClO2) or hydrogen peroxide (H2O2) gas and recovery methods are needed. Recovery methods should accurately quantify all viable cells, even those injured, to prevent overestimation of treatment effectiveness. This study was performed to determine the effect of different recovery media and supplements on the recovery of multiple strains of S. enterica and Enterococcus faecium NRRL B2354, from chlorine dioxide or hydrogen peroxide treated low moisture foods (LMF) black peppercorns, dried basil leaves, and chia seeds. Also, this study aimed to compare the log reduction of these two microorganisms to evaluate E. faecium NRRL B2354 as a surrogate for S. enterica. On average, recovery of S. enterica was 3.43 log and 4.77 log CFU/g from ClO2 and H2O2 treated LMFs, respectively on the selective media Xylose Lysine Deoxycholate agar, while the average recovery on non-selective media was 4.50 log CFU/g and 5.74 log CFU/g from ClO2 and H2O2 treated LMFs, respectively. The use of non-selective media was correlated with increased recovery compared to selective media. In further studies, addition of sodium pyruvate, ferrous sulfate, or 3'3'-thiodiproionate supplements to MTSAYE did not show increased recovery (P>0.05). On each treatment and LMF combination tested, there was no significant difference between the log reduction of S. enterica and E. faecium NRRL B2354, indicating its suitability as a surrogate under the test conditions. / Master of Science in Life Sciences / Spices, dried herbs, and seeds have become popular throughout the world for enhancing the flavor of food, but may also harbor harmful bacteria, including Salmonella enterica. It is US federal law under the Food Safety Modernization Act that these foods are safe to eat straight from processors since these foods are typically consumed raw. Novel treatment methods are being tested to kill harmful bacteria on these dried foods without adding water including chlorine dioxide fumigation and hydrogen peroxide fumigation. However, these processes can injure the bacteria without killing them. These injured bacteria might not be counted using traditional means which could lead to overestimating the effectiveness of a treatment. Different media types, used as part of the process to count the number of bacteria in a sample, were tested to determine their effect on recovery of injured S. enterica cells. Furthermore, the bacterium Enterococcus faecium NRRL B2354 was tested against S. enterica to evaluate, if the former, a relatively harmless microorganism, could be used by food processing plants to determine that their treatment processes meets regulatory standards. More injured S. enterica cells were recovered from each non-selective media tested, compared to the selective media. Although there isn't a significant difference in injured S. enterica recovery between any supplemented non-selective media, any non-selective media recovers more sub-lethally injured cells, and would give more accurate bacterial counts. Results also indicated that E. faecium NRRL B2354 is a suitable surrogate to the pathogen S. enterica for spices and herbs processed under the same conditions.
| Identifer | oai:union.ndltd.org:VTETD/oai:vtechworks.lib.vt.edu:10919/110836 |
| Date | 17 June 2022 |
| Creators | Garcia, Jose Octavio |
| Contributors | Food Science and Technology, Ponder, Monica A., Strawn, Laura K., Eifert, Joseph D. |
| Publisher | Virginia Tech |
| Source Sets | Virginia Tech Theses and Dissertation |
| Language | English |
| Detected Language | English |
| Type | Thesis |
| Format | ETD, application/pdf |
| Rights | In Copyright, http://rightsstatements.org/vocab/InC/1.0/ |
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