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SURVIVAL AND ATTACHMENT OF SALMONELLA ENTERICA ON ALMOND, HAZELNUT, AND BLACK PEPPER
Title
SURVIVAL AND ATTACHMENT OF SALMONELLA ENTERICA ON ALMOND, HAZELNUT, AND BLACK PEPPER
Creator
Zhai, Yang
Date
2016, 2016-05
Description
S. Enteritidis (SE) and S. Typhimurium (ST) are the two most common Salmonella enterica serovars that cause foodborne illnesses in U.S....
Show moreS. Enteritidis (SE) and S. Typhimurium (ST) are the two most common Salmonella enterica serovars that cause foodborne illnesses in U.S. Outbreaks of these serovars have been attributed to low moisture foods such as nuts and spices. However, little is known about the mechanisms of attachment on low moisture food surfaces. This study evaluated the associations between attachment and survival of Salmonella enterica serovars, storage temperatures, and surface characteristics of selected food samples. In the study, S. Enteritidis PT4 and S. Typhimurium LT2 were inoculated onto the surfaces of black peppercorns, almonds and hazelnuts at ~108 CFU/g. After 2 h air-drying, samples were stored at 4 and 25°C with 58 ± 2% relative humidity for up to 14 d. At specific time points, the food sample were washed two times in 1 × Phosphate Buffered Saline (PBS) to remove attached bacterial cells. The bacterial suspensions were serially diluted and plated on Brain Heart Infusion (BHI) and Xylose Lysine Deoxycholate (XLD) agar plates for enumeration. Significant differences (P<0.05) were found in the survival and attachment of SE and ST under all the conditions. ST can survive and attach better than SE at both 4 and 25°C. The decline rates on almonds, hazelnuts, and black peppercorns at 25°C were 0.348 ± 0.017, 0.273 ± 0.015, and 0.196 ± 0.017 log CFU/g per day for SE and 0.077 ± 0.008, 0.157 ± 0.008, and 0.048 ± 0.005 log CFU/g per day for ST, respectively. The attachment rates on almonds, hazelnuts and black peppercorns at 25°C were 18.71 ± 14.38, 1.56 ± 1.50, and 4.68 ± 0.76% for SE and 38.46 ± 11.32, 18.45 ± 7.73, and 56.30 ± 14.72% for ST, respectively. In addition, low temperature (i.e. 4°C) may contribute more to the survival of Salmonella than ambient temperature (i.e. 25°C). Certain surface characteristics (roughness & hydrophobicity) of hazelnut may probably result in weaker attachment of both Salmonella serovars. The results can be used to better understand the physiology of Salmonella enterica on low moisture foods and aid in developing effective control measures to reduce pathogen contamination.
M.S. in Food Safety and Technology, May 2016
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SALMONELLA SURVIVAL DURING INOCULATION AND STORAGE OF DRIED SPICES CONTAINING ANTIMICROBIAL COMPONENTS
Title
SALMONELLA SURVIVAL DURING INOCULATION AND STORAGE OF DRIED SPICES CONTAINING ANTIMICROBIAL COMPONENTS
Creator
Hu, Chuxuan
Date
2016, 2016-05
Description
To provide an adequate initial microbial level for spices containing antimicrobial compounds for use in stability testing of foodborne...
Show moreTo provide an adequate initial microbial level for spices containing antimicrobial compounds for use in stability testing of foodborne pathogens, a dry-transfer inoculation was designed and compared with a traditional aqueous inoculation protocol. A five serovar cocktail of Salmonella spp. was prepared at different concentrations (~11 log CFU/mL, ~8 log CFU/mL and ~4 log CFU/mL). It was inoculated onto 1g silica beads and four types of dried ground spices (clove, oregano, ginger, and black pepper). Both spices and beads were dried for 24h at ambient conditions (~22°C). Silica beads were then used as a carrier to inoculate the same four types of spices. The results suggest that dry-transfer of Salmonella via inoculated silica beads provided a greater starting inoculum than aqueous transfer alone and are a viable alternative to aqueous inoculation when spices contain antimicrobial components. This dry-transfer inoculated ground clove with 8.4 log CFU/g and 3.9 log CFU/g initial populations was then used to determine the survival of Salmonella on spices containing antimicrobial components. Salmonella spp. survival on silica beads with 9.2 log CFU/g and 5.9 log CFU/g initial populations and subsequent transfer to ground clove was also examined. Samples were enumerated at selected time point up to 210 d. Results of this study indicate that Salmonella transfer and recovery from beads and in ground clove was not affect by storage and that Salmonella may persist for an extended period of time. The calculation of recovery was, however, affected by detection limits in clove. To improve detection limits an oil extraction was used and compared to the BAM method (detection limit 3.7 log CFU/g). After oil extraction the clove samples were soaked for 1 h (or 24 h for low inoculum concentration) in TSB at 37ᵒC and subsequently enumerated on tryptic soy agar with 0.6% yeast extract and xylose lysine deoxycholate agars. The result demonstrates that the oil extraction detection method holds promise as an alternative method to detect Salmonella in dry spices containing antimicrobial components and can provide a lower detection limit (1.7 log CFU/g).
M.S. in Food Process Engineering, May 2016
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