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STUDY OF SALMONELLA SURVIVAL ON THE SURFACE OF FRUITS
Title
STUDY OF SALMONELLA SURVIVAL ON THE SURFACE OF FRUITS
Creator
Sui, Ke
Date
2017, 2017-05
Description
Salmonella enterica has been frequently linked to the major foodborne disease outbreaks. The molecular mechanisms underlying this pathogen...
Show moreSalmonella enterica has been frequently linked to the major foodborne disease outbreaks. The molecular mechanisms underlying this pathogen survival on the fresh fruit surface remain largely unexplored. In this study, the environmental factors that affect the survival of Salmonella strains on the surface of selected fruits were studied. Grape tomatoes (or cantaloupe peels) were inoculated in three separate trials with 1 mL Salmonella enterica serotypes Enteritidis or Typhimurium (approximately 1010-11 CFU/mL). Storage of grape tomatoes at 4 ℃ resulted in significant decrease in populations of S. Enteritidis; this trend was observed at both of the tested relative humidity with the D-value as 7.25±1.05 d and 7.28±2.34 d, respectively. At different temperatures, relative humidity only had marginal effects on the bacterial survival on the surface of grape tomato and cantaloupe. In addition, S. Typhimurium apparently survived better than S. Enteritidis on the surface of grape tomato. Furthermore, a transposonmutagenesis library with random transposon insertion mutants of S. Enteritidis and high-throughput sequencing analysis showed that the expression of genes rcsB and nlpD were hypothesized to be associated with the survival of S. Enteritidis on grape tomatoes. Inframe deletions of the two genes in S. Enteritidis were constructed by lambda red recombinase system and respective complementation mutants were also obtained for identification of the contribution of the two genes to the bacterial survival on the surface of grape tomato. Thus, this study provided microbiological and molecular microbiological basis to probe the roles of putative genes in Salmonella enterica survival on the surface of fresh fruits.
M.S. in Food Safety and Technology, May 2017
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GROWTH AND SURVIVAL OF SALMONELLA IN PARTIALLY SPROUTED PUMPKIN, SUNFLOWER, AND CHIA SEEDS SUBSEQUENTLY DRIED FOR DIRECT CONSUMPTION
Title
GROWTH AND SURVIVAL OF SALMONELLA IN PARTIALLY SPROUTED PUMPKIN, SUNFLOWER, AND CHIA SEEDS SUBSEQUENTLY DRIED FOR DIRECT CONSUMPTION
Creator
Wang, Can
Date
2017, 2017-05
Description
Products based on dried, partially sprouted seeds have been associated with foodborne salmonellosis. Typically, sprouted seeds have been a...
Show moreProducts based on dried, partially sprouted seeds have been associated with foodborne salmonellosis. Typically, sprouted seeds have been a major concern with respect to foodborne illness, but little is known about the risks associated with dried partial sprouted seed products. Previous studies suggest that low-temperature, highhumidity storage conditions may provide an alternative means to inactivate Salmonella for those processors opposed to traditional thermal processing. The objective of this study was to determine the growth of Salmonella during germination of pumpkin, sunflower, and chia seeds, and the survival of Salmonella during drying and storage under variable temperature and relative humidity (RH) conditions. Pumpkin, sunflower, and chia seeds were dry inoculated at 5 log CFU/g with 4 serotype mixture of Salmonella using a dry transfer method, and then soaked in sterile water at 25 and 37°C for 24 h. Salmonella and total aerobic mesophilic plate counts (APC) were determined on xylose lysine deoxycholate (XLD) and tryptic soy agar supplemented with 0.6% yeast extract (TSAYE), respectively. Seeds using this procedure were drained and dried at 25, 51 and 60°C. The water activity (aw) and microbial population of seeds were monitored during drying. Seeds soaked and dried at 25oC were utilized for subsequently storage studies. Portions of dried chia seeds were ground into powder, then pumpkin, sunflower and chia seeds and chia seeds powder were stored at either 37 or 45oC at three different RH levels. The aw and microbial population of seed samples were monitored during storage. During the seed soaking, Salmonella and APC increased approximately 3 log CFU/g. Some decreases were observed at the end of the growth period, as may be expected after stationary phase. Drying at 60oC to a aw of 0.1 resulted in over 6-log CFU/g loss in bacterial population in partially sprouted pumpkin and sunflower seeds, and 5-log CFU/g loss in partially sprouted chia seeds. However, seeds dried at 25oC bring the aw to 0.5 had only approximately a 1-log CFU/g loss in bacterial population. The highest temperature (45oC) and RH (76%) storage condition had the greatest inactivation effect. At 45oC and 76%RH, Salmonella in pumpkin and sunflower seeds were below detection limit after 4 d and 7 d respectively. Salmonella populations in chia seeds and chia seeds powder were still detectable after 7 d regardless of the treatment condition. Salmonella is capable of survival during the manufacture of partially sprouted seeds including both drying and storage steps. Mild thermal treatment coupled with high RH storage condition holds promise for Salmonella inactivation in pumpkin and sunflower seeds but is less effective for chia seeds and chia seeds powder. Dried, partially sprouted seeds that are used as ingredients or consumed directly without further processing are a high-risk food product. Such products must be treated to eliminate foodborne pathogens that may cause foodborne illness.
M.S. in Food Science, May 2017
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