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Influence of water activity on processing resistance of Salmonella serovars and implications on sanitization of pistachios by heat and ozone

Pena-Melendez, Marilia
http://rave.ohiolink.edu/etdc/view?acc_num=osu1322610404

Abstract Details

2011, Master of Science, Ohio State University, Food Science and Technology.
Recent salmonellosis outbreaks due to consumption of low moisture foods such as nuts have been well documented. Low water activity (aw) plays an important role in these foods because it limits the growth of microorganisms, especially foodborne pathogens. Additionally, the cross-protective effect that happens in microorganisms when they are exposed to more than one stress condition (e.g. low aw and heat) is well documented and has become a concern to the food industry. The objectives of this study were to: (i) investigate the effect of low aw, physiological state, and type of humectants on the heat resistance of three Salmonella enterica serovars (Saintpaul 02-109, Tennessee 2053H, and Elmsbuettel 1236H); (ii) evaluate the use of a heat-ozone combination treatment to reduce populations of Salmonella Enteritidis on inoculated pistachios, (iii) determine the effect of inoculation method and storage time on the effectiveness of the heat-ozone combination treatments; and (iv) assess the potential of using a heat resistant pistachio isolate, Enterococcus faecium OSY 31284, as a Salmonella surrogate when determining the effectiveness of heat-ozone combination treatments. For the first part of this study, Salmonella serovars that were adapted or non-adapted to low aw were heat-treated at 55°C for up to 45 min; samples were removed at 5 min intervals. Lowering aw was achieved by modifying Tryptic Soy Broth (TSB) composition to contain 20% glycerol (aw 0.94), 4% NaCl (aw 0.97), or 35% sucrose (aw 0.95). Results showed that type of humectant and physiological state (adapted vs. non-adapted) significantly affected Salmonella D55°C-value (P<0.05). Cells adapted in 20% glycerol showed lower D55°C-values, compared to the non-adapted cells. Presence of NaCl and sucrose in the broth had a protective effect under both the adapted and non-adapted conditions for the three serovars tested as compared to glycerol. For the second part of the study, pistachios were inoculated with either Salmonella Enteritidis or E. faecium OSY 31284. In addition to variations in bacterial species, other variables tested were inoculation methods (vacuum and no vacuum) and storage times (24hrs and 72hrs); all possible combinations were performed. Treatments were comprised of heat (5% brine at 70°C for 10 minutes), ozonation (160 g/m3, 12.5 psig, 30 min holding time), heat followed by ozonation or ozonation followed by heat. Populations of the inoculated bacteria were determined before and after treatments. Results showed significant reduction of E. faecium on pistachios when treated with heat-ozone combinations (P<0.05), but the reduction was not significantly greater than that achieved by heat alone. Various treatments inactivated Salmonella Enteritidis to a greater extent than that observed with E. faecium. For both bacteria, the application of gaseous ozone alone showed little reduction. Additionally, inoculation method alone and storage time alone did not have a significant effect on the log reductions of both bacteria. However, the interaction of 72hrs storage and inoculation using vacuum influenced the efficacy of the treatments the most. The data also suggest that E. faecium is not a suitable surrogate for Salmonella when evaluating pistachio decontamination processes, because the survivors of the two bacteria in response to combination treatments differ by more than 2 log/g.
Ahmed E. Yousef, PhD (Advisor)
Luis Rodriguez-Saona, PhD (Committee Member)
Sheryl Barringer, PhD (Committee Member)
84 p.
Food Science
ozone; low water activity; Salmonella; pistachios

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Citations

  • Pena-Melendez, M. (2011). Influence of water activity on processing resistance of Salmonella serovars and implications on sanitization of pistachios by heat and ozone [Master's thesis, Ohio State University]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=osu1322610404

    APA Style (7th edition)

  • Pena-Melendez, Marilia. Influence of water activity on processing resistance of Salmonella serovars and implications on sanitization of pistachios by heat and ozone. 2011. Ohio State University, Master's thesis. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=osu1322610404.

    MLA Style (8th edition)

  • Pena-Melendez, Marilia. "Influence of water activity on processing resistance of Salmonella serovars and implications on sanitization of pistachios by heat and ozone." Master's thesis, Ohio State University, 2011. http://rave.ohiolink.edu/etdc/view?acc_num=osu1322610404

    Chicago Manual of Style (17th edition)

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