Semester

Spring

Date of Graduation

2009

Document Type

Thesis

Degree Type

MS

College

Davis College of Agriculture, Natural Resources and Design

Department

Animal and Nutritional Sciences

Committee Chair

Kristen Matak

Abstract

Peanut butter and peanut paste products were implicated as the vehicle of contamination in an outbreak of Salmonella Typhimurium that began in September 2008 and in the November 2006 outbreak of Salmonella Tennessee; therefore based on the apparent need for intervention measure, the purpose of this research was to evaluate the effectiveness of non-thermal electron beam irradiation for reduction of Salmonella serovars Tennessee (ATCC 10722) and Typhimurium (ATCC 14028) in creamy peanut butter. Each strain was studied independently. Peanut butter samples were inoculated with approximately 7.0 log CFU/g of Salmonella and exposed to e-beam doses ranging from 0--3.1 kGy. Doses were confirmed using film dosimetry. Survivors were enumerated by standard spread-plating on non-selective (tryptic soy agar; TSA) and selective (xylose lysine deoxycholate agar; XLD) media. Microbial counts (CFU/g) were log-converted and the slopes of the respective survivor curves were determined by linear regression. D10-values were calculated as the negative reciprocal of the slope of the survivor curve and were reported as mean values +/- standard deviation. One-way analysis of variance and Tukey's honestly significant difference test were used to determine differences. D10-values show that Salmonella Typhimurium was more resistant (0.82 +/- 0.02 and 0.73 +/- 0.01 kGy on TSA and XLD, respectively) than Salmonella Tennessee (0.72 +/- 0.02 and 0.60 +/- 0.01 kGy on TSA and XLD, respectively) to e-beam irradiation (P<0.05). The recovery on growth and selective media was different (P<0.05), indicating cell injury. Microbial analyses were conducted after 4, 6, 8, and 14 d of storage. The rate of microbial decline was significant over the 14 d storage period (P<0.05); the greatest reductions were seen at target e-beam dose 2.5 kGy at day 14 (P<0.05). Salmonella Tennessee and Salmonella Typhimurium mean survivor populations exposed to e-beam irradiation in peanut butter will decline overtime. E-beam irradiation may be an effective processing step for the non-thermal inactivation of Salmonella in peanut butter.

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