Food Science and Technology Department
Date of this Version
Low-moisture foods contaminated with Salmonella spp. have been implicated in several foodborne illness outbreaks in the United States. The food industry has to incorporate preventive control in their process and validate thermal processes to assure food safety. The thermal destruction of Enterococcus faecium ATTC 8459 and Salmonella spp. was determined at 3 water activity levels (0.11, 0.18 and 0.33) at 80ºC, 85ºC and 90ºC. Aerobic plates counts petrifilms were used as non-selective medium for both bacteria, Enterobacteriaceae petrifilms were used as selective medium for Salmonella spp., and peptone water modified with sodium azide as a selective medium for Enterococcus faecium. Significant differences were observed for both organisms between the two media with higher D-values on the non-selective medium (p Salmonella spp. were 112.87 min, 61.01 min and 32.36 min at 80ºC, 85ºC and 90ºC, respectively in wheat flour at water activity of 0.11. At water activity of 0.18, the D-values of Salmonella spp. were 59.05 min, 30.90 min and 18.78 min at 80ºC, 85ºC and 90ºC, respectively. The D-values of Salmonella spp. were 25.10 min, 13.25 min and 6.22 min at 80ºC, 85ºC and 90ºC, respectively at aw 0.33. Higher D-values were observed for Enterococcus faecium ATTC 8459 compared to Salmonella spp., at all the conditions of the study, with no significant differences (p≥0.05), except at the water activity of 0.18 at 85ºC (pEnterococcus faecium ATTC 8459 were 117.97 min, 64.31 min and 38.24 min at 80ºC, 85ºC and 90ºC, respectively in wheat flour at water activity of 0.11. At water activity of 0.18, the D-values of Enterococcus faecium ATTC 8459 were 65.26 min, 50.49 min and 19.17 min at 80ºC, 85ºC and 90ºC, respectively. The D-values of Enterococcus faecium ATTC 8459 were 29.01 min, 15.09 min and 9.71 min at 80ºC, 85ºC and 90ºC, respectively at water activity of 0.33. The z-values were determined at each water activity, and there were no significant differences between the three (3) water activities (p≥0.05). Salmonella spp. and Enterococcus faecium had approximately the same z-values. The z-values of Salmonella spp. ranged from 16.53 to 18.50ºC, while the z-values of Enterococcus faecium ranged from 18.80 to 21.61ºC. These results suggest that Enterococcus faecium ATTC 8459 can be used as a surrogate for Salmonella spp. in wheat flour at the three levels of water activity used in the study.
Advisors: Harshavardhan Thippareddi & Jeyamkondan Subbiah
A THESIS Presented to the Faculty of The Graduate College at the University of Nebraska In Partial Fulfillment of Requirements For the Degree of Master of Science, Major: Food Science and Technology, Under the Supervision of Professors Harshavardhan Thippareddi and Jeyamkondan Subbiah. Lincoln, Nebraska: December, 2015
Copyright (c) 2015 Didier Dodier