Radiosensitization of Escherichia coli and Salmonella typhi in presence of active compounds
Introduction
Irradiation is a process with excellent potential to control or eliminate foodborne pathogens in food. According to the microbiological hurdle concept (Suresh et al., 1992), the combination of irradiation in presence of various natural or synthetic active compounds would help to increase the radiosensitization of food pathogens, such as Escherichia coli and Salmonella typhi (Lacroix and Ouattara, 2000; Giroux et al., 2001; Kim et al (1995a), Kim et al (1995b); Mahrour et al., 2003). The objective of this work was to determine the efficiency of various active compounds to improve the radiosensitization of E. coli and S. typhi in ground beef.
Section snippets
Handling of the meat
Ground beef containing 23% of fat was purchased at a local supermarket (IGA, Laval, Qc, Canada) and transported to the Canadian Irradiation Centre (CIC) under refrigerated conditions (4±2°C). The ground beef was vacuum-packed in portions of 450 g, sterilised by irradiation at −80°C according Chiasson et al. (2004).
Preparation of bacterial cultures
E. coli (ATCC 25922) and S. typhi (ATCC 19430) were obtained from the American Type Culture Collection (Rockville, MD, USA) and maintained at −80°C in tryptic soy broth (TSB; Difco
Statistical analysis
The kinetic of bacteria destruction during irradiation treatment in presence of active compounds was evaluated by linear regression. The D10 values were calculated and statistic analysis were done according to Chiasson et al. (2004).
E. coli
The influence of various active compounds on the radiosensitization of E. coli in ground beef is shown in Table 1. Results shows that the irradiation sensitivity of E. coli in ground beef without active compound was 0.126 kGy. The most effective active compound was trans-cinnamaldehyde (1.5%). This compound improve significantly (p⩽0.05) the efficiency of the irradiation treatment was 71%. D10 value was evaluated at 0.037 kGy. The addition of thymol (1.15%) and thyme (2.33%) was also very
Discussion
As determined previously by Helander et al., 1998, trans-cinnamaldehyde has a strong antimicrobial activity. This compound acts by inhibiting the amino acid decarboxylase in target bacteria (Wendakoon and Sakaguchi, 1995). The mechanism by which microorganisms are inhibited by thymol or other phenolic compounds involves a sensitization of the phospholipid bilayer of the cell membrane, causing an increase in permeability and leakage of vital intracellular constituents (Juven et al., 1994) or
Conclusion
The combination of various active compounds and the use of irradiation treatment had a synergistic effect on the irradiation sensitivity of E. coli and S. typhi. For both bacteria, trans-cinnamaldehyde was the most effective compounds in increasing the irradiation sensitivity in ground beef.
Acknowledgements
Authors are grateful to MDS Nordion for their financial support to realize this project, an to Inrs-Institut Armand-Frappier for the postdoctoral fellowship to B.O. We also thank MDS Nordion International for the irradiation operations.
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