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Applied and Environmental Microbiology, April 2009, p. 1901-1907, Vol. 75, No. 7
0099-2240/09/$08.00+0     doi:10.1128/AEM.02531-08
Copyright © 2009, American Society for Microbiology. All Rights Reserved.

Elimination of Escherichia coli O157:H7 from Alfalfa Seeds through a Combination of High Hydrostatic Pressure and Mild Heat{triangledown}

Hudaa Neetoo,1 Thompson Pizzolato,2 and Haiqiang Chen1*

Department of Animal and Food Sciences, University of Delaware, Newark, Delaware 19716-2150,1 Department of Plant and Soil Sciences, University of Delaware, Newark, Delaware 19716-13032

Received 5 November 2008/ Accepted 2 February 2009

Escherichia coli O157:H7 has been associated with contaminated seed sprout outbreaks. The majority of these outbreaks have been traced to sprout seeds contaminated with low levels of pathogens. Sanitizing sprout seeds presents a unique challenge in the arena of produce safety in that even a low residual pathogen population remaining on contaminated seed after treatments appears capable of growing to very high levels during sprouting. In this study, the effectiveness of high-pressure treatment in combination with low and elevated temperatures was assessed for its ability to eliminate E. coli O157:H7 on artificially contaminated alfalfa seeds. Inoculated seed samples were treated at 600 MPa for 2 min at 4, 20, 25, 30, 35, 40, 45, and 50°C. The pressure sensitivity of the pathogenic bacteria was strongly dependent on the treatment temperature. At 40°C, the process was adequate in eliminating a 5-log-unit population on the seeds with no adverse effect on seed viability. Three treatments carried out at reduced pressure levels and/or extended treatment time, 550 MPa for 2 min at 40°C, 300 MPa for 2 min at 50°C, and 400 MPa for 5 min at 45°C, were equally lethal to the pathogen. When all three treatments were compared in terms of their impact on seed viability, the process of 550 MPa for 2 min at 40°C was the most desirable, achieving final germination percentages and sprout sizes statistically similar to those of control untreated seeds (P > 0.05).

* Corresponding author. Mailing address: Department of Animal and Food Sciences, University of Delaware, Newark, DE 19716-2150. Phone: (302) 831-1045. Fax: (302) 831-2822. E-mail: haiqiang{at}udel.edu

{triangledown} Published ahead of print on 13 February 2009.

Applied and Environmental Microbiology, April 2009, p. 1901-1907, Vol. 75, No. 7
0099-2240/09/$08.00+0     doi:10.1128/AEM.02531-08
Copyright © 2009, American Society for Microbiology. All Rights Reserved.





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