Inactivation of Escherichia coli O157:H7, Listeria monocytogenes, Salmonella enterica and Shigella flexneri on spinach leaves by X-ray.
Several recent foodborne disease outbreaks associated with leafy green vegetables, including spinach, have been reported. X-ray is a non-thermal technology that has shown promise for reducing pathogenic and spoilage bacteria on spinach leaves. Inactivation of inoculated Escherichia coli O157:H7, Listeria monocytogenes, Salmonella enterica and Shigella flexneri on spinach leaves using X-ray at different doses (0.1, 0.2, 0.3, 0.5, 0.75, 1.0, 1.5 and 2.0 kGy) was studied. The effect of X-ray on color quality and microflora counts (mesophilic counts, psychrotrophic counts and yeast and mold counts) of untreated and treated spinach was also determined. A mixture of three strains of each tested organism was spot inoculated (100 microl) onto the surface of spinach leaves (approximately 8-9 log ml(-1)), separately, and air-dried, followed by treatment with X-ray at 22 degrees C and 55-60% relative humidity. Surviving bacterial populations on spinach leaves were evaluated using a nonselective medium (tryptic soy agar) with a selective medium overlay for each bacteria; E. coli O157:H7 (CT-SMAC agar), L. monocytogenes (MOA), and S. enterica and S. flexneri (XLD). More than a 5 log CFU reduction/leaf was achieved with 2.0 kGy X-ray for all tested pathogens. Furthermore, treatment with X-ray significantly reduced the initial inherent microflora on spinach leaves and inherent levels were significantly (p < 0.05) lower than the control sample throughout refrigerated storage for 30 days. Treatment with X-ray did not significantly affect the color of spinach leaves, even when the maximum dose (2.0 kGy) was used.
Mahmoud
Barakat S M
BS
Coastal Research & Extension Center, Mississippi State University, 3411 Frederic St, Pascagoula, MS 39567, USA. bm547@msstate.edu<bm547@msstate.edu>
Bachman
Gary
G
Linton
Richard H
RH
D004755:Enterobacteriaceae / Q000302:isolation & purification / Q000528:radiation effects*; D019453:Escherichia coli O157 / Q000302:isolation & purification / Q000528:radiation effects; D005514:Food Irradiation / Q000379:methods*; D008089:Listeria monocytogenes / Q000302:isolation & purification / Q000528:radiation effects*; D050296:Microbial Viability / Q000187:drug effects*; D018515:Plant Leaves / Q000382:microbiology / Q000528:radiation effects; D019779:Salmonella enterica / Q000302:isolation & purification / Q000528:radiation effects; D012763:Shigella flexneri / Q000302:isolation & purification / Q000528:radiation effects; D018724:Spinacia oleracea / Q000382:microbiology* / Q000528:radiation effects; D014965:X-Rays