| Alfalfa sprouts, which are widely consumed in salads and sandwiches, have been implicated in nine major Escherichia coli O157:H7 and Salmonella related outbreaks since 1995. Decontamination treatments involving chemicals, thermal and non-thermal methods like UV light, gamma irradiation, high pressure processing, etc., are available for reduction of pathogenic microorganisms on seeds and sprouts. However, there has been no single treatment, which can eliminate pathogens completely.; Ozone, electrolyzed oxidizing (EO) water, and pulsed UV light are emerging technologies that have been shown to possess microbicidal and virucidal properties. This research was undertaken to investigate their bactericidal effect on E. coli O157:H7 contaminated alfalfa seeds and sprouts, without hampering seed germination and quality.; Alfalfa seeds inoculated with a five-strain E. coli O157:H7 cocktail were mechanically agitated in water containing 4, 8, 10, and 21 ppm ozone for 2, 4, 8, 16, 32, and 64 min at 4°C. Population reductions ranged between 0.40–1.75 log10 CFU/g. Alternatively, direct ozone sparging of seeds in water, for similar time intervals, reduced populations by 2.21 log10 CFU/g for 64-min treatment. Ozone sparged seeds subsequently exposed to heat at 40, 50 and 60°C for 3 h, reduced populations to undetectable levels (4–4.8 log10 CFU/g) at 60°C. However, enrichment was positive for E. coli O157:H7. Directly sparged seeds were also subjected to low hydrostatic pressure of 12 psi (83 kPa) for 5 min. The highest inactivation was 2.03 log10 CFU/g at 32-min treatment and was not significantly different (P > 0.05) from air pressurization. Addition of surfactants like Tween 20, Tween 80, SPAN 20, and SPAN 80 during pressurization significantly reduced ozone's effectiveness from 2.03 to 1.37 log10 CFU/g. Hydrostatic pressure treatments at 8 and 12 psi (55 and 83 kPa) without direct ozone sparging were not significantly different. The reductions ranged between 0.72–1.62 log10 CFU/g for the 12 psi treatment. Ozone did not have detrimental effect on seed germination in all the treatments. Immersion of inoculated alfalfa sprouts in water containing 21-ppm ozone for 64 min reduced the populations by 0.85 log10 CFU/g. Direct ozone sparging resulted in 2.19 log10 CFU/g reduction, while direct ozone sparging followed by exposure to low hydrostatic pressure at 12 psi (83 kPa) resulted in 2 log10 CFU/g. Treatments were also done by creating a vacuum of 25 inches (635 mm) Hg prior to introducing ozone gas in an airtight chamber containing either dry seeds or seeds immersed in water. (Abstract shortened by UMI.)... |
