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Reduction of Salmonella and Shiga toxin-producing Escherichia coli on alfalfa seeds and sprouts using an ozone generating system

Mohammad, Zahra, Kalbasi-Ashtari, Ahmad, Riskowski, Gerald, Castillo, Alejandro
International journal of food microbiology 2019 v.289 pp. 57-63
Salmonella, Shiga toxin-producing Escherichia coli, alfalfa, color, exposure duration, food safety, ozonation, ozone, pathogens, risk reduction, seed germination, seeds, serotypes, shelf life
Several outbreaks of illness have been associated with consumption of alfalfa sprouts contaminated with Shiga toxin-producing Escherichia coli (STEC) and Salmonella. The ozone application was investigated as an intervention. Alfalfa seeds were inoculated with cocktails of 3 Salmonella strains, including serotypes Typhimurium, Agona and Saintpaul, and 3 strains of Shiga toxin-producing Escherichia coli (STEC) including serotypes O104:H4, O157:H7 and O121:H19 with a final load of 7.0 log CFU/ml. Then, the inoculated seeds, and the sprouts obtained from these seeds were separately subjected to aqueous ozone treatment containing (5 mg/L) ozone for varied times of exposure. The mean log reductions for Salmonella achieved on seeds after 10, 15, and 20 min of ozone exposure were 1.6 ± 0.5, 1.7 ± 0.3, 2.1 ± 0.5, respectively and 1.5 ± 0.4, 1.6 ± 0.4, 2.1 ± 0.5 for STEC, respectively. For sprouts obtained from the inoculated seed, the mean log reductions for Salmonella after 10, 15, and 20 min exposure times were 0.7 ± 0.2, 1.1 ± 0.4, 3.6 ± 0.2, respectively, whereas the mean log reductions for STEC were 0.7 ± 0.1, 1.2 ± 0.3 and 1.8 ± 0.2, respectively. At each contact time, there were no differences in log reductions between pathogens on seeds (P > 0.05), whereas on sprouts, the reductions obtained at 20 min were significantly greater (P < 0.05) for Salmonella than for STEC. On both seeds and sprouts, the exposure time had significant (P < 0.05) effects on log reductions of Salmonella and STEC. The weight, color properties and shelf life of ozonated sprouts were also tested. The ozonation did not have negative effects on germination (%), color and mass of sprouts in comparison with the controls. This study confirmed that it is possible to substantially reduce Salmonella and STEC by using a low ozone concentration (5 mg/L) and reduce food safety risk with less concern about the safety for processing workers of this treatment, this without affecting seed germination. This procedure may be a promising intervention to reduce Salmonella and STEC from alfalfa seeds and sprouts.