Submitted to: Journal of Food Protection
Publication Type: Peer reviewed journal
Publication Acceptance Date: 10/14/2001
Publication Date: 10/14/2002
Citation: Interpretive Summary: Outbreaks of foodborne illness due to alfalfa sprouts contaminated with bacterial human pathogens have been numerous in number since 1995 in the US. The original source of these pathogens is believed to be seed used for sprouting. New, effective means of sanitizing sprouting seed are needed. In this study the effectiveness of ozone as a sanitizer was studied. Seed inoculated in the laboratory with the pathogen Escherichia coli O157:H7 wa soaked for up to 64 min in water that had been pretreated to contain up to 21 parts per million of ozone. Direct bubbling of ozone into the seed/water mixture during treatment was also tested. Both methods were ineffective in significantly reducing the level of the pathogen on the seed. However, a combination treatment of direct bubbling of ozone followed by placing the treated seed in an oven held at 60 C for 3 hours reduced the level of the pathogen by 99.99% or more without adversely affecting seed germination. Sprout growers to help insure the microbial safety of their product can us the combination sanitizing treatment.
Technical Abstract: Alfalfa seeds inoculated with a five-strain cocktail of Escherichia coli O157:H7 were treated in pre-ozonated water containing 4, 8, 10, and 21 ppm ozone for 2, 4, 8, 16, 32, and 64 min at 4 C. Direct ozone sparging of seeds in water was used as an alternative mode of ozone treatment. Ozone- sparged seeds were also subsequently exposed to heat treatment at 40, 50, and 60 C for 3 h. Since E. coli O157:H7 was released from inoculated seed during treatment, the rate of release of cells on inoculated seeds soaked in 0.1% peptone water for up to 64 min was also determined. The overall reduction of E. coli O157:H7 on seeds treated with pre-ozonated water ranged from 59.6-98.2% (0.40-1.75 log10 CFU/g) similar to control values for water alone. Treatment with higher ozone concentrations enhanced inactivation, but contact time longer than 8 min did not result in significantly higher percentage reductions (P<0.05). For seeds treated by ozone sparging, a 92.1% (1.12 log 10 CFU/g) reduction was achieved using a 2-min contact time, and a 99.4% (2.21 log 10 CFU/g) reduction was achieved with a 64-min contact time, but again values were similar to control values for water alone. Treatment of ozone-sparged seeds at 60oC for 3h reduced the population to an undetectable level by direct plating and did not have detrimental effect on seed germination percentage.