Influence of Relative Humidity

Influence of relative humidity, temperature and sanitizer treatment in inactivating Escherichia coli O157:H7 on radish seeds.

Institute of Food Technologists Annual Meeting, New Orleans,Jun 30, 2008, Jihyun Bang, Korea University, Seoul, Republic of Korea; Hoikyung Kim, Korea University, Seoul, Republic of Korea; Youngjun Lee, Korea University, Seoul, Republic of Korea; Jee-Hoon Ryu, Korea University, Seoul, Republic of Korea. 

Radish sprouts have been implicated as vehicles in outbreaks of Escherichia coli O157:H7 infections, thereby raising concerns on cultivating seeds free from the pathogen. We determined the influences of relative humidity (RH), temperature, and sanitizer treatment in inactivating E. coli O157:H7 on radish seeds. Radish seeds inoculated with E. coli O157:H7 at population of 5.4 log CFU/g were incubated with 43, 85, 93, or 100% RH at 25, 35, or 45°C for 40 days, and the populations of survivors and germination rates of the seeds were determined. E. coli O157:H7 were not recovered on seeds stored with 85% RH at 35°C after 40 days. At 45°C, the bacterium was completely removed from seeds under 85, 93, and 100% RH within 15, 10 and 10 days, respectively. However, germination rates of the seeds decreased by 28 - 99%. Since the storage of seeds at 45°C for longer than 10 days caused reduction in germination rate of seeds, ClO2 (200 ppm, pH 6) treatment was applied prior to the storage. Seeds inoculated with E. coli O157:H7 at 6.8 log CFU/g were treated with ClO2 for 5 min, dried for 2 h at room temperature, and stored with 43, 85, 93, or 100% RH at 45°C. The bacterium was not recovered when the seeds were stored with 100% RH at 45°C for 2 days and the seeds showed germination rate of 89%. According to our observations, various hurdle stresses including application of sanitizer, RH, and temperature effectively inactivated E. coli O157:H7 on radish seeds without reduction in germination rates of the seeds. These results will be useful in developing effective strategies and practices to ensure microbiological safety of fresh sprout products.