Decontamination method using heat and relative humidity for radish seeds achieves a 7-log reduction of Escherichia coli O157:H7 without affecting product quality

• A novel decontamination method using heat and relative humidity (RH) was developed.
• E. coli O157:H7 on radish seeds were inactivated without affecting product quality.
• The optimum was 65 °C/45% RH for 24 h (7.0 log CFU/g reduction and 85.4% germination).
• This technology is simple, clean, and efficient for large-scale industrial applications.

We developed a novel decontamination method to inactivate Escherichia coli O157:H7 on radish seeds without adversely affecting seed germination or product quality. The use of heat (55, 60, and 65 °C) combined with relative humidity (RH; 25, 45, 65, 85, and 100%) for 24 h was evaluated for effective microbial reduction and preservation of seed germination rates. A significant two-way interaction of heat and RH was observed for both microbial reduction and germination rate (P < 0.0001). Increases in heat and RH were associated with corresponding reductions in E. coli O157:H7 and in germination rate (P < 0.05). The order of lethality for the different treatments was generally as follows: no treatment < 55 °C/25–65% RH ≒ 60 °C/25–45% RH ≒ 65 °C/25% RH < 55 °C/85% RH = 60 °C/65% RH < 55 °C/100% RH = 60 °C/85–100% RH = 65 °C/45–100% RH. The most effective condition, 65 °C/45% RH, completely inactivated E. coli O157:H7 on the seeds (7.0 log CFU/g reduction) and had no significant effect on the germination rate (85.4%; P > 0.05) or product quality. The method uses only heat and relative humidity without chemicals, and is thus applicable as a general decontamination procedure in spout producing plants where the use of growth chambers is the norm.