Effect of different heat treatments on bacillus subtilis spores inactivated by ultraviolet irradiation

The influence of a combination of ultraviolet (UV) irradiation with infrared radiation heating (IRH) and conductive heating (CH) on the inactivation of bacterial spores (Bacillus subtilis) was investigated at 20, 30, 40, and 50°C on the surface of agar plates. The survival curves of B. subtilis spores were convex downward. Generally, the inactivation efficiency of UV irradiation with IRH was greater than that with CH for B. subtilis spores. A 4.1 log reduction of B. subtilis spores was obtained by 60 sec of UV irradiation with IRH at 50°C. The highest decimal reduction time was obtained at around 30°C of IRH. These variations in the inactivation characteristics of UV irradiation might be caused by differences in the UV and IR absorption characteristics of spores exposed at different temperatures.