COMBINED EFFECTS OF TEMPERATURE AND PRESSURE ON STERILIZATION OF BACILLUS-SUBTILIS SPORES

Effect of pressure from 0.1 MPa to 400 MPa on death rate of Bacillus subtilis spores during heating treatment from 298-degrees-K to 381-degrees-K were investigated. A sample tube made of silicon rubber (I.D. = 4 mm, L = 100 mm), containing spore suspension (ca, 1.0(7) spores/ml, pH 7.0, 1/15 M phosphate buffer), was inserted into a pressure vessel (I.D. = 8 mm, L = 180 mm), then the vessel was heated in a constant temperature bath under controlled pressure. Even in a moderate temperature range from 298-degrees-K to 338-degrees-K, pressure influenced the death rate, though the survival curves did not obey the first order rate equation. In this temperature range, the relationships between log (spore survivors) and log (time) showed a clear linear correlation, indicating that the spores do not die completely under the high pressure conditions only. On the contrary, pressure influenced so much the survivors of the spores, and the death curves obeyed the first order rate equation in a high temperature range from 368-degrees-K to 381-degrees-K, and a remarkable decrease of spores was measured during come up time of the heating under constant pressure. The death rate constant increased with an increase of the pressure. These results showed that the pressurized heating sterilization process can shorten the heating time or decrease the sterilization temperature for complete spore death.