FIG. 4.

Effect of heat (65°C at 0.1 MPa), combined heat and pressure treatment (65°C and 600 MPa), or pressure pulse treatment (65°C and 600 and 0.1 MPa) on the inactivation of spores of the DPA-deficient B. subtilis mutant CIP 76.26. Spores were obtained from medium with external DPA (•, ▪, and ▴) or medium without external DPA (○, □, and ▵). • and ○, continuous pressurization at 600 MPa and 65°C; ▴ and ▵, pressure pulse, 600 MPa and 65°C for 2 min, followed by 0.1 MPa and 65°C; ▪ and □, 0.1 MPa and 65°C. Data shown are means of at least two independent experiments, and the standard deviations were generally less than 0.66 log units. Lines dropping below the x axis indicate spore counts below the detection limit (log [N/N₀] = −6, where N and N₀ are as defined for Fig. 1).