Purpose: Study the resistance of nonproteolytic C. botulinum types B, E and F spores exposed to combined high pressure and thermal processing.
Methods: Spores of 17 nonproteolytic strains of C. botulinum (8 type B, 7 type E, and 2 type F) were prepared using biphasic media. Individual strains spores were diluted in ACES buffer (0.05 M, pH 7) to 105-106 CFU/ml and placed into a modified sterile transfer pipette, heat-sealed and subjected to a combination of 80°C and high pressures (600, 650 and 700 MPa) for up to 15 min in a laboratory scale high pressure test system (Model PT-100). Survivors were determined by plating using PYGS agar medium.
Results: Nonproteolytic type E strain spores demonstrated much less resistant than type B or F strains processed at 80°C and 650 to 700 MPa for up to 15 min. All type E strains were reduced by > 6 logs within 5 minutes under these conditions.
Among type B strains, Kap9-B appears to be the most resistant type B strain, resulting in reductions of 2.7, 5.3 and 5.5 logs, coinciding with D-values 7.7, 3.4, and 1.8 min at 80°C and 600, 650 and 700 MPa, respectively. Of the two type F strains, 610-F was the most resistant of the two F strains, showing 2.6, 4.5 and 5.3 log reductions with D values of 8.9, 4.3 and 1.8 min at 80°C and 600, 650 and 700 MPa, respectively.
Significance: C. botulinum types B and F appear to be the most resistant of the nonproteolytic strains of C. botulinum to high pressure and thermal processing with strains 610-F and Kap9-B appearing to be the most resistant.