THERMAL-RESISTANCE OF NONPROTEOLYTIC TYPE-B AND TYPE-E CLOSTRIDIUM-BOTULINUM SPORES IN PHOSPHATE BUFFER AND TURKEY SLURRY

The heat resistance of nonproteolytic type B and type E Clostridium bo tulinum spores in phosphate buffer and turkey slurry was determined fr om 70 to 90 degrees C. Thermal-death times were determined in vials he ated using a water bath. Recovery of heat-injured spores was on reinfo rced clostridial medium (RCM) and tryptic soy agar (TSA) with and with out added lysozyme (10 mu g/ml). Decimal-reduction times (D-values) we re determined by fitting a survival model to the data using a curve-fi tting program. The apparent or measured heat resistance was maximum wi th RCM supplemented with lysozyme. The D-values at 80 degrees C for ty pe E spores in buffer ranged from 1.03 min for strain Whitefish to 4.5 1 min for strain Saratoga The D-value for the most heat-resistant nonp roteolytic type B strain KAP B5 in buffer was 4.31 min at 80 degrees C . The z-values in buffer for all strains were very similar, ranging fr om 8.35 to 10.08 degrees C. Turkey slurry offered protection to the sp ores with a concomitant increase in heat resistance. The D-values in t urkey slurry ranged from 51.89 min at 70 degrees C to 1.18 min at 85 d egrees C for type E strain Alaska (z = 9.90 degrees C) and from 32.53 min at 75 degrees C to 0.80 min at 90 degrees C for nonproteolytic typ e B strain KAP B5 (z = 9.43 degrees C). Thermal-death-time values from this study will assist food processors to design thermal processes th at ensure safety against nonproteolytic C. botulinum in cook/chill foo ds.