Thermal Inactivation of Salmonella in Peanut Butter

The objective of this study was to determine the rates of thermal inactivation of three Salmonella Tennessee strains in peanut butter associated with an outbreak and to compare them to the rates of inactivation of Salmonella strains of other serotypes (Enteritidis, Typhimurium, and Heidelberg) (SSOS) and of clinical isolates of Salmonella Tennessee from sporadic cases (STSC). Commercial peanut butter was inoculated with Salmonella isolates and heated at 71, 77, 83, and 90 degrees C. The thermal inactivation curves were upwardly concave, indicating rapid death at the beginning (20 min) of heating followed by lower death rates thereafter. The first-order kinetics approach and nonlinear Weibull model were used to fit the inactivation curves and describe the rates of thermal inactivation of Salmonella in peanut butter. The calculated minimum times needed to obtain a 7-log reduction at 90 degrees C for the composited three outbreak-associated strains were significantly greater (P < 0.05) than those of SSOS and STSC. Approximately 120 min were needed to reduce the outbreak strains of Salmonella Tennessee by 7 log, whereas 86 and 55 min were needed for SSOS and STSC, respectively. These results indicate that the outbreak-associated Salmonella strains were more thermotolerant than the other Salmonella strains tested, and this greater thermal resistance was not serotype specific. Thermal treatments of peanut butter at 90 degrees C for less than 30 min are not sufficient to kill large populations (5 log CFU/g) of Salmonella in highly contaminated peanut butter.