Purpose: Many Salmonella serovars have been isolated from low-moisture foods and have also been linked to outbreaks; however, the thermal resistance among serovars has not been thoroughly evaluated.
Methods: Since variation in survival and subsequent thermal resistance among Salmonella serotypes is unknown, we quantified survival over four months and subsequently determined the thermal resistance of 32 strains of Salmonella representing four different serotypes inoculated at eight log CFU/g onto flax seed.
Results: Reduction in cell numbers over time was nonlinear and survival/inactivation rate parameters were determined from the Geeraerd model. Over a four month period, the average kmax for Salmonella Enteriditis strains was 0.8±0.1; significantly higher than that for Salmonella Agona, which was 0.5±0.1. To quantify the subsequent heat resistance of Salmonella strains after two and four months of storage, inoculated flaxseeds were subjected to vacuum steam pasteurization at 72±1°C for 0.5, 0.75, 1, 1.25, 1.5, 2, and 3 min. After two months of storage, kmax values ranged from four to six. After four months of storage, average kmax was 7.0±2.0, 5.8±0.8, 4.6±1.2, and 4.3±0.8 for serotypes Salmonella Enteriditis, Salmonella Montevideo, Salmonella Tennessee, and Salmonella Agona, respectively. After four months, Salmonella Enteriditis had a higher inactivation rate than the other serovars. With increased storage time, the heat resistance of serovar Tennessee strains increased 2.3-fold.
Significance: These results showed that survival on flax seed varies among these four serotypes, with strains of serotype Agona exhibiting the highest survival after four months. Also, results demonstrated that adaptation to low moisture conditions increased the thermal resistance of serovar Tennessee.