DESTRUCTION OF SALMONELLA SPECIES HEATED IN AQUEOUS SALT-SOLUTIONS BY MICROWAVE-ENERGY

Concentrations of 0.1, 0.5, 0.75, 1.0, and 1.25% wt/vol (0.017, 0.085, 0.13, 0.17, and 0.21 M, respectively) sodium chloride were added to 0.3 mM phosphate buffer, pH 6.8, and heated by microwave energy to study the relationship between salt concentration, temperatures achieved, and microbial destruction. Heating Salmonella spp. in saline solutions for a constant time (45 s) or to a constant final temperature (60-degrees-C) was also investigated. Fiberoptic thermometry was employed to obtain a temperature profile at specific sites within the solution. When heating for a constant time period, a minimum concentration of 0.75% wt/vol NaCl was necessary to afford Salmonella spp. significantly (P = 0.05) greater protection than the phosphate buffer control. Sodium, potassium, magnesium, and calcium chloride (1.0% wt/vol) in 0.3 mM phosphate buffer were also inoculated with a mixture of Salmonella spp. and heated by microwave energy. Of the salts examined, solutions containing NaCl consistently achieved the highest final surface temperature and largest temperature gradient from the surface to the bottom of the container. The amount of destruction of Salmonella spp. heated to a mixed mean final temperature of 60-degrees-C in buffer containing 1.0% wt/vol concentrations of NaCl, KCl, CaCl2, and MgCl2 was 56.4, 71.2, 72.8, and 88.7%, respectively. No relationship was found between the valency of the cation used and final temperatures achieved.