Microbiological and chemical investigation of ohmic heating of particulate foods using a 5 kW ohmic system

Lethality within food particles undergoing ohmic heating was investigated using microbiological and chemical marker measurements. Meatballs containing spores of B. stearothermophilus and precursors of chemical markers were thermally processed in a starch solution with 30-40% solids content using a 5 kilowatt (kW) ohmic system. Different temperatures, flow rates, holding tube lengths, and fluid electrical conductivities were used. Lethalities observed under various processing conditions were consistent with predictions. Higher lethality was observed, microbiologically and chemically, at the center of the meatballs rather than near the surface. A good correlation between the marker yield and the bacterial survivor population was obtained under various processing conditions. The results indicate that the chemical markers may be used to evaluate the distribution of lethality among different particles and the contribution to lethality of different holding sections. The results also suggest that sterility of ohmically heated particulate foods may be evaluated, to a first approximation, based on the fluid temperature and the residence time (i.e., holding tube geometry/flow rate).