Thermal processing of suspended food particles in cans with end-over-end agitation

Heating rate index (f(h)), heating lag factor (j(h)) and accumulated lethal ity (F-o) were determined in the plastic, 307 diameter retortable bowls dur ing tests at 7 rotation speeds (0-30 rpm), and 3 radial positions (R-1 = 0 mm, R-2 = 115 mm, R3 = 175 mm). End-over-end (EOE) rotation from 0 to 30 rp m significantly influenced all parameters, however, the effect of rotation speed was non-linear, such that higher rpm did not always improve heating r ates. Substantial improvements in heating of the particle portion were seen at relatively low rpm. Although less important than rpm, even small(115 mm ) radial position differences significantly altered F-o in some cases (p le ss than or equal to 0.05). The effect of immobilization of food particles o n the end of a thermocouple, investigated with Bacillus stearothermophilus ATCC 7953 spores sealed in differential scanning calorimetry (DSC) pans, re vealed significantly lower lethality delivered to freely moving particles t han to particles immobilized in the can center. A Hydrophobic Grid Membrane (HGM) technique allowed rapid and convenient enumeration of surviving spor es. The bioindicator approach provided a more conservative estimate of mini mum lethality than rigid thermocouples positioned in the center of particle s within cans. (C) 1999 Canadian Institute of Food Science and Technology. Published by Elsevier Science Ltd. All rights reserved.