Indicators of bacterial lethality in semirigid plastic food containers during thermal processing

Thermocouple methods which have been used traditionally for gathering time-temperature data for agitated retort processes have some physical limitations in that thermocouples located in the centres of containers cannot accurately simulate free-moving particles. For this reason alternative approaches have been taken to measure, understand and model such thermal processes, and this was the purpose of the research carried out in these studies.;Thermal diffusively was determined for a potato/alginate gel in order to determine the thermal characteristics of the gel and thereby ascertain its ability to function as a model food particle. Thermal diffusivity was found to average 2.048 x 10--7 m2/s. Visualisation based on video recording of 307 diameter plastic OMNI RTM bowls containing four food-simulating particles were conducted in a Lagarde steam/air retort simulator to evaluate the effect of rotation on particle movement.;Thermal processing studies were carried out during agitated processes in order to investigate heating of 307 diameter plastic OMNIRTM bowls at various rotational speeds (0, 5, 10, and 15 rpm). Since the goal was to understand processes under production conditions, the degree of positional effect was investigated. Bowls positioned at the axial centre and the outside edge heated faster than bowls positioned in the intermediate portion of the retort basket. Studies in the Lagarde were carried out with rigid thermocouples to determine if the flexible thermocouple gave a better model of the temperature history within a freely moving particle in random motion during heating. Flexible thermocouples were found to yield lower values for jh, fh and tB than the rigid thermocouple.;A further stage of this research was aimed at assessing the effects of rotational thermal processes on populations of microorganisms. Suspensions of Bacillus stearothermophilus ATCC 7953 were placed into DSC pans, hermetically sealed and incorporated into the centres of potato/alginate particles (18 mm in diameter). Positional effects were determined as well as rotational effects at 0, 15 and 30 rpm. Studies were done with particles immobilised on rigid thermocouples positioned at the centres of containers as well as on flexible probes (to simulate a flexible thermocouple). With flexibly anchored and freely moving particles there was close agreement for IS values, while for the rigidly held particles and the liquid contents of the container there was close agreement for IS values.;A final study made use of the thermal indicator concept with Clostridium pasteurianum, Bacillus coagulans, and lysozyme to evaluate pasteurisation of tomato-based sauces compared to traditional temperature history methods. Measured lethalities were found to be greater than calculated lethalities for all containers. (Abstract shortened by UMI.).