MICROBIAL HEAT-RESISTANCE DETERMINATIONS BY THE MULTIPOINT SYSTEM WITH THE THERMORESISTOMETER TR-SC - IMPROVEMENT OF THIS METHODOLOGY

The thermoresistometer TR-SC for microbial heat resistance determinati ons by the multipoint system was improved. In manual mode (for the det ermination of high D-t values) the need of pipetting was eliminated: S elected volumes of heated menstruum were collected directly into plati ng medium by means of an automatic sampling valve operated by a soleno id activated by a timer. In the automatic mode, used for the determina tions of very low D-t values, the inoculation of menstruum, equilibrat ed at the required temperature and the collection of samples during th e experiment, were made fully automatic. The injection of the inoculum was made with a solenoid operated syringe, and samples were collected , with a specially adapted sample collector, directly into tubes conta ining melted plating medium. The maximum number of samples per unit of time was increased to 52 samples/s. The minimum detectable D-t value was reduced from 0.009 to 0.0009 min without decreasing precision (SD = 0.00017). This improvement eliminated the chance of handling errors, and reduced time and effort required for heat resistance determinatio ns. This modification makes this method especially suitable for the de termination, by the multipoint system, of very low D-t values such as needed in experiments at ultrahigh temperatures.