Heat resistance of Talaromyces flavus ascospores as determined by a two phase slug flow heat exchanger

Heat resistance of Talaromyces flavus was determined using two methods. Standard thermal death time vials were used to determine the heat resistance of T. flavus ascospores, from 80 to 90 °C with a decimal reduction time D90 of 6.2 min. A continuous two-phase slug flow heat exchanger System with heating, holding and cooling sections was used to determine the heat resistance from 90 to 100 °C. Inoculated heating medium was pumped through 1.85 mm ID tubing in ‘slugs’ separated by air bubbles to interrupt laminar flow. Varying pump speed, length of tubing in the heating bath and temperature allowed collection of data under varied heating conditions. D90 with the slug flow heat exchanger system was 6.4 min, indicating the two methods were comparable, z values were 6.7 and 6.4 °C, respectively. The slug flow heat exchanger system permits rapid determination of heat resistance over a range of temperatures. Because of minimum come-up time the slug flow heat exchanger can be used at temperatures near the upper limit of heat resistance for the microorganism being tested.