An ultrasonic method for assessing the residence time distribution of particulate foods during ohmic heating

The residence time distribution (RTD) was investigated using ultrasound dur ing continuous ohmic heating of 1) starch solution and 2) carrot particles/ starch solution mixtures. For liquid experiments, a copper pigment was used as a tracer. Ultrasonic sensors were placed at the end of the tube to meas ure changes in sound attenuation. The copper concentration was determined i n samples taken at time intervals. For particulate foods, one kilogram of c arrot/solution mixtures was introduced. Results of the ultrasonic method we re compared to carrots weights in collected samples. Variations of sound at tenuation illustrated well the RTD of solutions and carrot particles. Resul ts of the ultrasonic method agreed with the pigment method for liquid and t he gravimetric method for particulate foods.