Determination of lethality during aseptic processing of particulate foods

Experimental and modelling studies were conducted to ascertain the effect of viscosity, flow rate, particle size, particle concentration on the residence time distribution of particles during non-Newtonian flow in a holding tube. Another program was written to determine the temperature distribution within particles during flow in the heat exchanger, holding tube, and cooling section of an aseptic processing system. Based on this, the lethality of different processes was determined depending on the target microorganism. The extent of nutrient retention and enzyme destruction was also computed. Experimental studies indicated that an increase in viscosity, flow rate or particle concentration decreased the mean and minimum residence time while an increase in particle concentration resulted in the opposite effect. In addition, it was found that an increase in viscosity widened the residence time distribution (RTD), while an increase in flow rate, particle size or particle concentration narrowed the RTD. Process lethality decreased from 8.0 to 2.3 mins when particle size increased from 1.0 to 1.5 cm; decreased from 5.9 to 4.0 mins when particle concentration increased from 30 to 50%; and decreased from 6.5 to 3.0 mins when the heat transfer coefficient decreased from 300 to 200 W/m²-K.