Determination of Thermal Inactivation Kinetics by the Multipoint Method in a Pilot Plant Tubular Heat Exchanger

Heat resistance determinations, necessary for the design of safe thermal treatments, are usually performed in batch systems, but those on continuous systems are more realistic. In continuous systems, samples and temperatures are only taken from the inlet and outlet. Therefore, microbial inactivation kinetics and heat-labile compound degradation on these systems remain a black box. A pilot-scale heat exchanger, with several temperature sensors and sampling tubes along the system, was built. The aims of this research were to determine the residence time distribution, the flow type, and the inactivation kinetics of Salmonella Senftenberg and Staphylococcus aureus on the heat exchanger. Microbial inactivation data were obtained both under isothermal and non-isothermal conditions and compared to those obtained in a batch system. Flow was estimated as turbulent. Under isothermal conditions, similar inactivation levels were reached for S. aureus in both equipments (batch or continuous). Under non-isothermal conditions, for both microorganisms, higher inactivation of the population was observed in the last step of the treatment in the heat exchanger than in the batch system. These differences could be attributed to faster heating rates in the heat exchanger. The heat exchanger used in this investigation is a suitable tool to understand microbial inactivation kinetics in continuous systems.