A computational fluid dynamics study on the effect of sterilization temperatures on bacteria deactivation and vitamin destruction

Abstract
The optimization of thermal processes such as sterilization relies on the accuracy of relevant kinetic data for bacterial inactivation and quality evolution. It is also dependent on the geometry and heating mechanism involved in the process. In these processes or systems, profiles of temperature distribution, bacteria concentration and concentrations of vitamins C (ascorbic acid), B1 (thiamin) and B2 (riboflavin) in a can filled with cherry juice during thermal sterilization have been obtained through numerical simulations. Different heating medium temperatures of 121, 130 and 140°C were tested. In order to generate these profiles, the continuity, momentum and energy equations are solved numerically, together with those of bacteria and vitamins concentrations, using the computational fluid dynamics code PHOENICS, combined with reaction kinetics models. Natural convection that occurs during thermal sterilization of viscous liquid (concentrated cherry juice, 74 °Brix) in a cylindrical can heated from all sides has been studied in this work. The simulations show clearly the dependences of the concentration of live bacteria and different vitamins on both the temperature distribution and the flow pattern as sterilization proceeds. The results also show that the best sterilization temperature may not always be 121 °C, depending on the quality requirements imposed on individual food material of concern.