MODELING OF SHRINKAGE, MICROBIAL SPOILAGE AND COLOR DEGRADATION OCCURRING IN CONVECTIVE DRYING OF VEGETABLES

摘要

In this work, the formulation of a theoretical model aimed at providing a complete description of vegetables convective drying was presented. The proposed approach was based on the coupling of four different models. In particular, a multiphase transport phenomena model predicted the simultaneous transfer of momentum, heat and mass, occurring in both the drying chamber and the food. A structural mechanics model estimated the sample deformations, strictly related to food shrinkage, as due to moisture loss. A product decontamination model calculated the microbial inactivation kinetics of Listeria monocytogenes and, finally, a macroscopic model estimated the vegetables color changes, expressed in terms of the Hunter parameters. The system of non-linear, unsteady-state, partial differential equations modeling the drying process was solved by an Arbitrary-Lagrangian-Eulerian-based finite elements formulation, which, by a proper modification of the integration domains (food and air), allowed accounting for shrinkage effects. The effects of operating conditions on drying performance were ascertained by analyzing the time evolution of several variables. Among these, the spatial distributions of temperature, water activity, moisture content, strain and stress, as well as the variation of food dimensions, as due shrinkage, the color degradation, chosen as a reference quality parameter, and the microbial population decay, chosen as a measure of food safety, were considered as the most important.