Modeling sterilization value and nutrient degradation in the thermal processing of liquid foods under diffusive laminar flow with associations of tubular heat exchangers

摘要

Thermal processing of a liquid food under diffusive laminar flow was modeled coupling fluid flow, heat transfer, diffusion, and inactivation/degradation kinetics. Model considers associated countercurrent tubular exchangers for heating and cooling and the holding tube. Axial and radial distributions of temperature and concentration in the food product (non-Newtonian power-law flow) were accounted and parameters for effective diffusion of heat and mass were used to model enhanced transfer from corrugate tubes or coils. Heat exchanged with environment was included. A case study of 40.2 degrees Brix blackberry juice pasteurization is presented, and results discussed. Influence of effective diffusivities, inlet heating media temperature and product flow rate were analyzed, and it was possible to minimize anthocyanin degradation while meeting food safety requirements (5-log reduction on yeasts) considering the contributions from the whole process.Practical applicationsMathematical modeling of a chemical process based on first principles, also called physical or phenomenological models, is a powerful tool to couple fluid flow, heat transfer, mass diffusion, and reaction kinetics, thus creating a virtual prototype of the process that is useful for design, analysis, control, and optimization. The model presented considers important features that are often neglected in process design, but without unnecessarily increasing complexity and computational requirements, such as in a CFD model (computational fluid dynamics) that requires a detailed representation of the geometry and specialized software and hardware for simulation. Lower computational times allow the use of this model to solve optimization or predictive control problems with a reliable representation of transport phenomena and reaction kinetics.