Heat And Mass Transfer Modeling And Device For Dry-Blanching And Dehydration Of Apple Slice By Infrared Heating

Blanching and dehydration are two essential processing steps used to extend the shelf-life of fruits and vegetables by inactivating enzymes and lowering water activity of the products. A recently developed medium-far infrared simultaneous dry-blanching and dehydration (IDBD) technology has many advantages over the existing processing methods. In this process blanching and dehydration can be achieved in a single step rather than the two steps used at present. The infrared heating system was designed to be used for blanching of fruits and vegetables and it can be controlled automatically. In order to analyze the heat and mass transfer mechanism and enzyme inactivation kinetics a numerical model method was used in the study. In the models, heat conduction transfer obeys the Fourier's law and mass diffusion transfer obeys Fick's law under one dimensional transfer. Both absorption at the surface and penetration of the infrared radiation to the sample were considered. At the surface the infrared radiation and free convection were considered as the boundary conditions and the penetration of the infrared radiation was considered as the energy generation in the samples in the heat transfer equation. To study the effectiveness of the dry-blanching method, the enzyme activities of Polyphenol oxidase (PPO) and Peroxidase (POD) were determined to be the indicators in this study. And in the models the enzyme inactivation was represented by first order kinetics. The parameters, k_r,ref,T_ref, and Ea of PPO and POD in apple in the equations were adopted from the literature. Heat and mass transfer models coupled with enzyme inactivation models were solved with the finite element method. In order to validate the...