Abstract

The aim of this paper was to study the effect of a convective continuum industrial drying process on microstructural changes, bulk density, and total soluble solids of apple slices (inner and surface) and their relationship with drying mechanisms. Experiments were carried out with a conveyor dryer (Proctor & Schwartz, model k97058) that includes three continuum stages (A, B, and C). Apple samples (Granny Smith) were taken in accordance with drying equipment feasibility; raw materials were obtained at dryer input, partially dried apple samples between stages A and B and between stages B and C, and dried apple samples were obtained at dryer output. Moisture content and bulk density were determined for all apple samples, and total soluble solids content of whole apple samples and their external surface were determined. Some apple samples were rapidly frozen (-195.8 degrees C) for observation by scanning electron microscopy (SEM). Results showed the presence of two possible drying mechanisms: evaporation at the beginning of the drying process (stage A) and liquid water transport in stages B and C. A remarkable difference in the total soluble solids content and microstructure between external and internal zones of apple samples was experimentally determined. More studies at industrial scale are needed to improve the final quality of dried products.