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?°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.

THE OBJECTIVE OF THIS STUDY WAS TO APPLY ELECTROHYDRODYNAMIC (EHD) AS A PRETREATMENT, INCLUDING SEVERAL VOLTAGES AND AN APPLICATION TIME OF LESS THAN 1 H, COMBINED WITH FREEZE DRYING (FD) TO DETERMINE THEIR INFLUENCE ON DRYING KINETICS AND DRYING RATE, FINAL MOISTURE CONTENT, REHYDRATION RATE, AND WATER ABSORPTION CAPACITY, ALSO, REHYDRATION AND WATER ABSORPTION CAPACITY RATES DERIVED FROM THE WEIBULL MODEL. THE BEST COMBINATION WAS COMPARED WITH SUN DRYING (SD) AND FD. INITIAL DRYING RATE INCREASED BECAUSE EHD INFLUENCED THE MOISTURE CONTENT ON THE PRODUCT SURFACE AS EXPOSURE VOLTAGE INCREASED. REHYDRATION AND WATER ABSORPTION HAD A HETEROGENEOUS BEHAVIOR, REGARDLESS OF VOLTAGE. THE 30 KV-30 MIN PRETREATMENT HAD BETTER DRYING KINETICS AND RATE AND WAS THEREFORE COMPARED WITH FD AND SD, SHOWING BETTER RESULTS IN THE DRYING PARAMETERS. HOWEVER, FOR REHYDRATION BEFORE 2.5 H, FD BEHAVED BETTER. THE WEIBULL MODEL HAD A GOOD FIT TO THE EXPERIMENTAL DATA FOR THE THREE TREATMENTS. CRUST FORMATION WAS GREATER IN THE SD TREATMENT, FOLLOWED BY EHD COMBINED WITH FD, WHICH WAS REFLECTED IN REHYDRATION.

THE AIMS OF THIS STUDY WERE TO BUILD PDMS MICROMODELS THAT SIMULATED PLANT-BASED FOOD MATERIAL, AND USE THEM TO INVESTIGATE THE DRYING MECHANISMS AT PORE-SCALE, THE DRYING FRONT MORPHOLOGIES AND THE DRYING CURVES DURING THE ISOTHERMAL DRYING PROCESS. MICROMODELS WERE BUILT USING A MODIFIED PHOTOLITHOGRAPHIC TECHNIQUE. THREE NORMAL PORE SIZE DISTRIBUTION FUNCTIONS WERE DEVELOPED TO SIMULATE THE PLASMODESMA, INTERCELLULAR SPACE, AND CELL WALL. MICROMODELS WERE IMPREGNATED WITH A PYRANINE AQUEOUS SOLUTION AND PLACED ON A BALANCE ILLUMINATED WITH ULTRAVIOLET LIGHT. ISOTHERMAL DRYING WAS DEVELOPED BY NATURAL CONVECTION (20 °C). DRYING FRONT MORPHOLOGIES DISPLAYED A HIERARCHICAL BEHAVIOR IN WHICH PORES WITH THE LARGEST DIAMETER DRIED FIRST. DRAINAGE AND SURFACE EVAPORATION SEQUENCES AND INTERNAL EVAPORATION CONTROLLED THE DRYING OF PDMS MICROMODELS. THE MICROMODELS WERE USEFUL TO SIMULATE PLANT-BASED FOOD MATERIAL AND STUDY ISOTHERMAL DRYING OF SUCH POROUS MEDIA. THE RESULTS LED TO THE PROPOSAL OF SOME DRYING MECHANISMS THAT WERE INVOLVED.