ABSTRACT Different drying accelerators were studied to improve vegetable drying: acetone (AC), ethanol (ET), isopropanol (ISO) and acetic acid (AA). Pre-treatments were performed by immersion of pumpkin cylinders. Convective drying was performed at 40 °C and air velocity 1 m/s. Different aspects were evaluated: drying kinetics, structural changes (microstructure and macrostructure), thermal profile and viscoelastic and rehydration behaviours. The microstructure was modified by pre-treatments, being more pronounced with AC and AA. Thinner cell walls, changes on turgor and extraction of components and air were reported, affecting the mass transfer. Moreover, the microstructural changes reinforced anisotropy and also affected the macrostructure, changing the viscoelastic behaviour. All pre-treatments resulted in a super-diffusive behaviour, decreasing the drying time from 9% (ISO) to 22% (...

Different drying accelerators were studied to improve vegetable drying: acetone (AC), ethanol (ET), isopropanol (ISO) and acetic acid (AA). Pre-treatments were performed by immersion of pumpkin cylinders. Convective drying was performed at 40 degrees C and air velocity 1 m/s. Different aspects were evaluated: drying kinetics, structural changes (microstructure and macrostructure), thermal profile and viscoelastic and rehydration behaviours. The microstructure was modified by pre-treatments, being more pronounced with AC and AA. Thinner cell walls, changes on turgor and extraction of components and air were reported, affecting the mass transfer. Moreover, the microstructural changes reinforced anisotropy and also affected the macrostructure, changing the viscoelastic behaviour. All pre-treatments resulted in a super-diffusive behaviour, decreasing the drying time from 9% (ISO) to 22% (AC)...

Ultrasound was combined with ethanol to improve different aspects of carrot convective drying, evaluating both processing and product quality. The ultrasound in water treatment resulted in cellular swelling and small impact on texture. Differently, the ultrasound in ethanol and ethanol treatments modified both carrot microstructure (cell wall modifications of parenchymatic tissue) and macrostructure (shrinkage and resistance to perforation). Pre-treatments with ultrasound in ethanol and ethanol improved the drying kinetics, reducing the processing time (similar to 50%) and the energy consumption (42-62%). These pre-treatments also enhanced rehydration, whose initial rate and water retention were higher than the control. In addition, the carotenoid content was preserved after drying, for all the treatments. Any impact on shrinkage was observed. A mechanistic discussion, based on structura...