Search

Ultrasonic-assisted drying is an effective technique for accelerating drying processes, particularly for products with high porosity. The structural changes induced by pulsed electric field (PEF) treatment can make low-porosity products more susceptible to the effects of ultrasound during drying. This study aimed to investigate the influence of PEF treatment on the structure of low-porosity products, such as butternut squash, and to evaluate its effect on ultrasonic-assisted drying. PEF pretreatment altered the physicochemical and microstructural properties of butternut squash. Thus, the higher the energy input, the higher the cell disintegration rate, the lower the shearing force and the lower the water holding capacity. For the same energy input applied, no influence was observed from the different combinations of pulse number and electric field intensity used. The microstructural analysis also showed greater effects with increasing intensity of PEF treatments. All these changes affected the subsequent drying, increasing the drying rate of conventional drying. Moreover, PEF pretreatment enhanced the ultrasound effects when applied during drying, reducing drying time by up to 47% when moderate PEF intensity was used. Therefore, PEF pretreatment under the appropriate conditions could make ultrasound-assisted drying of low-porosity products, such as butternut squash, more feasible.

Apple pomace, the by-product of the cider industry, contains a high content of antioxidant compounds and dietary fiber. Drying would allow its preservation for a later use. The aim of this study was to evaluate the effect of the drying temperature on the drying kinetics, antioxidant properties and the fiber characteristics. For this, drying experiments were performed at different temperatures (40–120 °C). The increase in temperature enhanced the drying rate, as was shown by the effective diffusivity and mass transfer coefficient identified by modelling. The influence of temperature was quantified through the activation energy (38.21 kJ/mol). Regarding the retention of antioxidant properties, the best results were found at 80–100 °C while 40–60 °C was the best temperature range for the fiber characteristics. Therefore, 80 °C could be an adequate temperature for drying of cider apple pomace, as it represents a good balance between kinetics, and antioxidant and fiber properties.