PEF as pretreatment to ultrasound-assisted convective drying: Influence on quality parameters of orange peel

Pulsed electric field (PEF) pretreatments and ultrasound (US) application are techniques previously used to enhance the drying operation, not only increasing the kinetics but improving product quality. Because PEF pretreatments could affect product structure and US influence depends on the internal structure of products, the combination of both techniques could have a synergistic effect. Thus, the influence of the combined application of pulsed electric field (PEF) pretreatments and ultrasound (US) during drying on the color, total phenolic content, ascorbic acid and antioxidant activity of orange peel was studied. To this end, a series of drying experiments (50 degrees C) was performed without and with ultrasound application (20.5 kW/m3) and with and without PEF pretreatments (1.20 kV/cm) for two different times, 200 mu s (0.37 kJ/kg) and 600 mu s (1.12 kJ/kg). Thus, when individually applied, ultrasound significantly shortened the drying time, and PEF pretreatments slightly extended the process. However, the shortest drying time was observed combining 200 mu s PEF pretreatment and ultrasound. This combination also provided the more similar color parameter to the fresh samples and significantly increased the percentage of phenolic compound retention. In addition, every treatment with PEF exhibited a similar percentage of ascorbic acid retention, and only the longer pretreatment (600 mu s) produced a reduction in the antioxidant activity retention. Therefore, the combined use of a PEF pretreatment and ultrasound application during orange peel drying can lead to an interesting way both to shorten the drying process and preserve important compounds.