Accelerated Drying and Improved Color Properties of Red Pepper by Pretreatment of Pulsed Electric Fields

Abstract

A pulsed electric field (PEF) treatment was applied to red pepper (Capsicum annuum L.) as a drying pretreatment. The PEF treatment was conducted with electric field strength of 1.0–2.5 kV/cm using a fixed pulse width of 30 µs and at a pulse frequency of 100 Hz. The PEF treatment times were 1, 2, and 4 s. PEF treatment resulted in cell membrane disruption, without visible changes in the surface structure of red pepper. The degree of cell membrane disruption was field strength dependent. Drying of control and PEF-pretreated samples was conducted at 45°C. The untreated control reached the target moisture ratio of 0.15 after 4.9 h of drying, whereas the PEF-pretreated sample (2.5 kV/cm, 100 Hz, 4 s) required only 3.2 h for the same moisture ratio, indicating a 34.7% reduction in drying time. Even the shortest PEF pretreatment (2.5 kV/cm, 100 Hz, 1 s) required 3.9 h to reach the target moisture ratio, which corresponded to a 20.4% reduction in drying time. The reduction in drying time by PEF pretreatment was beneficial to color quality of dried red pepper, because greater than 10% increases in b* value and the American Spice Trade Association (ASTA) unit were observed. The drying curves of control and PEF-pretreated red pepper were analyzed using thin-layer drying models. Five models were fitted to the drying data, and Page's model was selected as the best representative model to describe the drying procedure.