Effect of Pulsed Electric Field Pretreatment on Drying Kinetics, Color, and Texture of Parsnip and Carrot

Abstract

The aim of the study was to evaluate the effect of pulsed electric field (PEF) pretreatment on drying kinetics and on color and textural changes in sliced parsnip and carrot. Cell disintegration index measured in parsnips after PEF pretreatment significantly differed from the ones measured for carrots and, consequently, the reduction of the time needed to dry both samples to a final moisture content up to 5% (wet basis). The drying time of the PEF pretreated parsnip was reduced by up to 28% at 70 °C and by up to 21% at 60 °C in carrot, in comparison to untreated samples. The PEF pretreatment influenced the effective diffusivity of water into the samples going from 50 °C to 70 °C: in carrots it ranged between 1.61 × 10^-10 and 3.04 × 10^-10 (m² /s), although, in parsnip, it ranged between 1.97 × 10^-10 and 3.06 × 10^-10 (m² /s). Also, PEF pretreatment influenced color changes: PEF pretreated dried carrots showed a significant (p < .05) reduction in lightness values (L^* ) compared to untreated dried ones, although PEF pretreated parsnip had a significant (p < .05) increase in redness values (a^* ). The PEF treatment did not affect the mechanical properties (p > .05) of carrot and parsnip dried at 50 and 60 °C, whereas at 70 °C a significant increase (p < .05) of the force required to cut both root slices was detected. The choice of a PEF pretreatment of foods to be dried should be related to shorten the drying time and to minimize the loss in quality properties mentioned above.

Practical application: Dry carrots and parsnip slices can be used as food ingredients for further food preparations but also as healthy snacks, thanks to their health benefits. Pulsed electric field (PEF) resulted to be an effective pretreatment for carrots and parsnips before undergoing convective drying, because it reduced the drying time (up to 28% in parsnip and 21% in carrot slices) and, particularly at mild temperatures (50 to 60 °C), it did not affect the texture properties of both carrot and parsnip. PEF pretreatment of these roots before convective heating can be surely suggested as industrial application.

Keywords: carrot; diffusivity; drying; parsnip; pulsed electric field.