Pulsed electric field treatment for solid-liquid extraction of red beetroot pigment

Extractability of red pigment from red beetroot was investigated using pulsed electric field (PEF) treated tissue in a solid-liquid extraction process. Thin disks of the tissue were subjected to PEF at different intensities and, 3-4 min after the treatment, the release of red pigment and ionic species into an isotonic solution was measured in situ using a spectrophotometer and a conductivity meter. The highest degree of extraction achieved with PEF was compared with that of freezing and mechanical pressing. Subjected to 270 rectangular pulses of 10 Vs at 1 kV/cm field strength, with an energy consumption of 7 kJ/kg, the samples released about 90%,) of total red colouring and ionic content following I h aqueous extraction. The increase in tissue electric conductivity after PEF treatment correlated approximately linearly with the extraction yield of red pigment and ionic species only up to an extraction level of 60-800%. No differential permeabilization of the intracellular components was found. Higher degree of variation of the extractability of pigment and ionic species at intermediate PEF treatments was interpreted as related to non-homogenous permeabilization of the tissue due to cell size. (C) 2003 Elsevier Ltd. All rights reserved.