Permeabilization of Plant Tissues by Monopolar Pulsed Electric Fields: Effect of Frequency

Abstract

Pulsed electric fields (PEF) nonthermally induce cell membrane permeabilization and thereby improve dehydration and extraction efficiencies in food plant materials. Effects of electrical field strength and number of pulses on plant tissue integrity have been studied extensively. Two previous studies on the effect of pulse frequency, however, did not provide a clear view: one study suggested no effect of frequency, while the other found a greater impact on tissue integrity at lower frequency. This study establishes the effect of pulse frequency on integrity of onion tissues. Changes in electrical characteristics, ion leakage, texture parameters, and percent weight loss were quantified for a wide range of pulse frequencies under conditions of fixed field strength and pulse number. Optical microscopy and viable-cell staining provided direct visualization of effects on individual cells. The key finding is that lower frequencies (f < 1 Hz) cause more damage to tissue integrity than higher frequencies (f = 1 to 5000 Hz). Intriguingly, the optical microscopy observations demonstrate that the speed of intracellular convective motion (that is, cytoplasmic streaming) following PEF application is strongly correlated with PEF frequency. We provide the first in situ visualization of the intracellular consequence of PEF at different frequencies in a plant tissue. We hypothesize that cytoplasmic streaming plays a significant role in moving conductive ionic species from permeabilized cells to the intercellular space between plant cells, making subsequent pulses more efficacious at sufficiently low frequencies. The results suggest that decreasing the pulse frequency in PEF may minimize the number of pulses needed to achieve a desired amount of permeabilization, thus lowering the total energy consumption. Practical Application: PEF cause pores to be formed in plant cell membranes, thereby improve moisture removal and potential extraction of desirable components. This study used in situ microscopic evaluation of onion cells, as they were pulsed with electric fields at different frequencies, to determine whether frequency was an important parameter. We illustrate that membranes were more effectively broken at lower frequencies as compared to higher frequencies. Application of this information will allow for improved design of PEF systems for more energy efficient dehydration or extraction of plant tissues.

Acoustic emission as a tool to assess the changes induced by pulsed electric field in apple tissue

“…Authors proposed to explain this phenomenon by crosslinking reactions of pectin or by the compaction of the cell layers within the tissue. In turn, the other works conducted on onion did not revealed any impact of PEF treatment carried out at constant electric field intensity but with varying frequency on the textural maximum puncture force (Asavasanti et al, 2011). What is worth emphasizing at the very beginning of the course of the compression curves, when the applied strain was smaller, PEF treated samples were characterized by lower forces, as discussed further.…”

“…Moreover, in this method similarly to the electrical conductivity disintegration index, it is necessary to establish the totally damaged sample, which can be ambiguous in some cases and there is no standard protocol of treatment in order to obtain the totally disintegrated sample. In many cases the totally disintegrated samples is obtained by freezing and thawing (Asavasanti, Ersus, Ristenpart, Stroeve, & Barrett, 2010;Lebovka, Praporscic, & Vorobiev, 2004b) by double freezing and thawing (Asavasanti, Ristenpart, Stroeve, & Barrett, 2011), by severe PEF treatment (Lebovka, Shynkaryk, & Vorobiev, 2007;Wiktor et al, 2015) or by combination of PEF treatment and freezing-thawing (Grimi et al, 2010). The texture and acoustic properties, after the colour of the food product, play a significant role in positive or negative perception of the product which refers to the sensory evaluation made by consumers during choosing the food product (Chanvrier, Jakubczyk, Gondek, & Gumy, 2014;Cybulska, Zdunek, & Konstankiewicz, 2011;Giacosa et al, 2015;Kutyła-Olesiuk, Nowacka, Wesoły, & Ciosek, 2013;Śledź, Nowacka, Wiktor, Selke, & Witrowa-Rajchert, 2013).…”

Effect of pulsed electric field processing on carotenoid extractability of carrot purée

“…The PEF‐induced breakage in plant tissue at different frequencies was studied by Asavasanti et al . (), and the results revealed that a larger number of cells are irreversibly permeabilised at low frequency.…”

Effect of pulsed electrical fields on the structural properties that affect french fry texture during processing

“…By increasing field strength, pulse duration and number of pulses, the density (number and size) of pores in the cell membrane and in the cell wall increases, and can cause rupture of the membrane (Asavasanti, Ristenpart, Stroeve, & Barrett, 2011;Pereira, Galindo, Vicente, & Dejmek, 2009;Gómez Galindo, Vernier, Dejmek, Vicente, & Gundersen, 2008;Arevalo, Ngadi, Bazhal, & Raghavan, 2004;Bazhal, Lebovka, & Vorobiev, 2003;Fincan & Dejmek, 2002;Knorr & Angersbach, 1998;Zimmermann, 1986). The cell may also be damaged by the overheating of the membrane surface, or chemical imbalances caused by transport out of the cell.…”