Effects of Pulsed Electric Field on the Viscoelastic Properties of Potato Tissue

Abstract

We have investigated whether transient permeabilization would give rise to transient or permanent changes in the potato tissue texture. The changes on the viscoelastic properties of potato tissue exposed to PEF during small-amplitude oscillatory dynamic rheological measurements were monitored. The elastic (G') and viscous moduli (G") were measured every 30 s after the delivery of the pulse and the loss tangent (tan-δ) change calculated. Our results, supported by similar measurements on osmotically dehydrated control samples, clearly show that PEF causes a rapid change of the viscoelastic properties of the tissue that could be attributed to a partial loss in turgor pressure. This would be an expected consequence of electroporation. The recovery of tan-δ to values similar to those before pulsation, strongly suggests recovery of cell membrane properties and turgor. Materials and Methods SamplesPotato tubers (Solanum tuberosum L. cv. Bintje) grown in the south of Sweden, were manually washed and peeled. A rectangular cross-section sample, 15 mm long and 6.0 mm wide, was obtained from the phloem parenchyma tissue using a pair of parallel sharp blades. PEF treatment• Samples were treated at nominal field strength range of 30 to 500 V/cm, with single rectangular pulses of 1 ms, 10 µs and 100 µs, delivered axially to the tissue;• Osmotically pre-treated samples were subjected to a single 1 ms pulse in the range of 30 to 500 V/cm. Additionally, a sequence of 9 rectangular pulses of 500 V/cm of 1 ms each was also tested;• The pulsation for each PEF treatment was given 150 to 200 s after the start of the small-amplitude oscillatory dynamic rheological measurements;• Five measurements were done for each condition. Small-amplitude oscillatory dynamic rheological measurementsThe potato sample was placed on the lower plate of the rheometer. The upper plate was brought into contact with the sample until a normal force of 1 N was reached. Measurements of the tan-d were recorded in the oscillatory mode as a function of time at intervals of 30 s The oscillation stress amplitude was 0.1 % and the frequency 1 Hz. Stress sweeps were applied to verify that data were acquired within the linear viscoelastic regime. • Sample impedance was measured prior to pulsing and 30 s to 2 min after pulsing by using a low voltage sinusoidal wave form (V s ) at 5 V and 1 kHz, by turning on switch A; Experimental setup• The resistance of the tissue samples during the pulsing period was done by turning on switch B, to deliver the high pulse voltage (V t ) from pulse generator;• After PEF, response voltage (V f ) was monitored and recorded through the reference resistor (R f ) by using a digital oscilloscope. The impedance (I) of the tissue was calculated through Equation 1[1];• Electrical resistance of the tissue during pulsing period was calculated through Equation 1 by using V t instead V f . Results Tan-δ measurement during PEF treatment• Tan-δ change was calculated by subtracting the tan-δ values measured at time intervals of 30 s after pul...

The effect of pulsed electric field pre-treatments prior to deep-fat frying on quality aspects of potato fries

“…This result can be attributed to PEF-induced textural changes of the potato tissue. Electroporation may actually cause partial loss in turgor pressure, impairing plant tissue firmness (Lebovka et al, 2004;Pereira, Galindo, Vicente, & Dejmek, 2009). Table 2 also shows lightness and green-to-red colour parameter as well as images of the treated potato cubes.…”

Enhanced Extraction from Solid Foods and Biosuspensions by Pulsed Electrical Energy

“…It was demonstrated that the insulating properties of the cell membrane (potato, apple and fish tissues) can be recovered within several seconds after pulse termination [2]. The reversible permeabilization of the potato cell was confirmed by transient changes in the viscoelastic properties after PEF application with a single 10-5, 10-4 or 10-3 s rectangular pulse and electric field strength E ranging from 30 to 500 V/cm [73]. According to calorimetric data, PEF application resulted in a strong metabolic response of potato tissue dependent on the pulsing conditions [31,33].…”

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

“…It is well known that conductivity in the membrane increases immediately after the pulsed treatment (Angersbach, Heinz, & Knorr, 2000) and the membrane becomes more permeable as the conductivity increases (Pereira, Galindo, Vicente, & Dejmek, 2009;Gómez Galindo, Vernier, Dejmek, Vicente, & Gundersen, 2008;Bazhal, Lebovka, & Vorobiev, 2003). This increase in membrane permeability seems to re-establish the equilibrium between the electrochemical and electrical potential differences between the cell plasma and the extracellular surroundings (Raso-Pueyo & Heinz, 2010).…”

“…It is generally agreed that if the amplitude and duration of the treatment is not too high, the membrane returns from the state of high conductance to its initial state (Chernomordik et al, 1987). Under those conditions, the membrane can reseal, the viability of the cell is maintained (Guderjan, Töpfl, Angersbach, & Knorr, 2005), and metabolic activity can be restored (Pereira, Galindo, Vicente, & Dejmek, 2009). This is known as the "reversible electric breakdown' as the conductance of the cell is increased (Weaver, Powell, Mintzer, Sloan, & Ling, 1984).…”

“…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.…”