Pulsed electric field in combination with vacuum impregnation with trehalose improves the freezing tolerance of spinach leaves

Pulsed electric fields in combination with vacuum infusion have been utilized to impregnate cells with trehalose, aiming at substantially improving the freezing tolerance of spinach leaves. Spinach samples were first treated with ten trains of bi-polar, rectangular electric field pulses with a nominal electric field strength of 580 V/cm and immediately immersed in a 40% (w/w) solution of trehalose under vacuum for 20 min. The samples were kept in the trehalose solution for 2.5 h at atmospheric pressure, immersed in deionised water at 4 ºC overnight, frozen in liquid nitrogen and thawed in water at room temperature. The leaves were evaluated for cell damage with microscopic observations and wilting tests. The results provided evidence that the impregnation with trehalose by the combined actions of electric fields and vacuum impregnation drastically improved the freezing tolerance of the spinach leaves

Effect of pulsed electric fields on the germination of barley seeds

[Excerpt] Introduction: There is only little information available in the literature about the effect of reversible electropermeabilization on plant cells and tissues. We here present a first exploration of the effect of pulsed electric fields (PEF) on barley seed germination. PEF is used as a physical means of stressing the seeds and affect their metabolism. [...]info:eu-repo/semantics/publishedVersio

Poboljšanje metaboličke aktivnosti bakterije Lactobacillus plantarum 564 pomoću elektroporacije

The exposure of bacterial cells to pulsed electric fields (PEF) leads to the reversible formation of pores in the cell membrane if an applied energy is below the critical level. Therefore, the effect of electric field pulses with amplitudes below 14 kV/cm and the applied energy up to 12.2 J/cm3 on the growth of Lactobacillus plantarum 564 cells was investigated. After PEF treatments, the growth of lactobacilli in De Man-Rogosa-Sharpe broth at 37 °C was monitored by isothermal calorimetry, absorbance and plate counts. All the applied treatments resulted in a higher growth rate of PEF-treated cells during early and mid-log phase, especially bacterial samples treated with lower field intensities (1.3–5.5 J/cm3). The transport of ions and molecules through the cell membrane (which facilitates the growth of electroporated lactobacilli) was particularly evident in the mid-exponential growth phase, where the doubling time was reduced more than 3 times after the exposure to electric pulses of 5.5 J/cm3. The heat production rate during the growth of electroporated cells was also higher, indicating the enhanced metabolic activity of PEF-treated cells. Moreover, the electroporated cells had a better acidification ability than the untreated ones. It can be summarized that the applied PEF treatments with an energy input of below 12 J/cm3 potentially induce reversible electroporation of the cell membrane, which has a positive impact on the growth and metabolic activity of the cells of lactobacilli.Izlaganje bakterija pulsirajućim električnim poljima uzrokuje reverzibilno stvaranje pora na staničnoj membrani, ako je energija električnog polja ispod kritične razine. Stoga je istražen utjecaj pulsirajućih električnih polja na rast stanica bakterije Lactobacillus plantarum 564 primjenom polja jačine do 12.2 J/cm3, tj. amplituda manjih od 14 kV/cm. Rast laktobacila u De Man-Rogosa-Sharpe bujonu na 37 °C nakon tretmana praćen je pomoću izotermalne kalorimetrije, te mjerenjem apsorbancije i ukupnog broja stanica. Utvrđeno je da su stanice izložene pulsirajućem električnom polju brže rasle tijekom rane i srednje logaritamske faze, što je naročito bilo izraženo kod stanica tretiranih poljima niskog intenziteta (1.3-5.5 J/cm3). Transport iona i molekula kroz staničnu membranu (što olakšava rast elektroporiranih laktobacila) bio je posebno izražen tijekom eksponencijalne faze rasta, kad je generacijsko vrijeme stanica tretiranih pulsevima energije od 5.5 J/cm3 bilo trostruko kraće. Tijekom rasta tretiranih stanica oslobođena je veća količina topline, što znači da se metabolička aktivnost stanica povećala nakon tretmana. Osim toga, elektroporirane su stanice jače zakiseljavale sredinu. Iz dobivenih se rezultata može zaključiti da pulsirajuća električna polja jačine manje od 12.2 J/cm3 uzrokuju reverzibilnu elektroporaciju stanične membrane, što ima pozitivan učinak na rast i metaboličku aktivnost stanica laktobacila

Modeling electroporation of the non-treated and vacuum impregnated heterogeneous tissue of spinach leaves

Uniform electroporation of the heterogeneous structure of spinach leaf cross section is a technological challenge that is addressed in this investigation. Three dimensional models were created with cells arranged in specific tissue types, considering a leaf with its air fraction and a leaf where the air fraction was replaced by a solution of known properties using vacuum impregnation. The models were validated before electroporation, in the frequency domain, where alternating voltage and current signal at frequencies from 20 Hz to I MHz were used to measure conductivity of the tissue. They were also validated through measurements of current during electroporation when a single 250 mu s rectangular pulse with amplitudes ranging from 50 to 500 V was applied. Model validations show that both the frequency dependent conductivity and electroporation are well predicted. The importance of the wax layer and stomata in the model is thoroughly discussed. Industrial relevance: Our aim was to investigate electroporation of the spinach leaf by developing a model which would enable us to meet the technological challenge of achieving uniform electroporation in a highly heterogeneous structure in the context of a process aimed at improving freezing stability of plant foods. Pulsed electric field treatment may be used to introduce the cryoprotectant molecules into the cells, and hence improve the structure and properties of frozen food plants. (C) 2014 Elsevier Ltd. All rights reserved

Pulsed electric field-induced cell permeabilisation of potato tissue lead to sustained metabolic changes

Metabolite profiling was used to characterize stress responses of potato tissue subjected to reversible electroporation, providing insights on how potato tissue responds to a physical stimulus such as pulsed electric fields (PEF), which is an artificial stress. Wounded potato tissue was subjected to field strengths ranging from 200 to 400 V/cm, with a single rectangular pulse of 1 ms. Electroporation was demonstrated by propidium iodide staining of the cells nucleae. Metabolic profiling of data obtained through GC/TOF-MS complemented with orthogonal projections to latent structures (OPLS) clustering analysis showed that 24 h after the application of PEF, potato metabolism shows PEF-specific responses characterized by the changes in the hexose pool that may involve starch and ascorbic acid degradation

Metabolomic evaluation of pulsed electric field-induced stress on potato tissue

Metabolite profiling was used to characterize stress responses of potato tissue subjected to reversible electroporation, providing insights on how potato tissue responds to a physical stimulus such as pulsed electric fields (PEF), which is an artificial stress. Wounded potato tissue was subjected to field strengths ranging from 200 to 400 V/cm, with a single rectangular pulse of 1 ms. Electroporation was demonstrated by propidium iodide staining of the cell nucleae. Metabolic profiling of data obtained through GC/TOF-MS and UPLC/TOF-MS complemented with orthogonal projections to latent structures clustering analysis showed that 24 h after the application of PEF, potato metabolism shows PEF-specific responses characterized by the changes in the hexose pool that may involve starch and ascorbic acid degradation.The Royal Physiographic Society in Lund, SwedenPortuguese Foundation of Science (FCT), PortugalDepartment of Cell and Organism Biology, Lund Universit

Effects of pulsed electrical fields on the texture of potato tissue

The application of pulsed electric fields (PEF) to cellular tissue is known to affect permanently or transiently the state of cell membranes, this is reflected in the electric properties of the tissue. Permanent permeabilization is known to affect the texture of the tissue. We have investigated whether low intensities of PEF would give rise to transient or permanent changes in texture. In this study, changes on the viscoelastic properties of potato tissues exposed to PEF during small-amplitude oscillatory dynamic rheological measurements were monitored. Potato tissue was subjected to field strengths ranging from 30 to 500 V/cm, with a single rectangular pulse of 10 µs, 100 µs or 1 ms. The elastic (G) and viscous (G&) moduli were measured every 30 s after the delivery of the pulse and the tan delta change calculated. The results were correlated with measurements of changes on electrical resistance during the delivery of the pulse. Interestingly, there is a drastic increase of tan delta 30 s after the application of the pulse, followed by a decrease 1 min after pulsation. This response is strongly influenced by the intensity and width of the pulse. Moreover, at high field strengths, the observed electroporation of the tissue reached similar levels when pulse widths of 1 ms and 100 µs were applied. 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 the tan delta to values similar to those before pulsation, strongly suggests recovery of plasma membrane properties and turgor. These viscoelastic changes were shown to be independent of the total degree of permeabilization.info:eu-repo/semantics/publishedVersio

Modeling electroporation of the non-treated and vacuum impregnated heterogeneous tissue of spinach leaves

Uniform electroporation of the heterogeneous structure of spinach leaf cross section is a technological challenge that is addressed in this investigation. Three dimensional models were created with cells arranged in specific tissue types, considering a leaf with its air fraction and a leaf where the air fraction was replaced by a solution of known properties using vacuum impregnation. The models were validated before electroporation, in the frequency domain, where alternating voltage and current signal at frequencies from 20 Hz to 1 MHz were used to measure conductivity of the tissue. They were also validated through measurements of current during electroporation when a single 250 μs rectangular pulse with amplitudes ranging from 50 to 500 V was applied. Model validations show that both the frequency dependent conductivity and electroporation are well predicted. The importance of the wax layer and stomata in the model is thoroughly discussed. Industrial relevance: Our aim was to investigate electroporation of the spinach leaf by developing a model which would enable us to meet the technological challenge of achieving uniform electroporation in a highly heterogeneous structure in the context of a process aimed at improving freezing stability of plant foods. Pulsed electric field treatment may be used to introduce the cryoprotectant molecules into the cells, and hence improve the structure and properties of frozen food plants