N.I. Lebovka

Pulsed-Electric-Fields-Induced Effects in Plant Tissues: Fundamental Aspects and Perspectives of Applications

The purpose of this contribution is to review the existing approaches to pulsed electric field (PEF) application as a tool for enhancing the processing of plant tissues. The PEF-treatment as a nonthermal method, which allows to preserve the natural quality, color, and vitamin constituents of food products. The numerous laboratory attempts to modernize the optimal PEF application protocols still lack universality. The problem is inherently multidisciplinary and integrates different biological, electrophysical, and chemical processes. The fundamental aspects of electroporation in application to plant tissues, electrically induced damage, optimal power consumption, synergetic effect of combined PEF-thermal treatment, and influence of pulse protocol parameters are presented and critically discussed. The experimental data on PEF-induced acceleration in expression, diffusion, and drying processes are also analyzed.

Impact of Electric Pulse Treatment on Selective Extraction of Intracellular Compounds from Saccharomyces cerevisiae Yeasts

Treatments by high-voltage electrical discharges (HVED, needle-plate electrode geometry, Uu2009=u200940xa0kV, tpu2009≈u20090.5xa0μs) and pulsed electric field (PEF, plate–plate electrode geometry, Eu2009=u20095–40xa0kV/cm, tpu2009≈u20098.3xa0μs) were evaluated as tools for selective extraction of different intracellular components from the wine Saccharomyces cerevisiae (bayanus) yeasts in a 0.5% (w/w) aqueous suspension. The pulses in the form of damped oscillations and exponential decay were applied in HVED and PEF modes of treatment, respectively. The extraction efficiency results obtained using HVED and PEF techniques were compared with those for high-pressure homogenization technique. The HVED and PEF treatments always resulted in incomplete damage of yeast cells, though efficiency of HVED was higher than that of PEF. The high selectivity of extraction of ionic substances, proteins, and nucleic acids was demonstrated; e.g., electric pulse treatments at Eu2009=u200940xa0kV/cm and Nu2009=u2009500 allowed extraction of ≈80% and ≈70% of ionic substances, ≈4% and ≈1% of proteins and ≈30% and ≈16% of nucleic acids in cases of HVED and PEF modes, respectively.

Pulsed Electric Field Assisted Pressure Extraction and Solvent Extraction from Mushroom (Agaricus Bisporus)

This work compares the efficiency of extraction and stability of extracts from mushroom (Agaricus bisporus) for different methods of extraction: pressure extraction (PE), pressure extraction assisted by pulsed electric field (PEu2009+u2009PEF), hot water extraction (WE; temperature, Tu2009=u2009343xa0K, time, tu2009=u20092xa0h), ethanol extraction (EE; Tu2009=u2009298xa0K, tu2009=u200924xa0h), and supplementary ethanol extraction from cakes of slices (SEE; Tu2009=u2009298xa0K, tu2009=u200924xa0h). PE was done at room temperature and 5xa0bar pressure (p). PEF treatment was done using bipolar near-rectangular pulse protocol. The traditional hot WE (Tu2009=u2009343xa0K, tu2009=u20092xa0h) gave the relatively high contents of proteins, total polyphenols and polysaccharides; however, the extracts were cloudy and their colloid stability was low. The extracts obtained using EE method were also cloudy and unstable. The sizes of particles in extracts, produced by WE and EE methods, were estimated asu2009≈u20090.25 andu2009≈u20095xa0μm, respectively. From the other side, the extracts, produced by PE and PEu2009+u2009PEF methods, were clear and their colloid stability was high. Moreover, both PE and PEu2009+u2009PEF methods allowed selective separation of different components. The PEu2009+u2009PEF method gave higher nucleic acid/proteins ratio as compared with that of PE method. Moreover, PEu2009+u2009PEF allowed production of mushroom extracts with high contents of fresh-like proteins and polysaccharides. Application of the EE method supplementary to the PE or PEu2009+u2009PEF techniques allowed for an effective extraction of the total polyphenols that was comparable with the efficiency of the WE method.

Impact of a pulsed electric field on damage of plant tissues: effects of cell size and tissue electrical conductivity.

Efficiency of pulsed electric field (PEF) induced permeabilization at 293 K in selected fruit and vegetable plant tissues (apple, potato, carrot, courgette, orange, and banana) at electric field strength (E) of 400 V·cm(-1), 1000 V·cm(-1) and pulse duration (t(p)) of 1000 μs was studied experimentally. The mean cell radius (〈r〉) was within 30 to 60 μm, and the ratio of electrical conductivities of the intact and damaged tissues (σ(i)/σ(d)) was within 0.07 to 0.79 for the studied tissues. Electroporation theory predicts higher damage for tissue with larger cells; however, the direct correlation between PEF damage efficiency and size of cell was not always observed. To explain this anomaly, a theoretical Monte Carlo model was developed and checked for parameters typical for potato tissue. The model showed a strong dependence of PEF damage efficiency and power consumption (W) on σ(i)/σ(d) ratio. The optimum value of electric field strength (E(opt)) was an increasing function of σ(i)/σ(d), and plant tissues with high σ(i)/σ(d) ratio (σ(i)/σ(d) ≈ 1) required application of a rather strong field (for example, E(opt) ≈ 3000 V·cm(-1) for σ(i)/σ(d) ≈ 0.8). However, the PEF treatment at a lower field (E ≈ 400 V·cm(-1)) allowed regulation of the selectivity of damage of cells in dependence of their size. A good qualitative correspondence between experimental data and simulation results were observed.