Eugène Vorobiev

Electrical treatment of apple cossettes for intensifying juice pressing

The impact of two types of electrical treatment, electro-osmotic (EO) and moderate electric field pulses (MEFP), on intensifying juice pressing from apple cossettes has been studied. The experiments were carried out in a laboratory filter-press cell fitted with the appropriate electrical treatment system. Both EO and MEFP treatments result in a significant intensification of juice yield. Energy consumption, however, is 50-100 times less for MEFP treatment. Since a significant appearance of electrolytic processes and ohmic heating is observed with EO treatment, this treatment is very limited. MEFP treatment does not have these drawbacks and reduces the juice coloration.

Pulsed electric field treatment of apple tissue during compression for juice extraction

Abstract The influence of pulsed electric field (PEF) simultaneous to pressure treatment on juice expression from fine-cut apple raw material has been investigated. Dependencies of specific conductivity σ , juice yield Y , instantaneous flow rate v and qualitative juice characteristics at different modes of PEF treatment are discussed. Three main compression phases were observed in a case of mechanical expression. A unified approach is proposed for juice yield data analysis allowing a reduction in data scattering caused by differences in the quality of samples. Simultaneous application of pressure and PEF treatment revealed a passive form of PEF-induced cell plasmolysis. Pressure provokes the damage of defect cells, enhances diffusion migration of moisture and depresses the cell resealing processes. PEF application at the moment when the press-cakes specific electrical conductivity reaches a minimum and the pressure achieves its constant value seemed to be the most optimal. It has been found that a combination of pressing and PEF treatment gives the optimum results and enhances the yield of juice significantly and improves its quality.

Pulsed electric field breakage of cellular tissues: visualisation of percolative properties

Results of numerical and experimental investigation of the electric breakage of a cellular material in pulsed electric fields (PEF) are presented. The numerical model simulates the conductive properties of a cellular material by a two-dimensional array of biological cells. The application of an external field in the form of an idealised square pulse sequence with a pulse duration ti, and a pulse repetition time Δt is assumed. The simulation model includes the known mechanisms of temporal and spatial evolution of the conductive properties of different microstructural elements in a tissue. The kinetics of breakage at different values of electric field strength E, ti and Δt was studied in the experimental investigation. A 5×55-mm cylindrical slab of apple was taken as a sample. The results of the experimental and numerical studies were compared. A hypothesis for the nature of tissue properties evolution after PEF treatment was proposed. This phenomenon was considered as a correlated percolation governed by two key processes: resealing of cells and moisture transfer processes inside the cellular structure. The breakage kinetics was shown to be very sensitive to the repetition times Δt of the PEF treatment. Correlated percolation patterns were observed in a case when Δt exceeded the characteristic time of the moisture transfer processes while random percolation patterns were observed in other cases. The long-term mode of the pulse repetition times in PEF treatment allows the experimental visualisation of macroscopic percolation channels in the sample. Considerable differences were observed between the damage kinetics at long and short repetition times both for experimental and simulation data.

Selective extraction from microalgae Nannochloropsis sp. using different methods of cell disruption.

This work studies the extraction of intracellular components from microalgae Nannochloropsis sp. with application of different cell disruption techniques, including pulsed electric field (PEF) (20kV/cm, 1-4ms, 13.3-53.1kJ/kg), high voltage electrical discharge (HVED) (40kV/cm, 1-4ms, 13.3-53.1kJ/kg), ultrasonication (USN) (200W, 1-8min, 12-96kJ/kg), and high pressure homogenization (HPH) (150MPa, 1-10 passes, 150-1500kJ/kg). The data evidence that electrically based disruption techniques (PEF and HVED) allowed selective extraction of water soluble ionic components and microelements, small molecular weight organic compounds and water soluble proteins. Microscopic and sedimentation stability analyses have shown that microalgae cells in HVED-treated suspension were noticeably agglomerated and could be easily settled in centrifuge. The electrically based disruption techniques were ineffective for delivery of pigments (e.g., chlorophylls or carotenoids) and their extraction required subsequent application of more potent disruption techniques. The obtained data have shown that HPH disruption technique was the most effective; however, this mode required the highest power consumption.

Electrocoagulation and coagulation by iron of latex particles in aqueous suspensions

The goal of coagulation of fine disperse latex particles of suspensions by dosing with iron ions is to enhance suspension clarification, promote sedimentation and improve their filterability. Two kinds of iron dosing were studied; by directly adding iron chloride or iron sulphate to suspensions or by electrolytic decomposition of iron electrodes (electrocoagulation process, EC). The chemical and electrical processes were examined by varying the pH value and the iron ions concentration in order to determine the optimal operating conditions. To minimise the energy consumption in EC, the suspension conductivity and the current density were varied. This paper shows that flocs in EC-treated suspensions had a higher density and tended to be larger than flocs formed in suspensions dosed with iron chloride or iron sulphate. The kinetics of settling and filtration of EC-treated suspensions were accelerated, demonstrating the interest of EC as an alternative to chemical conditioning.

The Effects of Conventional and Non-conventional Processing on Glucosinolates and Its Derived Forms, Isothiocyanates: Extraction, Degradation, and Applications

Abstract In recent decades, glucosinolates and isothiocyanates have attracted the interest of scientific community due to healthy properties of these bioactive compounds and their role as natural antimicrobials and anticarcinogenic agents. However, these compounds can lose their properties and transform into antinutrients depending on processing conditions. At this stage of investigation, there is a need in evaluation of the commonly accepted and new emerging methods in order to establish the optimum conditions for preserving healthy glucosinolates and isothiocyanates. This paper reviews the conventional and new promising technologies that can be useful for extraction of appropriate glucosinolates and isothiocyanates from natural sources (i.e., Brassica vegetables). The impact of different preservation processes on degradation of glucosinolates and isothiocyanates is also discussed.

Solid–liquid expression of cellular materials enhanced by pulsed electric field

Abstract The mechanism of solid–liquid expression enhanced by pulsed electric field (PEF) is studied for agrofood cellular materials. The application of PEF induces the permeabilization of cellular membranes and facilitates the subsequent cells rupture by mechanical compression. The solid–liquid expression was preceded by mechanical pre-compaction of sugar beet slices under a constant pressure, application of PEF treatment under the same pressure, and prolongation of mechanical compression after the PEF removal. The periods of solid–liquid expression enhanced by PEF are studied on the basis of press-cake electrical resistance measurement. The rheological model of solid–liquid expression with a fracture element can be used to estimate the compressibility characteristics of press-cake treated by PEF. A simple empirical equation predicted well the compression ratio of press-cake at different parameters of PEF. With increase of electrical energy input the liquid emanation from press-cake was intensified up to some level of expression, which seems to correspond to the destruction of quasi totality of cells.

New Approaches for the Use of Non-conventional Cell Disruption Technologies to Extract Potential Food Additives and Nutraceuticals from Microalgae

In recent decades, microalgae species have focused the attention of several research groups and food industry as they are a great source of nutritionally valuable compounds. The use of environmentally friendly technologies has led to researchers and food industry to develop new alternative processes that can extract nutritionally valuable compounds from different sources, including microalgae. This note describes the potential use of some non-conventional methods including sub- and supercritical fluid extraction, pulsed electric fields, high-voltage electric discharges, high-pressure homogenization, ultrasound- and microwave-assisted extraction, which involve cell disruption to recover nutritionally valuable compounds from microalgae and can help to comply with criteria of green chemistry concepts and sustainability.

Electroporation in Food Processing and Biorefinery

Electroporation is a method of treatment of plant tissue that due to its nonthermal nature enables preservation of the natural quality, colour and vitamin composition of food products. The range of processes where electroporation was shown to preserve quality, increase extract yield or optimize energy input into the process is overwhelming, though not exhausted; e.g. extraction of valuable compounds and juices, dehydration, cryopreservation, etc. Electroporation is—due to its antimicrobial action—a subject of research as one stage of the pasteurization or sterilization process, as well as a method of plant metabolism stimulation. This paper provides an overview of electroporation as applied to plant materials and electroporation applications in food processing, a quick summary of the basic technical aspects on the topic, and a brief discussion on perspectives for future research and development in the field. The paper is a review in the very broadest sense of the word, written with the purpose of orienting the interested newcomer to the field of electroporation applications in food technology towards the pertinent, highly relevant and more in-depth literature from the respective subdomains of electroporation research.

Enhanced expression of juice from soft vegetable tissues by pulsed electric fields: consolidation stages analysis

Abstract The expression behaviour of different soft vegetable tissues is compared. The detailed analysis of different consolidation stages is done for potato tissue. The primary consolidation Terzaghi’s coefficient C v is estimated as C v ≈(2.0±0.6)×10 −2 cm 2 /s. The logarithmic type of secondary consolidation is observed and the dependency of the consolidation processes on the applied pressure is discussed. The four main time constants that characterize the consolidation curve are defined: t 0 is the time of pre-consolidation stage, t 1 is the time of intensive liquid expression during the primary consolidation stage, t 2 is the time of transition to the secondary consolidation, and t d is the expected ‘theoretical’ time of complete liquid expression. At a pressure of P =5 bar, t 0 ≈10 s, t 1 ≈10 3 s, t 2 ≈10 4 s, and t d ≈6×10 4 s (17 h). Consolidation behaviour after application of pulsed electric fields (PEF) is studied. At low degrees of PEF treatments (electric field intensity E T PEF t t 1 ) and enhanced expression in the transitional time interval t 1 t t 2 was observed. It was concluded that substantial intensification of the pressing processes needs a rather high degree of PEF-induced tissue damage and low-level PEF-induced damages show notable effects only at large t > t 1 , which is disadvantageous from industrial point of view. It is shown that PEF should be applied after a pre-consolidation stage. But the time at which PEF treatment starts t PEF has no significant effect on the juice yield for the case when t 0 t PEF t 1 . An optimum value of PEF intensity E required for high intensification of juice expression at minimum electric power consumption lies in the interval of 400–600 V/cm.