Effect of ultrasound and green solvents addition on the oil extraction efficiency from rapeseed flakes.

The current procedure of rapeseed oil extraction is based on a first extraction step by pressing followed by a second extraction step with hexane. This solvent being toxic for the users, the consumers and the environment, its use could be forbidden within the coming years. Stimulated by a stringent regulation, the research activity for the replacement of toxic solvents shows a significant development. The aim of this study was to select alternative solvent to hexane such as ethanol or isopropanol, and, to adjust the oil extraction process by developing an ultrasound assisted method. The objective was to reach a comparable efficiency but also to enhance the oil quality. When applied to isopropanol, the ultrasound assisted extraction method has shown promising results, and comparable to those obtained with hexane (oil yield of 80% for hexane and 79% for isopropanol at optimum extraction conditions (20min of ultrasound pretreatment followed by 2h of additional solid/liquid extraction)). Conversely, in studied conditions, ethanol did not seem to be an appropriate alternative solvent to hexane as the extraction yields obtained by using this solvent were quite low.

Impact of ultrasounds and high voltage electrical discharges on physico-chemical properties of rapeseed straw's lignin and pulps.

In this study, ultrasound (US) and high voltage electrical discharges (HVED) were combined with chemical treatments (soda or organosolv) for rapeseed straw delignification. Delignification was improved by both physical pretreatments. US increased the extractability of hemicelluloses and HVED induced a partial degradation of cellulose. Best synergies were observed for HVED-soda and US-organosolv treatments. The obtained lignin fractions were characterized with 13C NMR and 2D 1H-13C HSQC. It was observed that the physical treatments affected the syringyl/guaiacyl (S/G) ratios. The values of S/G were ≈1.19, 1.31 and 1.75 for organosolv, HVED-organosolv and US-organosolv processes, suggesting recondensation reactions. The lignin fractions obtained from HVED-organosolv treatment contained less quantity of p-coumaric acid and ferulic acid as compared to those extracted by US-organosolv. Thermogravimetric analysis (TGA) revealed a better heat resistance of physically extracted lignins as compared to the control. The enzymatic digestibility increased by 24.92% when applying HVED to mild organosolv treatment.

Impact of pulsed-electric field and high-voltage electrical discharges on red wine microbial stabilization and quality characteristics.

AIMS: In this study, pulsed-electric fields (PEF) and high-voltage electrical discharges (HVED) are proposed as new techniques for the microbial stabilization of red wines before bottling. The efficiency of the treatment was then evaluated. METHODS AND RESULTS: PEF and HVED-treatments have been applied to wine for the inactivation of Oenococcus oeni CRBO 9304, O. oeni CRBO 0608, Pediococcus parvulus CRBO 2.6 and Brettanomyces bruxellensis CB28. Different treatment times (1, 2, 4, 6, 8 and 10 ms) were used at 20 kV cm(-1) for the PEF treatments and at 40 kV for the HVED treatments, which correspond to applied energies from 80 to 800 kJ l(-1) . The effects of the treatments on the microbial inactivation rate and on various characteristics of red wines (phenolic composition, chromatic characteristics and physico-chemical parameters) were measured. CONCLUSIONS: The application of PEF or HVED treatments on red wine allowed the inactivation of alteration yeasts (B. bruxellensis CB28) and bacteria (O. oeni CRBO 9304, O. oeni CRBO 0608 and P. parvulus CRBO 2.6). The electric discharges at 40 kV were less effective than the PEF even after 10 ms of treatments. Indeed, 4 ms of PEF treatment at 20 kV cm(-1) were sufficient to inactivate all micro-organisms present in the wines. Also, the use of PEF had no negative impact on the composition of wines compared to the HVED treatments. Contrary to PEF, the phenolics compounds were degraded after the HVED treatment and the physico-chemical composition of wine were modified with HVED. SIGNIFICANCE AND IMPACT OF THE STUDY: PEF technology seems to be an interesting alternative to stabilize microbiologically wines before bottling and without modifying their composition. This process offers many advantages for winemakers: no chemical inputs, low energy consumption (320 kJ l(-1) ), fast (treatment time of 4 ms) and athermal (ΔT ≈ 10°C).

Pulsed electric field pretreatment of rapeseed green biomass (stems) to enhance pressing and extractives recovery.

The objective of this study was to investigate the effects of pulsed electric field (PEF) pretreatment on the valorization of extractives (proteins and polyphenols) from rapeseed green biomass (stems) by pressing. The effect of pressure, electric field strength and pulse number on the juice expression yield, total polyphenols and total proteins content in the expressed juices were studied. Experiments conducted under optimal conditions (E = 8 kV/cm, tPEF = 2 ms, P = 10 bar) permitted to increase the juice expressed yield from 34% to 81%. Significant increases in total polyphenols content (0.48 vs. 0.10 g GAE/100g DM), in total proteins content (0.14 vs. 0.07 g BSA/100g DM) and in consolidation coefficient (9.0 × 10(-8) vs. 2.2 × 10(-8)m(2)/s) were also observed after PEF pretreatment. The recovered press cake was well dehydrated with an increase of dry matter content from 8.8% to 53.0%.

Ultrasound-assisted green solvent extraction of high-added value compounds from microalgae Nannochloropsis spp.

The aim of this work was to investigate ultrasound (US)-assisted green solvent extraction of valuable compounds from the microalgae Nannochloropsis spp. Individual green solvents (water, ethanol (EtOH), dimethyl sulfoxide (DMSO)) and binary mixture of solvents (water-DMSO and water-EtOH) were used for the extraction procedures. Maximum total phenolic compounds yield (Yp ≈ 0.33) was obtained after US pre-treatment (W=400 W, 15 min), being almost 5-folds higher compared to that found for the untreated samples and aqueous extraction (Yp ≈ 0.06). The highest yield of total chlorophylls (Yc ≈ 0.043) was obtained after US (W=400 W, 7.5 min), being more than 9-folds higher than those obtained for the untreated samples and aqueous extraction (Yc ≈ 0.004). The recovery efficiency decreased as DMSO>EtOH>H2O. The optimal conditions to recover phenolic compounds and chlorophylls from microalgae were obtained after US pre-treatment (400 W, 5 min), binary mixtures of solvents (water-DMSO and water-EtOH) at 25-30%, and microalgae concentration of 10%.

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.

Sedimentation stability and aging of aqueous dispersions of Laponite in the presence of cetyltrimethylammonium bromide.

This work discusses the sedimentation stability and aging of aqueous suspensions of Laponite in the presence of cetyltrimethylammonium bromide (CTAB). The concentration of Laponite was fixed at a constant level C(l)=2%wt, which corresponds to the threshold between equilibrium gel IG(1) and glass IG(2) states. The concentration of CTAB C(s) was within 0-0.3 %wt. In the presence of CTAB, the Laponite aqueous suspensions were unstable against sedimentation and separated into the upper and bottom layers (U and B layers, respectively). The dynamic light-scattering technique has revealed that addition of CTAB even at a rather small concentration, C(s)=0.0164 %wt (0.03 cation exchange capacity), induced noticeable changes in the aging dynamics of the U layer. It was explained by equilibration of CTAB molecules that were initially nonuniformly distributed between different Laponite particles. Accelerated stability analysis by means of analytical centrifugation with rotor speed ω=500-4000 rpm revealed three sedimentation regimes: continuous (I, C(s)<0.14 %wt), zonelike (II, 0.140.2%wt). It was demonstrated that the B layer was "soft" in the zonelike regime. The increase of ω resulted in its supplementary compressing and collapse of "soft" sediment above certain critical centrifugal acceleration. The physical nature of the observed behavior, accounting for enhancement of hydrophobic interactions between Laponite particles, is discussed.

Pressurised electro-osmotic dewatering of activated and anaerobically digested sludges: electrical variables analysis.

Pressurised electro-osmotic dewatering (PEOD) of two sewage sludges (activated and anaerobically digested) was studied under constant electric current (C.C.) and constant voltage (C.V.) with a laboratory chamber simulating closely an industrial filter. The influence of sludge characteristics, process parameters, and electrode/filter cloth position was investigated. The next parameters were tested: 40 and 80 A/m², 20, 30, and 50 V-for digested sludge dewatering; and 20, 40 and 80 A/m², 20, 30, and 50 V-for activated sludge dewatering. Effects of filter cloth electric resistance and initial cake thickness were also investigated. The application of PEOD provides a gain of 12 points of dry solids content for the digested sludge (47.0% w/w) and for the activated sludge (31.7% w/w). In PEOD processed at C.C. or at C.V., the dewatering flow rate was similar for the same electric field intensity. In C.C. mode, both the electric resistance of cake and voltage increase, causing a temperature rise by ohmic effect. In C.V. mode, a current intensity peak was observed in the earlier dewatering period. Applying at first a constant current and later on a constant voltage, permitted to have better control of ohmic heating effect. The dewatering rate was not significantly affected by the presence of filter cloth on electrodes, but the use of a thin filter cloth reduced remarkably the energy consumption compared to a thicker one: 69% of reduction energy input at 45% w/w of dry solids content. The reduction of the initial cake thickness is advantageous to increase the final dry solids content.

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.

Influence of salt, pH and polyelectrolyte on the pressure electro-dewatering of sewage sludge.

This paper deals with the influence of pH, salt and polyelectrolytes on the electro-dewatering (EOD) of agro-industrial sludge at 3% w/w of dry matter. Initially, a selection of polyelectrolyte types and doses was carried out for mechanical dewatering tests. Subsequent EOD tests were carried out in a laboratory two sided filter press at constant electric current density of 80 A/m(2) and at pressure of 5 bar. It was found that whatever was the initial value of pH, salt content or polyelectrolyte type, the EOD progressed always towards the same equilibrium point at around 50% w/w of dry matter. EOD rate and energy input was not affected by the presence of polyelectrolyte whatever was its charge density and molecular weight. However, EOD rate and specific energy consumption and repartition of liquid at anode and cathode sides were strongly influenced by the salt content (adjusted by Na(2)SO(4)) or by the initial pH (adjusted with H(2)SO(4) or NaOH). EOD performed better at lower salt content and at slightly acid pH. In optimum conditions, the process (EOD) required 2 h to reach dry matter of 40% w/w with specific energy consumption of 0.25 k Wh/kg of water removed for the treatment of conditioned sludge. For comparison, compression without electric field at 5 bar required 11 h to reach 22% w/w of dry matter. This work emphasizes and demonstrates that the electrolytic hydroxide and hydronium ions formed at the electrodes have considerable influence in the course of EOD.

Valorisation of grape pomace by the extraction of phenolic antioxidants: Application of high voltage electrical discharges.

The aim of this study was to optimise the electrically assisted extraction in order to obtain grape pomace extracts with high polyphenols content, which would be potentially interesting for applications as natural antioxidants. High voltage electrical discharges (HVED) were applied for intensification of the extraction. The effects of the energy input, the electrodes distance gap and the liquid-to-solid ratio were studied. Diffusion was then carried out in different mixtures of water and ethanol for one hour at 20, 30, 40 and 60°C. The most efficient extraction was (i) an HVED pre-treatment at 80kJ/kg with an electrodes distance of 5mm in a liquid-to-solid ratio of 5 followed by (ii) a diffusion with 30% ethanol in water at 60°C for 30min. The highest total polyphenols content reached 2.8±0.4gGAE/100gDM with a corresponding antioxidant activity of 66.8±3.1gTEAC/kgDM. The polyphenols extraction rate increased with temperature in accordance to an Arrhenius type of relationship: activation energy of 21.5±1.1kJ/mol for HVED treated systems against 0.5±0.2kJ/mol for untreated ones.

Influence of temperature and surfactant on Escherichia coli inactivation in aqueous suspensions treated by moderate pulsed electric fields.

This research employed a conductometric technique to estimate the inactivation kinetics of Escherichia coli cells in aqueous suspensions (1 wt.%) during simultaneous pulsed electric fields (PEF) and thermal treatments. The electric field strength was E=5 kV/cm, the effective PEF treatment time t(PEF) was within 0-0.2 s, the pulse duration t(i) was 10(-3) s, the medium temperature was 30-50 degrees C, and the time of thermal treatment t(T) was within 0-7000 s. The damage of E. coli was accompanied by cell size decrease and release of intracellular components. The synergy between PEF and thermal treatments on E. coli inactivation was clearly present. The non-ionic surfactant Triton X-100 additionally improved its inactivation. The characteristic damage time followed the Arrhenius law within the temperature range 30-50 degrees C with activation energies W=94+/-2 kJ mol(-1) and W=103+/-5 kJ mol(-1) with and without the presence of surfactant, respectively. Relations between cell aggregation, cell zeta-potentials and presence of surfactant were analysed.

Behavior of yeast cells in aqueous suspension affected by pulsed electric field.

This work discusses pulsed electric fields (PEF) induced effects in treatment of aqueous suspensions of concentrated yeast cells (S. cerevisiae). The PEF treatment was done using pulses of near-rectangular shape, electric field strength was within E=2-5 kV/cm and the total time of treatment was t(PEF)=10(-4)-0.1 s. The concentration of aqueous yeast suspensions was in the interval of C(Y)=0-22 (wt%), where 1% concentration corresponds to the cellular density of 2x10(8) cells/mL. Triton X-100 was used for studying non-ionic surfactant additive effects. The electric current peak value I was measured during each pulse application, and from these data the electrical conductivity sigma was estimated. The PEF-induced damage results in increase of sigma with t(PEF) increasing and attains its saturation level sigma approximately sigma(max) at long time of PEF treatment. The value of sigma(max) reflects the efficiency of damage. The reduced efficiency of damage at suspension volume concentration higher than phi(Y) approximately 32 vol% is explained by the percolation phenomenon in the randomly packed suspension of near-spherical cells. The higher cytoplasmic ions leakage was observed in presence of surfactant. Experiments were carried out in the static and continuous flow treatment chambers in order to reveal the effects of mixing in PEF-treatment efficiency. A noticeable aggregation of the yeast cells was observed in the static flow chamber during the PEF treatment, while aggregation was not so pronounced in the continuous flow chamber. The nature of the enhanced aggregation under the PEF treatment was revealed by the zeta-potential measurements: these data demonstrate different zeta-potential signs for alive and dead cells. The effect of the electric field strength on the PEF-induced extraction of the intracellular components of S. cerevisiae is discussed.

The early stages of Saccharomyces cerevisiae yeast suspensions damage in moderate pulsed electric fields.

The objectives of this study were to investigate the effects of pulsed electric fields (PEF) application to colloidal suspension of Saccharomyces cerevisiae. The electrical conductivity measurements during the PEF-treatment of S. cerevisiae suspensions were used to monitor the extent of cell damages in the intervals of electric field strength E = 3-15 kV/cm and time of PEF treatment t(PEF) = 10(-4) to 1s. At relatively small fields (E < 7.5 kV/cm) the early stages of yeast cells damages were observed. At such treatment conditions, the damage was incomplete and developed at long time of PEF treatment, below the value of E = 7.5 kV/cm which is commonly referred in literature as a threshold for this culture. Data obtained for the disintegration in conductivity experiments were found in good correlation with direct counting of yeast lethality using light microscopy. The PEF-induced lethality of the yeast cells and size flocs increased with the mixing of suspensions and the increase of temperature.

On the origin of the deviation from the first-order kinetics in inactivation of microbial cells by pulsed electric fields.

A computer model was developed for the estimation of the kinetics of microbial inactivation by pulsed electric field (PEF). The model is based on the electroporation theory of individual membrane damage, where spherical cell geometry and distribution of cell sizes are assumed. The variation of microbial cell sizes was assumed to follow a statistical probability distribution of the Gaussian type. Surviving kinetics was approximated by Weibull equation. The dependencies of two Weibull parameters (shape n and time tau, respectively) versus electric field intensity E and width of cell diameters distribution were studied.

Immobilization of Aspergillus clavatus in a membrane bioreactor.

The possibility of the immobilization of A. clavatus in a membrane bioreactor which contains the nuclear membrane is investigated. The immobilization of cells in this bioreactor permits to increase the time of the productive functioning of the cells and avoids the procedure of a biomass separation from the cultural liquid.